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Haploidentical bone marrow transplantation (BMT) is associated with a high risk of severe graft-versus-host disease (GVHD). While pan-T cell depletion of the graft is the most effective means of preventing severe GVHD, it is associated with delayed recovery of T cell function leading to fatal infections. We used two related Pseudomonas exotoxin-based immunotoxins, anti-Tac(Fv)-PE38 and anti-Tac(Fv)-PE38KDEL, that both target the IL-2 receptor on activated T cells, to specifically deplete alloreactive lymphocytes against haploidentical stimulators. The functional capacity of the remaining lymphocytes was tested in proliferative assays against the original haploidentical stimulator and pooled cells from other mismatched donors (third party). We varied the recombinant toxin concentration and schedule to determine the optimum conditions for selective depletion. In 10 experiments, the mean residual reactivity after depletion was 7.6 +/- 1.4% against the haploidentical stimulator and 64.2 +/- 5% against the third party, expressed as a percentage of the undepleted response to the same stimulators. Depletion was shown to be specific for mixed lymphocyte culture (MLC)-activated lymphocytes. The immunotoxin did not affect CFU-GM growth of normal BM cells. This selective depletion of haploidentical alloreactivity could be used to prevent GVHD while conserving immune recovery following haploidentical BMT., info:eu-repo/semantics/published

Major histocompatibility complex (MHC) class I antigens on tumour cell surfaces have been shown to modulate target susceptibility to natural killer (NK) cell-mediated lysis in some, although not all, systems investigated. MHC class II expression may also affect NK cell function, but the mechanism by which MHC class II antigen regulates NK cell activity has not been fully examined. In this study we induced HLA-DR1 expression by gene transfection into the classic NK-sensitive K562 cell line to study the interaction of NK cells with MHC class II molecules and the effect of brefeldin-A (BFA), an endogenous antigen-processing pathway blocker, on NK-target cell interaction. We demonstrated that the expression of HLA-DR1 on the cell surface reduced K562 cell susceptibility to NK lysis by peripheral blood monuclear cells and a NK cell line. The effect was demonstrable in prolonged (8 hr) cytotoxicity assays and was blocked by pretreatment of target cells with anti-HLA-DR antibody. Treatment of K562 DR transfectant with BFA abrogated the resistance of K562 transfectant to NK-mediated cytolysis. These findings indicate that HLA class II molecules regulate NK cell function and target recognition, and suggest that endogenous peptides presented through MHC molecules are responsible for regulating NK cytolysis., info:eu-repo/semantics/published

We studied 19 patients with chronic myeloid leukaemia (CML) to characterize T-cell autologous responses to leukaemia. Third party stimulated alloresponses in mixed lymphocyte reactions were normal in all patients. Using the helper T-lymphocyte precursor frequency (HTLPf) assay we demonstrated a low frequency of T helper cells recognizing autologous leukaemia cells from CML blood (1/850 000) and marrow (1/965 000). However, similar frequencies to autologous bone marrow and lymphoid cells were also found in normal individuals. In 11 patients studied, HLA-matched siblings had a higher HTLPf to leukaemia than the patient's autologous response (P < 0.004). Alloresponse in mixed lymphocyte reactions (MLR), and autologous HTLPf to leukaemia, were comparable at all stages of disease progression and time from diagnosis, and independent of treatment given. In order to generate autologous cytotoxic lymphocyte responses to CML, lymphocytes were stimulated with CML cells. Cultures were fed again with CML cells and examined for cytotoxicity after 21 d. Strong lymphokine-activated killer (LAK) cytotoxicity was found against K562 and Daudi cell lines, and to Epstein-Barr virus-transformed allogeneic and autologous lymphoblastoid cell lines. Autologous leukaemia cells were lysed to a lesser extent in only 3/13 patients tested. The findings indicate that immune reactivity in CML is normal but suggest that CML cells are relatively resistant to lysis by cytotoxic T cells. The results do not support the existence of a leukaemia-specific T-cell response in CML., info:eu-repo/semantics/published