Residual haemopoietic damage in the mouse after fractionated gamma-irradiation, down to 0.1 Gy per fraction

Long-term effects of plutonium-239 and radium-224 on the distribution and performance of pluripotent haemopoietic progenitor cells and their regulatory microenvironment

Experiments are described which investigate the long-term damage to haemopoietic progenitor cells (CFU-S) and their microenvironment in mouse marrow resulting from the administration of leukaemogenic amounts of plutonium-239 and radium-224. 239Pu (35 Bq g-1 body weight) and 224Ra (555 Bg g-1 body weight) were injected into 10-12-week-old mice, and numbers, proliferative activity and self-renewal capacity of CFU-S were measured at different locations in femoral marrow at intervals over the following 2 years. Parallel measurements were also made of the quality of the haemopoietic microenvironment by ectopic transplantation of bone marrow cells. There was some recovery from the initial effects of 239Pu on CFU-S numbers after 3-6 months, although the recovery was not maintained in all marrow fractions. Following 224Ra administration there was an initial transient increase in CFU-S numbers in the fraction of marrow furthest from bone surfaces but a considerable depression in numbers in other regions of marrow; there was no recovery between 3 and 6 months and subsequent recovery was not complete in all regions of marrow. The differential responses of CFU-S and the haemopoietic microenvironment following 224Ra or 239Pu administration seemed in some ways related to the metabolism of the radionuclides. There was a profound reduction in the ability of marrow to generate ossicles when transplanted under the kidney capsule as a result of the administration of either 224Ra or 239Pu, with only transient recoveries from the effects of 239Pu at 4 days and at 3 months after injection.

Interactions in recovery and in residual injury from sequential treatments of mouse haemopoietic and stromal marrow cell populations, using X-rays, cyclophosphamide and busulphan

The acute recovery of populations of day 11 CFU-S, iv-CFC and CFU-F in mouse bone marrow, following a test dose of X-rays, cyclophosphamide (CP) or busulphan (BUS) given to mice previously treated with repeated priming doses of X-rays or CP, was in general predictable from the amount of residual injury after the priming doses. A marked exception was iv-CFC after X-rays, which although amplified to near normal levels during the residual injury phase, recovered after the test irradiation from low levels of CFU-S. The amount of residual injury after sequential treatments of different agents was in general less than expected on the basis of the product of the effects of the individual agents. This was most marked for CP priming treatments, where the long-term recovery of day 11 CFU-S after the test dose remained persistently above control levels. Also, some correlation was found between improved stromal recovery (CFU-F) and the CFU-S content following the sequential treatment protocols.

The radiation response and recovery of bone marrow stroma with particular reference to long-term bone marrow cultures

There is evidence for long-term haematopoietic dysfunction in some patients treated with radiotherapy. Although the underlying mechanisms are unclear, both stem cell and environmental defects have been implicated. In the present article we review the evidence concerning the role of stromal cells. According to the endpoints used, a wide range of radiosensitivities for the stroma have been reported. Long-term bone marrow cultures provide a system in which both functional and regenerative aspects of the stroma can be studied. A dose of 5 Gy applied prior to the establishment of long-term bone marrow cultures decreases both the formation of a confluent adherent stromal layer and its capacity to support haematopoiesis. In contrast, in its fully established phase, the adherent layer displays a high radioresistance due to the low proliferative stress applied to its stromal populations. A dose of 10 Gy given to a fully established adherent layer does not prevent haematopoietic engraftment and sustained haematopoiesis. At doses above 100 Gy a macrophage-like and epithelioid cell-type become dominant, which preserve their ability of producing growth regulatory molecules at doses as high as 500 Gy. These data suggest that the main effect on the stroma is a delayed expression of irradiation damage due to the slow rate of turnover of stromal cells. So far, there is little evidence for persistent deficiencies in the functional roles of stromal cell populations.