Confirmatory detection of neutralizing antibodies to AAV gene therapy using a cell-based transduction inhibition assay

Successful treatment with adeno-associated virus (AAV)-based gene therapies can be limited by pre-existing anti-AAV antibodies. Cell-based transduction inhibition (TI) assays are useful to characterize the neutralizing potential of anti-AAV antibodies in patient samples. While these assays are commonly used, they are not specific for neutralizing antibodies (NAbs) against AAV, also detecting non-antibody-based factors that inhibit AAV transduction in vitro but may not substantially decrease efficacy in vivo. This paper describes the development and bioanalytical validation of a confirmatory assay to improve the specificity of detecting anti-AAV5 NAbs in cell-based TI assays. Samples that screen positive for transduction inhibitors are subsequently depleted of all classes of immunoglobulins using agarose resins conjugated with protein A, G, and L (AGL), which restores AAV5 transduction for NAb-containing samples. Unconjugated agarose resin serves as a mock control for non-specific depletion effects and facilitates normalization of the transduction efficiencies between an AGL- and mock-treated sample; the normalized value is termed the AGL/mock ratio. During validation, a confirmatory cut point for the AGL/mock ratio was derived; sensitivity, precision, selectivity, and matrix interference were also assessed. This confirmatory TI assay facilitates a characterization of humoral immunity to AAV gene therapy by reliably distinguishing NAbs from non-antibody-based neutralizing factors.

Monitoring cell-mediated immune responses in AAV gene therapy clinical trials using a validated IFN-γ ELISpot method

Adeno-associated virus (AAV)-based gene therapies have recently shown promise as a novel treatment for hereditary diseases. Due to the viral origin of the vector capsid, however, cellular immune response may be elicited that could eliminate transduced target cells. To monitor cellular immune responses in clinical trials, we optimized and bioanalytically validated a sensitive, robust, and reliable interferon-γ (IFN-γ) enzyme-linked immunospot (ELISpot) assay. For method performance validation, human peripheral blood mononuclear cells (PBMCs) were stimulated with peptides derived from AAV5 capsid proteins and the encoded transgene product, human blood clotting factor VIII (FVIII), in addition to positive controls, such as peptides from the 65-kDa phosphoprotein of cytomegalovirus. We statistically assessed the limit of detection and confirmatory cutpoint, evaluated precision and linearity, and confirmed specificity using HIV peptides. Robustness parameter ranges and sample stability periods were established. The validated IFN-γ ELISpot assay was then implemented in an AAV5-FVIII gene therapy clinical trial. Cellular immune responses against the AAV5 capsid were observed in most participants as soon as 2 weeks following dose administration; only limited responses against the transgene product were detected. These data underscore the value of using validated methods for monitoring cellular immunity in AAV gene therapy trials.

Validation of an IFN-gamma ELISpot assay to measure cellular immune responses against viral antigens in non-human primates

Adeno-Associated Virus (AAV)-based gene therapy vectors are in development for many inherited human disorders. In nonclinical studies, cellular immune responses mediated by cytotoxic T cells may target vector-transduced cells, which could impact safety and efficacy. Here, we describe the bioanalytical validation of an interferon-gamma (IFN-γ)-based Enzyme-Linked Immunospot (ELISpot) assay for measuring T cell responses against viral antigens in cynomolgus monkeys. Since ELISpots performed with antigen-derived peptides offer a universal assay format, method performance characteristics were validated using widely available peripheral blood mononuclear cells (PBMCs) responsive to cytomegalovirus peptides. The limit of detection and confirmatory cut point were established using statistical methods; precision, specificity, and linearity were confirmed. Monkey PBMCs from an AAV5 gene therapy study were then analyzed, using peptide pools spanning the vector capsid and transgene product. AAV5-specific T cell responses were detected only in 2 of 18 monkeys at Day 28, but not at Day 13 and 56 after vector administration, with no correlation to liver enzyme elevations or transgene expression levels. No transgene product-specific T cell responses occurred. In conclusion, while viral peptide-specific IFN-γ ELISpots can be successfully validated for monkey PBMCs, monitoring peripheral T cell responses in non-clinical AAV5 gene therapy studies was of limited value to interpret safety or efficacy.

