Resective, Ablative and Radiosurgical Interventions for Drug Resistant Mesial Temporal Lobe Epilepsy: A Systematic Review and Meta-Analysis of Outcomes

Objectives: One-third of individuals with focal epilepsy do not achieve seizure freedom despite best medical therapy. Mesial temporal lobe epilepsy (MTLE) is the most common form of drug resistant focal epilepsy. Surgery may lead to long-term seizure remission if the epileptogenic zone can be defined and safely removed or disconnected. We compare published outcomes following open surgical techniques, radiosurgery (SRS), laser interstitial thermal therapy (LITT) and radiofrequency ablation (RF-TC). Methods: PRISMA systematic review was performed through structured searches of PubMed, Embase and Cochrane databases. Inclusion criteria encompassed studies of MTLE reporting seizure-free outcomes in ≥10 patients with ≥12 months follow-up. Due to variability in open surgical approaches, only comparative studies were included to minimize the risk of bias. Random effects meta-analysis was performed to calculate effects sizes and a pooled estimate of the probability of seizure freedom per person-year. A mixed effects linear regression model was performed to compare effect sizes between interventions. Results: From 1,801 screened articles, 41 articles were included in the quantitative analysis. Open surgery included anterior temporal lobe resection as well as transcortical and trans-sylvian selective amygdalohippocampectomy. The pooled seizure-free rate per person-year was 0.72 (95% CI 0.66-0.79) with trans-sylvian selective amygdalohippocampectomy, 0.59 (95% CI 0.53-0.65) with LITT, 0.70 (95% CI 0.64-0.77) with anterior temporal lobe resection, 0.60 (95% CI 0.49-0.73) with transcortical selective amygdalohippocampectomy, 0.38 (95% CI 0.14-1.00) with RF-TC and 0.50 (95% CI 0.34-0.73) with SRS. Follow up duration and study sizes were limited with LITT and RF-TC. A mixed-effects linear regression model suggests significant differences between interventions, with LITT, ATLR and SAH demonstrating the largest effects estimates and RF-TC the lowest. Conclusions: Overall, novel "minimally invasive" approaches are still comparatively less efficacious than open surgery. LITT shows promising seizure effectiveness, however follow-up durations are shorter for minimally invasive approaches so the durability of the outcomes cannot yet be assessed. Secondary outcome measures such as Neurological complications, neuropsychological outcome and interventional morbidity are poorly reported but are important considerations when deciding on first-line treatments.

Tractography dissection variability: What happens when 42 groups dissect 14 white matter bundles on the same dataset?

White matter bundle segmentation using diffusion MRI fiber tractography has become the method of choice to identify white matter fiber pathways in vivo in human brains. However, like other analyses of complex data, there is considerable variability in segmentation protocols and techniques. This can result in different reconstructions of the same intended white matter pathways, which directly affects tractography results, quantification, and interpretation. In this study, we aim to evaluate and quantify the variability that arises from different protocols for bundle segmentation. Through an open call to users of fiber tractography, including anatomists, clinicians, and algorithm developers, 42 independent teams were given processed sets of human whole-brain streamlines and asked to segment 14 white matter fascicles on six subjects. In total, we received 57 different bundle segmentation protocols, which enabled detailed volume-based and streamline-based analyses of agreement and disagreement among protocols for each fiber pathway. Results show that even when given the exact same sets of underlying streamlines, the variability across protocols for bundle segmentation is greater than all other sources of variability in the virtual dissection process, including variability within protocols and variability across subjects. In order to foster the use of tractography bundle dissection in routine clinical settings, and as a fundamental analytical tool, future endeavors must aim to resolve and reduce this heterogeneity. Although external validation is needed to verify the anatomical accuracy of bundle dissections, reducing heterogeneity is a step towards reproducible research and may be achieved through the use of standard nomenclature and definitions of white matter bundles and well-chosen constraints and decisions in the dissection process.

Resection of the piriform cortex for temporal lobe epilepsy: a Novel approach on imaging segmentation and surgical application

BACKGROUND

The piriform cortex (PC) occupies both banks of the endorhinal sulcus and has an important role in the pathophysiology of temporal lobe epilepsy (TLE). A recent study showed that resection of more than 50% of PC increased the odds of becoming seizure free by a factor of 16.

OBJECTIVE

We report the feasibility of manual segmentation of PC and application of the Geodesic Information Flows (GIF) algorithm to automated segmentation, to guide resection.

METHODS

Manual segmentation of PC was performed by two blinded independent examiners in 60 patients with TLE (55% Left TLE, 52% female) with a median age of 35 years (IQR, 29-47 years) and 20 controls (60% Women) with a median age of 39.5 years (IQR, 31-49). The GIF algorithm was used to create an automated pipeline for parcellating PC which was used to guide excision as part of temporal lobe resection for TLE.

RESULTS

Right PC was larger in patients and controls. Parcellation of PC was used to guide anterior temporal lobe resection, with subsequent seizure freedom and no visual field or language deficit.

CONCLUSION

Reliable segmentation of PC is feasible and can be applied prospectively to guide neurosurgical resection that increases the chances of a good outcome from temporal lobe resection for TLE.

Occipitocervical instrumented fixation utilising patient-specific C2 3D-printed spinal screw trajectory guides in complex paediatric skeletal dysplasia

PURPOSE

Instability of the craniocervical junction in paediatric patients with skeletal dysplasia poses a unique set of challenges including anatomical abnormalities, poor bone quality, skeletal immaturity and associated general anaesthetic risks. Instrumented fixation provides optimal stabilisation and fusion rates. The small vertebrae make the placement of C2 pedicle screws technically demanding with low margins of error between the spinal canal and the vertebral artery.

METHODS

We describe a novel clinical strategy utilising 3D-printed spinal screw trajectory guides (3D-SSTG) for individually planned C2 pedicle and laminar screws. The technique is based on a pre-operative CT scan and does not require intraoperative CT imaging. This reduces the radiation burden to the patient and forgoes the associated time and cost. The time for model generation and sterilisation was < 24 h.

RESULTS

We describe two patients (3 and 6 years old) requiring occipitocervical instrumented fixation for cervical myelopathy secondary to Morquio syndrome with 3D-SSTGs. In the second case, bilateral laminar screw trajectories were also incorporated into the same guide due to the presence of high-riding vertebral arteries. Registration of the postoperative CT to the pre-operative imaging revealed that screws were optimally placed and accurately followed the predefined trajectory.

CONCLUSION

To our knowledge, we present the first clinical report of 3D-printed spinal screw trajectory guides at the craniocervical junction in paediatric patients with skeletal dysplasia. The novel combination of multiple trajectories within the same guide provides the intraoperative flexibility of potential bailout options. Future studies will better define the potential of this technology to optimise personalised non-standard screw trajectories.

Intraoperative overlay of optic radiation tractography during anteromesial temporal resection: a prospective validation study

OBJECTIVE

Anteromesial temporal lobe resection (ATLR) results in long-term seizure freedom in patients with drug-resistant focal mesial temporal lobe epilepsy (MTLE). There is significant anatomical variation in the anterior projection of the optic radiation (OR), known as Meyer's loop, between individuals and between hemispheres in the same individual. Damage to the OR results in contralateral superior temporal quadrantanopia that may preclude driving in 33%-66% of patients who achieve seizure freedom. Tractography of the OR has been shown to prevent visual field deficit (VFD) when surgery is performed in an interventional MRI (iMRI) suite. Because access to iMRI is limited at most centers, the authors investigated whether use of a neuronavigation system with a microscope overlay in a conventional theater is sufficient to prevent significant VFD during ATLR.

METHODS

Twenty patients with drug-resistant MTLE who underwent ATLR (9 underwent right-side ATLR, and 9 were male) were recruited to participate in this single-center prospective cohort study. Tractography of the OR was performed with preoperative 3-T multishell diffusion data that were overlaid onto the surgical field by using a conventional neuronavigation system linked to a surgical microscope. Phantom testing confirmed overlay projection errors of < 1 mm. VFD was quantified preoperatively and 3 to 12 months postoperatively by using Humphrey and Esterman perimetry.

RESULTS

Perimetry results were available for all patients postoperatively, but for only 11/20 (55%) patients preoperatively. In 1/20 (5%) patients, a significant VFD occurred that would prevent driving in the UK on the basis of the results on Esterman perimetry. The VFD was identified early in the series, despite the surgical approach not transgressing OR tractography, and was subsequently found to be due to retraction injury. Tractography was also used from this point onward to inform retractor placement, and no further significant VFDs occurred.

CONCLUSIONS

Use of OR tractography with overlay outside of an iMRI suite, with application of an appropriate error margin, can be used during approach to the temporal horn of the lateral ventricle and carries a 5% risk of VFD that is significant enough to preclude driving postoperatively. OR tractography can also be used to inform retractor placement. These results warrant a larger prospective comparative study of the use of OR tractography-guided mesial temporal resection.

Printing in a Pandemic: 3D printing solutions for healthcare during COVID-19. A Protocol for a PRISMA systematic review

Introduction

The COVID-19 pandemic had an unprecedented global socioeconomic impact. Responses to pandemics include strategies to accumulate vast stockpiles of vital medical equipment. In such times of desperation, 3D-printing could be a life-saving alternative.

Methods

We undertook a PRISMA systematic review of 3D printing solutions in response to COVID-19 utilising the PICO methodology. The objectives were to identify the uses of 3D printing during the COVID-19 pandemic, determine the extent of preclinical testing, comparison to commercial alternatives, presence of regulatory approvals and replicability regarding the description of the printing parameters and the availability of the print file.

