Functional and Radiologic Outcomes of Degenerative Versus Traumatic Full-Thickness Rotator Cuff Tears Involving the Supraspinatus Tendon

BACKGROUND

Arthroscopic rotator cuff repair (ARCR) is among the most commonly performed orthopaedic procedures. Several factors-including age, sex, and tear severity-have been identified as predictors for outcome after repair. The influence of the tear etiology on functional and structural outcome remains controversial.

PURPOSE

To investigate the influence of tear etiology (degenerative vs traumatic) on functional and structural outcomes in patients with supraspinatus tendon tears.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Patients undergoing ARCR from 19 centers were prospectively enrolled between June 2020 and November 2021. Full-thickness, nonmassive tears involving the supraspinatus tendon were included. Tears were classified as degenerative (chronic shoulder pain, no history of trauma) or traumatic (acute, traumatic onset, no previous shoulder pain). Range of motion, strength, the Subjective Shoulder Value, the Oxford Shoulder Score (OSS), and the Constant-Murley Score (CMS) were assessed before (baseline) and 6 and 12 months after ARCR. The Subjective Shoulder Value and the OSS were also determined at the 24-month follow-up. Repair integrity after 12 months was documented, as well as additional surgeries up to the 24-month follow-up. Tear groups were compared using mixed models adjusted for potential confounding effects.

RESULTS

From a cohort of 973 consecutive patients, 421 patients (degenerative tear, n = 230; traumatic tear, n = 191) met the inclusion criteria. The traumatic tear group had lower mean baseline OSS and CMS scores but significantly greater score changes 12 months after ARCR (OSS, 18 [SD, 8]; CMS, 34 [SD,18] vs degenerative: OSS, 15 [SD, 8]; CMS, 22 [SD, 15]) (P < .001) and significantly higher 12-month overall scores (OSS, 44 [SD, 5]; CMS, 79 [SD, 9] vs degenerative: OSS, 42 [SD, 7]; CMS, 76 [SD, 12]) (P≤ .006). At the 24-month follow-up, neither the OSS (degenerative, 44 [SD, 6]; traumatic, 45 [SD, 6]; P = .346) nor the rates of repair failure (degenerative, 14 [6.1%]; traumatic 12 [6.3%]; P = .934) and additional surgeries (7 [3%]; 7 [3.7%]; P = .723) differed between groups.

CONCLUSION

Patients with degenerative and traumatic full-thickness supraspinatus tendon tears who had ARCR show satisfactory short-term functional results. Although patients with traumatic tears have lower baseline functional scores, they rehabilitate over time and show comparable clinical results 1 year after ARCR. Similarly, degenerative and traumatic rotator cuff tears show comparable structural outcomes, which suggests that degenerated tendons retain healing potential.

Load-induced increase in muscle activity during 30° abduction in patients with rotator cuff tears and control subjects

BACKGROUND

Rotator cuff muscles stabilise the glenohumeral joint and contribute to the initial abduction phase with other shoulder muscles. This study aimed to determine if the load-induced increase in shoulder muscle activity during a 30° abduction test is influenced by asymptomatic or symptomatic rotator cuff pathologies.

MATERIALS AND METHODS

Twenty-five patients with unilateral rotator cuff tears (age, 64.3 ± 10.2 years), 25 older control subjects (55.4 ± 8.2 years) and 25 younger control subjects (26.1 ± 2.3 years) participated in this study. Participants performed a bilateral 30° arm abduction and adduction movement in the scapular plane with handheld weights (0-4 kg). Activity of the deltoid, infraspinatus, biceps brachii, pectoralis major, latissimus dorsi and upper trapezius muscles was analysed at maximum abduction angle after normalisation to maximum voluntary contraction. Shoulders were classified into rotator cuff tendinopathy, asymptomatic and symptomatic rotator cuff tears, and healthy based on magnetic resonance images. A linear mixed model (loads, shoulder types) with random effects (shoulder identification) was applied to the log-transformed muscle activities.

RESULTS

Muscle activity increased with increasing load in all muscles and shoulder types (P < 0.001), and 1-kg increments in additional weights were significant (P < 0.001). Significant effects of rotator cuff pathologies were found for all muscles analysed (P < 0.05). In all muscles, activity was at least 20% higher in symptomatic rotator cuff tears than in healthy shoulders (P < 0.001). Symptomatic rotator cuff tears showed 20-32% higher posterior deltoid (P < 0.05) and 19-25% higher pectoralis major (P < 0.01) activity when compared with asymptomatic tears.

CONCLUSIONS

Rotator cuff pathologies are associated with greater relative activity of shoulder muscles, even with low levels of additional load. Therefore, the inclusion of loaded shoulder tests in the diagnosis and rehabilitation of rotator cuff pathologies can provide important insight into the functional status of shoulders and can be used to guide treatment decisions.

LEVEL OF EVIDENCE

Level 2.

TRIAL REGISTRATION

Ethical approval was obtained from the regional ethics committee (Ethics Committee Northwest Switzerland EKNZ 2021-00182), and the study was registered at clinicaltrials.gov on 29 March 2021 (trial registration number NCT04819724, https://clinicaltrials.gov/ct2/show/NCT04819724 ).

Reduced proliferation of bone marrow MSC after allogeneic stem cell transplantation is associated with clinical outcome

Engraftment and differentiation of donor hematopoietic stem cells is decisive for the clinical success of allogeneic stem cell transplantation (alloSCT) and depends on the recipient's bone marrow (BM) niche. A damaged niche contributes to poor graft function after alloSCT; however, the underlying mechanisms and the role of BM multipotent mesenchymal stromal cells (MSC) are ill-defined. Upon multivariate analysis in 732 individuals, we observed a reduced presence of proliferation-capable MSC in BM aspirates from patients (N = 196) who had undergone alloSCT. This was confirmed by paired analysis in 30 patients showing a higher frequency of samples with a lack of MSC presence post-alloSCT compared with pre-alloSCT. This reduced MSC presence was associated with reduced survival of patients after alloSCT and specifically with impaired graft function. Post-alloSCT MSC showed diminished in vitro proliferation along with a transcriptional antiproliferative signature, upregulation of epithelial-mesenchymal transition and extracellular matrix pathways, and altered impact on cytokine release upon contact with hematopoietic cells. To avoid in vitro culture bias, we isolated the CD146+/CD45-/HLA-DR- BM cell fraction, which comprised the entire MSC population. The post-alloSCT isolated native CD146+MSC showed a similar reduction in proliferation capacity and shared the same antiproliferative transcriptomic signature as for post-alloSCT colony-forming unit fibroblast-derived MSC. Taken together, our data show that alloSCT confers damage to the proliferative capacity of native MSC, which is associated with reduced patient survival after alloSCT and impaired engraftment of allogeneic hematopoiesis. These data represent the basis to elucidate mechanisms of BM niche reconstitution after alloSCT and its therapeutic manipulation.

