Impact of pre-existing immunity on the development of de novo virus-specific TRM following live attenuated influenza vaccination

Abstract Live attenuated influenza vaccine (LAIV) elicits both humoral and cellular immune memory in children, but its efficacy is limited in adults. We hypothesize that pre-existing immunity from past infections and/or immunizations prevents the attenuated vaccine from establishing an immune response. To determine if we can overcome this limitation by increasing the antigenic distance of the vaccine strain from previous circulating seasonal strains, we generated a series of drifted LAIVs with successive mutations in the HA protein, allowing for increasing levels of escape from pre-existing antibody. We also inserted a CD8+ T cell epitope from the Sendai virus nucleoprotein (SeV-NP) as a readout for generation of a de novo TRM response following immunization. Surprisingly, we were unable to identify SeV-NP+ CD8+ TRM following LAIV immunization in PR8-immune mice, even with LAIV strains that can fully escape pre-existing antibody. As these data suggested a role for cell-mediated immunity in limiting LAIV efficacy, we investigated several scenarios to assess the impact of pre-existing LAIV-specific TRM in the upper and lower respiratory tract. Ultimately, we found that deletion of the immunodominant influenza NP366–374 epitope was sufficient to escape pre-existing CD8+ TRM and to establish de novo CD8+ TRM. Combined, these studies demonstrate that both pre-existing humoral and cellular immunity can limit the effectiveness of LAIV, thereby informing future design of vaccine vectors against respiratory pathogens. Supported by grants from NIH (F31 HL156639-01, R35 HL150803)