Cancer Immunotherapy Using γδT Cells: Dealing with Diversity

Innate and adaptive effector immune drivers of cytomegalovirus disease in lung transplantation: a double-edged sword

Up to 90% of the global population has been infected with cytomegalovirus (CMV), a herpesvirus that remains latent for the lifetime of the host and drives immune dysregulation. CMV is a critical risk factor for poor outcomes after solid organ transplant, though lung transplant recipients (LTR) carry the highest risk of CMV infection, and CMV-associated comorbidities compared to recipients of other solid organ transplants. Despite potent antivirals, CMV remains a significant driver of chronic lung allograft dysfunction (CLAD), re-transplantation, and death. Moreover, the extended utilization of CMV antiviral prophylaxis is not without adverse effects, often necessitating treatment discontinuation. Thus, there is a critical need to understand the immune response to CMV after lung transplantation. This review identifies key elements of each arm of the CMV immune response and highlights implications for lung allograft tolerance and injury. Specific attention is paid to cellular subsets of adaptive and innate immune cells that are important in the lung during CMV infection and reactivation. The concept of heterologous immune responses is reviewed in depth, including how they form and how they may drive tissue- and allograft-specific immunity. Other important objectives of this review are to detail the emerging role of NK cells in CMV-related outcomes, in addition to discussing perturbations in CMV immune function stemming from pre-existing lung disease. Finally, this review identifies potential mechanisms whereby CMV-directed treatments may alter the cellular immune response within the allograft.

A new prognostic model based on gamma-delta T cells for predicting the risk and aiding in the treatment of clear cell renal cell carcinoma

BACKGROUND

ccRCC is the prevailing form of RCC, accounting for the majority of cases. The formation of cancer and the body's ability to fight against tumors are strongly connected to Gamma delta (γδ) T cells.

METHODS

We examined and analyzed the gene expression patterns of 535 individuals diagnosed with ccRCC and 72 individuals serving as controls, all sourced from the TCGA-KIRC dataset, which were subsequently validated through molecular biology experiments.

RESULTS

In ccRCC, we discovered 304 module genes (DEGRGs) that were ex-pressed differentially and linked to γδ T cells. A risk model for ccRCC was constructed using 13 differentially DEGRGs identified through univariate Cox and LASSO regression analyses, which were found to be associated with prognosis. The risk model exhibited outstanding performance in both the training and validation datasets. The comparison of immune checkpoint inhibitors and the tumor immune microenvironment between the high- and low-risk groups indicates that immunotherapy could lead to positive results for low-risk patients. Moreover, the inhibition of ccRCC cell proliferation, migration, and invasion was observed in cell culture upon knocking down TMSB10, a gene associated with different types of cancers.

CONCLUSIONS

In summary, we have created a precise predictive biomarker using a risk model centered on γδ T cells, which can anticipate clinical results and provide direction for the advancement of innovative targeted therapies.

The capability of heterogeneous γδ T cells in cancer treatment

γδ T cells, a specialized subset of T lymphocytes, have garnered significant attention within the realm of cancer immunotherapy. Operating at the nexus between adaptive and innate immunological paradigms, these cells showcase a profound tumor discernment repertoire, hinting at novel immunotherapeutic strategies. Significantly, these cells possess the capability to directly identify and eliminate tumor cells without reliance on HLA-antigen presentation. Furthermore, γδ T cells have the faculty to present tumor antigens to αβ T cells, amplifying their anti-tumoral efficacy.Within the diverse and heterogeneous subpopulations of γδ T cells, distinct immune functionalities emerge, manifesting either anti-tumor or pro-tumor roles within the tumor microenvironment. Grasping and strategically harnessing these heterogeneous γδ T cell cohorts is pivotal to their integration in tumor-specific immunotherapeutic modalities. The aim of this review is to describe the heterogeneity of the γδ T cell lineage and the functional plasticity it generates in the treatment of malignant tumors. This review endeavors to elucidate the intricate heterogeneity inherent to the γδ T cell lineage, the consequential functional dynamics in combating malignancies, the latest advancements from clinical trials, and the evolving landscape of γδ T cell-based oncological interventions, while addressing the challenges impeding the field.

Challenges and new technologies in adoptive cell therapy

Adoptive cell therapies (ACTs) have existed for decades. From the initial infusion of tumor-infiltrating lymphocytes to the subsequent specific enhanced T cell receptor (TCR)-T and chimeric antigen receptor (CAR)-T cell therapies, many novel strategies for cancer treatment have been developed. Owing to its promising outcomes, CAR-T cell therapy has revolutionized the field of ACTs, particularly for hematologic malignancies. Despite these advances, CAR-T cell therapy still has limitations in both autologous and allogeneic settings, including practicality and toxicity issues. To overcome these challenges, researchers have focused on the application of CAR engineering technology to other types of immune cell engineering. Consequently, several new cell therapies based on CAR technology have been developed, including CAR-NK, CAR-macrophage, CAR-γδT, and CAR-NKT. In this review, we describe the development, advantages, and possible challenges of the aforementioned ACTs and discuss current strategies aimed at maximizing the therapeutic potential of ACTs. We also provide an overview of the various gene transduction strategies employed in immunotherapy given their importance in immune cell engineering. Furthermore, we discuss the possibility that strategies capable of creating a positive feedback immune circuit, as healthy immune systems do, could address the flaw of a single type of ACT, and thus serve as key players in future cancer immunotherapy.

Biological characteristics of γδT cells and application in tumor immunotherapy

Human γδT cells are a special immune cell type which exist in small quantities in the body, do not require processing and presentation for antigen recognition, and have non-major histocompatibility complex (MHC)-restricted immune response. They play an important role in the body's anti-tumor, anti-infection, immune regulation, immune surveillance and maintenance of immune tolerance. This article reviews the generation and development of human γδT cells, genetic characteristics, classification, recognition and role of antigens, and research progress in tumor immunotherapy.

