γδ T-cell reconstitution after HLA-haploidentical hematopoietic transplantation depleted of TCR-αβ+/CD19+ lymphocytes

Post-transplant cyclophosphamide or cell selection in haploidentical allogeneic hematopoietic cell transplantation?

BACKGROUND

One major limitation for broader applicability of allogeneic hematopoietic cell transplantation (allo-HCT) in the past was the lack of HLA-matched histocompatible donors. Preclinical mouse studies using T-cell depleted haploidentical grafts led to an increased interest in the use of ex vivo T-cell depleted (TCD) haploidentical allo-HCT. TCD grafts through negative (T-cell depletion) or positive (CD34+ cell selection) techniques have been investigated to reduce the risk of graft-versus-host disease (GVHD) given the known implications of alloreactive T cells. A more practical approach to deplete alloreactive T cells in vivo using high doses of cyclophosphamide after allografting has proved to be feasible in overcoming the HLA barrier. Such approach has extended allo-HCT feasibility to patients for whom donors could not be found in the past. Nowadays, haploidentical donors represent a common donor source for patients in need of an allo-HCT. The broad application of haploidentical donors became possible by understanding the importance of depleting alloreactive donor T cells to facilitate engraftment and reduce incidence and severity of GVHD. These techniques involve ex vivo graft manipulation or in vivo utilization of pharmacologic agents, notably post-transplant cyclophosphamide (PTCy).

DISCUSSION

While acknowledging that no randomized controlled prospective studies have been yet conducted comparing TCD versus PTCy in haploidentical allo-HCT recipients, there are two advantages that would favor the PTCy, namely ease of application and lower cost. However, emerging data on adverse events associated with PTCy including, but not limited to cardiac associated toxicities or increased incidence of post-allograft infections, and others, are important to recognize.

Model-Based Antithymocyte Globulin in αβhaplo-Hematopoietic Stem Cell Transplantation Facilitates Engraftment, Expedites T Cell Recovery, and Mitigates the Risk of Acute Graft-versus-Host Disease

In αβ T-cell/CD19 B-cell depleted hematopoietic stem cell transplantation (αβhaplo-HSCT) recipients, antithymocyte globulin (ATG; Thymoglobulin) is used for preventing graft rejection and graft-versus-host disease (GVHD). The optimal dosing remains to be established, however. Here we present the first comparative analysis of 3 different ATG dosing strategies and their impact on immune reconstitution and GVHD. Our study aimed to evaluate the effects of 3 distinct dosing strategies of ATG on engraftment success, αβ+ and γδ+ T cell immune reconstitution, and the incidence and severity of acute GVHD in recipients of αβhaplo-HSCT. This comparative analysis included 3 cohorts of pediatric patients with malignant (n = 36) or nonmalignant (n = 8) disease. Cohorts 1 and 2 were given fixed ATG doses, whereas cohort 3 received doses via a new nomogram, based on absolute lymphocyte count (ALC) and body weight (BW). Cohort 3 showed a 0% incidence of day 100 grade II-IV acute GVHD, compared to 48% in cohort 1 and 27% in cohort 2. Furthermore, cohort 3 (the ALC/BW-based cohort) had a significant increase in CD4+ and CD8+ naïve T cells by day 90 (P = .04 and .03, respectively). Additionally, we found that the reconstitution and maturation of γδ+ T cells post-HSCT was not impacted across all 3 cohorts. Cumulative ATG exposure in all cohorts was lower than previously reported in T cell-replete settings, with a lower pre-HSCT exposure (<40 AU*day/mL) correlating with engraftment failure (P = .007). Conversely, a post-HSCT ATG exposure of 10 to 15 AU*day/mL was optimal for improving day 100 CD4+ (P = .058) and CD8+ (P = .03) immune reconstitution without increasing the risk of relapse or nonrelapse mortality. This study represents the first comparative analysis of ATG exposure in αβhaplo-HSCT recipients. Our findings indicate that (1) a 1- to 2-fold ATG to ATLG bioequivalence is more effective than previously established standards, and (2) ATG exposure post-HSCT does not adversely affect γδ+ T cell immune reconstitution. Furthermore, a model-based ATG dosing strategy effectively reduces graft rejection and day 100 acute GVHD while also promoting early CD4+/CD8+ immune reconstitution. These insights suggest that further optimization, including more distal administration of higher ATG doses within an ALC/BW-based strategy, will yield even greater improvements in outcomes.

Cell therapies and its derivatives as immunomodulators in vascularized composite allotransplantation

The adverse effects of traditional pharmaceutical immunosuppressive regimens have been a major obstacle to successful allograft survival in vascularized composite tissue allotransplantation (VCA) cases. Consequently, there is a pressing need to explore alternative approaches to reduce reliance on conventional immunotherapy. Cell therapy, encompassing immune-cell-based and stem-cell-based regimens, has emerged as a promising avenue of research. Immune cells can be categorized into two main systems: innate immunity and adaptive immunity. Innate immunity comprises tolerogenic dendritic cells, regulatory macrophages, and invariant natural killer T cells, while adaptive immunity includes T regulatory cells and B regulatory cells. Investigations are currently underway to assess the potential of these immune cell populations in inducing immune tolerance. Furthermore, mixed chimerism therapy, involving the transplantation of hematopoietic stem and progenitor cells and mesenchymal stem cells (MSC), shows promise in promoting allograft tolerance. Additionally, extracellular vesicles (EVs) derived from MSCs offer a novel avenue for extending allograft survival. This review provides a comprehensive summary of cutting-edge research on immune cell therapies, mixed chimerism therapies, and MSCs-derived EVs in the context of VCAs. Findings from preclinical and clinical studies demonstrate the tremendous potential of these alternative therapies in optimizing allograft survival in VCAs.

CAR products from novel sources: a new avenue for the breakthrough in cancer immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has transformed cancer immunotherapy. However, significant challenges limit its application beyond B cell-driven malignancies, including limited clinical efficacy, high toxicity, and complex autologous cell product manufacturing. Despite efforts to improve CAR T cell therapy outcomes, there is a growing interest in utilizing alternative immune cells to develop CAR cells. These immune cells offer several advantages, such as major histocompatibility complex (MHC)-independent function, tumor microenvironment (TME) modulation, and increased tissue infiltration capabilities. Currently, CAR products from various T cell subtypes, innate immune cells, hematopoietic progenitor cells, and even exosomes are being explored. These CAR products often show enhanced antitumor efficacy, diminished toxicity, and superior tumor penetration. With these benefits in mind, numerous clinical trials are underway to access the potential of these innovative CAR cells. This review aims to thoroughly examine the advantages, challenges, and existing insights on these new CAR products in cancer treatment.

Validation of analytical methods for the production of expanded γδ T lymphocytes useful for therapeutic purposes

The use of γδ T lymphocytes as advanced therapeutic medicinal product has attracted much interest in the last years. Indeed, such cells are an ideal tool for the reconstitution of the immune system in patients receiving hematopoietic stem cell transplantation, due to their MHC-independent anti-tumor and anti-viral activities. We have here setup a protocol for the production of pure and functional γδ T lymphocytes, expanded from healthy donors' mononuclear cells, and validated the analytical methods to identify them and to analyze their potency. Next, we performed stability studies to ensure that the cell product (γδ T cells) can be used after freezing and thawing. Notably, such protocol can be promptly translated to GMP-facility, since it has been designed using only clinical grade reagents.

