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  • Title: CD4+ T Cell and NK Cell Interplay Key to Regression of MHC Class Ilow Tumors upon TLR7/8 Agonist Therapy.
    Author: Doorduijn EM, Sluijter M, Salvatori DC, Silvestri S, Maas S, Arens R, Ossendorp F, van der Burg SH, van Hall T.
    Journal: Cancer Immunol Res; 2017 Aug; 5(8):642-653. PubMed ID: 28637878.
    Abstract:
    One of the next challenges in cancer immunotherapy is the resistance of tumors to T-cell-based treatments through loss of MHC class I. Here, we show that under these circumstances, the Toll-like receptor (TLR)-7/8 ligand imiquimod, but not the TLR3 ligand poly I:C or TLR9 ligand CpG, mediated an effective antitumor response. The rejection of these immune-escaped cancers was mediated by NK cells and CD4+ T cells, whereas activated CD8+ T cells were dispensable. Application of the innate immune stimulator at a distant site activated NK cells and thereby elicited tumor-specific T-cell responses in tumor-bearing mice. Mechanistically, imiquimod activated NK cells to kill tumor cells, resulting in release of tumor antigens and induction of tumor-specific CD4+ T cells. These T helper cells provoked a strong induction of CXCL9 and CXCL10 in the tumor environment. Simultaneously, imiquimod induced the expression of the cognate chemokine receptor CXCR3 on peripheral lymphocytes. This ignited intratumoral CD4+ T-cell infiltration and accumulation, which was critical for tumor rejection; CXCR3 blocking antibodies mitigated the clinical response. In the effector phase, NK cell recruitment to tumors and their activation depended on CD4+ T cells. Together, we have uncovered a potent immune axis of tumor-specific CD4+ T cells and NK cells that eliminates escaped MHC-Ilow tumors. Cancer Immunol Res; 5(8); 642-53. ©2017 AACR.
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