Modeling In Vitro Osteoarthritis Phenotypes in a Vascularized Bone Model Based on a Bone-Marrow Derived Mesenchymal Cell Line and Endothelial Cells

The subchondral bone and its associated vasculature play an important role in the onset of osteoarthritis (OA). Integration of different aspects of the OA environment into multi-cellular and complex human, in vitro models is therefore needed to properly represent the pathology. In this study, we exploited a mesenchymal stromal cell line/endothelial cell co-culture to produce an in vitro human model of vascularized osteogenic tissue. A cocktail of inflammatory cytokines, or conditioned medium from mechanically-induced OA engineered microcartilage, was administered to this vascularized bone model to mimic the inflamed OA environment, hypothesizing that these treatments could induce the onset of specific pathological traits. Exposure to the inflammatory factors led to increased network formation by endothelial cells, reminiscent of the abnormal angiogenesis found in OA subchondral bone, demineralization of the constructs, and increased collagen production, signs of OA related bone sclerosis. Furthermore, inflammation led to augmented expression of osteogenic (alkaline phosphatase (ALP) and osteocalcin (OCN)) and angiogenic (vascular endothelial growth factor (VEGF)) genes. The treatment, with a conditioned medium from the mechanically-induced OA engineered microcartilage, also caused increased demineralization and expression of ALP, OCN, ADAMTS5, and VEGF; however, changes in network formation by endothelial cells were not observed in this second case, suggesting a possible different mechanism of action in inducing OA-like phenotypes. We propose that this vascularized bone model could represent a first step for the in vitro study of bone changes under OA mimicking conditions and possibly serve as a tool in testing anti-OA drugs.

Fluoroscopy of the Elbow: A Cadaveric Study Defining New Standard Projections to Visualize Important Anatomical Landmarks

Background

Despite new 3-dimensional imaging modalities, 2-dimensional fluoroscopy remains the standard intraoperative imaging modality. The elbow has complex anatomy, and defined standard fluoroscopic projections are lacking. Therefore, the aim of this study was to define standard projections of the elbow for intraoperative fluoroscopy.

Methods

This study consisted of 2 parts. In part I, dissected cadaveric elbows were examined under fluoroscopy, and their radiographic anatomical features were assessed, with focus on projections showing defined anatomical landmarks. In part II, projections from part I were verified on entire cadavers to simulate intraoperative imaging. Standard projections for anteroposterior (AP) and lateral views as well as oblique and axial views were recorded.

Results

Eight standardized projections could be defined and included 3 AP, 1 lateral, 2 oblique, and 2 axial views. By applying these specific projections, we could visualize the epicondyles, the trochlea with its medial and lateral borders, the capitellum, the olecranon, the greater sigmoid notch, the coronoid process including its anteromedial facet, the proximal radioulnar joint with the radial tuberosity, and the anterior and posterior joint lines of the distal part of the humerus. These standard projections were reliably obtained using a specific sequence.

Conclusions

Knowledge about radiographic anatomy and standard projections is essential for visualizing important landmarks. With the presented standard projections of the elbow, important anatomical landmarks can be clearly examined. Thus, fluoroscopic visualization of anatomical fracture reduction and correct implant placement should be facilitated.

Clinical Relevance

This basic science cadaveric study defines fluoroscopic standard projections of the elbow essential for visualization of anatomical landmarks during surgery.

Prognostische Faktoren der arthroskopischen Rotatorenmanschettenrekonstruktion

Hintergrund

Rupturen der Rotatorenmanschette sind eine der häufigsten Erkrankungen des Bewegungsapparats. Die klinischen und strukturellen Ergebnisse nach einer arthroskopischen Rotatorenmanschettenrekonstruktion (ARCR) sind im Allgemeinen gut, aber hinsichtlich der großen Schwankungsbreite der postoperativen Resultate noch verbesserungsfähig.

Fragestellung

Ziel dieser Literaturübersicht ist es, einen Überblick über prognostische Faktoren zu geben, die das postoperative Ergebnis nach ARCR beeinflussen.

Material und Methoden

Systematische Reviews, welche prognostische Faktoren für das Outcome nach ARCR analysieren, wurden in diese Übersichtsarbeit eingeschlossen. Die Literatursuche erfolgte in den Datenbanken Embase, Medline (Ovid) und Scopus. In die Auswertung wurden nur prognostischen Faktoren eingeschlossen, welche in mindestens zwei Übersichtsarbeiten beschrieben wurden.

Ergebnisse

Sieben systematische Reviews mit insgesamt 332 eingeschlossenen Artikeln wurden ausgewertet. Postoperative Ergebnisse waren Patientenzufriedenheit, Lebensqualität sowie funktionelle und strukturelle Ergebnisse. Sechzehn prognostische Faktoren wurden identifiziert und in patientenbezogene, rupturbezogene und behandlungsbezogene prognostische Faktoren untergliedert.

Schlussfolgerung

Anhand von patienten-, ruptur- und behandlungsbezogenen prognostischen Faktoren soll in Zukunft ein Vorhersagemodell erstellt werden können, um die individuellen Heilungschancen nach ARCR vorherzusagen und dem Patienten eine präzise Therapieempfehlung abgeben zu können.

Treatment of Periprosthetic Femoral Fractures Vancouver Type B2: Revision Arthroplasty Versus Open Reduction and Internal Fixation With Locking Compression Plate

Introduction:

The Vancouver algorithm recommends revision arthroplasty (RA) for Vancouver type B2 (VTB2) fractures. However, open reduction and internal fixation (ORIF) using locking compression plates (LCP) may be a valid and less invasive alternative treatment.

Materials and Methods:

Between January 2007 and March 2017, we retrospectively recruited all patients treated with either ORIF with LCP or RA for VTB2 fractures in our clinic. All of the following were reviewed: the length of hospital stay, the operating time, the need for blood transfusions during and/or after surgery, implant-related and patient-related complications, need for revision surgery, and the radiological outcome. Additionally, the functional outcome was investigated.

