The complexities of T-cell dysfunction in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy characterized by profound alterations and defects in the T-cell compartment. This observation has gained renewed interest as T-cell treatment strategies, which are successfully applied in more aggressive B-cell malignancies, have yielded disappointing results in CLL. Despite ongoing efforts to understand and address the observed T-cell defects, the exact mechanisms and nature underlying this dysfunction remain largely unknown. In this review, we examine the supporting signals from T cells to CLL cells in the lymph node niche, summarize key findings on T-cell functional defects, delve into potential underlying causes, and explore novel strategies for reversing these deficiencies. Our goal is to identify strategies aimed at resolving CLL-induced T-cell dysfunction which, in the future, will enhance the efficacy of autologous T-cell-based therapies for CLL patients.

Ferritin heavy chain supports stability and function of the regulatory T cell lineage.

Regulatory T (TREG) cells develop via a program orchestrated by the transcription factor forkhead box protein P3 (FOXP3). Maintenance of the TREG cell lineage relies on sustained FOXP3 transcription via a mechanism involving demethylation of cytosine-phosphate-guanine (CpG)-rich elements at conserved non-coding sequences (CNS) in the FOXP3 locus. This cytosine demethylation is catalyzed by the ten-eleven translocation (TET) family of dioxygenases, and it involves a redox reaction that uses iron (Fe) as an essential cofactor. Here, we establish that human and mouse TREG cells express Fe-regulatory genes, including that encoding ferritin heavy chain (FTH), at relatively high levels compared to conventional T helper cells. We show that FTH expression in TREG cells is essential for immune homeostasis. Mechanistically, FTH supports TET-catalyzed demethylation of CpG-rich sequences CNS1 and 2 in the FOXP3 locus, thereby promoting FOXP3 transcription and TREG cell stability. This process, which is essential for TREG lineage stability and function, limits the severity of autoimmune neuroinflammation and infectious diseases, and favors tumor progression. These findings suggest that the regulation of intracellular iron by FTH is a stable property of TREG cells that supports immune homeostasis and limits the pathological outcomes of immune-mediated inflammation.

A Bispecific γδ T-cell Engager Targeting EGFR Activates a Potent Vγ9Vδ2 T cell-Mediated Immune Response against EGFR-Expressing Tumors.

Vγ9Vδ2 T cells are effector cells with proven antitumor efficacy against a broad range of cancers. This study aimed to assess the antitumor activity and safety of a bispecific antibody directing Vγ9Vδ2 T cells to EGFR-expressing tumors. An EGFR-Vδ2 bispecific T-cell engager (bsTCE) was generated, and its capacity to activate Vγ9Vδ2 T cells and trigger antitumor activity was tested in multiple in vitro, in vivo, and ex vivo models. Studies to explore safety were conducted using cross-reactive surrogate engagers in nonhuman primates (NHP). We found that Vγ9Vδ2 T cells from peripheral blood and tumor specimens of patients with EGFR+ cancers had a distinct immune checkpoint expression profile characterized by low levels of PD-1, LAG-3, and TIM-3. Vγ9Vδ2 T cells could be activated by EGFR-Vδ2 bsTCEs to mediate lysis of various EGFR+ patient-derived tumor samples, and substantial tumor growth inhibition and improved survival were observed in in vivo xenograft mouse models using peripheral blood mononuclear cells (PBMC) as effector cells. EGFR-Vδ2 bsTCEs exerted preferential activity toward EGFR+ tumor cells and induced downstream activation of CD4+ and CD8+ T cells and natural killer (NK) cells without concomitant activation of suppressive regulatory T cells observed with EGFR-CD3 bsTCEs. Administration of fully cross-reactive and half-life extended surrogate engagers to NHPs did not trigger signals in the safety parameters that were assessed. Considering the effector and immune-activating properties of Vγ9Vδ2 T cells, the preclinical efficacy data and acceptable safety profile reported here provide a solid basis for testing EGFR-Vδ2 bsTCEs in patients with EGFR+ malignancies.

