Extracorporeal irradiation of blood (ECIB) in man. II. Treatment of acute myelocytic leukemia.

LL PRESENT FORMS OF THERAPY for acute myelocytic leukemia (AML) injure or destroy normal as well as leukemic cells. The action of anti-metabolic chemotherapeutic drugs is largely directed at disrupting flucleic acid synthesis and, thus, replication of cells. The alkylating agents and whole body radiation are effective in reducing cell production by slowing the generative cycle and directly killing both replicating and interphase cells. We hoped to achieve effective treatment of AML and, at the same time, avoid injury to normal cells by irradiating circulating leukemic cells in an extracorporeal circuit that diverted blood, alone, through a radiation field. At least two theoretical consequences can be considered as a result of killing leukemic cells in this manner. First, if circulating cells are functioning or potential leukemic stem cells, and especially if they are exchanging with tissue counterparts, one may be able to deplete the body of a large reservoir of leukemic stem cells. Lajtha and co-workers1 and Oliver and Shepstone2 have discussed this possibility. If the reservoir of leukemic stem cells is then signfficantly reduced by ECIB, one may have a greater probability of obtaining a chemotherapeutic remission.3 If there is a self-regulating peripheral blood compartment of cells as has been postulated in chronic myelocytic leukemia,4 ECIB might well prove to be effective treatment. Second, killing leukemic cells in the peripheral blood may influence leukemic cell growth by altering feedback mechanisms which theoretically may have some role in determining population size. The established chemotherapy of AML has proven to be rather disappoint-