Phase I study of zoledronic acid combined with escalated doses of interleukine-2 for early in vivo generation of Vγ9Vδ2 T-cells after haploidentical stem cell transplant with posttransplant cyclophosphamide

The presence of donor Vγ9Vδ2 T-cells after haploidentical hematopoietic stem cell transplant (h-HSCT) has been associated with improved disease-free survival. These cells kill tumor cells in a non-MHC restricted manner, do not induce graft-versus-host disease (GVHD), and can be generated by stimulation with zoledronic acid (ZA) in combination with interleukin-2 (IL-2). This monocentric phase I, open-label, dose-escalating study (ClinicalTrials.gov: NCT03862833) aimed at evaluating the safety and possibility to generate Vγ9Vδ2 T-cells early after h-HSCT. It applied a standard 3 + 3 protocol to determine the maximum tolerated dose (MTD) of increasing low-doses of IL-2 (5 days [d] per week, 4 weeks) in combination with a single dose of ZA, starting both the first Monday after d + 15 posttransplant. Vγ9Vδ2 T-cell monitoring was performed by multiparameter flow cytometry on blood samples and compared with a control cohort of h-HSCT recipients. Twenty-six patients were included between April 2019 and September 2022, 16 of whom being ultimately treated and seven being controls who received h-HSCT only. At the three dose levels tested, 1, 0, and 1 dose-limiting toxicities were observed. MTD was not reached. A significantly higher number of Vγ9Vδ2 T-cells was observed during IL-2 treatment compared with controls. In conclusion, early in vivo generation of Vγ9Vδ2 T-cells is feasible after h-HSCT by using a combination of ZA and repeated IL-2 infusions. This study paves the way to a future phase 2 study, with the hope to document lesser posttransplant relapse with this particular adaptive immunotherapy.

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

γδ T cells: origin and fate, subsets, diseases and immunotherapy

The intricacy of diseases, shaped by intrinsic processes like immune system exhaustion and hyperactivation, highlights the potential of immune renormalization as a promising strategy in disease treatment. In recent years, our primary focus has centered on γδ T cell-based immunotherapy, particularly pioneering the use of allogeneic Vδ2+ γδ T cells for treating late-stage solid tumors and tuberculosis patients. However, we recognize untapped potential and optimization opportunities to fully harness γδ T cell effector functions in immunotherapy. This review aims to thoroughly examine γδ T cell immunology and its role in diseases. Initially, we elucidate functional differences between γδ T cells and their αβ T cell counterparts. We also provide an overview of major milestones in γδ T cell research since their discovery in 1984. Furthermore, we delve into the intricate biological processes governing their origin, development, fate decisions, and T cell receptor (TCR) rearrangement within the thymus. By examining the mechanisms underlying the anti-tumor functions of distinct γδ T cell subtypes based on γδTCR structure or cytokine release, we emphasize the importance of accurate subtyping in understanding γδ T cell function. We also explore the microenvironment-dependent functions of γδ T cell subsets, particularly in infectious diseases, autoimmune conditions, hematological malignancies, and solid tumors. Finally, we propose future strategies for utilizing allogeneic γδ T cells in tumor immunotherapy. Through this comprehensive review, we aim to provide readers with a holistic understanding of the molecular fundamentals and translational research frontiers of γδ T cells, ultimately contributing to further advancements in harnessing the therapeutic potential of γδ T cells.

Graft-versus-host disease is associated with skewed γδ T-cell clonality after umbilical cord blood transplantation in children with nonmalignant diseases

BACKGROUND AIMS

The γδ T-cells (GDT) are a subpopulation of lymphocytes expressing a distinct T-cell receptor coded by the TRG and TRD genes. GDTs may have immunoregulatory function after stem cell transplantation (SCT), but the relationship between GDT clonality and acute graft-versus-host disease (aGVHD) is not known.

METHODS

We prospectively studied spectratype complex complexity of TCR Vγ (γ) and TCR Vδ (δ) pre-SCT and at approximately day 100 and day 180 post-SCT in a cohort of immunocompetent children receiving allogeneic umbilical cord blood SCT for nonmalignant diseases, with identical reduced-intensity conditioning and aGVHD prophylaxis.

RESULTS

We studied 13 children undergoing SCT at a median age of 0.9 years (total range 0.4-16.6). In those with grade 0-1 aGVHD (N = 10), the spectratype complexity of most γ and δ genes was not significantly different from baseline at day 100 or day 180 post-SCT, and there was balanced expression of genes at the γ and δ loci. In those with grade 3 aGVHD (N = 3), spectratype complexity was significantly below baseline at day 100 and day 180, and there was relative overexpression of δ2. CD3+ cell counts were also lower in participants with grade 3 aGVHD.

CONCLUSIONS

Recovery of a polyclonal GDT repertoire is an early part of immunological recovery after SCT. γ and δ gene expression is balanced in young children before and after SCT. Severe aGVHD is associated with GDT oligoclonality post-SCT and with skewed expression of δ2, which has not been previously reported. This association may reflect aGVHD therapy or aGVHD-associated immune dysregulation. Further studies of GDT clonality during the early post-SCT period may establish whether abnormal GDT spectratype precedes the clinical manifestations of aGVHD.

EBV-induced T-cell responses in EBV-specific and nonspecific cancers

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus associated with various malignancies, including B-lymphoma, NK and T-lymphoma, and epithelial carcinoma. It infects B lymphocytes and epithelial cells within the oropharynx and establishes persistent infection in memory B cells. With a balanced virus-host interaction, most individuals carry EBV asymptomatically because of the lifelong surveillance by T cell immunity against EBV. A stable anti-EBV T cell repertoire is maintained in memory at high frequency in the blood throughout persistent EBV infection. Patients with impaired T cell immunity are more likely to develop life-threatening lymphoproliferative disorders, highlighting the critical role of T cells in achieving the EBV-host balance. Recent studies reveal that the EBV protein, LMP1, triggers robust T-cell responses against multiple tumor-associated antigens (TAAs) in B cells. Additionally, EBV-specific T cells have been identified in EBV-unrelated cancers, raising questions about their role in antitumor immunity. Herein, we summarize T-cell responses in EBV-related cancers, considering latency patterns, host immune status, and factors like human leukocyte antigen (HLA) susceptibility, which may affect immune outcomes. We discuss EBV-induced TAA-specific T cell responses and explore the potential roles of EBV-specific T cell subsets in tumor microenvironments. We also describe T-cell immunotherapy strategies that harness EBV antigens, ranging from EBV-specific T cells to T cell receptor-engineered T cells. Lastly, we discuss the involvement of γδ T-cells in EBV infection and associated diseases, aiming to elucidate the comprehensive interplay between EBV and T-cell immunity.

CAR-Modified Vγ9Vδ2 T Cells Propagated Using a Novel Bisphosphonate Prodrug for Allogeneic Adoptive Immunotherapy

The benefits of CAR-T therapy could be expanded to the treatment of solid tumors through the use of derived autologous αβ T cell, but clinical trials of CAR-T therapy for patients with solid tumors have so far been disappointing. CAR-T therapy also faces hurdles due to the time and cost intensive preparation of CAR-T cell products derived from patients as such CAR-T cells are often poor in quality and low in quantity. These inadequacies may be mitigated through the use of third-party donor derived CAR-T cell products which have a potent anti-tumor function but a constrained GVHD property. Vγ9Vδ2 TCR have been shown to exhibit potent antitumor activity but not alloreactivity. Therefore, in this study, CAR-T cells were prepared from Vγ9Vδ2 T (CAR-γδ T) cells which were expanded by using a novel prodrug PTA. CAR-γδ T cells suppressed tumor growth in an antigen specific manner but only during a limited time window. Provision of GITR co-stimulation enhanced anti-tumor function of CAR-γδ T cells. Our present results indicate that, while further optimization of CAR-γδ T cells is necessary, the present results demonstrate that Vγ9Vδ2 T cells are potential source of 'off-the-shelf' CAR-T cell products for successful allogeneic adoptive immunotherapy.

