Identification, selection, and expansion of non-gene modified alloantigen-reactive Tregs for clinical therapeutic use

Biomaterial-Based Therapeutic Delivery of Immune Cells

Immune cell therapy (ICT) is a transformative approach used to treat a wide range of diseases including type 1 diabetes, sickle cell disease, disorders of the hematopoietic system, and certain forms of cancers. Despite excellent clinical successes, the scope of adoptively transferred immune cells is limited because of toxicities like cytokine release syndrome and immune effector cell-associated neurotoxicity in patients. Furthermore, reports suggest that such treatment can impact major organ systems including cardiac, renal, pulmonary, and hepatic systems in the long term. Additionally, adoptively transferred immune cells cannot achieve significant penetration into solid tissues, thus limiting their therapeutic potential. Recent studies suggest that biomaterial-assisted delivery of immune cells can address these challenges by reducing toxicity, improving localization, and maintaining desired phenotypes to eventually regain tissue function. In this review, recent efforts in the field of biomaterial-based immune cell delivery for the treatment of diseases, their pros and cons, and where these approaches stand in terms of clinical treatment are highlighted.

Intragraft regulatory T cells in the modern era: what can high-dimensional methods tell us about pathways to allograft acceptance?

Replacement of diseased organs with transplanted healthy donor ones remains the best and often only treatment option for end-stage organ disease. Immunosuppressants have decreased the incidence of acute rejection, but long-term survival remains limited. The broad action of current immunosuppressive drugs results in global immune impairment, increasing the risk of cancer and infections. Hence, achievement of allograft tolerance, in which graft function is maintained in the absence of global immunosuppression, has long been the aim of transplant clinicians and scientists. Regulatory T cells (Treg) are a specialized subset of immune cells that control a diverse array of immune responses, can prevent allograft rejection in animals, and have recently been explored in early phase clinical trials as an adoptive cellular therapy in transplant recipients. It has been established that allograft residency by Tregs can promote graft acceptance, but whether intragraft Treg functional diversification and spatial organization contribute to this process is largely unknown. In this review, we will explore what is known regarding the properties of intragraft Tregs during allograft acceptance and rejection. We will summarize recent advances in understanding Treg tissue residency through spatial, transcriptomic and high-dimensional cytometric methods in both animal and human studies. Our discussion will explore properties of intragraft Tregs in mediating operational tolerance to commonly transplanted solid organs. Finally, given recent developments in Treg cellular therapy, we will review emerging knowledge of whether and how these adoptively transferred cells enter allografts in humans. An understanding of the properties of intragraft Tregs will help lay the foundation for future therapies that will promote immune tolerance.

Treatment update for vitiligo based on autoimmune inhibition and melanocyte protection

INTRODUCTION

The treatment of vitiligo remains challenging due to the complexity of its pathogenesis, influenced by genetic factors, oxidative stress and abnormal cell adhesion that collectively impact melanocyte survival and trigger immune system attacks, resulting in melanocyte death. Melanocytes in vitiligo are believed to exhibit genetic susceptibility and defects in cellular mechanisms, such as defects in autophagy, that reduce their ability to resist oxidative stress, leading to increased expression of the pro-inflammatory protein HSP70. The low expression of adhesion molecules, such as DDR1 and E-cadherin, accelerates melanocyte damage and antigen exposure. Consequently, autoimmune attacks centered on IFN-γ-CXCR9/10-CXCR3-CD8⁺ T cells are initiated, causing vitiligo.

AREAS COVERED

This review discusses the latest knowledge on the pathogenesis of vitiligo and potential therapeutic targets from the perspective of suppressing autoimmune attacks and activating melanocytes functions.

EXPERT OPINION

Vitiligo is one of the most challenging dermatological diseases due to its complex pathogenesis with diverse therapeutic targets. Immune suppression, such as corticosteroids and emerging JAK inhibitors, has proven effective in disease progression. However, during the early stages of the disease, it is also important to optimize therapeutic strategies to activate melanocytes for alleviating oxidative stress and improving treatment outcomes.