Results:

Fifty-nine patients were recruited. Thirty-five (59.3%) patients underwent RA, while 24 (40.7%) patients received ORIF with LCP. The median surgical time was 137.50 minutes in the LCP group compared to 160.00 minutes in the RA group (P = .051). Three (12.5%) patients in the LCP group and 10 (28.6%) patients in the RA group experienced an implant-associated complication (P = .131). Patient-related complications occurred in 3 (12.5%) patients in the LCP group versus 6 (17.1%) patients in the RA group (P = .628). The mean preoperative Parker mobility score was 9 points in both groups and decreased in both groups to a mean of 5 points in the LCP and 7 points in the RA group.

Discussion:

Open reduction and internal fixation with LCP seems to be a less invasive procedure for VTB2 fractures in comparison to RA. It is a bone-sparing procedure that can be advantageous for further revision operations. Moreover, some fractures can only be anatomically reduced by ORIF with LCP, whereas for proximal fractures with a radiologically unambiguously loosened stem RA might be advantageous.

Conclusion:

In line with previously published studies, our data suggest that ORIF using LCP is a valid treatment option for VTB2 fractures.

Psychometric Properties of the German Version of the Pain Vigilance and Awareness Questionnaire (PVAQ) in Pain-Free Samples and Samples with Acute and Chronic Pain

Purpose

The way individuals attend to pain is known to have a considerable impact on the experience and chronification of pain. One method to assess the habitual “attention to pain” is the Pain Vigilance and Awareness Questionnaire (PVAQ). With the present study, we aimed to test the psychometric properties of the German version of the PVAQ across pain-free samples and across patients with acute and chronic pain.

Method

Two samples of pain-free individuals (student sample (N = 255)/non-student sample (N = 362)) and two clinical pain samples (acute pain patients (N = 105)/chronic pain patients (N = 36)) were included in this cross-sectional evaluation of the German PVAQ. Factor structure was assessed using exploratory and confirmatory factor analyses. Reliability was assessed using internal consistency (Cronbach’s alpha). Construct validity was tested by assessing correlations between PVAQ and theoretically related constructs.

Results

Exploratory factor analysis (non-student sample) and confirmatory factor analysis (student sample, acute pain patient sample) suggested that a two-factor solution best fitted our data (“attention to pain,” “attention to changes in pain”). Internal consistency ranged from acceptable to good in all four samples. As hypothesized, the PVAQ correlated significantly with theoretically related constructs in all four samples, suggesting good construct validity in pain-free individuals and in pain patients.

Conclusion

The German PVAQ shows good psychometric properties across samples of pain-free individuals and patients suffering from pain that are comparable to PVAQ versions of other languages. Thus, the German PVAQ seems to be a measure of pain vigilance equally valid as found in other countries.

The effect of plant growth-promoting rhizobacteria on the phytoextraction of Cd and Zn by Brassica napus L

The test strains Bacteroidetes bacterium (Ba), Pseudomonas fluorescens (Pf) and Variovorax sp. (Va) were selected in advance for their in vitro capability for growth promotion of rapeseed in the presence of increased concentrations of Cd, Cu, Pb and Zn in the medium. In the pot experiment, the strains were used for single Ba, Pf, Va or combined Ba + Pf, Ba + Va, Pf + Va, and Ba + Pf + Va inoculation of B. napus growing in contaminated soil from alluvial deposits. The positive effect of bacterial strains on plant growth was observed in vitro, but was not confirmed in situ in the contaminated soil, where the tested strains inhibited biomass production, rather than stimulating it. However, single inoculation with Ba significantly increased the chlorophyll content and K⁺ concentration in the leaves. The inoculation of rapeseed with Ba and Va strains was indicated to be the most promising combination for phytoextraction of Cd and Zn from contaminated soil. Combined inoculation with Pf+Va and Pf + Ba+Va significantly decreased the concentration of heavy metals in the roots of rapeseed. We conclude that suitable combinations of PGPR can control the metal uptake of B. napus, selectively increasing either metal extraction or metal stabilization in the rhizosphere and offering promising applications in soil remediation.

Sentinel node metastasis mitotic rate (SN-MMR) as a prognostic indicator of rapidly progressing disease in patients with sentinel node-positive melanomas

Risk stratification of sentinel lymph node biopsy (SNB)-positive patients with malignant melanoma differs among current classification systems. To improve classification of patients with rapidly progressive disease who may profit from adjuvant therapy with novel immune or targeted treatment modalities, a single-center retrospective analysis was performed including all melanoma patients diagnosed with a positive SN at a university-based skin cancer center over a 10-year period (2002-2012) (96 of 419 patients). Sentinel node metastasis mitotic rate (SN-MMR) and further histologic parameters were determined by blinded histological re-evaluation and correlated with clinical follow-up (overall [OS], melanoma-specific [MSS], and disease-free survival [DFS]). Median follow-up was 53 months. In univariate analyses, SN tumor penetrative depth (TPD), maximum tumor diameter (MTD), number of positive SN, SN-MMR and the S-, Rotterdam, RDC, Hannover I and II classification systems correlated with OS, MSS and DFS. Multivariate Cox regression analyses showed that a binary classification system based only on the SN-MMR (<1 vs. ≥1 mitoses/mm2 ) was the strongest independent prognostic indicator for all endpoints analyzed. Kaplan-Meier analyses confirmed binary SN-MMR to be superior to stratify patients into high- and low-risk groups (45.45% vs. 87.92% 5-yr MSS). The general prognostic validity of the published SN classification systems was confirmed. The novel SN-MMR classification system may improve discrimination of patients with slowly and rapidly progressive disease. We therefore propose its implementation into clinical practice as the SN-MMR can be easily and reliably determined in routine pathology reports. Its prognostic value for the selection of patients amenable to adjuvant therapies should be studied in clinical trials.

Tightly regulated 'all-in-one' lentiviral vectors for protection of human hematopoietic cells from anticancer chemotherapy

Successful application of gene therapy strategies may require stringently regulated transgene expression. Along this line, we describe a doxycycline (Dox)-inducible 'all-in-one' lentiviral vector design using the pTET-T11 (TII) minimal-promoter and a reverse transactivator protein (rtTA2S-M2) driven by the phosphoglycerate kinase promoter allowing for tight regulation of transgene expression (Lv.TII vectors). Vector design was evaluated in human hematopoietic cells in the context of cytidine deaminase (hCDD)-based myeloprotective gene therapy. Upon Dox administration, a rapid (16-24 h) and dose-dependent (>0.04 μg ml(-1) Dox) onset of transgene expression was detected in Lv.TII.CDD gene-modified K562 cells as well as in primary human CD34(+) hematopoietic cells. Importantly, in both cell models low background transgene expression was observed in the absence of Dox. Functionality of Dox-inducible hCDD expression was demonstrated by >10-fold increase in cytosine arabinoside (1-β-d-arabinofuranosylcytosine, Ara-C) resistance of Lv.TII.CDD-transduced K562 cells. In addition, Lv.TII.CDD-transduced CD34(+)-derived myeloid cells were protected from up to 300 nm Ara-C (control affected from 50 nm onwards). These data clearly demonstrate the suitability of our self-inactivating lentiviral vector to induce robust, tightly regulated transgene expression in human hematopoietic cells with minimal background activity and highlight the potential of our construct in myeloprotective gene therapy strategies.

