Transferrin receptor expression by blast cells in acute lymphoblastic leukemia correlates with white cell count & immunophenotype.

Transferrin receptor (TR) expression by blast cells in 127 cases of acute lymphoblastic leukemia (ALL) at presentation and 19 cases at relapse was examined using three anti-TR monoclonal antibodies to find its correlation with prognostic features such as the total leucocyte count (TLC), the morphology of blast cells and their cytochemical and immunophenotypic properties, as well as age and sex of the patients. Blasts in 62 per cent of thymic (T) ALL cases at presentation showed significant TR expression as compared to only 10.9 per cent in common ALL (CALL) (P < 0.001). This differential expression of TR was also observed among cases with > 50 x 10(9)/l TLC, while in cases with < 50 x 10(9)/ l TLC no such pattern was observed (30% TR positivity in T-ALL vs 20% TR positivity in non-T-ALL). Furthermore, the percentage of TR positive blasts was significantly higher (P < 0.005) in cases with > 50 x 10(9)/l TLC as compared to those with < 50 x 10(9)/l (48.3-54.4% vs 24.9-28.8%). In contrast to CALL cases at presentation, those at relapse showed a very high TR positivity (54-66%), similar to the T-ALL cases (53-84%). This suggests a high proliferative rate of blast cells in ALL at relapse, irrespective of its immunophenotype. There was no correlation of TR expression with blast cell morphology (FAB L1 vs L2), their cytochemical properties and sex of the patients. However, a significantly higher incidence of TR positivity was observed in patients above 10 yr of age compared to those below 10 yr (47% vs 15%; P < 0.001). The incidence of T-ALL was also significantly higher in the former group (56%) compared to the latter (33%) (P < 0.005). Our data suggest that by virtue of its association with features of poor prognosis, e.g., age above 10 yr, expression of thymic markers, high leucocyte count and disease relapse, TR expression by blast cells in ALL could serve as a biological marker of poor prognosis.