CD4 and severe combined immunodeficiency: The hypothesis that, in addition to CD4+ T cells, macrophages could be prominent contributors to the cART-resistant reservoir of infectious proviruses has been further supported by the recent evidence that mice with severe combined immunodeficiency (SCID) reconstituted with human myeloid cells in the absence of CD4+ T cells can undergo both acute and chronic HIV-1 infection with establishment of an inducible HIV-1 reservoir, at least in some animals20.