Human primary T-cell immortalization by Tax. (A) Schematic representation of the vectors used in this study to synthesize the HIV pseudotype viral particles expressing HTLV-1 Tax protein. (B) BHK-HTLV LTR-βGal and CMMT HIV LTR-βGal established cell lines were infected with negative control virus or Tax-expressing viral particles. βGal expression was monitored to test the infectivity of Tax pseudovirus. (C) FACS analysis of CD4, CD8, and CD25 T-cell receptors in PBMCs (nontransduced control cell line) or Tax-transduced PBMCs (PBMC-Tax.3). (D) Soft agar colony formation assay on Tax-transduced PBMCs or negative control virus. (E) Proliferation of Tax-transduced PBMCs (PBMC-Tax.3) in the presence or absence of IL-2. (F) Western blot of Tax expression in a mixed population of Tax-transduced PBMCs after 4 weeks of culturing. PBMCs and CEM served as negative controls. The HTLV-I–transformed cell lines MT4 and C8166 were positive controls for Tax expression. (G) Western blot analysis of Tax-affected proteins in nontransduced PBMCs and Tax-transduced PBMCs.