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We conducted a multicenter prospective single-arm phase 1/2 study that assesses the outcome of αβ T-cell depleted allogeneic hematopoietic stem cell transplantation (allo-HSCT) of peripheral blood derived stem cells from matched related, or unrelated donors (10/10 and 9/10) in adults, with the incidence of acute graft-versus-host disease (aGVHD) as the primary end point at day 100. Thirty-five adults (median age, 59; range, 19-69 years) were enrolled. Conditioning consisted of antithymocyte globulin, busulfan, and fludarabine, followed by 28 days of mycophenolic acid after allo-HSCT. The minimal follow-up time was 24 months. The median number of infused CD34+ cells and αβ T cells were 6.1 × 106 and 16.3 × 103 cells per kg, respectively. The cumulative incidence (CI) of aGVHD grades 2-4 and 3-4 at day 100 was 26% and 14%. One secondary graft failure was observed. A prophylactic donor lymphocyte infusion (DLI) (1 × 105 CD3+ T cells per kg) was administered to 54% of the subjects, resulting in a CI of aGVHD grades 2-4 and 3-4 to 37% and 17% at 2 years. Immune monitoring revealed an early reconstitution of natural killer (NK) and γδ T cells. Cytomegalovirus reactivation associated with expansion of memory-like NK cells. The CI of relapse was 29%, and the nonrelapse mortality 32% at 2 years. The 2-year CI of chronic GVHD (cGVHD) was 23%, of which 17% was moderate. We conclude that only 26% of patients developed aGVHD 2-4 after αβ T-cell–depleted allo-HSCT within 100 days and was associated with a low incidence of cGVHD after 2 years. This trial was registered at www.trialregister.nl as #NL4767.

Purpose of review: The outcome of allogeneic stem cell transplantation (allo-HCT) is still compromised by relapse and complications. NK cells and γδT cells, effectors which both function through MHC-unrestricted mechanisms, can target transformed and infected cells without inducing Graft-versus-Host Disease (GVHD). Allo-HCT platforms based on CD34+ selection or αβ-TCR depletion result in low grades of GVHD, early immune reconstitution (IR) of NK and γδT cells and minimal usage of GVHD prophylaxis. In this review we will discuss strategies to retain and expand the quantity, diversity and functionality of these reconstituting innate cell types. Recent findings: Bisphosphonates, IL-15 cytokine administration, specific antibodies, checkpoint inhibitors and (CMV based) vaccination are currently being evaluated to enhance IR. All these approaches have shown to potentially enhance both NK and γδT cell immuno-repertoires. Summary: Rapidly accumulating data linking innate biology to proposed clinical immune interventions, will give unique opportunities to unravel shared pathways which determine the Graft-versus-Tumor effects of NK and γδT cells.

Relapse is the most frequent cause of treatment failure after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Natural killer (NK) cells and γδ T cells reconstitute early after allo-HSCT, contribute to tumor immunosurveillance via major histocompatibility complex–independent mechanisms and do not induce graft-versus-host disease. Here we performed a quantitative and qualitative analysis of the NK and γδ T cell repertoire in healthy individuals, recipients of HLA-matched sibling or unrelated donor allo-HSCT (MSD/MUD-HSCT) and umbilical cord blood-HSCT (UCB-HSCT). NK cells are present at high frequencies in all allo-HSCT recipients. Immune reconstitution (IR) of vδ2+ cells depended on stem cell source. In MSD/MUD-HSCT recipients, vδ2+ comprise up to 8% of the total lymphocyte pool, whereas vδ2+ T cells are barely detectable in UCB-HSCT recipients. Vδ1+ IR was driven by CMV reactivation and was comparable between MSD/MUD-HSCT and UCB-HSCT. Strategies to augment NK cell mediated tumor responses, similar to IL-15 and antibodies, also induced vδ2+ T cell responses against a variety of different tumor targets. Vδ1+ γδ T cells were induced less by these same stimuli. We also identified elevated expression of the checkpoint inhibitory molecule TIGIT (T cell Ig and ITIM domain), which is also observed on tumor-infiltrating lymphocytes and epidermal γδ T cells. Collectively, these data show multiple strategies that can result in a synergized NK and γδ T cell antitumor response. In the light of recent developments of low-toxicity allo-HSCT platforms, these interventions may contribute to the prevention of early relapse.

