PDCD1 and neoplasm: Analysis of host T cells demonstrated significant PD-1 upregulation on normal host T cells, both CD4 and CD8, in syngeneic mice bearing T-ALL5 relative to non-tumor-bearing C57BL/6 controls (Fig. 5A) and a trend toward increased PD-1 expression in mice bearing T-ALL3 (Fig. 5B).