Twenty children who were in unmaintained full haematological remission after treatment for acute lymphoblastic leukaemia (ALL) showed a significantly lower incidence of granulocyte-macrophage progenitor cells (GM-CFC) in the bone marrow compared to controls. This low incidence lasted for up to at least 3 years after the cessation of chemotherapy. There was no tendency to higher values with longer times after treatment, and the low incidence was not predictive of relapse.

Long-term cultures from ALL bone marrows and from controls achieved similar levels of production of mature cells through the whole period of culture (6 weeks). However, cultures from patients’ bone marrow had on average about 5 times lower numbers of GM-CFC, indicating that the level of mature cell production was achieved by a higher level of post-GM-CFC amplification than needed in the controls. This is taken to be due to compensatory mechanisms operative during stressed haemopoiesis which appears to be a long-lasting effect after current chemotherapy of ALL.