(892) Contribution of Influenza H5 Head and Stalk Domains to the Development of Functional Non-Neutralizing Antibodies Following Mucosal rH5-NE Vaccination
Graduate Student University of Maryland, Baltimore Potomac, Maryland, United States
Disclosure(s):
Raymond L. Ash: No financial relationships to disclose
Introduction/Rationale: In a prior Phase 1 trial we showed that an intranasal (IN) recombinant hemagglutinin (HA) H5 vaccine (rH5; A/Indo/05) nanoemulsion-adjuvanted (rH5 NE) and given on days 1 and 29 effectively primed the immune system. Participants received rH5 NE (25–100 µg; IN; n=24), unadjuvanted rH5 (100 µg; IN; n=7), or placebo (n=6). Only rH5 NE recipients exhibited significant increases in HAI titers after a heterologous intramuscular (IM) H5N1 booster on day 197, confirming successful mucosal priming. Anti-H5 antibody-dependent cell cytotoxicity (ADCC) activity also demonstrated this priming effect. Here, we evaluated whether rH5 NE elicited cross reactive ADCC and antibody-dependent cell phagocytosis (ADCP) responses to diverse H5 HAs and examined contributions of HA head and stalk domains.
Methods: Plasma from days 1, 57, and 225 was analyzed. ADCC was assessed using beads coated with whole, head only, or stalk only H5 HAs incubated with plasma and exposed to a CD16a expressing reporter cell line. ADCP was quantified by THP 1 uptake of antigen-coated AF488–beads. ADCC seroconversion was defined as a ≥4 fold increase; ADCP seroconversion as a ≥2 fold increase.
Results: By day 57, 33% (8/24) rH5 NE recipients showed ADCC seroconversion to A/Indo/05 whole HA, rising to 50% after the day-197 IM boost. Unadjuvanted rH5 and placebos seroconverted only after boosting (4/7=57% & 4/6=67%, respectively). Similar trends were seen for A/Viet/04 and A/cow Tx/24. Head specific ADCC seroconversion in rH5 NE reached 46% (11/24) at day 57 and 88% (21/24) at day 225, whereas unadjuvanted rH5 responded only at day 225 (4/7=57%). Placebos showed no responses. Stalk specific ADCC was largely preexisting across all groups, with minimal vaccine induced increases. ADCP trends mirrored ADCC findings.
Conclusion: Intranasal rH5 NE induces cross reactive ADCC and ADCP responses driven primarily by antibodies targeting the H5-head, supporting its capacity to induce effective mucosal priming.
