Depletion of alloreactive T cells via CD69: implications on antiviral, antileukemic and immunoregulatory T lymphocytes

Genetic engineering strategies to enhance antitumor reactivity and reduce alloreactivity for allogeneic cell-based cancer therapy

The realm of cell-based immunotherapy holds untapped potential for the development of next-generation cancer treatment through genetic engineering of chimeric antigen receptor (CAR)-engineered T (CAR-T) cell therapies for targeted eradication of cancerous malignancies. Such allogeneic "off-the-shelf" cell products can be advantageously manufactured in large quantities, stored for extended periods, and easily distributed to treat an exponential number of cancer patients. At current, patient risk of graft-versus-host disease (GvHD) and host-versus-graft (HvG) allorejection severely restrict the development of allogeneic CAR-T cell products. To address these limitations, a variety of genetic engineering strategies have been implemented to enhance antitumor efficacy, reduce GvHD and HvG onset, and improve the overall safety profile of T-cell based immunotherapies. In this review, we summarize these genetic engineering strategies and discuss the challenges and prospects these approaches provide to expedite progression of translational and clinical studies for adoption of a universal cell-based cancer immunotherapy.

Genetic Ablation of HLA Class I, Class II, and the T-cell Receptor Enables Allogeneic T Cells to Be Used for Adoptive T-cell Therapy

Adoptive immunotherapy can induce sustained therapeutic effects in some cancers. Antitumor T-cell grafts are often individually prepared in vitro from autologous T cells, which requires an intensive workload and increased costs. The quality of the generated T cells can also be variable, which affects the therapy's antitumor efficacy and toxicity. Standardized production of antitumor T-cell grafts from third-party donors will enable widespread use of this modality if allogeneic T-cell responses are effectively controlled. Here, we generated HLA class I, HLA class II, and T-cell receptor (TCR) triple-knockout (tKO) T cells by simultaneous knockout of the B2M, CIITA, and TRAC genes through Cas9/sgRNA ribonucleoprotein electroporation. Although HLA-deficient T cells were targeted by natural killer cells, they persisted better than HLA-sufficient T cells in the presence of allogeneic peripheral blood mononuclear cells (PBMC) in immunodeficient mice. When transduced with a CD19 chimeric antigen receptor (CAR) and stimulated by tumor cells, tKO CAR-T cells persisted better when cultured with allogeneic PBMCs compared with TRAC and B2M double-knockout T cells. The CD19 tKO CAR-T cells did not induce graft-versus-host disease but retained antitumor responses. These results demonstrated the benefit of HLA class I, HLA class II, and TCR deletion in enabling allogeneic-sourced T cells to be used for off-the-shelf adoptive immunotherapy.

Unique features and clinical importance of acute alloreactive immune responses

Allogeneic stem cell transplantation (allo-SCT) can cure some patients with hematopoietic malignancy, but this relies on the development of a donor T cell alloreactive immune response. T cell activity in the first 2 weeks after allo-SCT is crucial in determining outcome, despite the clinical effects of the early alloreactive immune response often not appearing until later. However, the effect of the allogeneic environment on T cells is difficult to study at this time point due to the effects of profound lymphopenia. We approached this problem by comparing T cells at week 2 after allograft to T cells from autograft patients. Allograft T cells were present in small numbers but displayed intense proliferation with spontaneous cytokine production. Oligoclonal expansions at week 2 came to represent a substantial fraction of the established T cell pool and were recruited into tissues affected by graft-versus-host disease. Transcriptional analysis uncovered a range of potential targets for immune manipulation, including OX40L, TWEAK, and CD70. These findings reveal that recognition of alloantigen drives naive T cells toward a unique phenotype. Moreover, they demonstrate that early clonal T cell responses are recruited to sites of subsequent tissue damage and provide a range of targets for potential therapeutic immunomodulation.

Alloreactive response T cells at 2 weeks after allo-SCT displayed intense proliferation with spontaneous cytokine production, and were recruited into tissues affected by GvHD.

Donor-derived CD19 chimeric antigen receptor T cells

PURPOSE OF REVIEW

As immunotherapy matures into possible front-line therapy, new approaches are necessary to expand the capacity to treat more patients. Although most technologies for chimeric antigen receptor (CAR) therapies require autologous T cells, 'off the shelf' sources are highly desired.

RECENT FINDINGS

Sources of T cells for modification with CARs include cord blood and either related or unrelated allogeneic donors. Strategies to manipulate these sources focus on reducing the risk of alloreactivity, while maintaining the potential for high function and long persistence associated with successful CAR T-cell therapies.

SUMMARY

Recent research implies that manipulating nonautologous T-cell sources can result in well tolerated and effective products, but work remains to determine if these approaches will reach the efficacy of autologous products.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Expression of a dominant T-cell receptor can reduce toxicity and enhance tumor protection of allogeneic T-cell therapy

Due to the lack of specificity for tumor antigens, allogeneic T-cell therapy is associated with graft-versus-host disease. Enhancing the anti-tumor specificity while reducing the graft-versus-host disease risk of allogeneic T cells has remained a research focus. In this study, we demonstrate that the introduction of 'dominant' T-cell receptors into primary murine T cells can suppress the expression of endogenous T-cell receptors in a large proportion of the gene-modified T cells. Adoptive transfer of allogeneic T cells expressing a 'dominant' T-cell receptor significantly reduced the graft-versus-host toxicity in recipient mice. Using two bone marrow transplant models, enhanced anti-tumor activity was observed in the presence of reduced graft-versus-host disease. However, although transfer of T-cell receptor gene-modified allogeneic T cells resulted in the elimination of antigen-positive tumor cells and improved the survival of treated mice, it was associated with accumulation of T cells expressing endogenous T-cell receptors and the development of delayed graft-versus-host disease. The in-vivo deletion of the engineered T cells, mediated by endogenous mouse mammary tumor virus MTV8 and MTV9, abolished graft-versus-host disease while retaining significant anti-tumor activity of adoptively transferred T cells. Together, this study shows that the in-vitro selection of allogeneic T cells expressing high levels of a 'dominant' T-cell receptor can lower acute graft-versus-host disease and enhance anti-tumor activity of adoptive cell therapy, while the in-vivo outgrowth of T cells expressing endogenous T-cell receptors remains a risk factor for the delayed onset of graft-versus-host disease.

