Depletion of T regulatory cells through selection of CD127-positive cells results in a population enriched in memory T cells: implications for anti-tumor cell therapy

TNFR2 blockade of regulatory T cells unleashes an antitumor immune response after hematopoietic stem-cell transplantation

Background

Targeting immune checkpoints that inhibit antitumor immune responses has emerged as a powerful new approach to treat cancer. We recently showed that blocking the tumor necrosis factor receptor-type 2 (TNFR2) pathway induces the complete loss of the protective function of regulatory T cells (Tregs) in a model of graft-versus-host disease (GVHD) prevention that relies on Treg-based cell therapy. Here, we tested the possibility of amplifying the antitumor response by targeting TNFR2 in a model of tumor relapse following hematopoietic stem-cell transplantation, a clinical situation for which the need for efficient therapeutic options is still unmet.

Method

We developed appropriate experimental conditions that mimic patients that relapsed from their initial hematological malignancy after hematopoietic stem-cell transplantation. This consisted of defining in allogeneic bone marrow transplantation models developed in mice, the maximum number of required tumor cells and T cells to infuse into recipient mice to develop a model of tumor relapse without inducing GVHD. We next evaluated whether anti-TNFR2 treatment could trigger alloreactivity and consequently antitumor immune response. In parallel, we also studied the differential expression of TNFR2 on T cells including Treg from patients in post-transplant leukemia relapse and in patients developing GVHD.

Results

Using experimental conditions in which neither donor T cells nor TNFR2-blocking antibody per se have any effect on tumor relapse, we observed that the coadministration of a suboptimal number of T cells and an anti-TNFR2 treatment can trigger alloreactivity and subsequently induce a significant antitumor effect. This was associated with a reduced percentage of activated CD4⁺ and CD8⁺ Tregs. Importantly, human Tregs over-expressed TNFR2 relative to conventional T cells in healthy donors and in patients experiencing leukemia relapse or cortico-resistant GVHD after hematopoietic stem cell transplantation.

Conclusions

These results highlight TNFR2 as a new target molecule for the development of immunotherapies to treat blood malignancy relapse, used either directly in grafted patients or to enhance donor lymphocyte infusion strategies. More widely, they open the door for new perspectives to amplify antitumor responses against solid cancers by directly targeting Tregs through their TNFR2 expression.

Human Apoptotic Cells, Generated by Extracorporeal Photopheresis, Modulate Allogeneic Immune Response

The induction of specific and sustainable tolerance is a challenging issue in organ transplantation. The discovery of the immunosuppressive properties of apoptotic cells in animal models has paved the way for their use in human transplantation. In this work, we aimed to define a stable, reproducible, and clinically compatible production procedure of human apoptotic cells (Apo-cells). Using a clinically approved extracorporeal photopheresis technique, we have produced and characterized phenotypically and functionally human apoptotic cells. These Apo-cells have immunosuppressive properties proved in vitro and in vivo in NOD/SCID/γC mice by their capacity to modulate an allogeneic response following both a direct and an indirect antigen presentation. These results brought the rationale for the use of Apo-cells in tolerance induction protocol for organ transplantation.

Targeting Aurora kinase A and JAK2 prevents GVHD while maintaining Treg and antitumor CTL function

Graft-versus-host disease (GVHD) is a leading cause of nonrelapse mortality after allogeneic hematopoietic cell transplantation. T cell costimulation by CD28 contributes to GVHD, but prevention is incomplete when targeting CD28, downstream mammalian target of rapamycin (mTOR), or Aurora A. Likewise, interleukin-6 (IL-6)-mediated Janus kinase 2 (JAK2) signaling promotes alloreactivity, yet JAK2 inhibition does not eliminate GVHD. We provide evidence that blocking Aurora A and JAK2 in human T cells is synergistic in vitro, prevents xenogeneic GVHD, and maintains antitumor responses by cytotoxic T lymphocytes (CTLs). Aurora A/JAK2 inhibition is immunosuppressive but permits the differentiation of inducible regulatory T cells (iT_regs) that are hyperfunctional and CD39 bright and efficiently scavenge adenosine triphosphate (ATP). Increased iT_reg potency is primarily a function of Aurora A blockade, whereas JAK2 inhibition suppresses T helper 17 (T_H17) differentiation. Inhibiting either Aurora A or JAK2 significantly suppresses T_H1 T cells. However, CTL generated in vivo retains tumor-specific killing despite Aurora A/JAK2 blockade. Thus, inhibiting CD28 and IL-6 signal transduction pathways in donor T cells can increase the T_reg/T_conv ratio, prevent GVHD, and preserve antitumor CTL.