Results

Literature searches of MEDLINE (OVID interface)/ PubMed identified 601 studies. Of these, 10 studies fulfilled the inclusion and exclusion criteria. Reported uses of 3D printing included personal protective equipment (PPE), nasopharyngeal swabs and adjunctive anaesthetic equipment. Few studies undertook formal safety and efficacy testing before clinical use with only one study comparing to the commercial equivalent. Six articles made their model print files available for wider use.

Conclusion

We describe a protocol for a systematic review of 3D-printed healthcare solutions in response to COVID-19. This remains a viable method of producing vital healthcare equipment when supply chains are exhausted. We hope that this will serve as a summary of innovative 3D-printed solutions during the peak of the pandemic and also highlight concerns and omissions regarding safety and efficacy testing that should be addressed urgently in preparation for a subsequent resurgences and future pandemics.

Computer Assisted Planning for Curved Laser Interstitial Thermal Therapy

Laser interstitial thermal therapy (LiTT) is a minimally invasive alternative to conventional open surgery for drug-resistant focal mesial temporal lobe epilepsy (MTLE). Recent studies suggest that higher seizure freedom rates are correlated with maximal ablation of the mesial hippocampal head, whilst sparing of the parahippocampal gyrus (PHG) may reduce neuropsychological sequelae. Current commercially available laser catheters are inserted following manually planned straight-line trajectories, which cannot conform to curved brain structures, such as the hippocampus, without causing collateral damage or requiring multiple insertions. The clinical feasibility and potential of curved LiTT trajectories through steerable needles has yet to be investigated. This is the focus of our work. We propose a GPU-accelerated computer-assisted planning (CAP) algorithm for steerable needle insertions that generates optimized curved 3D trajectories with maximal ablation of the amygdalohippocampal complex and minimal collateral damage to nearby structures, while accounting for a variable ablation diameter ( 5-15mm). Simulated trajectories and ablations were performed on 5 patients with mesial temporal sclerosis (MTS), which were identified from a prospectively managed database. The algorithm generated obstacle-free paths with significantly greater target area ablation coverage and lower PHG ablation variance compared to straight line trajectories. The presented CAP algorithm returns increased ablation of the amygdalohippocampal complex, with lower patient risk scores compared to straight-line trajectories. This is the first clinical application of preoperative planning for steerable needle based LiTT. This study suggests that steerable needles have the potential to improve LiTT procedure efficacy whilst improving the safety and should thus be investigated further.

Refining Planning for Stereoelectroencephalography: A Prospective Validation of Spatial Priors for Computer-Assisted Planning With Application of Dynamic Learning

Objective: Stereoelectroencephalography (SEEG) is a procedure in which many electrodes are stereotactically implanted within different regions of the brain to estimate the epileptogenic zone in patients with drug-refractory focal epilepsy. Computer-assisted planning (CAP) improves risk scores, gray matter sampling, orthogonal drilling angles to the skull and intracerebral length in a fraction of the time required for manual planning. Due to differences in planning practices, such algorithms may not be generalizable between institutions. We provide a prospective validation of clinically feasible trajectories using “spatial priors” derived from previous implantations and implement a machine learning classifier to adapt to evolving planning practices.

Methods: Thirty-two patients underwent consecutive SEEG implantations utilizing computer-assisted planning over 2 years. Implanted electrodes from the first 12 patients (108 electrodes) were used as a training set from which entry and target point spatial priors were generated. CAP was then prospectively performed using the spatial priors in a further test set of 20 patients (210 electrodes). A K-nearest neighbor (K-NN) machine learning classifier was implemented as an adaptive learning method to modify the spatial priors dynamically.

Results: All of the 318 prospective computer-assisted planned electrodes were implanted without complication. Spatial priors developed from the training set generated clinically feasible trajectories in 79% of the test set. The remaining 21% required entry or target points outside of the spatial priors. The K-NN classifier was able to dynamically model real-time changes in the spatial priors in order to adapt to the evolving planning requirements.

Conclusions: We provide spatial priors for common SEEG trajectories that prospectively integrate clinically feasible trajectory planning practices from previous SEEG implantations. This allows institutional SEEG experience to be incorporated and used to guide future implantations. The deployment of a K-NN classifier may improve the generalisability of the algorithm by dynamically modifying the spatial priors in real-time as further implantations are performed.

An Exit Strategy for Resuming Nonemergency Neurosurgery after Severe Acute Respiratory Syndrome Coronavirus 2: A United Kingdom Perspective

INTRODUCTION

Substantial healthcare resources have been diverted to manage the effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, and nonemergency neurosurgery has been effectively closed. As we begin to emerge from the crisis, we will need to manage the backlog of nonemergency neurosurgical patients whose treatment has been delayed and remain responsive to further possible surges of SARS-CoV-2 infections.

METHODS

In the present study, we aimed to identify the core themes and challenges that will limit resumption of a normal neurosurgical service after the SARS-CoV-2 pandemic and to provide pragmatic advice and solutions that could be of utility to clinicians seeking to resume nonemergency neurosurgical care. We reviewed the relevant international policies, a wide range of journalistic and media sources, and expert opinion documents to address the stated aims.

RESULTS

We have presented and discussed a range of factors that could become potential barriers to resuming full elective neurosurgical provision and important steps that must be completed to achieve pre-SARS-CoV-2 surgical capacity. We also explored how these challenges can be overcome and outlined the key requirements for a successful neurosurgical exit strategy from the pandemic.

CONCLUSION

The performance of nonemergency neurosurgery can start once minimum criteria have been fulfilled: 1) a structured prioritization of surgical cases; 2) virus infection incidence decreased sufficiently to release previously diverted healthcare resources; 3) adequate safety criteria met for patients and staff, including sufficient personal protective equipment and robust testing availability; and 4) maintenance of systems for rapid communication at organizational and individual levels.

Computer-Assisted Versus Manual Planning for Stereotactic Brain Biopsy: A Retrospective Comparative Pilot Study

BACKGROUND

Stereotactic brain biopsy is among the most common neurosurgical procedures. Planning an optimally safe surgical trajectory requires careful attention to a number of features including the following: (1) traversing the skull perpendicularly; (2) minimizing trajectory length; and (3) avoiding critical neurovascular structures.

OBJECTIVE

To evaluate a platform, SurgiNav, for automated trajectory planning in stereotactic brain biopsy.

METHODS

A prospectively maintained database was searched between February and August 2017 to identify all adult patients who underwent stereotactic brain biopsy and for whom postoperative imaging was available. In each case, the standard preoperative, T1-weighted, gadolinium-enhanced magnetic resonance imaging was used to generate a model of the cortex. A surgical trajectory was then generated using computer-assisted planning (CAP) , and metrics of the trajectory were compared to the trajectory of the previously implemented manual plan (MP).

RESULTS

Fifteen consecutive patients were identified. Feasible trajectories were generated using CAP in all patients, and the mean angle determined using CAP was more perpendicular to the skull than using MP (10.0° vs 14.6° from orthogonal; P = .07), the mean trajectory length was shorter (38.5 vs 43.5 mm; P = .01), and the risk score was lower (0.27 vs 0.52; P = .03).

CONCLUSION

CAP for stereotactic brain biopsy appears feasible and may be safer in selected cases.

Computer-assisted planning for minimally invasive anterior two-thirds laser corpus callosotomy: A feasibility study with probabilistic tractography validation

•

Laser interstitial thermal therapy (LITT) is a novel minimally invasive technique for the treatment of epilepsy.

•

We test computer assisted planning with LITT to disrupt seizure spread.

•

Trajectory parameters and models were automatically generated from a single T1 image.

•

Probabilistic tractography revealed comparable interhemispheric disconnection to blinded expert surgeons.

Background

Anterior two-thirds corpus callosotomy is an effective palliative neurosurgical procedure for drug-refractory epilepsy that is most commonly used to treat drop-attacks. Laser interstitial thermal therapy is a novel stereotactic ablative technique that has been utilised as a minimally invasive alternative to resective and disconnective open neurosurgery. Case series have reported success in performing laser anterior two-thirds corpus callosotomy. Computer-assisted planning algorithms may help to automate and optimise multi-trajectory planning for this procedure.

Objective

To undertake a simulation-based feasibility study of computer-assisted corpus callostomy planning in comparison with expert manual plans in the same patients.

Methods

Ten patients were selected from a prospectively maintained database. Patients had previously undergone diffusion-weighted imaging and digital subtraction angiography as part of routine SEEG care. Computer-assisted planning was performed using the EpiNav™ platform and compared to manually planned trajectories from two independent blinded experts. Estimated ablation cavities were used in conjunction with probabilistic tractography to simulate the expected extent of interhemispheric disconnection.

Results

Computer-assisted planning resulted in significantly improved trajectory safety metrics (risk score and minimum distance to vasculature) compared to blinded external expert manual plans. Probabilistic tractography revealed residual interhemispheric connectivity in 1/10 cases following computer-assisted planning compared to 4/10 and 2/10 cases with manual planning.

Conclusion

Computer-assisted planning successfully generates multi-trajectory plans capable of LITT anterior two-thirds corpus callosotomy. Computer-assisted planning may provide a means of standardising trajectory planning and serves as a potential new tool for optimising trajectories. A prospective validation study is now required to determine if this translates into improved patient outcomes.