Potent nonimmunosuppressive cyclophilin inhibitors with improved pharmaceutical properties and decreased transporter inhibition

Nonimmunosuppressive cyclophilin inhibitors have demonstrated efficacy for the treatment of hepatitis C infection (HCV). However, alisporivir, cyclosporin A, and most other cyclosporins are potent inhibitors of OATP1B1, MRP2, MDR1, and other important drug transporters. Reduction of the side chain hydrophobicity of the P4 residue preserves cyclophilin binding and antiviral potency while decreasing transporter inhibition. Representative inhibitor 33 (NIM258) is a less potent transporter inhibitor relative to previously described cyclosporins, retains anti-HCV activity in cell culture, and has an acceptable pharmacokinetic profile in rats and dogs. An X-ray structure of 33 bound to rat cyclophilin D is reported.

Mutations in envelope gp120 can impact proteolytic processing of the gp160 precursor and thereby affect neutralization sensitivity of human immunodeficiency virus type 1 pseudoviruses

The design of an efficient human immunodeficiency virus (HIV) immunogen able to generate broad neutralizing antibodies (NAbs) remains an elusive goal. As more data emerge, it is becoming apparent that one important aspect of such an immunogen will be the proper representation of the envelope protein (Env) as it exists on native virions. Important questions that are yet to be fully addressed include what factors dictate Env processing, how different Env forms are represented on the virion, and ultimately how these issues influence the development and efficacy of NAbs. Recent data have begun to illuminate the extent to which changes in gp41 can impact the overall structure and neutralizing sensitivity of Env. Here, we present evidence to suggest that minor mutations in gp120 can significantly impact Env processing. We analyzed the gp120 sequences of 20 env variants that evolved in multiple macaques over 8 months of infection with simian/human immunodeficiency virus 89.6P. Variant gp120 sequences were subcloned into gp160 expression plasmids with identical cleavage motifs and gp41 sequences. Cells cotransfected with these plasmids and delta env genomes were able to produce competent virus. The resulting pseudoviruses incorporated high levels of Env onto virions that exhibited a range of degrees of virion-associated Env cleavage (15 to 40%). Higher levels of cleavage correlated with increased infectivity and increased resistance to macaque plasma, HIV immunoglobulin, soluble CD4, and human monoclonal antibodies 4E10, 2F5, and b12. Based on these data, we discuss a model whereby changes in gp120 of 89.6P impact Env processing and thereby mediate escape from a range of neutralizing agents.

Surgical complications of simultaneous pancreas-kidney transplantation: a 16-year-experience at one center

Fifty-one simultaneous pancreas-kidney transplants (SPKT) were performed between 1988 and 2004 in patients of mean age 34 years and 23 years duration of diabetes treatment. All kidney and pancreas recipients were on maintenance hemodialysis therapy prior to SPKT. The pancreas with duodenal segment and the kidneys were harvested from cadaveric heart-beating donors. Cold ischemia time in UW solution varied from 4 to 14 hours (mean, 9 hours 35 minutes). Twenty patients had the duodenal segment sutured to the urinary bladder, and the remaining 31 grafts were drained to an isolated ileal loop. Quadruple immunosuppression was administered as well as an anticoagulant and antibiotic prophylaxis. Forty-nine patients (49/51, 96%) regained insulin independence in the immediate postoperative period; 44 (86%) displayed immediate graft function. The remaining patients experienced postoperative ATN, the longest duration was 18 days. Of 51 patients, 38 (14.5%) are alive (follow-up, 6 to 180 months), 26 (68.5%) have good pancreatic function, and 34 (89%), good kidney function. Nineteen (50%) patients regard their quality of life as improved compared to their pretransplant status, which is mainly attributed to being dialysis and insulin free. Of 19 patients, 14 (74%) reported measuring glycemia regularly due to fear of losing the pancreas graft. Of 19 persons, seven (37%) returned to work after transplantation. Four (8.3%) lost their kidney graft secondary to vascular complications (n = 2) or rejection (n = 2). Four pancreas grafts with bladder drainage required conversion to enteric drainage owing to persistent urinary infections or urinary fistulae. Fifteen (29%) patients lost their pancreatic grafts within 1 year of transplantation due to the following: vascular complications (n = 12), septic complications (n = 1), or rejection (n = 2). Thirteen patients died within 1 year after transplantation, 5 of septic complications, 5 of neuroinfection, 1 of pulmonary embolism, and 2 of myocardial infarction. In conclusion, SPKT is a successful treatment for diabetic nephropathy, burdened by the possibility of serious complications.

