BI-51013

Activation and translocation of protein kinases C is a key event in the regulation of T lymphocyte activation, proliferation and function. Stimulation of human peripheral blood lymphocytes with the monoclonal antibody BMA 031 raised against the T cell antigen receptor led to a bimodal activation of protein kinases C. The immediate activation and translocation of the protein kinase C isoform PKC-alpha was followed by activation and translocation of the protein kinase C-beta isoenzyme after 90 min of stimulation. Pretreatment of the cells with cholera toxin for 90 min completely abolished activation of protein kinase C-alpha. In sharp contrast, activation and translocation of protein kinase C-beta was not influenced by the bacterial toxin, suggesting that activation and translocation of different protein kinase C isoenzymes are regulated by distinct mechanisms of transmembrane signalling coupled to the T cell antigen receptor/CD3 complex. The expression of high affinity IL-2 receptors was completely inhibited by cholera toxin, while IL-2 synthesis and secretion were not influenced in BMA 031-stimulated human lymphocytes. Extensive control experiments have shown that the effects of cholera toxin were not mediated by its B subunit, and were independent of elevation of intracellular cAMP concentration, suggesting that cholera toxin interfered with a signalling pathway leading to activation of protein kinase C-alpha, which could be responsible for the inhibition of IL-2 receptor expression. This hypothesis was substantiated by the finding that upon introduction of antibodies against protein kinase C-alpha, IL-2 receptor gene expression was completely suppressed. The results suggest, that protein kinase C-alpha might be the major protein kinase C isoenzyme of a signal transduction cascade regulating IL-2 receptor expression in stimulated human lymphocytes.

Acute graft-versus host disease (GVHD), one of the major complications of allogeneic bone marrow transplantation (BMT), occurs in 30-50% of all patients transplanted from HLA-identical sibling donors and in 50-80% of all patients transplanted from an unrelated or HLA-mismatched family donor, despite GVHD prophylaxis with methotrexate and cyclosporin. We report our experience with OKT3/BMA031 treatment in 14 patients with severe steroid-resistant GVHD following allogeneic BMT. Three of 5 patients treated in the early post-transplant period with OKT3 remitted and 2 of 3 became long-term survivors. Two patients treated for extensive chronic GVHD showed only minor responses. Five of 7 patients treated with BMA031 showed a partial remission; no complete remission was seen after treatment with this antibody. Shortly after the introduction of OKT3 or BMA031 therapy a rapid decline of the lymphocyte count, especially the CD3+ subset, was observed coinciding with a relative increase of CD56+ lymphocytes and of gamma/delta TCR+ T cells. Increasing numbers of CD3+ lymphocytes preceded recurrence of acute GVHD in three patients. In contrast, persisting CD3-lymphocytopenia was associated with complete clearance of acute GVHD. The incidence of infectious complications following OKT3 or BMA031 therapy was high (42%). Thus, to improve treatment results of severe acute GVHD, prophylactic or pre-emptive strategies are required to reduce the rate of fatal viral and fungal infections.