Immunosuppression and serious infections in children with acute lymphoblastic leukaemia: a comparison of three chemotherapy regimes.

Eighty-four children presenting with acute lymphoblastic leukaemia were entered into a trial designed to test the effect on host toxicity of regular drug-free periods during chemotherapy. Patients received the same total dose of drugs either continuously (daily), intermittently (a 5 d course every 3 weeks) or in an intermediate way between these two (a 14 d course followed by a 7 d gap). Mean neutrophil counts were lower in the intermittent group and fell significantly at 6 week intervals, after courses which included prednisolone and vincristine in addition to methotrexate and 6-mercaptopurine. Mean lymphocyte counts, mitotic response to phytohaemagglutinin and plasma immunoglobulin levels were significantly lower in the continuous group. The results in the intermediate group fell between those of the other two groups. All six remission deaths occurred in the 42 patients in the continuous group, who had a much higher incidence of infections (mostly viral and protozoal) than the other two groups. It is concluded that the intermittent chemotherapy schedule permits the maintenance of a lymphocyte population size and function which provides a satisfactory level of defence against infection without prejudice to its anti-leukaemic effect.