Specific removal of alloreactive T-cells to prevent GvHD in hemopoietic stem cell transplantation: rationale, strategies and perspectives

Hemopoietic stem cell transplantation (HSCT) is a standard procedure for treatment of malignant and non-malignant hematological diseases. HSCT donors include HLA-identical siblings, matched or mismatched unrelated donors and haploidentical related donors. Graft-versus-host disease (GvHD), mediated by donor alloreactive T-cells in the graft, can be triggered by minor histocompatibility antigens in HLA-identical pairs, by alleles at loci not considered for MUD-matching or by the mismatched haplotype in haplo-HSCT. Therefore, removal of donor T-cells, that contain the alloreactive precursors, is required, but T-cell depletion associates with opportunistic infections and with reduced graft-versus-leukemia effect. Selective T-cell depletion strategies have been introduced, like removal of αβ T-lymphocytes and of naive T-cells, two subsets including the alloreactive precursors, but the ultimate goal is specific removal of alloreactive T-cells. Here we review the different approaches to deplete alloreactive T-cells only and discuss pros and cons, specificity, efficiency and efficacy. Combinations of different methods and innovative approaches are also proposed for depleting specific alloreactive T-cells with high efficiency.

Haploidentical HSCT: a 15-year experience at San Raffaele

Hematopoietic SCT (HSCT) from HLA haploidentical family donors is a promising therapy for high-risk hematological malignancies. In the past 15 years at San Raffaele Scientific Institute, we investigated several transplant platforms and post transplant cellular-based interventions. We showed that T cell-depleted haploidentical transplantation followed by the infusion of genetically modified donor T cells (TK007 study, Eudract-2005-003587-34) promotes fast and wide immune reconstitution and GvHD control. This approach is currently tested in a phase III multicenter randomized trial (TK008 study, NCT00914628). We targeted patients with advanced leukemia with a sirolimus-based, calcineurin inhibitor-free prophylaxis of GvHD to allow the safe infusion of unmanipulated PBSCs from haploidentical family donors (TrRaMM study, Eudract 2007-5477-54). Results of these approaches are summarized and discussed.

Preventing stem cell transplantation-associated viral infections using T-cell therapy

Hematopoietic stem cell transplantation is the treatment of choice for many hematologic malignancies and genetic diseases. However, viral infections continue to account for substantial post-transplant morbidity and mortality. While antiviral drugs are available against some viruses, they are associated with significant side effects and are frequently ineffective. This review focuses on the immunotherapeutic strategies that have been used to prevent and treat infections over the past 20 years and outlines different refinements that have been introduced with the goal of moving this therapy beyond specialized academic centers.

Depletion of Alloreactive T-Cells by Anti-CD137-Saporin Immunotoxin

Depletion of alloreactive T-lymphocytes from allogeneic bone marrow tansplants may prevent graft-versus-host disease (GVHD) without impairing donor cell engraftment, immunity, and the graft-versus-leukemia (GVL) effect. Alloreactive T-cells may be identified by their expression, upon activation, of CD137, a costimulatory receptor and putative surrogate marker for antigen-specific effector T-cells. In this context, we tested the use of anti-CD137-saporin immunotoxin to selectively deplete mouse and human alloreactive T-cells. Anti-CD137 antibodies were internalized by cells within 4 h of binding to the cell surface CD137, and anti-CD137-saporin immunotoxin effectively killed polyclonally activated T-cells or antigen-stimulated T-cells. Transfer of donor T-cells after allodepletion with anti-CD137-saporin immunotoxin failed to induce any evident expression of GVHD; however, a significant GVL effect was observed. Targeting of CD137 with an immunotoxin was also effective in killing polyclonally activated or alloreactive human T-cells. Our results indicate that anti-CD137-saporin immunotoxin may be used to deplete alloreactive T-cells prior to bone marrow transplantation and thereby prevent GVHD and the relapse of leukemia.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

Adoptive immunotherapy with genetically modified lymphocytes in allogeneic stem cell transplantation

Hematopoietic stem cell transplantation from a healthy donor (allo-HSCT) represents the most potent form of cellular adoptive immunotherapy to treat malignancies. In allo-HSCT, donor T cells are double edge-swords: highly potent against residual tumor cells, but potentially highly toxic, and responsible for graft versus host disease (GVHD), a major clinical complication of transplantation. Gene transfer technologies coupled with current knowledge on cancer immunology have generated a wide range of approaches aimed at fostering the immunological response to cancer cells, while avoiding or controlling GVHD. In this review, we discuss cell and gene therapy approaches currently tested in preclinical models and in clinical trials.

Accelerating immune reconstitution after hematopoietic stem cell transplantation

Viral infections remain a significant cause of morbidity and mortality after hematopoietic stem cell transplantation. Pharmacologic agents are effective against some pathogens, but they are costly and can be associated with significant toxicities. Thus, many groups have investigated adoptive T-cell transfer as a means of hastening immune reconstitution and preventing and treating viral infections. This review discusses the immunotherapeutic strategies that have been explored.

Optimization of methodology for production of CD25/CD71 allodepleted donor T cells for clinical use

BACKGROUND AIMS

Immunotherapy with allodepleted donor T cells improves immunity after T cell-depleted hematopoietic stem cell transplantation. We developed a methodology for selective depletion of alloreactive T cells after activation with host antigen-presenting cells by targeting T cells up-regulating CD25 and CD71. Combined depletion of these cells yields a pool of allodepleted donor T cells with antiviral properties with minimal capacity to cause graft-versus-host disease.

