Abstract
BackgroundRejection of transplanted tumors by the immune system is a rare event in syngeneic hosts, and is considered to be dependent on the local interaction of defensive immune reactions and tumor tolerance mechanisms. Here, we have enlisted the aid of a unique set of embryo-aggregated lineage chimeric mice derived from C57/BL6 and FVB donors to study the interplay between local and systemic tumor immunity and tolerance in rejection of mouse B16 melanoma cells, syngeneic to the C57/BL6 donor strain.MethodsTwo variants of embryo-aggregated chimeric mice with either variable or no contribution of C57-derived cells to their skin were generated by the fusion of different ratios of morula stage blastomers. Chimeric mice were analyzed for s.c. growth of B16 tumors in comparison to their respective donor strains as well as normal F1 hybrids, and the relative frequencies of cellular components of the immune system by FACS analysis of peripheral blood or lymph node cells.ResultsB16 tumors grew significantly faster in mice with full chimerism in their skin as compared to syngeneic C57 or semi-syngeneic C57 × FVB F1 hosts. In contrast, s.c. tumor growth was either absent or significantly reduced in chimeric mice lacking C57-derived cells in their skin, but tolerant to C57 tissue in other organs. Comparison of the relative frequencies of various immune cells in the periphery via FACS-analysis did not reveal any significant differences between the two types of chimeric mice with respect to their donor strains.ConclusionOur data suggest a complex interplay between mechanisms of local peripheral tolerance and innate antitumor mechanisms possibly involving NK cell allorecognition as a basis for the differential growth or rejection of B16 tumors in these unique chimeric mice, which we suggest to constitute a valuable new model system for the study of immune-mediated tumor rejection.
Highlights
Rejection of transplanted tumors by the immune system is a rare event in syngeneic hosts, and is considered to be dependent on the local interaction of defensive immune reactions and tumor tolerance mechanisms
Variations in chimerism were especially notable in the contribution of C57 to the skin of chimeric mice, ranging from black and white segmented over minor patches of black to pure white (FVB) coat colour (Fig. 1)
Individual chimeric mice showed dramatic differences in terms of growth or rejection of s.c. injected B16 melanoma cells of C57 origin, which was clearly correlated with the level of skin chimerism (Table 1)
Summary
Rejection of transplanted tumors by the immune system is a rare event in syngeneic hosts, and is considered to be dependent on the local interaction of defensive immune reactions and tumor tolerance mechanisms. As shown in a series of elegant studies by North and colleagues in the 1980's [2], establishment of a tumor-specific cytotoxic T cell response per se usually is not sufficient to eradicate transplanted tumors or restrict their growth. This state of "concomitant" tumor immunity has been attributed to tumor tolerance via active immune suppression mechanisms exerted by tumorspecific suppressor T cells [3,4]. Tumors may grow and eventually kill their hosts despite systemic antitumor immunity, due to localized tumor-antigen-specific suppression of the co-existing protective immune response
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