Furthermore, although we have thoroughly characterized the behavior of TCRTg101 in leukemia-bearing animals and have identified the cells that present antigen to TCRTg101, without knowing the nature of the Tg101 antigen, we are unable to draw conclusions regarding the natural affinity of this CD8+ T cell clone for cognate antigen and the impact on its behavior in vivo, nor are we able to identify and investigate the biology of endogenous CD8+ T cells reactive to the antigen. The gene discussed is CD8A; the disease is leukemia.