In vitro study of alloreactivity and microchimerism after injection of dendritic cells and anti-CD4 monoclonal antibody in a combination of Lewis-Wistar Furth rats: preliminary data

Injection of donor-derived OX62+ splenic dendritic cells with anti-CD4 monoclonal antibody generates CD4+CD25+FOXP3+ regulatory T cells that prolong allograft skin survival indefinitely and abrogate production of donor-specific antibodies in a rat model

OBJECTIVE

To examine in a rat model the ability of donor dendritic cells and anti-CD4 monoclonal antibody (mAb) to generate donor-specific CD4+CD25+ regulatory T cells (Tregs) and to evaluate the capacity of these Tregs to prolong skin allograft survival and abrogate the production of donor-specific antibodies after skin grafting.

MATERIALS AND METHODS

OX62+ (nonplasmacytoid) splenic dendritic cells were isolated from Fischer rats using magnetic beads and injected (2 x 10(6)) into Lewis rat recipients with or without treatment with a nondepleting anti-CD4 (W3/25) mAb. After 4 weeks, splenic CD4+CD25+FOXP3+ T cells were harvested using magnetic beads from conditioned animals and injected (1 x 10(6)) into naïve Lewis recipients (day 1) before they received a skin graft from a Fischer (n = 4) or a third-party (Norway; n = 4) donor rat. Donor-specific antibodies were detected in recipient blood using flow cytometric cross-matches with donor lymphocytes from day 0 to day 30 after grafting.

RESULTS

After injection of conditioned CD4+CD25+FOXP3+ T cells, Lewis recipients accepted skin grafts from Fischer donors indefinitely (>100 days) but rejected third-party skin grafts. Donor-specific antibodies were detected at low levels in only 1 recipient receiving conditioned Tregs before grafting. Naive Tregs did not prolong skin graft survival.

CONCLUSION

These preliminary data suggest that splenic dendritic cells in combination with an anti-CD4 mAb induce donor-specific Tregs that indefinitely prolong allogeneic skin graft survival and inhibit donor-specific antibody production. Experiments are under way to determine whether this protocol can inhibit chronic lesions after heart transplantation in this model.

Chimerism in Lymphoid Tissues and Donor-Specific Antibody Response After Injection of Allogenic Splenic Dendritic Cells From Fischer Rats to Lewis Recipients

The aim of this work was to study cellular chimerism achieved in lymphoid tissues and production of antidonor lymphocyte antibodies after injection of splenic dendritic cells (DCs) from Fischer F344 rats to Lewis recipients, a model of chronic rejection. DCs isolated from the spleen expressed OX62 (95%), CD80 (70%), and CD86 (80%). Two doses of these nonplasmacytoid splenic DCs from Fischer rats (2 x 10(6) and 5 x 10(6)), which had been labeled ex vivo with a TRITC fluorochrome (PKH26), were injected to Lewis recipients. Using fluorescence microscopy TRITC positive cells were localized at day 15 and day 45 in frozen sections from spleen, thymus, mesenteric lymph nodes, heart, liver, kidney, and skin (n = 5 per group). Donor-specific antibodies were sought with flow cytometric crossmatches in serum samples taken at 7, 15, 30, and 45 days. TRITC-positive DCs were essentially localized in the spleen, the thymus, and lymph nodes of Lewis recipients. The majority of DCs were detected in the spleen (14.9 +/- 3.3 and 14.3 +/- 0.9 DCs/per high power field respectively at day 45). A significant number of DCs was also detected in the thymus and mesenteric lymph nodes at both times. Only some scattered TRITC-positive cells were observed in other organs. The number of DCs was stable over time and did not depend on the injected dose. A positive flow cytometric cross-match was observed at day 30 in all recipients independent of the injected dose. These data showed that 2 x 10(6) mature, nonplasmocytoid DCs from F344 rats injected to Lewis recipients induced stable chimerism in primary and secondary lymphoid organs and a humoral response to donor antigens.

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 (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.

Donor-derived hematopoietic cells in organ transplantation: a major step toward allograft tolerance?

Infusion of donor-derived cells can improve organ allograft survival in animal models. Under certain conditions, it can even induce tolerance (i.e., unlimited organ survival without any maintenance immunosuppressive therapy). Use of nonmyeloablative regimens allows engraftment of donor-derived bone marrow cells, induction of mixed chimerism, and tolerance in rodents. High doses of bone marrow cells together with anti-T-cell antibodies can even result in mixed chimerism without cytoablative host conditioning. Cultured donor-derived CD34+ cells or donor-derived immature (or even mature) dendritic cells associated with monoclonal antibodies directed against co-stimulatory molecules might also induce tolerance. Among the numerous experimental protocols leading to tolerance of solid organs in animal models, how can we find our bearings in human transplantation? Numerous problems have yet to be solved: the type and amount of donor-derived cells (including stromal cells) to be used, the timing for infusion of donor cells in keeping with organ transplantation, the route of infusion (should it be intravenous, into the portal vein?), and the conditioning regimen. The first clinical trials would appear to indicate that tolerance induction in humans using donor-derived cells is a relatively safe solution that is both promising and realistic.

Thymic dendritic cells traffic to thymi of allogeneic recipients and prolong graft survival

We have demonstrated that murine thymic dendritic cells (DCs) isolated from donor mice have the capability to home to thymi of fully allogeneic recipients after intravenous injections, where they induce T cell deletions and prolong donor-strain airway and skin graft survival. In contrast, infused splenic DCs immigrated poorly to thymi, and did not affect graft survival. These findings suggest that preferential homing may be an important mechanistic difference among subpopulations of DCs that mediate immune functions and illustrate a novel methodology that could have utility for induction of specific immunologic nonreactivity to allografts, or other disease-associated antigens.

Dendritic cells and second signal blockade: a step toward allograft tolerance?

The ultimate goal of clinical organ transplantation is to induce immunological tolerance to the allograft. Dendritic cells, the main antigen-presenting cells, are a complex system including numerous subsets, capable of inducing T-cell activation, and thus initiating an immune response, but also of inducing tolerance. In organ transplantation, the problem is even more complex because of the coexistence of dendritic cells from the donor, responsible for direct recognition of foreign antigens by T cells, and dendritic cells from the recipient, responsible for indirect antigen presentation to host T cells. Among the various methods of immunomanipulation aiming at inducing tolerance, blockade of the second signal pathway by monoclonal antibodies (anti-CD28, anti-B7, anti CD40, anti-CD40L, CTLA4-Ig) has yielded promising but incomplete results. Viral transfection of recipient immature dendritic cells encoding for immunosuppressive or apoptotic molecules, such as interleukin 10, transforming growth factor-beta, CTLA4-Ig, or Fas ligand, is also able to induce hyporesponsiveness. Another very promising method consists of associating donor cells (bone marrow cells, CD34+ cells, dendritic cells) and polyclonal or monoclonal antibodies (anti-CD4, anti-CD40L, CTLA4-Ig) to induce microchimerism and partial tolerance. Reflecting on these data would seem to be an interesting direction for future prospects.