CD8A and viral infectious disease: HPgV may indirectly lead to hematopoietic dysfunction of the bone marrow by affecting the homeostasis of the immune system, or it may induce excessive immune responses in the body, causing immune cells to attack hematopoietic stem and progenitor cells in the bone marrow, leading to AA.[21,22] Research by Zhang, Tian et al has demonstrated that following viral infection, CD8 + cytotoxic T cells become overactivated and release cytotoxic factors such as perforin and granzyme B, which induce apoptosis in hematopoietic stem cells.