Aplastic presentation of acute lymphoblastic leukemia: evidence for cellular inhibition of normal hematopoietic progenitors.

Childhood acute lymphoblastic leukemia (ALL) may rarely present with blood and bone marrow findings suggestive of aplastic anemia. Although numerous examples of ALL presenting with this phenomenon have been reported, there is no accepted explanation for the pathogenesis of this preleukemic hypoplasia. We report a case of a child with ALL whose initial presentation was characterized by pancytopenia and bone marrow hypoplasia and who had repeated episodes of pancytopenia at times of systemic relapse. In vitro coculture experiments demonstrated that the leukemic cells from this patient were inhibitory for the growth of myeloid, erythroid, and megakaryocytic progenitor cells from normal peripheral blood. This inhibitory effect exhibited a dose-dependent relationship with the number of added lymphoblasts and persisted when the lymphoblasts were irradiated to prevent leukemic cell growth. Inhibitory activity was not present in media conditioned by the growth of the patient's lymphoblasts, nor was it present in lymphoblasts from three other children with ALL with similar immunophenotype but without marrow aplasia. These data suggest that the aplastic presentation of ALL may be attributable to inhibitory properties intrinsic to the leukemic cells rather than to other host factors.