Factor VIII moiety of recombinant Factor VIII Fc fusion protein impacts Fc effector function and CD16+ NK cell activation

Recombinant Factor VIII-Fc fusion protein (rFVIIIFc) is an enhanced half-life therapeutic protein product used for the management of hemophilia A. Recent studies have demonstrated that rFVIIIFc interacts with Fc gamma receptors (FcγR) resulting in the activation or inhibition of various FcγR-expressing immune cells. We previously demonstrated that rFVIIIFc, unlike recombinant Factor IX-Fc (rFIXFc), activates natural killer (NK) cells via Fc-mediated interactions with FcγRIIIA (CD16). Additionally, we showed that rFVIIIFc activated CD16+ NK cells to lyse a FVIII-specific B cell clone. Here, we used human NK cell lines and primary NK cells enriched from peripheral blood leukocytes to study the role of the FVIII moiety in rFVIIIFc-mediated NK cell activation. Following overnight incubation of NK cells with rFVIIIFc, cellular activation was assessed by measuring secretion of the inflammatory cytokine IFNγ by ELISA or by cellular degranulation. We show that anti-FVIII, anti-Fc, and anti-CD16 all inhibited indicating that these molecules were involved in rFVIIIFc-mediated NK cell activation. To define which domains of FVIII were involved, we used antibodies that are FVIII domain-specific and demonstrated that blocking FVIII C1 or C2 domain-mediated membrane binding potently inhibited rFVIIIFc-mediated CD16+ NK cell activation, while targeting the FVIII heavy chain domains did not. We also show that rFVIIIFc binds CD16 with about five-fold higher affinity than rFIXFc. Based on our results we propose that FVIII light chain-mediated membrane binding results in tethering of the fusion protein to the cell surface, and this, together with increased binding affinity for CD16, allows for Fc-CD16 interactions to proceed, resulting in NK cellular activation. Our working model may explain our previous results where we observed that rFVIIIFc activated NK cells via CD16, whereas rFIXFc did not despite having identical IgG1 Fc domains.

Emerging approaches to induce immune tolerance to therapeutic proteins

Immunogenicity affects the safety and efficacy of therapeutic proteins. This review is focused on approaches for inducing immunological tolerance to circumvent the immunogenicity of therapeutic proteins in the clinic. The few immune tolerance strategies that are used in the clinic tend to be inefficient and expensive and typically involve global immunosuppression, putting patients at risk of infections. The hallmark of a desirable immune tolerance regimen is the specific alleviation of immune responses to the therapeutic protein. In the past decade, proof-of-principle studies have demonstrated that emerging technologies, including nanoparticle-based delivery of immunomodulators, cellular targeting and depletion, cellular engineering, gene therapy, and gene editing, can be leveraged to promote tolerance to therapeutic proteins. We discuss the potential of these novel approaches and the barriers that need to be overcome for translation into the clinic.

Dosing Strategy of Immunoglobulin (IgG) Replacement Therapies in Obese and Overweight Patients with Primary Immunodeficiency Diseases (PIDDs): A Meta-Analysis of Clinical Trials

The current dosing strategy of immune globulin products for the treatment of primary immunodeficiency diseases (PIDDs) in the USA is based on total body weight (BW). The aim of our study was to assess the relationship between dose and trough level, and to determine whether an alternative dosing strategy should be considered for patients who are overweight or obese. We analyzed data in a total of 533 patients from 11 studies. We modeled the relationship between trough level and dose per week using a linear mixed model. We used an over-dispersed Poisson model to model the relationship between infection and trough level. In these analyses, we then combined the study-specific treatment effects using a random-effect or fixed-effect model. The mean administered dose per week was 9.77, 14.00, or 18.17 g in patients who were normal weight, overweight, or obese, respectively. Compared with a patient of normal weight, a 1 g increase in dose per week in a patient who was overweight was associated with a smaller increase in the trough level, 0.08 g/L less (95%CI -0.14 to -0.03 g/L), and a 1 g increase in dose per week in a patient who was obese was associated with a much smaller increase in trough level, 0.01 g/L less (95% CI -0.07 to 0.06 g/L). Last, for a 1 unit (g/L) increase in trough level, the expected number of infections remained the same, with a multiplicative factor of 1.01 (95%CI 0.98-1.04). Overall, we found no compelling evidence to justify a reconsideration of the current dosing strategy based on total BW for patients with PIDDs who are overweight or obese.

A structural homology approach to identify potential cross-reactive antibody responses following SARS-CoV-2 infection

The emergence of the novel SARS-CoV-2 virus is the most important public-health issue of our time. Understanding the diverse clinical presentations of the ensuing disease, COVID-19, remains a critical unmet need. Here we present a comprehensive listing of the diverse clinical indications associated with COVID-19. We explore the theory that anti-SARS-CoV-2 antibodies could cross-react with endogenous human proteins driving some of the pathologies associated with COVID-19. We describe a novel computational approach to estimate structural homology between SARS-CoV-2 proteins and human proteins. Antibodies are more likely to interrogate 3D-structural epitopes than continuous linear epitopes. This computational workflow identified 346 human proteins containing a domain with high structural homology to a SARS-CoV-2 Wuhan strain protein. Of these, 102 proteins exhibit functions that could contribute to COVID-19 clinical pathologies. We present a testable hypothesis to delineate unexplained clinical observations vis-à-vis COVID-19 and a tool to evaluate the safety-risk profile of potential COVID-19 therapies.

Epitope diversity of SARS-CoV-2 hyperimmune intravenous human immunoglobulins and neutralization of variants of concern

Hyperimmune immunoglobulin (hCoV-2IG) generated from SARS-CoV-2 convalescent plasma (CP) are under evaluation in clinical trials. Here we explored the antibody epitope repertoire, and virus neutralizing capacity of six hCoV-2IG batches as well as nine CP against SARS-CoV-2 and emerging variants of concern (VOCs). Epitope-mapping by gene-fragment phage display library spanning the SARS-CoV-2 spike demonstrated broad recognition of multiple antigenic sites spanning the entire spike that was higher for hCoV-2IG than CP, with predominant binding to the fusion peptide. In the pseudovirus neutralization assay and in the wild-type SARS-CoV-2 PRNT assay, hCoV-2IG lots showed higher titers against the WA-1 strain compared with CP. Neutralization of VOCs were reduced to different extent by hCoV-2IG lots but were higher than CP. Significant reduction of hCoV-2IG binding was observed to RBD-E484K followed by RBD-N501Y (but not RBD-K417N). This study suggests that post-exposure treatment with hCoV-2IG could be preferable to CP.

