Reverse mutational scanning of spike BA.2.86 identifies the epitopes contributing to immune escape from polyclonal sera

The recently detected Omicron BA.2.86 lineage contains more than 30 amino acid mutations relative to BA.2. BA.2.86 and its JN.1 derivative evade neutralization by serum antibodies of fully vaccinated individuals. In this study, we elucidate epitopes driving the immune escape of BA.2.86 and JN.1 via pseudovirus neutralization. Thus, we have generated 33 BA.2.86 mutants, each reverting a single mutation back to BA.2. We use this library in an approach that we call reverse mutational scanning to define distinct neutralization titers against each epitope. Mutations within the receptor binding domain at K356T, V483{Delta}, and to a lesser extent N460K, A484K, and F486P enhance immune escape. Interestingly, 16insMPLF within the spike N-terminal domain and P621S within S1/S2 also significantly contribute to antibody escape of BA.2.86. Upon XBB.1.5 booster vaccination, neutralization titers against JN.1 and BA.2.86 improve considerably, and a residual immune escape is driven by 16insMPLF, N460K, E554K, and to a lesser extent P621S, and A484K. EDITORS SUMMARYSARS COV2 Omicron lineage BA.2.86 has over 30 mutations compared to the parental BA.2 lineage. Here Bdeir and colleagues apply reverse mutational scanning to determine which among these mutations present in Omicron BA.2.86 are epitopes linked to immune escape from antibody recognition.