Natural killer (NK) cells are an important component of anti-cancer immunity, and their activity is regulated by an array of activating and inhibitory receptors. In mice, the inhibitory NKR-P1B receptor is expressed in NK cells and recognizes the C-type lectin-related protein-b (Clr-b) ligand. NKR-P1B:Clr-b interactions represent a ‘missing-self’ recognition system to monitor cellular levels of Clr-b on healthy and diseased cells. Here, we report an important role for NKR-P1B:Clr-b interactions in tumor immunosurveillance in MMTV-PyVT mice, which develop spontaneous mammary tumors. MMTV-PyVT mice on NKR-P1B-deficient genetic background developed mammary tumors earlier than on wild-type (WT) background. A greater proportion of tumor-infiltrating NK cells downregulate expression of the transcription factor Eomesodermin (EOMES) in NKR-P1B-deficient mice compared to WT mice. Tumor-infiltrating NK cells also downregulated CD49b expression but gain CD49a expression and exhibit effector functions, such as granzyme B upregulation and proliferation in mammary tumors. However, unlike the EOMES + NK cells, the EOMES ‒ NK cell subset is unable to respond to further in vitro stimulation and exhibits phenotypic alterations associated with immune dysfunction. These alterations included increased expression of PD-1, LAG-3, and TIGIT and decreased expression of NKp46, Ly49C/I, CD11b, and KLRG-1. Furthermore, tumor-infiltrating NKR-P1B-deficient NK cells exhibited an elevated dysfunctional immune phenotype compared to WT NK cells. These findings demonstrate that the NKR-P1B receptor plays an important role in mammary tumor surveillance by regulating anti-cancer immune responses and functional homeostasis in NK cells.

Invariant natural killer T cells (iNKT) are responsible for the production of pro-inflammatory cytokines which induce a systemic immune response. They are distinctive in possessing an invariant T-cell receptor that recognizes glycolipid antigens presented by the class I major histocompatibility complex-related protein CD1d, conserved across multiple mammalian species in a class of proteins well-renowned for their high degree of polymorphism. This receptor’s first identified antigen is the potent α-galactose ceramide, KRN7000, a glycosphingolipid isolated from bacteria that were found on a Japanese marine sponge. The corresponding terrestrial antigen remained unidentified until quite recently, when diacylglycerol-containing glycolipids, reported to activate iNKT cells, were isolated from Streptococcus pneumoniae. We report the total synthesis and immunological re-evaluation of these two glycolipids. The compounds are unable to meaningfully activate iNKT cells. Computational modelling shows that these ligands, while being capable of interacting with the CD1d receptor, create a different surface for the binary complex that makes formation of the ternary complex with the iNKT T-cell receptor difficult. Together these results suggest that the reported activity might have been due to an impurity in the original isolated sample and highlights the importance of taking care when reporting biological activity from isolated natural products.

<p>Invariant natural killer T cells (iNKT), a subclass of white blood cells, are responsible for the production of pro-inflammatory cytokines which induce a systemic immune response. They are distinctive in having an invariant T-cell receptor that recognizes glycolipid antigens presented by the class I major histocompatibility complex-related protein CD1d, which is conserved across multiple mammalian species in a class of proteins well-renowned for their high degree of polymorphism. This receptor’s first identified antigen is the potent KRN7000, a glycosphingolipid isolated from bacteria that were found on a Japanese marine sponge. The corresponding terrestrial antigen remained unidentified until quite recently, when diacylglycerol-containing glycolipids, reported to activate iNKT cells, were isolated from <i>Streptococcus pneumoniae</i>. We report the total synthesis and immunological re-evaluation of these two glycolipids. The compounds are unable to activate iNKT cells. Computational modelling shows that these ligands, while being capable of interacting with the CD1d receptor, create a different surface for the binary complex that makes formation of the ternary complex with the iNKT T-cell receptor difficult. Together these results suggest that the reported activity might have been due to an impurity in the original isolated sample, and highlights the importance of taking care when reporting biological activity from isolated natural products.<b></b></p>

Invariant natural killer T cells (iNKT) are responsible for the production of pro-inflammatory cytokines which induce a systemic immune response. They are distinctive in possessing an invariant T-cell receptor that recognizes glycolipid antigens presented by the class I major histocompatibility complex-related protein CD1d, conserved across multiple mammalian species in a class of proteins well-renowned for their high degree of polymorphism. This receptor’s first identified antigen is the potent α-galactose ceramide, KRN7000, a glycosphingolipid isolated from bacteria that were found on a Japanese marine sponge. The corresponding terrestrial antigen remained unidentified until quite recently, when diacylglycerol-containing glycolipids, reported to activate iNKT cells, were isolated from Streptococcus pneumoniae. We report the total synthesis and immunological re-evaluation of these two glycolipids. The compounds are unable to meaningfully activate iNKT cells. Computational modelling shows that these ligands, while being capable of interacting with the CD1d receptor, create a different surface for the binary complex that makes formation of the ternary complex with the iNKT T-cell receptor difficult. Together these results suggest that the reported activity might have been due to an impurity in the original isolated sample and highlights the importance of taking care when reporting biological activity from isolated natural products.