The induction of mixed hematopoietic chimerism following allogeneic stem cell transplantation is a potential treatment modality for numerous nonmalignant diseases and generates a robust state of donor-specific tolerance. However, despite several promising results in murine studies, the translation to nonhuman primate models and clinical trials has proven to be more difficult. In contrast to specific pathogen-free bred laboratory mice, the immune system of humans has been in repeated contact with numerous pathogens, resulting in a broad memory-T-cell repertoire. Crossreactivity of the virus-specific memory-T-cell pool against alloantigens has been described in a phenomenon called heterologous immunity. In this study, we demonstrate, in a murine stem cell transplantation model, that heterologous immunity is likely to be an important barrier for the induction of mixed hematopoietic chimerism after immunologic conditioning in the absence of cytoreduction. Additional T-cell depletion or a brief cyclosporine treatment can be applied to overcome the barrier of heterologous immunity.

Adoptive transfer of antigen-specific T cells is an attractive means to provide cancer patients with immune cells of a desired specificity and the efficacy of such adoptive transfers has been demonstrated in several clinical trials. Because the T cell receptor is the single specificity-determining molecule in T cell function, adoptive transfer of TCR genes into patient T cells may be used as an alternative approach for the transfer of tumor-specific T cell immunity. On theoretical grounds, TCR gene therapy has two substantial advantages over conventional cellular transfer. First, it circumvents the demanding process of in vitro generation of large numbers of specific immune cells. Second, it allows the use of a set of particularly effective TCR genes in large patient groups. Conversely, TCR gene therapy may be associated with a number of specific problems that are not confronted during classical cellular therapy. Here we review our current understanding of the potential and possible problems of TCR gene therapy, as based on in vitro experiments, mouse model systems and phase I clinical trials. Furthermore, we discuss the prospects of widespread clinical application of this gene therapy approach for the treatment of human cancer.

Adoptive transfer of TCR gene-modified T cells has been proposed as an attractive approach to target tumors for which it is difficult or impossible to induce strong tumor-specific T cell responses by vaccination. Whereas the feasibility of generating tumor Ag-specific T cells by gene transfer has been demonstrated, the factors that determine the in vivo effectiveness of TCR-modified T cells are largely unknown. We have analyzed the value of a number of clinically feasible strategies to enhance the antitumor potential of TCR modified T cells. These experiments reveal three factors that contribute greatly to the in vivo potency of TCR-modified T cells. First, irradiation-induced host conditioning is superior to vaccine-induced activation of genetically modified T cells. Second, increasing TCR expression through genetic optimization of TCR sequences has a profound effect on in vivo antitumor activity. Third, a high precursor frequency of TCR modified T cells within the graft is essential. Tumors that ultimately progress in animals treated with this optimized regimen for TCR-based adoptive cell transfer invariably display a reduced expression of the target Ag. This suggests TCR gene therapy can achieve a sufficiently strong selective pressure to warrant the simultaneous targeting of multiple Ags. The strategies outlined in this study should be of value to enhance the antitumor activity of TCR-modified T cells in clinical trials.

Transfer of either allogeneic or genetically modified T cells as a therapy for malignancies can be accompanied by T cell-mediated tissue destruction. The introduction of an efficient “safety switch” can potentially be used to control the survival of adoptively transferred cell populations and as such reduce the risk of severe graft-vs-host disease. In this study, we have tested the value of an inducible caspase 9-based safety switch to halt an ongoing immune attack in a murine model for cell therapy-induced type I diabetes. The data obtained in this model indicate that self-reactive T cells expressing this conditional safety switch show unimpaired lymphopenia- and vaccine-induced proliferation and effector function in vivo, but can be specifically and rapidly eliminated upon triggering. These data provide strong support for the evaluation of this conditional safety switch in clinical trials of adoptive cell therapy.

Minor histocompatibility antigen (MiHAg) differences between donor and recipient in MHC-matched allogeneic hematopoietic stem cell transplantation (allo-HSCT) often result in graft-versus-host disease (GVHD). While MiHAg-specific T-cell responses can in theory be directed against a large number of polymorphic differences between donor and recipient, in practice, T-cell responses against only a small set of MiHAgs appear to dominate the immune response, and it has been suggested that immunodominance may predict an important contribution to the development of GVHD. Here, we addressed the feasibility of graft engineering by ex vivo removal of T cells with 1 or more defined antigen specificities in a well-characterized experimental HSCT model (B6 → BALB.B). We demonstrate that immunodominant H60- and H4-specific CD8+ T-cell responses can be effectively suppressed through MHC class I tetramer–mediated purging of the naive CD8+ T cell repertoire. Importantly, the development of GVHD occurs unimpeded upon suppression of the immunodominant MiHAg-specific T-cell response. These data indicate that antigen-specific graft engineering is feasible, but that parameters other than immunodominance may be required to select T-cell specificities that are targeted for removal.

