Defective expression of T cell antigens in chronic lymphocytic leukaemia: relationship to T cell dysfunction

Summary. In chronic lymphocytic leukaemia (CLL) peripheral blood T cells have a variety of functional abnormalities. To explore more extensively the T cell status of B‐CLL patients, surface immunoglobulin‐negative cells were isolated by sheep erythrocyte rosetting (ER) and the membrane phenotypes of the ER + cells defined by immunofluorescence utilizing monoclonal antibodies (MAb). In 11 of 18 CLL patients (CLL group I) there was excellent correlation between ER + and T3 (mature T cell marker) positivity. In the remaining patients (CLL group II), only 5–45% of ER+ cells were T3 positive, suggesting that many rosetting cells were non‐T, However, the ER+, T3 negative cells were nonreactive with OKM‐1 (MAb which detects monocytes and ‘null’ lymphocytes) or with OKT11, 9.6, and 35.1, MAb against the T cell E receptor. Moreover ER +, T3 negative cells were not stained with OKT4, OKT8, OKT6, OKT9, or OKT10. Treatment of group II ER + cells with neuraminidase increased (from 27% to 74%) the mean percentages of T3 positive cells detected, but not other membrane antigens. ER+ cells from group II patients, compared with normal and group I patients, exhibited diminished proliferative responses to PHA and Con‐A (P<0.01) and supported poorly pokeweed mitogeninduced proliferation of normal allogeneic B cells (P<0.01). Thus, in approximately one‐third of the CLL patients studied, many ER+ cells poorly express a number of membrane antigens characteristic of normal mature T cells, one of which (T3) is unmasked by neuraminidase treatment. This phenotypic abnormality appears to be associated with significant T cell dysfunction in vitro and may, at least in part, contribute to the commonly encountered immunological defects present in these patients.