Induction of tolerance to bone marrow allografts by donor-derived host nonreactive ex vivo-induced central memory CD8 T cells

Generation of Non-Alloreactive Antiviral Central Memory CD8 Human Veto T Cells for Cell Therapy

Previous studies in mice demonstrated that CD8 T cells exhibit marked veto activity enhancing engraftment in several models for T cell-depleted bone marrow (TDBM) allografting. To reduce the risk of graft-versus-host disease (GVHD) associated with allogeneic CD8 veto T cells, these studies made use of naive CD8 T cells stimulated against third-party stimulators under cytokine deprivation and subsequent expansion in the presence of IL-15. More recently, it was shown that mouse CD8 veto T cells can be generated by stimulating CD8 memory T cells from ovalbumin immunized mice under cytokine deprivation, using ovalbumin as a third-party antigen. These cells also exhibited substantial enhancement of BM allografting without GVHD. In this study, we tested the hypothesis that stimulation and expansion of human CD8 memory T cells under IL-15 and IL-7 deprivation during the early phase of activation against recall viral antigens can lead to substantial loss of alloreactive T clones while retaining marked veto activity. Memory CD8 T cells were enriched by removal of CD45RA+, CD4+, and CD56+ cells from peripheral blood of cytomegalovirus (CMV)- and Epstein-Barr virus (EBV)-positive donors. In parallel, CD14+ monocytes were isolated; differentiated into mature dendritic cells (mDCs); pulsed with a library of CMV, EBV, adenovirus, and BK virus peptides; and irradiated. The CD8 T cell-enriched fraction was then cultured with the pulsed mDCs in the presence of IL-21 for 3 days, after which IL-15 and IL-7 were added. After 12 days of culture, the cells were tested by limiting dilution analysis for the frequency of alloreactive T cell clones and their veto activity. In preclinical runs using GMP reagents, we established that within 12 days of culture, a large number of highly homogenous CD8 T cells, predominantly expressing a central memory phenotype, could be harvested. These cells exhibited marked veto activity in vitro and >3-log depletion of alloreactivity. Based on these preclinical data, a phase 1-2 clinical trial was initiated to test the safety and efficacy of these antiviral CD8 central memory veto cells in the context of nonmyeloablative (NMA) T cell-depleted haploidentical hematopoietic stem cell transplantation (HSCT). In 2 validation runs and 11 clinical runs using GMP reagents, >1 × 1010 cells were generated from a single leukapheresis in 12 out of 13 experiments. At the end of 12 days of culture, there were 97 ± 2.5% CD3+CD8+ T cells, of which 84 ± 9.0% (range, 71.5% to 95.1%) exhibited the CD45RO+CD62L+ CM phenotype. Antiviral activity tested by intracellular expression of INF-γ and TNF-α and showed an average of 38.8 ± 19.6% positive cells on 6 hours of stimulation against the viral peptide mixture. Our results demonstrate a novel approach for depleting alloreactive T cell clones from preparations of antiviral CD8 veto cells. Based on these results, a phase 1-2 clinical trial is currently in progress to test the safety and efficacy of these veto cells in the context of NMA haploidentical T cell-depleted HSCT. Studies testing the hypothesis that these non-alloreactive CD8 T cells could potentially offer a platform for off-the-shelf veto chimeric antigen receptor T cell therapy in allogenic recipients, are warranted.

Engineered T-cell Receptor T Cells for Cancer Immunotherapy

Engineering immune cells to target cancer is a rapidly advancing technology. The first commercial products, chimeric-antigen receptor (CAR) T cells, are now approved for hematologic malignancies. However, solid tumors pose a greater challenge for cellular therapy, in part because suitable cancer-specific antigens are more difficult to identify and surrounding healthy tissues are harder to avoid. In addition, impaired trafficking of immune cells to solid tumors, the harsh immune-inhibitory microenvironment, and variable antigen density and presentation help tumors evade immune cells targeting cancer-specific antigens. To overcome these obstacles, T cells are being engineered to express defined T-cell receptors (TCR). Given that TCRs target intracellular peptides expressed on tumor MHC molecules, this provides an expanded pool of potential targetable tumor-specific antigens relative to the cell-surface antigens that are targeted by CAR T cells. The affinity of TCR T cells can be tuned to allow for better tumor recognition, even with varying levels of antigen presentation on the tumor and surrounding healthy tissue. Further enhancements to TCR T cells include improved platforms that enable more robust cell expansion and persistence; coadministration of small molecules that enhance tumor recognition and immune activation; and coexpression of cytokine-producing moieties, activating coreceptors, or mediators that relieve checkpoint blockade. Early-phase clinical trials pose logistical challenges involving production, large-scale manufacturing, and more. The challenges and obstacles to successful TCR T-cell therapy, and ways to overcome these and improve anticancer activity and efficacy, are discussed herein.