Computer-Assisted Planning for Stereoelectroencephalography (SEEG)

Stereoelectroencephalography (SEEG) is a diagnostic procedure in which multiple electrodes are stereotactically implanted within predefined areas of the brain to identify the seizure onset zone, which needs to be removed to achieve remission of focal epilepsy. Computer-assisted planning (CAP) has been shown to improve trajectory safety metrics and generate clinically feasible trajectories in a fraction of the time needed for manual planning. We report a prospective validation study of the use of EpiNav (UCL, London, UK) as a clinical decision support software for SEEG. Thirteen consecutive patients (125 electrodes) undergoing SEEG were prospectively recruited. EpiNav was used to generate 3D models of critical structures (including vasculature) and other important regions of interest. Manual planning utilizing the same 3D models was performed in advance of CAP. CAP was subsequently employed to automatically generate a plan for each patient. The treating neurosurgeon was able to modify CAP generated plans based on their preference. The plan with the lowest risk score metric was stereotactically implanted. In all cases (13/13), the final CAP generated plan returned a lower mean risk score and was stereotactically implanted. No complication or adverse event occurred. CAP trajectories were generated in 30% of the time with significantly lower risk scores compared to manually generated. EpiNav has successfully been integrated as a clinical decision support software (CDSS) into the clinical pathway for SEEG implantations at our institution. To our knowledge, this is the first prospective study of a complex CDSS in stereotactic neurosurgery and provides the highest level of evidence to date.

Stereoelectroencephalography electrode placement: Detection of blood vessel conflicts

OBJECTIVE

Various forms of vascular imaging are performed to identify vessels that should be avoided during stereoelectroencephalography (SEEG) planning. Digital subtraction angiography (DSA) is the gold standard for intracranial vascular imaging. DSA is an invasive investigation, and a balance is necessary to identify all clinically relevant vessels and not to visualize irrelevant vessels that may unnecessarily restrict electrode placement. We sought to estimate the size of vessels that are clinically significant for SEEG planning.

METHODS

Thirty-three consecutive patients who underwent 354 SEEG electrode implantations planned with computer-assisted planning and DSA segmentation between 2016 and 2018 were identified from a prospectively maintained database. Intracranial positions of electrodes were segmented from postimplantation computed tomography scans. Each electrode was manually reviewed using "probe-eye view" with the raw preoperative DSA images for vascular conflicts. The diameter of vessels and the location of conflicts were noted. Vessel conflicts identified on raw DSA images were cross-referenced against other modalities to determine whether the conflict could have been detected.

RESULTS

One hundred sixty-six vessel conflicts were identified between electrodes and DSA-identified vessels, with 0-3 conflicts per electrode and a median of four conflicts per patient. The median diameter of conflicting vessels was 1.3 mm (interquartile range [IQR] = 1.0-1.5 mm). The median depth of conflict was 31.0 mm (IQR = 14.3-45.0 mm) from the cortical surface. The addition of sulcal models to DSA, magnetic resonance venography (MRV), and T1 + gadolinium images, as an exclusion zone during computer-assisted planning, would have prevented the majority of vessel conflicts. We were unable to determine whether vessels were displaced or transected by the electrodes.

SIGNIFICANCE

Vascular segmentation from DSA images was significantly more sensitive than T1 + gadolinium or MRV images. Electrode conflicts with vessels 1-1.5 mm in size did not result in a radiologically detectable or clinically significant hemorrhage and could potentially be excluded from consideration during SEEG planning.

Multicenter validation of automated trajectories for selective laser amygdalohippocampectomy

Objective

Laser interstitial thermal therapy (LITT) is a novel minimally invasive alternative to open mesial temporal resection in drug‐resistant mesial temporal lobe epilepsy (MTLE). The safety and efficacy of the procedure are dependent on the preplanned trajectory and the extent of the planned ablation achieved. Ablation of the mesial hippocampal head has been suggested to be an independent predictor of seizure freedom, whereas sparing of collateral structures is thought to result in improved neuropsychological outcomes. We aim to validate an automated trajectory planning platform against manually planned trajectories to objectively standardize the process.

Methods

Using the EpiNav platform, we compare automated trajectory planning parameters derived from expert opinion and machine learning to undertake a multicenter validation against manually planned and implemented trajectories in 95 patients with MTLE. We estimate ablation volumes of regions of interest and quantify the size of the avascular corridor through the use of a risk score as a marker of safety. We also undertake blinded external expert feasibility and preference ratings.

Results

Automated trajectory planning employs complex algorithms to maximize ablation of the mesial hippocampal head and amygdala, while sparing the parahippocampal gyrus. Automated trajectories resulted in significantly lower calculated risk scores and greater amygdala ablation percentage, whereas overall hippocampal ablation percentage did not differ significantly. In addition, estimated damage to collateral structures was reduced. Blinded external expert raters were significantly more likely to prefer automated to manually planned trajectories.

Significance

Retrospective studies of automated trajectory planning show much promise in improving safety parameters and ablation volumes during LITT for MTLE. Multicenter validation provides evidence that the algorithm is robust, and blinded external expert ratings indicate that the trajectories are clinically feasible. Prospective validation studies are now required to determine if automated trajectories translate into improved seizure freedom rates and reduced neuropsychological deficits.

Automated fiber tract reconstruction for surgery planning: Extensive validation in language-related white matter tracts

Diffusion MRI and tractography hold great potential for surgery planning, especially to preserve eloquent white matter during resections. However, fiber tract reconstruction requires an expert with detailed understanding of neuroanatomy. Several automated approaches have been proposed, using different strategies to reconstruct the white matter tracts in a supervised fashion. However, validation is often limited to comparison with manual delineation by overlap-based measures, which is limited in characterizing morphological and topological differences. In this work, we set up a fully automated pipeline based on anatomical criteria that does not require manual intervention, taking advantage of atlas-based criteria and advanced acquisition protocols available on clinical-grade MRI scanners. Then, we extensively validated it on epilepsy patients with specific focus on language-related bundles. The validation procedure encompasses different approaches, including simple overlap with manual segmentations from two experts, feasibility ratings from external multiple clinical raters and relation with task-based functional MRI. Overall, our results demonstrate good quantitative agreement between automated and manual segmentation, in most cases better performances of the proposed method in qualitative terms, and meaningful relationships with task-based fMRI. In addition, we observed significant differences between experts in terms of both manual segmentation and external ratings. These results offer important insights on how different levels of validation complement each other, supporting the idea that overlap-based measures, although quantitative, do not offer a full perspective on the similarities and differences between automated and manual methods.

Increasing the accuracy of 3D EEG implantations

OBJECTIVE

The accuracy of stereoelectroencephalography (SEEG) electrode implantation is an important factor in maximizing its safety. The authors established a quality assurance (QA) process to aid advances in implantation accuracy.

METHODS

The accuracy of three consecutive modifications of a frameless implantation technique was quantified in three cohorts comprising 22, 8, and 23 consecutive patients. The modifications of the technique aimed to increase accuracy of the bolt placement.

RESULTS

The lateral shift of the axis of the implanted bolt at the level of the planned entry point was reduced from a mean of 3.0 ± 1.6 mm to 1.4 ± 0.8 mm. The lateral shift of the axis of the implanted bolt at the level of the planned target point was reduced from a mean of 3.8 ± 2.5 mm to 1.6 ± 0.9 mm.

CONCLUSIONS

This QA framework helped to isolate and quantify the factors introducing inaccuracy in SEEG implantation, and to monitor ongoing accuracy and the effect of technique modifications.

TP3-5 Structural connectivity driven stereoelectroencephalography (SEEG) electrode targeting in suspected pseudotemporal and temporal plus epilepsy

Objectives

One third of patients with drug resistant focal mesial temporal lobe epilepsy (MTLE) fail to achieve long-term seizure freedom following temporal lobe resections. Reasons for failure may include ictal onset outside the temporal lobe (TL), termed ‘pseudotemporal lobe epilepsy’ (pTLE), with propagation from strongly connected neighboring areas or temporal plus (TL+) epilepsy, when the epileptogenic zone primarily involves the temporal lobe and also extends to neighboring regions. In such cases the perisylvian and orbito-frontal (OF) cortices, cingulum and temporo-parieto-occipital junction may be implicated. Stereoelectroencephalography (SEEG) is a procedure in which electrodes are stereotactically placed within predefined brain regions to delineate the SOZ and allows evaluation of deep anatomical structures adjacent to the TL. SEEG electrode contacts sample from a core radius of 3–5 mm. It is unclear which sub-regions of target structures should be preferentially implanted to optimally detect the network involved in seizure onset and rapid propagation. Using normalized average group templates of structural connectivity from patients with hippocampal sclerosis (HS), we determine the greatest connectivity to critical sub-regions and based upon this propose optimal locations for SEEG targeting.

Design

Observational cross-sectional study.

Subjects

Twelve patients with HS (6 right) that had undergone SEEG and pre-operative diffusion imaging were identified from a prospectively maintained database.

Methods

Whole brain connectomes with 10 million tracts were generated using cortical seed regions derived from whole brain GIF parcellations. Normalized group templates were generated separately for right and left HS patients. Orbitofrontal cortex (OF), insula (INS), cingulum (Cing) and temporo-parietal-occipital junction (supramarginal gyrus, angular gyrus, precuneus, fusiform gyrus and lingual gyrus) were segmented into surgically targetable subregions. All subregions had similar volumes. Connectivity of the amygdalohippocampal complex (AHC) was defined based on the number of streamlines terminating in the subregions of interest.

Results

Left HS showed preferential connections to the ipsilateral: posterior part of lateral OF cortex, posterior short gyrus of anterior INS, posterior part of the posterior Cing, middle part of lingual gyrus, posterior part of precuneus and middle part of fusiform gyrus. Right HS showed preferential connections to the ipsilateral: posterior part of the lateral OF cortex, anterior long gyrus of posterior INS, posterior part of posterior Cing, anterior part of lingual gyrus and posterior part of precuneus.

