CLINICOPROGNOSTIC RELEVANCE OF QUANTITATIVE IMMUNOPHENOTYPING IN B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA WITH EMPHASIS ON THE EXPRESSION OF CD20 ANTIGEN AND SURFACE IMMUNOGLOBULINS

Expression of CD20, evaluated as antibody binding capacity (ABC) (i.e. absolute number of molecules of antibody per cell), was analyzed usin g flow cytometry on leukemic cells of 93 previously untreated patients , all fulfilling strict criteria of ''immunologically typical'' (i.e. CD5(+), CD23(+)) B-cell chronic lymphocytic leukemia (CLL). Although c hanges of CD20 antigen density did not correlate with clinical paramet ers representative of either tumor mass (i.e. clinical stage, histolog ical pattern of bone marrow involvement, absolute peripheral blood lym phocytosis) or disease progression (i.e. lymphocyte doubling time), a trend toward a better life-expectancy was observed in the low CD20 exp ression group compared with the high CD20 expression group (p=0.05; re lative risk of death, 0.51, 95% confidence interval, 0.24-1.04). Given the correlation between CD20 ABC and mean fluorescence intensity (MFI ) of light chain (LC) surface immunoglobulins (Sm Ig) (r=0.481, p<0.00 01), as well as the impact of MFI of Sm Ig LC on overall survival (p=0 .01; relative risk of death 0.44; 95% confidence interval; 0.10 to 0.7 6), we tried to verify whether a combination of B-cell markers, evalua ted in a quantitative manner, could have additive prognostic propertie s. To this purpose we gave a value of 1 or 0 to each B-cell marker acc ording to whether it was expressed at a low (i.e. CD20 ABC<17.9x10(3) molecules/cell, MFI of LC Sm Ig<100) or high (i.e. CD20 ABC greater th an or equal to 17.9x10(3) molecules/cell, MFI of LC Sm Ig greater than or equal to 100) level thus allowing patient stratification into two groups with scores of 2 and 0-1, respectively. Survival of patients wh o scored 2 was significantly longer than that of patients who scored 0 -1 (p=0.02; relative risk of death, 0.44; 95% confidence interval, 0.2 2-0.72). However, when quantitative changes of CD20 antigen and LC Sm Ig expression, either alone or in combination, were simultaneously ana lyzed in a Cox model which included usual clinico-hematological featur es, only absolute peripheral blood lymphocytosis (p=0.0001) and Binet clinical stages (p=0.0001) maintained their prognostic power unmodifie d. Although variability of CD20 and Sm Ig expression make it possible to appreciate biological heterogeneity of B-cell CLL better, however, they cannot substitute well-established clinico-hematological features in the prognostic assessment of B-CLL patients.