TCR-Vγδ usage distinguishes protumor from antitumor intestinal γδ T cell subsets

γδ T cells represent a substantial fraction of intestinal lymphocytes at homeostasis, but they also constitute a major lymphocyte population infiltrating colorectal cancers (CRCs); however, their temporal contribution to CRC development or progression remains unclear. Using human CRC samples and murine CRC models, we found that most γδ T cells in premalignant or nontumor colons exhibit cytotoxic markers, whereas tumor-infiltrating γδ T cells express a protumorigenic profile. These contrasting T cell profiles were associated with distinct T cell receptor (TCR)-Vγδ gene usage in both humans and mice. Longitudinal intersectional genetics and antibody-dependent strategies targeting murine γδ T cells enriched in the epithelium at steady state led to heightened tumor development, whereas targeting γδ subsets that accumulate during CRC resulted in reduced tumor growth. Our results uncover temporal pro- and antitumor roles for γδ T cell subsets.

γδ T Cells in the Tumor Microenvironment-Interactions With Other Immune Cells

A growing number of studies have shown that γδ T cells play a pivotal role in mediating the clearance of tumors and pathogen-infected cells with their potent cytotoxic, cytolytic, and unique immune-modulating functions. Unlike the more abundant αβ T cells, γδ T cells can recognize a broad range of tumors and infected cells without the requirement of antigen presentation via major histocompatibility complex (MHC) molecules. Our group has recently demonstrated parts of the mechanisms of T-cell receptor (TCR)-dependent activation of Vγ9Vδ2+ T cells by tumors following the presentation of phosphoantigens, intermediates of the mevalonate pathway. This process is mediated through the B7 immunoglobulin family-like butyrophilin 2A1 (BTN2A1) and BTN3A1 complexes. Such recognition results in activation, a robust immunosurveillance process, and elicits rapid γδ T-cell immune responses. These include targeted cell killing, and the ability to produce copious quantities of cytokines and chemokines to exert immune-modulating properties and to interact with other immune cells. This immune cell network includes αβ T cells, B cells, dendritic cells, macrophages, monocytes, natural killer cells, and neutrophils, hence heavily influencing the outcome of immune responses. This key role in orchestrating immune cells and their natural tropism for tumor microenvironment makes γδ T cells an attractive target for cancer immunotherapy. Here, we review the current understanding of these important interactions and highlight the implications of the crosstalk between γδ T cells and other immune cells in the context of anti-tumor immunity.

Novel γδ T cell-based prognostic signature to estimate risk and aid therapy in hepatocellular carcinoma

BACKGROUND

Numerous studies have revealed that gamma delta (γδ) T cell infiltration plays a crucial regulatory role in hepatocellular carcinoma (HCC) development. Nonetheless, a comprehensive analysis of γδ T cell infiltration in prognosis evaluation and therapeutic prediction remains unclear.

METHODS

Multi-omic data on HCC patients were obtained from public databases. The CIBERSORT algorithm was applied to decipher the tumor immune microenvironment (TIME) of HCC. Weighted gene co-expression network analysis (WGCNA) was performed to determine significant modules with γδ T cell-specific genes. Kaplan-Meier survival curves and receiver operating characteristic analyses were used to validate prognostic capability. Additionally, the potential role of RFESD inhibition by si-RFESD in vitro was investigated using EdU and CCK-8 assays.

RESULTS

A total of 16,421 genes from 746 HCC samples (616 cancer and 130 normal) were identified based on three distinct cohorts. Using WGCNA, candidate modules (brown) with 1755 significant corresponding genes were extracted as γδ T cell-specific genes. Next, a novel risk signature consisting of 11 hub genes was constructed using multiple bioinformatic analyses, which presented great prognosis prediction reliability. The risk score exhibited a significant correlation with ICI and chemotherapeutic targets. HCC samples with different risks experienced diverse signalling pathway activities. The possible interaction of risk score with tumor mutation burden (TMB) was further analyzed. Subsequently, the potential functions of the RFESD gene were explored in HCC, and knockdown of RFESD inhibited cell proliferation in HCC cells. Finally, a robust prognostic risk-clinical nomogram was developed and validated to quantify clinical outcomes.

CONCLUSIONS

Collectively, comprehensive analyses focusing on γδ T cell patterns will provide insights into prognosis prediction, the mechanisms of immune infiltration, and advanced therapy strategies in HCC.

The Role of γδ T Cells as a Line of Defense in Viral Infections after Allogeneic Stem Cell Transplantation: Opportunities and Challenges

In the complex interplay between inflammation and graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (allo-HSCT), viral reactivations are often observed and cause substantial morbidity and mortality. As toxicity after allo-HSCT within the context of viral reactivations is mainly driven by αβ T cells, we describe that by delaying αβ T cell reconstitution through defined transplantation techniques, we can harvest the full potential of early reconstituting γδ T cells to control viral reactivations. We summarize evidence of how the γδ T cell repertoire is shaped by CMV and EBV reactivations after allo-HSCT, and their potential role in controlling the most important, but not all, viral reactivations. As most γδ T cells recognize their targets in an MHC-independent manner, γδ T cells not only have the potential to control viral reactivations but also to impact the underlying hematological malignancies. We also highlight the recently re-discovered ability to recognize classical HLA-molecules through a γδ T cell receptor, which also surprisingly do not associate with GVHD. Finally, we discuss the therapeutic potential of γδ T cells and their receptors within and outside the context of allo-HSCT, as well as the opportunities and challenges for developers and for payers.

The Contribution of Human Herpes Viruses to γδ T Cell Mobilisation in Co-Infections

γδ T cells are activated in viral, bacterial and parasitic infections. Among viruses that promote γδ T cell mobilisation in humans, herpes viruses (HHVs) occupy a particular place since they infect the majority of the human population and persist indefinitely in the organism in a latent state. Thus, other infections should, in most instances, be considered co-infections, and the reactivation of HHV is a serious confounding factor in attributing γδ T cell alterations to a particular pathogen in human diseases. We review here the literature data on γδ T cell mobilisation in HHV infections and co-infections, and discuss the possible contribution of HHVs to γδ alterations observed in various infectious settings. As multiple infections seemingly mobilise overlapping γδ subsets, we also address the concept of possible cross-protection.

