CD4 and infection: This antibody-mediated cross-reactivitywas further supported by adoptive plasma transfer experiments, which showed thatantibodies elicited by the mRNA-OC43 vaccine conferred protection to mice againstMHV infection, underscoring the importance of humoral immunity in cross-protection.Interestingly, unlike previous reports that highlight a key role for virus-specificCD8+ and CD4+ T cells in cross-protection (21, –, 24), our model did notreveal a cross-protective role for these T cell subsets in the context of MHVinfection.