Although the latter mechanism of SARS-CoV-2 entry may contribute to infection of cortical cells, its efficiency in T21 cells is likely to be diminished due to an altered activity of lysosomal enzymes caused by accumulation of the APP-βCTF[69] and/or overexpression of cystatin-B [139], an endogenous inhibitor of cathepsin-B and -L [26, 33, 127]. The gene discussed is CSTB; the disease is infection.