Thymectomy and Thymic Grafts in Mouse Viral Leukemia.

Abstract

Gross passage leukemia virus A, injected into Z mice (less than 1 week old) produced leukemia in 15 of 22 intact mice (mean latency 135 days); in 0 of 17 mice thymectomized at 4 to 6 weeks of age; and in 2 of 20 mice thymectomized and grafted with one lobe of normal thymus from uninjected Z mice (109, 225 days). Two of 19 uninjected Z mice, thymectomized and grafted with thymus from virus-injected mice, developed leukemia with tumor in the grafts (274, 369 days). None of 18 normal Z mice developed leukemia. In similar experiments in Ak/Z mice, leukemia occurred in 14 of 15 virus-injected intact mice (mean latency 110 days), and in 4 of 25 virus-injected thymectomized mice. Incidence of spontaneous leukemia in uninjected Ak/Z mice was about 60% (10 to 12 months). None of 18 uninjected Ak/Z mice, thymectomized at 6 to 8 weeks of age, developed lymphoid leukemia. Twenty-four of 44 virus-injected thymectomized mice, each grafted with thymus from uninjected young Ak and Z mice, developed generalized leukemia at less than 1 year of age. Six had a large lymphoma at Z thymus graft site, one at Ak graft site also. Seven others had a large lymphoma at Ak graft site only. Three others had a large tumor at Ak graft and a small tumor at Z graft sites. The remaining 8 had generalized leukemia; in some, small thymic grafts were infiltrated with leukemic cells. Bioassays for immunogenetic character of 22 of the 24 leukemias and tumors arising in thymic grafts were performed on Ak, Z, and Ak/Z mice. Three leukemias failed to grow in any recipients. In 8 cases, grafts took in Ak/Z only (excluding those with uncertain typing); in 4 cases, in Ak and Ak/Z mice; and in 1 case in Z and Ak/Z mice. Spontaneous Ak leukemias grew in Ak and Ak/Z, but not in Z mice. Virus-induced Z leukemias grew in Z and Ak/Z, but not in Ak mice. Virus-induced Ak/Z leukemias grew in Ak/Z but, unexpectedly, 3 of 4 grew also in Z, and 2 of these also in Ak mice. These data indicate that a thymic factor, other than cell, supplied by normal thymus grafts may carry to completion viral leukemogenesis prevented by thymectomy.