Induced Regulatory T Cells as Immunotherapy in Allotransplantation and Autoimmunity: Challenges and Opportunities.

Regulatory T cells (Tregs) play a crucial role in the homeostasis of the immune response. Tregs are mainly generated in the thymus and are characterized by the expression of Foxp3, which is considered the Treg master transcription factor. In addition, Tregs can be induced from naïve CD4+ T cells to express Foxp3 under specific conditions both in vivo (pTregs) and in vitro (iTregs). Both subsets tTregs and pTregs are necessary for the establishment of immune tolerance to self and non-self antigens. Although it has been postulated that iTregs may be less stable compared to tTregs, mainly due to epigenetic differences, accumulating evidence in animal models shows that iTregs are stable in vivo and could be used for the treatment of inflammatory disorders including autoimmune diseases and allogeneic transplant rejection. In this review, we describe the biological characteristics of induced T regs, the key factors involved in iTreg transcriptional, metabolic and epigenetic regulation and discuss recent advances for de novo generation of stable Tregs and their use as immunotherapeutic tools in different experimental models. Moreover, we discuss the challenges and considerations for the application of iTregs in clinical trials and describe the new approaches proposed to achieve in vivo stability, including functional or metabolic reprogramming and epigenetic editing.

Highly purified and functionally stable in vitro expanded allospecific Tr1 cells expressing immunosuppressive graft-homing receptors as new candidates for cell therapy in solid organ transplantation.

The development of new strategies based on the use of Tr1 cells has taken relevance to induce long-term tolerance, especially in the context of allogeneic stem cell transplantation. Although Tr1 cells are currently identified by the co-expression of CD49b and LAG-3 and high production of interleukin 10 (IL-10), recent studies have shown the need for a more exhaustive characterization, including co-inhibitory and chemokines receptors expression, to ensure bona fide Tr1 cells to be used as cell therapy in solid organ transplantation. Moreover, the proinflammatory environment induced by the allograft could affect the suppressive function of Treg cells, therefore stability of Tr1 cells needs to be further investigated. Here, we establish a new protocol that allows long-term in vitro expansion of highly purified expanded allospecific Tr1 (Exp-allo Tr1). Our expanded Tr1 cell population becomes highly enriched in IL-10 producers (> 90%) and maintains high expression of CD49b and LAG-3, as well as the co-inhibitory receptors PD-1, CTLA-4, TIM-3, TIGIT and CD39. Most importantly, high dimensional analysis of Exp-allo Tr1 demonstrated a specific expression profile that distinguishes them from activated conventional T cells (T conv), showing overexpression of IL-10, CD39, CTLA-4 and LAG-3. On the other hand, Exp-allo Tr1 expressed a chemokine receptor profile relevant for allograft homing and tolerance induction including CCR2, CCR4, CCR5 and CXCR3, but lower levels of CCR7. Interestingly, Exp-allo Tr1 efficiently suppressed allospecific but not third-party T cell responses even after being expanded in the presence of proinflammatory cytokines for two extra weeks, supporting their functional stability. In summary, we demonstrate for the first time that highly purified allospecific Tr1 (Allo Tr1) cells can be efficiently expanded maintaining a stable phenotype and suppressive function with homing potential to the allograft, so they may be considered as promising therapeutic tools for solid organ transplantation.

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+CD25hiCTV- 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-ß), IL-2, and rapamycin. After 4 weeks, alloTregs were expanded up to 2,300 times the initial numbers with a purity of >95% (CD4+CD25hiFOXP3+). 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.

Chimeric Antigen Receptor (CAR) T Cell Therapy for Cancer. Challenges and Opportunities: An Overview.

The use of immunotherapy as an alternative treatment for cancer patients has become of great interest in the scientific community as it is required to overcome many of the currently unsolved problems such as tumor escape, immunosuppression and unwanted unspecific toxicity. The use of chimeric antigen receptor T cells has been a very successful strategy in some hematologic malignancies. However, the application of CAR T cells has been limited to solid tumors, and this has aimed the development of new generation of CARs with enhanced effectivity and specificity. Here, we review the state of the art of CAR T cell therapy with special emphasis on the current challenges and opportunities.