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SARS-CoV-2 hCoV-2IG demonstrate highly diverse antibody epitope profile

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SARS-CoV-2 hCoV-2IG lots neutralized SARS-CoV-2 variants better than CP

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Significant reduction of hCoV-2IG binding to RBD-E484K compared with unmutated RBD

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Higher hCoV-2IG dose would be required for SARS-CoV-2 variant infected patients

Pharmacokinetics and Efficacy of Human Hyperimmune Intravenous Immunoglobulin Treatment of SARS-CoV-2 Infection in Adult Syrian Hamsters

Background

Following the failure of antibody therapies in treating COVID-19 hospitalized patients we investigated the impact of viral replication on the pharmacokinetics (PK) and efficacy of a hyperimmune SARS-CoV-2 Immune Globulin (CoVIG) product in treatment of SARS-CoV-2 infection using the adult Syrian hamster model.

Methods

The CoVIG was manufactured from plasma donors who had recovered from COVID-19. The dose used (400 mg/kg) was based on the dose given in clinical trials to hospitalized COVID-19 patients. Hamsters were given a single dose of CoVIG two days after challenge with the SARS-CoV-2 virus (isolate NY/PV08410/2020), followed by sampling of blood, nasal, tracheal and lung tissues at different time points. The blood samples were assayed for anti-SARS-CoV-2 spike binding and used to calculate PK parameters. Nasal washes, trachea, and lung samples were assayed for viral replication by PCR (sgRNA).

Results

CoVIG-treated hamsters showed a reduction in viral replication in the lower respiratory tract, but minimally in the upper respiratory tract, following challenge with SARS-CoV-2. Challenge with SARS-CoV-2 resulted in altered PK parameters proportionate to viral replication, resulting in decreased area under the curve (AUC), accelerated clearance and shorter half-life of CoVIG.

Conclusions

These data indicate that in the presence of actively replicating SARS-CoV-2 virus, PK parameters are altered and should trigger an adjustment in dosing of CoVIG.

Considerations on activity assay discrepancies in factor VIII and factor IX products

New modified coagulation factor VIII (FVIII) and factor IX (FIX) products have been designed to improve the treatment of individuals with hemophilia A and B by increasing the interval between dosing. Although these FVIII and FIX molecules have been structurally modified to improve the circulation time, the changes have also influenced their behavior in functional assays in comparison with traditional plasma-derived or recombinant coagulation factors. The assignment of potencies for these products can be problematic because discordance in factor activity values between the commonly used one-stage clotting and chromogenic substrate assays is often observed. Discrepancies in potency assay values also exist when different assay kits and reagents are used in the same assay type. Ideally, all FVIII and FIX products should be calibrated against the World Health Organization (WHO) International Standards (IS) because the assignment of potencies in international units (IU) helps maintain treatment tradition and meaningful references for manufacturers, patients, and clinicians. The discrepant measurements, attributed to the modified structural and functional properties of these products, are manifested in their lack of commutability with the WHO IS for FVIII or FIX. Herein, we discuss the considerations upon which an assay is chosen for potency assignment and postadministration monitoring of a new factor product, which include the validity of the assay calibrated with the IS, the meaning of the potency values in IU, standards of care for patients, clinical relevance between the assigned potency value and recovery value from clinical laboratories, and patient safety.

Factor VIII-Fc Activates Natural Killer Cells via Fc-Mediated Interactions With CD16

The most challenging complication associated with Factor VIII (FVIII) replacement therapy is the development of neutralizing anti-drug antibodies, or inhibitors, which occur in 23-35% of severe (FVIII level <1%) hemophilia A (HA) patients and are a serious hindrance to effective management of HA. Consequently, strategies that can either prevent anti-FVIII inhibitors from developing or "tolerize" individuals who develop such antibodies represent a clinically important unmet need. One intervention for patients with high-titer inhibitors is immune tolerance induction (ITI) therapy. Although ITI therapy is the only clinically proven strategy to eradicate anti-FVIII inhibitors, mechanisms of inhibitor reduction remain unknown. Factor VIII Fc-fusion (rFVIIIFc) is an enhanced half-life antihemophilic factor used in replacement therapy for HA. Fc-fusion is a successful protein bio-engineering platform technology. In addition to enhancement of plasma half-life via neonatal Fc receptor (FcRn) binding, other Fc-mediated interactions, including engagement with Fc gamma receptors (FcγR), may have immunological consequences. Several case reports and retrospective analyses suggest that rFVIIIFc offers superior outcomes with respect to ITI compared to other FVIII products. Previously we and others demonstrated rFVIIIFc interactions with activating FcγRIIIA/CD16. Here, we investigated if rFVIIIFc activates natural killer (NK) cells via CD16. We demonstrated rFVIIIFc signaling via CD16 independent of Von Willebrand Factor (VWF):FVIII complex formation. We established that rFVIIIFc potently activated NK cells in a CD16-dependent fashion resulting in IFNγ secretion and cytolytic perforin and granzyme B release. We also demonstrated an association between rFVIIIFc-mediated NK cell IFNγ secretion levels and the high-affinity (158V) CD16 genotype. Furthermore, we show that rFVIIIFc-activated CD16⁺ NK cells were able to lyse a B-cell clone (BO2C11) bearing an anti-FVIII B-cell receptor in an antibody-dependent cellular cytotoxicity (ADCC) assay. These in vitro findings provide an underlying molecular mechanism that may help explain clinical case reports and retrospective studies suggesting rFVIIIFc may be more effective in tolerizing HA patients with anti-FVIII inhibitors compared to FVIII not linked to Fc. Our in vitro findings suggest a potential use of Fc-fusion proteins acting via NK cells to target antigen-specific B-cells, in the management of unwanted immune responses directed against immunogenic self-antigens or therapeutic protein products.

Factor VIII-Fc activates natural killer cells via Fc-mediated interactions with CD16

FactorVIII Fc-fusion (rFVIIIFc) is an enhanced half-life antihemophilic factor usedin replacement therapy of hemophilia A. Fc-fusion is a successful protein bio-engineering platform technology. In addition to enhancement of plasmahalf-life via neonatal Fc receptor (FcRn) binding, other Fc-mediatedinteractions, including engagement with Fc gamma receptors (FcγR), may haveimmunological consequences. Previouslywe and others demonstrated rFVIIIFc interactions with activatingFcγRIIIA/CD16. Here, we investigated ifrFVIIIFc activates natural killer (NK) cells via CD16. We demonstrated rFVIIIFc signaling via CD16independent of Von Willebrand Factor (VWF):FVIII complex formation. We established that rFVIIIFc potentlyactivated NK cells in a CD16-dependent fashion resulting in IFNγ secretion andcytolytic perforin and granzyme B release. We also demonstrated an association between rFVIIIFc-mediated NK cellIFNγ secretion levels and the high affinity (158V) CD16 genotype. Furthermore, we show that rFVIIIFc-activatedCD16+ NK cells were able to lyse a B-cell clone bearing ananti-FVIII BCR (BO2C11) in an antibody-dependent cellular cytotoxicity (ADCC)assay. These findings provide anunderlying molecular mechanism that may help explain clinical case reports andretrospective studies that suggest rFVIIIFc may be more effective in tolerizinghemophilia A patients with anti-FVIII inhibitory antibodies compared to FVIIInot linked to Fc. Our findings suggest apotential use of Fc-fusion proteins acting via NK cells to target B-cells, inthe management of unwanted immune responses directed against immunogenicself-antigens or therapeutic protein products.