Conclusions

Using whole brain connectomes we determine surgically feasible targets in sub-regions based on greatest connectivity to the AHC. We propose that SEEG targeting utilizing computer-assisted planning may improve the understanding of the overall network connectivity in order to enhance the diagnostic utility of the SEEG implantation. SEEG electrode placement within structures associated with pTLE and TL +may aid in delineating the SOZ if the correct sub-regions are targeted. This should be evaluated prospectively.

WP1-15 Computer-assisted versus manual planning for stereotactic brain biopsy: retrospective comparative pilot study

Objectives

Stereotactic brain biopsy is among the most common neurosurgical procedures. Planning a safe surgical trajectory requires careful attention to a number of features including:

traversing the skull perpendicularly;

avoiding critical neurovascular structures; and

minimising trajectory length.

The aim of this study was to develop a platform, SurgiNav, for automated trajectory planning in stereotactic brain biopsy.

Methods

A prospectively maintained database was searched between February and August 2017 to identify all adult patients that underwent stereotactic brain biopsy in whom post-operative imaging was available. In each case, the standard pre-operative T1-weighted gadolinium-enhanced MRI was used to generate models of the cortex and vasculature. A surgical trajectory was then generated using automated computer-assisted planning (CAP) and metrics compared to the trajectory of the implemented manual plan (MP) using the paired T-test.

Results

15 consecutive patients were identified; who had a diagnostic biopsy and there were no immediate complications. Feasible trajectories were generated using CAP in 12 patients, and in these the mean trajectory length using CAP was comparable to MP (31.7 mm vs. 37.1 mm; p=0.3), and mean angle was similarly perpendicular from orthogonal (9.3° vs. 15.3° p=0.1), but the risk-metric was significantly lower (0.16 vs. 0.48; p=0.03).

Conclusions

Computer-assisted planning for stereotactic brain biopsy appears feasible in most cases and may be safer in selected cases.

P31 Optimising trajectories in computer assisted planning for cranial laser interstitial thermal therapy: a machine learning approach

Objectives

Optimal trajectory planning for cranial laser interstitial thermal therapy (cLITT) in drug resistant focal mesial temporal lobe epilepsy (MTLE).

Design

A composite ablation score of ablated AHC minus ablated PHG volumes were calculated and normalised. Random forest and linear regression were implemented to predict composite ablation scores and determine the optimal entry and target point combinations to maximize this.

Subjects

Ten patients with hippocampal sclerosis were included.

Methods

Computer Assisted Planning (CAP) cLITT trajectories were generated using entry regions that include the inferior occipital gyri (IOG), middle occipital gyri (MOG), inferior temporal gyri (ITG) and middle temporal gyri (MTG). Target points were varied by sequential erosions and transformations of the centroid of the amygdala. In total 760 trajectory combinations were generated per patient and ablation volumes were calculated based on a conservative 15 mm maximum ablation diameter.

Results

Linear regression was superior to random forest predictions. Linear regression indicated that maximal composite ablation scores were associated with entry points that clustered around the junction of the IOG, MOG and MTG. The optimal target point was a translation of the centroid of the amygdala anteriorly and medially.

Conclusions

Machine learning techniques accurately predict composite ablation scores with linear regression outperforming the random forest approach. Optimal CAP entry points for cLITT maximize ablation of the AHC and spare the PHG.

Optimizing Trajectories for Cranial Laser Interstitial Thermal Therapy Using Computer-Assisted Planning: A Machine Learning Approach

Laser interstitial thermal therapy (LITT) is an alternative to open surgery for drug-resistant focal mesial temporal lobe epilepsy (MTLE). Studies suggest maximal ablation of the mesial hippocampal head and amygdalohippocampal complex (AHC) improves seizure freedom rates while better neuropsychological outcomes are associated with sparing of the parahippocampal gyrus (PHG). Optimal trajectories avoid sulci and CSF cavities and maximize distance from vasculature. Computer-assisted planning (CAP) improves these metrics, but the combination of entry and target zones has yet to be determined to maximize ablation of the AHC while sparing the PHG. We apply a machine learning approach to predict entry and target parameters and utilize these for CAP. Ten patients with hippocampal sclerosis were identified from a prospectively managed database. CAP LITT trajectories were generated using entry regions that include the inferior occipital, middle occipital, inferior temporal, and middle temporal gyri. Target points were varied by sequential AHC erosions and transformations of the centroid of the amygdala. A total of 7600 trajectories were generated, and ablation volumes of the AHC and PHG were calculated. Two machine learning approaches (random forest and linear regression) were investigated to predict composite ablation scores and determine entry and target point combinations that maximize ablation of the AHC while sparing the PHG. Random forest and linear regression predictions had a high correlation with the calculated values in the test set (ρ = 0.7) for both methods. Maximal composite ablation scores were associated with entry points around the junction of the inferior occipital, middle occipital, and middle temporal gyri. The optimal target point was the anteromesial amygdala. These parameters were then used with CAP to generate clinically feasible trajectories that optimize safety metrics. Machine learning techniques accurately predict composite ablation score. Prospective studies are required to determine if this improves seizure-free outcome while reducing neuropsychological morbidity following LITT for MTLE.

Computer-assisted planning for the insertion of stereoelectroencephalography electrodes for the investigation of drug-resistant focal epilepsy: an external validation study

OBJECTIVE

One-third of cases of focal epilepsy are drug refractory, and surgery might provide a cure. Seizure-free outcome after surgery depends on the correct identification and resection of the epileptogenic zone. In patients with no visible abnormality on MRI, or in cases in which presurgical evaluation yields discordant data, invasive stereoelectroencephalography (SEEG) recordings might be necessary. SEEG is a procedure in which multiple electrodes are placed stereotactically in key targets within the brain to record interictal and ictal electrophysiological activity. Correlating this activity with seizure semiology enables identification of the seizure-onset zone and key structures within the ictal network. The main risk related to electrode placement is hemorrhage, which occurs in 1% of patients who undergo the procedure. Planning safe electrode placement for SEEG requires meticulous adherence to the following: 1) maximize the distance from cerebral vasculature, 2) avoid crossing sulcal pial boundaries (sulci), 3) maximize gray matter sampling, 4) minimize electrode length, 5) drill at an angle orthogonal to the skull, and 6) avoid critical neurological structures. The authors provide a validation of surgical strategizing and planning with EpiNav, a multimodal platform that enables automated computer-assisted planning (CAP) for electrode placement with user-defined regions of interest.

METHODS

Thirteen consecutive patients who underwent implantation of a total 116 electrodes over a 15-month period were studied retrospectively. Models of the cortex, gray matter, and sulci were generated from patient-specific whole-brain parcellation, and vascular segmentation was performed on the basis of preoperative MR venography. Then, the multidisciplinary implantation strategy and precise trajectory planning were reconstructed using CAP and compared with the implemented manually determined plans. Paired results for safety metric comparisons were available for 104 electrodes. External validity of the suitability and safety of electrode entry points, trajectories, and target-point feasibility was sought from 5 independent, blinded experts from outside institutions.

RESULTS

CAP-generated electrode trajectories resulted in a statistically significant improvement in electrode length, drilling angle, gray matter-sampling ratio, minimum distance from segmented vasculature, and risk (p < 0.05). The blinded external raters had various opinions of trajectory feasibility that were not statistically significant, and they considered a mean of 69.4% of manually determined trajectories and 62.2% of CAP-generated trajectories feasible; 19.4% of the CAP-generated electrode-placement plans were deemed feasible when the manually determined plans were not, whereas 26.5% of the manually determined electrode-placement plans were rated feasible when CAP-determined plans were not (no significant difference).

CONCLUSIONS

CAP generates clinically feasible electrode-placement plans and results in statistically improved safety metrics. CAP is a useful tool for automating the placement of electrodes for SEEG; however, it requires the operating surgeon to review the results before implantation, because only 62% of electrode-placement plans were rated feasible, compared with 69% of the manually determined placement plans, mainly because of proximity of the electrodes to unsegmented vasculature. Improved vascular segmentation and sulcal modeling could lead to further improvements in the feasibility of CAP-generated trajectories.

Getting the best outcomes from epilepsy surgery

Neurosurgery is an underutilized treatment that can potentially cure drug‐refractory epilepsy. Careful, multidisciplinary presurgical evaluation is vital for selecting patients and to ensure optimal outcomes. Advances in neuroimaging have improved diagnosis and guided surgical intervention. Invasive electroencephalography allows the evaluation of complex patients who would otherwise not be candidates for neurosurgery. We review the current state of the assessment and selection of patients and consider established and novel surgical procedures and associated outcome data. We aim to dispel myths that may inhibit physicians from referring and patients from considering neurosurgical intervention for drug‐refractory focal epilepsies. Ann Neurol 2018;83:676–690

Automated trajectory planning for laser interstitial thermal therapy in mesial temporal lobe epilepsy

OBJECTIVE

Surgical resection of the mesial temporal structures brings seizure remission in 65% of individuals with drug-resistant mesial temporal lobe epilepsy (MTLE). Laser interstitial thermal therapy (LiTT) is a novel therapy that may provide a minimally invasive means of ablating the mesial temporal structures with similar outcomes, while minimizing damage to the neocortex. Systematic trajectory planning helps ensure safety and optimal seizure freedom through adequate ablation of the amygdalohippocampal complex (AHC). Previous studies have highlighted the relationship between the residual unablated mesial hippocampal head and failure to achieve seizure freedom. We aim to implement computer-assisted planning (CAP) to improve the ablation volume and safety of LiTT trajectories.

