Do intrahematopoietic lineage switches occur in vivo?
Can lineage switches also be shown to occur in vivo, under physiologic conditions, or are they restricted to experimental manipulations in cell culture? The existing knowledge, accumulated over many years of research, would suggest that the answer is no. Thus the concept that cells may “change their mind” during differentiation flies in the face of the belief that hematopoiesis is a linear process with multilineage progenitors becoming restricted in a stepwise but irreversible fashion. The following examples illustrate this point: (1) The fact that lethally irradiated mice receiving transplants of short-term repopulating (STR) cells do not survive suggests that these cells cannot convert into long-term repopulating (LTR) cells in vivo. (2) The existence of progenitors that are apparently exclusively committed to the production of restricted progeny (CLPs, common multipotent progenitors [CMPs], granulocyte/macrophage progenitors [GMPs], MEPs, B- and T-cell progenitors44 45) would also a