Gamma delta TCR anti-CD3 bispecific molecules (GABs) as novel immunotherapeutic compounds

Background

γ9δ2 T cells hold great promise as cancer therapeutics because of their unique capability of reacting to metabolic changes with tumor cells. However, it has proven very difficult to translate this promise into clinical success.

Methods

In order to better utilize the tumor reactivity of γ9δ2T cells and combine this with the great potential of T cell engager molecules, we developed a novel bispecific molecule by linking the extracellular domains of tumor-reactive γ9δ2TCRs to a CD3-binding moiety, creating gamma delta TCR anti-CD3 bispecific molecules (GABs). GABs were tested in vitro and in vivo for ability to redirect T lymphocytes to a variety of tumor cell lines and primary patient material.

Results

GABs utilizing naturally occurring high affinity γ9δ2TCRs efficiently induced αβT cell mediated phosphoantigen-dependent recognition of tumor cells. Reactivity was substantially modulated by variations in the Vδ2 CDR3-region and the BTN2A1-binding HV4-region between CDR2 and CDR3 of the γ-chain was crucial for functionality. GABs redirected αβT cells against a broad range of hematopoietic and solid tumor cell lines and primary acute myeloid leukemia. Furthermore, they enhanced infiltration of immune cells in a 3D bone marrow niche and left healthy tissues intact, while eradicating primary multiple myeloma cells. Lastly, GABs constructed from natural high affinity γ9δ2TCR sequences significantly reduced tumor growth in vivo in a subcutaneous myeloma xenograft model.

Conclusions

We conclude that GABs allow for the introduction of metabolic targeting of cancer cells to the field of T cell engagers.

Allogeneic Stem Cell Transplantation Platforms With Ex Vivo and In Vivo Immune Manipulations: Count and Adjust

Various allogeneic (allo) stem cell transplantation platforms have been developed over the last 2 decades. In this review we focus on the impact of in vivo and ex vivo graft manipulation on immune reconstitution and clinical outcome. Strategies include anti-thymocyte globulin- and post-transplantation cyclophosphamide-based regimens, as well as graft engineering, such as CD34 selection and CD19/αβT cell depletion. Differences in duration of immune suppression, reconstituting immune repertoires, and associated graft-versus-leukemia effects and toxicities mediated through viral reactivations are highlighted. In addition, we discuss the impact of different reconstituting repertoires on donor lymphocyte infusions and post allo pharmacological interventions to enhance tumor control. We advocate for precisely counting all graft ingredients and therapeutic drug monitoring during conditioning in the peripheral blood, and for adjusting dosing accordingly on an individual basis. In addition, we propose novel trial designs to better assess the impact of variations in transplantation platforms in order to better learn from our diversity of "counts" and potential "adjustments." This will, in the future, allow daily clinical practice, strategic choices, and future trial designs to be based on data guided decisions, rather than relying on dogma and habits.

Patients with gastrointestinal irritability after TGN1412-induced cytokine storm displayed selective expansion of gut-homing αβ and γδT cells

Following infusion of the anti-CD28 superagonist monoclonal antibody TGN1412, three of six previously healthy, young male recipients developed gastrointestinal irritability associated with increased expression of 'gut-homing' integrin β7 on peripheral blood αβT cells. This subset of patients with intestinal symptoms also displayed a striking and persistent expansion of putative Vδ2+ γδT cells in the circulation which declined over a 2-year period following drug infusion, concordant with subsiding gut symptoms. These data demonstrate that TGN1412-induced gastrointestinal symptoms were associated with dysregulation of the 'gut-homing' pool of blood αβ and γδT cells, induced directly by the antibody and/or arising from the subsequent cytokine storm.

Allogeneic CAR Cell Therapy-More Than a Pipe Dream

Adoptive cellular immunotherapy using immune cells expressing chimeric antigen receptors (CARs) has shown promise, particularly for the treatment of hematological malignancies. To date, the majority of clinically evaluated CAR cell products have been derived from autologous immune cells. While this strategy can be effective it also imposes several constraints regarding logistics. This includes i) availability of center to perform leukapheresis, ii) necessity for shipment to and from processing centers, and iii) time requirements for product manufacture and clinical release testing. In addition, previous cytotoxic therapies can negatively impact the effector function of autologous immune cells, which may then affect efficacy and/or durability of resultant CAR products. The use of allogeneic CAR cell products generated using cells from healthy donors has the potential to overcome many of these limitations, including through generation of “off the shelf” products. However, allogeneic CAR cell products come with their own challenges, including potential to induce graft-versus-host-disease, as well as risk of immune-mediated rejection by the host. Here we will review promises and challenges of allogeneic CAR immunotherapies, including those being investigated in preclinical models and/or early phase clinical studies.

γ9δ2T cell diversity and the receptor interface with tumor cells

γ9δ2T cells play a major role in cancer immune surveillance, yet the clinical translation of their in vitro promise remains challenging. To address limitations of previous clinical attempts using expanded γ9δ2T cells, we explored the clonal diversity of γ9δ2T cell repertoires and characterized their target. We demonstrated that only a fraction of expanded γ9δ2T cells was active against cancer cells and that activity of the parental clone, or functional avidity of selected γ9δ2 T cell receptors (γ9δ2TCRs), was not associated with clonal frequency. Furthermore, we analyzed the target-receptor interface and provided a 2-receptor, 3-ligand model. We found that activation was initiated by binding of the γ9δ2TCR to BTN2A1 through the regions between CDR2 and CDR3 of the TCR γ chain and modulated by the affinity of the CDR3 region of the TCRδ chain, which was phosphoantigen independent (pAg independent) and did not depend on CD277. CD277 was secondary, serving as a mandatory coactivating ligand. We found that binding of CD277 to its putative ligand did not depend on the presence of γ9δ2TCR, did depend on usage of the intracellular CD277, created pAg-dependent proximity to BTN2A1, enhanced cell-cell conjugate formation, and stabilized the immunological synapse (IS). This process critically depended on the affinity of the γ9δ2TCR and required membrane flexibility of the γ9δ2TCR and CD277, facilitating their polarization and high-density recruitment during IS formation.