METHODS

Twenty-five patients who had previously undergone LiTT for MTLE were studied retrospectively. The EpiNav platform was used to automatically generate an optimal ablation trajectory, which was compared with the previous manually planned and implemented trajectory. Expected ablation volumes and safety profiles of each trajectory were modeled. The implemented laser trajectory and achieved ablation of mesial temporal lobe structures were quantified and correlated with seizure outcome.

RESULTS

CAP automatically generated feasible trajectories with reduced overall risk metrics (P < .001) and intracerebral length (P = .007). There was a significant correlation between the actual and retrospective CAP-anticipated ablation volumes, supporting a 15 mm diameter ablation zone model (P < .001). CAP trajectories would have provided significantly greater ablation of the amygdala (P = .0004) and AHC (P = .008), resulting in less residual unablated mesial hippocampal head (P = .001), and reduced ablation of the parahippocampal gyrus (P = .02).

SIGNIFICANCE

Compared to manually planned trajectories CAP provides a better safety profile, with potentially improved seizure-free outcome and reduced neuropsychological deficits, following LiTT for MTLE.

Improving patient safety during introduction of novel medical devices through cumulative summation analysis

OBJECTIVE The aim of this study was to implement cumulative summation (CUSUM) analysis as an early-warning detection and quality assurance system for preclinical testing of the iSYS1 novel robotic trajectory guidance system. METHODS Anatomically accurate 3D-printed skull phantoms were created for 3 patients who underwent implantation of 21 stereoelectroencephalography electrodes by surgeons using the current standard of care (frameless technique). Implantation schema were recreated using the iSYS1 system, and paired accuracy measures were compared with the previous frameless implantations. Entry point, target point, and implantation angle accuracy were measured on postimplantation CT scans. CUSUM analysis was undertaken prospectively. RESULTS The iSYS1 trajectory guidance system significantly improved electrode entry point accuracies from 1.90 ± 0.96 mm (mean ± SD) to 0.76 ± 0.57 mm (mean ± SD) without increasing implantation risk. CUSUM analysis was successful as a continuous measure of surgical performance and acted as an early-warning detection system. The surgical learning curve, although minimal, showed improvement after insertion of the eighth electrode. CONCLUSIONS The iSYS1 trajectory guidance system did not show any increased risk during phantom preclinical testing when used by neurosurgeons who had no experience with its use. CUSUM analysis is a simple technique that can be applied to all stages of the IDEAL (idea, development, exploration, assessment) framework as an extra patient safety mechanism. Further clinical trials are required to prove the efficacy of the device.

Robot-assisted stereotactic brain biopsy: systematic review and bibliometric analysis

INTRODUCTION

Stereotactic brain biopsy represents one of the earliest applications of surgical robotics. The aim of the present systematic review and bibliometric analysis was to evaluate the literature supporting robot-assisted brain biopsy and the extent to which the scientific community has accepted the technique.

METHODS

The Cochrane and PubMed databases were searched over a 30-year period between 1st of January 1988 and 31st of December 2017. Titles and abstracts were screened to identify publications that met the following criteria: (1) featured patients with brain pathology, (2) undergoing stereotactic brain biopsy, (3) reporting robot-assisted surgery, and (4) outcome data were provided. The reference lists of selected studies were also sought, and expert opinion sought to identify further eligible publications. Selected manuscripts were then reviewed, and data extracted on effectiveness and safety. The status of scientific community acceptance was determined using a progressive scholarly acceptance analysis.

RESULTS

All identified studies were non-randomised, including 1 retrospective cohort study and 14 case series or reports. The diagnostic biopsy rate varied from 75 to 100%, and the average target accuracy varied from 0.9 to 4.5 mm. Use of the robot was aborted in two operations owing to geometric inaccessibility and an error in image registration but no associated adverse events were reported. A compounding progressive scholarly acceptance analysis suggested a trend towards acceptance of the technique by the scientific community.

CONCLUSIONS

In conclusion, robot-assisted stereotactic brain biopsy is an increasingly mainstream tool in the neurosurgical armamentarium. Further evaluation should proceed along the IDEAL framework with research databases and comparative trials.

Accuracy of intracranial electrode placement for stereoencephalography: A systematic review and meta-analysis

OBJECTIVE

Stereoencephalography (SEEG) is a procedure in which electrodes are inserted into the brain to help define the epileptogenic zone. This is performed prior to definitive epilepsy surgery in patients with drug-resistant focal epilepsy when noninvasive data are inconclusive. The main risk of the procedure is hemorrhage, which occurs in 1-2% of patients. This may result from inaccurate electrode placement or a planned electrode damaging a blood vessel that was not detected on the preoperative vascular imaging. Proposed techniques include the use of a stereotactic frame, frameless image guidance systems, robotic guidance systems, and customized patient-specific fixtures.

METHODS

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, a structured search of the PubMed, Embase, and Cochrane databases identified studies that involve the following: (1) SEEG placement as part of the presurgical workup in patients with (2) drug-resistant focal epilepsy for which (3) accuracy data have been provided.

RESULTS

Three hundred twenty-six publications were retrieved, of which 293 were screened following removal of duplicate and non-English-language studies. Following application of the inclusion and exclusion criteria, 15 studies were included in the qualitative and quantitative synthesis of the meta-analysis. Accuracies for SEEG electrode implantations have been combined using a random-effects analysis and stratified by technique.

SIGNIFICANCE

The published literature regarding accuracy of SEEG implantation techniques is limited. There are no prospective controlled clinical trials comparing different SEEG implantation techniques. Significant systematic heterogeneity exists between the identified studies, preventing any meaningful comparison between techniques. The recent introduction of robotic trajectory guidance systems has been suggested to provide a more accurate method of implantation, but supporting evidence is limited to class 3 only. It is important that new techniques are compared to the previous "gold-standard" through well-designed and methodologically sound studies before they are introduced into widespread clinical practice.

The Assessment of Distortion in Neurosurgical Image Overlay Projection

BACKGROUND

Numerous studies have demonstrated the superiority of neuronavigation during neurosurgical procedures compared to non-neuronavigation-based procedures. Limitations to neuronavigation systems include the need for the surgeons to avert their gaze from the surgical field and the cost of the systems, especially for hospitals in developing countries. Overlay projection of imaging directly onto the patient allows localization of intracranial structures. A previous study using overlay projection demonstrated the accuracy of image coregistration for a lesion in the temporal region but did not assess image distortion when projecting onto other anatomical locations. Our aim is to quantify this distortion and establish which regions of the skull would be most suitable for overlay projection.

METHODS

Using the difference in size of a square grid when projected onto an anatomically accurate model skull and a flat surface, from the same distance, we were able to calculate the degree of image distortion when projecting onto the skull from the anterior, posterior, superior, and lateral aspects. Measuring the size of a square when projected onto a flat surface from different distances allowed us to model change in lesion size when projecting a deep structure onto the skull surface.

RESULTS

Using 2 mm as the upper limit for distortion, our results show that images can be accurately projected onto the majority (81.4%) of the surface of the skull.

CONCLUSION

Our results support the use of image overlay projection in regions with ≤2 mm distortion to assist with localization of intracranial lesions at a fraction of the cost of existing methods.

Introduction of Sprotte needles to a single-centre acute neurology service: before and after study

Objectives

To introduce atraumatic (Sprotte) lumbar puncture needles and compare complication rates with traumatic (Quincke) needles.

Design

Complication rates associated with traumatic needle use were retrospectively analysed over a four-week period. Atraumatic needles were then implemented and a prospective analysis of the complication rates was undertaken for a further six weeks.

Setting

A single-centre acute neurology unit in a London teaching hospital

Participants

Traumatic needles (n = 24 patients); atraumatic needles (n = 36 patients)

Main outcome measures

Headache rates, use of over-the-counter medications, further medical assistance, time off work, nausea and vomiting, traumatic taps (as per the count of red blood cells per millilitre in the first sample of cerebrospinal fluid [CSF]) and back pain.

Results

A comparison of traumatic and atraumatic needles revealed a significant reduction in the incidence of post-lumbar puncture headaches (*P < 0.01), headaches requiring over-the-counter medication (*P < 0.00001), need for further medical assistance (*P < 0.006), time off work (*P < 0.003), nausea and vomiting (*P < 0.01) and traumatic taps as per the count of red blood cells per millilitre in the first sample of CSF (*P < 0.02). There was no significant difference in the incidence of back pain (P > 0.05).

Conclusions

Most complication outcomes are significantly lower with the use of atraumatic lumbar puncture needles. We present for the first time in the literature that the rate of ‘traumatic taps’ are significantly lower with atraumatic needles. The implementation of atraumatic needles in an acute neurology service is safe and produces reliable, reproducible results in keeping with previously published randomized controlled trials.