Regulatory T-cell therapy approaches

Regulatory T cells (Tregs) have enormous therapeutic potential to treat a variety of immunopathologies characterized by aberrant immune activation. Adoptive transfer of ex vivo expanded autologous Tregs continues to progress through mid- to late-phase clinical trials in several disease spaces and has generated promising preliminary safety and efficacy signals to date. However, the practicalities of this strategy outside of the clinical trial setting remain challenging. Here, we review the current landscape of regulatory T-cell therapy, considering emergent approaches and technologies presenting novel ways to engage Tregs, and reflect on the progress necessary to deliver their therapeutic potential to patients.

Anti-HLA-A2-CAR Tregs prolong vascularized mouse heterotopic heart allograft survival

Alloantigen-specific regulatory T cell (Treg) therapy is a promising approach for suppressing alloimmune responses and minimizing immunosuppression after solid organ transplantation. Chimeric antigen receptor (CAR) targeting donor alloantigens can confer donor reactivity to Tregs. However, CAR Treg therapy has not been evaluated in vascularized transplant or multi-MHC mismatched models. Here, we evaluated the ability of CAR Tregs targeting HLA-A2 (A2-CAR) to prolong the survival of heterotopic heart transplants in mice. After verifying the in vitro activation, proliferation, and enhanced suppressive function of A2-CAR Tregs in the presence of A2-antigen, we analyzed the in vivo function of Tregs in C57BL/6 (B6) mice receiving A2-expressing heart allografts. A2-CAR Treg infusion increased the median survival of grafts from B6.HLA-A2 transgenic donors from 23 to 99 days, whereas median survival with polyclonal Treg infusion was 35 days. In a more stringent model of haplo-mismatched hearts from BALB/cxB6.HLA-A2 F1 donors, A2-CAR Tregs slightly increased median graft survival from 11 to 14 days, which was further extended to >100 days when combined with a 9-day course of rapamycin treatment. These findings demonstrate the efficacy of CAR Tregs, alone or in combination with immunosuppressive agents, toward protecting vascularized grafts in fully immunocompetent recipients.

Advances in vitiligo: Update on therapeutic targets

Vitiligo, whose treatment remains a serious concern and challenge, is an autoimmune skin disease characterized by patches of depigmentation. The increasing application of molecular-targeted therapy in skin diseases, such as psoriasis and systemic lupus erythematosus, has dramatically improved their condition. Besides, there is a favorable effect of repigmentation in the treatment of the above diseases combined with vitiligo, implying that molecular-targeted therapy may also have utility in vitiligo treatment. Recently, the role of cytokine and signaling pathways in vitiligo pathogenesis are increasingly recognized. Thus, investigations are underway targeting the molecules described above. In this paper, we present a synopsis of current practices in vitiligo treatment and introduce the improvement in identifying new molecular targets and applying molecular-targeted therapies, including those under development in vitiligo treatment, providing valuable insight into establishing further precision medicine for vitiligo patients.

Small spleen peptides prevent development of psoriatic arthritis via restoration of peripheral tolerance

The major challenge in the treatment of autoimmune diseases is the restoration of the impaired peripheral immune tolerance that always accompanies the development of such diseases. Here, we show that small splenic peptides (SSPs) of whole spleen extract efficiently suppress the development of psoriatic arthritis in vivo, even in the presence of sustained levels of pro-inflammatory cytokines. SSPs target dendritic cells (DCs) and convert them into tolerogenic cells, which in turn differentiate naive CD4⁺ cells into Foxp3-expressing T regulatory cells (Tregs). The latter requires direct contact between SSP-activated DCs and naive CD4⁺ T cells via PD-1 and CTLA4 immune checkpoint receptors of T cells. Finally, depletion of Foxp3⁺ Tregs in vivo abrogated the protective effect of SSPs on psoriatic arthritis development. We hypothesize that SSPs represent an intrinsic component of the adaptive immune system responsible for the physiological maintenance of peripheral tolerance and that therapeutically administered SSPs are able to restore imbalanced peripheral tolerance in autoimmune diseases.