Dosing Considerations for Antibodies Against COVID-19

At present, no cure is available for COVID-19 but vaccines, antiviral drugs, immunoglobulins, or the combination of immunoglobulins with antiviral drugs have been suggested and are in clinical trials. The purpose of this paper is to discuss the role of a pharmacokinetic and viral load analysis as a basis for adjusting immunoglobulin dosing to treat COVID-19. We reviewed the pre-clinical and clinical literature that describes the impact of a high antigen load on pharmacokinetic data following antibody treatment. Representative examples are provided to illustrate the effect of high viral and tumor loads on antibody clearance. We then highlight the implications of these factors for facilitating the development and dosing of hyperimmune anti-SARS CoV2 immunoglobulin. Both nonclinical and clinical examples indicate that high antigen loads, whether they be viral, bacterial, or tumoral in origin, result in increased clearance and decreased area under the curve and half-life of antibodies. A dosing strategy that matches the antigen load can be achieved by giving initially high doses and adjusting the frequency of dosing intervals based on pharmacokinetic parameters. We suggest that study design and dose selection for immunoglobulin products for the treatment of COVID-19 require special considerations such as viral load, antibody-virus interaction, and dosing adjustment based on the pharmacokinetics of the antibody.

Considerations for Optimizing Dosing of Immunoglobulins Based on Pharmacokinetic Evidence

Immunoglobulins (IGs) are widely used for the treatment of immunodeficiency syndromes and several autoimmune diseases. In neonates, IGs have been used for the treatment of alloimmune thrombocytopenia, in neonatal infections and in the rare cases of neonatal Kawasaki disease. This review aims to examine the various dosing regimens of IGs following intravenous (IV) and subcutaneous (SC) administration, pharmacokinetics (PK) of IGs, and the importance of trough values for the prevention of infections in patients with primary immune deficiency (PID). The review also focuses on the mechanism of catabolism of IGs and the impact on the half-life of IGs. Data and reviews were obtained from the literature and the FDA package inserts. The authors suggest that for dosing, the PK of IGs should be evaluated on the baseline-corrected concentrations since this approach provides an accurate estimate of half-life and clearance of IGs. We also suggest employing clearance as a primary PK parameter for dosing determination of IGs. We suggest that IV dosing would be more effective if given more frequently to adjust for the increased clearance at high doses and because the baseline-corrected half-life is much shorter than the baseline-uncorrected half-life. Regarding SC administration, the dose should be adjusted based on the absolute bioavailability (determined against IV dosing) of the product. Finally, we highlight clinical and PK data gaps for optimum and individualized dosing of IGs.

Considerations for pharmacokinetic assessment of immunoglobulins: Gammagard in very low birth weight neonates with and without baseline-correction

BACKGROUND

Immunoglobulins are widely used across multiple therapeutic areas such as immunodeficiency syndromes, infection and autoimmune diseases. The pharmacokinetics (PK) of immunoglobulins are well characterized in adults, but very little is known about the PK of immunoglobulins in neonates and infants.

OBJECTIVE

The objective of the present study was to characterize the PK of Gammagard, an immunoglobulin, in very low birth weight preterm neonates.

METHOD

Gammagard concentration-time data from very low birth weight neonates (bodyweight range 0.78-1.38 kg, n = 20) following intravenous administration of 500 mg/kg and 750 mg/kg were obtained from the literature. The data were analyzed with and without baseline correction using extensive blood samples (8 blood samples). Model-independent (non-compartmental) analysis was used to characterize the PK of Gammagard.

RESULTS

Based on uncorrected baseline concentration-time data, the clearance and half-life of Gammagard were 3.1 ± 0.7 mL/day and 22 ± 6 days, respectively. Based on corrected baseline concentration-time data, the clearance and half-life of Gammagard were 20.2 ± 7.4 mL/day and 5.3 ± 2.2 days, respectively.

CONCLUSION

The dose of immunoglobulins should be adjusted based on the PK of baseline corrected rather than baseline uncorrected profiles because baseline corrected PK parameters especially half-life reconciles with PK principles.

Fc-fusion drugs have C1q/FcγR binding and signaling properties that can affect their immunogenicity

Fusing the IgG1 constant region (Fc-domain) to therapeutic proteins increases their plasma half-life via neonatal Fc receptor (FcRn) binding. However, potential interactions with other Fc-binding molecules including complement C1q and Fc gamma receptors (FcγR) can have immunological consequences. Our previous studies in a mouse model suggest that engagement of the Fc-Factor IX (FIX) to FcγR on APC and NKT cells could alter the immunogenicity of the FIX moiety. Here, we conducted a comparative study of FDA-approved Fc-fusion proteins to assess their potential for C1q binding as well as FcγR binding and signaling. Binding of soluble drug to C1q was measured by ELISA, and FcγR binding and signaling was evaluated using BW5147:FcγR-ζ reporter cell lines. We demonstrate that rFIXFc and rFVIIIFc bound C1q as well as activating and inhibitory FcγRs (I, IIA, IIB, IIIA). These therapeutic proteins also signaled via FcγRIIIA, and to a lesser extent via FcγRI and FcγRIIB. Other Fc-fusion drugs (TNFR-Fc; CTLA4-Fc) bound FcγRI (TNFR-Fc also bound FcγRIIIA), but did not result in FcγR signaling. As predicted, a control anti-CD20 monoclonal antibody modified for enhanced FcγRIIIA engagement, bound and signaled via FcγRIIIA, while the parent molecule did not; supporting our use of BW5147: FcγR-ζ reporter cells for the assessment of Fc:FcγR interactions. Our studies show that Fc-fusion drugs have distinct C1q/FcγR binding and signaling properties. Moreover, FcγR binding does not predict signaling. Our studies suggest that Fc-FcγR engagement can influence the immunogenicity to Fc-fusion drugs as both fusion partners influence this interaction. Future investigations will elucidate the underlying molecular mechanisms.