γδ-Enriched CAR-T cell therapy for bone metastatic castrate-resistant prostate cancer

Immune checkpoint blockade has been largely unsuccessful for the treatment of bone metastatic castrate-resistant prostate cancer (mCRPC). Here, we report a combinatorial strategy to treat mCRPC using γδ-enriched chimeric antigen receptor (CAR) T cells and zoledronate (ZOL). In a preclinical murine model of bone mCRPC, γδ CAR-T cells targeting prostate stem cell antigen (PSCA) induced a rapid and significant regression of established tumors, combined with increased survival and reduced cancer-associated bone disease. Pretreatment with ZOL, a U.S. Food and Drug Administration-approved bisphosphonate prescribed to mitigate pathological fracture in mCRPC patients, resulted in CAR-independent activation of γδ CAR-T cells, increased cytokine secretion, and enhanced antitumor efficacy. These data show that the activity of the endogenous Vγ9Vδ2 T cell receptor is preserved in CAR-T cells, allowing for dual-receptor recognition of tumor cells. Collectively, our findings support the use of γδ CAR-T cell therapy for mCRPC treatment.

αβ+ /CD19+ -depleted haploidentical stem cell transplantation for children with acute leukemia: Is there a protective effect of increased γδ+ T-cell content in the graft?

BACKGROUND

Haploidentical hematopoietic stem cell transplantation (HSCT) with depletion of αβ⁺ T cells and CD19⁺ B cells has emerged as a viable alternative to traditional donors for treating acute leukemia in children. As the use of this innovative approach continues to grow and more experience is gained, it is essential to identify and comprehend the key factors that contribute to successful transplantation and improved outcomes.

METHODS

We conducted a retrospective analysis of single-center data from 27 children with acute lymphoblastic leukemia and 11 children with acute myeloid leukemia who underwent haploidentical HSCT with depletion of αβ⁺ T cells and CD19⁺ B cells between the years 2013 and 2020.

RESULTS

Engraftment was successful in 35 out of 38 patients (92%), who were all children conditioned using either a total body irradiation-based regimen or a treosulfan, fludarabine, and thiotepa regimen engrafted successfully. The 5-year overall survival and event-free survival rates were 51% and 42%, respectively. There were no cases of grade III-IV acute graft-versus-host disease, and only two patients developed chronic graft-versus-host disease. Patients with a higher content of γδ⁺ T cells in the graft demonstrated a longer event-free survival.

CONCLUSIONS

αβ⁺ /CD19⁺ -depleted haploidentical hematopoietic stem cell transplantation can offer long-term remission for children with acute leukemia with minimal graft-versus-host disease.

Personalized hematopoietic stem cell transplantation for inborn errors of immunity

Patients with inborn errors of immunity (IEI) have been transplanted for more than 50 years. Many long-term survivors have ongoing medical issues showing the need for further improvements in how hematopoietic stem cell transplantation (HSCT) is performed if patients in the future are to have a normal quality of life. Precise genetic diagnosis enables early treatment before recurrent infection, autoimmunity and organ impairment occur. Newborn screening for severe combined immunodeficiency (SCID) is established in many countries. For newly described disorders the decision to transplant is not straight-forward. Specific biologic therapies are effective for some diseases and can be used as a bridge to HSCT to improve outcome. Developments in reduced toxicity conditioning and methods of T-cell depletion for mismatched donors have made transplant an option for all eligible patients. Further refinements in conditioning plus precise graft composition and additional cellular therapy are emerging as techniques to personalize the approach to HSCT for each patient.

Hematopoietic Stem Cell Transplantation in Thalassemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only consolidated, potentially curative treatment for patients with transfusion-dependent thalassemia major. In the past few decades, several new approaches have reduced the toxicity of conditioning regimens and decreased the incidence of graft-versus-host disease, improving patients' outcomes and quality of life. In addition, the progressive availability of alternative stem cell sources from unrelated or haploidentical donors or umbilical cord blood has made HSCT a feasible option for an increasing number of subjects lacking an human leukocyte antigen (HLA)-identical sibling. This review provides an overview of allogeneic hematopoietic stem cell transplantation in thalassemia, reassesses current clinical results, and discusses future perspectives.

Harnessing novel strategies and cell types to overcome immune tolerance during adoptive cell therapy in cancer

Cell therapy encompasses an expanding spectrum of cell-based regimes for the treatment of human ailments, such as the use of immune cells, in particular T cells, for combating tumors and the modulation of inflammatory immune responses. In this review, we focus on cell therapy in the immuno-oncology space, which is largely driven by interests and demands from the clinics for better solutions to target various hard-to-treat cancers. We discuss recent advances in various types of cell therapies, including T cell receptor-T cells, chimeric antigen receptor (CAR)-T cells, tumor-infiltrating lymphocytes and natural killer cells. Particularly, the present review focuses on the strategies to improve therapeutic responses by either enhancing tumor recognition or the resilience of infused immune cells within tumor microenvironment. Finally, we discuss the potential of other innate or innate-like immune cell types currently being explored as promising CAR-cell alternatives that seek to address the limitations of conventional adoptive cell therapies.

Large Scale Ex Vivo Expansion of γδ T cells Using Artificial Antigen-presenting Cells

Higher γδ T cell counts in patients with malignancies are associated with better survival. However, γδ T cells are rare in the blood and functionally impaired in patients with malignancies. Promising results are reported on the treatment of various malignancies with in vivo expansion of autologous γδ T cells using zoledronic acid (zol) and interleukin-2 (IL-2). Here we demonstrated that zol and IL-2, in combination with a novel genetically engineered K-562 CD3scFv/CD137L/CD28scFv/IL15RA quadruplet artificial antigen-presenting cell (aAPC), efficiently expand allogeneic donor-derived γδ T cells using a Good Manufacturing Practice (GMP) compliant protocol sufficient to achieve cell doses for future clinical use. We achieved a 633-fold expansion of γδ T cells after day 10 of coculture with aAPC, which exhibited central (47%) and effector (43%) memory phenotypes. In addition, >90% of the expanded γδ T cells expressed NKG2D, although they have low cell surface expression of PD1 and LAG3 inhibitory checkpoint receptors. In vitro real-time cytotoxicity analysis showed that expanded γδ T cells were effective in killing target cells. Our results demonstrate that large-scale ex vivo expansion of donor-derived γδ T cells in a GMP-like setting can be achieved with the use of quadruplet aAPC and zol/IL-2 for clinical application.

CAR-T cell therapy in multiple myeloma: Current limitations and potential strategies

Over the last decade, the survival outcome of patients with multiple myeloma (MM) has been substantially improved with the emergence of novel therapeutic agents, such as proteasome inhibitors, immunomodulatory drugs, anti-CD38 monoclonal antibodies, selective inhibitors of nuclear export (SINEs), and T cell redirecting bispecific antibodies. However, MM remains an incurable neoplastic plasma cell disorder, and almost all MM patients inevitably relapse due to drug resistance. Encouragingly, B cell maturation antigen (BCMA)-targeted chimeric antigen receptor T (CAR-T) cell therapy has achieved impressive success in the treatment of relapsed/refractory (R/R) MM and brought new hopes for R/R MM patients in recent years. Due to antigen escape, the poor persistence of CAR-T cells, and the complicated tumor microenvironment, a significant population of MM patients still experience relapse after anti-BCMA CAR-T cell therapy. Additionally, the high manufacturing costs and time-consuming manufacturing processes caused by the personalized manufacturing procedures also limit the broad clinical application of CAR-T cell therapy. Therefore, in this review, we discuss current limitations of CAR-T cell therapy in MM, such as the resistance to CAR-T cell therapy and the limited accessibility of CAR-T cell therapy, and summarize some optimization strategies to overcome these challenges, including optimizing CAR structure, such as utilizing dual-targeted/multi-targeted CAR-T cells and armored CAR-T cells, optimizing manufacturing processes, combing CAR-T cell therapy with existing or emerging therapeutic approaches, and performing subsequent anti-myeloma therapy after CAR-T cell therapy as salvage therapy or maintenance/consolidation therapy.

