Although data from experimental models suggest that certain immunocompetent units are preferentially inhibited by drugs, the suppressive effects of chemotherapy upon various cell compartments in man have not been characterized. In this study we compared the effect of long-term combination chemotherapy upon T-lymphocytes in the bone marrow and peripheral blood of children with acute lymphocytic leukemia (ALL) in remission. The “in vitro” response to phytohemagglutinin (PHA) was used as index of T-lymphocyte function. After 2 to 3 years of immunosuppressive therapy, in half of the patients the response to PHA was significantly greater in bone marrow than in peripheral blood cultures. This contrasts with the results obtained after cessation of chemotherapy when 14 of 15 patients had greater response in peripheral blood than in bone marrow. We conclude that in some children with ALL in remission, long-term immunosuppressive therapy produces a relative increment of a PHA-responsive cell population in bone marrow, possibly by a selective sequestration of T-cells in this compartment.

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