Adoptive transfer of T-cell receptor (TCR) genes has been proposed as an attractive approach for immunotherapy in cases where the endogenous T-cell repertoire is insufficient. While there are promising data demonstrating the capacity of TCR-modified T cells to react to foreign antigen encounter, the feasibility of targeting tumor-associated self-antigens has not been addressed. Here we demonstrate that T-cell receptor gene transfer allows the induction of defined self-antigen–specific T-cell responses, even when the endogenous T-cell repertoire is nonreactive. Furthermore, we show that adoptive transfer of T-cell receptor genes can be used to induce strong antigen-specific T-cell responsiveness in partially MHC-mismatched hosts without detectable graft versus host disease. These results demonstrate the feasibility of using a collection of “off the shelf” T-cell receptor genes to target defined tumor-associated self-antigens and thereby form a clear incentive to test this immunotherapeutic approach in a clinical setting.

The transfer of T cell receptor (TCR) genes can be used to induce immune reactivity toward defined antigens to which endogenous T cells are insufficiently reactive. This approach, which is called TCR gene therapy, is being developed to target tumors and pathogens, and its clinical testing has commenced in patients with cancer. In this study we show that lethal cytokine-driven autoimmune pathology can occur in mouse models of TCR gene therapy under conditions that closely mimic the clinical setting. We show that the pairing of introduced and endogenous TCR chains in TCR gene-modified T cells leads to the formation of self-reactive TCRs that are responsible for the observed autoimmunity. Furthermore, we demonstrate that adjustments in the design of gene therapy vectors and target T cell populations can be used to reduce the risk of TCR gene therapy-induced autoimmune pathology.

Analogous to the clinical use of recombinant high-affinity Abs, transfer of TCR genes may be used to create a T cell compartment specific for self-Ags to which the endogenous T cell repertoire is immune tolerant. In this study, we show in a spontaneous prostate carcinoma model that the combination of vaccination with adoptive transfer of small numbers of T cells that are genetically modified with a tumor-specific TCR results in a marked suppression of tumor development, even though both treatments are by themselves without effect. These results demonstrate the value of TCR gene transfer to target otherwise nonimmunogenic tumor-associated self-Ags provided that adoptive transfer occurs under conditions that allow in vivo expansion of the TCR-modified T cells.

To broaden the applicability of adoptive T cell therapy to cancer types for which tumor-specific T cells cannot routinely be isolated, an effort has been made to develop the transfer of tumor-specific TCR genes into autologous T cells as a novel immunotherapeutic approach. Although such TCR-modified T cells have been shown to react to Ag encounter and can be used to break tolerance to defined self-Ags, the persistence and capacity for renewed expansion of TCR-modified T cells has not been analyzed. To establish whether TCR-transduced T cells can provide recipients with long-term Ag-specific immune protection, we analyzed long-term function of TCR transduced T cells in mouse model systems. We demonstrate that polyclonal populations of T cells transduced with a class I restricted OVA-specific TCR are able to persist in vivo and respond upon re-encounter of cognate Ag as assessed by both proliferation and cytolytic capacity. These experiments indicate that TCR gene transfer can be used to generate long-term Ag-specific T cell responses and provide a useful model system to assess the factors that can promote high-level persistence of TCR-modified T cells.

Adoptive cell transfer therapy using tumor-infiltrating lymphocytes for patients with metastatic melanoma has demonstrated significant objective response rates. One major limitation of these current therapies is the frequent inability to isolate tumor-reactive lymphocytes for treatment. Genetic engineering of peripheral blood lymphocytes with retroviral vectors encoding tumor antigen-specific T-cell receptors (TCRs) bypasses this restriction. To evaluate the efficacy of TCR gene therapy, a murine treatment model was developed. A retroviral vector was constructed encoding the pmel-1 TCR genes targeting the B16 melanoma antigen, gp100. Transduction of C57BL/6 lymphocytes resulted in efficient pmel-1 TCR expression. Lymphocytes transduced with this retrovirus specifically recognized gp100-pulsed target cells as measured by interferon-gamma secretion assays. Upon transfer into B16 tumor-bearing mice, the genetically engineered lymphocytes significantly slowed tumor development. The effectiveness of tumor treatment was directly correlated with the number of TCR-engineered T cells administered. These results demonstrated that TCR gene therapy targeting a native tumor antigen significantly delayed the growth of established tumors. When C57BL/6 lymphocytes were added to antigen-reactive pmel-1 T cells, a reduction in the ability of pmel-1 T cell to treat B16 melanomas was seen, suggesting that untransduced cells may be deleterious to TCR gene therapy. This model may be a powerful tool for evaluating future TCR gene transfer-based strategies.

