Epidemic influenza virus nucleoprotein gene incorporated into vaccine influenza virus strain genome to optimize systemic and local T-cell immune response against live attenuated influenza vaccine

Introduction. Optimization of the vaccine-induced T-cell repertoire is one of the strategies to expand the spectrum of protective potential for live attenuated influenza vaccine (LAIV). LAIV cross-protective properties can be improved by introducing the nucleoprotein (NP) gene derived from epidemic parental virus into vaccine strain genome, i.e. by replacing the classical 6:2 genome formula with 5:3. The main objective of the present study was to detail evaluation for virus-specific systemic and tissue-resident memory T-cells subsets in mice immunized with seasonal H1N1 LAIV of the genome formula 6:2 and 5:3. Materials and methods. Two H1N1 LAIV strains with varying NP genes (LAIV 6:2 and LAIV 5:3) were generated using reverse genetics techniques. C57BL/6J mice were immunized intranasally with the vaccine candidates, twice, 3 weeks apart. Cells from the spleen and lung tissues were isolated 7 days after booster immunization to be stimulated with whole H1N1 influenza virus for assessing cytokine-producing memory CD44+CD62L– T-cells as well as expression of CD69 and CD103 surface markers using flow cytometry. Humoral murine serum immunity against H1N1 virus was assessed by ELISA. Results. The LAIV 5:3 vs classical 6:2 vaccine strain carrying the epidemic parental NP gene induced significantly more pronounced humoral immune response against recent influenza virus. The group of mice immunized with LAIV 5:3 demonstrated higher levels of virus-specific CD4+ and CD8+ effector memory T cells (TEM) in the spleen, including a subset of polyfunctional (IFNγ+TNFα+IL-2+) CD4+ TEM, compared to LAIV 6:2 group. Virus-specific memory T cell levels in lung tissues after immunization with LAIV 5:3 vs LAIV 6:2 also tended to increase, but no significant difference in stimulated tissue-resident CD69+CD103– and CD69+CD103+ T cells between the groups were found. Conclusion. Modification of the seasonal LAIV strain genome for updating its epitope composition allowed to enhance the virus-specific T-cell immune response both at systemic level and in lung tissues, thereby shoeing that the effectiveness of the vaccine against circulating influenza viruses can be potentially increased.