Large-Scale Generation of Human Allospecific Induced Tregs With Functional Stability for Use in Immunotherapy in Transplantation.

Regulatory T cells play an important role in the control of autoimmune diseases and maintenance of tolerance. In the context of transplantation, regulatory T cells (Tregs) have been proposed as new therapeutic tools that may induce allospecific tolerance toward the graft, avoiding the side effects induced by generalized immunosuppressors. Although most clinical trials are based on the use of thymic Tregs in adoptive therapy, some reports suggest the potential use of in vitro induced Tregs (iTregs), based on their functional stability under inflammatory conditions, indicating an advantage in a setting of allograft rejection. The aim of this work was to generate and expand large numbers of allospecific Tregs that maintain stable suppressive function in the presence of pro-inflammatory cytokines. Dendritic cells were derived from monocytes isolated from healthy donors and were co-cultured with CTV-labeled naïve T cells from unrelated individuals, in the presence of TGF-ß1, IL-2, and retinoic acid. After 7 days of co-culture, proliferating CD4+CD25++CTV- cells (allospecific iTregs) were sorted and polyclonally expanded for 6 weeks in the presence of TGF-ß1, IL-2, and rapamycin. After 6 weeks of polyclonal activation, iTregs were expanded 230,000 times, giving rise to 4,600 million allospecific iTregs. Allospecific iTregs were able to specifically suppress the proliferation of autologous CD4+ and CD8+ T cells in response to the allo-MoDCs used for iTreg generation, but not to third-party allo-MoDCs. Importantly, 88.5% of the expanded cells were CD4+CD25+FOXP3+, expressed high levels of CCR4 and CXCR3, and maintained their phenotype and suppressive function in the presence of TNF-α and IL-6. Finally, analysis of the methylation status of the FOXP3 TSDR locus demonstrated a 40% demethylation in the purified allospecific iTreg, prior to the polyclonal expansion. Interestingly, the phenotype and suppressive activity of expanded allospecific iTregs were maintained after 6 weeks of expansion, despite an increase in the methylation status of the FOXP3 TSDR. In conclusion, this is the first report that demonstrates a large-scale generation of allospecific iTregs that preserve a stable phenotype and suppressor function in the presence of pro-inflammatory cytokines and pave the way for adoptive cell therapy with iTregs in transplanted patients.

Methylation of FOXP3 TSDR Underlies the Impaired Suppressive Function of Tregs from Long-term Belatacept-Treated Kidney Transplant Patients.

Regulatory T cells (Tregs) are considered key players in the prevention of allograft rejection in transplanted patients. Belatacept (BLT) is an effective alternative to calcineurin inhibitors that appears to preserve graft survival and function; however, the impact of this drug in the homeostasis of Tregs in transplanted patients remains controversial. Here, we analyzed the phenotype, function, and the epigenetic status of the Treg-specific demethylated region (TSDR) in FOXP3 of circulating Tregs from long-term kidney transplant patients under BLT or Cyclosporine A treatment. We found a significant reduction in the proportion of CD4+CD25hiCD127lo/-FOXP3+ T cells in all patients compared to healthy individual (controls). Interestingly, only BLT-treated patients displayed an enrichment of the CD45RA+ "naïve" Tregs, while the expression of Helios, a marker used to identify stable FOXP3+ thymic Tregs remained unaffected. Functional analysis demonstrated that Tregs from transplanted patients displayed a significant reduction in their suppressive capacity compared to Tregs from controls, which is associated with decreased levels of FOXP3 and CD25. Analysis of the methylation status of the FOXP3 gene showed that BLT treatment results in methylation of CpG islands within the TSDR, which could be associated with the impaired Treg suppression function. Our data indicate that analysis of circulating Tregs cannot be used as a marker for assessing tolerance toward the allograft in long-term kidney transplant patients. Trial registration number IM103008.