Expansion of T memory stem cells with superior anti-tumor immunity by Urolithin A-induced mitophagy.

T memory stem cells (TSCM) display increased self-renewal and prolonged survival capabilities, thus preventing T cell exhaustion and promoting effective anti-tumor T cell responses. TSCM cells can be expanded by Urolithin A (UA), which is produced by the commensal gut microbiome from foods rich in ellagitannins and is known to improve mitochondrial health. Oral UA administration to tumor-bearing mice conferred strong anti-tumor CD8+ T cell immunity, whereas ex vivo UA pre-treated T cells displayed improved anti-tumor function upon adoptive cell transfer. UA-induced TSCM formation depended on Pink1-mediated mitophagy triggering cytosolic release of the mitochondrial phosphatase Pgam5. Cytosolic Pgam5 dephosphorylated ß-catenin, which drove Wnt signaling and compensatory mitochondrial biogenesis. Collectively, we unravel a critical signaling pathway linking mitophagy to TSCM formation and suggest that the well-tolerated metabolic compound UA represents an attractive option to improve immune therapy.

Memory CD8+ T cell responses to cancer.

Long-lived memory CD8+ T cells play important roles in tumor immunity. Studies over the past two decades have identified four subsets of memory CD8+ T cells - central, effector, stem-like, and tissue resident memory - that either circulate through blood, lymphoid and peripheral organs, or reside in tissues where cancers develop. In this article, we will review studies from both pre-clinical mouse models and human patients to summarize the phenotype, distribution and unique features of each memory subset, and highlight specific roles of each subset in anti-tumor immunity. Moreover, we will discuss how stem-cell like and resident memory CD8+ T cell subsets relate to exhausted tumor-infiltrating lymphocytes (TIL) populations. These studies reveal how memory CD8+ T cell subsets together orchestrate durable immunity to cancer.

Alteration of CCR6+CD95+CD4+ naïve T cells in HIV-1 infected patients: Implication for clinical practice.

The profound deficiency of Th17 cells contributes to HIV disease progression. The mechanisms of their perturbation remain unclear. Recently, CCR6+CD95+CD4+ naïve T cells (CCR6+CD95+CD4+ TNA), identified as pre-committed Th17 precursors, were recognized as a subpopulation of CD4+ T cells with stem cell properties. Following phenotypical identification, we evaluated their level in patients during chronic HIV infection and following antiretroviral therapy (ART) using flow cytometry. The levels of CCR6+CD95+CD4+ TNA were decreased during chronic HIV infection and correlated with CD4+ T cell counts. Immunological responders harbored higher frequency of CCR6+CD95+CD4+ TNA, which was associated with CD4/CD8 T cell ratio. Immunological non-responders with lower frequency of CCR6+CD95+CD4+ TNA failed to exhibit a correlation between CCR6+CD95+CD4+ TNA and CCR6+CD95+CD4+ TCM, and displayed elevated ratio of CCR6+CD95+CD4+ TCM/TNA. The number of CCR6+CD95+CD4+ TNA was increased following early ART. These findings shed light on the importance of targeting pre-committed Th17 precursors that enhance immune reconstitution.

CD4(+) CD44(v.low) cells are unique peripheral precursors that are distinct from recent thymic emigrants and stem cell-like memory cells.

CD4(+) CD44(v.low) cells are peripheral precursor T cells that inhibit lymphopenia by generating a large CD4(+) T cell pool containing balanced numbers of naïve, memory, and regulatory Foxp3(+) cells with a diverse TCR repertoire. Recent thymic emigrants (RTE) and stem cell-like memory T cells (T(SCM)) can also replenish a T cell pool. In this study we formally test whether CD44(v.low) cells are the same population as RTE and T(SCM). Our data show that, in contrast to RTE, CD44(v.low) cells express high levels of CD45RB and low levels of CD24. Moreover, CD44(v.low) cells isolated from mice devoid of RTE retain their capacity to repopulate lymphopenic mice with naïve and memory cells and Foxp3(+) Tregs. In addition, CD44(v.low) cells do not express IL-2Rß, Sca-1, and CXCR3, the phenotypic hallmarks of T(SCM). Overall, these data demonstrate that CD44(v.low) cells are neither RTE nor T(SCM).

Combination of Epstein-Barr virus nuclear antigen 1, 3 and lytic antigen BZLF1 peptide pools allows fast and efficient stimulation of Epstein-Barr virus-specific T cells for adoptive immunotherapy.

BACKGROUND: Epstein-Barr virus (EBV) infection is a major cause of morbidity following hematopoietic stem cell transplantation. EBV-infected B cells may not respond to rituximab treatment and may lead to a life-threatening post-transplantation lymphoproliferative disorder. Adoptive cellular immunotherapy using EBV-lymphoblastoid cell lines (LCL) as stimulating antigen has proved effective in restoring specific immunity. However, EBV presents several immunodominant antigens, and developing a swift and effective clinical-grade immunotherapy relies on the definition of a Good Manufacturing Practices (GMP) universal stimulating antigen. METHODS: Peripheral blood mononuclear cells (PBMCs) from six donors with a cellular immune response against EBV were immunoselected after stimulation with a new EBV antigen associated with an EBNA3 peptide pool. RESULTS: After immunoselection, a mean of 0.53 ± 0.25 × 106 cells was recovered consisting of a mean of 24.77 ± 18.01% CD4⁺-secreting interferon (IFN)-γ and 51.42 ± 26.92% CD8⁺-secreting IFN-γ. The T memory stem cell sub-population was identified. EBV-specific T cells were expanded in vitro, and their ability to secrete IFN-γ and to proliferate after re-stimulation with EBV antigen was confirmed. A specific lysis was observed against autologous target cells pulsed with EBV peptide pools (57.6 ± 11.5%) and against autologous EBV-LCL (18.3 ± 7.3%). A mean decrease of 94.7 ± 3.3% in alloreactivity against third-party donor mononuclear cells with EBV-specific T cells was observed compared with PBMCs before selection. CONCLUSIONS: Our results show that a combination of peptide pools including EBNA3 is needed to generate EBV-specific T cells with good specific cytotoxicity and devoid of alloreactivity, but as yet GMP grade is not fully achieved.

Generation of CAR-TSCM: CAR-T with super clutch.

CAR-T therapy has demonstrated effectiveness in hematological malignancies and is now striding into solid tumor areas. One of the main roadblocks of CAR-T therapy is T cell exhaustion normally aroused by T cell terminal differentiation due to persistent contact with antigen in vivo or in vitro manufacturing process. TSCM positions as the first, and pivotal step of naïve T cell differentiation to downstream memory and effector stages. Researchers highly seek to restrain CAR-T cells at the TSCM stage during manufacture as TSCM percentage in CAR-T products is strongly associated with better treatment response. We reviewed the recent strategies regarding CAR-TSCM generation from aspects of starting source, manufacturing process, CAR assembly, transcription factor and metabolism regulation, etc.