Humanized MISTRG as a preclinical in vivo model to study human neutrophil-mediated immune processes.

Introduction: MISTRG mice have been genetically modified to allow development of a human myeloid compartment from engrafted human CD34+ haemopoietic stem cells, making them particularly suited to study the human innate immune system in vivo. Here, we characterized the human neutrophil population in these mice to establish a model that can be used to study the biology and contribution in immune processes of these cells in vivo. Methods and results: We could isolate human bone marrow neutrophils from humanized MISTRG mice and confirmed that all neutrophil maturation stages from promyelocytes (CD11b-CD16-) to end-stage segmented cells (CD11b+CD16+) were present. We documented that these cells possessed normal functional properties, including degranulation, reactive oxygen species production, adhesion, and antibody-dependent cellular cytotoxicity towards antibody-opsonized tumor cells ex vivo. The acquisition of functional capacities positively correlated with the maturation state of the cell. We found that human neutrophils were retained in the bone marrow of humanized MISTRG mice during steady state. However, the mature segmented CD11b+CD16+ human neutrophils were released from the bone marrow in response to two well-established neutrophil-mobilizing agents (i.e., G-CSF and/or CXCR4 antagonist Plerixafor). Moreover, the neutrophil population in the humanized MISTRG mice actively reacted to thioglycolate-induced peritonitis and could infiltrate implanted human tumors, as shown by flow cytometry and fluorescent microscopy. Discussion: These results show that functional human neutrophils are generated and can be studied in vivo using the humanized MISTRG mice, providing a model to study the various functions of neutrophils in inflammation and in tumors.

Proteomics reveals unique identities of human TGF-ß-induced and thymus-derived CD4+ regulatory T cells.

The CD4+ regulatory T (Treg) cell lineage, defined by FOXP3 expression, comprises thymus-derived (t)Treg cells and peripherally induced (p)Treg cells. As a model for Treg cells, studies employ TGF-ß-induced (i)Treg cells generated from CD4+ conventional T (Tconv) cells in vitro. Here, we describe how human iTreg cells relate to human blood-derived tTreg and Tconv cells according to proteomic analysis. Each of these cell populations had a unique protein expression pattern. iTreg cells had very limited overlap in protein expression with tTreg cells, regardless of cell activation status and instead shared signaling and metabolic proteins with Tconv cells. tTreg cells had a uniquely modest response to CD3/CD28-mediated stimulation. As a benchmark, we used a previously defined proteomic signature that discerns ex vivo naïve and effector Treg cells from Tconv cells and includes conserved Treg cell properties. iTreg cells largely lacked this Treg cell core signature and highly expressed e.g. STAT4 and NFATC2, which may contribute to inflammatory responses. We also used a proteomic signature that distinguishes ex vivo effector Treg cells from Tconv cells and naïve Treg cells. iTreg cells contained part of this effector Treg cell signature, suggesting acquisition of pTreg cell features. In conclusion, iTreg cells are distinct from tTreg cells and share limited features with ex vivo Treg cells at the proteomic level.

Amino acids at position 5 in the peptide/MHC binding region of a public virus-specific TCR are completely inter-changeable without loss of function.

Anti-viral T-cell responses are usually directed against a limited set of antigens, but often contain many T cells expressing different T-cell receptors (TCRs). Identical TCRs found within virus-specific T-cell populations in different individuals are known as public TCRs, but also TCRs highly-similar to these public TCRs, with only minor variations in amino acids on specific positions in the Complementary Determining Regions (CDRs), are frequently found. However, the degree of freedom at these positions was not clear. In this study, we used the HLA-A*02:01-restricted EBV-LMP2FLY -specific public TCR as model and modified the highly-variable position 5 of the CDR3ß sequence with all 20 amino acids. Our results demonstrate that amino acids at this particular position in the CDR3ß region of this TCR are completely inter-changeable, without loss of TCR function. We show that the inability to find certain variants in individuals is explained by their lower recombination probability rather than by steric hindrance.

