Thymidine phosphorylase: a possible marker of cell maturation in acute myeloid leukaemia.

Thymidine Phosphorylase activity has been measured in two populations of human Acute Myeloid Leukaemia cells (AML) and in normal human macrophages. During short-term culture in vitro of AML cells the activity of this enzyme increases progressively and approaches that of normal non-dividing macrophages at a time when the leukaemia cells in culture show evidence of maturation as assayed by functional, enzymatic and morphological criteria. It is suggested that the level of Thymidine Phosphorylase activity may be a marker of maturation in AML.