Blockade of CD40 pathway enhances the induction of immune tolerance by immature dendritic cells genetically modified to express cytotoxic T lymphocyte antigen 4 immunoglobulin

Background. Immature dendritic cells (DCs) have the tolerogenic potential to induce alloantigen-specific immune tolerance. Cytotoxic T lymphocyte antigen 4 immunoglobulin (CTLA41g) gene-modified immature DCs have been shown to maintain their tolerogenicity and prolong allograft survival to some extent. We investigated whether blockade of CD40 pathway by anti-CD40 ligand (L) monoclonal antibody (mAb) could enhance the immune tolerance induction by immature DCs genetically modified to express CTLA41g (DC-CTLA41g). Methods. The tolerogenic properties of DC-CTIA41g were analyzed. In the vascularized heterotopic heart transplantation murine model, 2x10(6) DC-CTLA41g were infused intravenously into recipients, with or without a concomitant administration of anti-CD40L mAb 7 days before transplantation. Host responses to donor alloantigen were quantified by mixed leukocyte reaction and CTL assays. Donor major histocompatibility complex class 11 (Ia(b)) expression in recipient lymph nodes was detected posttransplantation by semiquantitative reverse transcriptase-polymerase chain reaction. Results. The allostimulatory activity of DC-CTLA41g was reduced. DC-CTLA41g also induced alloantigen-specific T-cell hyporesponsiveness and polarized T helper 2 cytokine production. Pretreatment of the recipients with DC-CTLA41g modestly prolonged allograft survival, without long-term allograft acceptance. Combined administration of DC-CTLA41g and anti-CD40L mAb significantly prolonged cardiac allograft survival, with long-term (> 100 days) survival of 50% of the allografts in the pretreated recipients. More potent donor-specific inhibition of immune response against alloantigens and increased microchimerism. were observed in these recipients. Conclusions. Blockade of CD40 pathway with anti-CD40L mAb potentiates the tolerogenic potential of DC-CTIA41g and enhances the induction of antigen-specific immune tolerance more effectively.