Hyperactivation of mTORC1 and mTORC2 by multiple oncogenic events causes addiction to eIF4E-dependent mRNA translation in T-cell leukemia

High activation of the PI3K-AKT-mTOR pathway is characteristic for T-cell acute lymphoblastic leukemia (T-ALL). The activity of the master regulator of this pathway, PTEN, is often impaired in T-ALL. However, experimental evidence suggests that input from receptor tyrosine kinases (RTKs) is required for sustained mTOR activation, even in the absence of PTEN. We previously reported the expression of Neurotrophin receptor tyrosine kinases (TRKs) and their respective ligands in primary human leukemia samples. In the present study we aimed to dissect the downstream signaling cascades of TRK-induced T-ALL in a murine model and show that T-ALLs induced by deregulated receptor tyrosine kinase signaling acquire activating mutations in Notch1 and lose PTEN during clonal evolution. Some clones additionally lost one allele of the homeodomain transcription factor Cux1. All events independently led to a gradual hyperactivation of both mTORC1 and mTORC2 signaling. We dissected the role of the individual mTOR complexes by shRNA knockdown and found that the separate depletion of mTORC1 or mTORC2 reduced the growth of T-ALL blasts, but was not sufficient to induce apoptosis. In contrast, knockdown of the mTOR downstream effector eIF4E caused a striking cytotoxic effect, demonstrating a critical addiction to cap-dependent mRNA-translation. Although high mTORC2-AKT activation is commonly associated with drug-resistance, we demonstrate that T-ALL displaying a strong mTORC2-AKT activation were specifically susceptible to 4EGI-1, an inhibitor of the eIF4E-eIF4G interaction. To decipher the mechanism of 4EGI-1, we performed a genome-wide analysis of mRNAs that are translationally regulated by 4EGI-1 in T-ALL. 4EGI-1 effectively reduced the ribosomal occupancy of mRNAs that were strongly upregulated in T-ALL blasts compared with normal thymocytes including transcripts important for translation, mitochondria and cell cycle progression, such as cyclins and ribosomal proteins. These data suggest that disrupting the eIF4E-eIF4G interaction constitutes a promising therapy strategy in mTOR-deregulated T-cell leukemia.

Effects of formic acid and phytase supplementation on digestibility and use of phosphorus and zinc in growing pigs

Two studies, arranged according to a 4 × 4 Latin square design, were conducted to assess effects of dietary acidification on fungal 3-phytase (PHY) efficacy in growing pigs. In Exp. 1, effects of supplementing 500 units/kg feed of PHY and 4.7 g/kg HCOOH either alone or in combination on the use of P and Zn in growing pigs fed a pelleted diet based on wheat (Triticum aestivum), barley (Hordeum vulgare), and soybean (Glycine max) meal were investigated. In Exp. 2 the same dietary treatments were fed except that PHY supplementation was increased to 1000 units/kg. In both experiments, PHY supplementation increased (P < 0.05) P digestibility and retention. A PHY × HCOOH supplementation interaction on P balance was observed (P < 0.05), indicating that the combination of the additives may increase P digestibility and retention. Effects of HCOOH and PHY on Zn use followed a similar pattern. Supplementation of 1000 units/kg of PHY further increased P and Zn retention compared to supplementation of 500 units/kg. In conclusion, the present study indicated that HCOOH supplementation to diets with microbial PHY may increase PHY efficacy.

Selection for Evi1 activation in myelomonocytic leukemia induced by hyperactive signaling through wild-type NRas

Activation of NRas signaling is frequently found in human myeloid leukemia and can be induced by activating mutations as well as by mutations in receptors or signaling molecules upstream of NRas. To study NRas-induced leukemogenesis, we retrovirally overexpressed wild-type NRas in a murine bone marrow transplantation (BMT) model in C57BL/6J mice. Overexpression of wild-type NRas caused myelomonocytic leukemias ∼3 months after BMT in the majority of mice. A subset of mice (30%) developed malignant histiocytosis similar to mice that received mutationally activated NRas(G12D)-expressing bone marrow. Aberrant Ras signaling was demonstrated in cells expressing mutationally active or wild-type NRas, as increased activation of Erk and Akt was observed in both models. However, more NRas(G12D) were found to be in the activated, GTP-bound state in comparison with wild-type NRas. Consistent with observations reported for primary human myelomonocytic leukemia cells, Stat5 activation was also detected in murine leukemic cells. Furthermore, clonal evolution was detected in NRas wild-type-induced leukemias, including expansion of clones containing activating vector insertions in known oncogenes, such as Evi1 and Prdm16. In vitro cooperation of NRas and Evi1 improved long-term expansion of primary murine bone marrow cells. Evi1-positive cells upregulated Bcl-2 and may, therefore, provide anti-apoptotic signals that collaborate with the NRas-induced proliferative effects. As activation of Evi1 has been shown to coincide with NRAS mutations in human acute myeloid leukemia, our murine model recapitulates crucial events in human leukemogenesis.

Efficient in vivo regulation of cytidine deaminase expression in the haematopoietic system using a doxycycline-inducible lentiviral vector system

Regulated transgene expression may reduce transgene-specific and genotoxic risks associated with gene therapy. To prove this concept, we have investigated the suitability of doxycycline (Dox)-inducible human cytidine deaminase (hCDD) overexpression from lentiviral vectors to mediate effective myeloprotection while circumventing the lymphotoxicity observed with constitutive CDD activity. Rapid Dox-mediated transgene induction associated with a 6-17-fold increase in drug resistance was observed in 32D and primary murine bone marrow (BM) cells. Moreover, robust Dox-regulated transgene expression in the entire haematopoietic system was demonstrated for primary and secondary recipients of hCDD-transduced R26-M2rtTA transgenic BM cells. Furthermore, mice were significantly protected from myelosuppressive chemotherapy as evidenced by accelerated recovery of granulocytes (1.9±0.6 vs 1.3±0.3, P=0.034) and platelets (883±194 vs 584±160 10(3) per μl, P=0.011). Minimal transgene expression in the non-induced state and no overt cellular toxicities including lymphotoxicity were detected. Thus, using a relevant murine transplant model our data provide conclusive evidence that drug-resistance transgenes can be expressed in a regulated fashion in the lymphohaematopoietic system, and that Dox-inducible systems may be used to reduce myelotoxic side effect of anticancer chemotherapy or to avoid side effects of high constitutive transgene expression.

