BCL2 and deltaretrovirus infections: The search combined controlled vocabulary and free-text terms related to deltaretrovirus infection and apoptosis, including: “HTLV-1,” “HTLV-2,” “BLV,” “Adult T-cell Leukemia/Lymphoma (ATLL),” “HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP),” “BCL-2 family,” “BCL-like proteins,” “apoptosis,” and “cell survival.”