BY55 MONOCLONAL-ANTIBODY DELINEATES WITHIN HUMAN CORD-BLOOD AND BONE-MARROW LYMPHOCYTES DISTINCT CELL SUBSETS MEDIATING CYTOTOXIC ACTIVITY

We had previously reported, using BY55 monoclonal antibody, a cell sur face 80-kDa protein restricted to human functional peripheral blood cy totoxic lymphocytes with either natural killer CD3(-) or cytotoxic T l ymphocyte CD3(+)CD8(+) phenotype. In the present report, we studied th e cytotoxic lymphocytes in adult bone marrow and newborn cord blood as these organs are commonly used as sources of hematological stem cells for allogeneic transplantation. Our results showed that BY55 mAb labe led only 5-10% of the bone marrow lymphocytes, which included a major proportion of CD3(+)CD8(+) cytotoxic T lymphocytes. Interestingly, wit hin cord blood cells, BY55(+) lymphocytes represented 20-35% of the ly mphocytes corresponding exclusively to a CD3(-) cell subset. Furthermo re, we detected in cord blood no cytotoxic T lymphocyte activity but w e demonstrated that the CD3(-)BY55(+) cell subset contained the whole natural killer activity.