Scale-up and manufacturing of clinical-grade self-inactivating γ-retroviral vectors by transient transfection

The need for γ-retroviral (gRV) vectors with a self-inactivating (SIN) design for clinical application has prompted a shift in methodology of vector manufacturing from the traditional use of stable producer lines to transient transfection-based techniques. Herein, we set out to define and optimize a scalable manufacturing process for the production of gRV vectors using transfection in a closed-system bioreactor in compliance with current good manufacturing practices (cGMP). The process was based on transient transfection of 293T cells on Fibra-Cel disks in the Wave Bioreactor. Cells were harvested from tissue culture flasks and transferred to the bioreactor containing Fibra-Cel in the presence of vector plasmid, packaging plasmids and calcium-phosphate in Dulbecco's modified Eagle's medium and 10% fetal bovine serum. Virus supernatant was harvested at 10-14 h intervals. Using optimized procedures, a total of five ecotropic cGMP-grade gRV vectors were produced (9 liters each) with titers up to 3.6 × 10(7) infectious units per milliliter on 3T3 cells. One GMP preparation of vector-like particles was also produced. These results describe an optimized process for the generation of SIN viral vectors by transfection using a disposable platform that allows for the generation of clinical-grade viral vectors without the need for cleaning validation in a cost-effective manner.

Relevance of an academic GMP Pan-European vector infra-structure (PEVI)

In the past 5 years, European investigators have played a major role in the development of clinical gene therapy. The provision of substantial funds by some individual member states to construct GMP facilities makes it an opportune time to network available gene therapy GMP facilities at an EU level. The integrated coordination of GMP production facilities and human skills for advanced gene and genetically-modified (GM) cell therapy, can dramatically enhance academic-led "First-in-man" gene therapy trials. Once proof of efficacy is gathered, technology can be transferred to the private sector which will take over further development taking advantage of knowledge and know-how. Complex technical challenges require existing production facilities to adapt to emerging technologies in a coordinated manner. These include a mandatory requirement for the highest quality of production translating gene-transfer technologies with pharmaceutical-grade GMP processes to the clinic. A consensus has emerged on the directions and priorities to adopt, applying to advanced technologies with improved efficacy and safety profiles, in particular AAV, lentivirus-based and oncolytic vectors. Translating cutting-edge research into "First-in-man" trials require that pre-normative research is conducted which aims to develop standard assays, processes and candidate reference materials. This research will help harmonise practices and quality in the production of GMP vector lots and GM-cells. In gathering critical expertise in Europe and establish conditions for interoperability, the PEVI infrastructure will contribute to the demands of the advanced therapy medicinal products* regulation and to both health and quality of life of EU-citizens.

Correction of B-cell development in Btk-deficient mice using lentiviral vectors with codon-optimized human BTK

X-linked agammaglobulinemia (XLA) is the most common primary immunodeficiency (PID) in man and caused by mutations in the Bruton's tyrosine kinase (BTK) gene. XLA is characterized by a B-cell differentiation arrest in bone marrow, absence of mature B cells and immunoglobulins (Igs), and recurrent bacterial infections. We used self-inactivating lentiviral vectors expressing codon-optimized human BTK under the control of three different ubiquitous or B cell-specific promoters. Btk-/- mice engrafted with transduced cells showed correction of both precursor B-cell and peripheral B-cell development. Lentiviral vectors containing the wildtype BTK sequence did not correct the phenotype. All treated mice with codon-optimized BTK exhibited the recovery of B1 cells in the peritoneal cavity, and of serum IgM and IgG3 levels. Calcium mobilization responses upon B-cell receptor stimulation as well as in vivo responses to T cell-independent antigens were restored. Viral promoters overexpressing BTK >100-fold above normal resulted in erythro-myeloid proliferations independent of insertional mutagenesis. However, transplantation into secondary Btk-/- recipients using cellular promoters resulted in functional restoration of peripheral B cells and IgM levels, without any adverse effects. In conclusion, transduction of human BTK corrects B-cell development and antigen-specific antibody responses in Btk-/- mice, thus indicating the feasibility of lentiviral gene therapy for XLA, provided that BTK expression does not vastly exceed normal levels.

Mechanisms controlling titer and expression of bidirectional lentiviral and gammaretroviral vectors

Bidirectional lentiviral vectors mediate expression of two or more cDNAs from a single internal promoter. In this study, we examined mechanisms that control titer and expression properties of this vector system. To address whether the bidirectional design depends on lentiviral (LV) backbone components, especially the Rev/Rev responsive element (RRE) system, we constructed similar expression cassettes for LV and gammaretroviral (GV) vectors. Bidirectional expression levels could be adjusted by the use of different internal promoters. Furthermore, removal of the constitutive RNA transport element of Mason-Pfizer monkey virus, used in first generation bidirectional LV vectors, improved gene expression. Titers of bidirectional vectors were approximately 10-fold reduced in comparison to unidirectional vectors, independent of the Rev/RRE interaction. We reasoned that titer reductions were due to the formation of interfering double-stranded RNA in packaging cells. Indeed, cotransfection of Nodamuravirus B2 protein, an RNA interference suppressor, increased bidirectional vector titers at least fivefold. We validated the potential of high titer bidirectional vectors by coexpressing a fluorescent marker with O(6)-methylguanine-DNA methyltransferase from integrating, or with Cre recombinase from integrating and non-integrating GV and LV backbones. This allowed for the tracking of chemoprotected and recombined cells by fluorescence marker expression.