Public T-Cell Receptors (TCRs) Revisited by Analysis of the Magnitude of Identical and Highly-Similar TCRs in Virus-Specific T-Cell Repertoires of Healthy Individuals.

Since multiple different T-cell receptor (TCR) sequences can bind to the same peptide-MHC combination and the number of TCR-sequences that can theoretically be generated even exceeds the number of T cells in a human body, the likelihood that many public identical (PUB-I) TCR-sequences frequently contribute to immune responses has been estimated to be low. Here, we quantitatively analyzed the TCR-repertoires of 190 purified virus-specific memory T-cell populations, directed against 21 epitopes of Cytomegalovirus, Epstein-Barr virus and Adenovirus isolated from 29 healthy individuals, and determined the magnitude, defined as prevalence within the population and frequencies within individuals, of PUB-I TCR and of TCR-sequences that are highly-similar (PUB-HS) to these PUB-I TCR-sequences. We found that almost one third of all TCR nucleotide-sequences represented PUB-I TCR amino-acid (AA) sequences and found an additional 12% of PUB-HS TCRs differing by maximally 3 AAs. We illustrate that these PUB-I and PUB-HS TCRs were structurally related and contained shared core-sequences in their TCR-sequences. We found a prevalence of PUB-I and PUB-HS TCRs of up to 50% among individuals and showed frequencies of virus-specific PUB-I and PUB-HS TCRs making up more than 10% of each virus-specific T-cell population. These findings were confirmed by using an independent TCR-database of virus-specific TCRs. We therefore conclude that the magnitude of the contribution of PUB-I and PUB-HS TCRs to these virus-specific T-cell responses is high. Because the T cells from these virus-specific memory TCR-repertoires were the result of successful control of the virus in these healthy individuals, these PUB-HS TCRs and PUB-I TCRs may be attractive candidates for immunotherapy in immunocompromised patients that lack virus-specific T cells to control viral reactivation.

Identification of Functional HLA-A*01:01-Restricted Epstein-Barr Latent Membrane Protein 2-Specific T-Cell Receptors.

BACKGROUND: Adoptive transfer of genetically engineered T cells expressing antigen-specific T-cell receptors (TCRs) is an appealing therapeutic approach for Epstein-Barr virus (EBV)-associated malignancies of latency type II/III that express EBV antigens (LMP1/2). Patients who are HLA-A*01:01 positive could benefit from such products, since no T cells recognizing any EBV-derived peptide in this common HLA allele have been found thus far. METHODS: HLA-A*01:01-restricted EBV-LMP2-specific T cells were isolated using peptide major histocompatibility complex (pMHC) tetramers. Functionality was assessed by production of interferon gamma (IFN-γ) and cytotoxicity when stimulated with EBV-LMP2-expressing cell lines. Functionality of primary T cells transduced with HLA-A*01:01-restricted EBV-LMP2-specific TCRs was optimized by knocking out the endogenous TCRs of primary T cells (∆TCR) using CRISPR-Cas9 technology. RESULTS: EBV-LMP2-specific T cells were successfully isolated and their TCRs were characterized. TCR gene transfer in primary T cells resulted in specific pMHC tetramer binding and reactivity against EBV-LMP2-expressing cell lines. The mean fluorescence intensity of pMHC-tetramer binding was increased 1.5-2 fold when the endogenous TCRs of CD8+ T cells was knocked out. CD8+/∆TCR T cells modified to express EBV-LMP2-specific TCRs showed IFN-γ secretion and cytotoxicity toward EBV-LMP2-expressing malignant cell lines. CONCLUSIONS: We isolated the first functional HLA-A*01:01-restricted EBV-LMP2-specific T-cell populations and TCRs, which can potentially be used in future TCR gene therapy to treat EBV-associated latency type II/III malignancies.

