GZMB and COVID-19: Exhausted T cells are considered dysfunctional, typically failing to clear infected cells and with progressive loss of IL‐2, TNFα, IFNγ and granzyme B.29, 30Immune checkpoint receptors were upregulated in COVID‐19 (i.e. PD‐1), indicating ‘lymphocyte exhaustion’, as shown previously.29, 30