Lack of Antidonor Alloantibody Does Not Indicate Lack of Immune Sensitization: Studies of Graft Loss in a Haploidentical Hematopoietic Cell Transplantation Swine Model

Abstract

Loss of chimerism is an undesirable outcome of allogeneic hematopoietic cell transplantation (HCT) after reduced-intensity conditioning. Understanding the nature of cellular and humoral immune responses to HCT after graft loss could lead to improved retransplantation strategies. We investigated the immunologic responses after graft loss in miniature swine recipients of haploidentical HCT that received reduced-intensity conditioning. After the loss of peripheral blood chimerism, antidonor cellular responses were present without detectable antidonor antibody. Reexposure to donor hematopoietic cells after graft loss induced a sensitized antidonor cellular response. No induced antidonor antibody response could be detected despite evidence of cellular sensitization to donor cells. In contrast, unconditioned animals exposed repeatedly to similar doses of haploidentical donor cells developed antidonor antibody responses. These results could have important implications for the design of treatment strategies to overcome antidonor responses in HCT and improve the outcome of retransplantation after graft loss.

Tolerance of Vascularized Islet-Kidney Transplants in Rhesus Monkeys

“…In our previous studies using similar mild conditioning protocols for hematopoietic cell Tx in swine, we found that in vitro MLR responses did not correlate well with donor kidney graft acceptance . Data generated using this same ITC conditioning protocol in swine suggest that exposure to donor cells using this novel conditioning protocol results in robust, stable immune modulation of donor‐specific antibody responses together with transient immunomodulation of T cell responses ( and unpublished data). The mechanism of immunomodulation mediated by allogeneic cells in this model is unrelated to HSC engraftment.…”

Donor Lymphocyte Infusion–Mediated Graft-versus-Host Responses in a Preclinical Swine Model of Haploidentical Hematopoietic Cell Transplantation

“…In mice, central deletional tolerance and peripheral regulatory mechanisms have been shown to control allo-immune responses [33][34][35][36]. Because donor T cells are not depleted and host T cells are partially and transiently depleted in this large animal model [24,25,37], unlike the complete donor and host T cell depletion that can be achieved in rodent studies, we speculate that immune regulatory T cell mechanisms are involved in controlling both donor antihost and host antidonor responses [30,38]. We are currently exploring the mechanism of immunoregulation in this model.…”

“…CML assays were performed as previously described [24,25]. Briefly, responders (4 × 10 5 cells) and stimulators (4 × 10 5 cells; irradiated with 25 Gy) were cultured together for 5 days.…”

“…PBMCs from non-inbred Yucatan or Yorkshire pigs were used as thirdparty positive control stimulators and targets. The percent specific lysis was calculated as previously reported [24][25][26]: percent specific lysis = average experimental release (cpms) -average spontaneous release (cpm)/average max release (cpm) -average spontaneous release (cpm).…”

CD3e-immunotoxin spares CD62LloTregs and reshapes organ-specific T-cell composition by preferentially depleting CD3ehiT cells

“…The CD3e-IT-mediated transient chimerism, instead, facilitated the robust and stable humoral immune modulation of donor-specific antibody responses. (44) Treg infiltration into an allograft has been reported in a miniature swine model, suggesting a potential local regulatory component. (4) Nevertheless, the survival and roles of Tregs in CD3e-IT-mediated tolerance induction remain unclear.…”