Fusion of Fc domain to Factor IX (FIX) modulates the Th2 biased response to FIX and triggers Th1 immunity in hemophilia B treated mice

Fusion of the IgG1 constant region domain (Fc) to therapeutic proteins increases the plasma half-life of drugs via binding to the neonatal Fc receptor (FcRn). However, potential interactions with Fc gamma-receptors (FcγR) expressed by immune cells may effect the immunogenicity of these drugs. The coagulation factors VIII (FVIII) and IX (FIX) for the treatment of hemophilia A & B (HA & HB) are the only drugs available with and without Fc fusion and offer an opportunity to experimentally study the effect of Fc fusion. Anti FVIII & FIX antibodies (ADAs) and rare cases of anaphylaxis in HB patients, are serious safety concerns. Using a mouse model for HB, we compared the immune responses to infusions of recombinant human FIX (hFIX) and hFIX fused to mouse IgG2a-Fc (hFIX-mFc). The mFc allowed species-specific Fc-FcγR interactions and prevented immune response to the foreign hFc. Treatment with hFIX-mFc caused earlier onset of anti-FIX IgG and elicited higher FIX-neutralizing antibody levels. Treatment with hFIX triggered Th2 biased immunity i.e., elevated plasma IgE titers, and Th2 cytokine profile of FIX-specific CD4 T cells and a few anaphylactic events. The fusion of Fc altered the response to a Th1 type with increased plasma IFN-γ levels, and IFN-γ secretion by effector CD4 T cells. hFIX-mFc binds to soluble FcγRs and FcγRs on natural killer cells (which also secrete IFNγ) and antigen presenting cells (dendritic cells, and macrophages source of IL-12). We show that Fc fusion enhances the presentation of hFIX to CD4 T cells. We propose that high plasma availability and targeting of APC provide plausible mechanisms by which the Fc fusion may modulate the CD4 T cell response to hFIX towards a Th1 like response, thus avoiding allergic responses.

Modulating immunogenicity of factor IX by fusion to an immunoglobulin Fc domain: a study using a hemophilia B mouse model

Essentials Fc-fusion increases a therapeutic's half-life, but FcγR interactions may impact immunogenicity. Species-specific Fc-FcγR interactions allow for mechanistic in vivo studies using mouse models. Fc fusion modulates the immune response to factor IX in hemophilia B mice by eliciting Th1 bias. This model could inform future studies of IgE-associated anaphylaxis in hemophilia B patients.

SUMMARY

Background Fc fusion is a platform technology used to increase the circulating half-life of protein and peptide therapeutics. However, there are potential immunological consequences with this approach, such as changes in the molecule's immunogenicity as well as possible interactions with a repertoire of Fc receptors (FcR) that can modulate immune responses. Objectives/Methods Using a mouse hemophilia B (HB) model, we compared the immune responses to infusions of recombinant human factor IX (hFIX) and hFIX fused to mouse IgG2a-Fc (hFIX-mFc). The mFc was employed to allow species-specific Fc-FcγR interactions. Results Although treatment with hFIX-mFc altered the early development of anti-FIX IgG, no significant differences in anti-FIX antibody titers were observed at the end of the treatment regimen (5 weeks) or upon anamnestic response (5 months). However, treatment with hFIX-mFc elicited higher FIX-neutralizing antibody levels and resulted in reduced IgE titers compared with the hFIX-treated group. Additionally, differences in plasma cytokine levels and in vitro CD4+ T-cell responses suggest that whereas hFIX treatment triggered a Th2-biased immune response, hFIX-mFc treatment induced Th1-biased CD4+ T cells. We also show that hFIX-mFc bound to soluble FcγRs and engaged with FcγRs on different cell types, which may impact antigen presentation. Conclusions These studies provide a model system to study how Fc-fusion proteins may affect immune mechanisms. We used this model to demonstrate a plausible mechanism by which Fc fusion may modulate the IgE response to hFIX. This model may be appropriate for investigating the rare but severe IgE-mediated anaphylaxis reaction to hFIX infusions in HB patients.

Poly(I:C) Induces Human Lung Endothelial Barrier Dysfunction by Disrupting Tight Junction Expression of Claudin-5

Viral infections are often accompanied by pulmonary microvascular leakage and vascular endothelial dysfunction via mechanisms that are not completely defined. Here, we investigated the effect of the Toll-like receptor 3 (TLR3) ligand polyinosinic-polycytidylic acid [Poly(I:C)], a synthetic analog of viral double-stranded RNA (dsRNA) commonly used to simulate viral infections, on the barrier function and tight junction integrity of primary human lung microvascular endothelial cells. Poly(I:C) stimulated IL-6, IL-8, TNFα, and IFNβ production in conjunction with the activation of NF-κB and IRF3 confirming the Poly(I:C)-responsiveness of these cells. Poly(I:C) increased endothelial monolayer permeability with a corresponding dose- and time-dependent decrease in the expression of claudin-5, a transmembrane tight junction protein and reduction of CLDN5 mRNA levels. Immunofluorescence experiments revealed disappearance of membrane-associated claudin-5 and co-localization of cytoplasmic claudin-5 with lysosomal-associated membrane protein 1. Chloroquine and Bay11-7082, inhibitors of TLR3 and NF-κB signaling, respectively, protected against the loss of claudin-5. Together, these findings provide new insight on how dsRNA-activated signaling pathways may disrupt vascular endothelial function and contribute to vascular leakage pathologies.

Immune responses to chimeric human-FIX-mouse-Fc fusion protein in a hemophilia B mouse model (THER2P.963)

The fusion of a protein with the Fc-region of an antibody is used to increase the circulating half-life of therapeutic proteins. Using a mouse hemophilia B (HB) model we compared the immune responses to infusions of recombinant human FIX (rFIX) and human FIX-mouse Fc (hFIX-mFc) fusion protein. HB mice received weekly IV injection of rFIX or hFIX-mFc for 5 weeks. Anti-FIX IgG, IgE and cytokines were measured. Splenic cells were used to determine FIX-specific T and B cell functional and memory responses. Our results showed that, following IV treatment with rFIX or hFIX-mFc, there are no statistically significant differences in the titers of anti-FIX IgG Ab and numbers of long term memory B cells. However, a significantly larger proportion of mice treated with rFIX developed elevated titers of total IgE which correlated with a Th2 bias following rFIX. In contrast, hFIX-mFc induced a Th1-like response and no detectable IgE. Our study suggests, that in mice, hFIX-mFc fusion protein promotes a Th1-like response and is less likely than rFIX to induce an IgE response, which may lead to anaphylaxis, a rare severe adverse event associated with the treatment of HB patients.

Fc fusion as a platform technology: potential for modulating immunogenicity

The platform technology of fragment crystallizable (Fc) fusion, in which the Fc region of an antibody is genetically linked to an active protein drug, is among the most successful of a new generation of bioengineering strategies. Immunogenicity is a critical safety concern in the development of any protein therapeutic. While the therapeutic goal of generating Fc-fusion proteins has been to extend half-life, there is a critical mass of literature from immunology indicating that appropriate design of the Fc component has the potential to engage the immune system for product-specific outcomes. In the context of Fc-fusion therapeutics, a review of progress in understanding Fc biology suggests the prospect of engineering products that have an extended half-life and are able to modulate the immune system.

