Establishment Of Hematopoietic Chimerism Research Articles

Mechanisms of Tolerance Induction by Hematopoietic Chimerism: The Immune Perspective.

SummaryHematopoietic chimerism is one of the effective approaches to induce tolerance to donor‐derived tissue and organ grafts without administration of life‐long immunosuppressive therapy. Although experimental efforts to develop such regimens have been ongoing for decades, substantial cumulative toxicity of combined hematopoietic and tissue transplants precludes wide clinical implementation. Tolerance is an active immunological process that includes both peripheral and central mechanisms of mutual education of coresident donor and host immune systems. The major stages include sequential suppression of early alloreactivity, establishment of hematopoietic chimerism and suppressor cells that sustain the state of tolerance, with significant mechanistic and temporal overlap along the tolerization process. Efforts to devise less toxic transplant strategies by reduction of preparatory conditioning focus on modulation rather than deletion of residual host immunity and early reinstitution of regulatory subsets at the central and peripheral levels. Stem Cells Translational Medicine 2017;6:700–712

Combined Bone Marrow and Kidney Transplantation for the Induction of Specific Tolerance.

The induction of specific tolerance, in order to avoid the detrimental effects of lifelong systemic immunosuppressive therapy after organ transplantation, has been considered the “Holy Grail” of transplantation. Experimentally, tolerance has been achieved through clonal deletion, through costimulatory blockade, through the induction or infusion of regulatory T-cells, and through the establishment of hematopoietic chimerism following donor bone marrow transplantation. The focus of this review is how tolerance has been achieved following combined bone marrow and kidney transplantation. Preclinical models of combined bone marrow and kidney transplantation have shown that tolerance can be achieved through either transient or sustained hematopoietic chimerism. Combined transplants for patients with multiple myeloma have shown that organ tolerance and prolonged disease remissions can be accomplished with such an approach. Similarly, multiple clinical strategies for achieving tolerance in patients without an underlying malignancy have been described, in the context of either transient or durable mixed chimerism or sustained full donor hematopoiesis. To expand the chimerism approach to deceased donor transplants, a delayed tolerance approach, which will involve organ transplantation with conventional immunosuppression followed months later by bone marrow transplantation, has been successful in a primate model. As combined bone marrow and organ transplantation become safer and increasingly successful, the achievement of specific tolerance may become more widely applicable.

Donor-Specific Tolerance Is Induced after Nonmyeloablative Conditioning and Allogeneic Hematopoietic Cell Transplantation and May Persist after Graft Rejection.

The association between stable hematopoietic chimerism and donor specific tolerance (DST) for solid organ grafts was demonstrated clinically and in different experimental models. However, the existing data also demonstrate that the establishment of hematopoietic chimerism does not always correlate with the development of DST, especially for skin grafts. As these issues could have major implications for organ transplantation in general, the present study was undertaken to assess DST in recipients with transient or stable hematopoietic cell (HC) chimerism established after nonmyeloablative conditioning regimens. In a canine model of allogeneic hematopoietic cell transplantation (HCT) after nonmyeloablative conditioning, DST to skin grafts was evaluated in DLA-identical recipients with stable mixed hematopoietic chimerism (MC) (n=11), or following transient HC engraftment (n=22). There was a significant improvement in the survival of DLA-identical HC donor-derived skin grafts in recipients with stable MC compared to normal recipients (n=7; P<0.0001). However, HC donor-derived skin grafts in 4 recipients with MC developed an inflammatory reaction without skin graft loss consistent with a chronic rejection process. Survival of DLA-identical HC donor-derived skin grafts was also significantly prolonged in recipients after transient HC engraftment compared to normal recipients (P=0.002). However, a chronic inflammatory process without graft loss developed in all of the HC donor-derived skin grafts from this group. An increased time to rejection of the hematopoietic graft was significantly associated with an improved survival of the subsequent skin graft (P=0.02). The time to rejection of third-party (DLA-nonidentical) skin grafts (n=40) was the same in recipients with stable MC and previous HC graft as well as normals (median- 8 days). Autologous skin grafts (n=40) survived for the duration of follow-up without developing chronic inflammation. Extended HC donor-specific skin graft survival (>15 days) was predictive of subsequent stable engraftment at second HCT in recipients with previous graft rejection after first HCT. Five of 6 dogs with extended survival of the skin graft beyond day 15 became stable MC after second HCT compared to 0/9 dogs with skin grafts surviving less than 11 days (P=0.0008). In this model, DST to skin grafts in recipients with stable MC after nonmyeloablative HCT may not be complete, and chronic inflammation may develop without loss of that graft. Partial DST may persist after rejection of HC grafts established with nonmyeloablative conditioning. Further investigations are required to understand the mechanisms responsible for DST after allogeneic HCT.

