Determinants recognized by human cytotoxic T cells on a natural hybrid class I HLA molecule.

The major histocompatibility complex class I HLA molecules are the primary determinants recognized by allogeneic cytotoxic T lymphocytes (CTL), and serve as restricting elements for CTL recognition of viral, chemical, or minor histocompatibility antigens. HLA-Aw69 is a naturally occurring hybrid class I molecule that we have used to investigate the regions of class I antigens involved in human CTL recognition. HLA-Aw69 appears to have resulted from an exon shuffle between two closely related class I genes: the alpha 1 domain of HLA-Aw69 is identical to that of HLA-Aw68, while the alpha 2 and alpha 3 domains are identical to HLA-A2. The determinants recognized by human allogeneic CTL clones specific for HLA-A2, -Aw68, and/or -Aw69 fall into three patterns: (a) CTL determinants are located on both the alpha 1 and alpha 2 domains; (b) interaction of the alpha 1 and alpha 2 domains results in new combinatorial determinants; (c) interaction of the alpha 1 and alpha 2 domains in the hybrid molecule results in the loss of CTL determinants that are present on both parental molecules. Thus, using human CTL clones, target cells, and HLA molecules, we show that the interaction of the alpha 1 and alpha 2 domains alters CTL determinants in ways not directly predictable from primary structure.

Human allospecific cytolytic T lymphocyte lysis of a murine cell transfected with HLA-A2.

A variety of molecules are involved in the interaction of human allospecific cytolytic T lymphocytes (CTL) with target cells. Monoclonal antibodies specific for these molecules inhibit CTL-target conjugate formation and/or lysis. To further study recognition and lysis of targets by human CTL, we used a murine mastocytoma cell line transfected with the histocompatibility leukocyte antigen (HLA)-A2 gene (P815-A2+) as a target for human HLA-A2-specific CTL. We find that only a subset of human HLA-A2-specific CTL can lyse murine P815-A2+ cells, suggesting that the murine cells may lack one or more accessory molecules needed for CTL recognition and lysis.

Absence of cell surface LFA-1 as a mechanism of escape from immunosurveillance.

During studies of T-cell recognition of autologous tumour cells, a number of tumour cell lines derived from patients with lymphoma proved to be poor stimulators of both autologous and allogeneic T-cell responses. Analysis of the tumour cell surface molecules indicated that expression of the lymphocyte-function-associated antigen, LFA-1, was lacking, whereas normal leucocytes from these patients expressed normal levels of LFA-1. Examination of other lymphoid tumours revealed that most high grade lymphomas, but not most low or intermediate grade lymphomas, do not express the LFA-1 molecule. Furthermore, in an initial survey, the tumours from 5 of 7 patients with non-relapsing large cell lymphomas expressed LFA-1 whereas only 3 of 18 patients with relapsing lymphomas had tumours that did so. These findings suggest that tumour cells lacking surface LFA-1 cannot initiate an effective immune response in vivo. This lack of immunogenicity might contribute to escape from immunosurveillance.

Identification and characterization of two novel lymphocyte function-associated antigens, L24 and L25.

We describe the function and cell distribution of two novel cell surface antigens, L24 and L25. These antigens are broadly distributed on human lymphocytes. Monoclonal antibodies specific for these molecules block lysis by Class I- and II-specific cytotoxic T lymphocytes, but do not affect any other T cell functions tested. Anti-L24 antibody immunoprecipitates a molecule composed of two disulfide-linked monomers of 140 kd each. Anti-L25 antibody immunoprecipitates three proteins of 150, 85, and 75 kd. The study of these and other function associated molecules may provide insight into mechanisms of cytotoxic T lymphocyte recognition and/or function.

Function and cell distribution of KC-1, a novel natural killer cell-associated antigen.

Natural killer (NK) cell have been implicated in immune responses to tumor and viral antigens. We describe here a monoclonal antibody, anti-KC-1, that blocks lysis of NK targets by fresh but not activated NK cells. Anti-KC-1 has no effect on cytotoxic T lymphocyte activity or on antibody-dependent cellular cytotoxicity. This antibody may be useful in the analysis of NK cell activation and the mechanism of lysis.