Subacute SARS-CoV-2 replication can be controlled in the absence of CD8+T cells in cynomolgus macaques

Author summary SARS-CoV-2 infection presents a wide spectrum of clinical manifestations ranging from asymptomatic to fatal respiratory failure. The determinants for failure in viral control and/or fatal disease progression have not been elucidated fully. Both acquired immune effectors, antibodies and CD8(+) T cells, are considered to contribute to viral control. However, it remains unknown whether a deficiency in either of these two arms is directly linked to failure in the control of SARS-CoV-2 replication. In the present study, to know the requirement of CD8(+) T cells for viral control after the establishment of infection, we examined the effect of CD8(+) cell depletion by monoclonal anti-CD8 antibody administration in the subacute phase on SARS-CoV-2 replication in cynomolgus macaques. Unexpectedly, our analysis revealed no significant impact of CD8(+) cell depletion on viral replication, indicating that subacute SARS-CoV-2 replication can be controlled in the absence of CD8(+) T cells. CD8(+) T-cell responses may contribute to viral control in SARS-CoV-2 infection, but this study suggests that CD8(+) T-cell dysfunction may not solely lead to viral control failure or fatal disease progression. SARS-CoV-2 infection presents clinical manifestations ranging from asymptomatic to fatal respiratory failure. Despite the induction of functional SARS-CoV-2-specific CD8(+) T-cell responses in convalescent individuals, the role of virus-specific CD8(+) T-cell responses in the control of SARS-CoV-2 replication remains unknown. In the present study, we show that subacute SARS-CoV-2 replication can be controlled in the absence of CD8(+) T cells in cynomolgus macaques. Eight macaques were intranasally inoculated with 10(5) or 10(6) TCID50 of SARS-CoV-2, and three of the eight macaques were treated with a monoclonal anti-CD8 antibody on days 5 and 7 post-infection. In these three macaques, CD8(+) T cells were undetectable on day 7 and thereafter, while virus-specific CD8(+) T-cell responses were induced in the remaining five untreated animals. Viral RNA was detected in nasopharyngeal swabs for 10-17 days post-infection in all macaques, and the kinetics of viral RNA levels in pharyngeal swabs and plasma neutralizing antibody titers were comparable between the anti-CD8 antibody treated and untreated animals. SARS-CoV-2 RNA was detected in the pharyngeal mucosa and/or retropharyngeal lymph node obtained at necropsy on day 21 in two of the untreated group but undetectable