Single-Cell Transcriptomics Reveals Discrete Steps in Regulatory T Cell Development in the Human Thymus.

CD4+CD25+FOXP3+ regulatory T (Treg) cells control immunological tolerance. Treg cells are generated in the thymus (tTreg) or in the periphery. Their superior lineage fidelity makes tTregs the preferred cell type for adoptive cell therapy (ACT). How human tTreg cells develop is incompletely understood. By combining single-cell transcriptomics and flow cytometry, we in this study delineated three major Treg developmental stages in the human thymus. At the first stage, which we propose to name pre-Treg I, cells still express lineage-inappropriate genes and exhibit signs of TCR signaling, presumably reflecting recognition of self-antigen. The subsequent pre-Treg II stage is marked by the sharp appearance of transcription factor FOXO1 and features induction of KLF2 and CCR7, in apparent preparation for thymic exit. The pre-Treg II stage can further be refined based on the sequential acquisition of surface markers CD31 and GPA33. The expression of CD45RA, finally, completes the phenotype also found on mature recent thymic emigrant Treg cells. Remarkably, the thymus contains a substantial fraction of recirculating mature effector Treg cells, distinguishable by expression of inflammatory chemokine receptors and absence of CCR7. The developmental origin of these cells is unclear and warrants caution when using thymic tissue as a source of stable cells for ACT. We show that cells in the major developmental stages can be distinguished using the surface markers CD1a, CD27, CCR7, and CD39, allowing for their viable isolation. These insights help identify fully mature tTreg cells for ACT and can serve as a basis for further mechanistic studies into tTreg development.

Magnitude of Off-Target Allo-HLA Reactivity by Third-Party Donor-Derived Virus-Specific T Cells Is Dictated by HLA-Restriction.

T-cell products derived from third-party donors are clinically applied, but harbor the risk of off-target toxicity via induction of allo-HLA cross-reactivity directed against mismatched alleles. We used third-party donor-derived virus-specific T cells as model to investigate whether virus-specificity, HLA restriction and/or HLA background can predict the risk of allo-HLA cross-reactivity. Virus-specific CD8pos T cells were isolated from HLA-A*01:01/B*08:01 or HLA-A*02:01/B*07:02 positive donors. Allo-HLA cross-reactivity was tested using an EBV-LCL panel covering 116 allogeneic HLA molecules and confirmed using K562 cells retrovirally transduced with single HLA-class-I alleles of interest. HLA-B*08:01-restricted T cells showed the highest frequency and diversity of allo-HLA cross-reactivity, regardless of virus-specificity, which was skewed toward multiple recurrent allogeneic HLA-B molecules. Thymic selection for other HLA-B alleles significantly influenced the level of allo-HLA cross-reactivity mediated by HLA-B*08:01-restricted T cells. These results suggest that the degree and specificity of allo-HLA cross-reactivity by T cells follow rules. The risk of off-target toxicity after infusion of incompletely matched third-party donor-derived virus-specific T cells may be reduced by selection of T cells with a specific HLA restriction and background.

GPA33 is expressed on multiple human blood cell types and distinguishes CD4+ central memory T cells with and without effector function.

The Ig superfamily protein glycoprotein A33 (GPA33) has been implicated in immune dysregulation, but little is known about its expression in the immune compartment. Here, we comprehensively determined GPA33 expression patterns on human blood leukocyte subsets, using mass and flow cytometry. We found that GPA33 was expressed on fractions of B, dendritic, natural killer and innate lymphoid cells. Most prominent expression was found in the CD4+ T cell compartment. Naïve and CXCR5+ regulatory T cells were GPA33high , and naïve conventional CD4+ T cells expressed intermediate GPA33 levels. The expression pattern of GPA33 identified functional heterogeneity within the CD4+ central memory T cell (Tcm) population. GPA33+ CD4+ Tcm cells were fully undifferentiated, bona fide Tcm cells that lack immediate effector function, whereas GPA33- Tcm cells exhibited rapid effector functions and may represent an early stage of differentiation into effector/effector memory T cells before loss of CD62L. Expression of GPA33 in conventional CD4+ T cells suggests a role in localization and/or preservation of an undifferentiated state. These results form a basis to study the function of GPA33 and show it to be a useful marker to discriminate between different cellular subsets, especially in the CD4+ T cell lineage.

