Blockade of the CD40-CD40 ligand pathway potentiates the capacity of donor-derived dendritic cell progenitors to induce long-term cardiac allograft survival

Background. Failure of costimulatory molecule deficient donor dendritic cells (DCs) to induce indefinite allograft acceptance may be a result of the "late" up regulation of these molecules on the DCs after interaction with host T cells. Ligation of CD40 on antigen-presenting cells by its cognate ligand CD40L is thought to induce expression of CD80 (B7-1) and CD86 (B7-2). We examined the influence of anti-CD40L monoclonal antibody (mAb) on the capacity of donor-derived DC progenitors to induce long-term allograft survival. Methods, High purity DC progenitors were grown from B10 (H2(b)) mouse bone marrow in granulocyte-macrophage colony-stimulating factor and transforming growth factor beta 1 (TGF beta 1). Mature DC were propagated in granulocyte-macrophage colony-stimulating factor and interleukin-4. Their phenotype was characterized by flow cytometric analysis and their function by mixed leukocyte reactivity. Anti-donor cytotoxic T lymphocyte activity in grafts and spleens of vascularized heart allograft recipients was also assessed. Results. The TGF beta-cultured cells were (1) DEC 205-positive, MHC class II-positive, CD80(dim), CD86(dim), and CD40(dim), (2) poor stimulators of naive allogeneic T-cell proliferation, and (3) able to prolong significantly B10 cardiac allograft survival in C3H (H2(k)) recipients when given (2x10(6) i.v.) 7 days before organ transplantation (median survival time [MST] 26 days vs. 12 days in controls, and 5 days in interleukin-4 DC-treated animals). Their allostimulatory activity was further diminished by addition of anti-CD40L mAb at the start of the mixed leukocyte cultures. Anti-CD40L mAb alone (250 mu g/mouse, i.p.; day -7) did not prolong cardiac graft survival (MST 12 days). In contrast, TGF beta-cultured DCs + anti-CD40L mAb extended graft survival to a MST of 77 days, and inhibited substantially the anti-donor cytotoxic T lymphocyte activity of graft-infiltrating cells and host spleen cells assessed 8 days after transplant. Conclusions. The CD40-CD40L pathway appears important in regulation of allogeneic DC-T-cell functional interaction in vivo; its blockade increases markedly the potential of costimulatory molecule-deficient DCs of donor origin to induce long-lasting allograft survival.