Session: 801. Gene Therapy and Transfer: Poster II
Hematology Disease Topics & Pathways:
Hemophilia, Diseases, Bleeding and clotting
Aims: To determine the prevalence of preexisting antibody-mediated immunity against AAV2, AAV5 and AAV8 and the association between AAV8-specific humoral and cell‑mediated responses in adult patients with HA and HB in an international prospective, epidemiological study.
Methods: This ongoing seroprevalence study involved adult male patients (18–75 years of age) with severe HA (<1% plasma FVIII activity) or severe/moderate HB (≤2% plasma FIX activity) recruited from hemophilia treatment centers in the United States and Europe (NCT03185897). Participants consented to collection of peripheral blood at either a single or multiple annual outpatient study visits, in order to explore fluctuations of the immune response over time. Local ethics committee approval was obtained. Titers for anti-AAV2, anti-AAV5 and anti-AAV8 neutralizing antibodies (NAbs) were determined using a cell-based transduction inhibition assay, with seropositivity defined as a titer ≥1:5. Titers for anti-AAV2, anti-AAV5 and anti-AAV8 binding antibodies (BAbs) were quantitated by indirect enzyme-linked immunosorbent assay (ELISA), with seropositivity defined as a titer ≥1:80. Cell‑mediated immune responses to AAV8 peptide antigens were measured in peripheral blood mononuclear cells using an interferon-γ enzyme-linked immunospot (ELISpot) assay. Samples with a signal ≥3 times background and >60 spots per million cells were defined as positive.
Results: Here we present data from patients who completed at least a single visit at the time of the interim, one year data cut (November 9, 2018). Of 242 patients enrolled (mean ± SD age: 35.3 ± 11.4 years), 194 patients had HA and 48 patients had HB. The overall co-prevalence of NAbs and BAbs to AAV2, AAV5 and AAV8 was 39.7% (HA: 38.1%, 72/189; HB: 45.8%, 22/48) and 16.1% (HA: 16.5%, 31/188; HB: 14.6%, 7/48) respectively, with further details shown in Table 1. Overall, 38.3% of patients (82/214) exhibited a T cell–mediated immune response to AAV8 peptide antigens (HA: 35.9%, 61/170; HB: 47.7%, 21/44). Among patients with AAV-8–specific NAbs, 37.9% (39/103) demonstrated positive AAV8-specific ELISPOT results. (HA: 35.7%, 30/84; HB: 47.4%, 9/19).
Conclusion: The findings from this ongoing study demonstrate that approximately 50% of patients with hemophilia have preexistent NAb responses to AAV2, AAV5 or AAV8 with 40% demonstrating co-prevalence to all 3 evaluated AAV serotypes. Similar percentages of patients exhibited a positive cellular response to AAV8 antigens. Further, patients with HB demonstrated a slightly higher co-prevalence and a higher cellular response than patients with HA. In the combined HA and HB cohorts, co-prevalence was almost 40% for AAV8-specific humoral and T-cell mediated immunity. These data will add to our appreciation of preexisting AAV immunity that prevent patient participation in gene therapy trials.
Disclosures: Rajavel: Baxalta US Inc., a Takeda company: Employment, Equity Ownership. Ayash-Rashkovsky: Baxalta US Inc., a Takeda company: Employment, Equity Ownership. Tang: Baxalta US Inc., a Takeda company: Employment, Equity Ownership. Gangadharan: Baxalta Innovations GmbH, a Takeda company: Employment. de la Rosa: Baxalta Innovations GmbH, a Takeda company: Employment. Ewenstein: Baxalta US Inc., a Takeda company: Employment, Equity Ownership, Other: a Takeda stock owner.