Long-term survival of transferred lymphocytes. (a) Kinetics of PCR reactions for GAPDH and TK. The numbers of cycles chosen for semiquantitative analysis are indicated. (b) Spleen cells of mice expressing TK under the CD4 promoter were injected into sham-operated (black bars) or splenectomized (white bars) recipients. Four weeks later, homing of transferred cells was assessed by PCR analysis of the TK gene in DNA extracts (reflecting infiltrating donor cells) and RT-PCR analysis of TK mRNA in RNA extracts (reflecting infiltrating T cells) of different organs. TK RT-PCR data were normalized to GAPDH mRNA levels determined by RT-PCR (mean ± SEM, n = 4 mice per group). M, mesenteric; P+I, para-aortic and inguinal; LN, lymph nodes.