Immune activation induces immortalization of LTR-Tax CD4⁺ T cells. Cultures of stimulated LTR-Tax and control CD4⁺ T cells (3 independent mice each) were propagated with IL-2 (80 U/mL). (A) Cells numbers were determined weekly for up to 12 weeks (means ± SD). (B) Tax mRNA levels from the LTR-Tax cells were assayed by Q-PCR at the indicated times. Expression increased during weeks 2 and 3 of cell culture, and then decreased with time.