Cardiac allograft survival in rhesus primates treated with combined total lymphoid irradiation and rabbit antithymocyte globulin.

Eighteen abdominal heterotopic cardiac allografts were performed in outbred rhesus primates. For immunosuppression seven animals received six 100-rad/day total lymphoid irradiation (TLI) doses the week preceding transplant and three 3-mg/kg i.m. rabbit antithymocyte globulin (RATG) doses on postoperative days -1, 0, and +1; five animals were given this RATG dose but no irradiation; three were given TLI alone; and three were given no immunosuppressive therapy. Circulating T lymphocyte counts were monitored in all animals (rosettes). Graft survival in the combined TLI-RATG therapy group (169 +/- 15 days) was significantly greater than in untreated (11 +/- 1 days), RATG alone (22 +/- 12 days), or TLI alone (38 +/- 6 days) treated animals (P less than 0.001, 0.0001, and 0.001, respectively). The animals receiving combined TLI-RATG therapy also achieved significantly greater and more prolonged T lymphopenia than that obtained in the other three groups. Six of seven cardiac allografts placed in animals receiving TLI-RATG therapy were removed electively before cessation of electrical activity; however, in four of these rejection pathology was noted. Thus, it seems that combined TLI-RATG therapy may be of benefit in the management of transplant recipients, but its use will probably not abolish these patients' requirements for immunosuppressive maintenance measures.