The optimal time for peripheral stem cell harvest may be predicted by recovery of blood count following priming doses of chemotherapy. Bone marrow growth factors have also been used to enhance yield. Both these manoeuvres may necessitate alterations to standard treatment programmes. In order to determine whether adequate peripheral stem cell yields could be obtained without altering chemotherapy regimens, 18 children with either leukaemia or solid tumours were studied. Circulating bone marrow progenitor cells were estimated by CFU-GM cultures in soft agar. There were 8 males and 10 females, median age 5.6 years (range 2-13 years). Six out of 13 studies in leukaemia patients were done when the bone marrow contained significant leukaemic blasts, and in 2 of 9 studies in patients with solid tumours, there was active infiltration of the bone marrow. In 15 of 23 studies, a rise in CFU-GM levels to greater than 1,000 x 10(3)/l were observed following postchemotherapy aplasia. Maximum CFU-GM levels were maintained for only 1-2 days and could be predicted by the achievement of a total white cell count in the region of 2 x 10(9)/l and platelet count around 100 x 10(9)/l. Neutrophil recovery did not predict the rise in CFU-GM levels. A rapid rise in monocyte levels also preceded maximum CFU-GM levels. Predictably, the CFU-GM counts were lower in patients who were heavily pretreated, but in several children, the counts were sufficient to predict an adequate harvest to be used in conjunction with bone marrow autotransplantation. It is concluded that in children with active bone marrow recovery, chemotherapy priming or the use of bone marrow growth factors may not be necessary to achieve useful stem cell harvests.
