The use of human interleukin 4 (IL4) in the generation of tumoricidal effector cells derived from cancer patients undergoing either interleukin 2/lymphokine activated killer cells (IL2/LAK) therapy or tumor derived activated cell (TDAC) therapy was examined in the present study. Human IL4 alone did not generate LAK cells from patients undergoing IL2/LAK therapy when cultured in media containing 2% AB serum (five out of six patients). However, when the serum free medium, Aim V, was used, IL4 did generate LAK cells (eight out of nine patients), although not as cytotoxic as those activated with IL2. When cells were cultured in both IL2 and IL4 during the generation of LAK cells (3-7 days), better cell recoveries were frequently observed. The cytolytic activity of these cells against Daudi target cells was slightly reduced when compared to that response induced by IL2. This inhibition of LAK activity by IL4 was dose dependent with 1,000 U/ml IL4 producing maximal effects. This form of inhibition did not correlate with any phenotypic differences between those cells cultured in IL2 and those cells cultured in IL2 plus IL4. The IL4 mediated inhibition was also observed when the cells were cultured in Aim V medium which contains indomethacin. This inhibition induced by IL4 could not be overcome by using supra-optimal IL2. In addition to its effect during the generation of IL2 induced LAK cells, IL4 also appeared to reduce the cytolytic activity of pre-activated mature LAK cells. These results suggest that IL4 has a complex role in regulating the actions of LAK cells induced by lymphokines. When IL4 was used with IL2 during the first 5 weeks of growth of TDAC, an enhanced growth was observed when compared to the growth of TDAC when only one lymphokine was used. Besides the growth enhancement of TDAC, a better cytolytic response was observed when both lymphokines were used together. Thus, for the best growth of TDAC both IL2 and IL4 are required.
One model to explain the high frequency of alloreactive T cells proposes that allogeneic MHC molecules are recognized together with host cell-derived peptides. A model system was developed to investigate the relevance of this mechanism by expression of H-2Dd or H-2Ld in 174xCEM.T2 (T2) cells. This human cell line contains a mutation in its Ag-processing pathway that should restrict the association of endogenous peptides with cell surface class I molecules. CTL generated by stimulating C57BL/6 (H-2b) responder cells with H-2Dd or H-2Ld transfectants of the human B cell line C1R or the murine T cell lymphoma EL4 were assayed for their ability to recognize alloantigenic determinants on these transfectants. The major fraction of the H-2Dd-specific allogeneic CTL response, generated in a MLC or under clonal limiting dilution conditions, was composed of T cells that recognized H-2Dd expressed on C1R or EL4 cells, but failed to recognize this molecule on T2 cells. Clonal analysis indicated that approximately one-third of these CTL recognized determinants that were unique to H-2Dd expressed on C1R stimulator cells whereas the remainder recognized determinants that were also found on EL4 transfectants. Less than 10% of H-2Dd-reactive CTL recognized the T2 transfectant, and these clones also killed C1R-Dd and EL4-Dd. This result suggests that the great majority of H-2Dd-specific alloreactive CTL recognize determinants that are formed by a complex of H-2Dd with endogenous peptides that are absent or significantly reduced in T2 cells. Based on recognition of human or murine transfectants, these CTL exhibit some level of specificity for the structure or composition of the bound peptides. Examination of allogeneic CTL specific for H-2Ld revealed populations similar to those described for H-2Dd. In addition, a major new population was present that recognized determinants shared between C1R-Ld and T2-Ld but not present on EL4-Ld. These results are consistent with the idea that the alloreactive response to H-2Ld is also largely dependent on the presence of bound peptide. However, they also may indicate that the H-2Ld molecule expressed on T2 cells is occupied by one or more peptides that are shared with other human, but not murine, cells. The significance of these results to current models of alloreactivity is discussed.
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