Induction of Chimerism in Rhesus Macaques through Stem Cell Transplant and Costimulation Blockade-Based Immunosuppression

Abstract

A strategy for producing high-level hematopoietic chimerism after non-myeloablative conditioning has been established in the rhesus macaque. This strategy relies on hematopoietic stem cell transplantation after induction with a non-myeloablative dose of busulfan and blockade of the IL2-receptor in the setting of mTOR inhibition with sirolimus and combined CD28/CD154 costimulation blockade. Hematopoietic stem cells derived from bone marrow and leukopheresis products both were found to be successful in inducing highlevel chimerism. Mean peripheral blood peak donor chimerism was 81% with a median chimerism duration of 145 days. Additional immune modulation strategies, such as pre-transplant CD8 depletion, donor-specific transfusion, recipient thymectomy or peritransplant deoxyspergualin treatment did not improve the level or durability of chimerism. Recipient immunologic assessment suggested that chimerism occurred amidst donor-specific down-regulation of alloreactive T cells, and the reappearance of vigorous T-mediated alloreactivity accompanied rejection of the transplants. Furthermore, viral reactivation constituted a significant transplant-related toxicity and may have negatively impacted the ability to achieve indefinite survival of transplanted stem cells. Nevertheless, this chimerisminduction regimen induced amongst the longest-lived stem cell chimerism reported to date for non-human primates and thus represents a platform upon which to evaluate emerging tolerance-induction strategies.

Pharmacokinetics, Toxicity, and Functional Studies of the Selective Kv1.3 Channel Blocker 5-(4-Phenoxybutoxy)Psoralen in Rhesus Macaques

“…A control of CMV replication was compromised as indicated by the rise in CMV DNA by day 21. However, the observed increase in CMV DNA copies appears to be well below the levels that have been reported to be associated with CMV-related illness in RM (42,43). Importantly, CMV DNA copy number decreased to levels near baseline following the discontinuation of PAP-1 treatment and no signs of illness were evident throughout the entire course of the study.…”

GVHD after haploidentical transplantation: a novel, MHC-defined rhesus macaque model identifies CD28− CD8+ T cells as a reservoir of breakthrough T-cell proliferation during costimulation blockade and sirolimus-based immunosuppression

“…Given that the animals who developed GVHD died rapidly, while they were still lymphopenic, it was not technically possible to acquire sufficient flow-sorted putative regulatory cells from these animals to verify their suppressor function with the use of in vitro suppression assays. 22 Thus, these results cannot be taken as proof that CD4 ϩ T cells with regulatory function expanded during GVHD. However, they are suggestive that counterregulatory forces may be activated during the rapid, T-cell expansion and severe tissue destruction that occurs during untreated GVHD.…”

“…22 If PCR-based chimerism determination was not possible, divergent donor-and recipient-specific microsatellite markers were used, 31 by comparing peak heights of the donor-and recipient-specific amplicons. T-cell chimerism was determined by sorting CD3 ϩ /CD20 Ϫ (T cells) with a FACSAria cell sorter (Becton Dickinson) before molecular analysis for donor-specific microsatellite amplicons or PCR products.…”

“…21 In addition, in both primate and clinical studies of solid-organ transplantation, significant rejection risks have been noted despite costimulation blockade, with adjunctive memory T cell-directed therapies sometimes required for prolonged allograft survival. 8,22,23 Furthermore, although anergy to GVHD-inducing alloantigens can be induced by ex vivo exposure of BM to recipient antigen-presenting cells (APCs) in the presence of CTLA4Ig, 24 in both murine and canine models of GVHD, results of investigations into the efficacy of in vivo CD28-and CD40-directed costimulation blockade have been mixed: both successes and failures have been documented for the inhibition of GVHD. [25][26][27][28][29][30] Understanding the mechanisms underlying both the successes and failures of costimulation blockade for GVHD prevention will be critical if this strategy is to be used widely in clinical transplantation.…”

Frontiers in Nephrology

“…97 It has also been used as a means to facilitate chimerism. 98,99 Although many co-stimulatory molecules have been identified and tested experimentally, only one, CD28, is targeted by a clinically available agent. CD28 is the most studied T cell co-stimulatory receptor, and its inhibition has been shown to mediate the classic effects of costimulation blockade (reviewed by Salomon and Bluestone 100 ).…”