Strong Expansion of Human Regulatory T Cells for Adoptive Cell Therapy Results in Epigenetic Changes Which May Impact Their Survival and Function

Adoptive transfer of regulatory T cells (Treg) is a promising new therapeutic option to treat detrimental inflammatory conditions after transplantation and during autoimmune disease. To reach sufficient cell yield for treatment, ex vivo isolated autologous or allogenic Tregs need to be expanded extensively in vitro during manufacturing of the Treg product. However, repetitive cycles of restimulation and prolonged culture have been shown to impact T cell phenotypes, functionality and fitness. It is therefore critical to scrutinize the molecular changes which occur during T cell product generation, and reexamine current manufacturing practices. We performed genome-wide DNA methylation profiling of cells throughout the manufacturing process of a polyclonal Treg product that has proven safety and hints of therapeutic efficacy in kidney transplant patients. We found progressive DNA methylation changes over the duration of culture, which were donor-independent and reproducible between manufacturing runs. Differentially methylated regions (DMRs) in the final products were significantly enriched at promoters and enhancers of genes implicated in T cell activation. Additionally, significant hypomethylation did also occur in promoters of genes implicated in functional exhaustion in conventional T cells, some of which, however, have been reported to strengthen immunosuppressive effector function in Tregs. At the same time, a set of reported Treg-specific demethylated regions increased methylation levels with culture, indicating a possible destabilization of Treg identity during manufacturing, which was independent of the purity of the starting material. Together, our results indicate that the repetitive TCR-mediated stimulation lead to epigenetic changes that might impact functionality of Treg products in multiple ways, by possibly shifting to an effector Treg phenotype with enhanced functional activity or by risking destabilization of Treg identity and impaired TCR activation. Our analyses also illustrate the value of epigenetic profiling for the evaluation of T cell product manufacturing pipelines, which might open new avenues for the improvement of current adoptive Treg therapies with relevance for conventional effector T cell products.

Towards regulatory cellular therapies in solid organ transplantation

Organ transplantation is a modern medical success story. However, since its inception it has been limited by the need for pharmacological immunosuppression. Regulatory cellular therapies offer an attractive solution to these challenges by controlling transplant alloresponses through multiple parallel suppressive mechanisms. A number of cell types have seen an accelerated development into human trials and are now on the threshold of a long-awaited breakthrough in personalized transplant therapeutics. Here we assess recent developments with a focus on the most likely candidates, some of which have already facilitated successful immunosuppression withdrawal in early clinical trials. We propose that this may constitute a promising approach in clinical transplantation but also evaluate outstanding issues in the field, providing cause for cautious optimism.

Highly Purified Alloantigen-Specific Tregs From Healthy and Chronic Kidney Disease Patients Can Be Long-Term Expanded, Maintaining a Suppressive Phenotype and Function in the Presence of Inflammatory Cytokines

The adoptive transfer of alloantigen-specific regulatory T cells (^alloTregs) has been proposed as a therapeutic alternative in kidney transplant recipients to the use of lifelong immunosuppressive drugs that cause serious side effects. However, the clinical application of ^alloTregs has been limited due to their low frequency in peripheral blood and the scarce development of efficient protocols to ensure their purity, expansion, and stability. Here, we describe a new experimental protocol that allows the long-term expansion of highly purified allospecific natural Tregs (nTregs) from both healthy controls and chronic kidney disease (CKD) patients, which maintain their phenotype and suppressive function under inflammatory conditions. Firstly, we co-cultured CellTrace Violet (CTV)-labeled Tregs from CKD patients or healthy individuals with allogeneic monocyte-derived dendritic cells in the presence of interleukin 2 (IL-2) and retinoic acid. Then, proliferating CD4⁺CD25^hiCTV⁻ Tregs (allospecific) were sorted by fluorescence-activated cell sorting (FACS) and polyclonally expanded with anti-CD3/CD28-coated beads in the presence of transforming growth factor beta (TGF-β), IL-2, and rapamycin. After 4 weeks, ^alloTregs were expanded up to 2,300 times the initial numbers with a purity of >95% (CD4⁺CD25^hiFOXP3⁺). The resulting allospecific Tregs showed high expressions of CTLA-4, LAG-3, and CD39, indicative of a highly suppressive phenotype. Accordingly, expanded ^alloTregs efficiently suppressed T-cell proliferation in an antigen-specific manner, even in the presence of inflammatory cytokines (IFN-γ, IL-4, IL-6, or TNF-α). Unexpectedly, the long-term expansion resulted in an increased methylation of the specific demethylated region of Foxp3. Interestingly, ^alloTregs from both normal individuals and CKD patients maintained their immunosuppressive phenotype and function after being expanded for two additional weeks under an inflammatory microenvironment. Finally, phenotypic and functional evaluation of cryopreserved ^alloTregs demonstrated the feasibility of long-term storage and supports the potential use of this cellular product for personalized Treg therapy in transplanted patients.