METHODS

Mature dendritic cells were irradiated and used to stimulate donor peripheral blood mononuclear cells for 4 days. The co-culture was stained with anti-CD71-biotin followed by CliniMACS CD25 and Anti-Biotin Reagents (Miltenyi Biotec GmbH; Bergisch Gladbach, Germany) before depletion on the CliniMACS Plus (Miltenyi Biotec GmbH). Residual alloreactivity was tested by flow cytometry, a secondary mixed lymphocyte reaction and limiting dilution analysis, and specific anti-viral immunity with pentamer staining. The large-scale protocol was tested under current good manufacturing practice conditions in five donor-recipient pairs of human leukocyte antigen-matched volunteer donors.

RESULTS

We developed a closed-system methodology using cell differentiation bags for cell culture and the COBE2991 Cell Processor (CaridianBCT, Lakewood, CO, USA). We also validated an anti-CD71-biotin generated for ex vivo clinical use. In five large-scale runs, the depleted fraction demonstrated excellent viability (99.9%), minimal residual expression of CD3/CD25 and CD3/CD71 (<0.2%) and passed tests for Mycoplasma, endotoxin, bacterial and fungal sterility. In secondary mixed lymphocyte reaction assays, the median response to host after allodepletion was 0%, whereas responses to third-party peripheral blood mononuclear cells were preserved (median, 105%; range 37%-350%). Limiting dilution analysis assays also demonstrated a reduction in response to host (median, -1.11 log) with preservation of third-party responses, and testing with human leukocyte antigen-restricted pentamers showed that populations of Epstein-Barr virus-specific and cytomegalovirus-specific CD8(+) T cells were retained after depletion.

CONCLUSIONS

We optimized a protocol for the combined immunomagnetic depletion of alloreactive CD25/CD71 T cells under current good manufacturing practice conditions and tested the efficacy in five donor-recipient pairs.

T cell depletion in paediatric stem cell transplantation

Haematopoietic stem cell transplantation (HSCT) can be a curative procedure for a growing number of paediatric diseases, but as the indications for HSCT grow, so does the need to find suitable stem cell donors. When the preferred option of a genoidentical sibling donor is not available alternative donors, including unrelated adult or umbilical cord blood donors, or haploidentical related donors may be considered. Outcome following alternative donor HSCT has improved over the past 20 years but graft-versus-host disease (GvHD) remains a significant obstacle. T cell depletion (TCD) for non-genoidentical grafts aims to reduce the morbidity and mortality associated with GvHD, but this intervention has not led directly to improved survival due to delayed immune reconstitution and increased infections, graft rejection and increased rates of disease relapse. Limited data from the paediatric population, however, suggest some encouraging results for children undergoing haploidentical HSCT: a move from positive selection of CD34(+) haematopoietic stem cells towards negative depletion of specific cell subsets in order to retain useful accessory cells within the graft appears to enhance immune reconstitution and improve disease-free survival. Here we review recent paediatric outcome data for T cell-depleted HSCT, explore the role of serotherapy in conditioning regimens and look at future possibilities to improve outcome, including novel allodepletion techniques, suicide gene therapy and pathogen-specific immunotherapy.

An effective immune-monitoring protocol based on gene expression profiles in the peripheral T-cell fraction reactive to graft antigens

BACKGROUND

The ability to induce tolerance, or at least minimize the need for immunosuppressive therapy, is a high priority in organ transplantation. Accomplishing this goal requires a novel method for determining when a patient has become tolerant to or is rejecting their graft. Here, we sought to develop an efficient monitoring protocol based on gene expression profiles of recipient T cells in murine skin and islet allograft models.

METHODS

Unlike previous studies, here, gene expression analysis was focused on donor antigen-reactive T cells, which were prepared by collecting CD69(+) T cells from cocultures of recipient peripheral T cells and donor antigen-presenting cells. Candidate tolerance and rejection biomarker genes were selected from a CD69(+) T-cell microarray analysis, and their expression levels were measured in the recipient CD69(+) T-cell fraction using quantitative reverse transcription polymerase chain reaction.

RESULTS

Our new monitoring protocol was capable of precisely detecting the immune status of recipients relative to their graft regardless of the organ received, whether they were taking immunosuppressive drugs, or different strains of origin.

CONCLUSIONS

Gene expression analysis focusing on recipient CD69(+) T cells as the donor antigen-reactive T-cell population could be used as an effective and sensitive method for monitoring transplant patients.

Immunotherapeutic approaches to improve graft-versus-tumor effect and reduce graft-versus-host disease

The therapeutic efficacy of allogeneic stem cell transplantation is mainly based on the alloreactive immune response of the graft against the host. However, the graft-versus-host process can be viewed as a double-edged sword since it is responsible for both the beneficial graft-versus-tumor effect and the deleterious graft-versus-host disease. During the last two decades, intensive research has been focused on the development of novel immunotherapeutic methods aimed to dissociate graft-versus-host disease from graft-versus-tumor effect. A brief description of these efforts is discussed in this review.

A foundation for universal T-cell based immunotherapy: T cells engineered to express a CD19-specific chimeric-antigen-receptor and eliminate expression of endogenous TCR

Clinical-grade T cells are genetically modified ex vivo to express a chimeric antigen receptor (CAR) to redirect specificity to a tumor associated antigen (TAA) thereby conferring antitumor activity in vivo. T cells expressing a CD19-specific CAR recognize B-cell malignancies in multiple recipients independent of major histocompatibility complex (MHC) because the specificity domains are cloned from the variable chains of a CD19 monoclonal antibody. We now report a major step toward eliminating the need to generate patient-specific T cells by generating universal allogeneic TAA-specific T cells from one donor that might be administered to multiple recipients. This was achieved by genetically editing CD19-specific CAR(+) T cells to eliminate expression of the endogenous αβ T-cell receptor (TCR) to prevent a graft-versus-host response without compromising CAR-dependent effector functions. Genetically modified T cells were generated using the Sleeping Beauty system to stably introduce the CD19-specific CAR with subsequent permanent deletion of α or β TCR chains with designer zinc finger nucleases. We show that these engineered T cells display the expected property of having redirected specificity for CD19 without responding to TCR stimulation. CAR(+)TCR(neg) T cells of this type may potentially have efficacy as an off-the-shelf therapy for investigational treatment of B-lineage malignancies.

