Recombinant T cell receptors with defined specificity against tumor cells are a promising experimental approach in the elimination of residual leukemia and lymphoma cells. It is so far unresolved whether regulatory T cells with suppressor activities impair the efficiency of cytolytic T cells grafted with a recombinant immunoreceptor. The frequency of regulatory T cells is highly increased in tumor patients and their suppressive function seems to play a role in the fail of an autologous T cell response against the malignant cells.
In this study we analyzed the antigen-triggered, specific activation of receptor grafted T cells in the presence or absence of regulatory CD4+CD25high T cells. CD3+ T cells were grafted with CEA-specific immunoreceptors containing the CD3-zeta signaling domain for T cell activation. Co-cultivation of receptor grafted effector T cells together with regulatory T cells repressed proliferation of the effector cells and decreased IL-2 secretion. Secretion of IFN-gamma and IL-10 was not impaired. Interestingly, the cytotoxicity of grafted effector T cells towards CEA-expressing tumor cells was not impaired by regulatory T cells in vitro.
To evaluate the relevance in vivo, we used a Crl:CD1 Nu/Nu mouse model to assess growth of CEA+ tumor cells in the presence of receptor grafted effector T cells and of regulatory T cells. Mice inoculated with tumor cells together with CD3+ effector T cells without immunoreceptor and regulatory T cells developed earlier tumors with faster growth kinetics compared to mice that were inoculated with tumor cells, CD3+ T cells and CD4+CD25- control T cells. Using effector T cells that were equipped with a recombinant CEA-specific CD3-zeta immunoreceptor, 2 of 5 mice developed a tumor in the presence of regulatory T cells while none of the mice developed a tumor in the absence of regulatory T cells.
Taken together, regulatory T cells obviously impair an antigen-specific, anti-tumor T cell attack in vivo. This seems to be due to repression of proliferation of the effector T cells and not to diminished cytotoxicity. These findings have major impact on the design of clinical studies involving adoptively transferred effector T cells.
Disclosure: No relevant conflicts of interest to declare.