Intriguingly, while HTLV-1 infects both CD4+ and CD8+ T cells and induces the clonal expansion of both cell types [35,123], the vast majority of ATL cases are CD4+ T cell leukemia, suggesting that some CD8+ T cell-specific factors could restrict the leukemogenic potential of HTLV-1 in this cell type. The gene discussed is CD4; the disease is T-cell leukemia.