IL-2 promotes early Treg reconstitution after allogeneic hematopoietic cell transplantation

Graft-versus-host disease (GvHD) remains a major cause of transplant-related mortality. Interleukin-2 (IL-2) plus sirolimus (SIR) synergistically reduces acute GvHD in rodents and promotes regulatory T cells. This phase II trial tested the hypothesis that IL-2 would facilitate STAT5 phosphorylation in donor T cells, expand regulatory T cells, and ameliorate GvHD. Between 16th April 2014 and 19th December 2015, 20 patients received IL-2 (200,000 IU/m2 thrice weekly, days 0 to +90) with SIR (5-14 ng/mL) and tacrolimus (TAC) (3-7 ng/mL) after HLA-matched related or unrelated allogeneic hematopoietic cell transplantation (HCT). The study was designed to capture an increase in regulatory T cells from 16.0% to more than 23.2% at day +30. IL-2/SIR/TAC significantly increased regulatory T cells at day +30 compared to our published data with SIR/TAC (23.8% vs. 16.0%, P=0.0016; 0.052 k/uL vs. 0.037 k/uL, P=0.0163), achieving the primary study end point. However, adding IL-2 to SIR/TAC led to a fall in regulatory T cells by day +90 and did not reduce acute or chronic GvHD. Patients who discontinued IL-2 before day +100 showed a suggested trend toward less grade II-IV acute GvHD (16.7% vs. 50%, P=0.1475). We surmise that the reported accumulation of IL-2 receptors in circulation over time may neutralize IL-2, lead to progressive loss of regulatory T cells, and offset its clinical efficacy. The amount of phospho-STAT3+ CD4+ T cells correlated with donor T-cell activation and acute GvHD incidence despite early T-cell STAT5 phosphorylation by IL-2. Optimizing IL-2 dosing and overcoming cytokine sequestration by soluble IL-2 receptor may sustain lasting regulatory T cells after transplantation. However, an approach to target STAT3 is needed to enhance GvHD prevention. (clinicaltrials.gov identifier: 01927120).

Generation of Human Alloantigen-Specific Regulatory T Cells under Good Manufacturing Practice-Compliant Conditions for Cell Therapy

Natural regulatory T cells (Tregs) may have a great therapeutic potential to induce tolerance in allogeneic cells and organ transplantations. In mice, we showed that alloantigen-specific Tregs (spe-Tregs) were more efficient than polyclonal Tregs (poly-Tregs) in controlling graft-versus-host disease (GVHD). Here we describe a clinical-grade compliant method for generating human spe-Tregs. Tregs were enriched from leukapheresis products with anti-CD25 immunomagnetic beads, primed twice by allogeneic mature monocyte-derived dendritic cells (mDCs), and cultured during 3 weeks in medium containing interleukin 2 (IL-2), IL-15, and rapamycin. After 3 weeks of culture, final cell products were expanded 8.3-fold from the initial CD25+ purifications. Immunophenotypic analyses of final cells indicate that they were composed of 88 ± 2.6% of CD4+ T cells, all expressing Treg-specific markers (FOXP3, Helios, GARP, LAP, and CD152). Spe-Tregs were highly suppressive in vitro and also in vivo using a xeno-GVHD model established in immunodeficient mice. The specificity of their suppressive activity was demonstrated on their ability to significantly suppress the proliferation of autologous effector T cells stimulated by the same mDCs compared to third-party mDCs. Our data provide evidence that functional alloantigen Tregs can be generated under clinical-grade compliant conditions. Taking into account that 130 × 106 CD25+ cells can be obtained at large scale from standard leukapheresis, our cell process may give rise to a theoretical final number of 1 × 109 spe-Tregs. Thus, using our strategy, we can propose to prepare spe-Tregs for clinical trials designed to control HLA-mismatched GVHD or organ transplantation rejection.

Adoptive immunotherapy for cancer

Recent clinical success has underscored the potential for immunotherapy based on the adoptive cell transfer (ACT) of engineered T lymphocytes to mediate dramatic, potent, and durable clinical responses. This success has led to the broader evaluation of engineered T-lymphocyte-based adoptive cell therapy to treat a broad range of malignancies. In this review, we summarize concepts, successes, and challenges for the broader development of this promising field, focusing principally on lessons gleaned from immunological principles and clinical thought. We present ACT in the context of integrating T-cell and tumor biology and the broader systemic immune response.

Regulating the regulators in cancer-immunosuppression in multiple myeloma (MM)

An effective immune response requires a prompt but measured action against the pathological insult, to prevent over-zealous inflammatory-mediated tissue destruction. In cancer, defective or incompetent immune responses may paradoxically result in disease progression despite an immune attempt at elimination. Tumour-induced immunosuppression may not only result from soluble factors and altered antigenicity, but also from cellular-mediated tumour-induced immune evasion. Multiple myeloma (MM) is associated with both cellular and humoral immune deficiencies and increased T(Reg) cells. In vitro modelling has indicated that the tumour cells directly induce functional T(Reg) cells. In light of this recent evidence, it now seems that the most promising and synergistic approaches for cancer immunotherapy would involve specific anti-tumour immunity and simultaneous reduction of tumour-induced immune-regulation. This review sets out the basic understanding of the human immune response, its dysregulation in cancer and proposes how this knowledge may influence future treatment strategies to maximise the anti-tumour immune response.