CD4 and viral infectious disease: For generating HIV-resistant immune cells, previous studies have used CCR5 gene modification in HSPCs, CD4+ T lymphocytes, and iPSCs and showed their resistance against viral infection.61, 62, 63 However, CCR gene modification in immune cells cannot prevent the advent of non-CCR5-tropic variants, as observed in a patient at 20 months after allogeneic stem cell transplantation of CCR5 delta32.60