Shifts in expression of cell membrane phenotypes in childhood lymphoid malignancies at relapse.

To determine if cell membrane phenotypes change under the selective pressures of therapy we have conducted a prospective study of 54 children with lymphoid malignancies of T-like, B-like, common, and null cell types. Membrane phenotypes were determined at diagnosis in all patients and again 1-24 mo later in 18 children who either failed induction therapy or had one or more relapses. In 7 patients the cells tested were from relapse sites different than those of the original diagnoses. The data indicate that at relapse most children with lymphoid neoplasias had the same cell membrane phenotype as established at diagnosis, and suggest that the site of relapse did not affect the expression of cell surface markers. However, there were three exceptions: (1) a child initially diagnosed as having null cell acute lymphocytic leukemia had 90% T-antigen-positive blasts in her second-relapse bone marrow; (2) only membrane IgM was present on relapse blasts from a B-cell lymphoma that had both membrane IgM and IgD before initiation of treatment; (3) at diagnosis, bone marrow blasts from a child with T-like leukemia expressed both T antigen and E receptors, but at relapse, bone marrow and pleural fluid cells expressed only T antigens. We postulate that these phenotype shifts may be due to selective effects of therapy on cells at different stages of differentiattion.