Canine allogeneic bone marrow transplantation. Technique and variables influencing engraftment

We have studied the toxicity and immune suppression of supralethal total body irradiation (800-2000 rads, 60Co) at three dose intensities (10 rads/min, 49 rads/min, and 100 rads/min). In 79 intensively supported radiation control animals, the LD50(5) (tn 5 days) for these dose intensities is estimated to be 1556, 941, and 921 rads, respectively. A biomodal pattern of early (median 4 days) and late (median 9 days) deaths was observed corresponding to histopathological evidence of the intestinal and hematopoietic radiation syndromes. Random donor bone marrow transplants were performed in 83 animals to test immune suppression afforded by 800 rads and 1000 rads at dose intensities of either 10 rads/min or 49 rads/min. Bone marrow cell dose was varied to analyze its effect on engraftment. A greater degree of immunosuppression with less toxicity was achieved at the lower dose intensity. A minimum dose of 3-5 X 10(8) nucleated allogeneic bone marrow cells/kg (readily obtainable from living donors) resulted in a high percentage of engraftment with lethal graft-versus-host disease following conditioning with 1,000 rads midplane at 10 rads/min, the optimum regimen employed.