Hyperimmune globulins and same-day thrombotic adverse events as recorded in a large healthcare database during 2008-2011

Thrombotic events (TEs) are rare serious complications following administration of hyperimmune globulin (HIG) products. Our retrospective claims-based study assessed occurrence of same-day TEs following administration of HIGs during 2008-2011 and examined potential risk factors using HealthCore's Integrated Research Database (HIRD(SM) ) and laboratory testing of products' procoagulant Factor XIa activity by U.S. Food and Drug Administration. Multivariable regression was used to estimate same-day TE risk for different products. Of 101,956 individuals exposed to 23 different HIG product groups, 86 (0.84 per 1,000 persons) had a TE diagnosis code (DC) recorded on the same day as HIG administration. Unadjusted same-day TE DC rates (per 1,000 persons) ranged from 0.4 to 148.9 for different products. GamaSTAN S/D IG >10 cc had statistically significantly higher same-day TE DC risk compared to Tetanus IG (OR = 57.57; 95% CI = 19.72-168.10). Increased TE risk was also observed with older age (≥45 years), prior thrombotic events, and hypercoagulable state(s). Laboratory investigation identified elevated Factor XIa activity for GamaSTAN S/D, HepaGam B, HyperHep B S/D, WinRho SDF, HyperRHO S/D full dose, and HyperTET S/D. Our study, for the first time, identified increase in the same-day TE DC risk with GamaSTAN S/D IG >10 cc and suggests potentially elevated TE risk with other HIGs.

Poly (I:C) induces human endothelial barrier dysfunction by disrupting tight junction expression of claudin-5 (P4197)

Viral infections are often accompanied by pulmonary microvascular leakage and vascular endothelial dysfunction via mechanisms that are not completely defined. Here, we investigated the effect of the Toll-like receptor 3 ligand Poly (I:C), a synthetic analog of viral double-stranded RNA commonly used to simulate viral infections, on the barrier function and tight junction integrity of primary human lung microvascular cells. Poly (I:C) produced a dose- and time-dependent increase in endothelial monolayer permeability accompanied by a corresponding decrease in the expression of claudin-5, a transmembrane tight junction protein. Immunofluorescence experiments revealed disappearance of membrane-associated claudin-5 and co-localization of internalized claudin-5 with lysosomal-associated membrane protein 1 (LAMP-1), a marker of lysosomes, suggesting enhanced lysosomal degradation of claudin-5. Poly (I:C) also induced a dose- and time-dependent cleavage of TLR3 and TRIF as well as activation of NF-kB and IRF3, but not IRF7 (MyD88-dependent pathway), consistent with the direct stimulation of the TLR3 signaling. Pronounced inflammatory response with the release of IL-6, IL-8, MCP-1 and RANTES and a hallmark TLR3-mediated type 1 IFN production (IFNbeta) was also observed. Together, these findings provide new insight on how virally-activated signaling pathways may disrupt vascular endothelial function and contribute to vascular leakage pathologies.

Aptamers as a sensitive tool to detect subtle modifications in therapeutic proteins

Therapeutic proteins are derived from complex expression/production systems, which can result in minor conformational changes due to preferential codon usage in different organisms, post-translational modifications, etc. Subtle conformational differences are often undetectable by bioanalytical methods but can sometimes profoundly impact the safety, efficacy and stability of products. Numerous bioanalytical methods exist to characterize the primary structure of proteins, post translational modifications; protein-substrate/protein/protein interactions and functional bioassays are available for most proteins that are developed as products. There are however few analytical techniques to detect changes in the tertiary structure of proteins suitable for use during drug development and quality control. For example, x-ray crystallography and NMR are impractical for routine use and do not capture the heterogeneity of the product. Conformation-sensitive antibodies can be used to map proteins. However the development of antibodies to represent sufficient epitopes can be challenging. Other limitations of antibodies include limited supply, high costs, heterogeneity and batch to batch variations in titer. Here we provide proof-of-principle that DNA aptamers to thrombin can be used as surrogate antibodies to characterize conformational changes. We show that aptamers can be used in assays using either an ELISA or a label-free platform to characterize different thrombin products. In addition we replicated a heat-treatment procedure that has previously been shown to not affect protein activity but can result in conformational changes that have serious adverse consequences. We demonstrate that a panel of aptamers (but not an antibody) can detect changes in the proteins even when specific activity is unaffected. Our results indicate a novel approach to monitor even small changes in the conformation of proteins which can be used in a routine drug-development and quality control setting. The technique can provide an early warning of structural changes during the manufacturing process that could have consequential outcomes downstream.

Plasma derivatives: new products and new approaches

The infusion of plasma-derived or recombinant factors to treat bleeding disorders such as hemophilia A and B is a success story in the management of a chronic disease. The effectiveness of this approach is however limited by challenges with adverse effects of treatment. The most notable of these are the development of inhibitory antibodies that target the protein therapeutic. The current standard of care for management of hemophiliacs is prophylactic treatment that includes frequent infusions of a Factor VIII product. Failure to comply with the prophylactic regimen is a major hurdle in the management of these patients. We discuss here more recent findings that argue for a pharmacogenetic approach to understanding (and eventually circumventing) immunogenicity. We also review strategies used to bioengineer coagulation factors to extend the half-lives of coagulation proteins. The rapid progress in the last few years to bioengineer coagulation factors in different ways to attain this goal is described. Finally, novel technologies and potential products are emerging that utilize synthetic molecules in lieu of replacement proteins obviating the limitations associated with replacement therapies.

Excess of serotonin affects neocortical pyramidal neuron migration

The serotonin transporter (SERT) is a key molecule involved in the homeostasis of extracellular levels of serotonin and is regulated developmentally. Genetic deletion of SERT in rodents increases extracellular levels of serotonin and affects cellular processes involved in neocortical circuit assembly such as barrel cortex wiring and cortical interneuron migration. Importantly, pharmacological blockade of SERT during brain development leads to phenotypes relevant to psychiatry in rodents and to an increased risk for autism spectrum disorders in humans. Furthermore, developmental adversity interacts with genetically-driven variations of serotonin function in humans and nonhuman primates to increase the risk for a variety of stress-related phenotypes. In this study, we investigate whether an excess of serotonin affects the migration of neocortical pyramidal neurons during development. Using in utero electroporation combined with time-lapse imaging to specifically monitor pyramidal neurons during late mouse embryogenesis, we show that an excess of serotonin reversibly affects the radial migration of pyramidal neurons. We further identify that the serotonin receptor 5-HT(6) is expressed in pyramidal neuron progenitors and that 5-HT(6) receptor activation replicates the effects of serotonin stimulation. Finally, we show that the positioning of superficial layer pyramidal neurons is altered in vivo in SERT knockout mice. Taken together, these results indicate that a developmental excess of serotonin decreases the migration speed of cortical pyramidal neurons, affecting a fundamental step in the assembly of neural circuits. These findings support the hypothesis that developmental dysregulation of serotonin homeostasis has detrimental effects on neocortical circuit formation and contributes to increased vulnerability to psychiatric disorders.

