Evaluation of T and B memory cell responses elicited by the pandemic H1N1 vaccine in HIV-infected and HIV-uninfected individuals

Background This study was to compare B and T memory cells elicited by a single dose monovalent 2009 influenza A (H1N1) vaccine (strain A/California/7/2009 H1N1) in HIV⁺ and HIV⁻ groups, and to analyze the impact of the prior seasonal vaccines to the immunogenicity of this vaccine. Methods Blood samples were collected before vaccination (day 0) and at days 28 and 180. Participants were categorized into HIV⁻/LAIV, HIV⁻/TIV and HIV⁺/TIV subgroups according to the trivalent live-attenuated or inactivated (LAIV or TIV) seasonal influenza vaccines they received previously. The IgG⁺ memory B cells (B_Mem) and IFNγ⁺ T cells were measured against antigens including the H1N1 vaccine, the hemagglutinin (HA) and neuraminidase (NA) proteins or peptide pools of the pandemic and the seasonal H1N1 strains, respectively. Results Overall B_Mem responses increased significantly at day 28 but returned to baseline by day 180 in all three subgroups. The average frequency of the H1N1-specific B_Mem at day 28 for the HIV⁻/LAIV, HIV⁻/TIV and HIV⁺/TIV groups was 2.14%, 1.26% and 1.67%, respectively, and the average fold change was 14.39, 3.81 and 3.93, respectively. The differences of B_Mem between HIV⁻/LAIV and the two TIV subgroups were significant. For the IFNγ response, the overall spot counts ranged widely between 0 and 958/10⁶ PBMCs. The group average spot counts to H1N1 vaccine was 89, 102, and 30 at day 28 for HIV⁻/LAIV, HIV⁻/TIV and HIV⁺/TIV subgroups, respectively. The average increase of IFNγ response at day 28 vs day 0 in all three subgroups did not reach 2-fold. Conclusion Participants with a prior LAIV seasonal vaccine, as compared to a TIV seasonal vaccine, responded significantly better to the monovalent H1N1 vaccine. Excluding LAIV participants, no difference was seen between the HIV⁺ and HIV⁻ subject groups in terms of B_Mem. The B_Mem response declined at 6 months.