Recombinant subunit rotavirus trivalent vaccine candidate: physicochemical comparisons and stability evaluations of three protein antigens

Abstract Although live attenuated rotavirus (RV) vaccines are available globally to provide protection against enteric RV disease, efficacy is substantially lower in low to middle income settings leading to interest in alternative vaccines. One promising candidate is a trivalent non-replicating rotavirus (NRRV) vaccine, comprised of three truncated rotavirus VP8 subunit proteins fused to the P2 CD4+ epitope from tetanus toxin (P2-VP8-P[4/6/8]). A wide variety of analytical techniques were employed to compare the physicochemical properties of these three recombinant fusion proteins. Various environmental stresses were used to evaluate antigen stability and elucidate degradation pathways. P2-VP8-P[4] and P2-VP8-P[6] displayed similar physical stability profiles as function of pH and temperature while P2-VP8-P[8] was relatively more stable. Forced degradation studies revealed similar chemical stability profiles with Met1 most susceptible to oxidation, the single Cys residue (at position 173/172) forming inter-molecular disulfide bonds (P2-VP8-P[6] was most susceptible), and Asn7 undergoing the highest levels of deamidation. These results are visualized in a structural model of the NRRV antigens. The establishment of key structural attributes of each antigen, along with corresponding stability-indicating methods, have been applied to vaccine formulation development efforts (see companion paper), and will be utilized in future analytical comparability assessments.