Abstract: Single chain polypeptide forms of HLA-E useful in manipulating and ascertaining natural killer (NK) cell function are disclosed. The single chain trimer (SCT) form of HLA-E is comprised of the signal peptide from human beta-2 microglobulin (&bgr;2m), a canonical HLA-E binding peptide, a fifteen amino acid linker, mature human &bgr;2m, a twenty amino acid linker, and mature HLA-E heavy chain. The single chain dimer (SCD) form of HLA-E is comprised of the signal peptide from human &bgr;2m, mature human &bgr;2m, a twenty amino acid linker, and mature HLA-E heavy chain. The disclosed polypeptides can be used to inhibit NK cell cytotoxicity and cytokine production, enumerate and/or purify NK cell subsets, and identify biologically relevant HLA-E ligands. The disclosed HLA-E SCT and SCD nucleic acid sequences can be used a platform for synthesis of additional biologically active major histocompatibility class I protein single chain trimers and dimers.

Abstract: The invention comprises exploiting viral stealth mechanisms to eliminate pig MHC class I cell-surface expression. PK(15) (pig kidney) cells stably transfected with the Herpes Simplex Virus (HSV) ICP47 gene [PK(15)-ICP47 cells] exhibited a dramatic reduction of MHC class I cell-surface expression when compared to untransfected PK(15) cells. To test the effect of down-regulation of porcine MHC class I on human cellular immune responses, a human CD8+ enriched T cell line (anti-PK15 T cells) with reactivity towards PK(15) cells was derived by repeated stimulation of human T cells with PK(15) cells stably transfected with the co-stimulatory molecule B7.1 [PK(15)-B7.1 cells]. Anti-PK15 T cells efficiently lysed PK(15) cells but not PK(15)-ICP47 (class I negative) cells. Consistent with effector function, anti-PK15 T cells showed a robust proliferative response to PK(15)-B7.1 cells but did not proliferate at all to PK(15)-B7.1 cells which also expressed HSV ICP47.