DLA-identical marrow grafts after low-dose total-body irradiation : addition of viable donor peripheral blood mononuclear cells does not enhance engraftment

Total-body irradiation (TBI)* (400 cGy) delivered at a dose rate of 7 cGy/min from opposing super(60)Co sources is marrow-lethal in dogs, with only 1 of 28 animals showing hematopoietic recovery and survival. In previous studies, we have used otherwise supralethal doses of TBI, 450, 600, 700, 800, and 920 cGy, respectively, to explore approaches to treating radiation accidents. The studies found that the use of marrow allografts from DLA-identical littermates after TBI resulted in survival of 67% of irradiated dogs, either with successful and complete allografts, sustained mixed chimerism, or ultimate autologous marrow recovery after delayed rejection of the allograft. The incidence of successful and sustained allografts or stable mixed chimerism increased in direct proportion to increases in the dose of TBI. At the barely supralethal dose of 450 cGy of TBI, 3 of 10 dogs died with radiation-induced marrow aplasia after acute rejection of the marrow allografts, while seven survived-two with complete allograft, two with sustained mixed chimerism, and three with autologous marrow recovery after late rejection of the allografs. The dose of 450 cGy of TBI seemed, therefore, best suited to explore ways of enhancing allogeneic marrow engraftment.