LEVELS OF EXPRESSION OF CD52 IN NORMAL AND LEUKEMIC B-CELLS AND T-CELLS - CORRELATION WITH IN-VIVO THERAPEUTIC RESPONSES TO CAMPATH-1H

The CD52 antigen is expressed on most normal and neoplastic lymphoid c ells. The reshaped humanized IgG1 anti-CD52 monoclonal antibody (Campa th-1H) has been used in the treatment of hemopoietic and non-hemopoiet ic diseases for its ability to induce lymphocyte depletion both in vit ro and in vivo., Good activity has been shown in patients with chronic T and B cell leukemias, in particular T-prolymphocytic leukemia (T-PL L). However, the response to treatment is not uniform and this variabi lity may depend on differences in the level of antigen expression on t he leukemic cells. To test this hypothesis, we used quantitative flow cytometry to investigate the intensity of the expression of CD52 in 45 cases of lymphoid leukemia, 24 with B-cell chronic lymphocytic leukem ia (CLL), 21 with T-PLL and 12 normal controls. Normal T lymphocytes e xpressed higher CD52 antigen than B lymphocytes (p < 0.005) and the an tigen was also significantly higher in T-PLL compared to CLL (p < 0.00 1). Moreover, the differences in CD52 expression were somewhat higher in Campath-1H treated patients who responded than in non responders. A lthough other factors may play a role in the response to Campath-1H in vivo, the quantitative estimation of CD52 expression may provide a ra tionale for the greater response in T-PLL and help select those patien ts with a higher probability of responding to this therapy. (C) 1998 E lsevier Science Ltd. All rights reserved.