Cardiac allograft acceptance after localized bone marrow transplantation by isolated limb perfusion in nonmyeloablated recipients.

Donor-specific tolerance to cardiac grafts may be induced by hematopoietic chimerism. This study evaluates the potential of localized bone marrow transplantation (BMT) performed by isolated limb (IL) perfusion to induce tolerance to secondary cardiac grafts without myeloablative conditioning. BALB/c recipients (H2d) preconditioned with lethal and sublethal doses of busulfan were injected i.v. and IL with 10(7) whole bone marrow cells (wBMCs) from B10 donors (H2(b)). Two hours after IL infusion of PKH-labeled wBMCs into myeloablated hosts, there were few labeled cells in the host peripheral blood (p < 0.001 versus i.v.) and femurs of the infused limb contained 57% +/- 7% PKH-labeled blasts (p < 0.001 versus 8% +/- 0.6% after i.v.). Femurs of the noninfused limbs contained 60-70 PKH-labeled blasts (p < 0.001 versus i.v.-BMT) after 2 days and 47% +/- 5% of 0.32 x 10(7) donor cells (p < 0.001 versus 78% +/- 4% of 1.2 x 10(7) donor cells in infused femurs) after 4 weeks. The survival rates of myeloablated hosts were 90% and 80% after i.v. and IL infusion, respectively, and the chimeras had 78%-84% donor peripheral blood cells. In recipients conditioned with 35 mg/g busulfan, the levels of donor chimerism in peripheral blood were 33% +/- 4% and 21% +/- 4% at 3 weeks after i.v.- and IL-BMT, respectively. Transplantation of donor-matched (H2(b)) secondary vascularized hearts in these chimeras after 3 weeks resulted in graft survival for periods exceeding 8 weeks, while third-party (H2(k)) allografts were acutely rejected (p < 0.001 versus H2(b)). These data indicate that IL perfusion is a reliable alternative procedure for establishment of hematopoietic chimerism and donor-specific tolerance without myeloablative conditioning.

Long-term discordant xenogeneic (porcine-to-primate) bone marrow engraftment in a monkey treated with porcine-specific growth factors.

Mixed allogeneic hematopoietic chimerism has previously been reliably achieved and shown to induce tolerance to fully MHC-mismatched allografts in mice and monkeys. However, the establishment of hematopoietic chimerism has been difficult to achieve in the discordant pig-to-primate xenogeneic model. To address this issue, two cynomolgus monkeys were conditioned by whole body irradiation (total dose 300 cGy) 6 and 5 days before the infusion of pig bone marrow (BM). Monkey anti-pig natural antibodies were immunoadsorbed by extracorporeal perfusion of monkey blood through a pig liver, immediately before the intravenous infusion of porcine BM (day 0). Cyclosporine was administered for 4 weeks and 15-deoxyspergualin for 2 weeks. One monkey received recombinant pig cytokines (stem cell factor and interleukin 3) for 2 weeks, whereas the other received only saline as a control. Both monkeys recovered from pancytopenia within 4 weeks of whole body irradiation. Anti-pig IgM and IgG antibodies were successfully depleted by the liver perfusion but returned to pretreatment levels within 12-14 days. Methylcellulose colony assays at days 180 and 300 revealed that about 2% of the myeloid progenitors in the BM of the cytokine-treated recipient were of pig origin, whereas no chimerism was detected in the BM of the untreated control monkey at similar times. The chimeric animal was less responsive by mixed lymphocyte reaction to pig-specific stimulators than the control monkey and significantly hyporesponsive when compared with a monkey that had rejected a porcine kidney transplant. To our knowledge, this is the first report of long-term survival of discordant xenogeneic BM in a primate recipient.