Production, purification, and characterization of human alpha1 proteinase inhibitor from Aspergillus niger

Human alpha one proteinase inhibitor (alpha1-PI) was cloned and expressed in Aspergillus niger, filamentious fungus that can grow in defined media and can perform glycosylation. Submerged culture conditions were established using starch as carbon source, 30% dissolved oxygen concentration, pH 7.0 and 28 degrees C. Eight milligrams per liter of active alpha1-PI were secreted to the growth media in about 40 h. Controlling the protein proteolysis was found to be an important factor in the production. The effects of various carbon sources, pH and temperature on the production and stability of the protein were tested and the product was purified and characterized. Two molecular weights variants of the recombinant alpha1-PI were produced by the fungus; the difference is attributed to the glycosylated part of the molecule. The two glycoproteins were treated with PNGAse F and the released glycans were analyzed by HPAEC, MALDI/TOF-MS, NSI-MS(n), and GC-MS. The MALDI and NSI- full MS spectra of permethylated N-glycans revealed that the N-glycans of both variants contain a series of high-mannose type glycans with 5-20 hexose units. Monosaccharide analysis showed that these were composed of N-acetylglucos-amine, mannose, and galactose. Linkage analysis revealed that the galactosyl component was in the furanoic conformation, which was attaching in a terminal non-reducing position. The Galactofuranose-containing high-mannnose type N-glycans are typical structures, which recently have been found as part of several glycoproteins produced by Aspergillus niger.

Expression of human alpha1-proteinase inhibitor in Aspergillus niger

Background

Human α₁-proteinase inhibitor (α₁-PI), also known as antitrypsin, is the most abundant serine protease inhibitor (serpin) in plasma. Its deficiency is associated with development of progressive, ultimately fatal emphysema. Currently in the United States, α₁-PI is available for replacement therapy as an FDA licensed plasma-derived (pd) product. However, the plasma source itself is limited; moreover, even with efficient viral inactivation steps used in manufacture of plasma products, the risk of contamination from emerging viruses may still exist. Therefore, recombinant α₁-PI (r-α₁-PI) could provide an attractive alternative. Although r-α₁-PI has been produced in several hosts, protein stability in vitro and rapid clearance from the circulation have been major issues, primarily due to absent or altered glycosylation.

Results

We have explored the possibility of expressing the gene for human α₁-PI in the filamentous fungus Aspergillus niger (A. niger), a system reported to be capable of providing more "mammalian-like" glycosylation patterns to secretable proteins than commonly used yeast hosts. Our expression strategy was based on fusion of α₁-PI with a strongly expressed, secreted leader protein (glucoamylase G2), separated by dibasic processing site (N-V-I-S-K-R) that provides in vivo cleavage. SDS-PAGE, Western blot, ELISA, and α₁-PI activity assays enabled us to select the transformant(s) secreting a biologically active glycosylated r-α₁-PI with yields of up to 12 mg/L. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis further confirmed that molecular mass of the r-α₁-PI was similar to that of the pd-α₁-PI. In vitro stability of the r-α₁-PI from A. niger was tested in comparison with pd-α₁-PI reference and non-glycosylated human r-α₁-PI from E. coli.

Conclusion

We examined the suitability of the filamentous fungus A. niger for the expression of the human gene for α₁-PI, a medium size glycoprotein of high therapeutic value. The heterologous expression of the human gene for α₁-PI in A. niger was successfully achieved to produce the secreted mature human r-α₁-PI in A. niger as a biologically active glycosylated protein with improved stability and with yields of up to 12 mg/L in shake-flask growth.

Development and evaluation of an ELISA for quantification of human alpha-1-proteinase inhibitor in complex biological mixtures

Human alpha-1-proteinase inhibitor(1) (alpha(1)-PI) is the most abundant serine protease inhibitor in plasma. Its major function is inhibition of neutrophil elastase in lungs. alpha(1)-PI deficiency may result in severe, ultimately fatal emphysema. Three plasma-derived (pd-) alpha(1)-PI products are licensed in the US for replacement therapy of deficient patients. The recombinant versions (r-alpha(1)-PI), proposed as alternatives to pd-alpha(1)-PI products, have been under intensive investigation. For accurate determination of alpha(1)-PI from different sources and in various forms, there is an obvious need for reliable standardized assays for alpha(1)-PI quantification and potency measurements. As a part of our multi-step research focused on alpha(1)-PI structure-function investigation, we have established a simple and reproducible double-sandwich ELISA based on commercially available polyclonal antibodies. The developed ELISA allows the quantification of both pd-alpha(1)-PI and r-alpha(1)-PI in various complex matrices. A validation of the ELISA was performed with the working range of the assay (3.1-50 ng/ml) established on the bases of the following parameters: linearity (3-100 ng/ml, r(2)=0.995); accuracy (87.3-114.6% recovery); intra-assay precision (%CV, 2.8%); inter-assay plate-to-plate precision (3.9% per day and 4.1% day-to-day); detection limit (1.10 ng/ml); and quantification limit (3.34 ng/ml). The analytical performance of the alpha(1)-PI ELISA indicates that this assay can be used for monitoring concentration levels of alpha(1)-PI in multi-component biological matrices, based on the following: (a) quantification of r-alpha(1)-PI in various fermentation mixtures (E. coli and A. niger); (b) investigation of alpha(1)-PI enzymatically digested in the conditions of harsh fungal proteolysis; (c) evaluation of thermally polymerized alpha(1)-PI; (d) quantification of alpha(1)-PI in human serum; and (e) comparative quantification of alpha(1)-PI in commercially available products.

Brucella abortus bacA mutant induces greater pro-inflammatory cytokines than the wild-type parent strain

The inner-membrane protein BacA affects Brucella LPS structure. A bacA deletion mutant of Brucella abortus, known as KL7 (bacA(mut)-KL7), is attenuated in BALB/c mice and protects against challenge. Thus, bacA mutation was a candidate for incorporation into live attenuated vaccines. We assessed bacA(mut)-KL7 in 2 additional mouse strains: the more resistant C57BL/6 that produces interferon-gamma throughout the infection and the highly susceptible interferon-gamma-deficient C57BL/6 in which brucellae exhibit continual exponential growth. While it was hypothesized that bacA(mut)-KL7 would exhibit even greater attenuation relative to its parent strain B. abortus 2308 in C57BL/6 mice than it did in BALB/c mice, this was not the case. Moreover, it was more pathogenic in C57BL/6 interferon-gamma-deficient mice than 2308 causing abscesses and wasting even though the splenic loads of bacA(mut)-KL7 were significantly lower. These 2 observations were correlated, respectively, with an ability of IFNgamma-activated macrophages to equivalently control strains 2308 and bacA(mut)-KL7 and the ability of bacA(mut)-KL7 organism and its LPS to induce greater amounts of pro-inflammatory cytokines than 2308. We conclude that attenuation properties of bacA mutation are dependent upon the nature of the host but more importantly that bacterial gene deletion can result in increased host pathology without an increase in bacterial load, crucial considerations for vaccine design.