Separating the wheat from the chaff: Making sense of Treg heterogeneity for better adoptive cellular therapy.

Regulatory T (Treg) cells are essential for immunological tolerance and can be used to suppress unwanted or excessive immune responses through adoptive cellular therapy. It is increasingly clear that many subsets of Treg cells exist, which have different functions and reside in different locations. Treg cell therapies may benefit from tailoring the selected subset to the tissue that must be protected as well as to characteristics of the immune response that must be suppressed, but little attention is given to this topic in current therapies. Here, we will discuss how three major axes of heterogeneity can be discerned among the Treg cell population, which determine function and lineage fidelity. A first axis relates to the developmental route, as Treg cells can be generated from immature T cells in the thymus or from already mature Tconv cells in the immunological periphery. Heterogeneity furthermore stems from activation history (naïve or effector) and location (lymphoid or peripheral tissues). Each of these axes bestows specific properties on Treg cells, which are further refined by additional processes leading to yet further variation. A critical aspect impacting on Treg cell heterogeneity is TCR specificity, which determines when and where Treg cells are generated as well as where they exhibit their effector functions. We will discuss the implications of this heterogeneity and the role of the TCR for the design of next generation adoptive cellular therapy with Treg cells.

T cells expanded from renal cell carcinoma display tumor-specific CD137 expression but lack significant IFN-γ, TNF-α or IL-2 production.

Metastatic renal cell carcinoma (RCC) has a poor prognosis. Recent advances have shown beneficial responses to immune checkpoint inhibitors, such as anti-PD-1/PD-L1 antibodies. As only a subset of RCC patients respond, alternative strategies should be explored. Patients refractory to anti-PD-1 therapy may benefit from autologous tumor-infiltrating lymphocyte (TIL) therapy. Even though efficient TIL expansion was reported from RCC lesions, it is not well established how many RCC TIL products are tumor-reactive, how well they produce pro-inflammatory cytokines in response to autologous tumors, and whether their response correlates with the presence of specific immune cells in the tumor lesions. We here compared the immune infiltrate composition of RCC lesions with that of autologous kidney tissue of 18 RCC patients. Tcell infiltrates were increased in the tumor lesions, and CD8+ Tcell infiltrates were primarily of effector memory phenotype. Nine out of 16 (56%) tested TIL products we generated were tumor-reactive, as defined by CD137 upregulation after exposure to autologous tumor digest. Tumor reactivity was found in particular in TIL products originating from tumors with ahigh percentage of infiltrated Tcells compared to autologous kidney, and increased CD25 expression on CD8+ Tcells. Importantly, although TIL products had the capacity to produce the key effector cytokines IFN-γ, TNF-α or IL-2, they failed to produce significant amounts in response to autologous tumor digests. In conclusion, TIL products from RCC lesions contain tumor-reactive Tcells. Their restricted tumor-specific cytokine production requires further investigation of immunosuppressive factors in RCC and subsequent optimization of RCC-derived TIL culture conditions.

Stable human regulatory T cells switch to glycolysis following TNF receptor 2 costimulation.