Suppressive activity of Vδ2+ γδ T cells on αβ T cells is licensed by TCR signaling and correlates with signal strength

Despite recent progress in the understanding of γδ T cells' roles and functions, their interaction with αβ T cells still remains to be elucidated. In this study, we sought to clarify what precisely endows peripheral Vδ2+ T cells with immunosuppressive function on autologous αβ T cells. We found that negatively freshly isolated Vδ2+ T cells do not exhibit suppressive behavior, even after stimulation with IL-12/IL-18/IL-15 or the sheer contact with butyrophilin-3A1-expressing tumor cell lines (U251 or SK-Mel-28). On the other hand, Vδ2+ T cells positively isolated through TCR crosslinking or after prolonged stimulation with isopentenyl pyrophosphate (IPP) mediate strong inhibitory effects on αβ T cell proliferation. Stimulation with IPP in the presence of IL-15 induces the most robust suppressive phenotype of Vδ2+ T cells. This indicates that Vδ2+ T cells' suppressive activity is dependent on a TCR signal and that the degree of suppression correlates with its strength. Vδ2+ T cell immunosuppression does not correlate with their Foxp3 expression but rather with their PD-L1 protein expression, evidenced by the massive reduction of suppressive activity when using a blocking antibody. In conclusion, pharmacologic stimulation of Vδ2+ T cells via the Vδ2 TCR for activation and expansion induces Vδ2+ T cells' potent killer activity while simultaneously licensing them to suppress αβ T cell responses. Taken together, the study is a further step to understand-in more detail-the suppressive activity of Vδ2+ γδ T cells.

TEG011 persistence averts extramedullary tumor growth without exerting off-target toxicity against healthy tissues in a humanized HLA-A*24:02 transgenic mice

γδT cells play an important role in cancer immunosurveillance and are able to distinguish malignant cells from their healthy counterparts via their γδTCR. This characteristic makes γδT cells an attractive candidate for therapeutic application in cancer immunotherapy. Previously, we have identified a novel CD8α-dependent tumor-specific allo-HLA-A*24:02-restricted Vγ5Vδ1TCR with potential therapeutic value when used to engineer αβT cells from HLA-A*24:02 harboring individuals. αβT cells engineered to express this defined Vγ5Vδ1TCR (TEG011) have been suggested to recognize spatial changes in HLA-A*24:02 present selectively on tumor cells but not their healthy counterparts. However, in vivo efficacy and toxicity studies of TEG011 are still limited. Therefore, we extend the efficacy and toxicity studies as well as the dynamics of TEG011 in vivo in a humanized HLA-A*24:02 transgenic NSG (NSG-A24:02) mouse model to allow the preparation of a first-in-men clinical safety package for adoptive transfer of TEG011. Mice treated with TEG011 did not exhibit any graft-versus-host disease-like symptoms and extensive analysis of pathologic changes in NSG-A24:02 mice did not show any off-target toxicity of TEG011. However, loss of persistence of TEG011 in tumor-bearing mice was associated with the outgrowth of extramedullary tumor masses as also observed for mock-treated mice. In conclusion, TEG011 is well tolerated without harming HLA-A*24:02⁺ expressing healthy tissues, and TEG011 persistence seems to be crucial for long-term tumor control in vivo.

γδ T-cell Receptors Derived from Breast Cancer-Infiltrating T Lymphocytes Mediate Antitumor Reactivity

γδ T cells in human solid tumors remain poorly defined. Here, we describe molecular and functional analyses of T-cell receptors (TCR) from tumor-infiltrating γδ T lymphocytes (γδ TIL) that were in direct contact with tumor cells in breast cancer lesions from archival material. We observed that the majority of γδ TILs harbored a proinflammatory phenotype and only a minority associated with the expression of IL17. We characterized TCRγ or TCRδ chains of γδ TILs and observed a higher proportion of Vδ2⁺ T cells compared with other tumor types. By reconstructing matched Vδ2^- TCRγ and TCRδ pairs derived from single-cell sequencing, our data suggest that γδ TILs could be active against breast cancer and other tumor types. The reactivity pattern against tumor cells depended on both the TCRγ and TCRδ chains and was independent of additional costimulation through other innate immune receptors. We conclude that γδ TILs can mediate tumor reactivity through their individual γδ TCR pairs and that engineered T cells expressing TCRγ and δ chains derived from γδ TILs display potent antitumor reactivity against different cancer cell types and, thus, may be a valuable tool for engineering immune cells for adoptive cell therapies.

In the Absence of a TCR Signal IL-2/IL-12/18-Stimulated γδ T Cells Demonstrate Potent Anti-Tumoral Function Through Direct Killing and Senescence Induction in Cancer Cells

Abundant IFN-γ secretion, potent cytotoxicity, and major histocompatibility complex-independent targeting of a large spectrum of tumors make γδ T cells attractive candidates for cancer immunotherapy. Upon tumor recognition through the T-cell receptor (TCR), NK-receptors, or NKG2D, γδ T cells generate the pro-inflammatory cytokines TNF-α and IFN-γ, or granzymes and perforin that mediate cellular apoptosis. Despite these favorable potentials, most clinical trials testing the adoptive transfer of pharmacologically TCR-targeted and expanded γδ T cells resulted in a limited response. Recently, the TCR-independent activation of γδ T cells was identified. However, the modulation of γδ T cell’s effector functions solely by cytokines remains to be elucidated. In the present study, we systematically analyzed the impact of IL-2, IL-12, and IL-18 in parallel with TCR stimulation on proliferation, cytokine production, and anti-tumor activity of γδ T cells. Our results demonstrate that IL-12 and IL-18, when combined, constitute the most potent stimulus to enhance anti-tumor activity and induce proliferation and IFN-γ production by γδ T cells in the absence of TCR signaling. Intriguingly, stimulation with IL-12 and IL-18 without TCR stimulus induces a comparable degree of anti-tumor activity in γδ T cells to TCR crosslinking by killing tumor cells and driving cancer cells into senescence. These findings approve the use of IL-12/IL-18-stimulated γδ T cells for adoptive cell therapy to boost anti-tumor activity by γδ T cells.