The humanized anti-HLA-DR moAb, IMMU-114, depletes APCs and reduces alloreactive T cells: implications for preventing GVHD

In contrast to the conventional immunosuppressive agents and nonselective T-cell-depleting antibodies, selective depletion of donor alloreactive T cells and/or host APCs, particularly DCs, represents a novel approach that can effectively control GVHD with less or no impairment of T-cell-mediated antiviral and GVL immunity. Here we report that IMMU-114, a humanized anti-human leukocyte antigen-DR (HLA-DR) moAb, efficiently depleted human PBMCs of all APCs, including B cells, monocytes, myeloid DC type-1 (mDC1), mDC2 and plasmacytoid DCs (pDCs). Early and late apoptosis of mDC1, mDC2 and pDCs, and late apoptosis of all APC subsets, were increased by IMMU-114 treatment. Although IMMU-114 had little, if any, effect on the survival and apoptosis of non-B lymphocytes (>80% of which are T cells and ∼1-2% of T cells express HLA-DR), it selectively inhibited the proliferation of purified HLA-DR(+) T cells rather than HLA-DR(-) T cells. As a consequence, IMMU-114 treatment resulted in suppressed T-cell proliferation and reduced CD25(+) alloreactive T cells in allogeneic MLRs. Given the critical roles of APCs and alloreactive T cells in the pathogenesis of GVHD, these results suggest that IMMU-114 may have therapeutic potential against GVHD.

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.

Human regulatory T cells with alloantigen specificity are more potent inhibitors of alloimmune skin graft damage than polyclonal regulatory T cells

Graft rejection by the immune system is a major cause of transplant failure. Lifelong immunosuppression decreases the incidence of graft rejection; however, nonspecific immunosuppression results in increased susceptibly to infection and cancer. Regulatory T cells (T(regs)), which suppress the activation of the immune system and induce tolerance, are currently under evaluation for use in clinical transplantation. Ex vivo expanded polyclonal T(regs) that are introduced into transplant recipients alter the balance of T effector cells to T(regs); however, experimental data suggest that alloantigen-specific T(regs) would be more effective at preventing graft rejection. We have developed a method to enrich alloantigen-specific human T(regs) based on the coexpression of activation markers, CD69 and CD71. These T(regs) could be readily expanded in vitro and demonstrated potent antigen-specific suppression. In a humanized mouse model of alloimmune-mediated injury of human skin grafts, alloantigen-specific T(regs) resulted in a significant reduction in clinically relevant indicators of dermal tissue injury when compared with polyclonal T(regs), restoring a histology comparable to healthy skin. This method of human allospecific T(reg) selection should be scalable to the clinic. The improved in vivo efficacy of alloantigen-specific T(regs) over polyclonal T(regs) shown here suggests that generating "customized" T(regs) with defined anti-donor allospecificities may improve current practice in clinical immunotherapy.

Cell surface delivery of TRAIL strongly augments the tumoricidal activity of T cells

PURPOSE

Adoptive T-cell therapy generally fails to induce meaningful anticancer responses in patients with solid tumors. Here, we present a novel strategy designed to selectively enhance the tumoricidal activity of T cells by targeted delivery of TNF-related apoptosis-inducing ligand (TRAIL) to the T-cell surface.

EXPERIMENTAL DESIGN

We constructed two recombinant fusion proteins, anti-CD3:TRAIL and K12:TRAIL. Tumoricidal activity of T cells in the presence of these fusion proteins was assessed in solid tumor cell lines, primary patient-derived malignant cells, and in a murine xenograft model.

RESULTS

When added to T cells, K12:TRAIL and anti-CD3:TRAIL selectively bind to the T-cell surface antigens CD3 and CD7, respectively, leading to cell surface accretion of TRAIL. Subsequently, anti-CD3:TRAIL and K12:TRAIL increased the tumoricidal activity of T cells toward cancer cell lines and primary patient-derived malignant cells by more than 500-fold. Furthermore, T-cell surface delivery of TRAIL strongly inhibited tumor growth and increased survival time of xenografted mice more than 6-fold.

CONCLUSIONS

Targeted delivery of TRAIL to cell surface antigens of T cells potently enhances the tumoricidal activity of T cells. This approach may be generally applicable to enhance the efficacy of adoptive T-cell therapy.

Depletion of alloreactive T-cells in vitro using the proteasome inhibitor bortezomib preserves the immune response against pathogens

Current graft-versus-host disease (GVHD) inhibition approaches lead to abrogation of pathogen-specific T-cell responses. We propose an approach to inhibit GVHD without hampering immunity against pathogens: in vitro depletion of alloreactive T cells with the preoteasome inhibitor bortezomib. We show that PBMCs stimulated with allogeneic cells and treated with bortezomib greatly reduce their ability to produce IFN-γ when re-stimulated with the same allogeneic cells, but mainly preserve their ability to respond to citomegalovirus stimulation. Unlike in vivo administration of immunosuppressive drugs or other strategies of allodepletion, in vitro allodepletion with bortezomib maintains pathogen-specific T cells, representing a promising alternative for GVHD prophylaxis.

Advances in adoptive immunotherapy to accelerate T-cellular immune reconstitution after HLA-incompatible hematopoietic stem cell transplantation

Although partially HLA-mismatched hematopoietic stem cell transplantation (HSCT) has become an important therapeutic option for children with primary immunodeficiencies, delayed reconstitution of the T-cell compartment remains a major clinical concern. Adoptive immunotherapies to provide recipients with a protective and diverse T-cell repertoire in the months following HSCT are warranted. In order to improve T-cell reconstitution after T-cell-depleted HSCT, different strategies are currently being studied. Some are based on administration of modified mature T cells (e.g., allodepleted T cells or pathogen-specific T cells). Others aim at accelerating de novo thymopoiesis from donor-derived hematopoietic stem cells in vivo via the administration of thymopoietic agents or the transfer of large numbers of T-cell precursors generated ex vivo. The present article will provide a brief summary of recent advances in the field of allodepletion and adoptive transfer of pathogen-specific T cells and a detailed discussion of strategies for enhancing thymopoiesis in vivo.

