Studies on the development of human acute myeloid leukaemia xenografts in immune-deprived mice: comparison with cells in short-term culture.

Human AML cells from the blood of a series of patients have been implanted subcutaneously into mice immune-suppressed by thymectomy and total-body irradiation. Solid tumours resulted from 18 out of 19 samples and their growth was compared with the proliferation of AML cells in culture. In 17 cases tumours grew to a maximum size and then spontaneously regressed. Cells from one patient produced tumours which did not regress and could be retransplanted into freshly immune-suppressed mice. Cells from a human promyelocytic cell line (HL60) also produced nonregressing and retransplantantable tumours. Normal human mononuclear bone marrow cells implanted s.c. produced a growth pattern similar to that of the majority of AML cells. A second inoculum of AML cells into animals with regressing tumours also produced tumours and thus regression cannot be accounted for on the basis of returning immunity. AML cells placed into short-term suspension culture invariably matured to monocyte/macrophage type cells and/or granulocytic cells as identified by cytochemical staining. However, no correlation was observed between proliferation or maturation of cells in culture, and tumour growth in vivo. Cells derived from disaggregated AML tumours also showed evidence of myeloid differentiation suggesting that tumour regression is due to maturation of leukaemic cells.