Analysis of T-cell differentiation antigens in acute lymphatic leukemia using monoclonal antibodies.

Leukemic cells in 134 patients with ALL were analyzed by a panel of mouse monoclonal antibodies. Two antibodies are reactive with all peripheral blood T cells but define different surface antigens (Leu-1 and Leu-4). Two other antibodies react with antigens that are restricted to suppressor/cytotoxic T cells (Leu-2) and to helper T cells (Leu-3). We also used antibodies to the receptor for sheep red blood cells (SRBC) (Leu-5) and to a human "TL-like" antigen that is found on most thymocytes but not in peripheral T cells (Leu-6). An antibody to the human p29.34 "Ia-like" molecule was also tested. Of the 134 ALL patients, 17 had a predominance of SRBC-rosetting (Leu-5+) lymphoblasts ("T" ALL), expressing different surface phenotypes defined by this panel of monoclonal antibodies. These phenotypes were not readily classifiable according to a scheme of sequential stages of normal differentiation proposed. Moreover, the lymphoblasts in 8 of 113 patients not expressing conventional B- to T-cell markers ("null" ALL) reacted with the monoclonal anti-T-cell antibodies. This study suggests that the classification of lymphoblasts in ALL based on the reactivities observed with this panel of mouse monoclonal antibodies is not easily reconciled with current models of normal T-cell differentiation. However, it should be emphasized that the precise sequence of antigenic expression by cells undergoing thymic differentiation is still not fully known, and further phenotypic analysis of ALL cells might contribute to an improved understanding of this malignancy.