Similarly, given the long estimated half-life of memory CD4+ and CD8+ T cells of 200 days (4), we varied the number of virus-specific T cells present in the BALF from values similar to those observed immediately following infection clearance (≅65 cells/ml from BAL) to what might be observed 2 years after initial infection (≅5 cells/ml from BAL). This evidence concerns the gene CD8A and infection.