Tolerance induction after organ transplantation, "delayed tolerance," via the mixed chimerism approach: planting flowers in a battle field

Abstract

We have previously reported that peri-transplant conditioning leads to successful induction of renal allograft tolerance via the mixed chimerism approach in nonhuman primates (NHP) and humans. However, this strategy requires treatments beginning six days prior to transplantation, which limits its relevance only to living donor transplant recipients. To extend the clinical applicability of this approach, we developed a novel regimen “delayed tolerance,” with which the recipient initially undergoes organ transplantation with conventional immunosuppression, followed by conditioning and donor bone marrow transplantation (DBMT) at a later date. This approach might be likened to “planting flowers in a battle field.” That is, the recipient’s immunologic environment after organ transplantation is like a battlefield filled with hostile innate and adaptive immune-responses directed against donor antigeneic specificities. Implanting fragile donor hematopoietic progenitors into this environment and encouraging them to bloom in this vicious field requires special treatments.

In our NHP studies recently published in The American Journal of Transplantation, we showed that such “delayed tolerance,” in fact, can be induced in NHP through the mixed chimerism approach, if specific modifications to overcome/avoid donor-specific memory T cell responses are provided. These modifications include adequate depletion of CD8 memory T cells and timing of donor bone marrow administration to minimize levels of pro-inflammatory cytokines. This article addendum will provide a short summary of the original paper with our additional insights and interpretations.

Keywords: bone marrow transplantation; chimerism; kidney transplantation; memory T cell; tolerance.

Figure 1. Renal allograft survival in the delayed tolerance (deaths due to infectious complication censored). Simple compression of the previously effective 6-d therapeutic protocol into a 24-h period (D) failed to induce chimerism and also led to unacceptable toxicity. The conditioning regimen that was successful in simultaneous kidney and bone marrow transplantation (SKBMT) failed to induce long-term allograft survival in the delayed tolerance protocol at 4 mo (B). When anti-CD8 mAb was added to the original regimen, approximately 70% of recipients achieved long-term survival (A). However, this modified regimen with anti-CD8 mAb was not successful in recipients of the delayed tolerance protocol at 1 mo (C).

Figure 2. γIFN Tmem responses measure by ELISPOT after KTx. Post KTx anti-donor responses were measured by ELISPOT in various populations, Bulk(PBMCs), Tmem(CD16^-CD95⁺), CD8 Mem(CD16^-CD8⁺CD95⁺) and CD4 Mem(CD16^-CD4⁺CD95⁺). Tmem responses declined in a time dependent fashion.

Figure 3. Lymphocyte subset and chimerism induction in the Delayed Protocol. (A) In recipients treated with the conditioning regimen without anti-CD8 mAb, rapid homeostatic recovery of CD8⁺ Tmem was observed after day 5. CD4⁺ T cells were not completely deleted with a nadir around 100/mm³. (B) By adding humanized anti-CD8 mAb to the conditioning regimen, CD8 Tmems were effectively suppressed until day 30. CD4 Tmem levels were even higher after administration of the modified regimen. (C) All recipients who received the delayed protocol at 4 mo without anti-CD8 mAb (4M) failed to develop chimerism. By adding humanized anti-CD8 mAb to the conditioning regimen, recipients consistently developed multilineage chimerism despite the presence of residual CD4 Tmem.