A study published in Nature reveals that purified IgG from convalescent rhesus macaques can protect naive recipients against SARS-CoV-2 infection in a dose-dependent manner. The research shows that even low antibody titres can provide protection, while higher titres are needed for effective treatment. The study also highlights the role of cellular immunity, particularly CD8+ T cells, in protection when antibody levels are suboptimal. These findings have implications for the development of SARS-CoV-2 vaccines and immune-based therapies. The study demonstrates that adoptive transfer of IgG from convalescent macaques can significantly reduce viral load in infected animals, with higher doses providing greater protection. CD8 depletion studies indicate that cellular immunity contributes to protection against rechallenge with SARS-CoV-2. The research underscores the importance of both humoral and cellular immune responses in protecting against SARS-CoV-2, and provides insights into the immunological determinants of protection in rhesus macaques. The findings suggest that vaccines should aim to induce both potent and durable humoral and cellular immune responses. The study also highlights the potential therapeutic use of convalescent plasma for SARS-CoV-2 treatment, although high antibody titres are required for efficacy. The research provides a proof-of-concept that antibodies can protect against SARS-CoV-2 in a dose-dependent manner, and that cellular immune responses may be important when antibody levels are below the threshold required for protection. The study has important implications for the development of vaccines and immune-based therapies against SARS-CoV-2.A study published in Nature reveals that purified IgG from convalescent rhesus macaques can protect naive recipients against SARS-CoV-2 infection in a dose-dependent manner. The research shows that even low antibody titres can provide protection, while higher titres are needed for effective treatment. The study also highlights the role of cellular immunity, particularly CD8+ T cells, in protection when antibody levels are suboptimal. These findings have implications for the development of SARS-CoV-2 vaccines and immune-based therapies. The study demonstrates that adoptive transfer of IgG from convalescent macaques can significantly reduce viral load in infected animals, with higher doses providing greater protection. CD8 depletion studies indicate that cellular immunity contributes to protection against rechallenge with SARS-CoV-2. The research underscores the importance of both humoral and cellular immune responses in protecting against SARS-CoV-2, and provides insights into the immunological determinants of protection in rhesus macaques. The findings suggest that vaccines should aim to induce both potent and durable humoral and cellular immune responses. The study also highlights the potential therapeutic use of convalescent plasma for SARS-CoV-2 treatment, although high antibody titres are required for efficacy. The research provides a proof-of-concept that antibodies can protect against SARS-CoV-2 in a dose-dependent manner, and that cellular immune responses may be important when antibody levels are below the threshold required for protection. The study has important implications for the development of vaccines and immune-based therapies against SARS-CoV-2.