[Advancement of the medical doctorate]

The medical doctorate and the subsequent advanced research qualification in medicine have an exceptional position within the natural sciences. While, in the German system, graduation to the degree of a medical doctor is often an initiation into scientific practice, the in-depth scientific education of medical doctors may be achieved in various configurations. In recent years, structured programs for doctorates in medicine and natural sciences have found increasing acceptance, following recommendations of national scientific councils ("Deutsche Forschungsgemeinschaft" and "Hochschulrat"). Hannover Medical School has been offering such programs for a number of years. The StrucMed program increases the quality of medical doctorate studies, typically performed in the third and fourth years of university studies. The Hannover Biomedical Research School (HBRS) combines several programs for a doctorate in natural sciences, creating a platform for an internationally oriented education of post-graduates in various disciplines of life sciences. Evaluating the achievements and career paths of the trainees will contribute to the successful integration of research work in an efficiency-oriented clinical environment.

Transgene optimization significantly improves SIN vector titers, gp91phox expression and reconstitution of superoxide production in X-CGD cells

Gene therapy has proven to be of potential value for the correction of inherited hematopoietic disorders. However, the occurrence of severe side effects in some of the clinical trials has questioned the safety of this approach and has hampered the use of long terminal repeat-driven vectors for the treatment of a large number of patients. The development of self-inactivating (SIN) vectors with reduced genotoxicity provides an alternative to the currently used vectors. Our initial attempts to use SIN vectors for the correction of a myeloid disorder, chronic granulomatous disease, failed due to low vector titers and poor transgene expression. The optimization of the transgene cDNA (gp91(phox)) resulted in substantially increased titers and transgene expression. Most notably, transgene optimization significantly improved expression of a second cistron located downstream of gp91(phox). Thus, optimization of the transgene sequence results in higher expression levels and increased therapeutic index allowing the use of low vector copy numbers per transduced cell and weaker internal promoters.

Leukemia induction after a single retroviral vector insertion in Evi1 or Prdm16

Insertional activation of cellular proto-oncogenes by replication-defective retroviral vectors can trigger clonal dominance and leukemogenesis in animal models and clinical trials. Here, we addressed the leukemogenic potential of vectors expressing interleukin-2 receptor common gamma-chain (IL2RG), the coding sequence required for correction of X-linked severe combined immunodeficiency. Similar to conventional gamma-retroviral vectors, self-inactivating (SIN) vectors with strong internal enhancers also triggered profound clonal imbalance, yet with a characteristic insertion preference for a window located downstream of the transcriptional start site. Controls including lentivirally transduced cells revealed that ectopic IL2RG expression was not sufficient to trigger leukemia. After serial bone marrow transplantation involving 106 C57Bl6/J mice monitored for up to 18 months, we observed leukemic progression of six distinct clones harboring gamma-retroviral long terminal repeat (LTR) or SIN vector insertions in Evi1 or Prdm16, two functionally related genes. Three leukemic clones had single vector integrations, and identical clones manifested with a remarkably similar latency and phenotype in independent recipients. We conclude that upregulation of Evi1 or Prdm16 was sufficient to initiate a leukemogenic cascade with consistent intrinsic dynamics. Our study also shows that insertional mutagenesis is required for leukemia induction by IL2RG vectors, a risk to be addressed by improved vector design.

[Gene therapy of SCID-X1]

X-linked severe combined immunodeficiency (SCID-X1) is an inherited disease caused by inactivating mutations in the gene encoding the interleukin 2 receptor common gamma chain (IL2RG), which is located on the X-chromosome. Affected boys fail to develop two major effector cell types of the immune system (T cells and NK cells) and suffer from a functional B cell defect. Although drugs such as antibiotics can offer partial protection, the boys normally die in the first year of life in the absence of a curative therapy. For a third of the children, bone marrow transplantation from a fully matched donor is available and can cure the disease without major side effects. Mismatched bone marrow transplantation, however, is complicated by severe and potentially lethal side effects. Over the past decade, scientists worldwide have developed new treatments by introducing a correct copy of the IL2RG-cDNA. Gene therapy was highly effective when applied in young children. However, in a few patients the IL2RG-gene vector has unfortunately caused leukaemia. Activation of cellular proto-oncogenes by accidental integration of the gene vector has been identified as the underlying mechanism. In future clinical trials, improved vector technology in combination with other protocol modifications may reduce the risk of this side effect.

Neuropsychological and neurophysiologic effects of carbamazepine and levetiracetam

BACKGROUND

The relative effects of levetiracetam (LEV) and carbamazepine (CBZ) on cognitive and neurophysiologic measures are uncertain.

METHODS

The effects of LEV and CBZ were compared in healthy adults using a randomized, double-blind, two-period crossover design. Outcome measures included 11 standard neuropsychological tests and the score from a cognitive-neurophysiologic test of attention and memory. Evaluations were conducted at screening, baseline pre-drug treatment, end of each maintenance phase (4 weeks), and end of each washout period after drug treatment.

RESULTS

A total of 28 adults (17 women) with mean age of 33 years (range 18 to 51) completed the study. Mean maintenance doses (+/-SD) were CBZ = 564 mg/day (110) and LEV = 2,000 mg/day (0). CBZ was adjusted to mid-range therapeutic level. Mean serum levels (+/-SD) were CBZ = 7.5 mcg/mL (1.5) and LEV = 32.2 mcg/mL (11.2). An overall composite score including all measures revealed worse effects for CBZ compared to LEV (p <or= 0.001) in the primary analysis and for CBZ (p <or= 0.001) and LEV (p <or= 0.05) compared to non-drug in secondary analyses. Across the 34 individual variables, CBZ was worse than LEV on 44% (15/34); none favored CBZ. Compared to the non-drug average, CBZ was worse for 76% (26/34), and LEV was worse for 12% (4 of 34). Sensitivity and specificity of standard neuropsychological tests and the cognitive-neurophysiologic test were determined to direct future studies; detection was most accurate by the cognitive-neurophysiologic test.

CONCLUSIONS

Levetiracetam produces fewer untoward neuropsychological and neurophysiologic effects than carbamazepine in monotherapy at the dosages and timeframes employed in this study.

Remarkable leukemogenic potency and quality of a constitutively active neurotrophin receptor, ΔTrkA

Neurotrophins and their receptors play a key role in neurogenesis and survival. However, we and others have recently obtained evidence for a potential involvement of this receptor system in leukemia. To investigate mechanisms underlying the leukemogenic potential of activated neurotrophin receptor signaling, we analyzed in vivo leukemogenesis mediated by deltaTrkA, a mutant of TRKA (tropomyosin-related kinase A) isolated from a patient with acute myeloid leukemia (AML). Retroviral expression of deltaTrkA in myeloid 32D cells induced AML in syngeneic C3H/Hej mice (n=11/11, latency approximately 4 weeks). C57Bl/6J mice transplanted with deltaTrkA-transduced primary lineage negative (Lin-) bone marrow cells died of a transient polyclonal AML (n=7/15, latency of <12 days). Serial transplantation of AML cells did not re-induce this disease but rather acute lymphoblastic leukemia (ALL, latency >78 days). All primary recipients surviving the early AML developed clonal ALL or myeloid leukemia (latency >72 days) that required additional genetic lesions. PI3K and mTOR-raptor were identified as the crucial mediators of leukemic transformation, whereas STAT and MAP kinase signaling pathways were not activated. Thus, our findings reveal potent and unique transforming properties of altered neurotrophin receptor signaling in leukemogenesis, and encourage further analyses of neurotrophin receptors and downstream signaling events in hematological malignancies.