Chlamydia Pneumoniae Infection: An Additional Factor for Chronic Allograft Rejection

INTRODUCTION

Chronic rejection (CHR) of organ allografts, one of the most significant problems in modern transplantation, is not fully understood. This study sought to evaluate the influence of selected parameters on late kidney transplant function.

PATIENTS AND METHOD

The studied group consisted of eighty-six patients who received allogeneic transplants between 1988 and 1999 for leukocyte Chlamydia pneumoniae-DNA, immunoglobulin (Ig)A/IgG anti-C pneumoniae, blood lipids, ischemic damage in the donor and during organ preservation, HLA mismatch, and acute rejection episodes.

RESULTS

Eighty-six patients were segregated as 26 patients (30%) with histologically proven chronic graft rejection (CHR[+]) and 59 patients (70%) without (CHR[-]). The presence of C pneumoniae-DNA in peripheral blood leukocytes was significantly more frequent in CHR(+) than CHR(-) group (46% vs 20%). Patients with leukocytes positive for C pneumoniae-DNA more frequently (50%) had CHR than patients negative for C pneumoniae-DNA (22%). CHR(+) patients showed significantly lower HDL levels (47 mg/dL vs 58 mg/dL) and higher triglyceride levels (193 mg/dL vs 148 mg/dL). To study the cumulative effect of differences between the CHR(+) and CHR(-) groups, we applied a multiple binary logistic regression analysis. An econometric model enabled us to calculate the probability of CHR for a given patient taking into account covariates chosen by means of stepwise selection: the presence of C pneumoniae-DNA in blood leukocytes, the use of continuous pulsatile perfusion in hypothermia, myocardial infarction occurrence, and triglyceride concentrations.

CONCLUSION

The presence of C pneumoniae-DNA in peripheral blood leukocytes increased the risk of CHR, which may be predicted by a multifactor analysis of chosen parameters.

Quality of Life After Simultaneous Pancreas–Kidney Transplantation

Even recipients with satisfactory function of transplanted pancreas and kidney may show physical and/or social disability due to diabetic complications. Our aims were to evaluate diabetic complications influencing recipient quality of life and to assess patients' psychosociological status. Nineteen patients with functioning grafts who consented to take part in the study, underwent clinical evaluation and answered questions regarding their quality of life. Results showed excellent endocrine pancreatic function in 17 patients. In most recipients, insulin activity and C-peptide levels were elevated owing to systemic venous drainage. Opthalmological examination revealed blindness in 7 patients (in 4 cases with onset following SPKTx) and retinopathy in 13 patients (in 5 cases it appeared after SPKTx). Assessment of the cardiovascular system revealed satisfactory cardiac function in 16 of 19 patients; 4 patients underwent amputation of a lower limb following SPKTx. All 19 recipients admitted to a great benefit of transplantation; most patients declared ability to organize their life activity and social functions and 4 had regular employment. Conversely, most patients were afraid of graft loss, and half were often sad and even depressed.