Target tumor microenvironment by innate T cells

The immunosuppressive tumor microenvironment (TME) remains one of the most prevailing barriers obstructing the implementation of effective immunotherapy against solid-state cancers. Eminently composed of immunosuppressive tumor associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs) among others, the TME attenuates the effects of immune checkpoint blockade and adoptive cell therapies, mandating a novel therapy capable of TME remediation. In this review we explore the potential of three innate-like T cell subsets, invariant natural killer T (iNKT), mucosal-associated invariant T (MAIT) cells, and gamma delta T (γδT) cells, that display an intrinsic anti-TAM/MDSC capacity. Exhibiting both innate and adaptive properties, innate-like T cell types express a subset-specific TCR with distinct recombination, morphology, and target cell recognition, further supplemented by a variety of NK activating receptors. Both NK activating receptor and TCR activation result in effector cell cytotoxicity against targeted immunosuppressive cells for TME remediation. In addition, innate-like T cells showcase moderate levels of tumor cell killing, providing dual antitumor and anti-TAM/MDSC function. This latent antitumor capacity can be further bolstered by chimeric antigen receptor (CAR) engineering for recognition of tumor specific antigens to enhance antitumor targeting. In contrast with established CAR-T cell therapies, adoption of these innate-like cell types provides an enhanced safety profile without the risk of graft versus host disease (GvHD), due to their non-recognition of mismatched major histocompatibility complex (MHC) molecules, for use as widely accessible, allogeneic “off-the-shelf” cancer immunotherapy.

Gamma delta T-cell reconstitution after allogeneic HCT: A platform for cell therapy

Allogeneic Hematopoietic stem cell transplantation (allo-HCT) is a curative platform for several hematological diseases. Despite its therapeutic benefits, the profound immunodeficiency associated with the transplant procedure remains a major challenge that renders patients vulnerable to several complications. Today, It is well established that a rapid and efficient immune reconstitution, particularly of the T cell compartment is pivotal to both a short-term and a long-term favorable outcome. T cells expressing a TCR heterodimer comprised of gamma (γ) and delta (δ) chains have received particular attention in allo-HCT setting, as a large body of evidence has indicated that γδ T cells can exert favorable potent anti-tumor effects without inducing severe graft versus host disease (GVHD). However, despite their potential role in allo-HCT, studies investigating their detailed reconstitution in patients after allo-HCT are scarce. In this review we aim to shed lights on the current literature and understanding of γδ T cell reconstitution kinetics as well as the different transplant-related factors that may influence γδ reconstitution in allo-HCT. Furthermore, we will present data from available reports supporting a role of γδ cells and their subsets in patient outcome. Finally, we discuss the current and future strategies to develop γδ cell-based therapies to exploit the full immunotherapeutic potential of γδ cells in HCT setting.

Revolution of CAR Engineering For Next-Generation Immunotherapy In Solid Tumors

Chimeric antigen receptor (CAR)-T cells have enormous potentials for clinical therapies. The CAR-T therapy has been approved for treating hematological malignancies. However, their application is limited in solid tumors owing to antigen loss and mutation, physical barriers, and an immunosuppressive tumor microenvironment. To overcome the challenges of CAR-T, increasing efforts are put into developing CAR-T to expand its applied ranges. Varied receptors are utilized for recognizing tumor-associated antigens and relieving immunosuppression. Emerging co-stimulatory signaling is employed for CAR-T activation. Furthermore, other immune cells such as NK cells and macrophages have manifested potential for delivering CAR. Hence, we collected and summarized the last advancements of CAR engineering from three aspects, namely, the ectodomains, endogenous domains, and immune cells, aiming to inspire the design of next-generation adoptive immunotherapy for treating solid tumors.

CAR-T Cell Therapy in Hematological Malignancies: Current Opportunities and Challenges

Chimeric antigen receptor T (CAR-T) cell therapy represents a major breakthrough in cancer treatment, and it has achieved unprecedented success in hematological malignancies, especially in relapsed/refractory (R/R) B cell malignancies. At present, CD19 and BCMA are the most common targets in CAR-T cell therapy, and numerous novel therapeutic targets are being explored. However, the adverse events related to CAR-T cell therapy might be serious or even life-threatening, such as cytokine release syndrome (CRS), CAR-T-cell-related encephalopathy syndrome (CRES), infections, cytopenia, and CRS-related coagulopathy. In addition, due to antigen escape, the limited CAR-T cell persistence, and immunosuppressive tumor microenvironment, a considerable proportion of patients relapse after CAR-T cell therapy. Thus, in this review, we focus on the progress and challenges of CAR-T cell therapy in hematological malignancies, such as attractive therapeutic targets, CAR-T related toxicities, and resistance to CAR-T cell therapy, and provide some practical recommendations.

HAPLOIDENTICAL STEM CELL TRANSPLANTATION AFTER TCR αβ+AND CD19+ CELLS DEPLETION IN CHILDREN WITH CONGENITAL NON-MALIGNANT DISEASE

BACKGROUND

. Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents a valuable alternative for children with non-malignant disease and ex-vivo negative selection of TCR αβ⁺-cells is an emerging graft manipulation option that carries several potential advantages in terms of reduced risk of Graft versus Host Disease (GvHD) and improved immune reconstitution.

METHODS

. We reported all consecutive patients with a diagnosis of non-malignant disease who received a TCR-αβ⁺ and CD19⁺depleted haplo-HSCT at "IRCCS Istituto Giannina Gaslini" from 2013 to 2019; the conditioning regimen was myeloablative or non-myeloablative, depending on underlying disease; all patients received anti-thymocyte globulin and rituximab. No post-transplant GvHD prophylaxis was given in presence of a TCR-αβ⁺ cell-dose in the graft lower than the threshold of 1 × 10⁵/kg of the recipient's weight.

RESULTS

. Among 20 HSCTs, engraftment occurred in 17 (85%) after a median of 14 and 12 days from graft infusion for neutrophils and platelets respectively. Primary graft failure was diagnosed in 3 (15%) patients, two (10%) experienced secondary rejection; all of these underwent a second HSCT. The cumulative incidence of a-GvHD and c-GvHD was 15% (2 grade 1, 1 grade 4) at 90 days and 5% (1 grade 1) at 7 months, respectively. Cytomegalovirus reactivation requiring pre-emptive treatment was observed in 9 patients (45%). One patient developed a JC virus-related progressive multifocal leukoencephalopathy, successfully managed with donor-derived virus-specific T-cell infusions. A complete immunological recovery was reached in most patients within 6 months. After a median follow-up of 4 years, 18 patients are alive, with a cumulative survival probability of 90%.

