A cDNA encoding mouse PD-1, a member of the immunoglobulin superfamily was previously isolated from apoptosis-induced cells by subtractive hybridization. To determine the structure and chromosomal location of the human PD-1 gene, we screened a human T cell cDNA library by mouse PD-1 probe and isolated a cDNA coding for the human PD-1 protein. The deduced amino acid sequence of human PD-1 was 60% identical to the mouse counterpart, and a putative tyrosine kinase-association motif was well conserved. The human PD-1 gene was mapped to 2q37.3 by chromosomal in situ hybridization. (C) 1994 Academic Press, Inc.