Immune responses elicited in rainbow trout through the administration of infectious pancreatic necrosis virus-like particles

Virus like particles (VLPs) against viral pathogens not only constitute a novel approach for the development of antiviral vaccines for an specific virus, but also for the creation of multivalent vaccines in which antigens from other pathogens may be expressed on the surface of these VLPs. Despite positive results on protection for many of these VLPs in both fish and mammals, not many studies have focused on the immune response triggered by these particles; studies that may provide hints for the identification of immune mechanisms responsible for antiviral protection, which are mostly unknown in fish. In the current work, we have studied the levels of transcription of several immune genes in the spleen of rainbow trout (Oncorhynchus mykiss) intraperitoneally injected with VLPs from infectious pancreatic necrosis virus (IPNV) focusing on the chemokine response as well as the response of genes related to interferon (IFN) production. Surprisingly, the capacity of VLPs to induce chemokines differed from that of live IPNV, suggesting a direct effect of viral replication on the chemokine response in this organ. While VLPs up-regulated the transcription of CK3, CK10 and CXCd and down-modulated CK5B, CK6 and CK9 transcription, a previous study in which the transcription of γIP, CXCd, CK1, CK3, CK5B, CK6, CK7A, CK9 and CK12 had been studied demonstrated that IPNV only significantly up-regulated CK6 and down-modulated CK3 in the spleen. On the other hand, the administration of VLPs produced a strong mobilization to the peritoneum of CD4(+), IgM(+), IgT(+) and CD83(+) leukocytes similar to that induced by the live viral infection. In both cases, this leukocyte recruitment seemed to be greatly mediated through CK3, CK5B, CK9 and CK10 chemokine production. These results together with the fact that VLPs strongly induced non-specific lymphocyte proliferation and specific anti-IPNV antibody production point to VLPs as excellent candidates for vaccine development.

Genetic analysis of aquabirnaviruses isolated from wild fish reveals occurrence of natural reassortment of infectious pancreatic necrosis virus

In this study, we report the sequencing of the whole genome [including the 5' and 3' non-coding regions (NCR) of both segments A and B] of seven birnavirus strains isolated from wild fish from the Flemish Cap (FC) fishery at Newfoundland, Canada. From analysis and comparison of the sequences, most of the FC isolates clustered with the North American reference strains West Buxton (WB), Dry Mill and Jasper. One strain was included in the same genotype as the European strain Ab. In addition, at least in one case cohabitation of both type strains in an individual fish was demonstrated. These results clearly suggest the acquisition of the viruses from two different sources. The prevalence of the American type is easily explained by the close proximity of this fishing bank to the American coast whereas, although surprising, the presence of the European type strain could be because of migration of fish from European waters. In one strain, segment A and B sequences were typed differently (WB and Ab, respectively). These findings indicate natural reassortment between two strains of aquabirnaviruses in a host.

Development of a subunit vaccine for infectious pancreatic necrosis virus using a baculovirus insect/larvae system

Various attempts to develop a vaccine against infectious pancreatic necrosis virus (IPNV) have not yielded consistent results. Thus, at present, no commercial vaccine is available that can be used with confidence to immunize fry of salmon and trout. We generated a cDNA clone of the large genome segment A of an IPNV Sp strain and expressed all structural protein genes in insect cells and larvae using a baculovirus expression system. Green fluorescent protein was also coexpressed as a reporter molecule. High yields of IPNV proteins were obtained and the structural proteins self assembled to form virus-like particles (VLPs). We tested the immunogenicity of the putative VLP antigen in immersion vaccine experiments (two concentrations) in rainbow trout (Oncorhynchus mykiss) fry, and by intraperitoneal immunisation of Atlantic salmon (Salmo salar) pre-smolts using an oil adjuvant formulation. Rainbow trout were challenged by immersion using either the Sp or the VR-299 strain of IPNV two or three weeks post-vaccination, while Atlantic salmon were bath challenged with Sp strain after two months, after parr-smolt transformation. In the rainbow trout fry challenged two weeks post-immunization, cumulative mortality rates three weeks post challenge were 14 % in the fry that had received the highest dose versus 8 % in the control groups. No indication of protection was seen in repeated trials using a lower dose of antigen and challenge three weeks post-immunisation. The cumulative mortality rate of intraperitoneally immunised Atlantic salmon post-smolts four weeks post challenge was lower (56%) than in the control fish (77%), showing a dose-response pattern.

Molecular characterization of Sp serotype strains of infectious pancreatic necrosis virus exhibiting differences in virulence

Infectious pancreatic necrosis virus (IPNV), a prototype virus of the family Birnaviridae, exhibits a high degree of antigenic variability, pathogenicity and virulence in salmonid species. The Genomic Segment A encodes all the structural (VP2 and VP3) and nonstructural (NS) proteins, whereas Segment B encodes the viral RNA-dependent RNA polymerase (VP1). We tested 3 different IPNV isolates (Sp103, Sp116 and Sp122) isolated during field outbreaks in Norway for their ability to cause mortality in fry and post-smolt of Atlantic salmon Salmo salar L. The cumulative mortality following experimental challenge in fry was 29% for Sp122 followed by 19% for Sp116 and 15% for Sp103. In post-smolt, the corresponding mortality rates were 79, 46 and 16%, respectively. Comparisons of the deduced amino acid sequences of Segments A and B of all 3 Sp strains revealed substitutions of residues in 13 positions, of which 6 are in VP2, 2 in VP3, and 5 in VP1. Our results suggest that these residues, especially those in the outer capsid VP2, may be involved in the virulence of IPNV. Genome Segment A of the Sp serotype is 3097 nucleotides long and contains a major open reading frame (ORF) encoding a polyprotein of 972 amino acids, which initiates at the second in-frame start codon at Position 119. This was ascertained by making mutants of Segment A clone using site-directed mutagenesis, followed by in vitro transcription-coupled translation reaction and immunoprecipitation analyses. In addition, Segment A also encodes a 15 kDa arginine-rich non-structural protein from a small ORF, preceding and partially overlapping the polyprotein ORF, which is truncated to 12 kDa in the virulent Sp122 strain. Moreover, Segment A could encode a novel, putative 25 kDa protein from another ORF between VP2 and VP4 coding regions, which is only detected in the Sp serotype. Segment B is 2777 nucleotides long and encodes in a single large ORF (a polypeptide of 844 amino acid residues), VP1.

A novel transcutaneous plasmid-dimethylsulfoxide delivery technique for avian nucleic acid immunization

In this report, we show that dimethylsulfoxide (DMSO) enhances liposome-mediated transfection of nucleic acid in chicken macrophage cells and that this could be exploited for the transcutaneous delivery of naked DNA through the intact skin of chickens. We found that DMSO enhanced transfection efficiencies of lipofectamine and polyethyleneimine in HD-11 chicken macrophage cells. Based on this principle, we showed that transcutaneous delivery of a DNA plasmid-dimethylsulfoxide mixture (1:1) to untreated skin of chickens results in a wide distribution of the plasmid in the body. Distribution studies were done using plasmids encoding enhanced green fluorescent protein (EGFP) reporter gene and a bivalent DNA vaccine coding for infectious bursal disease virus (IBDV) and Newcastle disease virus (NDV) immunogenic protein genes. This bivalent vaccine induced mucosal and systemic immune responses, as evidenced by IgA and IgM production in the tears and serum of vaccinated chickens. Mucosal immune responses in the tears after topical vaccination were significantly higher (P < 0.05) than after i.m. delivery of the same DNA vaccine and were characterized by the absence of an IgG response. The biodistribution of plasmid indicated that topical delivery with DMSO resulted in a wide distribution and persistence of the plasmid until 15 weeks post-primary vaccination. Both delivery methods resulted in insert-specific message being made in several body tissues, but after topical delivery the virus-specific mRNA could be detected in the bone marrow of one out of three chickens until 15 weeks post-primary vaccination. Furthermore, transcutaneous delivery of this DNA vaccine using DMSO conferred protection from challenge with virulent IBDV (86% survival) and NDV (86% survival). This novel transcutaneous method of delivery of a DNA vaccine shows promise as being an easy and effective way to deliver nucleic acids through intact skin for vaccination or therapeutic purposes.

Molecular determinants of virulence, cell tropism, and pathogenic phenotype of infectious bursal disease virus

Infectious bursal disease viruses (IBDVs), belonging to the family Birnaviridae, exhibit a wide range of immunosuppressive potential, pathogenicity, and virulence for chickens. The genomic segment A encodes all the structural (VP2, VP4, and VP3) and nonstructural proteins, whereas segment B encodes the viral RNA-dependent RNA polymerase (VP1). To identify the molecular determinants for the virulence, pathogenic phenotype, and cell tropism of IBDV, we prepared full-length cDNA clones of a virulent strain, Irwin Moulthrop (IM), and constructed several chimeric cDNA clones of segments A and B between the attenuated vaccine strain (D78) and the virulent IM or GLS variant strain. Using the cRNA-based reverse-genetics system developed for IBDV, we generated five chimeric viruses after transfection by electroporation procedures in Vero or chicken embryo fibroblast (CEF) cells, one of which was recovered after propagation in embryonated eggs. To evaluate the characteristics of the recovered viruses in vivo, we inoculated 3-week-old chickens with D78, IM, GLS, or chimeric viruses and analyzed their bursae for pathological lesions 3 days postinfection. Viruses in which VP4, VP4-VP3, and VP1 coding sequences of the virulent strain IM were substituted for the corresponding region in the vaccine strain failed to induce hemorrhagic lesions in the bursa. In contrast, viruses in which the VP2 coding region of the vaccine strain was replaced with the variant GLS or virulent IM strain caused rapid bursal atrophy or hemorrhagic lesions in the bursa, as seen with the variant or classical virulent strain, respectively. These results show that the virulence and pathogenic-phenotype markers of IBDV reside in VP2. Moreover, one of the chimeric viruses containing VP2 sequences of the virulent strain could not be recovered in Vero or CEF cells but was recovered in embryonated eggs, suggesting that VP2 contains the determinants for cell tropism. Similarly, one of the chimeric viruses containing the VP1 segment of the virulent strain could not be recovered in Vero cells but was recovered in CEF cells, suggesting that VP1 contains the determinants for cell-specific replication in Vero cells. By comparing the deduced amino acid sequences of the D78 and IM strains and their reactivities with monoclonal antibody 21, which binds specifically to virulent IBDV, the putative amino acids involved in virulence and cell tropism were identified. Our results indicate that residues Gln at position 253 (Gln253), Asp279, and Ala284 of VP2 are involved in the virulence, cell tropism, and pathogenic phenotype of virulent IBDV.