Innate Immune Responses in the Outcome of Haploidentical Hematopoietic Stem Cell Transplantation to Cure Hematologic Malignancies

In the context of allogeneic transplant platforms, human leukocyte antigen (HLA)-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents one of the latest and most promising curative strategies for patients affected by high-risk hematologic malignancies. Indeed, this platform ensures a suitable stem cell source immediately available for virtually any patents in need. Moreover, the establishment in recipients of a state of immunologic tolerance toward grafted hematopoietic stem cells (HSCs) remarkably improves the clinical outcome of this transplant procedure in terms of overall and disease free survival. However, the HLA-mismatch between donors and recipients has not been yet fully exploited in order to optimize the Graft vs. Leukemia effect. Furthermore, the efficacy of haplo-HSCT is currently hampered by several life-threatening side effects including the onset of Graft vs. Host Disease (GvHD) and the occurrence of opportunistic viral infections. In this context, the quality and the kinetic of the immune cell reconstitution (IR) certainly play a major role and several experimental efforts have been greatly endorsed to better understand and accelerate the post-transplant recovery of a fully competent immune system in haplo-HSCT. In particular, the IR of innate immune system is receiving a growing interest, as it recovers much earlier than T and B cells and it is able to rapidly exert protective effects against both tumor relapses, GvHD and the onset of life-threatening opportunistic infections. Herein, we review our current knowledge in regard to the kinetic and clinical impact of Natural Killer (NK), γδ and Innate lymphoid cells (ILCs) IRs in both allogeneic and haplo-HSCT. The present paper also provides an overview of those new therapeutic strategies currently being implemented to boost the alloreactivity of the above-mentioned innate immune effectors in order to ameliorate the prognosis of patients affected by hematologic malignancies and undergone transplant procedures.

HMGN2: An Antitumor Effector Molecule of γδT Cells

γδT cells function in the regulation of T-cell activation in cancer and have been identified as a novel target for cancer immunotherapy. Activated γδT cells release a series of cytotoxic molecules-including granulysin, perforin, Fas/Fas ligand (Fas-L), and granzymes A and B-to kill target cells. Our previous research has shown that high mobility group nucleosomal-binding domain 2 (HMGN2), which is expressed at a high level in activated CD8T cells, is an antitumor effector molecule of CD8T cells. In the present study, we examined the expression and antitumor effects of HMGN2 in γδT cells. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy donors with a PBMC separation column. PMBCs were stimulated with isopentenyl pyrophosphate (IPP) and interleukin-2 (IL-2) for 10 days for activation and expansion. Activated γδT cells were isolated from IPP-pretreated PBMCs with a Moflo XDP flow cytometry sorter. The expression of HMGN2 in γδT cells was detected by flow cytometry and enzyme-linked immunosorbent assay. The cytotoxic effects of γδT cells and HMGN2 were analyzed by carboxyfluorescein succinimidyl ester labeling. IPP combined with IL-2 induced significant activation and expansion of γδT cells in vitro. HMGN2 was constitutively expressed in γδT cells. IPP-activated γδT cells expressed a high level of HMGN2 that could be detected intracellularly and in the supernatant. Moreover, supernatants of purified γδT cells were sufficient to kill tumor cells and could be blocked with anti-human HMGN2 antibody. This study suggests that HMGN2 is an antitumor effector molecule of γδT cells.

Translating gammadelta (γδ) T cells and their receptors into cancer cell therapies

Clinical responses to checkpoint inhibitors used for cancer immunotherapy seemingly require the presence of αβT cells that recognize tumour neoantigens, and are therefore primarily restricted to tumours with high mutational load. Approaches that could address this limitation by engineering αβT cells, such as chimeric antigen receptor T (CAR T) cells, are being investigated intensively, but these approaches have other issues, such as a scarcity of appropriate targets for CAR T cells in solid tumours. Consequently, there is renewed interest among translational researchers and commercial partners in the therapeutic use of γδT cells and their receptors. Overall, γδT cells display potent cytotoxicity, which usually does not depend on tumour-associated (neo)antigens, towards a large array of haematological and solid tumours, while preserving normal tissues. However, the precise mechanisms of tumour-specific γδT cells, as well as the mechanisms for self-recognition, remain poorly understood. In this Review, we discuss the challenges and opportunities for the clinical implementation of cancer immunotherapies based on γδT cells and their receptors.

Evaluating in vivo efficacy - toxicity profile of TEG001 in humanized mice xenografts against primary human AML disease and healthy hematopoietic cells

BACKGROUND

γ9δ2T cells, which express Vγ9 and Vδ2 chains of the T cell receptor (TCR), mediate cancer immune surveillance by sensing early metabolic changes in malignant leukemic blast and not their healthy hematopoietic stem counterparts via the γ9δ2TCR targeting joined conformational and spatial changes of CD277 at the cell membrane (CD277J). This concept led to the development of next generation CAR-T cells, so-called TEGs: αβT cells Engineered to express a defined γδTCR. The high affinity γ9δ2TCR clone 5 has recently been selected within the TEG format as a clinical candidate (TEG001). However, exploring safety and efficacy against a target, which reflects an early metabolic change in tumor cells, remains challenging given the lack of appropriate tools. Therefore, we tested whether TEG001 is able to eliminate established leukemia in a primary disease model, without harming other parts of the healthy hematopoiesis in vivo.