Gene therapy for the treatment of HIV has long been a goal of many investigators. The majority of trials have involved the use of lymphocytes transduced with vectors promoting resistance to HIV infection or replication. Unfortunately, the results have been less than encouraging with low-level marking and, more importantly, clearance of these lymphocytes from the circulation. Conversely, gene-modified hematopoietic stem cells appear able to introduce foreign transgenes while avoiding immunologic clearance. Furthermore, the use of less toxic conditioning regimens for allogeneic transplantation provides an attractive approach to conferring HIV resistance while allowing treatment of HIV-related disorders such as malignancies. This combination of nonmyeloablative allogeneic transplantation using gene-modified hematopoietic stem cell theoretically overcomes the high transplant mortality associated with traditional conditioning regimens in patients with HIV as well as providing a self-renewing source of HIV-resistant cells. To assess the safety and feasibility of such an approach, a clinical protocol was initiated in those patients infected with HIV with a hematologic malignancy meeting the standard indications for allogeneic transplantation and provided here is an update to the previously published original report. Only patient 1 received genetically modified cells. Both patients tolerated the procedure with no effect on viral load and improved CD4 counts, and patient 1 remains in complete remission from acute myelogenous leukemia 3 years post transplant. Patient 2 also achieved clinical remission from chemorefractory Hodgkin's disease but died of relapsed disease 12 months after transplantation. Vector-transduced cells remain detectable at low levels more than 3 years post-transplantation, suggesting the potential for gene therapy as a reasonable goal for the treatment of HIV.

To assess the safety and efficacy of nonmyeloablative allogeneic transplantation in patients with HIV infection, a clinical protocol was initiated in patients with refractory hematologic malignancies and concomitant HIV infection. The results from the first 2 patients are reported. The indications for transplantation were treatment-related acute myelogenous leukemia and primary refractory Hodgkin disease in patients 1 and 2, respectively. Only patient 1 received genetically modified cells. Both patients tolerated the procedure well with minimal toxicity, and complete remissions were achieved in both patients, but patient 2 died of relapsed Hodgkin disease 12 months after transplantation. Patient 1 continues in complete remission with undetectable HIV levels and rising CD4 counts, and with both the therapeutic and control gene transfer vectors remaining detectable at low levels more than 2 years after transplantation. These results suggest that nonmyeloablative allogeneic transplantation in the context of highly active antiretroviral therapy is feasible in patients with treatment-sensitive HIV infection.

To investigate the correlation between the incA I47T mutation in Chlamydia trachomatis and the nonfusogenic phenotype, the incA genes of 25 isolates were sequenced. Four major sequence types were identified. Seven isolates (28%) had the I47T mutation. Isolates representing the four sequence types expressed IncA in the membrane of one large single inclusion. In conclusion, the incA I47T mutation is not associated with the nonfusogenic phenotype.

IMMUNOBIOLOGY T-cell immunotherapy of human cancers is in most cases dependent on circumventing the tolerance of T cells to tumor-associated antigens. One approach to circumvent T-cell tolerance would be formed by HLA-mismatched bone marrow transplantation (BMT) coupled to donor lymphocyte infusion

Top of pageAbstract Adoptive therapy with allogeneic or tumor-specific T cells has shown substantial clinical effects for several human tumors, but the widespread application of this strategy remains a daunting task. As an alternative to the adoptive transfer of T cells, we and others have examined the feasibility of transfer of T cell receptor genes into recipient T cells. The antigen-specificity of T lymphocytes is solely determined by the T cell receptor (TCR) α and β chains. Consequently, genetic transfer of TCR chains may form an appealing strategy to impose a desirable tumor-antigen specificity onto cytotoxic or helper T cell populations. In this strategy, autologous or donor-derived T cell populations are equipped with a TCR of defined reactivity in short-term ex vivo cultures, and re-infusion of the redirected cells is used to supply T cell reactivity against defined tumor-specific antigens. We have previously described the genetic introduction of an antigen-specific T cell receptor into peripheral T cells in a mouse model system1. These experiments reveal that T cells that are redirected by TCR gene transfer expand dramatically upon in vivo antigen encounter and efficiently home to effector sites. While these data demonstrated that redirected T cells can function in vivo, two issues that are essential for the application of this strategy in the human setting2 remained unaddressed: - Can redirected T cells function in an allogeneic, partially MHC-mismatched setting? - Can redirected T cells be used to target specific tissues in settings where the endogenous T cell repertoire fails due to self-tolerance? We have now addressed these two issues in murine model systems. Collectively, these data suggest that redirection of T cells by TCR gene therapy forms a viable new strategy for the rapid induction of tumor-specific immunity.