Induction of apoptosis in vitro by the 17-kDa nonstructural protein of infectious bursal disease virus: possible role in viral pathogenesis

Infectious bursal disease virus (IBDV) causes severe immunodeficiency in young chickens by destroying the precursors of antibody-producing B cells in the bursa of Fabricius. It has been shown that IBDV infection induces apoptosis in chicken embryo and tissue culture cells. We previously reported that an IBDV mutant lacking the expression of 17-kDa nonstructural (NS) protein exhibited decreased apoptotic effects in cell culture as compared to the parental IBDV, suggesting that the NS protein may be involved in induction of apoptosis. Here, we report that the NS protein of IBDV alone is capable of inducing apoptosis in cell culture. Transfection of chicken B-lymphocyte cell line (RP9) and chicken embryo fibroblast cells with a plasmid DNA, containing the NS protein gene under the control of the immediate-early promoter-enhancer region of human cytomegalovirus, induced programmed cell death in both cell lines. Apoptosis changes, such as chromatin condensation, DNA fragmentation, and the appearance of apoptotic nuclear bodies, were observed in cell cultures 48-h posttransfection. As reported earlier, the mutant IBDV grew to lower titers with slower replication kinetics and lower cytopathogenicity when compared to that of the parental virus. Here, we demonstrate that the mutant virus is closely associated with cells and its yield from the supernatant was approximately 30-fold lower than the wild-type due to increased cell association, indicating a deficiency in lysis of virus-infected cells. Taken together, our results indicate that the NS protein of IBDV is highly cytotoxic, which brings about the release of the viral progeny from cells, and thus play an important role in viral pathogenesis.

A recombinant Eimeria protein inducing interferon-gamma production: comparison of different gene expression systems and immunization strategies for vaccination against coccidiosis

A rabbit antiserum against an 18- to 27-kD native protein fraction (F3) from Eimeria acervulina merozoites identified a cDNA (3-1E) containing a 1086-base pair insertion with an open reading frame of 170 amino acids (predicted molecular weight, 18,523). The recombinant 3-1E cDNA expressed in Escherichia coli produced a 60-kD fusion protein and a 23-kD protein after factor Xa treatment of the fusion protein. Both proteins were reactive with the F3 antiserum by western blot analysis. A rabbit antiserum against a synthetic peptide deduced from the amino acid sequence of the 3-1E cDNA reacted with a 27-kD recombinant 3-1E protein expressed in Sf9 insect cells and a 20-kD native protein expressed by E. acervulina sporozoites and Eimeria tenella sporozoites and merozoites. By immunofluorescence staining, a monoclonal antibody produced against the recombinant 3-1E protein reacted with sporozoites and merozoites of E. acervulina, E. tenella, and Eimeria maxima. Spleen lymphocytes from E. acervulina-immune chickens showed antigen-specific proliferation and interferon (IFN)-gamma production upon stimulation with the recombinant 3-1E protein, indicating that the protein activates cell-mediated immunity during coccidiosis. Immunization of chickens with either the E. coli- or Sf9-expressed recombinant 3-1E protein with adjuvant, or direct injection of the 3-1E cDNA, induced protective immunity against live E. acervulina. Simultaneous injection of the recombinant 3-1E protein, or the 3-1E cDNA, with cDNAs encoding chicken IFN-gamma or interleukin (IL)-2/15 further enhanced protective immunity. These results indicate that the recombinant E. acervulina 3-1E cDNA or its polypeptide product may prove useful as vaccines against avian coccidiosis.

Possible involvement of the double-stranded RNA-binding core protein sigmaA in the resistance of avian reovirus to interferon

Treatment of primary cultures of chicken embryo fibroblasts with a recombinant chicken alpha/beta interferon (rcIFN) induces an antiviral state that causes a strong inhibition of vaccinia virus and vesicular stomatitis virus replication but has no effect on avian reovirus S1133 replication. The fact that avian reovirus polypeptides are synthesized normally in rcIFN-treated cells prompted us to investigate whether this virus expresses factors that interfere with the activation and/or the activity of the IFN-induced, double-stranded RNA (dsRNA)-dependent enzymes. Our results demonstrate that extracts of avian-reovirus-infected cells, but not those of uninfected cells, are able to relieve the translation-inhibitory activity of dsRNA in reticulocyte lysates, by blocking the activation of the dsRNA-dependent enzymes. In addition, our results show that protein sigmaA, an S1133 core polypeptide, binds to dsRNA in an irreversible manner and that clearing this protein from extracts of infected cells abolishes their protranslational capacity. Taken together, our results raise the interesting possibility that protein sigmaA antagonizes the IFN-induced cellular response against avian reovirus by blocking the intracellular activation of enzyme pathways dependent on dsRNA, as has been suggested for several other viral dsRNA-binding proteins.

Induction of protective immunity in chickens immunised with plasmid DNA encoding infectious bursal disease virus antigens

Direct DNA inoculations were used to determine the efficacy of gene immunisation of chickens to elicit protective immune responses against infectious bursal disease virus (IBDV). The vp2 gene of IBDV strains GP40 and D78, and the vp2-vp4-vp3 encoding segment of strain D78 were cloned in an expression vector which consisted of human cytomegalovirus (HCMV) immediate early enhancer and promoter, adenovirus tripartite leader sequences and SV40 polyadenylation signal. For purification of vaccine-quality plasmid DNA from E. coli, an effective method was developed. Chickens were vaccinated by inoculation of DNA by two routes (intramuscular and intraperitoneal). Two weeks later, chickens were boosted with DNA, and at 2 weeks post-boost, they were challenged with virulent IBDV strain. Low to undetectable levels of IBDV-specific antibodies and no protection were observed with DNA encoding VP2. However, plasmids encoding VP2-VP4-VP3 induced IBDV-specific antibodies and protection in the chickens. DNA immunisation opens a new approach to the development of gene vaccines for chickens against infectious diseases.

Insect larval expression process is optimized by generating fusions with green fluorescent protein

The insect larvae/baculovirus protein production process was dramatically simplified by expressing fusion proteins containing green fluorescent protein (GFP) and the product-of-interest. In this case, human interleukin-2 (hIL-2) and chloramphenicol acetyl-transferase (CAT) were model products. Specifically, our fusion construct was comprised of a histidine affinity ligand for simplified purification using immobilized metal affinity chromatography (IMAC), the UV-optimized GFP (GFPuv) as a marker, an enterokinase cleavage site for recovery of the product from the fusion, and the product, hIL-2 or CAT. Both the approximately 52 kDa GFPuv/hIL-2 and approximately 63 kDa GFPuv/CAT fusions were expressed in Trichoplusia ni larvae at 9.0 microg-hIL-2 and 24.1 microg-CAT per larva, respectively. The GFP enabled clear identification of the infection process, harvest time, and more importantly, the quantity of product protein. Because the GFP served as a marker, this technique obviates the need for in-process Western analyses (during expression, separation, and purification stages). As a purification marker, GFP facilitated rapid identification of product-containing elution fractions (Cha et al., 1999b), as well as product-containing waste fractions (e.g., cell pellet). Also, because the fluorescence intensity was linear with hIL-2 and CAT, we were able to select the highest-producing larvae. That is, three fold more product was found in the brightest larva compared to the average. Finally, because the GFP is attached to the product protein and the producing larvae can be selected, the infection and production processes can be made semi-continuous or continuous, replacing the current batch process. These advantages should help to enable commercialization of larvae as expression hosts.

Chimeric infectious bursal disease virus-like particles expressed in insect cells and purified by immobilized metal affinity chromatography

Chimeric virus-like particles (VLPs) of infectious bursal disease virus (IBDV) were produced by coinfecting Spodoptera frugiperda (Sf-9) insect cells with two recombinant baculoviruses, vIBD-7 and vEDLH-22. vIBD-7 encodes VP2, VP3, and VP4 of the IBDV structural proteins. vEDLH-22 encodes VP2 with five histidine residues at the carboxy-terminus (VP2H). Coinfection produced hybrid VLPs composed of VP2, VP2H, and VP3. The additional histidine residues on VP2H enabled the efficient purification of VLPs based on immobilized metal affinity chromatography (IMAC). These results demonstrated that the VLPs formed are comprised of chimeric subunits with attached affinity ligands, and further, that sufficient His5 ligand was available for binding to the IMAC metal-chelating resin. Additionally, these novel particles were fully characterized for antigenicity by a series of monoclonal antibodies, and appeared identical to the two wild-type IBDV strains contributing subunits to the chimeric VLP. IMAC purification provides a promising low-cost and simple scheme to purify VLPs as vaccines.

