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The potential immunosuppressive effect of an anti-CD154 monoclonal antibody (mAb) on the pathogenic autoreactive T-cell response was evaluated using an in vitro culture system with glycoprotein IIb/IIIa (GPIIb/IIIa)-reactive T cells from patients with immune thrombocytopenic purpura (ITP). The anti-CD154 mAb did not inhibit T-cell proliferation, but suppressed anti-GPIIb/IIIa antibody production, in bulk peripheral blood mononuclear cell cultures stimulated with GPIIb/IIIa. Repeated antigenic stimulation of GPIIb/IIIa-reactive CD4(+) T-cell lines in the presence of anti-CD154 mAb resulted in the loss of proliferative capacity and helper function for promoting anti-GPIIb/IIIa antibody production. These anergic T-cell lines showed a cytokine profile of low interferon gamma and high interleukin 10 and suppressed anti-GPIIb/IIIa antibody production. Our results indicate that blockade of the CD40/CD154 interaction induces generation of autoantigen-specific anergic CD4(+) T cells with regulatory function and could be a therapeutic option for suppressing pathogenic autoimmune responses in patients with ITP.

Cytotoxic T lymphocytes (CTLs) can kill target cells by the granule/exocytosis pathway or the Fas-mediated apoptosis pathway. The sensitivity of chronic lymphocytic leukemia (CLL) B cells to CTL-mediated apoptosis before and after CD40 activation was examined. Resting or CD40-activated CLL cells were found to be equally sensitive to class I-restricted CTL-mediated killing. Despite expressing CD95, the CD40-activated CLL target cells were found to be resistant to apoptosis induced by CH11, an IgM CD95 monoclonal antibody (mAb). Consistent with this, inhibitors of caspases, which are involved in the Fas-induced apoptotic pathway (eg, N-carbobenzoxy-Val-Ala-Asp fluoromethyl ketone [z-VAD-fmk]), were unable to block destruction of CLL target cells by CTL. In addition, preincubation of the effector T cells with the anti-Fas ligand mAb NOK-2 failed to inhibit their subsequent ability to kill CLL target cells. On the other hand, CTL activity was blocked by inhibitors of the granule exocytosis pathway such as ethylene-glyco-tetra-acetic acid or concanamycin A. These results indicate that CD40 activation does not impair the sensitivity of CLL cells to Fas-independent CTL-mediated apoptosis. (Blood. 2000;95:3853-3858)

Because activated T cells were previously shown to induce proliferation of human normal B-cell precursors (BCP) via the CD40 pathway, we investigated the effects of T cells on leukemic blasts isolated from patients with B-lineage acute lymphoblastic leukemia (BCP-ALL). An anti-CD3 activated human CD4+ T-cell clone was found to induce significant call proliferation in four of nine BCP-ALL samples analyzed. In one of these cases, the T-cell effect was clearly dependent on interaction between CD40 and its ligand. Accordingly, a more thorough analysis was performed on this particular leukemia (case 461, adult early pre-B-ALL, mBCR+, Philadelphia+, i(9q)+). Thus, autologous CD4+ T cells isolated from the patient were also able to induce CD40-dependent proliferation of the leukemic blasts. Analysis of the phenotype after coculture showed that, among the CD19+ cells, a proportion gradually lost expression of CD10 and CD34, whereas some cells acquired CD23. In addition, and in contrast with normal BCP, activated T cells promoted maturation of a subset of the case 461 leukemic cells into surface IgM+ cells. The leukemic origin of the cycling and the maturing cells was assessed by the presence of i(9q), a chromosomal abnormality associated with this leukemia and evidenced by fluorescence in situ hybridization. Taken together, these results show that leukemic BCP can be activated via CD40 but that not all cases display detectable stimulation in response to T cells despite their expression of CD40. In addition, the present data suggest that CD4+ T cells could potentially play a role in the physiology of BCP-ALL.