Noga Or-Geva

Murine anti–third-party central-memory CD8+ T cells promote hematopoietic chimerism under mild conditioning: lymph-node sequestration and deletion of anti-donor T cells

Transplantation of T cell-depleted BM (TDBM) under mild conditioning, associated with minimal toxicity and reduced risk of GVHD, offers an attractive therapeutic option for patients with nonmalignant hematologic disorders and can mediate immune tolerance to subsequent organ transplantation. However, overcoming TDBM rejection after reduced conditioning remains a challenge. Here, we address this barrier using donorderived central memory CD8(+) T cells (Tcms), directed against third-party antigens. Our results show that fully allogeneic or (hostXdonor)F1-Tcm, support donor chimerism (> 6 months) in sublethally irradiated (5.5Gy) mice, without GVHD symptoms. Chimerism under yet lower irradiation (4.5Gy) was achieved by combining Tcm with short-term administration of low-dose Rapamycin. Importantly, this chimerism resulted in successful donor skin acceptance, whereas third-party skin was rejected. Tracking of host anti-donor T cells (HADTCs), that mediate TDBMT rejection, in a novel bioluminescence-imaging model revealed that Tcms both induce accumulation and eradicate HADTCs in the LNs,concomitant with their elimination from other organs, including the BM. Further analysis with 2-photon microcopy revealed that Tcms form conjugates with HADTCs, resulting in decelerated and confined movement of HADTCs within the LNs in an antigen-specific manner. Thus, anti-third-party Tcms support TDBMT engraftment under reduced-conditioning through lymph-node sequestration and deletion of HADTCs, offering a novel and potentially safe approach for attaining stable hematopoietic chimerism.

The evolution of T-cell depletion in haploidentical stem-cell transplantation

T‐cell depletion (TCD) can prevent the onset of graft‐versus‐host disease (GvHD) in animal models of bone marrow transplantation; this manipulation enabled the successful application in the 1980s of T‐cell depleted bone marrow (BM) for the treatment of babies with severe combined immune deficiency (SCID). However, in leukaemia patients, implementation of T‐cell depletion has been more difficult, especially due to high rate of graft‐rejection, leukaemia relapse and delayed immune reconstitution. These hurdles were gradually overcome by modifying the cell composition of the graft, and by reducing the toxicities associated with conditioning protocols. Although no ‘gold standard’ TCD method exists, T‐cell depletion in its modern forms could offer clinical benefit, even for patients with a matched sibling donor.

Exercising ‘veto’ power to make haploidentical hematopoietic stem cell transplantation a safe modality for induction of immune tolerance

Haploidentical hematopoietic stem cell transplantation (haploSCT) offers a curative procedure for patients with malignant and nonmalignant hematological diseases, as well as an expanding number of inherited disorders. HaploSCT is likely the best unmatched source of HSCT, on account of high availability and willingness of donors, possibility of secondary grafting or post-transplant T-cell therapy and increased graft-versustumor (GVT) reactivity. Regrettably, haploSCT has traditionally been associated with higher transplant related mortality (TRM) rates as compared with transplants from MHC-matched donors, thereby limiting its application. High TRM was a direct result of increased frequency and severity of graft

A new approach for eradication of residual lymphoma cells by host nonreactive anti-third-party central memory CD8 T cells.

Generation of T cells endowed with graft-versus-leukemia (GVL) and depleted of graft-versus-host (GVH) activity represents a highly desirable goal in bone marrow transplantation (BMT). Here, we demonstrate that donor anti-third-party CD8 T cells with central memory phenotype (Tcm) exhibit marked GVL reactivity through a unique T-cell receptor-independent mechanism. Thus, in a residual disease mouse model, Tcm therapy following autologous BMT led to significant survival prolongation, with 30% to 40% of the treated mice displaying long-term tumor-free survival. A more impressive finding was that infusion of donor Tcm in an allogeneic model rapidly eliminated residual lymphoma cells and led to long-term survival of 100% in the absence of GVH disease. Collectively, the strong GVL reactivity of anti-third-party Tcm, coupled with their demonstrated enhancement of bone marrow allografting, suggests that the use of Tcm therapy in conjunction with allogeneic T-cell-depleted BMT could be of particular benefit in patients with B-cell malignancies who cannot tolerate intensive myeloablative conditioning.

Toward Safer CD34+ Megadose T-Cell-Depleted Transplants Following Reduced Intensity and Nonmyeloablative Conditioning Regimens

Haploidentical hematopoietic cell transplantation (haplo-HCT) offers a curative procedure for patients with malignant and nonmalignant hematological diseases, as well as an expanding number of inherited disorders. Haplo-HCT is likely the best HLA-related unmatched source of hematopoietic cell transplantation (HCT). Over the past decade, haplo-HCT has emerged as an important clinical option in the treatment of neoplastic hematologic diseases, especially for patients who lack a HLA-matched sibling donor (MSD). The risk of graft-versus-host disease (GvHD) and graft rejection associated with such transplants has been markedly reduced by extensive T-cell depletion (TCD) for GvHD prevention and escalated doses of CD34+ progenitors (i.e., megadose) to overcome graft rejection. Haplo-HCT in the context of TCD and nonmyeloablative (NMA) conditioning is associated with minimal risk for GvHD but with risk of higher rates of graft rejection. Thus new approaches to address this challenge are being developed. If successful, non-myeloablative haplo-HCT potentially could offer a highly attractive and safer treatment modality for patients with different hematological diseases or a platform for organ transplantation and cell therapy by addition of CD34+ cell megadose. In this chapter, we describe novel approaches for chimerism induction with CD34+ megadose in settings of TCD and NMA conditioning regimens, based on insights regarding the mechanism by which CD34+ megadose transplants overcome graft rejection.

Immune tolerance induction by nonmyeloablative haploidentical HSCT combining T-cell depletion and posttransplant cyclophosphamide

The establishment of safe approaches to attain durable donor-type chimerism and immune tolerance toward donor antigens represents a major challenge in transplantation biology. Haploidentical hematopoietic stem cell transplantation (HSCT) is currently used for cancer therapy either as a T-cell-depleted megadose HSCT following myeloablative conditioning or with T-cell-replete HSCT following nonmyeloablative conditioning (NMAC) and high-dose posttransplant cyclophosphamide (PTCY). The latter approach suffers from a significant rate of chronic graft-versus-host disease (GVHD), despite prolonged immunosuppression. The use of T-depleted grafts, although free of GVHD risk, is not effective after NMAC because of graft rejection. We now demonstrate in mice conditioned with NMAC that combining the power of high-dose PTCY with T-cell-depleted megadose HSCT can overcome this barrier. This approach was evaluated in 2 patients with multiple myeloma and 1 patient with Hodgkin lymphoma. The first myeloma patient now followed for 25 months, exhibited full donor-type chimerism in the myeloid and B-cell lineages and mixed chimerism in the T-cell compartment. The second myeloma patient failed to attain chimerism. Notably, the low toxicity of this protocol enabled a subsequent successful fully myeloablative haploidentical HSCT in this patient. The third patients was conditioned with slightly higher total body irradiation and engrafted promptly. All patients remain in remission without GVHD. Both engrafted patients were able to control cytomegalovirus reactivation. Enzyme-linked immunospot analysis revealed immune tolerance toward donor cells. Our results demonstrate a novel and safer nonmyeloablative haplo-HSCT offering a platform for immune tolerance induction as a prelude to cell therapy and organ transplantation.