Studies of hematopoietic stem cells spared by 5-fluorouracil.

Abstract

Mouse marrow cells were exposed to 5-fluorouracil (FU) either in vivo or in vitro and the effects on the hematopoietic stem cell compartment were studied. The drug was highly toxic to bone marrow cells including the spleen colony-forming unit (CFU-S) population. The small population of stem cells surviving FU, however, caused a different pattern of spleen colony growth when injected into lethally irradiated mice. Whereas numbers of spleen colonies caused by normal marrow cells remained constant during an 8-14 d period after transplantation, spleen colonies derived from FU-treated marrow cells increased by as much as 100-fold during this time. This effect on stem cells was dose dependent both in vitro and in vivo. When FU was given in vivo, the day 14/day 8 ratio of colonies was greatest 1 d after injection and, over the next 7 d, returned to a near-normal value, that is, unity. A number of studies have shown that the stem cell compartment is heterogeneous with respect to self-replicative capacity and developmental potential. An age structure for the stem cell compartment has been proposed wherein cells with a short mitotic history are more likely to self-replicate than they are to differentiate; hence they are more primitive. 'Older' stem cells with a longer mitotic history are, according to the hypothesis, more likely to differentiate. 5-fluorouracil may be toxic to the older stem cells and selectively spare the more primitive subpopulation. Although the surviving cells may not themselves be able to form spleen colonies, they may give rise to an older cohort of cells more likely to differentiate and form spleen colonies. It is the requisite developmental maturation within the stem cell compartment that may be responsible for the delay in appearance of spleen colonies derived from FU-treated marrow. Our results support this explanation and identify the locus of at least part of this activity as the bone marrow. We found that the FU-treated marrow did not cause an increase in spleen colony numbers between 8 and 14 d in hosts with a long-standing marrow aplasia, due to the incorporation of 89Sr into bone. I propose that the delayed spleen colony appearance in normal hosts is the result of developmental maturation of the primitive stem cell compartment that survives FU and is responsible for spleen colonies arising around day 14. This maturation, at least initially, occurs in the marrow and leads to the replenishment of the more differentiated CFU-S subsets ablated by FU, which are normally responsible for spleen colonies appearing earlier after transplantation.

Effects of lethal irradiation in zebrafish and rescue by hematopoietic cell transplantation

“…This suggests that HSCs are spared, and that sublethal irradiation may be useful for enriching stem cell subsets akin to the use of 5-fluorouracil treatment in mice. 27,28 The response to sublethal irradiation may also be useful for genetic screens designed to uncover functional defects in the repopulation of blood cells by HSCs. Since spermatogonial progenitors are also transiently ablated in the testis, abnormal repopulation of this organ could simultaneously be assessed to find stem cell mutations in the male germ line.…”

Purification and analysis of rat hematopoietic stem cells by flow cytometry

“…This is important because the following theories all imply that the HSC compartment is heterogeneous: that HSC reside in niches that influence their self-replication (151, that microenvironments direct their differentiation (61, that HSC are characterized by an age structure (181, that HSC generate CFU-S through a marrow-dependent maturational step (24), and that HSC maintain normal hematopoiesis through clonal selection (14). These theories could be directly tested if HSC with different phenotypes could be isolated.…”

Characterization of a human hematopoietic progenitor cell capable of forming blast cell containing colonies in vitro.

“…To facilitate the enrichment of CFU-B 1, a number of physical and immunological characteristics ofthese cells could be utilized (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Another means of obtaining enriched populations of CFU-BI might be to pharmacologically purge the marrow of more differentiated elements by in vitro exposure to chemotherapeutic agents (29,30). Van Zant has previously shown that in vitro exposure of murine marrow cells to 5-fluorouracil (5-FU) results in the direct, rapid kill of more differentiated progenitor cells and the selective sparing of primitive pluripotent hematopoietic stem cells (30).…”

“…Another means of obtaining enriched populations of CFU-BI might be to pharmacologically purge the marrow of more differentiated elements by in vitro exposure to chemotherapeutic agents (29,30). Van Zant has previously shown that in vitro exposure of murine marrow cells to 5-fluorouracil (5-FU) results in the direct, rapid kill of more differentiated progenitor cells and the selective sparing of primitive pluripotent hematopoietic stem cells (30). 5-FU does not require in vivo metabolism for this effect to occur.…”