Challenges of T cell therapies for virus-associated diseases after hematopoietic stem cell transplantation

IMPORTANCE OF THE FIELD

Hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematological malignancies and genetic disorders. The majority of patients do not have a human leukocyte antigen (HLA) identical sibling donor, and alternative stem cell sources include HLA-matched or mismatched unrelated donors and haploidentical related donors. However, alternative donor HSCT are associated with three major complications i) graft rejection; ii) graft-versus-host disease (GvHD); and iii) delayed immune reconstitution leading to viral infections and relapse.

AREAS COVERED IN THIS REVIEW

Graft rejection and the risk of GvHD can be significantly reduced by using intensive conditioning regimens, including in vivo T cell depletion as well as ex vivo T cell depletion of the graft. However, the benefits of removing alloreactive T cells from the graft are offset by the concomitant removal of T cells with anti-viral or anti-tumor activity as well as the profound delay in endogenous T cell recovery post-transplant. Thus, opportunistic infections, many of which are not amenable to conventional small-molecule therapeutics, are frequent in these patients and are associated with significant morbidity and high mortality rates. This review discusses current cell therapies to prevent or treat viral infections/reactivations post-transplant.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the current state of cell therapy to prevent and treat viral infections post-HSCT, and will be introduced to preclinical studies designed to develop and validate new manufacturing procedures intended to improve therapeutic efficacy and reduce associated toxicities.

TAKE HOME MESSAGE

Reconstitution of HSCT recipients with antigen-specific T cells, produced either by allodepletion or in vitro reactivation, can offer an effective strategy to provide both immediate and long-term protection without harmful alloreactivity.

Efficient lysis of rhabdomyosarcoma cells by cytokine-induced killer cells: implications for adoptive immunotherapy after allogeneic stem cell transplantation

BACKGROUND

Rhabdomyosarcoma is the most common soft tissue sarcoma in childhood and has a poor prognosis. Here we assessed the capability of ex vivo expanded cytokine-induced killer cells to lyse both alveolar and embryonic rhabdomyosarcoma cell lines and investigated the mechanisms involved.

DESIGN AND METHODS

Peripheral blood mononuclear cells from six healthy donors were used to generate and expand cytokine-induced killer cells. The phenotype and composition of these cells were determined by multiparameter flow cytometry, while their cytotoxic effect against rhabdomyosarcoma cells was evaluated by a europium release assay.

RESULTS

Cytokine-induced killer cells efficiently lysed cells from both rhabdomyosarcoma cell lines. Antibody-mediated masking of either NKG2D molecule on cytokine-induced killer cells or its ligands on rhabdomyosarcoma cells (major histocompatibility antigen related chain A and B and UL16 binding protein 2) diminished this effect by 50%, suggesting a major role for the NKG2D molecule in rhabdomyosarcoma cell killing. No effect was observed after blocking CD11a, CD3 or TCRalphabeta molecules on cytokine-induced killer cells or CD1d on rhabdomyosar-coma cells. Remarkably, cytokine-induced killer cells used tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to activate caspase-3, as the main caspase responsible for the execution of apoptosis. Accordingly, blocking TRAIL receptors on embryonic rhabdomyosarcoma cell lines significantly reduced the anti-tumor effect of cytokine-induced killer cells. About 50% of T cells within the cytokine-induced killer population had an effector memory phenotype, 20% had a naïve phenotype and approximately 30% of the cells had a central memory phenotype. In addition, cytokine-induced killer cells expressed low levels of activation-induced markers CD69 and CD137 and demonstrated a low alloreactive potential.

CONCLUSIONS

Our data suggest that cytokine-induced killer cells may be used as a novel adoptive immunotherapy for the treatment of patients with rhabdomyosarcoma after allogeneic stem cell transplantation.

Clinical expansion of cord blood-derived T cells for use as donor lymphocyte infusion after cord blood transplantation

Allogeneic stem cell transplantation (SCT) from cord blood (CB) as a stem cell source is a promising alternative when no human leukocyte antigen-matched donor is found. Donor lymphocyte infusion (DLI) is a possible treatment modality for threatening graft failure or relapse of an underlying malignancy after transplantation. Ethical and logistical reasons limit the possibility of DLI in the setting of CB SCT. To remedy this restriction, we performed expansion of donor T cells in vitro from CB grafts in a clinical setting for use as future DLI and characterized the expanded cells in comparison to T cells from CB acquired ex vivo and adult peripheral blood. T cells were expanded from grafts used for transplantation, upon CD3/CD28 crosslinking and culture in interleukin-2. Phenotype and function of T cells were assessed by flow cytometry and mixed lymphocyte culture assays. T-cell receptor repertoire distribution was evaluated with polymerase chain reaction-based spectratyping. We were able to amplify T cells to sufficient amounts for DLI in 13 out of 13 initiated expansions. Expanded T cells presented with an activated phenotype and could be induced to produce cytokines by a nonspecific stimulus. When exposed to allogeneic targets, expanded CB T cells proliferated at comparable levels to their ex vivo and adult blood counterparts. In summary, clinical expansion of CB T cells for DLI is feasible and may be a future modality for treatment of graft failure or relapse after SCT.

