The combined actions of NK and T lymphocytes are necessary to reject an EGFP+ mesenchymal tumor through mechanisms dependent on NKG2D and IFN gamma

Better understanding of the mechanisms that mediate spontaneous immune rejections ought to be important in the quest for improvements in immunotherapy of cancer. A set of intraperitoneal tumors of mesenchymal origin that had been chemically induced in ubiquitously expressing EGFP transgenic mice provided a model in which both T and NK cells were absolutely required for tumor rejection. Tumor cells were traceable because of being fluorescent and readily grafted in RAG1(-/-) immunodeficient mice, whereas they were rejected in a majority of syngeneic C57BL/6 and EGFP-transgenic mice. Tumor-cell clones with the highest EGFP expression tended to be rejected, but a direct involvement of EGFP as the antigen recognized for the immune rejections was ruled out. Rejections were absolutely dependent on NK cells as well as on CD4(+) and CD8(+) T lymphocytes according to selective depletion studies. Furthermore, CD8(+) and CD4(+) T lymphocytes as well as NK cells were detected in the inflammatory infiltrate that mediates tumor rejection along with some DC. The effects of IFN gamma, produced at the tumor site by T and NK lymphocytes, were only required at the malignant cell level and were necessary for tumor eradication. NK recognition of tumor cells was mediated by the NKG2D-activating receptor and blocking its function in vivo partially interfered with rejection. Therefore, complete rejection of these mesenchymal tumors requires a concerted set of activities including direct tumor-cell destruction and IFN gamma production that are mediated by both NK and T cells.

Cellular liaisons of natural killer lymphocytes in immunology and immunotherapy of cancer

There is compelling evidence for the role of natural killer (NK) cells in tumor immunosurveillance and their beneficial effects on many experimentally successful immunotherapy strategies. NK cells mediate cell contact-dependent cellular cytotoxicity and produce pro-inflammatory cytokines, but do not rearrange antigen receptors. Their activation depends on various germline-encoded receptors, including CD16, which mediates recognition of antibody-coated target cells. NK cytotoxicity is checked by a repertoire of inhibitory receptors that scan adequate expression of major histocompatibility complex class I molecules on the potential target cell. Functional cross-talk of NK and dendritic cells suggests a critical role for NK cells in the initiation and regulation of cellular immunity. Considerable knowledge on the molecular basis of NK recognition/activation contrasts with a lack of successful translational research on these matters. However, there is plenty of opportunity for targeted intervention of inhibitory/activatory surface receptors and for adoptive cell therapy with autologous or allogeneic NK cells.