Egg-adaptive mutations of human influenza H3N2 virus are contingent on natural evolution

Abstract

Egg-adaptive mutations in influenza hemagglutinin (HA) often emerge during the production of egg-based seasonal influenza vaccines, which contribute to the largest share in the global influenza vaccine market. While some egg-adaptive mutations have minimal impact on the HA antigenicity (e.g. G186V), others can alter it (e.g. L194P). Here, we show that the preference of egg-adaptive mutation in human H3N2 HA is strain-dependent. In particular, Thr160 and Asn190, which are found in many recent H3N2 strains, restrict the emergence of L194P but not G186V. Our results further suggest that natural amino acid variants at other HA residues also play a role in determining the preference of egg-adaptive mutation. Consistently, recent human H3N2 strains from different clades acquire different mutations during egg passaging. Overall, these results demonstrate that natural mutations in human H3N2 HA can influence the preference of egg-adaptation mutation, which has important implications in seed strain selection for egg-based influenza vaccine.

Seasonal antigenic prediction of influenza A H3N2 using machine learning

“…4b ). Mutations at site 225 can alter the fitness landscape of epitope B 30 , and a mutation at this site was linked to egg-passaging adaptation in isolates circulating from 2019 to 2021 31 .…”

Hemagglutinin destabilization in H3N2 vaccine reference viruses skews antigenicity and prevents airborne transmission in ferrets

“…1, F to H ). Of note, the other egg-based wild-type vaccine reference viruses or reassortant vaccine seed viruses of A/SG/Infimh, A/CH/8060, and A/HK/4801 also had HA1-T160K and HA1-L194P egg-adaptive mutations, and those of A/TX/50 and A/CH/9715293 had HA1-G186V (table S1) ( 45 , 46 ). Cell-based A/TX/50 and A/HK/5738 did not have egg-adaptive mutations and had relatively stable HA proteins (pH 5.2 to 5.5) ( Table 2 ).…”

Predictive evolutionary modelling for influenza virus by site-based dynamics of mutations

“…The H1N1 A/Puerto Rico/8/1934 (PR8) eight-plasmid reverse genetic system was used to produce the recombinant influenza virus with the predicted HA and NA genes 50 . Chimeric 6:2 recombinant viruses with six internal genes from PR8 (PB2, PB1, PA, NP, M, and NS) and 2 genes (HA and NA) from strain of interest were synthesized by Sangon Technology (Guangzhou, China) and were cloned into the pHW2000 vector 51 . The HEK 293T cells and hMDCK cells were then mixed at a ratio of 2:1 one-day before transfection and co-cultured in a 6-well plate until they reached 70% confluence.…”

“…The H1N1 A/Puerto Rico/8/1934 (PR8) eight-plasmid reverse genetic system was used to produce the recombinant influenza virus with the predicted HA and NA genes 50 . Chimeric 6:2 recombinant viruses with six internal genes from PR8 (PB2, PB1, PA, NP, M, and NS) and 2 genes (HA and NA) from strain of interest were synthesized by Sangon Technology (Guangzhou, China) and were cloned into the pHW2000 vector 51 hMDCK cells were prepared in a 12-well plate at least 24 hours before PRNT and cultured until obtaining a 100% confluent monolayer in each well. Two-fold serial dilutions of antiserum from 1:10 to 1:1280 were prepared, where each 100 μL was mixed with 100 PFU of viruses and incubated at 37°C for 1 hour.…”