METHODS

Separate sets of NSG mice were respectively injected with primary human acute myeloid leukemia (AML) blasts and cord blood-derived human progenitor cells from healthy donors. These mice were then treated with TEG001 and mock cells. Tumor burden and human cells engraftment were measured in peripheral blood and followed up over time by quantifying for absolute cell number by flow cytometry. Statistical analysis was performed using non-parametric 2-tailed Mann-Whitney t-test.

RESULTS

We successfully engrafted primary AML blasts and healthy hematopoietic cells after 6-8 weeks. Here we report that metabolic cancer targeting through TEG001 eradicated established primary leukemic blasts in vivo, while healthy hematopoietic compartments derived from human cord-blood remained unharmed in spite of TEGs persistence up to 50 days after infusion. No additional signs of off-target toxicity were observed in any other tissues.

CONCLUSION

Within the limitations of humanized PD-X models, targeting CD277J by TEG001 is safe and efficient. Therefore, we have initiated clinical testing of TEG001 in a phase I first-in-human clinical trial (NTR6541; date of registration 25 July 2017).

Functional Plasticity of Gamma Delta T Cells and Breast Tumor Targets in Hypoxia

Interactions between immune and tumor cells in the tumor microenvironment (TME) often impact patient outcome, yet remain poorly understood. In addition, the effects of biophysical features such as hypoxia [low oxygen (O₂)] on cells within the TME may lead to tumor evasion. Gamma delta T cells (γδTcs) naturally kill transformed cells and are therefore under development as immunotherapy for various cancers. Clinical trials have proven the safety of γδTc immunotherapy and increased circulating γδTc levels correlate with improved patient outcome. Yet, the function of γδTc tumor infiltrating lymphocytes in human breast cancer remains controversial. Breast tumors can be highly hypoxic, thus therapy must be effective under low O₂ conditions. We have found increased infiltration of γδTc in areas of hypoxia in a small cohort of breast tumors; considering their inherent plasticity, it is important to understand how hypoxia influences γδTc function. In vitro, the cell density of expanded primary healthy donor blood-derived human γδTc decreased in response to hypoxia (2% O₂) compared to normoxia (20% O₂). However, the secretion of macrophage inflammatory protein 1α (MIP1α)/MIP1β, regulated on activation, normal T cell expressed and secreted (RANTES), and CD40L by γδTc were increased after 40 h in hypoxia compared to normoxia concomitant with the stabilization of hypoxia inducible factor 1-alpha protein. Mechanistically, we determined that natural killer group 2, member D (NKG2D) on γδTc and the NKG2D ligand MHC class I polypeptide-related sequence A (MICA)/B on MCF-7 and T47D breast cancer cell lines are important for γδTc cytotoxicity, but that MIP1α, RANTES, and CD40L do not play a direct role in cytotoxicity. Hypoxia appeared to enhance the cytotoxicity of γδTc such that exposure for 48 h increased cytotoxicity of γδTc against breast cancer cells that were maintained in normoxia; conversely, breast cancer lines incubated in hypoxia for 48 h prior to the assay were largely resistant to γδTc cytotoxicity. MICA/B surface expression on both MCF-7 and T47D remained unchanged upon exposure to hypoxia; however, ELISAs revealed increased MICA shedding by MCF-7 under hypoxia, potentially explaining resistance to γδTc cytotoxicity. Despite enhanced γδTc cytotoxicity upon pre-incubation in hypoxia, these cells were unable to overcome hypoxia-induced resistance of MCF-7. Thus, such resistance mechanisms employed by breast cancer targets must be overcome to develop more effective γδTc immunotherapies.

Early Reconstitution of NK and γδ T Cells and Its Implication for the Design of Post-Transplant Immunotherapy

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.

Human γδ T-Cell Control of Mucosal Immunity and Inflammation

Human γδ T-cells include some of the most common "antigen-specific" cell types in peripheral blood and are enriched yet further at mucosal barrier sites where microbial infection and tumors often originate. While the γδ T-cell compartment includes multiple subsets with highly flexible effector functions, human mucosal tissues are dominated by host stress-responsive Vδ1+ T-cells and microbe-responsive Vδ2+ T-cells. Widely recognized for their potent cytotoxicity, emerging data suggest that γδ T-cells also exert strong influences on downstream adaptive immunity to pathogens and tumors, in particular via activation of antigen-presenting cells and/or direct stimulation of other mucosal leukocytes. These unique functional attributes and lack of MHC restriction have prompted considerable interest in therapeutic targeting of γδ T-cells. Indeed, several drugs already in clinical use, including vedolizumab, infliximab, and azathioprine, likely owe their efficacy in part to modulation of γδ T-cell function. Recent clinical trials of Vδ2+ T-cell-selective treatments indicate a good safety profile in human patients, and efficacy is set to increase as more potent/targeted drugs continue to be developed. Key advances will include identifying methods of directing γδ T-cell recruitment to specific tissues to enhance host protection against invading pathogens, or alternatively, retaining these cells in the circulation to limit peripheral inflammation and/or improve responses to blood malignancies. Human γδ T-cell control of mucosal immunity is likely exerted via multiple mechanisms that induce diverse responses in other types of tissue-resident leukocytes. Understanding the microenvironmental signals that regulate these functions will be critical to the development of new γδ T-cell-based therapies.

