17 Cooperstown beagles of known DL-A genotypes were exposed to supralethal total body irradiation and received a bone marrow allograft from a DL-A-identical donor; 11 littermate and 6 nonlittermate donor-recipient pairs were studied. The recipients are surviving uneventfully for 315, 364, 424, 440, 531, 531, 584, 605, 625, 635, and 649 days in the littermate group and for 211, 279, 280, 368, 479, and 480 days in the nonlittermate group. The radiation chimeras underwent bilateral nephrectomy and received a kidney allograft obtained from their respective marrow donor within 43–120 days after bone marrow transplantation. The renal allografts are surviving for 191, 200, 221, 234, 313, 349, 361, 377, 378, 405, 441, 444, 482, 557, 580, 581, and 586 days, respectively. 12 of 13 skin allografts obtained from the marrow donor are at present surviving in the recipients for 107, 110, 110, 110, 116, 122, 128, 143, 143, 162, 178, and 199 days, respectively; one graft was rejected at 84 days. In contrast, the radiation chimeras rejected 25 skin allografts obtained from DL-A-incompatible donors within 10.5–21 days (MST = 15.2 days). Skin transplants obtained from DL-A-identical siblings of the bone marrow donors were rejected within 20–36 days (MST = 25.8 days) in recipients of bone marrow cells obtained from littermate donors. Recipients of nonlittermate bone marrow transplants accorded such allografts a prolonged survival time of 27–76 days (MST = 56.2 days). Prospective selection of genotypically DL-A-identical donor-recipient pairs results in the regularly reproducible long-term survival of bone marrow allografts. The radiation chimeras produced in this manner have developed a donor-specific state of unresponsiveness to kidney and skin allografts. The results are consistent with the existence in the canine species of at least three closely linked genetic systems relevant to transplantation, including DL-A, MLC, and a possible bone marrow transplantation locus.

The establishment of a closely bred colony of beagles with known leukocyte group phenotypes has permitted an assessment of the role of leukocyte group antigens in conditioning the survival of renal allografts in the unmodified host. 22 kidney transplants obtained from leukocyte group-compatible donors were accorded a mean survival time of 25.5 days, as compared with 13.1 days for 27 transplants obtained from incompatible donors. Donor-recipient coefficients of correlation and Swisher erythrocyte group incompatibilities did not appear to affect the observed results. The mean survival time of 21 renal allografts performed in randomly selected mongrel dogs was 9.5 days. Availability of a carefully characterized and phenotyped canine population may be useful in further studies of the comparative immunogenicity of the major transplantable organs, and of methods designed to facilitate prolonged organ transplant survival in the mammalian host.