Correction of murine sickle cell disease by allogeneic haematopoietic cell transplantation with anti-3rd party veto cells

Despite advances in gene therapy allogeneic hematopoietic stem cell transplants (HSCT) remains the most effective way to cure sickle cell disease (SCD). However, there are substantial challenges including lack of suitable donors, therapy-related toxicity (TRM) and risk of graft-versus-host disease (GvHD). Perhaps the most critical question is when to do a transplant for SCD. Safer transplant protocols for HLA-disparate HSCT is needed before transplants are widely accepted for SCD. Although risk of GvHD and TRM are less with T-cell-deplete HSCT and reduced-intensity conditioning (RIC), transplant rejection is a challenge. We have reported graft rejection of T cell-depleted non-myeloablative HSCT can be overcome in wild type fully mis-matched recipient mice, using donor-derived anti-3rd party central memory CD8-positive veto cells combined with short-term low-dose rapamycin. Here, we report safety and efficacy of this approach in a murine model for SCD. Durable donor-derived chimerism was achieved using this strategy with reversal of pathological parameters of SCD, including complete conversion to normal donor-derived red cells, and correction of splenomegaly and the levels of circulating reticulocytes, hematocrit, and hemoglobin.

A strategy to protect off-the-shelf cell therapy products using virus-specific T-cells engineered to eliminate alloreactive T-cells

Background

The use of “off-the-shelf” cellular therapy products derived from healthy donors addresses many of the challenges associated with customized cell products. However, the potential of allogeneic cell products to produce graft-versus-host disease (GVHD), and their likely rejection by host alloreactive T-cells are major barriers to their clinical safety and efficacy. We have developed a molecule that when expressed in T-cells, can eliminate alloreactive T-cells and hence can be used to protect cell therapy products from allospecific rejection. Further, expression of this molecule in virus-specific T-cells (VSTs) should virtually eliminate the potential for recipients to develop GVHD.

Methods

To generate a molecule that can mediate killing of cognate alloreactive T-cells, we fused beta-2 microglobulin (B2M), a universal component of all human leukocyte antigen (HLA) class I molecules, to the cytolytic endodomain of the T cell receptor ζ chain, to create a chimeric HLA accessory receptor (CHAR). To determine if CHAR-modified human VSTs could eliminate alloreactive T-cells, we co-cultured them with allogeneic peripheral blood mononuclear cells (PBMC), and assessed proliferation of PBMC-derived alloreactive T-cells and the survival of CHAR-modified VSTs by flow cytometry.

Results

The CHAR was able to transport HLA molecules to the cell surface of Daudi cells, that lack HLA class I expression due to defective B2M expression, illustrating its ability to complex with human HLA class I molecules. Furthermore, VSTs expressing CHAR were protected from allospecific elimination in co-cultures with allogeneic PBMCs compared to unmodified VSTs, and mediated killing of alloreactive T-cells. Unexpectedly, CHAR-modified VSTs eliminated not only alloreactive HLA class I restricted CD8 T-cells, but also alloreactive CD4 T-cells. This beneficial effect resulted from non-specific elimination of activated T-cells. Of note, we confirmed that CHAR-modified VSTs did not affect pathogen-specific T-cells which are essential for protective immunity.

Conclusions

Human T-cells can be genetically modified to eliminate alloreactive T-cells, providing a unique strategy to protect off-the-shelf cell therapy products. Allogeneic cell therapies have already proved effective in treating viral infections in the stem cell transplant setting, and have potential in other fields such as regenerative medicine. A strategy to prevent allograft rejection would greatly increase their efficacy and commercial viability.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1988-y) contains supplementary material, which is available to authorized users.