Cellular immunotherapy on primary multiple myeloma expanded in a 3D bone marrow niche model

Bone marrow niches support multiple myeloma, providing signals and cell-cell interactions essential for disease progression. A 3D bone marrow niche model was developed, in which supportive multipotent mesenchymal stromal cells and their osteogenic derivatives were co-cultured with endothelial progenitor cells. These co-cultured cells formed networks within the 3D culture, facilitating the survival and proliferation of primary CD138+ myeloma cells for up to 28 days. During this culture, no genetic drift was observed within the genomic profile of the primary myeloma cells, indicating a stable outgrowth of the cultured CD138+ population. The 3D bone marrow niche model enabled testing of a novel class of engineered immune cells, so called TEGs (αβT cells engineered to express a defined γδTCR) on primary myeloma cells. TEGs were engineered and tested from both healthy donors and myeloma patients. The added TEGs were capable of migrating through the 3D culture, exerting a killing response towards the primary myeloma cells in 6 out of 8 donor samples after both 24 and 48 hours. Such a killing response was not observed when adding mock transduced T cells. No differences were observed comparing allogeneic and autologous therapy. The supporting stromal microenvironment was unaffected in all conditions after 48 hours. When adding TEG therapy, the 3D model surpassed 2D models in many aspects by enabling analyses of specific homing, and both on- and off-target effects, preparing the ground for the clinical testing of TEGs. The model allows studying novel immunotherapies, therapy resistance mechanisms and possible side-effects for this incurable disease.

NK Cells and γδT Cells for Relapse Protection After Allogeneic Hematopoietic Cell Transplantation (HCT)

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.

Tumor-infiltrating γδT cells predict prognosis and adjuvant chemotherapeutic benefit in patients with gastric cancer

Purpose : Tumor-infiltrating γδT cells (γδTILs) have different prognostic value and functions among various cancers. The aim of the present study was to evaluate the effect of γδTILs in gastric cancer. Patients and methods : A discovery set (n = 190) and a validation set (n = 273) were involved in this study. Patients with TNM II and III disease were used to predict response to 5-fluorouracil (5-FU)-based adjuvant chemotherapy (ACT) in both sets. γδTILs were defined as intense (γδT cells≥ 5/HPF) versus nonintense (γδT cells<5/HPF). Kaplan-Meier curve was plotted to analysis survival. Hazard ratio (HR) and 95%CI associated with γδTILs were evaluated by multivariable Cox models. Findings : The prognostic value of γδTILs in the discovery set (HR, 0.193; 95%CI, 0.097-0.383; P<0.001) was confirmed in the validation set (HR, 0.442; 95%CI, 0.251-0.779; P = 0.005) for overall survival (OS). Patients whose tumors with γδT cells≥ 5/HPF could benefit from ACT, with a reduced risk of compromised survival compared with those with γδT cells<5/HPF (HR, 0.086; 95%CI, 0.023-0.327; P<0.001 in discovery set; and HR, 0.077; 95%CI, 0.023-0.256; P<0.001 in validation set). Conclusion : The present study shows that intense γδT cells infiltration is an independent prognostic factor in patients with gastric cancer and is predictive of a survival benefit from adjuvant chemotherapy in patients with TNM II and III disease.

γδTCR immunoglobulin constant region domain exchange in human αβTCRs improves TCR pairing without altering TCR gene-modified T cell function

The adoptive genetic transfer of T cell receptors (TCRs) has been shown to be overall feasible and offer clinical potential as a treatment for different types of cancer. However, this promising clinical approach is limited by the serious potential consequence that exogenous TCR mispairing with endogenous TCR chains may lead to the risk of self-reactivity. In the present study, domain-exchange and three-dimensional modeling strategies were used to create a set of chimeric TCR variants, which were used to exchange the partial or complete constant region of αβTCR with corresponding γδTCR domains. The expression, assembly and function of the chimeric TCR variants were examined in Jurkat T cells and peripheral mononuclear blood cells (PBMCs). Genetically-encoded chimeras were fused with a pair of fluorescent proteins (ECFP/EYFP) to monitor expression and the pairing between chimeric TCRα chains and TCRβ chains. The fluorescence energy transfer based on confocal laser scanning microscopy showed that the introduction of γδTCR constant sequences into the αβTCR did not result in a global reduction of mispairing with endogenous TCR. However, the TCR harboring the immunoglobulin-like domain of the γδTCR constant region (i.e., TCR∆IgC), showed a higher expression and preferential pairing, compared with wild-type (wt)TCR. The function analysis showed that TCR∆IgC exhibited the same levels of interferon-γ production and cytotoxic activity, compared with wtTCR. Furthermore, these modified TCR-transduced T cells retained the classic human leukocyte antigen restriction of the original TCR. The other two chimeric TCRs, had either exchange of the cp+tm+ic domain or exchange of the whole C domain (Fig. 1). Ultimately, exchange of these domains demonstrated defective function in the transduced T cells. Taken together, these findings may provide further understanding of the γδTCR constant domain with implications for the improvement of TCR gene transfer therapy.

γδ T Cell-Mediated Immunity to Cytomegalovirus Infection

γδ T lymphocytes are unconventional immune cells, which have both innate- and adaptive-like features allowing them to respond to a wide spectrum of pathogens. For many years, we and others have reported on the role of these cells in the immune response to human cytomegalovirus in transplant patients, pregnant women, neonates, immunodeficient children, and healthy people. Indeed, and as described for CD8+ T cells, CMV infection leaves a specific imprint on the γδ T cell compartment: (i) driving a long-lasting expansion of oligoclonal γδ T cells in the blood of seropositive individuals, (ii) inducing their differentiation into effector/memory cells expressing a TEMRA phenotype, and (iii) enhancing their antiviral effector functions (i.e., cytotoxicity and IFNγ production). Recently, two studies using murine CMV (MCMV) have corroborated and extended these observations. In particular, they have illustrated the ability of adoptively transferred MCMV-induced γδ T cells to protect immune-deficient mice against virus-induced death. In vivo, expansion of γδ T cells is associated with the clearance of CMV infection as well as with reduced cancer occurrence or leukemia relapse risk in kidney transplant patients and allogeneic stem cell recipients, respectively. Taken together, all these studies show that γδ T cells are important immune effectors against CMV and cancer, which are life-threatening diseases affecting transplant recipients. The ability of CMV-induced γδ T cells to act independently of other immune cells opens the door to the development of novel cellular immunotherapies that could be particularly beneficial for immunocompromised transplant recipients.

