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.