The monoclonal antibody reacts with human CD90, also known as Thy-1 (thymus cell antigen-1). CD90 is a 25-35 kD receptor expressed on thymocytes, CD34+ prothymocytes, hematopoietic stem cells, neurons, a small subset of human fetal liver cells, cord blood cells, and bone marrow cells. CD90 is expressed on a subset of immature, CD34+ cells and a distinct subset of mature CD34- cells that are CD3+CD4+. The CD90+CD34+ population is enriched for cells capable of long-term culture. CD90 is involved in regulation of adhesion and signal transduction by T cells.