Tolerogenic Donor-Derived Dendritic Cells Risk Sensitization In Vivo owing to Processing and Presentation by Recipient APCs

Abstract

Modification of allogeneic dendritic cells (DCs) through drug treatment results in DCs with in-vitro hallmarks of tolerogenicity. Despite these observations, using murine MHC-mismatched skin and heart transplant models, donor-derived drug-modified DCs not only failed to induce tolerance but accelerated graft rejection. The latter was inhibited by recipient injection with anti-CD8 antibody, which removed both CD8+ T cells and CD8+ DCs. The discrepancy between in vitro and in vivo data could be explained, partly, by the presentation of drug-modified donor DC MHC-alloantigens by recipient antigen presenting cells (APCs) and activation of recipient T cells with indirect allospecificity, leading to the induction of alloantibodies. Furthermore, allogeneic MHC molecules expressed by drug treated DCs were rapidly processed and presented in peptide form by recipient APCs in vivo within hours of DC injection. Using T cell receptor-transgenic T cells, antigen presentation of injected OVA-pulsed DCs was detectable for ≤3 days whilst indirect presentation of MHC alloantigen by recipient APCs led to activation of T cells within 14 hours and was partially inhibited by reducing the numbers of CD8+ DCs in vivo. In support of this observation when mice lacking CD8+ DCs were pretreated with drug-modified DCs prior to transplantation, skin graft rejection kinetics were similar to non-DC treated controls. Interestingly, when the same mice were treated with anti-CD40L blockade plus drug-modified-DCs skin graft survival was prolonged, suggesting endogenous DCs were responsible for T cell priming. Altogether, these findings highlight the risks and limitations of negative vaccination using alloantigen bearing “tolerogenic” DCs.

Exploring cell-based tolerance strategies for hand and face transplantation

“…The possibility of non-specific immunosuppression by an expanded Treg population [190] is also a relevant consideration, as experienced with many current immunosuppressive protocols. The relative efficacy of third-party, donor, and recipient derived cells and the potential for donor regulatory cells to sensitize recipients to donor antigen is yet another hurdle that must be overcome before widespread clinical application of immunomodulatory cytotherapy [186,191].…”

Orchestration of transplantation tolerance by regulatory dendritic cell therapy or in-situ targeting of dendritic cells

“…This raises a cautionary note, however, since the quiescent status of host DC may be altered during end-stage diseases that necessitate organ transplantation. Moreover, in certain mouse models, DCreg therapies have been shown to sensitize recipients via the transfer of donor alloAg to host Ag-presenting cells (APC), followed by priming of indirect T cells and the production of IgG allo-Abs [19*,20]. Host sensitization has not however, been observed in NHP given donor-derived DCreg that prolong renal allograft survival [21**].…”

Constitutive expression of the anti-apoptotic Bcl-2 family member A1 in murine endothelial cells leads to transplant tolerance

“…We observed rapid rejection of donor hearts in recipient mice regardless of the expression of the A1 gene (mean survival time was day 6 and 7.5 for non-transgenic and ICAM-2/A1 transgenic donor hearts, respectively, p=0.08, Figure 2A). We have previously shown that 11 treatment of recipient mice with anti-CD8 antibody, to remove the contribution of CD8 + T cells to graft rejection, allowed prolongation of heart transplants in a complete mismatched transplant model [23]. In conjunction with anti-CD8 therapy treatment, given one day prior to and after heart transplantation, constitutive expression of A1 on ECs lead to significant heart transplant survival as compared to control hearts (mean survival time was 86 days versus 17 for ICAM-2/A1 hearts versus non-transgenic littermates, p<0.001 and Figure 2B).…”

“…Intra-abdominal heterotopic heart transplantation (either ICAM-2/A1 or nontransgenic grafts) was performed in CBA mice (Harlan), as previously described [23]. Heart allograft survival was assessed by direct abdominal palpation, where rejection was defined by complete cessation of cardiac impulses.…”