Adeno-Associated Viral Vector Mediated Gene Transfer for Hemophilia B

Abstract

5 Background: Hemophilia B (HB), an X-linked bleeding disorder, is ideally suited for gene therapy. We investigated a novel approach using peripheral vein infusion of a single dose of a serotype-8 pseudotyped self-complementary adeno-associated virus (AAV) vector expressing a codon-optimized coagulation factor IX (FIX) transgene (scAAV2/8-LP1-hFIXco). Methods: Six severe HB subjects (FIX ≤1%) were enrolled sequentially into one of three dose cohorts with two subjects in each group. Vector was administered without immunosuppression. The subjects were followed for 6–16 months post treatment. Results: AAV-mediated expression of FIX at 2–11% of normal was observed in all subjects. Four of the six have discontinued prophylaxis and remain free of spontaneous hemorrhage. The other two have increased the interval between FIX prophylaxes. A high-dose subject developed asymptomatic, transient elevation of serum transaminases associated with detection of AAV8 capsid specific T cells in peripheral blood. The second high-dose subject experienced a slight increase of liver enzymes, of less clear etiology. Treatment of each with a short course of steroids led to rapid normalization of the transaminases and maintenance of FIX levels in the 3–11% range. Conclusion: Peripheral vein administration of scAAV2/8-LP1-hFIXco was well tolerated and resulted in FIX transgene expression at levels sufficient to improve the bleeding phenotype. Immune-mediated clearance of AAV-transduced hepatocytes remains a concern but our data suggest that this process may be controlled with a short course of steroids without loss of transgene expression. Hence, our novel approach shows promise for gene therapy of HB and other protein deficiencies. (ClinicalTrials.gov number, NCT00979238) Disclosures: Nathwani: Amsterdam Molecular Therapeutics: Patents & Royalties. Gray:Amsterdam Molecular Therapeutics: Patents & Royalties. Davidoff:Amsterdam Molecular Therapeutics: Patents & Royalties.

Therapeutic AAV Gene Transfer to the Nervous System: A Clinical Reality

“…Most studies are forced to exclude patients with detectable levels of NABs to AAV, as it is expected they will not benefit from the gene therapy. Even then, AAV clinical studies for hemophilia showed that seronegative subjects developed transaminase elevations weeks after AAV administration, which in some patients was concomitant with a rise in AAV capsid-specific CD8+ cells and the loss of transgene expression (Manno et al, 2006;Mingozzi et al, 2007;Nathwani et al, 2011). In the SMA study in which AAV9 was given IV at high dose, asymptomatic elevation of transaminases was observed in some of the newborn subjects, who fortunately responded to prednisolone treatment (Mendell et al, 2017).…”

“…Currently utilized clinical strategies to side step or overcome immune concerns brought on by AAV gene therapies include the exclusion of patients with elevated anti-AAV antibodies from enrolling in clinical trials, administering in compartments that are thought to be immune privileged, including short-term immunosuppression regimens (e.g., oral prednisone; Mendell et al, 2017;Nathwani et al, 2011), or limiting the vector dose (Mendell et al, 2017). While these strategies have overall proven to be adequate in the ongoing clinical studies, it is clear they do not provide a solution for many of the outstanding concerns in the field.…”

Hitting the Target Without Pulling the Trigger

“…Such doses increase the likelihood of inducing AAV vector-specific cytotoxic T-cell-mediated immune responses that could clear the gene-modified cells and cause acute liver toxicity. [17][18][19] However, this obstacle could potentially be overcome by using transient immune suppression. 19,20 Despite these potential immune complications, the use of a site-specific integrating AAV vector may overcome potential concerns of insertional oncogenesis given that that AAV is known to integrate at a low but measurable rate (0.1-1% transduction events).…”

“…[17][18][19] However, this obstacle could potentially be overcome by using transient immune suppression. 19,20 Despite these potential immune complications, the use of a site-specific integrating AAV vector may overcome potential concerns of insertional oncogenesis given that that AAV is known to integrate at a low but measurable rate (0.1-1% transduction events). Nevertheless, with the exception of the emergence of hepatocellular carcinoma in neonatal mucopolysaccharidosis VII mice undergoing AAV gene therapy, 5 the overall oncogenic risk of using conventional AAV for gene therapy appears to be very low, 21 although this remains a largely unresolved issue.…”

“…Nevertheless, with the exception of the emergence of hepatocellular carcinoma in neonatal mucopolysaccharidosis VII mice undergoing AAV gene therapy, 5 the overall oncogenic risk of using conventional AAV for gene therapy appears to be very low, 21 although this remains a largely unresolved issue. 22 Although hepatic expression from conventional AAV vectors seems relatively stable based on the currently available clinical data 19,20 as well as on the many preclinical studies in a variety of smalland large-animal models, it is not known whether therapeutic expression will last for the entire life span of a treated patient. Expression from conventional AAV vectors typically declines as a result of hepatocyte turnover, albeit slowly.…”