Veto cells for safer nonmyeloablative haploidentical HSCT and CAR T cell therapy

Haploidentical donors are a readily available source for mismatched hematopoietic bone marrow transplantation. The application of this regimen is constantly increasing with the advent of methods that overcome T-cell alloreactions that occur due to human-leukocyte-antigen disparity between host and donor. One successful method to overcome both graft rejection and graft-vs-host disease is transplantation of large numbers T-cell-depleted (TCD) haploidentical stem cell grafts (haploSCT), after myeloablative conditioning. The success of stem cell dose escalation is attributed to a unique immunoregulatory cell-property, termed "veto-activity." However, engraftment of mismatched hematopoietic stem cells following reduced-intensity conditioning still represents a major challenge. Here, we describe how the addition of post-transplant high-dose cyclophosphamide can promote immune tolerance induction after megadose TCD haploSCT, following nonmyeloablative conditioning. We also discuss ways of harnessing the immune regulatory properties of adoptively transferred "veto" cells to support mixed chimerism further and confer tolerance to cell-therapies, such as CAR-T cells. These approaches will soon be tested in phase 1-2 clinical studies and may prove to be a safe and efficacious treatment for many disorders such as hemoglobinopathies, autoimmune diseases, and as a prelude for organ tolerance. Moreover, this approach could pave the way for "off-the-shelf" cell-therapy agents, making them cheaper and easily obtainable.

Xenotransplantation: Where Are We with Potential Kidney Recipients? Recent Progress and Potential Future Clinical Trials

PURPOSE

Inter-species transplantation, xenotransplantation, is becoming a realistic strategy to solve the organ shortage crisis. Here we focus on seminal publications that have driven research in xenotransplantation, as well as recently published literature and future endeavors.

RECENT FINDINGS

Advances in gene editing technology have allowed for the efficient production of multi-transgenic porcine donors leading improved xenograft survival in baboons, up to 2-years following heterotopic heart xenotransplantation and from weeks to several months following life-supporting kidney xenotransplanation. As technology evolves, additional challenges have arisen, including the development of proteinuria, early graft loss associated with porcine CMV, disparities in organ growth between donors and recipients as well as high-dose continuous immunosuppression requirements. To address these issues, our laboratory developed a tolerance-inducing protocol which has allowed for >6 months survival of a life-supporting kidney with further approaches currently underway to address the challenges mentioned above.

SUMMARY

Our recent findings, reviewed in this article, led us to develop methods to overcome obstacles, which, in conjunction with the work of others, are promising for future clinical applications of xenotransplantation.

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.

5-azacytidine promotes an inhibitory T-cell phenotype and impairs immune mediated antileukemic activity

Demethylating agent, 5-Azacytidine (5-Aza), has been shown to be active in treatment of myeloid malignancies. 5-Aza enhances anticancer immunity, by increasing expression of tumor-associated antigens. However, the impact of 5-Aza immune responses remains poorly understood. Here, T-cell mediated tumor immunity effects of 5-Aza, are investigated in vitro and in vivo. T-cells from healthy donors were treated with 5-Aza and analyzed by qRT-PCR and flow cytometry for changes in gene expression and phenotype. Functionality was assessed by a tumor lysis assay. Peripheral blood from patients treated with 5-Aza after alloSCT was monitored for changes in T-cell subpopulations. 5-Aza treatment resulted in a decrease in CD8+ T-cells, whereas CD4+ T-cells increased. Furthermore, numbers of IFN-γ+ T-helper 1 cells (Th1) were reduced, while Treg-cells showed substantial increase. Additionally, CD8+ T-cells exhibited limited killing capacity against leukemic target cells. In vivo data confirm the increase of Treg compartment, while CD8+ T-effector cell numbers were reduced. 5-Aza treatment results in a shift from cytotoxic to regulatory T-cells with a functional phenotype and a major reduction in proinflammatory Th1-cells, indicating a strong inhibition of tumor-specific T-cell immunity by 5-Aza.