CONCLUSION

. Haplo-HSCT after ex-vivo TCR-αβ⁺/CD19⁺ negative selection may be considered a good option for children with non-malignant diseases since it ensures a high engraftment rate with an acceptable risk of graft failure, very low incidence of significant GvHD, and good immune reconstitution with low frequency of severe virus-related disease. However, the control of viral infection/reactivation should be kept high in order to promptly provide pre-emptive treatments and approaches of antiviral adoptive immunotherapy.

Folate Receptor-Alpha Targeted 7x19 CAR-γδT Suppressed Triple-Negative Breast Cancer Xenograft Model in Mice

Background

Triple-negative breast cancer (TNBC) is the worst prognosis subtype of breast cancer due to lack of specific targets. Recent studies have shown that immunotherapy may solve that problem by targeting folate receptor-alpha (FRα).

Methods

Gene modified γδ T cells were manufactured to express FRa specific chimeric antigen receptor (FRa CAR) and secrete interleukin-7 (IL-7) and chemokine C–C motif ligand 19 (CCL19). CAR-γδT cells that secrete IL-7 and CCL19 (7 × 19 CAR-γδT) were evaluated for their antitumor activity both in vitro and in vivo.

Results

7 × 19 CAR-γδT showed remarkable antitumor activity in vitro. Combined with PBMC, 7 × 19 CAR-γδT inhibited TNBC xenograft model growth superiorly compared with single-application or conventional CAR-γδT cells. Histopathological analyses showed increased DC or T cells infiltration to tumor tissues.

Conclusion

Taken together, our results showed that 7 × 19 CAR-γδT have remarkable anti-TNBC tumor activity and showed a broad application prospect in the treatment of incurable TNBC patients.

Optimizing Blood Stem Cell Transplants Through Cellular Engineering

Haematopoietic stem cell transplants (HSCT) are used in the treatment of blood cancers, autoimmune diseases, and metabolic disorders. Over 1.5 million transplants have been performed around the world thus far. In an attempt to enhance the efficacy of the cells used for transplantation, efforts are underway to use cellular engineering to increase cell numbers through: (1) the expansion of hematopoietic stem and progenitor cells (HSPC); (2) cellular subset selection to remove cells that cause graft-versus-host disease (GvHD), while adding back cells, which can mediate anti-tumor and anti-viral immunity; (3) the use of immune regulatory cells, such as mesenchymal stromal cells (MSC) and regulatory T cells (Tregs) to control GvHD; (4) the use of immune effector cells to mount immunological control of tumor cells before, after, or independent of blood stem cell transplants.

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.

Is It Possible to Separate the Graft-Versus-Leukemia (GVL) Effect Against B Cell Acute Lymphoblastic Leukemia From Graft-Versus-Host Disease (GVHD) After Hematopoietic Cell Transplant?

Hematopoietic cell transplant is a curative therapy for many pediatric patients with high risk acute lymphoblastic leukemia. Its therapeutic mechanism is primarily based on the generation of an alloreactive graft-versus-leukemia effect that can eliminate residual leukemia cells thus preventing relapse. However its efficacy is diminished by the concurrent emergence of harmful graft-versus-host disease disease which affects healthly tissue leading to significant morbidity and mortality. The purpose of this review is to describe the interventions that have been trialed in order to augment the beneficial graft-versus leukemia effect post-hematopoietic cell transplant while limiting the harmful consequences of graft-versus-host disease. This includes many emerging and promising strategies such as ex vivo and in vivo graft manipulation, targeted cell therapies, T-cell engagers and multiple pharmacologic interventions that stimulate specific donor effector cells.

Allogeneic gamma delta T cells as adoptive cellular therapy for hematologic malignancies

Cancer immunotherapy, especially T-cell driven targeting, has significantly evolved and improved over the past decade, paving the way to treat previously refractory cancers. Hematologic malignancies, given their direct tumor accessibility and less immunosuppressive microenvironment compared to solid tumors, are better suited to be targeted by cellular immunotherapies. Gamma delta (γδ) T cells, with their unique attributes spanning the entirety of the immune system, make a tantalizing therapeutic platform for cancer immunotherapy. Their inherent anti-tumor properties, ability to act like antigen-presenting cells, and the advantage of having no major histocompatibility complex (MHC) restrictions, allow for greater flexibility in their utility to target tumors, compared to their αβ T cell counterpart. Their MHC-independent anti-tumor activity, coupled with their ability to be easily expanded from peripheral blood, enhance their potential to be used as an allogeneic product. In this review, the potential of utilizing γδ T cells to target hematologic malignancies is described, with a specific focus on their applicability as an allogeneic adoptive cellular therapy product.

T-cell depleted haploidentical hematopoietic cell transplantation for pediatric malignancy

Access to allogenic hematopoietic cell transplantation (HCT), a potentially curative treatment for chemotherapy-resistant hematologic malignancies, can be limited if no human leukocyte antigen (HLA) identical related or unrelated donor is available. Alternative donors include Cord Blood as well as HLA-mismatched unrelated or related donors. If the goal is to minimize the number of HLA disparities, partially matched unrelated donors are more likely to share 8 or 9 of 10 HLA alleles with the recipient. However, over the last decade, there has been success with haploidentical HCT performed using the stem cells from HLA half-matched related donors. As the majority of patients have at least one eligible and motivated haploidentical donor, recruitment of haploidentical related donors is frequently more rapid than of unrelated donors. This advantage in the accessibility has historically been offset by the increased risks of graft rejection, graft-versus-host disease and delayed immune reconstitution. Various ex vivo T-cell depletion (TCD) methods have been investigated to overcome the immunological barrier and facilitate immune reconstitution after a haploidentical HCT. This review summarizes historical and contemporary clinical trials of haploidentical TCD-HCT, mainly in pediatric malignancy, and describes the evolution of these approaches with a focus on serial improvements in the kinetics of immune reconstitution. Methods of TCD discussed include in vivo as well as ex vivo positive and negative selection. In addition, haploidentical TCD as a platform for post-HCT cellular therapies is discussed. The present review highlights that, as a result of the remarkable progress over half a century, haploidentical TCD-HCT can now be considered as a preferred alternative donor option for children with hematological malignancy in need of allogeneic HCT.

Modeling human yolk sac hematopoiesis with pluripotent stem cells

In the mouse, the first hematopoietic cells are generated in the yolk sac from the primitive, erythro-myeloid progenitor (EMP) and lymphoid programs that are specified before the emergence of hematopoietic stem cells. While many of the yolk sac-derived populations are transient, specific immune cell progeny seed developing tissues, where they function into adult life. To access the human equivalent of these lineages, we modeled yolk sac hematopoietic development using pluripotent stem cell differentiation. Here, we show that the combination of Activin A, BMP4, and FGF2 induces a population of KDR+CD235a/b+ mesoderm that gives rise to the spectrum of erythroid, myeloid, and T lymphoid lineages characteristic of the mouse yolk sac hematopoietic programs, including the Vδ2+ subset of γ/δ T cells that develops early in the human embryo. Through clonal analyses, we identified a multipotent hematopoietic progenitor with erythroid, myeloid, and T lymphoid potential, suggesting that the yolk sac EMP and lymphoid lineages may develop from a common progenitor.

