Recovery from the Middle East respiratory syndrome is associated with antibody and T cell responses

The Middle East respiratory syndrome coronavirus (MERS-CoV) causes a highly lethal pneumonia. MERS was recently identified as a candidate for vaccine development, but most efforts focus on antibody responses, which are often transient after CoV infections. CoV-specific T cells are generally long-lived, but the virus-specific T cell response has not been addressed in MERS patients. We obtained peripheral blood mononuclear cells and/or sera from 21 MERS survivors. We detected MERS-CoV-specific CD4⁺ and CD8⁺ T cell responses in all MERS survivors and demonstrated functionality by measuring cytokine expression after peptide stimulation. Neutralizing (PRNT₅₀) antibody titers measured in vitro predicted serum protective ability in infected mice and correlated with CD4⁺ but not CD8⁺ T cell responses; patients with higher PRNT₅₀ and CD4⁺ T cell responses had longer intensive care unit stays and prolonged virus shedding and required ventilation. Survivors with undetectable MERS-CoV-specific antibody responses mounted CD8⁺ T cell responses comparable with those of the whole cohort. There were no correlations between age, disease severity, comorbidities, and virus-specific CD8⁺ T cell responses. In conclusion, measurements of MERS-CoV-specific T cell responses may be useful for predicting prognosis, monitoring vaccine efficacy, and identifying MERS patients with mild disease in epidemiological studies and will complement virus-specific antibody measurements.