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CD4+ CD25high CD127low/- FOXP3+ T regulatory cells are responsible for maintaining immune tolerance and controlling excessive immune responses. Treg cell use in pre-clinical animal models showed the huge therapeutic potential of these cells in immune-mediated diseases and laid the foundations for their applications in therapy in humans. Currently, there are several clinical trials utilizing the adoptive transfer of Treg cells to reduce the morbidity in autoimmune disorders, allogeneic HSC transplantation, and solid organ transplantation. However, a large part of them utilizes total Treg cells without distinction of their biological variability. Many studies on the heterogeneity of Treg cell population revealed distinct subsets with different functions in the control of the immune response and induction of peripheral tolerance. Some of these subsets also showed a role in controlling the general homeostasis of non-lymphoid tissues. All these Treg cell subsets and their peculiar properties can be therefore exploited to develop novel therapeutic approaches. This review describes these functionally distinct subsets, their phenotype, homing properties and functions in lymphoid and non-lymphoid tissues. In addition, we also discuss the limitations in using Treg cells as a cellular therapy and the strategies to enhance their efficacy.

Regulatory T cells (Tregs) are a lymphocyte subset with intrinsic immunosuppressive properties that can be expanded in large numbers ex vivo and have been shown to prevent allograft rejection and promote tolerance in animal models. To investigate the safety, applicability, and biological activity of autologous Treg adoptive transfer in humans, we conducted an open‐label, dose‐escalation, Phase I clinical trial in liver transplantation. Patients were enrolled while awaiting liver transplantation or 6‐12 months posttransplant. Circulating Tregs were isolated from blood or leukapheresis, expanded under good manufacturing practices (GMP) conditions, and administered intravenously at either 0.5‐1 million Tregs/kg or 3‐4.5 million Tregs/kg. The primary endpoint was the rate of dose‐ limiting toxicities occurring within 4 weeks of infusion. The applicability of the clinical protocol was poor unless patient recruitment was deferred until 6‐12 months posttransplant. Thus, only 3 of the 17 patients who consented while awaiting liver transplantation were dosed. In contrast, all six patients who consented 6‐12 months posttransplant received the cell infusion. Treg transfer was safe, transiently increased the pool of circulating Tregs and reduced anti‐donor T cell responses. Our study opens the door to employing Treg immunotherapy to facilitate the reduction or complete discontinuation of immunosuppression following liver transplantation., CD4+Foxp3+ regulatory T cells isolated from either patients awaiting liver transplantation or recently transplanted recipients can be expanded in large numbers ex vivo and safely infused into recipients on immunosuppression.

Complex mechanisms underlying the maintenance of fully functional, proliferative, HIV-1-specific T-cell responses involve processes from early T-cell development through to the final stages of T-cell differentiation and antigen recognition. Virus-specific proliferative CD4 and CD8 T-cell responses, important for the control of infection, are observed in some HIV-1(+) patients during early stages of disease, and are maintained in long-term non-progressing subjects. In the vast majority of HIV-1(+) patients, full immune functionality is lost when proliferative HIV-1-specific T-cell responses undergo a variable progressive decline throughout the course of chronic infection. This appears irreparable despite administration of potent combination antiretroviral therapy, which to date is non-curative, necessitating life-long administration and the development of effective, novel, therapeutic interventions. While a sterilizing cure, involving clearance of virus from the host, remains a primary aim, a "functional cure" may be a more feasible goal with considerable impact on worldwide HIV-1 infection. Such an approach would enable long-term co-existence of host and virus in the absence of toxic and costly drugs. Effective immune homeostasis coupled with a balanced response appropriately targeting conserved viral antigens, in a manner that avoids hyperactivation and exhaustion, may prove to be the strongest correlate of durable viral control. This review describes novel concepts underlying full immune functionality in the context of HIV-1 infection, which may be utilized in future strategies designed to improve upon existing therapy. The aim will be to induce long-term non-progressor or elite controller status in every infected host, through immune-mediated control of viremia and reduction of viral reservoirs, leading to lower HIV-1 transmission rates.

Exploring the intricacies of CD8(+) T-cell epitope recognition using emerging technologies to combine assessment of affinity, phenotype and resulting polyfunctional efficacy advances our understanding of HIV-1 immunopathogenesis and disease progression. Complexities within T-cell antigen recognition, such as epitope:MHC binding, stability and affinity, appear to influence the distinction between protective and ineffective anti-HIV-1 immune responses, which are thought to govern rate of disease progression. This study utilises the novel ProImmune REVEAL and ProVE(R) technology of rapid peptide synthesis, binding and affinity assays, and pentamer synthesis in conjunction with flow cytometry and simultaneous assessment of multiple CD8(+) T-cell effector functions in response to HLA-B3501-restricted HIV-1 Gag peptides, to discover new T-cell epitopes. The predicted HLA-B3501-restricted peptides, HPVHAGPIA and YPLTSLRSL, and relevant pentamers were used in parallel to validate T-cell epitopes on clinical HIV-1(+) samples, confirming correlation between the expected superior immunogenicity of newly discovered epitopes and the ex vivo T-cell response. Such a platform should be employed in prophylactic and therapeutic vaccine settings.