Modified Live Attenuated Influenza B Virus Vaccines and Sex-driven Differences on Humoral Immune Responses in the DBA/2J Mouse Model

Influenza B virus (FLUBV) is a major respiratory pathogen of humans. Seasonal influenza vaccines include either one or both FLUBV lineage strains, Victoria, and Yamagata. Vaccine mismatch occurs frequently, particularly in countries where vaccines contain only one of the lineages. We have previously described the safety and efficacy of modified live attenuated FLUBV vaccines based on either virus with rearranged genomes (FluB-RAM and FluB-RANS) or carrying a PB1 segment with a combination of temperature sensitive mutations and a C-terminal HA tag (FluB-att). We compared side by side the immunological responses in female and male DBA/2J mice vaccinated with either one of these vaccines and those with isogenic backbones containing a chimeric HA segment carrying an N-terminal IgA inducing peptide (IGIP). Recombinant viruses with or without the IGIP modification were genetically stable over multiple passages in eggs. In mice, introduction of IGIP improved attenuation of the vaccine candidates, particularly for the FluB-RAM/IGIP compared with the non-IGIP FluB-RAM counterpart. In a prime-boost regimen, mice were completely protected against lethal challenge with a homologous FLUBV strain. Recombinant viruses induced neutralizing antibodies with hemagglutination inhibition titers ≥40. Antibodies against NA and NP were readily detected. Compared to male mice and regardless of the vaccine used, female mice showed a clear trend towards enhanced humoral and cross-reactive IgG and IgA anti-HA responses as well as against NA and NP. The presence of IGIP in the vaccine resulted in an overall trend towards reduced anti-HA responses but enhanced anti-NA and anti-NP responses, particularly of the IgA isotype. Mucosal and serological responses two weeks after challenge showed similar trends with clear differences observed based on sex, vaccine backbone, and whether the vaccine carried the IGIP modification. These findings are significant for the development of universal influenza vaccines.