Functional characterization of alloreactive T cells identifies CD25 and CD71 as optimal targets for a clinically applicable allodepletion strategy

Immunotherapy with allodepleted donor T cells (ADTs) improves immunity after T cell–depleted stem cell transplantation, but infection/relapse remain problematic. To refine this approach, we characterized the expression of surface markers/cytokines on proliferating alloreactive T cells (ATs). CD25 was expressed on 83% of carboxyfluorescein diacetate succinimidyl esterdim ATs, confirming this as an excellent target for allodepletion. Seventy percent of CD25− ATs expressed CD71 (transferrin receptor), identifying this as a novel marker to target ATs persisting after CD25 depletion. Comparison of residual alloreactivity after combined CD25/71 versus CD25 immunomagnetic depletion showed enhanced depletion of alloreactivity to host with CD25/71 depletion in both secondary (2°) mixed lymphocyte reactions (P < .01) and interferon-γ enzyme-linked immunospot assays (P < .05) with no effect on third-party responses. In pentamer/interferon-γ enzyme-linked immunospot assays, antiviral responses to cytomegalovirus, Epstein-Barr virus, and adenovirus were preserved after CD25/71 allodepletion. CD25/71 ADTs can be redirected to recognize leukemic targets through lentiviral transfer of a chimeric anti-CD19ζ T-cell receptor. Finally, we have established conditions for clinically applicable CD25/71 allodepletion under European Union Good Manufacturing Practice conditions, resulting in highly effective, reproducible, and selective depletion of ATs (median residual alloreactivity to host in 2° mixed lymphocyte reaction of 0.39% vs third-party response of 62%, n = 5). This strategy enables further clinical studies of adoptive immunotherapy with larger doses of ADTs to enhance immune reconstitution after T cell-depleted stem cell transplantation.

Selective depletion of alloreactive T lymphocytes using patient-derived nonhematopoietic stimulator cells in allograft engineering

BACKGROUND

Selective depletion of alloreactive T cells in vitro results in efficient graft-versus-host disease prophylaxis in allogeneic hematopoietic stem-cell transplantation, but it is accompanied by increased recurrence of leukemia. To spare donor T-cell-mediated graft-versus-leukemia immunity against hematopoiesis-restricted minor histocompatibility (minor-H) antigens, we explored the use of patient-derived nonhematopoietic antigen-presenting cells (APC) as allogeneic stimulators for selective allodepletion in leukemia-reactive donor T-cell lines.

METHODS

Primary keratinocytes, dermal fibroblasts, and bone marrow fibroblasts were generated from skin biopsies and diagnostic bone marrow aspirates of acute myeloid leukemia patients in vitro. Cell cultures were analyzed for expansion, phenotype, and immunostimulatory capacity in comparison with CD40-activated B cells as professional APC. In addition, nonhematopoietic APCs were used for selective allodepletion in vitro.

RESULTS

Patient-derived fibroblasts could be reliably expanded to large cell numbers, whereas keratinocytes had limited growth potential. Interferon-gamma-pretreated fibroblasts showed increased expression of human leukocyte antigen (HLA)-class I and II molecules, CD40, and CD54. Fibroblasts and CD40-activated B cells comparably stimulated HLA-A*0301-specific CD8 T cells after transient expression of HLA-A*0301 as a model alloantigen. Finally, fibroblasts could be effectively applied to selectively deplete alloreactivity within leukemia-reactive donor CD8 T-cell lines by targeting the activation-induced antigen CD137.

CONCLUSIONS

Primary fibroblasts can be efficiently used as allogeneic nonhematopoietic APC for selective depletion of donor T cells reactive to HLA and ubiquitously expressed minor-H antigen disparities in leukemia-stimulated CD8 T-cell lines. Therefore, harnessing alloreactivity to hematopoietic minor-H antigens in addition to leukemia-associated antigens might increase graft-versus-leukemia immunity of donor lymphocyte grafts in allogeneic hematopoietic stem-cell transplantation.

Use of CD137 to study the full repertoire of CD8+ T cells without the need to know epitope specificities

CD137 (4-1BB) is a member of the TNFR-family with costimulatory function, triggering prosurvival signals in activated T-cells. Upregulation of CD137 upon stimulation allows identifying and isolating live, human antigen-specific CD8+ T-cells of all phenotypes, and therefore provides a comprehensive detection method. Furthermore responses against antigen mixtures can be easily detected, enabling antigen discovery in a stepwise deconvoluting approach. In this article, we will discuss various aspects of this methodology, including potential pitfalls as well as a variety of applications, as illustrated by examples from our laboratory.

Induction of alloanergy in human donor T cells without loss of pathogen or tumor immunity

BACKGROUND

Human leukocyte antigen (HLA)-mismatched allogeneic hematopoietic stem cell transplantation (HSCT) is limited by acute graft-versus-host disease (aGvHD). Nonselective T-cell depletion effectively prevents severe aGvHD but profoundly impairs donor-derived immune reconstitution, increasing infection and disease relapse. The strategy of induction of alloantigen-specific hyporesponsiveness ("alloanergization") in donor bone marrow by allostimulation with costimulatory blockade before haploidentical transplantation has demonstrated early promise in reducing severe aGvHD. However, the differential effect of alloanergization on CD4+ and CD8+ donor T-cell subsets and the degree to which beneficial pathogen- and tumor-immune responses are retained have not been extensively examined.

METHODS

We used an in vitro model of alloanergization by allostimulation of human donor T cells with irradiated unrelated recipient peripheral blood mononuclear cells and costimulatory blockade with humanized monoclonal anti-B7.1 and B7.2 antibodies. Residual alloresponses were assessed by proliferation (thymidine uptake, carboxyfluorescein diacetate succinimidyl ester dye dilution) and cytotoxicity assays. Retention of human herpes virus and tumor-associated antigen (TAA)-specific immunity was measured with HLA-class I-restricted pentamers, intracellular cytokine secretion, and CD107a assay using 5-color flow cytometry.

RESULTS

Alloanergization of HLA-mismatched donor T cells efficiently and selectively abrogated recipient-specific alloproliferation in both CD4+ and CD8+ cells while preserving functional CD4+ and CD8+ immune responses to clinically important human herpes viruses and to the TAA WT1.

