CD318/CUB-domain-containing protein 1 expression on cord blood hematopoietic progenitors.

CUB-domain-containing protein 1 (CDCP1)/CD318 is a single transmembrane molecule highly expressed in colorectal cancer and leukemia. It has also been shown to be expressed in hematopoietic progenitor cells. In this study, we analyzed the expression of CD318 on cord blood hematopoietic stem and progenitor cells. Cord blood mononuclear cells were depleted of mature blood cell linage (Lin)-positive cells and then Lin-negative cells were sorted by flow cytometry based on the expression of CD34 and CD318. Analysis of sorted cells by colony-forming assay showed that CD34(+)CD318(+) cells produced more mixed colony forming units and erythroid burst forming unit-derived colonies than CD34(+)CD318(-) cells. These colonies were also produced by CD34(-)CD318(+) and CD34(-)CD318(-) cells, but were generally fewer in number. When sorted cells were cultured on a monolayer of human mesenchymal stem cells, CD34(+)CD318(+) cells proliferated more abundantly than CD34(+)CD318(-) cells, while CD34(-)CD318(+) and CD34(-)CD318(-) cells failed to proliferate. Transplantation of CD34(+)CD318(+) cells into non-obese diabetic/severe combined immunodeficient disease (NOD/SCID) mice resulted in efficient reconstitution of human cells, indicating that CD34(+)CD318(+) cells possess strong SCID-repopulating cell activity. These findings suggest that the co-expression of CD34 and CD318 identifies the immature character of hematopoietic stem cells.