Sunitinib-related thyroid dysfunction: A single-center retrospective and prospective evaluation

3092

Background: Sunitinib is a multi-target tyrosine kinase inhibitor with anti-angiogenic and anti-proliferative activity mediated by signal blockade of VEGFR1/2, KIT, PDGFRα/β, and FLT-3. Phase II/III trials have demonstrated efficacy of the oral agent in Imatinib-resistant GIST and advanced renal cell cancer (RCC). We observed several cases of thyroid dysfunction in GIST during treatment with sunitinib suggesting that the drug may be associated with hypothyroidism. We therefore assessed the incidence and severity of thyroid dysfunction in cancer patients treated with sunitinib. Methods: Thyroid function (serum TSH, T3 and free thyroxin index) and thyroid antibodies (anti-TPO, -Tg and TSH-R-Ab) were evaluated retrospectively in a cohort of patients with GIST in a Phase III trial and in an expanded access program (1st part of the investigation) and in a prospective cohort of RCC and GIST patients treated in the framework of expanded access programs (2nd part). Sunitinib was given at a daily oral dose of 50 mg 4 weeks on, 2 weeks off. Thyroid parameters were assessed on days 1 and 28 of each treatment cycle in the prospective cohort. We report here the first TSH results, the full data set will be available at ASCO. Results: We identified a total of 46 patients who received sunitinib, and 33 of these patients were evaluable for thyroid function. 14 patients were analyzed retrospectively (all GIST), 19 patients prospectively (8 GIST, 11 RCC). 7 of these 19 patients (37%) showed an elevated TSH (>5 mIU/L) during treatment. In the retrospective analysis of 14 patients with a median treatment duration of 44 weeks, 8 patients (57%) had developed hypothyroidism. All patients with GIST in randomized Phase III trial remaining under active treatment with sunitinib for 58–80 weeks show an increased TSH (up to 83 mIU/L) during the course of treatment, requiring hormone substitution. In a cohort of 11 patients with RCC, after 6 weeks of treatment, 3 patients already have an increased TSH. Conclusions: Sunitinib is associated with a high incidence of thyroid dysfunction which requires further study. The mechanism by which Sunitinib induces thyroid dysfunction is yet unclear.

No significant financial relationships to disclose.

Effect of treatment with sunitinib malate, a multitargeted tyrosine kinase inhibitor, on circulating plasma levels of VEGF, soluble VEGF receptors 2 and 3, and soluble KIT in patients with metastatic breast cancer

578

Background: Sunitinib malate (SU11248) is a multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activity that specifically inhibits VEGFR, PDGFR, KIT, RET and FLT3. In a phase II trial of 64 patients with refractory, metastatic breast cancer, sunitinib treatment resulted in an ∼11% objective response rate (Miller et al, ASCO 2005). To characterize potential biomarkers of biological response to sunitinib, we analyzed plasma levels of a panel of soluble proteins from patients in this trial. Methods: Patients received sunitinib in 6-week cycles comprised of 50 mg/day for 4 weeks followed by 2 weeks off treatment. Pre-dose plasma samples from 62 patients were obtained on days 1, 14, and 28 of the first cycle and days 1 and 28 of subsequent cycles. Plasma levels of VEGF, soluble VEGF receptor 2 (sVEGFR-2), soluble KIT (sKIT), and a novel biomarker, sVEGFR-3, were measured via ELISA analysis. Results: Plasma levels of each protein were modulated in most patients during the course of treatment. At the end of the first cycle, VEGF levels were increased more than 3-fold relative to baseline in 73% of cases, while sVEGFR-2 levels decreased by at least 30% in 88% of cases, and by >20% in all but 4 cases. In addition, levels of sVEGFR-3 were decreased by >30% in 82% of cases during the first cycle. For each of these markers, levels tended to return to near-baseline after 2 weeks off treatment. Longitudinal decreases in sKIT were also observed; decreases >50% by the end of cycle 2 were correlated with treatment outcomes for time-to-progression (P < 0.001) and survival (P = 0.03). Further analysis of correlations with pharmacokinetic and clinical parameters is ongoing. Conclusions: Sunitinib therapy is associated with increases in plasma VEGF and decreases in soluble VEGFRs and KIT. This panel of circulating proteins may have utility as pharmacodynamic biomarkers of sunitinib activity in patients with metastatic breast cancer. sVEGFR-3 may be a novel biomarker of the biological activity of sunitinib, while sKIT may be correlated with clinical response. Analysis of these and other biomarkers in larger studies of sunitinib in breast cancer may be warranted.

[Table: see text]

Analysis of circulating biomarkers of sunitinib malate in patients with unresectable neuroendocrine tumors (NET): VEGF, IL-8, and soluble VEGF receptors 2 and 3

4045

Background: Sunitinib malate (SU11248) is a multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activity that specifically inhibits VEGFR, PDGFR, KIT, RET, and FLT3. In a phase II trial of 109 patients with metastatic neuroendocrine tumors (NET), sunitinib treatment was associated with ORR and high rates of SD in patients with carcinoid and pancreatic islet cell tumors (Kulke et al, ASCO 2005). To characterize potential biomarkers of biological response to sunitinib, we analyzed plasma levels of a panel of soluble proteins from patients in this trial. Methods: Patients received sunitinib in 6-week cycles comprised of 50 mg/day for 4 weeks followed by 2 weeks off treatment. Pre-dose plasma samples from 106 patients were obtained on days 1 and 28 of multiple cycles. Plasma levels of VEGF, soluble VEGF receptor 2 (sVEGFR-2), interleukin-8 (IL-8), and a novel biomarker, sVEGFR-3, were measured via ELISA analysis. Results: Plasma levels of each protein were frequently modulated during the course of treatment. At the end of cycle 1, VEGF levels were increased more than 3-fold over baseline in ∼50% of all patients. Average baseline VEGF levels were higher in the islet cell group (62 vs. 40 pg/ml, P = 0.06). In cycle 1, sVEGFR-2 and sVEGFR-3 levels were significantly decreased by ≥30% in ∼60% and 70% of all patients, respectively (P < 0.0001). Levels tended to return to near-baseline after 2 weeks off treatment. The reduction in sVEGFR-3 levels in cycle 1 was, on average, greater in the subset of patients with PR (n=11) compared to others (45% vs. 38%). Overall, there was a 2.2-fold average increase in IL-8 levels by the end of cycle 1, and a larger proportional increase in IL-8 levels in patients exhibiting decreases in tumor size, patients who also tended to have lower baseline IL-8 levels. Further analysis of correlations with pharmacokinetic and clinical parameters is ongoing. Conclusions: Our results suggest that this panel of circulating proteins may be of utility as pharmacodynamic biomarkers of sunitinib activity in patients with advanced NET. sVEGFR-3 may be a novel biomarker of the biological activity of sunitinib in NET, and IL-8 may be of particular interest as a potential predictor of response.