The Diverse Roles of γδ T Cells in Cancer: From Rapid Immunity to Aggressive Lymphoma

γδ T cells are unique players in shaping immune responses, lying at the intersection between innate and adaptive immunity. Unlike conventional αβ T cells, γδ T cells largely populate non-lymphoid peripheral tissues, demonstrating tissue specificity, and they respond to ligands in an MHC-independent manner. γδ T cells display rapid activation and effector functions, with a capacity for cytotoxic anti-tumour responses and production of inflammatory cytokines such as IFN-γ or IL-17. Their rapid cytotoxic nature makes them attractive cells for use in anti-cancer immunotherapies. However, upon transformation, γδ T cells can give rise to highly aggressive lymphomas. These rare malignancies often display poor patient survival, and no curative therapies exist. In this review, we discuss the diverse roles of γδ T cells in immune surveillance and response, with a particular focus on cancer immunity. We summarise the intriguing dichotomy between pro- and anti-tumour functions of γδ T cells in solid and haematological cancers, highlighting the key subsets involved. Finally, we discuss potential drivers of γδ T-cell transformation, summarising the main γδ T-cell lymphoma/leukaemia entities, their clinical features, recent advances in mapping their molecular and genomic landscapes, current treatment strategies and potential future targeting options.

Bone Marrow-Resident Vδ1 T Cells Co-express TIGIT With PD-1, TIM-3 or CD39 in AML and Myeloma

Background: γδ T cells represent a unique T cell subpopulation due to their ability to recognize cancer cells in a T cell receptor- (TCR) dependent manner, but also in a non-major histocompatibility complex- (MHC) restricted way via natural killer receptors (NKRs). Endowed with these features, they represent attractive effectors for immuno-therapeutic strategies with a better safety profile and a more favorable anti-tumor efficacy in comparison to conventional αβ T cells. Also, remarkable progress has been achieved re-activating exhausted T lymphocytes with inhibitors of co-regulatory receptors e.g., programmed cell death protein 1 (PD-1), T cell immunoreceptor with Ig and ITIM domains (TIGIT) and of the adenosine pathway (CD39, CD73). Regarding γδ T cells, little evidence is available. This study aimed to immunophenotypically characterize γδ T cells from patients with diagnosed acute myeloid leukemia (AML) in comparison to patients with multiple myeloma (MM) and healthy donors (HD).

Methods: The frequency, differentiation, activation, and exhaustion status of bone marrow- (BM) derived γδ T cells from patients with AML (n = 10) and MM (n = 11) were assessed in comparison to corresponding CD4⁺ and CD8⁺ T cells and peripheral blood- (PB) derived γδ T cells from HDs (n = 16) using multiparameter flow cytometry.

Results: BM-infiltrating Vδ1 T cells showed an increased terminally differentiated cell population (TEMRAs) in AML and MM in comparison to HDs with an aberrant subpopulation of CD27⁻CD45RA⁺⁺ cells. TIGIT, PD-1, TIM-3, and CD39 were more frequently expressed by γδ T cells in comparison to the corresponding CD4⁺ T cell population, with expression levels that were similar to that on CD8⁺ effector cells in both hematologic malignancies. In comparison to Vδ2 T cells, the increased frequency of PD-1⁺-, TIGIT⁺-, TIM-3⁺, and CD39⁺ cells was specifically observed on Vδ1 T cells and related to the TEMRA Vδ1 population with a significant co-expression of PD-1 and TIM-3 together with TIGIT.

Conclusion: Our results revealed that BM-resident γδ T cells in AML and MM express TIGIT, PD-1, TIM-3 and CD39. As effector population for autologous and allogeneic strategies, inhibition of co-inhibitory receptors on especially Vδ1 γδ T cells may lead to re-invigoration that could further increase their cytotoxic potential.

Uncovering key targets of success for immunotherapy in pancreatic cancer

INTRODUCTION

Despite available treatment options, pancreatic ductal adenocarcinoma (PDAC) is frequently lethal. Recent immunotherapy strategies have failed to yield any notable impact. Therefore, research is focussed on unearthing new drug targets and therapeutic strategies to tackle this malignancy and attain more positive outcomes for patients.

AREAS COVERED

In this perspective article, we evaluate the main resistance mechanisms to immune checkpoint inhibitors (ICIs) and the approaches to circumvent them. We also offer an assessment of concluded and ongoing trials of PDAC immunotherapy. Literature research was performed on Pubmed accessible through keywords such as: 'pancreatic ductal adenocarcinoma,' 'immunotherapy,' 'immunotherapy resistance,' 'immune escape,' 'biomarkers.' Papers published between 2000 and 2021 were selected.

EXPERT OPINION

The tumor microenvironment is a critical variable of treatment resistance because of its role as a physical barrier and inhibitory immune signaling. Promising therapeutic strategies appear to be a combination of immunotherapeutics with other targeted treatments. Going forward, predictive biomarkers are required to improve patient selection. Biomarker-driven trials could enhance approaches for assessing the role of immunotherapy in PDAC.

Optimizing allogeneic grafts in hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is widely used in the treatment of hematological diseases. It is well known that allogeneic grafts play a key role in predicting transplantation prognosis. Hematopoietic stem cells (HSCs) are a functional part of grafts and are capable of reconstructing hematopoiesis and immunity, but purified HSCs have not been identified or isolated to date. In clinical practice, allogeneic grafts have been optimized to improve transplantation outcomes. The optimized grafts are considered to engraft successfully, reconstruct immunity rapidly, and exert a graft-vs-leukemia (GVL) effect without causing severe graft-vs-host disease (GvHD). In the last several decades, considerable efforts have been made in searching for optimized grafts based on different graft manipulation approaches and different graft sources. Currently, there is no uniform standard for optimized grafts in allogeneic transplantation. In the future, sorting out the cellular elements responsible for the effects of allo-HSCT might be a research direction for further optimization of grafts. In this review, we propose the concept of optimized grafts and summarize the recent advances made in the process of optimizing grafts.

CMV Infection and CMV-Specific Immune Reconstitution Following Haploidentical Stem Cell Transplantation: An Update

Haploidentical stem cell transplantation (haploSCT) has advanced to a common procedure for treating patients with hematological malignancies and immunodeficiency diseases. However, cure is seriously hampered by cytomegalovirus (CMV) infections and delayed immune reconstitution for the majority of haploidentical transplant recipients compared to HLA-matched stem cell transplantation. Three major approaches, including in vivo T-cell depletion (TCD) using antithymocyte globulin for haploSCT (in vivo TCD-haploSCT), ex vivo TCD using CD34 + positive selection for haploSCT (ex vivo TCD-haploSCT), and T-cell replete haploSCT using posttransplant cyclophosphamide (PTCy-haploSCT), are currently used worldwide. We provide an update on CMV infection and CMV-specific immune recovery in this fast-evolving field. The progress made in cellular immunotherapy of CMV infection after haploSCT is also addressed. Groundwork has been prepared for the creation of personalized avenues to enhance immune reconstitution and decrease the incidence of CMV infection after haploSCT.

The Role of Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) offers potentially curative treatment for many children with high-risk or relapsed acute leukemia (AL), thanks to the combination of intense preparative radio/chemotherapy and the graft-versus-leukemia (GvL) effect. Over the years, progress in high-resolution donor typing, choice of conditioning regimen, graft-versus-host disease (GvHD) prophylaxis and supportive care measures have continuously improved overall transplant outcome, and recent successes using alternative donors have extended the potential application of allotransplantation to most patients. In addition, the importance of minimal residual disease (MRD) before and after transplantation is being increasingly clarified and MRD-directed interventions may be employed to further ameliorate leukemia-free survival after allogeneic HSCT. These advances have occurred in parallel with continuous refinements in chemotherapy protocols and the development of targeted therapies, which may redefine the indications for HSCT in the coming years. This review discusses the role of HSCT in childhood AL by analysing transplant indications in both acute lymphoblastic and acute myeloid leukemia, together with current and most promising strategies to further improve transplant outcome, including optimization of conditioning regimen and MRD-directed interventions.