CONCLUSIONS

Retention of pathogen- and TAA-specific immunity after alloanergization demonstrates that this methodology, which is simple to apply, has potential to improve immune reconstitution while limiting alloreactivity after HLA-mismatched hematopoietic stem cell transplantation, and deserves additional evaluation in further human clinical trials.

Prevention of acute graft-vs-host disease by a single low-dose cyclophosphamide injection following allogeneic bone marrow transplantation

OBJECTIVE

Previously, we documented that conditioning based on donor-specific cell transfusion (DST) and subsequent selective depletion of activated donor-reactive cells by cyclophosphamide (CY) facilitates alloengraftment in a murine transplantation model. Transplantation event represents a strong immunogenic stimulus for host-reactive donor T cells that induce graft-vs-host disease (GVHD). Therefore, in this study, we addressed the question of whether a single posttransplantation CY administration (CY2) can prevent acute GVHD-related mortality without compromising engraftment of allogeneic transplant.

MATERIALS AND METHODS

Splenocyte-enriched C57BL/6 bone marrow was transplanted to BALB/c recipients after mild irradiation, and conditioning with DST and 100 mg/kg CY. Following transplantation, recipients were left untreated or given on a specified day a single CY2 injection (50 mg/kg). All animals were monitored for survival, chimerism, and clinical signs of GVHD. Experimental mice that received BCL1 leukemia cells before transplantation were monitored for leukemia-related mortality as well.

RESULTS

Animals that received no CY2 after transplantation died of acute GVHD. A single low-dose CY2 treatment within the first 5 days after transplantation prevented mortality in most recipients. However, only CY2 administration on days +1 or +5 preserved chimerism. Most chimeras survived GVHD-free for >200 days. Prolonged persistence of host-reactive T cells in mice (CY2 on day +5) permitted a reduction to be made in engraftment-essential irradiation dose and preserved a strong graft-vs-leukemia effect of transplantation.

CONCLUSION

Acute GVHD can be prevented in mice by a single properly timed posttransplantation low-dose CY administration.

Cytotoxic T lymphocytes as immune-therapy in haematological practice

Viral infections are a significant cause of morbidity and mortality, particularly in pediatric allogeneic haematopoietic stem cell transplant recipients. Effective therapies are limited and often associated with significant side effects. Adoptive transfer of virus-reactive T cells offers a means of reconstituting antiviral immunity and this approach has been successfully used to prevent and treat cytomegalovirus, Epstein-Barr virus, and adenovirus infections in vivo. This review outlines the clinical trials that have been performed to date, and will describe future initiatives to (a) develop strategies that can increase the breadth of the viruses that can be targeted, and (b) simplify the process to extend this technology to more centers so that cellular therapy to reconstitute immunity can be more widely applied.

T-cell therapy after hematopoietic stem cell transplantation

PURPOSE OF REVIEW

The separation of graft versus host disease from graft versus leukaemia reactivity and the reconstitution of immunity to infectious agents are the main goals of T-cell therapy after allogeneic hematopoietic stem cell transplantation. We describe how an improved understanding of T-cell mediated graft versus leukemia and of antiviral responses is providing effective approaches to T-cell immunotherapy.

RECENT FINDINGS

Over the past several years, researchers have developed strategies to eliminate alloreactive T cells from the graft, to expand naturally occurring regulatory T cells, and to select and expand antigen-specific T cells specific for tumor-associated or viral antigens. Incorporation of suicide genes allows the selective destruction of allodepleted or antigen-selected cells after infusion, further increasing the safety and potential applicability of these approaches.

SUMMARY

In this review we describe current strategies for adoptive T-cell immunotherapy after hematopoietic stem cell transplantation.

A clinical-scale selective allodepletion approach for the treatment of HLA-mismatched and matched donor-recipient pairs using expanded T lymphocytes as antigen-presenting cells and a TH9402-based photodepletion technique

Selective allodepletion is a strategy to eliminate host-reactive donor T cells from hematopoietic stem cell allografts to prevent graft-versus-host disease while conserving useful donor immune functions. To overcome fluctuations in activation-based surface marker expression and achieve a more consistent and effective allodepletion, we investigated a photodepletion process targeting activation-based changes in p-glycoprotein that result in an altered efflux of the photosensitizer TH9402. Expanded lymphocytes, generated using anti-CD3 and IL-2, were cocultured with responder cells from HLA-matched or -mismatched donors. Optimal results were achieved when cocultured cells were incubated with 7.5 muM TH9402, followed by dye extrusion and exposure to 5 Joule/cm(2) light energy at 5 x 10(6) cells/mL. In mismatched stimulator-responder pairs, the median reduction of alloreactivity was 474-fold (range, 43-fold to 864-fold) compared with the unmanipulated responder. Third-party responses were maintained with a median 1.4-fold (range, 0.9-fold to 3.3-fold) reduction. In matched pairs, alloreactive helper T-lymphocyte precursors were reduced to lower than 1:100 000, while third-party responses remained higher than 1:10 000. This establishes a clinical-scale process capable of highly efficient, reproducible, selective removal of alloreactive lymphocytes from lymphocyte transplant products performed under current Good Manufacturing Practice. This procedure is currently being investigated in a clinical trial of allotransplantation.