Vγ1+γδT, early cardiac infiltrated innate population dominantly producing IL-4, protect mice against CVB3 myocarditis by modulating IFNγ+ T response

Viral myocarditis (VMC) is an inflammation of the myocardium closely associated with Coxsackievirus B3 (CVB3) infection. Vγ1⁺γδT cells, one of early cardiac infiltrated innate population, were reported to protect CVB3 myocarditis while the precise mechanism not fully addressed. To explore cytokine profiles and kinetics of Vγ1⁺γδT and mechanism of protection against VMC, flow cytometry was conducted on cardiac Vγ1 cells in C57BL/6 mice following CVB3 infection. The level of cardiac inflammation, transthoracic echocardiography and viral replication were evaluated after monoclonal antibody depletion of Vγ1γδT. We found that Vγ1⁺γδT cells infiltration peaked in the heart at day3 post CVB3 infection and constituted a minor source of IFN-γ but major producers for early IL-4. Vγ1γδT cells were activated earlier holding a higher IL-4-producing efficiency than CD4⁺Th cells in the heart. Depletion of Vγ1⁺γδT resulted in a significantly exacerbated cardiac infiltration, increased T, macrophage and neutrophil population in heart homogenates and worse cardiomyopathy; which was accompanied by a significant expansion of peripheral IFNγ⁺CD4+ and CD8+T cells. Neutralization of IL-4 in mice resulted in an exacerbated acute myocarditis confirming the IL-4-mediated protective mechanism of Vγ1. Our findings identify a unique property of Vγ1⁺γδT cells as one dominant early producers of IL-4 upon CVB3 acute infection which is a key mediator to protect mice against acute myocarditis by modulating IFNγ-secreting T response.

Immuno-stimultory/regulatory gene expression patterns in advanced ovarian cancer

It has been established that a high degree of tumor-infiltrating T cells is associated with ovarian cancer prognosis. We hypothesized that tumors display an immune-related program of transcription that can act in a stimulatory or a regulatory manner. We analyzed transcriptome-wide gene expression data from 503 ovarian tumors from the Cancer Genome Atlas to identify genes that show differential prognoses when stratified by CD3 expression. Genes with immunological functions and tumor antigen genes were selected for analysis. We repeated our analysis in an independent validation study. Five genes showed stimulatory/regulatory patterns at a high level of confidence (Bonferroni p < 0.05). Three of these (MAGEA8, MPL, AMHR2) were validated and one (WT1) could not be evaluated. These patterns show specific prognostic effect only in conjunction with CD3 expression. When patients express multiple transcripts in poor prognosis directions, there is a dose response: increasingly regulatory type tumors are associated with higher stage, lower treatment response and shorter overall survival and progression free survival. The high-confidence set of transcripts (MAGEA8, MPL, AMHR2, WT1) and selected low-confidence hits (EPOR, TLR7) alone or in combination represent candidate prognosis markers for further investigation.

Orchestrating an immune response against cancer with engineered immune cells expressing αβTCRs, CARs, and innate immune receptors: an immunological and regulatory challenge

Over half a century ago, the first allogeneic stem cell transplantation (allo-SCT) initiated cellular immunotherapy. For several decades, little progress was made, and toxicity of allo-SCT remained a major challenge. However, recent breakthroughs have opened new avenues to further develop this modality and to provide less toxic and equally efficient interventions for patients suffering from hematological or solid malignancies. Current novel cellular immune interventions include ex vivo expansion and adoptive transfer of tumor-infiltrating immune cells or administration of drugs which antagonize tolerizing mechanisms. Alternatively, transfer of immune cells engineered to express defined T cell receptors (TCRs) and chimeric antigen receptors (CARs) has shown its potential. A valuable addition to ‘engineered’ adaptive immunity has emerged recently through the improved understanding of how innate immune cells can attack cancer cells without substantial side effects. This has enabled the development of transplantation platforms with limited side effects allowing early immune interventions as well as the design of engineered immune cells expressing innate immune receptors. Here, we focus on innate immune interventions and their orchestration with TCR- and CAR-engineered immune cells. In addition, we discuss how the exploitation of the full potential of cellular immune interventions is influenced by regulatory frameworks. Finally, we highlight and discuss substantial differences in the current landscape of clinical trials in Europe as compared to the USA. The aim is to stimulate international efforts to support regulatory authorities and funding agencies, especially in Europe, to create an environment that will endorse the development of engineered immune cells for the benefit of patients.

Untouched GMP-Ready Purified Engineered Immune Cells to Treat Cancer

PURPOSE

Engineering T cells with receptors to redirect the immune system against cancer has most recently been described as a scientific breakthrough. However, a main challenge remains the GMP-grade purification of immune cells selectively expressing the introduced receptor in order to reduce potential side effects due to poorly or nonengineered cells.

EXPERIMENTAL DESIGN

In order to test a novel purification strategy, we took advantage of a model γδT cell receptor (TCR), naturally interfering with endogenous TCR expression and designed the optimal retroviral expression cassette to achieve maximal interference with endogenous TCR chains. Following retroviral transduction, nonengineered and poorly engineered immune cells characterized by a high endogenous αβTCR expression were efficiently depleted with GMP-grade anti-αβTCR beads. Next, the engineered immune cells were validated for TCR expression, function against a panel of tumor cell lines and primary tumors and potential allo-reactivity. Engineered immune cells were further validated in two humanized mouse tumor models.

RESULTS

The untouched enrichment of engineered immune cells translated into highly purified receptor-engineered cells with strong antitumor reactivity both in vitro and in vivo. Importantly, this approach eliminated residual allo-reactivity of engineered immune cells. Our data demonstrate that even with long-term suboptimal interference with endogenous TCR chains such as in resting cells, allo-reactivity remained absent and tumor control preserved.

CONCLUSIONS

We present a novel enrichment method for the production of untouched engineered immune cells, ready to be translated into a GMP-grade method and potentially applicable to all receptor-modified cells even if interference with endogenous TCR chains is far from complete.