Increased Proliferation of Transplanted Mouse Bone Marrow Cells by Pre-irradiation of the Recipient

Abstract

THE transplantation of bone marrow cells from normal donor animals into heavily irradiated recipients rapidly restores haemopoiesis to normal. For example, we find that erythropoiesis in a heavily irradiated mouse is restored to normal within 7 days of the injection of 4 × 10⁶ bone marrow cells, although this is only 1 per cent of the normal number of bone marrow cells in a mouse. This very considerable capacity for restoration of erythropoiesis suggests that before transplantation the progenitor cells responsible for recovery of erythropoiesis are proliferating slowly, either all the cells dividing slowly or a small proportion of them dividing more rapidly. This has recently been confirmed by Becker et al.¹ by incubating bone marrow cells in vitro with tritiated thymidine of sufficient activity so that all the cells synthesizing DNA and incorporating the isotope are killed by the subsequent β-irradiation. For bone marrow cells from normal animals, they found less than 10 per cent of the cells in DNA synthesis, while for rapidly dividing cells (6 days after 900 r. whole-body irradiation with bone marrow transplantation) 65 per cent were in DNA synthesis.