The cytotoxic T lymphocyte response against a protein antigen does not decrease the antibody response to that antigen although antigen-pulsed B cells can be targets

The role of activated CD8+ T cells in shaping the dynamics of in vivo antigen presentation and immune responses is a subject receiving more attention. We studied whether cytotoxic T lymphocyte (CTL) would limit antibody responses by targeting antigen-specific B cells. A modified in vivo CTL assay was developed and used herein to demonstrate cytotoxicity in vivo, and to show that antigen-specific B cells that process exogenous antigen and present peptide in association with MHC class I can be the targets of CD8+ T cells. B cells from C57BL/6 mice immunized with ovalbumin (OVA)/alum were pulsed with OVA in vitro, and transferred into C57BL/6 recipient mice that had been immunized with vaccinia virus expressing SIINFEKL minigene to generate CD8+ CTL against K(b)/SIINFEKL. OVA-pulsed B220+ B cells from OVA-immunized mice were killed to a greater extent than B220+ B cells from naïve mice (28+/-20% versus 12+/-16%, p=0.0042). However, mice receiving vaccinia-SIINFEKL and generating CTL, did not appear to target endogenous B cells, since both primary and secondary antibody responses to OVA were unaffected. Our findings indicate that CTL responses to the protein antigen do not interfere with endogenous B cell responses, even though exogenous B cells expressing the CTL epitope can be efficiently lysed.

Inhibitory effects of B cells on antitumor immunity

B-cell functions in antitumor immunity are not well understood. In this study, we evaluated the role of B cells in the development of antitumor immunity using Friend murine leukemia virus gag-expressing mouse EL-4 (EL-4 gag), D5 mouse melanoma, or MCA304 mouse sarcoma cells. To screen tumors for susceptibility to B-cell-deficient immune environments, spleen cells from naive C57BL/6 [wild-type (WT)] and B-cell knockout (BKO) mice were cultured with irradiated tumor cells in vitro. When cells were stimulated with EL-4 gag or D5 (but not MCA304 tumors), IFN-gamma production from CD8 T cells and natural killer cells was markedly decreased in WT compared with BKO cultures. IFN-gamma production was correlated with CD40 ligand expression on the tumor and inversely with interleukin-10 (IL-10) production by B cells. Sorted WT B cells produced more IL-10 than CD40 knockout (CD40KO) B cells when cocultured with EL-4 gag or D5 (but not MCA304). IFN-gamma production by BKO cells was reduced by the addition of sorted naive WT B cells (partially by CD40KO B cells) or recombinant mouse IL-10. In vivo tumor progression mirrored in vitro studies in that WT mice were unable to control tumor growth whereas EL-4 gag and D5 tumors (but not MCA304) were eliminated in BKO mice. Robust in vivo antitumor CTLs developed only in BKO tumor-challenged mice. Our studies provide the first mechanistic basis for the concept that B-cell depletion could therapeutically enhance antitumor immune responses to certain tumors by decreasing IL-10 production from B cells.

Recombinant human alpha-1 proteinase inhibitor: towards therapeutic use

Human alpha-1-proteinase inhibitor is a well-characterized protease inhibitor with a wide spectrum of anti-protease activity. Its major physiological role is inhibition of neutrophil elastase in the lungs, and its deficiency is associated with progressive ultimately fatal emphysema. Currently in the US, only plasma-derived human alpha-1-proteinase inhibitor is available for augmentation therapy, which appears to be insufficient to meet the anticipated clinical demand. Moreover, despite effective viral clearance steps in the manufacturing process, the potential risk of contamination with new and unknown pathogens still exists. In response, multiple efforts to develop recombinant versions of human alpha-1-proteinase inhibitor, as an alternative to the plasma-derived protein, have been reported. Over the last two decades, various systems have been used to express the human gene for alpha-1-proteinase inhibitor. This paper reviews the recombinant versions of human alpha-1-proteinase inhibitor produced in various hosts, considers current major safety and efficacy issues regarding recombinant glycoproteins as potential therapeutics, and the factors that are impeding progress in this area(1).

Passive immunotherapy of Bacillus anthracis pulmonary infection in mice with antisera produced by DNA immunization

Because of the high failure rate of antibiotic treatment in patients with anthrax there is a need for additional therapies such as passive immunization with therapeutic antibodies. In this study, we used codon-optimized plasmid DNAs (DNA vaccines) encoding Bacillus anthracis protective antigen (PA) to immunize rabbits for producing anti-anthrax antibodies for use in passive immunotherapy. The antisera generated with these DNA vaccines were of high titer as measured by ELISA. The antisera were also able to protect J774 macrophage cells by neutralizing the cytotoxic effect of exogenously added anthrax lethal toxin, and of the toxin released by B. anthracis (Sterne strain) spores following infection. In addition, the antisera passively protected mice against pulmonary challenge with an approximate 50 LD50 dose of B. anthracis (Sterne strain) spores. The protection in mice was obtained when the antiserum was given 1h before or 1h after challenge. We further demonstrated that IgG and F(ab')2 components purified from anti-PA rabbit hyperimmune sera retained similar levels of neutralizing activities against both exogenously added B. anthracis lethal toxin and toxin produced by B. anthracis (Sterne strain) spores. The high titer antisera we produced will enable an immunization strategy to supplement antibiotic therapy for improving the survival of patients with anthrax.

Th1-like cytokine induction by heat-killed Brucella abortus is dependent on triggering of TLR9

In this report we provide evidence, for the first time, that bacterial DNA in the context of heat-killed Brucella abortus (HKBA) engages TLR9 in dendritic cells (DC), resulting in a Th1-like cytokine response. This is based on the findings that HKBA induction of IL-12p40 is: 1) abolished in DC from TLR9(-/-) mice; 2) blocked by suppressive oligodeoxynucleotides; 3) simulated by bacterial DNA derived from HKBA; and 4) abrogated by DNase or methylation of the DNA from HKBA. Furthermore, the effect of HKBA can be inhibited by chloroquine, indicating that endosomal acidification is required and supporting the notion that DNA from HKBA is interacting with TLR9 at the level of the endosome, as is the case with CpG oligodeoxynucleotides. In addition to DC, HKBA can elicit IL-12p40 secretion from macrophages, in which case the effect is wholly MyD88 dependent but only partially TLR9 dependent. This probably explains why HKBA effects in vivo are only partially reduced in TLR9(-/-), but absent in MyD88(-/-) mice. Because of their intimate interactions with T cells, the DC response is most likely to be critical for linking innate and adaptive immune responses, whereas the macrophage reaction may play a role in enhancing NK cell and bystander immune responses. In addition to IL-12p40, HKBA induces other Th1-like cytokines, namely, IFN-alpha and IFN-gamma, in a TLR9-dependent manner. These cytokines are important in protection against viruses and bacteria, and their induction enhances HKBA as a potential carrier for vaccines.

