The Production and Characterization of a Plant-Expressed M2e Protein Recombinant Immune Complex as a Universal Influenza A Vaccine Candidate

Influenza virus A (IVA) poses a serious threat to human health, killing over 25,000 Americans in the 2022 flu season alone. In the past 10 years, vaccine efficacy has varied significantly, ranging from 20-60% each season. Because IVA is subject to high antigenic shift and strain cocirculation, more effective IVA vaccines are needed to reduce the incidence of disease. Herein we report the production of a recombinant immune complex (RIC) vaccine “4xM2e” in Nicotiana benthamiana plants using agroinfiltration for use as a potential universal IVA vaccine candidate. RICs fuse antigen to the C-terminus of an immunoglobulin heavy chain with an epitope tag cognate to the antibody, promoting immune complex formation to increase immunogenicity. IVA matrix protein 2 ectodomain (M2e) is selected to serve as vaccine antigen for its high sequence conservation, as only a small number of minor mutations have occurred since its discovery in 1981 in the human sequence. However, there is some divergence in zoonotic IVA strains, and to account for this, we designed a combination of human consensus, swine, and avian M2e variants, 4xM2e. This was fused to the C terminus of the RIC platform to improve M2e immunogenicity and IVA strain coverage. The 4xM2e RIC was produced in N. benthamiana and verified with SDS-PAGE and Western blot assays, along with an analysis of complex formation and the potential for complement activation via complement C1q ELISA. With this work, we demonstrate the potential of RICs and plant-expression systems to generate universal IVA vaccine candidates.