Background: Immature dendritic cells (DCs) have the tolerogenic potential to induce alloantigen-specific immune tolerance. Cytotoxic T lymphocyte antigen 4 immunoglobulin (CTLA4Ig) 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 CTLA4Ig (DC-CTLA4Ig).
Methods: The tolerogenic properties of DC-CTLA4Ig were analyzed. In the vascularized heterotopic heart transplantation murine model, 2 x 10(6) DC-CTLA4Ig 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 II (Iab) expression in recipient lymph nodes was detected posttransplantation by semiquantitative reverse transcriptase-polymerase chain reaction.
Results: The allostimulatory activity of DC-CTLA4Ig was reduced. DC-CTLA4Ig also induced alloantigen-specific T-cell hyporesponsiveness and polarized T helper 2 cytokine production. Pretreatment of the recipients with DC-CTLA4Ig modestly prolonged allograft survival, without long-term allograft acceptance. Combined administration of DC-CTLA4Ig 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-CTLA4Ig and enhances the induction of antigen-specific immune tolerance more effectively.