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 backgrounds encoding a chimeric HA segment carrying an N-terminal peptide encoding the 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 regime, mice were completely protected against lethal challenge with a homologous FLUBV strain. Recombinant viruses induced antibodies against HA considered of protective value. 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. We developed three live attenuated vaccine candidates with re-arranged genome expressing the M2 or NS2 from the PB1 gene segment, and the IgA inducing peptide (IGIP) from the HA gene segment. DBAJ/2 mice were primed and boosted (3 weeks ppart) with the modified viruses to test safety and protection efficacy. Body weight was recoreded for up to 12 days post vaccination and clinical signs were monitored daily throughout the length of the study. Blood samples were collected at 19 days post-boost (dpb) to assess neutralizing antibody responses through HI and virus neutralization. In addition, sera were used to performa microarrays against multiple influenza A and B protein antigens. Three weeks after boost, mice were challenged with a lethal dose of B/Brisbane/60/2008 PB2 F406Y. Body weigh was recorded for up to 12 days post-challenge (dpc) and clinical signs for up to 14 dpc. Blood and nasal wash samples were collected at 14 dpc for serology and to determine antigen-specific IgG and IgA responses through microarray analysis.