CD8A and lymphopenia: Even though lymphopenia has been described as hallmark for severe COVID-19, it remains elusive whether it is caused by tissue infiltration or destruction of lymphocytes.17 As indicated by the T-cell signature of CONV, SARS-CoV-2 infection causes a differentiation of naive into effector CD8+ T cells, further supported by the significant increase of EM CD8+ T cells over time.