[Phenotypic changes in refractory and relapse acute lymphoblastic leukemias]

Out of a group of 220 acute lymphoblastic leukaemias (ALL) with phenotypic study at diagnosis, 18 were selected on which sequential studies were performed due to relapse (15 cases) or to lack of achievement of complete remission (primary resistant ALL, 3 cases). The purpose of this study was to analyse the incidence and characteristics of the possible antigenic changes with regard to the diagnosis. Along with the classic markers, a panel comprised of 20 monoclonal antibodies against lymphoid and myeloid antigens was used. Major phenotypic changes (acquisition of myeloid antigens CD13 and CD33) were found only in one case amongst the relapsing ALL (7%). Seven other patients (47%) showed minor phenotyping changes, including: 1) acquisition or loss of antigens (2 cases); 2) changes in more then 50% of any antigen's expression (4 cases); 3) both (1 case). These results might suggest that antigenic changes are rather frequent in relapsing ALL; however, none of such changes modified in our experience the phenotypic diagnosis so any change of this last should be regarded as an exceptional event. The majority of these antigenic changes consisted of the loss of maturation antigens (CD20) or acquisition of early markers (TdT, HLA-DR) or activation markers (CD38); this would mean that the relapsing blast cells show a functional status of activation and proliferation, with a phenotype more immature than that of the diagnosis, thus explaining the poorer prognosis of the patients in relapse. No phenotypic changes were found in the primary resistant ALL, which may indicate the persistence of the original cell clone without any alteration.