HA and M2 sequences alter the replication of 2013-16 H1 Live Attenuated Influenza Vaccine Infection in Human Nasal Epithelial Cell cultures

From 2013-2016, the H1N1 component of live, attenuated influenza vaccine (LAIV) performed very poorly in contrast to the inactivated influenza vaccine. We utilized a primary, differentiated human nasal epithelial (hNEC) culture system to assess the replication differences between isogenic LAIVs containing the HA segment from either A/Bolivia/559/2013 (rBol), which showed poor vaccine efficacy, and A/Slovenia/2903/2015 (rSlov), which had restored reasonable vaccine efficacy. While there were minimal differences in infectious virus production in Madin-Darby Canine Kidney (MDCK) cells, the rSlov LAIV showed markedly improved replication in hNEC cultures at both 32oC and 37oC, demonstrating that the HA segment alone could impact LAIV replication. The rSlov-infected hNEC cultures showed stronger production of interferon and proinflammatory chemokines which might also be contributing to the increased overall vaccine effectiveness of the rSlov LAIV through enhanced recruitment and activation of immune cells. The introduction of an M2-S86A mutation had no positive effects on H1 LAIV replication in hNEC cultures, in contrast to the increased infectious virus production seen with that mutation in an H3 LAIV. No obvious defects in viral RNA packaging were detected, suggesting the HA function may be driving the differential infectious virus production in hNEC cultures. The use of physiologically relevant temperatures and primary cell cultures demonstrated that candidate LAIVs can replicate efficiently, which is a necessary property for effective vaccines.