Cellular therapies in organ transplantation

Cellular therapy is a promising tool for improving the outcome of organ transplantation. Various cell types with different immunoregulatory and regenerative properties may find application for specific transplant rejection or injury-related indications. The current era is crucial for the development of cellular therapies. Preclinical models have demonstrated the feasibility of efficacious cell therapy in transplantation, early clinical trials have shown safety of several of these therapies, and the first steps towards efficacy studies in humans have been made. In this review, we address the current state of the art of cellular therapies in clinical transplantation and discuss monitoring tools and endpoints for these studies.

Treg Therapies Revisited: Tolerance Beyond Deletion

Induction of immune tolerance is the Holy Grail in transplantation medicine and autoimmunity. Currently, patients are required to use immunosuppressive drugs for the rest of their lives, resulting in unwanted side effects and complication from global suppression of the immune response. It is well established that regulatory T cells (Tregs) are critical for the maintenance of immune tolerance towards self-antigens by several mechanisms of immune regulation, in parallel with intrathymic deletion of self-reactive T cells during ontogeny. Therefore, approaches for increasing Treg numbers or function in vivo could provide an all-purpose solution for tolerance induction. Currently, most state-of-the-art therapeutics for treating autoimmune diseases or preventing allograft rejection work either by general immunosuppression or blocking inflammatory reactions and are non-specific. Hence, these approaches cannot provide satisfactory long-term results, let alone a cure. However, in animal models the therapeutic potential of Treg expansion for inducing effective tolerance has now been demonstrated in various models of autoimmunity and allogeneic transplantation. Here, we focus on therapies for increasing the size of the Treg pool by expanding endogenous Treg numbers in vivo or by adoptive transfer of Tregs. In particular, we discuss IL-2 based approaches (low dose IL-2, IL-2 complexes) for inducing Treg expansion in vivo as well as cell-based approaches (polyclonal, antigen specific, or cell engineered) for adoptive Treg therapy. We also mention new questions arising from the first clinical studies on Treg therapy in the fields of transplantation and autoimmunity.

The Therapeutic Potential of Regulatory T Cells: Challenges and Opportunities

Regulatory T cells (Tregs) are an immunosuppressive subgroup of CD4+ T cells which are identified by the expression of forkhead box protein P3 (Foxp3). The modulation capacity of these immune cells holds an important role in both transplantation and the development of autoimmune diseases. These cells are the main mediators of self-tolerance and are essential for avoiding excessive immune reactions. Tregs play a key role in the induction of peripheral tolerance that can prevent autoimmunity, by protecting self-reactive lymphocytes from the immune reaction. In contrast to autoimmune responses, tumor cells exploit Tregs in order to prevent immune cell recognition and anti-tumor immune response during the carcinogenesis process. Recently, numerous studies have focused on unraveling the biological functions and principles of Tregs and their primary suppressive mechanisms. Due to the promising and outstanding results, Tregs have been widely investigated as an alternative tool in preventing graft rejection and treating autoimmune diseases. On the other hand, targeting Tregs for the purpose of improving cancer immunotherapy is being intensively evaluated as a desirable and effective method. The purpose of this review is to point out the characteristic function and therapeutic potential of Tregs in regulatory immune mechanisms in transplantation tolerance, autoimmune diseases, cancer therapy, and also to discuss that how the manipulation of these mechanisms may increase the therapeutic options.