The inability to easily and efficiently introduce genes into primary T cells has hampered the investigation of the pathways controlling T cell fate. To enable adenoviral-mediated gene transfer into normal naïve T cells, transgenic (Tg) mice expressing the coxsackie/adenovirus receptor (CAR) in their T cell compartment were constructed. Whereas naïve T cells are resistant to adenoviral infection, Tg expression of CAR on T cells greatly facilitates adenoviral-mediated gene expression ex vivo, in vivo, and in differentiated T helper cells. Thus we have developed a technology for efficient gene delivery to naïve T cells. By using adenoviral vectors encoding specific inhibitors, we show that G1 cyclin-dependent kinase, NF-κB, and caspase activities are required for the proliferation of primary T cells. In addition, by expressing Bcl-x_L protein at a level that closely approximates mitogen-induced levels, we demonstrate that Bcl-x_L expression is sufficient to account for mitogen-mediated survival of primary T cells. Thus, adenoviral-mediated gene delivery to CAR Tg T cells should be useful for the analysis of many genes controlling T cell fate.