Reconstitution of FOXP3+ regulatory T cells (Tregs) after CD25-depleted allotransplantation in elderly patients and association with acute graft-versus-host disease

Selective depletion (SD) of host-reactive donor T cells from allogeneic stem-cell transplants (SCTs) using an anti-CD25 immunotoxin (IT) is a strategy to prevent acute graft-versus-host disease (aGvHD). There is concern that concurrent removal of regulatory T cells (T(regs)) with incomplete removal of alloactivated CD25(+) T cells could increase the risk of aGvHD. We therefore measured T(regs) in the blood of 16 patients receiving a T-cell-depleted allograft together with anti-CD25-IT-treated SD lymphocytes, in 13 of their HLA-identical donors, and in 10 SD products. T(regs) were characterized by intracellular staining for forkhead box protein 3 (FOXP3) and by quantitative reverse-transcription-polymerase chain reaction (qRT-PCR) for FOXP3 gene in CD4(+) cells. Patients received a median of 1.0 x 10(8)/kg SD T cells and a stem cell product containing a median of 0.25 x 10(4)/kg residual T cells. T(regs) reconstituted promptly after SCT and underwent further expansion. Of the CD4(+) T cells in SD products, 1.5% to 4.8% were CD25(-) T(regs). Acute GvHD (>or= grade II) was restricted to 5 patients whose donors had significantly (P = .019) fewer T(regs) compared with those without clinically significant aGvHD. These results suggest that rapid T(reg) reconstitution can occur following SD allografts, either from CD25(-) T(regs) escaping depletion, or from residual CD25(-) and CD25(+) T(regs) contained in the stem-cell product that expand after transplantation and may confer additional protection against GvHD.

The regulation of Foxp3 expression in regulatory CD4(+)CD25(+)T cells: multiple pathways on the road

Regulatory T cells (Treg cells) have been well documented to have a crucial physiological role in preventing the development of autoimmune diseases and keeping self-tolerance. Foxp3, a recently identified member of the forkhead transcription factors, serves as a master regulator for the development and function of CD4(+)CD25(+)Treg cells. Though it is well defined that Foxp3 expression is sufficient to program CD4(+)CD25(+)Treg cell development, the physiological factors initiating intracellular Foxp3 expression remain poorly understood so far. In the present manuscript, we try to summarize the recent advances regarding the regulatory roles of T-cell receptor (TCR), co-stimulatory molecules, interleukin-2 (IL-2), transforming growth factor-beta (TGF-beta) and beyond pathways on Foxp3 expression.

In vitro methotrexate as a practical approach to selective allodepletion

Graft-versus-host disease (GVHD) is a major cause of transplant-related morbidity and mortality in recipients of allogeneic hematopoietic stem cell transplantation. As GVHD is mediated predominantly by alloreactive donor T cells, selective allodepletion from the graft may alleviate GVHD, whereas potentially maintaining other advantages conferred by donor T cells, such as graft survival, antiviral immunity, and graft-versus-leukemia effect. In this study, we evaluated the ability of methotrexate, a clinically approved antimetabolite drug, to deplete alloreactive T cells in HLA-mismatched mixed lymphocyte reactions (MLR). We observed that methotrexate could inhibit the proliferation of alloreactive T cells in primary in vitro MLR. On reexposure of methotrexate-treated cells to the same allostimulus, a significant reduction in the alloreactive immune response was observed, whereas responses to third-party allostimuli and viral antigens were preserved. Thus, our results provide preclinical evidence that in vitro methotrexate treatment results in specific allodepletion and may be used as an effective agent for preventing GVHD.

Apoptosis-induced decrease of intrathyroidal CD4(+)CD25(+) regulatory T cells in autoimmune thyroid diseases

BACKGROUND

We previously showed that the proportion of CD4(+) T cells was lower and both the proportion and intensity of Fas expression on intrathyroidal CD4(+) T cells were higher in the thyroid than in the peripheral blood of patients with autoimmune thyroid disease (AITD).

OBJECTIVE

To clarify whether the intrathyroidal CD4(+)CD25(+) regulatory T (Treg) cells are decreased by Fas-mediated apoptosis in patients with AITD.

DESIGN

We examined intrathyroidal and peripheral lymphocytes in 20 patients with AITD (15 patients with Gravesâ disease and five patients with Hashimotoâs disease) and peripheral lymphocytes in 10 healthy volunteers by three-color flow cytometry.

MAIN OUTCOME

The proportion of CD4(+)CD25(+) cells was lower in the thyroid of patients with AITD than in the peripheral blood of the same patients or the peripheral blood of the healthy subjects. The proportions of CD4(+)CD25(+)CD69() cells and Forkhead box P3 (Foxp3)(+)CD4(+)CD25(+) cells, which constitute more specific Treg subsets than CD4(+)CD25(+) cells, were also lower in the thyroid than in the peripheral blood of patients with AITD. The proportion of apoptotic cells was higher among intrathyroidal CD4(+) cells than among peripheral CD4(+) cells and higher among intrathyroidal CD4(+)CD25(+) cells than among intrathyroidal CD4(+)CD25() cells.

CONCLUSION

These results indicate that intrathyroidal Treg cells are decreased in response to apoptosis in patients with AITD. This decrease in Treg cells may contribute to the incomplete regulation of autoreactive T cells in AITD.

Assay for monitoring in vitro selective depletion strategies in allogeneic stem cell transplantation

BACKGROUND

GvHD is a serious and potentially life-threatening side-effect of allogeneic BMT, caused by alloreactive cells attacking normal host cells. A number of different approaches have been attempted to remove allo-activated cells from the graft prior to transplantation. When developing such assays, there is a need to control for unwanted removal of cells, as well as depletion efficiency related to activation kinetics.

METHODS

The specific activation induced by the superantigens SEB and TSST-1 of T cells with defined Vbeta chains was utilized to follow activation of bystander cells and the kinetics of specific cellular activation by flow cytometry.

RESULTS

The activation marker CD69 was up-regulated on bystander T cells, and was only transiently highly expressed on the specific T cells, making this marker unreliable for removal of alloreactive cells. In contrast, CD25 was found only on specifically activated T cells and was stably expressed over several days. However, it was not detected on all specific cells until day 6. Likewise, proliferation occurred only in T cells expressing the expected Vbeta chains, with all activated cells having undergone at least one cell cycle by day 4.

DISCUSSION

In conclusion, our assay demonstrates that only temporary bystander activation occurs when polyclonally activating T cells by SEB or TSST-1, and that CD25, but not CD69, can be used for removal of specifically activated cells. Furthermore, this assay is useful for monitoring methods aiming at specific removal of cycling cells.