SIGNAL REQUIREMENT FOR INDUCTION OF MHC-UNRESTRICTED ANTITUMOR CYTOTOXICITY OF HUMAN T-CELL CD4+ CD8+ SUBPOPULATIONS/

The role of consignalling in the generation of MHC-unrestricted cytoto xicity of T cells was studied with CD4(+) and CD8(+) sub-populations h ighly purified (> 98%) by immunomagnetic cell sorting using OKT4 mab, Dynal anti-CD4 mab, OKT8 mab, Dynal anti-CD8 mab, and OKT3 mab. Cytoto xicity was determined in 4 h cytotoxicity assays against K562 tumor ce lls known to lack expression of MHC class 1 and class 2 antigens, thus avoiding interference with anti-CD4- or anti-CD8-mediated signalling. Signal transfer was induced via CD4, CD8, CD3, IL-2 receptor and RG r eceptor specifically interacting with a plant rhamnogalacturonan (RG). In CD8(+) cells, the first signal delivered by the set-ring mab (immo bilized OKT8 or Dynal anti-CD8 or OKT3) only induced low MHC-unrestric ted cytotoxicity but committed the cells to develop largely enhanced c ytolytic potential upon stimulation with a second (IL-2 or RG) or thir d (OKT3, IL-2, RG) signal. The highest cytolytic potential was achieve d by cumulative signalling via CD8, CD3, IL-2 receptor and RG receptor : The generation of MHC-unrestricted cytotoxicity of CD8(+) cells corr elated with increased effector cell/target cell conjugate formation. I n CD4(+) cells, OKT4 as sorting mab induced very low cytolytic potenti al, and a moderate committment to IL-2 signals but a stronger one to R G signals, yielding further cytotoxicity enhancement. The highest cyto lytic potential was obtained by cumulative signalling via CD4, IL-2 re ceptor and RG receptor. Dynal anti-CD4 mab was inefficient and OKT3, a s sorting mab of CD4(+) cells from CD8-depleted PNAC, appeared to bloc k subsequent OKT4-induced generation of MHC-unrestricted cytotoxicity by delivering a negative signal. Immobilized OKT3 as second signal pre sent in cultures of OKT4-sorted CD4(+) cells was inefficient. Surprisi ngly, soluble OKT3 together with IL-2 delivered a positive signal in c ultures of OKT4-sorted CD4(+) cells.