Target-cell sensitivity to natural killer-cell lysis is determined by the expression of a novel antigen in conjunction with major histocompatibility complex class-I molecules

Necrosis and apoptosis associated with distinct Ca2+ response patterns in target cells attacked by human natural killer cells

1. During the process of cell death, rises in cytosolic Ca2+ concentration ([Ca2+]i) together with structural changes were investigated in target cells attacked by purified CD3-,CD16+ human natural killer (NK) cells. 2. In the target cell line K562, a rapid [Ca2+]i rise to 1-2 microM occurred a few minutes after NK cell-target cell contact, immediately followed by leakage of the Ca2+ indicator dye fura-2 from the cell. Cells were permeabilized, but their chromatin was not fragmented. The changes were basically consistent with those seen in necrosis induced by activated complement. 3. In the target cell line MOLT-4, which expressed the apoptosis-inducing surface antigen Fas much more strongly than K562, the majority of attacked cells displayed a [Ca2+]i rise to 0.7-1 microM followed by a slow decline, often associated with diminishing [Ca2+]i oscillations. As a whole, [Ca2+]i remained higher than 150 nM for at least 1.5-3 h (approximately 100 nM in control cells). 4. MOLT-4 cells attacked by NK cells became bubble shaped within 20 min of the main [Ca2+]i rise reaching its peak, and then both the cell and chromatin were fragmented into small pieces. These findings were basically consistent with those in apoptosis induced by a monoclonal antibody against the surface antigen Fas. 5. NK cells induced both necrosis and apoptosis in cell lines insensitive to NK cells in the presence of an antibody against the major histocompatibility complex class I (antibody-dependent cell-mediated cytotoxicity, ADCC). The distinct Ca2+ responses patterns described above corresponded to necrosis or apoptosis in different cells stimulated by the common ADCC pathway. 6. Human NK cells were found to be capable of inducing necrosis (membrane damage) or apoptosis (nuclear damage) depending on the target cell types. The characteristic Ca2+ response profile was a good indicator for distinguishing between the modes of cell death induced by the cytotoxicity of the killer cells.

Glycophorin A protects K562 cells from natural killer cell attack. Role of oligosaccharides

Glycophorin A is a protein with an abundant glycosylation (60% carbohydrate by weight), and studies have suggested that resistance of target cells to natural killing may be correlated with the level of glycophorin A expression. To assess the role of glycophorin A and of its carbohydrates in sensitivity to lysis by natural killer (NK) cells, the glycoprotein was inserted into the membrane of K562 target cells using electropulsation. Peripheral blood lymphocytes were used as effector cells. When glycophorin A was inserted into the membrane, the level of resistance to NK cell attack increased with the number of glycophorin A molecules electroinserted. The resistance to lysis was not due to a defect in target cell-effector cell binding. Electroassociation of glycophorin A did not cause a decrease in the expression of either "positive signals" for NK cells (such as CD71, CD15, and CD32 antigens) or cellular adhesion molecules (CD18, CD29, CD54, and CD58). Furthermore, electroinsertion of glycophorin A did not trigger any "negative signals," such as class I HLA antigen expression. Finally, it was shown that the sialic acid and O-linked oligosaccharides of glycophorin A did not play any role in its effect against NK cells. Conversely, the unique N-linked oligosaccharide was shown to be essential for resistance to occur.

An evolutionary conserved target cell antigen along with MHC class I molecules influences susceptibility to murine NK cell lysis

We have previously characterized a novel monoclonal antibody (mAb), termed 18C2, which binds to and inhibits the lysis of target cells by human natural killer (NK) cells. We now show that the anti-target cell mAb 18C2 also recognizes a similar structure on the murine NK sensitive target cell YAC-1, as well as on NK resistant target cells P815 and EL-4, as observed by flow cytometry. Functional studies demonstrated that the mAb 18C2 inhibited the lysis of both NK sensitive YAC-1 target cells, as well as NK resistant target cell lines P815 and EL-4 by freshly-isolated nylon wool nonadherent (NWNA) NK cells, 5-day lymphokine activated killer (LAK) cells and adherent lymphokine activated killer (ALAK) cells. The inhibitory activity of the mAb 18C2 occurred at the target cell level only. Single cell conjugate assays as demonstrated that the structure recognized by the mAb 18C2 was involved in recognition between NK cells and NK target cells, as the mAb inhibited conjugate formation between a variety of effector cells and various target cell lines tested. Further, the role of major histocompatibility complex (MHC) class I antigens in NK cell cytotoxicity was examined. We observed that target cells expressing low levels of MHC class I antigens in association with the novel target cell antigen were more sensitive to NK cell lysis, as compared to cells that co-express higher levels of MHC class I antigen and the target cell antigen. Further, the presence of this antigen across different species suggests this target cell antigen/structure to be highly evolutionarily conserved.

Tumor therapy by immune recruitment with bispecific antibodies

Many strategies for experimental immunotherapy of cancers aim at inducing and expanding tumor-specific cytotoxic T-lymphocytes. One of the most promising approaches uses bispecific monoclonal antibodies (Bi-MAbs) which are able to accumulate and activate human effector cells at the tumor site. Human resting peripheral NK- or T cells targeted by appropriate Bi-MAbs to tumor cells expressing a tumor-associated antigen display multiple signs of activation including proliferation, cytokine secretion, upregulation of cytotoxic peptides and enzymes and induce an efficient tumor cell lysis in vivo. Moreover, tumor-bearing SCID which were treated by effector cell-triggering Bi-MAbs and human peripheral blood lymphocytes had complete regressions of established tumors and most or all animals were cured by human NK-cell or T-cell cytotoxicity, respectively. Local tumor site-specific activation of T-cells was demonstrated, and enhanced granzyme and perforin expression together with the results of inhibition experiments suggest both mechanisms as the major contributors to the cytolytic machinery of Bi-MAb-mediated T-cell cytotoxicity in vivo. The encouraging results of this approach, which is able to cure animals with even advanced disseminated tumors, together with the local site-specific effector cell activation, which suggests minimal side effects, warrant the clinical evaluation of this Bi-MAb approach. As lymphocytes from tumor patients can be adequately activated by the respective Bi-MAbs, the clinical application of Bi-MAbs promises to become a safe, efficient and simple approach which should be readily applicable to the treatment of human malignancies that cannot be cured by standard regimens.