Harnessing Mechanisms of Immune Tolerance to Improve Outcomes in Solid Organ Transplantation: A Review

Survival after solid organ transplantation (SOT) is limited by chronic rejection as well as the need for lifelong immunosuppression and its associated toxicities. Several preclinical and clinical studies have tested methods designed to induce transplantation tolerance without lifelong immune suppression. The limited success of these strategies has led to the development of clinical protocols that combine SOT with other approaches, such as allogeneic hematopoietic stem cell transplantation (HSCT). HSCT prior to SOT facilitates engraftment of donor cells that can drive immune tolerance. Recent innovations in graft manipulation strategies and post-HSCT immune therapy provide further advances in promoting tolerance and improving clinical outcomes. In this review, we discuss conventional and unconventional immunological mechanisms underlying the development of immune tolerance in SOT recipients and how they can inform clinical advances. Specifically, we review the most recent mechanistic studies elucidating which immune regulatory cells dampen cytotoxic immune reactivity while fostering a tolerogenic environment. We further discuss how this understanding of regulatory cells can shape graft engineering and other therapeutic strategies to improve long-term outcomes for patients receiving HSCT and SOT.

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.

HLA-haploidentical TCRαβ+/CD19+-depleted stem cell transplantation in children and young adults with Fanconi anemia

We report on the outcome of 24 patients with Fanconi anemia (FA) lacking an HLA matched related or unrelated donor, given an HLA-haploidentical T-cell receptor αβ (TCRαβ+) and CD19+ cell-depleted hematopoietic stem cell transplantation (HSCT) in the context of a prospective, single-center phase 2 trial. Sustained primary engraftment was achieved in 22 (91.6%) of 24 patients, with median time to neutrophil recovery of 12 days (range, 9-15 days) and platelet recovery of 10 days (range, 7-14 days). Cumulative incidences of grade 1 to 2 acute graft-versus-host disease (GVHD) and chronic GVHD were 17.4% (95% confidence interval [CI], 5.5%-35.5%) and 5.5% (95% CI, 0.8%-33.4%), respectively. The conditioning regimen, which included fludarabine, low-dose cyclophosphamide and, in most patients, single-dose irradiation was well tolerated; no fatal transplant-related toxicity was observed. With a median follow-up of 5.2 years (range, 0.3-8.7 years), the overall and event-free survival probabilities were 100% and 86.3% (95% CI, 62.8%-95.4%), respectively (2 graft failures and 1 case of poor graft function were considered as events). The 2 patients who experienced primary graft failure underwent a subsequent successful HSCT from the other parent. This is the first report of FA patients given TCRαβ+/CD19+-depleted haplo-HSCT in the context of a prospective trial, and the largest series of T-cell-depleted haplo-HSCT in FA reported to date. This trial was registered at www.clinicaltrials.gov as #NCT01810120.

"Ex-vivo" T-cell depletion in allogeneic hematopoietic stem cell transplantation: New clinical approaches for old challenges

Allogeneic transplantation still remains as standard of care for patients with high-risk hematological malignancies at diagnosis or after relapse. However, GvHD remains yet as the most relevant clinical complication in the early post-transplant period. TCD allogeneic transplant is now considered a valid option to reduce severe GvHD and to provide a platform for cellular therapy to prevent relapse disease or to treat opportunistic infections.

Transient antibody targeting of CD45RC inhibits the development of graft-versus-host disease

Allogeneic bone marrow transplantation (BMT) is a widely spread treatment of many hematological diseases, but its most important side effect is graft-versus-host disease (GVHD). Despite the development of new therapies, acute GVHD (aGVHD) occurs in 30% to 50% of allogeneic BMT and is characterized by the generation of effector T (Teff) cells with production of inflammatory cytokines. We previously demonstrated that a short anti-CD45RC monoclonal antibody (mAb) treatment in a heart allograft rat model transiently decreased CD45RChigh Teff cells and increased regulatory T cell (Treg) number and function allowing long-term donor-specific tolerance. Here, we demonstrated in rat and mouse allogeneic GVHD, as well as in xenogeneic GVHD mediated by human T cells in NSG mice, that both ex vivo depletion of CD45RChigh T cells and in vivo treatment with short-course anti-CD45RC mAbs inhibited aGVHD. In the rat model, we demonstrated that long surviving animals treated with anti-CD45RC mAbs were fully engrafted with donor cells and developed a donor-specific tolerance. Finally, we validated the rejection of a human tumor in NSG mice infused with human cells and treated with anti-CD45RC mAbs. The anti-human CD45RC mAbs showed a favorable safety profile because it did not abolish human memory antiviral immune responses, nor trigger cytokine release in in vitro assays. Altogether, our results show the potential of a prophylactic treatment with anti-human CD45RC mAbs in combination with rapamycin as a new therapy to treat aGVHD without abolishing the antitumor effect.

NK Cells and PMN-MDSCs in the Graft From G-CSF Mobilized Haploidentical Donors Display Distinct Gene Expression Profiles From Those of the Non-Mobilized Counterpart

A recent approach of hematopoietic stem cell (HSC) transplantation from haploidentical donors "mobilized" with G-CSF is based on the selective depletion of αβ T and B lymphocytes from the graft. Through this approach, the patient receives both HSC and mature donor-derived effector cells (including NK cells), which exert both anti-leukemia activity and protection against infections. We previously showed that donor HSC mobilization with G-CSF results in accumulation in the graft of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), capable of inhibiting in vitro the anti-leukemia activity of allogeneic NK cells. Here, we performed a detailed gene expression analysis on NK cells and PMN-MDSCs both derived from mobilized graft. Cytotoxicity assays and real time PCR arrays were performed in NK cells. Microarray technology followed by bioinformatics analysis was used for gene expression profiling in PMN-MDSCs. Results indicate that NK cells from the graft have a lower cytolytic activity as compared to those from non-mobilized samples. Further, mobilized PMN-MDSCs displayed a peculiar transcriptional profile distinguishing them from non-mobilized ones. Differential expression of pro-proliferative and immune-modulatory genes was detected in mobilized PMN-MDSCs. These data strengthen the concept that G-CSF-mobilized PMN-MDSCs present in the graft display unique molecular characteristics, in line with the strong inhibitory effect on donor NK cells.

Is Adoptive Cellular Therapy With Non-T-Cell Immune Effectors the Future?

ABSTRACT

Success from checkpoint blockade and adoptive cell therapy has brought a new hope in cancer immunotherapy. Adoptive cell therapy involves the isolation of immune cells, ex vivo activation and/or expansion, and reinfusion into the patients, and their effect can be dramatically increased by the incorporation of chimeric antigen receptors specific to molecules expressed on tumor cells. Chimeric antigen receptor T cells have shown exciting results in the treatment of liquid malignancies; nevertheless, they suffer from limitations including severe adverse effects such as cytokine release syndrome and neurotoxicity seen in patients as well as a potential for causing graft-versus-host disease in an allogeneic setting. It is thus imperial to explore innate immune cells including natural killer cells, macrophages, natural killer T cells, and γδ T cells. Here, we provide a broad overview of the major innate immune cells and their potential for adoptive cell therapy and chimeric antigen receptor engineering.