Characterization of antibodies to capsular polysaccharide antigens of Haemophilus influenzae type b and Streptococcus pneumoniae in human immune globulin intravenous preparations

The most common infections in primary immune deficiency disease (PIDD) patients involve encapsulated bacteria, mainly Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae (pneumococcus). Thus, it is important to know the titers of Hib- and pneumococcus-specific antibodies that are present in immune globulin (Ig) intravenous (IGIV) preparations used to treat PIDD. In this study, seven IGIV preparations were tested by enzyme-linked immunosorbent assay and opsonophagocytic activity for antibody titers to the capsular polysaccharides of Hib and five pneumococcal serotypes. Differences in Hib- and pneumococcus-specific antibody titer were observed among various IGIV preparations, with some products having higher- or lower-than-average titers. Opsonic activity also varied among preparations. As expected, IgG2 was the most active subclass of both binding and opsonic activity except against pneumococcal serotype 6B where IgG3 was the most active. This study determines antibody titers against capsular polysaccharides of Hib and pneumococcus in seven IGIV products that have been shown to be effective in reducing infections in PIDD patients. As donor antibody levels and manufacturing methods continue to change, it may prove useful from a regulatory point of view to reassess IGIV products periodically, to ensure that products maintain antibody levels that are important for the health of IGIV recipients.

Programming of CTL with heat-killed Brucella abortus and antigen allows soluble antigen alone to generate effective secondary CTL

Optimal generation of cytotoxic T cell (CTL) responses continues to be a challenge in the production of vaccines against pathogens such as HIV-1, in part because it is difficult to introduce soluble protein antigens (Ag) into the MHC class I pathway. Using heat-killed Brucella abortus (HKBA) as an adjuvant and ovalbumin (ova) protein as an Ag, we demonstrated that a high dose of Ag was required for systemic and effective CTL. In an adoptive transfer model, primary and secondary ova-specific OT-1 CD8 cell expansion by HKBA plus high dose of ova were partially CD4 T cell-dependent. Interestingly, primary stimulation with HKBA plus ova allowed effective secondary stimulation with ova alone that was equivalent to HKBA plus ova in terms of IFN-gamma production from Ag-specific CD8 cells. Thus a combination of adequate Ag dose, and selection of appropriate adjuvants can meet the threshold not only for primary effective CTL responses to soluble protein Ags but for secondary CTL responses following stimulation with protein Ag alone.

Identification of a novel immunodominant cytotoxic T lymphocyte epitope derived from human factor VIII in a murine model of hemophilia A

Gene therapy of hemophilia A could be complicated by the development of immune responses against the vector as well as the Factor VIII (FVIII) transgene. Previous efforts have been focused on identifying FVIII inhibitor antibody epitopes, whereas the cytotoxic T lymphocyte (CTL) epitopes have not been characterized. CTL would kill cells expressing such epitopes and thus limit the efficacy of gene therapy. To investigate CTL responses against human FVIII in a mouse model of hemophilia A, a computer algorithm program (BIMAS) was employed to predict CTL epitopes of human FVIII. The potential binding of these predicted peptides to MHC class I K(b) was evaluated in a TAP-deficient cell line. When recombinant vaccinia virus expressing B domain-deleted human FVIII (vv-FVIII) was used to immunize E16 hemophilia A mice, a specific CTL response against FVIII152-159 was generated. In contrast, a CTL response to four other FVIII peptides was not detected. Therefore, FVIII152-159 represents a dominant CTL epitope. Identification of this epitope raises the possibility that CTL response to FVIII gene-transduced cells can be diminished by deliberatively mutating the dominant CTL epitope while retaining the biologic function of FVIII for hemophilia A gene therapy.

Systemic and mucosal immunity in rhesus macaques immunized with HIV-1 peptide and gp120 conjugated to Brucella abortus

HIV vaccine testing in primates is an important method for determining the possibility of vaccine benefit in humans. Goals of HIV-1 vaccination include establishing neutralizing antibodies and a strong CD8(+) T-cell response. We tested a novel vaccine conjugate for its ability to elicit relevant immune responses to HIV proteins and peptides in rhesus macaques. A neutralizing epitope, V3 loop peptide from HIV-1 envelope, was coupled to heat-inactivated Brucella abortus (V3-HKBA). Rhesus macaques were immunized with this conjugate in the anterior thigh. After two immunizations V3-specific antibodies were found in the sera and at mucosal sites. Neutralizing activity of these antibodies was demonstrated by syncytia inhibition assays. Cellular immune recall responses were demonstrated by antigen-specific induction of interferon-gamma and Regulation on Activation Noraml T Cell Expressed and Secreted (RANTES) secretion in vitro. These results confirm and extend preliminary studies in mice that suggest HKBA is an effective carrier that promotes neutralizing antibody secretion at relevant mucosal sites, as well as cellular immune responses that are correlated with viral protection.

Scaling and crossovers in activated escape near a bifurcation point

Near a bifurcation point a system experiences a critical slowdown. This leads to scaling behavior of fluctuations. We find that a periodically driven system may display three scaling regimes and scaling crossovers near a saddle-node bifurcation where a metastable state disappears. The rate of activated escape W scales with the driving field amplitude A as ln W proportional, variant ( A(c) -A)(xi), where A(c) is the bifurcational value of A. With increasing field frequency the critical exponent xi changes from xi=3/2 for stationary systems to a dynamical value xi=2 and then again to xi=3/2. The analytical results are in agreement with the results of asymptotic calculations in the scaling region. Numerical calculations and simulations for a model system support the theory.

Treatment of anthrax infection with combination of ciprofloxacin and antibodies to protective antigen of Bacillus anthracis

Currently there is no effective treatment for inhalational anthrax beyond administration of antibiotics shortly after exposure. There is need for new, safe and effective treatments to supplement traditional antibiotic therapy. Our study was based on the premise that simultaneous inhibition of lethal toxin action with antibodies and blocking of bacterial growth by antibiotics will be beneficial for the treatment of anthrax. In this study, we tested the effects of a combination treatment using purified rabbit or sheep anti-protective antigen (PA) antibodies and the antibiotic ciprofloxacin in a rodent anthrax model. In mice infected with a dose of Bacillus anthracis Sterne strain corresponding to 10 LD(50), antibiotic treatment with ciprofloxacin alone only cured 50% of infected animals. Administration of anti-PA IgG in combination with ciprofloxacin produced 90-100% survival. These data indicate that a combination of antibiotic/immunoglobulin therapy is more effective than antibiotic treatment alone in a rodent anthrax model.