Following activation, conventional T (Tconv) cells undergo an mTOR-driven glycolytic switch. Regulatory T (Treg) cells reportedly repress the mTOR pathway and avoid glycolysis. However, here we demonstrate that human thymus-derived Treg (tTreg) cells can become glycolytic in response to tumour necrosis factor receptor 2 (TNFR2) costimulation. This costimulus increases proliferation and induces a glycolytic switch in CD3-activated tTreg cells, but not in Tconv cells. Glycolysis in CD3-TNFR2-activated tTreg cells is driven by PI3-kinase-mTOR signalling and supports tTreg cell identity and suppressive function. In contrast to glycolytic Tconv cells, glycolytic tTreg cells do not show net lactate secretion and shuttle glucose-derived carbon into the tricarboxylic acid cycle. Ex vivo characterization of blood-derived TNFR2hiCD4+CD25hiCD127lo effector T cells, which were FOXP3+IKZF2+, revealed an increase in glucose consumption and intracellular lactate levels, thus identifying them as glycolytic tTreg cells. Our study links TNFR2 costimulation in human tTreg cells to metabolic remodelling, providing an additional avenue for drug targeting.

GPA33: A Marker to Identify Stable Human Regulatory T Cells.

FOXP3-expressing regulatory T (Treg) cells safeguard immunological tolerance. Treg cells can be generated during thymic development (called thymic Treg [tTreg] cells) or derived from mature conventional CD4+ T cells that underwent TGF-ß-mediated conversion in the periphery (called peripheral Treg [pTreg] cells). Murine studies have shown that tTreg cells exhibit strong lineage fidelity, whereas pTreg cells can revert into conventional CD4+ T cells. Their stronger lineage commitment makes tTreg cells the safest cells to use in adoptive cell therapy, increasingly used to treat autoimmune and inflammatory disorders. Markers to distinguish human tTreg cells from pTreg cells have, however, not been found. Based on combined proteomic and transcriptomic approaches, we report that the Ig superfamily protein GPA33 is expressed on a subset of human Treg cells. GPA33 is acquired late during tTreg cell development but is not expressed on TGF-ß-induced Treg cells. GPA33 identifies Treg cells in human blood that lack the ability to produce effector cytokines (IL-2, IFN-γ, IL-17), regardless of differentiation stage. GPA33high Treg cells universally express the transcription factor Helios that preferentially marks tTreg cells and can robustly and stably be expanded in vitro even without rapamycin. Expanded GPA33high Treg cells are suppressive, unable to produce proinflammatory cytokines, and exhibit the epigenetic modifications of the FOXP3 gene enhancer CNS2, necessary for indelible expression of this critical transcription factor. Our findings thus suggest that GPA33 identifies human tTreg cells and provide a strategy to isolate such cells for safer and more efficacious adoptive cell therapy.

Polyfunctional tumor-reactive T cells are effectively expanded from non-small cell lung cancers, and correlate with an immune-engaged T cell profile.

Non-small cell lung cancer (NSCLC) is the second most prevalent type of cancer. With the current treatment regimens, the mortality rate remains high. Therefore, better therapeutic approaches are necessary. NSCLCs generally possess many genetic mutations and are well infiltrated by T cells (TIL), making TIL therapy an attractive option. Here we show that T cells from treatment naive, stage I-IVa NSCLC tumors can effectively be isolated and expanded, with similar efficiency as from normal lung tissue. Importantly, 76% (13/17) of tested TIL products isolated from NSCLC lesions exhibited clear reactivity against primary tumor digests, with 0.5%-30% of T cells producing the inflammatory cytokine Interferon (IFN)-γ. Both CD4+ and CD8+ T cells displayed tumor reactivity. The cytokine production correlated well with CD137 and CD40L expression. Furthermore, almost half (7/17) of the TIL products contained polyfunctional T cells that produced Tumor Necrosis Factor (TNF)-α and/or IL-2 in addition to IFN-γ, a hallmark of effective immune responses. Tumor-reactivity in the TIL products correlated with high percentages of CD103+CD69+CD8+ T cell infiltrates in the tumor lesions, with PD-1hiCD4+ T cells, and with FoxP3+CD25+CD4+ regulatory T cell infiltrates, suggesting that the composition of T cell infiltrates may predict the level of tumor reactivity. In conclusion, the effective generation of tumor-reactive and polyfunctional TIL products implies that TIL therapy will be a successful treatment regimen for NSCLC patients.