PLCG2 as a potential indicator of tumor microenvironment remodeling in soft tissue sarcoma

The tumor microenvironment (TME) plays an important role in the occurrence and development of soft tissue sarcoma (STS). A number of studies have shown that to inhibit tumor growth, the TME can be remodeled into an environment unsuitable for tumor proliferation. However, a lack of understanding exists regarding the dynamic regulation of TME.In this study, we used CIBERSORT and ESTIMATE calculation methods from the Cancer Genome Atlas (TCGA) database to calculate the proportion of tumor infiltrating immune cells (TICs) and the number of immune and stromal components in 263 STS samples. Differential expression genes (DEGs) shared by Immune Score and Stromal Score were obtained via difference analysis. Univariate Cox regression analysis and construction of protein-protein interaction (PPI) networks were applied to the DEGs.Through intersection analysis of univariate COX and PPI, PLCG2 was determined as the indicator. Further analysis showed that PLCG2 expression was positively correlated with the survival of STS patients. Gene set enrichment analysis (GSEA) showed that genes in the highly expressed PLCG2 group were enriched in immune-related activities. In the low-expression PLCG2 group, genes were enriched in the E2F, G2M, and MYC pathways. Difference analysis and correlation analysis showed that CD8+ T cells, gamma delta T cells, monocytes, and M1 macrophages were positively correlated with PLCG2 expression, indicating that PLCG2 may represent the immune status of TME.Therefore, the level of PLCG2 may aid in determining the prognosis of STS patients, especially the status of TME. These data provide additional insights into the remodeling of TME.

An Unconventional View of T Cell Reconstitution After Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is performed as curative-intent therapy for hematologic malignancies and non-malignant hematologic, immunological and metabolic disorders, however, its broader implementation is limited by high rates of transplantation-related complications and a 2-year mortality that approaches 50%. Robust reconstitution of a functioning innate and adaptive immune system is a critical contributor to good long-term patient outcomes, primarily to prevent and overcome post-transplantation infectious complications and ensure adequate graft-versus-leukemia effects. There is increasing evidence that unconventional T cells may have an important immunomodulatory role after allo-HCT, which may be at least partially dependent on the post-transplantation intestinal microbiome. Here we discuss the role of immune reconstitution in allo-HCT outcome, focusing on unconventional T cells, specifically mucosal-associated invariant T (MAIT) cells, γδ (gd) T cells, and invariant NK T (iNKT) cells. We provide an overview of the mechanistic preclinical and associative clinical studies that have been performed. We also discuss the emerging role of the intestinal microbiome with regard to hematopoietic function and overall immune reconstitution.

Co-Transplantation of Haploidentical Stem Cells and a Dose of Unrelated Cord Blood in Pediatric Patients with Thalassemia Major

Allogeneic stem cell transplantation is a cure for patients suffering from thalassemia major (TM). Historically, patients were limited by the selection of donors, while the advancement of haploidentical stem cell transplantation (haplo-SCT) has greatly expanded the donor pool. However, the outcomes of haplo-SCT in TM recipients vary between different programs. In this study, we retrospectively studied 73 pediatric TM patients (median age, 7 years; range, 3 to 14 years) who underwent haplo-cord transplantation. Both the estimated overall survival and transfusion-free survival were 95.26% (CI 95.77% to 96.23%). Neither primary nor secondary graft failures were observed. The median follow-up period was 811 days (range, 370 to 1433 days). Median neutrophil and platelet engraftment times were 22 days (range, 8 to 48 days) and 20 days (range, 8 to 99 days), respectively. Acute graft-versus-host disease (aGVHD) was observed in 52% of patients and of these, 25% developed grade III to IV aGVHD. Cord blood engraftment was associated with delayed immune recovery and increased aGVHD severity. Viral DNAemia occurred in a relatively high proportion of patients but only 7% of patients developed CMV disease, while another 7% of patients had post-transplantation lymphoproliferative disorder. Long-term complication outcomes were good. Only one patient developed extensive chronic GVHD. No surviving patients were reliant on blood transfusion by the time this manuscript was submitted. This is one of the largest studies on the outcomes of pediatric TM patients who received stem cell transplantations from alternative donors. The haplo-cord program is safe and practical for TM patients that do not have matched donors.

Immune reconstitution after T-cell replete HLA haploidentical hematopoietic stem cell transplantation using high-dose post-transplant cyclophosphamide

As HLA haploidentical related donors are quickly available, HLA haploidentical hematopoietic stem cell transplantation (haploHSCT) using high-dose post-transplant cyclophosphamide (PTCy) is now widely used. Recent basic and clinical studies revealed the details of immune reconstitution after T-cell replete haploHSCT using PTCy. T cells and NK cells in the graft proliferate abundantly at day 3 post-haploHSCT, and the PTCy eliminates these proliferating cells. After ablation of proliferating mature cells, donor-derived NK cell reconstitution occurs after the second week; however, recovering NK cells remain functionally impaired for at least several months after haploHSCT. PTCy depletes proliferating cells, resulting in the preferential accumulation of Treg and CD4+ T cells, especially the memory stem T cell (T_^SCM) phenotype. T_^SCM capable of both self-renewal and differentiation into effector T cells may play an important role in the first month of immune reconstitution. Subsequently, de novo T cells progressively recover but their levels remain well below those of donor CD4+ T cells at the first year after haploHSCT. The phenotype of recovering T cells after HSCT is predominantly effector memory, whereas B cells are predominantly phenotypically naive throughout the first year after haploHSCT. B cell recovery depends on de novo generation and they are not detected until week 4 after haploHSCT. At week 5, recovering B cells mostly exhibit an unconventional transitional cell phenotype and the cell subset undergoes maturation. Recent advances in immune reconstitution have improved our understanding of the relationship between haploHSCT with PTCy and the clinical outcome.

Engineering advanced logic and distributed computing in human CAR immune cells

The immune system is a sophisticated network of different cell types performing complex biocomputation at single-cell and consortium levels. The ability to reprogram such an interconnected multicellular system holds enormous promise in treating various diseases, as exemplified by the use of chimeric antigen receptor (CAR) T cells as cancer therapy. However, most CAR designs lack computation features and cannot reprogram multiple immune cell types in a coordinated manner. Here, leveraging our split, universal, and programmable (SUPRA) CAR system, we develop an inhibitory feature, achieving a three-input logic, and demonstrate that this programmable system is functional in diverse adaptive and innate immune cells. We also create an inducible multi-cellular NIMPLY circuit, kill switch, and a synthetic intercellular communication channel. Our work highlights that a simple split CAR design can generate diverse and complex phenotypes and provide a foundation for engineering an immune cell consortium with user-defined functionalities.

Most CAR designs lack control and computation features, limiting the sophistication of the engineered immune response. Here the authors leverage a split CAR design for engineering coordinated immune responses.

The role of the thymus in allogeneic bone marrow transplantation and the recovery of the peripheral T-cell compartment

As the thymus represents the primary site of T-cell development, optimal thymic function is of paramount importance for the successful reconstitution of the adaptive immunity after allogeneic hematopoietic stem cell transplantation. Thymus involutes as part of the aging process and several factors, including previous chemotherapy treatments, conditioning regimen used in preparation to the allograft, occurrence of graft-versus-host disease, and steroid therapy that impair the integrity of the thymus, thus affecting its role in supporting T-cell neogenesis. Although the pathways governing its regeneration are still poorly understood, the thymus has a remarkable capacity to recover its function after damage. Measurement of both recent thymic emigrants and T-cell receptor excision circles is valuable tools to assess thymic output and gain insights on its function. In this review, we will extensively discuss available data on factors regulating thymic function after allogeneic hematopoietic stem cell transplantation, as well as the strategies and therapeutic approaches under investigation to promote thymic reconstitution and accelerate immune recovery in transplanted patients, including the use of cytokines, sex-steroid ablation, precursor T-cells, and thymus bioengineering. Although none of them is routinely used in the clinic, these approaches have the potential to enhance thymic function and immune recovery, not only in patients given an allograft but also in other conditions characterized by immune deficiencies related to a defective function of the thymus.