Haploidentical SCT: the mechanisms underlying the crossing of HLA barriers

Research on the different mechanisms for crossing HLA barriers has progressed over the past 10 years. General outlines have come into view for a solution to this issue and are often presented as 'haploidentical SCT' immunology. In this review, we discuss several mechanisms that have recently been described in ex vivo and in vivo settings that can either avoid GVHD or promote hematopoietic reconstitution in haploidentical settings. The host and donor T-cell responses to allogeneic HLA molecules are a fundamental obstacle to the successful application of haploidentical transplantation, which results in unacceptably high incidences of GVHD and graft rejection. Thus, the T-cell response is a central factor in the establishment of a novel haploidentical transplant protocol with superior outcomes.

Decrease in pool of T lymphocytes with surface phenotypes of effector and central memory cells under influence of TCR transgenic β-chain expression

Peripheral T lymphocytes can be subdivided into naïve and antigen-experienced T cells. The latter, in turn, are represented by effector and central memory cells that are identified by different profiles of activation markers expression, such as CD44 and CD62L in mice. These markers determine different traffic of T lymphocytes in the organism, but hardly reproduce real antigenic experience of a T lymphocyte. Mechanisms of homeostasis maintenance of T lymphocytes with different activation phenotypes remain largely unknown. To investigate impact of T cell receptor (TCR) transgenic chains on formation of T lymphocytes, their peripheral survival and activation surface phenotypes, we have generated the transgenic mouse strain expressing transgenic β-chain of TCR 1D1 (belonging to the Vβ6 family) on the genetic background B10.D2(R101). Intrathymic development of T cells in these transgenic mice is not impaired. The repertoire of peripheral T lymphocytes in these mice contains 70-80% of T cells expressing transgenic β-chain and 20-30% of T cells expressing endogenous β-chains. The ratio of peripheral CD4⁺CD8⁻ and CD4⁻CD8⁺ T lymphocytes remained unchanged in the transgenic animals, but the percent of T lymphocytes with the "naïve" phenotype CD44⁻CD62L⁺ was significantly increased, whereas the levels of effector memory CD44⁺CD62L⁻ and central memory CD44⁺CD62L⁺ T lymphocytes were markedly decreased in both subpopulations. On the contrary, T lymphocytes expressing endogenous β-chains had surface phenotype of activated T cells CD44⁺. Thus, for the first time we have shown that the pool of T lymphocytes with different activation phenotypes depends on the structure of T cell receptors.

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.

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 use of donor-derived veto cells in hematopoietic stem cell transplantation

The induction of immune tolerance by specific agents, as opposed to general immune suppression, is a most desirable goal in transplantation biology. One approach to attain this goal is afforded by the use of donor-derived cells endowed with veto activity, which is the ability of a cell to specifically suppress only T cells directed against its antigens. A megadose of purified veto CD34(+) hematopoietic stem cells is already used in patients to allow hematopoietic stem cells transplantation (HSCT) across major genetic barriers, while avoiding severe graft versus host disease (GVHD). However, allowing engraftment of such T cell-depleted HSCT under safer reduced intensity conditioning (RIC) protocols still remains a challenge. Therefore, combining megadose of CD34(+) HSCT with other GVHD-depleted veto cells could enable facilitation of engraftment of HSCT under RIC without the adverse complication of GVHD. This approach might provide a safer modality for enabling engraftment of HSCT, enabling its application in elderly patients who cannot tolerate intensive protocols and to a variety of patients with non-malignant disorders, associated with longer life expectancy, in whom the use of a high risk conditioning cannot be considered.

Haploidentical hematopoietic transplantation: current status and future perspectives

For patients with hematologic malignancies at high risk of relapse who do not have matched donors, a suitable alternative stem cell source is the HLA-haploidentical 2 or 3-loci mismatched family donor who is readily available for nearly all patients. Transplantation across the major HLA barrier is associated with strong T-cell alloreactions, which were originally manifested as a high incidence of severe GVHD and graft rejection. The present review shows how these obstacles to successful transplantation were overcome in the last 15 years, making full haplotype-mismatched transplantation a clinical reality that provides similar outcomes to transplantation from matched unrelated donors. The review also discusses the advantages and drawbacks of current options for full haplotype-mismatched transplantation and highlights innovative approaches for re-building immunity after transplantation and improving survival.