Immunological reconstitution of nude mice transplanted with human malignant tumours

The effects of neonatal murine thymus grafts implanted in nude mice previously transplanted with three different human malignant tumours were studied. Reconstitution resulted in tumour rejection, which started 2-3 weeks after thymus implantation and was complete after 3-6 weeks. The rejection process showed a characteristic histologic picture with 3 phases, an early, an intermediate, and a late phase, which were similar in the 3 tumour types examined. Histological examination of lymphoid tissues of successfully thymus grafted mice showed reconstitution of varying degrees. Numbers of plaque forming cells (PFC) of the spleen of tumour transplanted, thymus grafted mice were equal to or higher than the numbers of PFC in normal BALB/c controls. Mice, thymus grafted only always showed intermediate PFC-values. Responses to the T-cell mitogen, phytohaemagglutinin-P (PHA) were only partially reconstituted, whether the nude mice were tumour transplanted or not. In addition tumour rejection in tumour-bearing nude mice treated with T-cells only, was studied. The rejection process was similar to that observed when a whole thymus gland was implanted. Finally, implantation of embryonic bovine thymus grafts was performed in tumour transplanted nude mice. When these grafts were accepted, tumours were also rejected. Possible mechanisms of reconstitution and the reasons for the varying results are discussed.