Blimp-1 Rather Than Hobit Drives the Formation of Tissue-Resident Memory CD8+ T Cells in the Lungs.

Tissue-resident memory CD8+ T (TRM) cells that develop in the epithelia at portals of pathogen entry are important for improved protection against re-infection. CD8+ TRM cells within the skin and the small intestine are long-lived and maintained independently of circulating memory CD8+ T cells. In contrast to CD8+ TRM cells at these sites, CD8+ TRM cells that arise after influenza virus infection within the lungs display high turnover and require constant recruitment from the circulating memory pool for long-term persistence. The distinct characteristics of CD8+ TRM cell maintenance within the lungs may suggest a unique program of transcriptional regulation of influenza-specific CD8+ TRM cells. We have previously demonstrated that the transcription factors Hobit and Blimp-1 are essential for the formation of CD8+ TRM cells across several tissues, including skin, liver, kidneys, and the small intestine. Here, we addressed the roles of Hobit and Blimp-1 in CD8+ TRM cell differentiation in the lungs after influenza infection using mice deficient for these transcription factors. Hobit was not required for the formation of influenza-specific CD8+ TRM cells in the lungs. In contrast, Blimp-1 was essential for the differentiation of lung CD8+ TRM cells and inhibited the differentiation of central memory CD8+ T (TCM) cells. We conclude that Blimp-1 rather than Hobit mediates the formation of CD8+ TRM cells in the lungs, potentially through control of the lineage choice between TCM and TRM cells during the differentiation of influenza-specific CD8+ T cells.

Determining the extent of maternal-foetal chimerism in cord blood.

During pregnancy, maternal T cells can enter the foetus, leading to maternal-foetal chimerism. This phenomenon may affect how leukaemia patients respond to transplantation therapy using stem cells from cord blood (CB). It has been proposed that maternal T cells, primed to inherited paternal HLAs, are present in CB transplants and help to suppress leukaemic relapse. Several studies have reported evidence for the presence of maternal T cells in most CBs at sufficiently high numbers to lend credence to this idea. We here aimed to functionally characterise maternal T cells from CB. To our surprise, we could not isolate viable maternal cells from CB even after using state-of-the-art enrichment techniques that allow detection of viable cells in heterologous populations at frequencies that were several orders of magnitude lower than reported frequencies of maternal T cells in CB. In support of these results, we could only detect maternal DNA in a minority of samples and at insufficient amounts for reliable quantification through a sensitive PCR-based assay to measure In/Del polymorphisms. We conclude that maternal microchimerism is far less prominent than reported, at least in our cohort of CBs, and discuss possible explanations and implications.

c-Maf-dependent Treg cell control of intestinal TH17 cells and IgA establishes host-microbiota homeostasis.

Foxp3+ regulatory T cells (Treg cells) are crucial for the maintenance of immune homeostasis both in lymphoid tissues and in non-lymphoid tissues. Here we demonstrate that the ability of intestinal Treg cells to constrain microbiota-dependent interleukin (IL)-17-producing helper T cell (TH17 cell) and immunoglobulin A responses critically required expression of the transcription factor c-Maf. The terminal differentiation and function of several intestinal Treg cell populations, including RORγt+ Treg cells and follicular regulatory T cells, were c-Maf dependent. c-Maf controlled Treg cell-derived IL-10 production and prevented excessive signaling via the kinases PI(3)K (phosphatidylinositol-3-OH kinase) and Akt and the metabolic checkpoint kinase complex mTORC1 (mammalian target of rapamycin) and expression of inflammatory cytokines in intestinal Treg cells. c-Maf deficiency in Treg cells led to profound dysbiosis of the intestinal microbiota, which when transferred to germ-free mice was sufficient to induce exacerbated intestinal TH17 responses, even in a c-Maf-competent environment. Thus, c-Maf acts to preserve the identity and function of intestinal Treg cells, which is essential for the establishment of host-microbe symbiosis.