Enhancement of tumor cell lysis by natural killer cells after blocking of HLA-monomorphic determinant using F(ab')2 fragment of W6/32

Interactions of NK cell receptor KIR3DL1*004 with chaperones and conformation-specific antibody reveal a functional folded state as well as predominant intracellular retention

Variable interaction between the Bw4 epitope of HLA-B and the polymorphic KIR3DL1/S1 system of inhibitory and activating NK cell receptors diversifies the development, repertoire formation, and response of human NK cells. KIR3DL1*004, a common KIR3DL1 allotype, in combination with Bw4(+) HLA-B, slows progression of HIV infection to AIDS. Analysis in this study of KIR3DL1*004 membrane traffic in NK cells shows this allotype is largely misfolded but stably retained in the endoplasmic reticulum, where it binds to the chaperone calreticulin and does not induce the unfolded protein response. A small fraction of KIR3DL1*004 folds correctly and leaves the endoplasmic reticulum to be expressed on the surface of primary NK and transfected NKL cells, in a form that can be triggered to inhibit NK cell activation and secretion of IFN-γ. Consistent with this small proportion of correctly folded molecules, trace amounts of MHC class I coimmunoprecipitated with KIR3DL1*004. There was no indication of any extensive intracellular interaction between unfolded KIR3DL1*004 and cognate Bw4(+) HLA-B. A similarly limited interaction of Bw4 with KIR3DL1*002, when both were expressed by the same cell, was observed despite the efficient folding of KIR3DL1*002 and its abundance on the NK cell surface. Several positions of polymorphism modulate KIR3DL1 abundance at the cell surface, differences that do not necessarily correlate with the potency of allotype function. In this context, our results suggest the possibility that the effect of Bw4(+) HLA-B and KIR3DL1*004 in slowing progression to AIDS is mediated by interaction of Bw4(+) HLA-B with the small fraction of cell surface KIR3DL1*004.

Resistance Against Natural Killer Cell Cytotoxicity: Analysis of Mechanisms

Target cell resistance against natural killer (NK) cell-mediated cytotoxicity obstructs NK cell-based immunotherapy of leukaemia. Several mechanisms of resistance have been described. Because of lack of simple assays for analysing these mechanisms, their relative impact on a given effector-target pair is mostly unknown. We here analysed the combination of the Granzyme B (GrB) enzyme-linked immunospot assay (ELISPOT) for the assessment of NK cell reactivity and cytotoxicity assays to estimate target cell escape mechanisms. Target cell recognition failure leads to negative GrB ELISPOT results, whereas target cell resistance shows positive GrB ELISPOT results in the absence of cytotoxicity. We confronted NK cells with the sensitive target cell line K562, and with the resistant cell lines ML2, SupB15 and Raji. ML2 cells sufficiently activated GrB-release whilst being resistant against cytotoxic granules of NK cells. Partial resistance of Raji results from the interaction of HLA class I with inhibitory killer immunglobulin-like receptors (KIR) on the NK cells. Failure of target recognition by HLA class I-KIR interaction, lacking ligands to stimulatory NK cell receptors and partial resistance to cytotoxic granules all contributed to resistance of SupB15. In conclusion, revealing the mechanisms of resistance against NK cell-mediated cytotoxicity may allow improving the results of NK-based immunotherapy.