Expression and purification of human interleukin-2 simplified as a fusion with green fluorescent protein in suspended Sf-9 insect cells

A fusion protein of human interleukin-2 (hIL-2) and green fluorescent protein (GFP) was expressed in insect Sf-9 cells infected with recombinant baculovirus derived from the Autographa californica nuclear polyhedrosis virus (AcNPV). This fusion protein was comprised of a histidine affinity ligand for simplified purification using immobilized metal affinity chromatography (IMAC), UV-optimized GFP (GFPuv) as a marker, an enterokinase cleavage site for recovery of hIL-2 from the fusion, and the model product hIL-2. Successful production of hIL-2 as a fusion protein (approximately 52,000 Da) with GFPuv was obtained. GFPuv enabled rapid monitoring and quantification of the hIL-2 by simply checking the fluorescence, obviating the need for Western blot and/or ELISA assays during infection and production stages. There was no increased 'metabolic burden' due to the presence of GFPuv in the fusion product. The additional histidine residues at the N-terminus enabled efficient one-step purification of the fusion protein using IMAC. Additional advantages of GFP as a fusion marker were seen, particularly during separation and purification in that hIL-2 containing fractions were identified simply by illumination with UV light. Our results demonstrated that GFP was an effective non-invasive on-line marker for the expression and purification of heterologous protein in the suspended insect cell/baculovirus expression system.

Green fluorescent protein as a noninvasive stress probe in resting Escherichia coli cells

We constructed and characterized three stress probe plasmids which utilize a green fluorescent protein as a noninvasive reporter in order to elucidate Escherichia coli cellular stress responses in quiescent or resting cells. Cellular stress levels were easily detected by fusing three heat shock stress protein promoter elements, those of the heat shock transcription factor sigma32, the protease subunit ClpB, and the chaperone DnaK, to the reporter gene gfpuv. When perturbed by a chemical or physical stress (such as a heat shock, nutrient [amino acid] limitation, or addition of IPTG [isopropyl-beta-D-thiogalactopyranoside], acetic acid, ethanol, phenol, antifoam, or salt [osmotic shock]), the E. coli cells produced GFPuv, which was easily detected within the cells as emitted green fluorescence. Temporal and amplitudinal mapping of the responses was performed, and the results revealed regions where quantitative delineation of cell stress was afforded.

Generation of infectious pancreatic necrosis virus from cloned cDNA

We developed a reverse genetics system for infectious pancreatic necrosis virus (IPNV), a prototype virus of the Birnaviridae family, with the use of plus-stranded RNA transcripts derived from cloned cDNA. Full-length cDNA clones of the IPNV genome that contained the entire coding and noncoding regions of RNA segments A and B were constructed. Segment A encodes a 106-kDa precursor protein which is cleaved to yield mature VP2, nonstructural protease, and VP3 proteins, whereas segment B encodes the RNA-dependent RNA polymerase VP1. Plus-sense RNA transcripts of both segments were prepared by in vitro transcription of linearized plasmids with T7 RNA polymerase. Transfection of chinook salmon embryo (CHSE) cells with combined transcripts of segments A and B generated infectious IPNV particles 10 days posttransfection. Furthermore, a transfectant virus containing a genetically tagged sequence was generated to confirm the feasibility of this system. The presence and specificity of the recovered virus were ascertained by immunofluorescence staining of infected CHSE cells with rabbit anti-IPNV serum and by nucleotide sequence analysis. In addition, 3'-terminal sequence analysis of RNA from the recovered virus showed that extraneous nucleotides synthesized at the 3' end during in vitro transcription were precisely trimmed or excluded during replication, and hence these were not incorporated into the genome. An attempt was made to determine if RNA-dependent RNA polymerase of IPNV and infectious bursal disease virus (IBDV), another birnavirus, can support virus rescue in heterologous combinations. Thus, CHSE cells were transfected with transcripts derived from IPNV segment A and IBDV segment B and Vero cells were transfected with transcripts derived from IBDV segment A and IPNV segment B. In either case, no infectious IPNV or IBDV particles were generated even after a third passage in cell culture, suggesting that viral RNA-dependent RNA polymerase is species specific. However, the reverse genetics system for IPNV that we developed will greatly facilitate studies of viral replication and pathogenesis and the design of a new generation of live attenuated vaccines.

Generation of a mutant infectious bursal disease virus that does not cause bursal lesions

A reverse genetics system for birnavirus, based on synthetic transcripts of the infectious bursal disease virus (IBDV) genome, was recently developed (E. Mundt and V. N. Vakharia, Proc. Natl. Acad. Sci. USA 93:11131-11136, 1996). To study the function of the 17-kDa nonstructural (NS) protein in viral growth and pathogenesis, we constructed a cDNA clone of IBDV segment A in which the first and only initiation codon (ATG) of NS protein was mutated to a stop codon (TAG). Transfection of Vero cells with combined transcripts of either modified or unmodified segment A, and with segment B, generated viable IBDV progeny. When chicken embryo fibroblast cells infected with transfectant viruses were analyzed by immunofluorescence assays using NS-specific antiserum, the mutant virus did not yield a fluorescence signal, indicating a lack of NS protein expression. Furthermore, replication kinetics and cytotoxic effects of the mutant virus were compared with those of the parental attenuated vaccine strain of IBDV (D78) in vitro. The mutant virus grew to slightly lower titers than D78 virus and exhibited decreased cytotoxic and apoptotic effects in cell culture. To evaluate the characteristics of the recovered viruses in vivo, we inoculated 3-week-old chickens with D78 or mutant virus and analyzed their bursa for histopathological lesions. The recovered D78 virus caused microscopic lesions and atrophy of the bursa, while the mutant virus failed to induce any pathological lesions or clinical signs of disease. In both instances, the virus was recovered from the bursa, and the presence or absence of mutation in these viruses was confirmed by nucleotide sequence analysis of NS gene. Although the mutant virus exhibited a delay in replication in vivo, it induced levels of IBDV neutralizing antibodies that were similar to those of D78 virus. In addition, no reversion of mutation was detected in the mutant virus recovered from inoculated chickens. These results demonstrate that NS protein is dispensable for viral replication in vitro and in vivo and that it plays an important role in viral pathogenesis. Thus, generation of such NS protein-deficient virus will facilitate the study of immunosuppression and aid in the development of live-attenuated vaccines for IBDV.

Butyrophilin is expressed in mammary epithelial cells from a single-sized messenger RNA as a type I membrane glycoprotein

We investigated the expression of butyrophilin in eukaryotic cells with a view to determining the number of mRNA species, the incorporation of the peptide chain into microsomes, and the topology of the processed protein in biological membranes. Butyrophilin is synthesized from a single sized mRNA in both bovine and murine lactating mammary tissue and associates with microsomal membranes with a type I topology (Nexo.Ccyto) via a single hydrophobic anchor in the middle of the sequence. Several isoelectric variants of the protein were detected in cellular membranes from lactating bovine mammary tissue and in the milk-fat-globule membrane. We found no evidence for soluble forms of butyrophilin in postmicrosomal supernatants. The 66-kDa protein appears to be subjected to limited proteolysis, giving rise to a 62-kDa fragment lacking the C terminus and to other more minor fragments of lower Mr in the milk-fat-globule membrane. Antipeptide antibodies to epitopes within the N- and C-terminal domains were used to show that butyrophilin retains a type I topology in plasma membranes when expressed in insect cells from a baculovirus vector, and in secreted milk-fat globules. These data do not agree with previous suggestions that butyrophilin may exist in cytoplasmic soluble forms, or be reorganized in the plane of the lipid bilayer during secretion in lipid droplets from mammary cells. The results are discussed with reference to the role butyrophilin may play as the principal scaffold for the assembly of a complex with xanthine oxidase and other proteins that functions in the budding and release of milk-fat globules from the apical surface during lactation.

Synthetic transcripts of double-stranded Birnavirus genome are infectious

We have developed a system for generation of infectious bursal disease virus (IBDV), a segmented double-stranded RNA virus of the Birnaviridae family, with the use of synthetic transcripts derived from cloned cDNA. Independent full-length cDNA clones were constructed that contained the entire coding and noncoding regions of RNA segments A and B of two distinguishable IBDV strains of serotype I. Segment A encodes all of the structural (VP2, VP4, and VP3) and nonstructural (VP5) proteins, whereas segment B encodes the RNA-dependent RNA polymerase (VP1). Synthetic RNAs of both segments were produced by in vitro transcription of linearized plasmids with T7 RNA polymerase. Transfection of Vero cells with combined plus-sense transcripts of both segments generated infectious virus as early as 36 hr after transfection. The infectivity and specificity of the recovered chimeric virus was ascertained by the appearance of cytopathic effect in chicken embryo cells, by immunofluorescence staining of infected Vero cells with rabbit anti-IBDV serum, and by nucleotide sequence analysis of the recovered virus, respectively. In addition, transfectant viruses containing genetically tagged sequences in either segment A or segment B of IBDV were generated to confirm the feasibility of this system. The development of a reverse genetics system for double-stranded RNA viruses will greatly facilitate studies of the regulation of viral gene expression, pathogenesis, and design of a new generation of live vaccines.

Synthetic pheromone biosynthesis activating neuropeptide gene expressed in a baculovirus expression system

A synthetic gene of the pheromone biosynthesis activating neuropeptide (PBAN) of corn earworm Helicoverpa zea, with and without a signal sequence of the cuticle protein of Drosophila melanogaster, was cloned behind the polyhedrin promoter of AcMNPV. Two recombinant baculoviruses were constructed and used to infect a number of insect cell lines including Sf9 and 5B1-4. High pheromonotropic activity was consistently obtained from 5B1-4 cell culture that was infected with the recombinant baculovirus vINV-4 containing the signal sequence. The PBAN gene-product was isolated by HPLC and analyzed by electrospray ionization mass spectrometry. Low levels of biological activity obtained from Sf9 cells infected with the recombinant virus vPBAN may be due to lack of proper amidation at the C-terminus of the expressed peptide or rapid proteolytic degradation of the product.