Live Adenovirus Type 4 Recombinants Induce Durable Neutralizing Antibody Responses to Influenza H5 with High Levels of Somatic Hypermutation in Humans

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OA16.01 Background: Induction of durable antibody responses capable of neutralizing diverse HIV-1 isolates is the most important goal in HIV vaccinology. Broad and potent HIV Env-specific antibodies isolated from humans are characterized by binding to conserved sites on Env and by high levels of hypermutation. Live virus recombinant vectors may provide prolonged exposure to transgene-encoded antigen and may more potently drive affinity maturation than non-replicating vectors. We report results of a small Phase 1 trial of mucosal immunization with live adenovirus type 4 encoding influenza H5 HA (Ad4-H5-Vtn) as a model antigen. We explored its ability to induce durable, broad neutralizing antibody responses through upper respiratory tract application. Methods: Live Ad4-H5Vtn (103-108 viral particles (VP)) was administered by tonsillar swab or by nasal spray in a dose escalation study. Controls received (1010 VP) as enteric-coated capsules. Neutralizing antibodies were measured by a pseudotype HA lentiviral vector system. B cells were isolated using fluorescent HA probes. Immunoglobulin genes were cloned for mutation analysis, and re-expressed to measure neutralization potency and breadth. Results: The vaccine was well tolerated and symptoms were consistent with mild URI. Tonsillar and nasal immunizations were the most immunogenic routes inducing neutralizing antibody responses at day 60 (ID50=809 and 666 respectively) which rose during the first 6 months. B cells that expanded early were specific for both H1 and H5 and were directed to the conserved stalk, with H5 HA-monospecific cells expanding by 6 months. The median level of hypermutation was 3.6% compared to germline at week 4 and 7.4% at weeks 34–52. However, some antibodies contained 13–34% mutation and neutralized group 1 and 2 viruses. Conclusions: A single dose of live recombinant Ad4-H5 can induce highly mutated antibodies, suggesting that mucosal administration is a promising platform for the induction of HIV-specific neutralizing antibodies.