We have previously shown that grafts with low doses of bone marrow (≤ 4 × 108 cells/kg) after 1200 R total-body irradiation (TBI) are successful in DLA-identical. but not DLA-nonidentical littermate or unrelated dogs, suggesting a locus of resistance associated with the major canine histocompatibility complex (DLA). Addition of viable donor blood leukocytes to the marrow inoculum has consistently overcome resistance, either by administration of an increased number of stem cells from the peripheral blood or through an effect mediated by lymphocytes. In-vitro-irradiated leukocytes have been ineffective. In the current study 8 dogs were given 1200 R TBI followed by 2.5 ± 1.4 × 108 marrow cells/kg and 7.7 ± 3.6 × 108 thoracic duct lymphocytes/kg from unrelated DLA-nonidentical donors. All 8 dogs showed prompt and sustained hemopoietic engraftment, and none rejected. Since canine thoracic duct lymphocytes have previously been shown not to contain hemopoietic stem cells, abrogation of resistance to canine marrow grafts appears to be related either to active suppression of residual host immunity or to enhancement of hemopoiesis by cell-cell interaction of thoracic duct lymphocytes with marrow cells. The latter mechanism is suggested by in vitro studies showing that dog thoracic duct lymphocytes cocultured with autologous marrow significantly increase the number of erythroid colonies.
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Deeg et al. (1979) studied this question.