[Table: see text]

A phase II study of sunitinib administered in a continuous daily regimen in patients with cytokine-refractory metastatic renal cell carcinoma (mRCC)

4529

Background: Renal cell carcinomas are known for their vascularity and production of high levels of VEGF. Sunitinib malate (SU11248), an oral, multitargeted tyrosine kinase inhibitor of multiple receptors including VEGFR, PDGFR, KIT, RET, and FLT3, has previously demonstrated significant efficacy in 168 patients (pts) with mRCC, with a 42% objective response rate (ORR) at 50 mg/day in 6-week (wk) cycles of 4 wks on treatment followed by 2 wks off. This study sought to determine the efficacy and safety of single-agent sunitinib in mRCC when administered in a continuous 37.5 mg/day regimen. Methods: Pts with histologically proven mRCC, refractory to a cytokine-based regimen, were enrolled in this open-label, multicenter, phase II study. Eligibility criteria included measurable disease, ECOG PS 0/1, and adequate organ function. Pts were randomized to receive sunitinib in the morning (AM) or in the evening (PM) at a dose of 37.5 mg/day, with individual doses subsequently titrated based on tolerability. The primary endpoint was RECIST-defined ORR. Secondary endpoints includedprogression-free survival, adverse events (AEs) and quality of life measures. Results: A total of 88/100 planned pts have been randomized to date: AM (43) and PM (45), and enrollment will be completed by end January 2006. 44 pts have been on continuous sunitinib treatment at 37.5 mg/day for >16 wks (3), >12 wks (9), >8 wks (12), and >4 wks (20). 2 pts (2.3%) discontinued (colon perforation and renal insufficiency) and 9 (10.2%) dose reduced to 25 mg/day due to grade 2/3 AEs: mucositis (2), hand-foot syndrome (2), thrombocytopenia (2), asthenia (1), nausea/diarrhea (1), and neutropenia (1). Preliminary efficacy data show some tumor shrinkage in the majority of patients evaluated at 4 wks, with 3 initial partial responses. There has been no significant difference between pts who received AM or PM doses. The most commonly reported AEs were mucositis, fatigue, hair/skin discoloration, and hand-foot syndrome. Conclusions: Sunitinib administered at a continuous dose of 37.5 mg/day was generally well tolerated; only a few patients required treatment breaks and/or dose reduction. Preliminary efficacy data are encouraging. Mature data will be presented.

[Table: see text]

Patterns of PET response after long-term sunitinib therapy in patients (pts) with imatinib (IM)-resistant gastrointestinal stromal tumors (GIST)

9547

Background: Sunitinib malate (previously known as SU11248) is an active therapy for GIST patients resistant to or intolerant of IM. During initial development, sunitinib was administered in 4–6 week cycles, with 2–4 weeks of drug dosing followed by 2 weeks off treatment. We previously reported suppression of tumor-related 18FDG avidity on PET imaging during sunitinib dosing, with rebound tumor uptake while off drug. This rebound, seen in 80% with initial PET suppression, did not correlate with lack of clinical benefit. We asked if this pattern persists in pts who benefited from long term (> 2 years) sunitinib therapy. Methods: Of 77 pts in our initial Phase I/II study, 7 remain on therapy with sunitinib for more than 2 years, 4 of whom had matched baseline PET and CT data to assess tumor metabolic activity on and off sunitinib dosing. PET scans were obtained at baseline, during initial treatment, during the off-treatment period, and again after > 2 years therapy. These 4 pts were followed for a median 39 months (range 35–45 months) and for a median of 35 cycles (range 27–47). Two achieved PR and two SD. Results: Initially, all 4 exhibited suppression of tumor FDG avidity with treatment followed by rebound during the off-treatment period. By 6 months, all showed complete suppression of FDG activity. After > 2 years on sunitinib, GIST lesions in 2 pts showed no activity on PET, even while off sunitinib, while GIST in 2 pts demonstrated rebound flare when off therapy. The GIST lesions have not progressed despite the transient metabolic rebound while off sunitinib. Conclusions: Metastatic lesions in pts with IM-resistant GIST benefiting from long-term sunitinib therapy display two patterns on PET imaging. GIST in certain pts who benefit from therapy demonstrates metabolic rebound of activity when off dosing, while lesions in other pts remain metabolically inert on PET even during the brief dosing breaks. Functional imaging may yield insights to differences in the underlying biology of GIST subtypes in different pts.

[Table: see text]

Overcoming promoter competition in packaging cells improves production of self-inactivating retroviral vectors

Retroviral vectors with self-inactivating (SIN) long-terminal repeats not only increase the autonomy of the internal promoter but may also reduce the risk of insertional upregulation of neighboring alleles. However, gammaretroviral as opposed to lentiviral packaging systems produce suboptimal SIN vector titers, a major limitation for their clinical use. Northern blot data revealed that low SIN titers were associated with abundant transcription of internal rather than full-length transcripts in transfected packaging cells. When using the promoter of Rous sarcoma virus or a tetracycline-inducible promoter to generate full-length transcripts, we obtained a strong enhancement in titer (up to 4 x 10(7) transducing units per ml of unconcentrated supernatant). Dual fluorescence vectors and Northern blots revealed that promoter competition is a rate-limiting step of SIN vector production. SIN vector stocks pseudotyped with RD114 envelope protein had high transduction efficiency in human and non-human primate cells. This study introduces a new generation of efficient gammaretroviral SIN vectors as a platform for further optimizations of retroviral vector performance.