Cell Receptor Diversity Research Articles

T Cell Repertoire Diversity Is Decreased in Type 1 Diabetes Patients

Type 1 diabetes mellitus (T1D) is an immune-mediated disease. The autoreactive T cells in T1D patients attack and destroy their own pancreatic cells. In order to systematically investigate the potential autoreactive T cell receptors (TCRs), we used a high-throughput immune repertoire sequencing technique to profile the spectrum of TCRs in individual T1D patients and controls. We sequenced the T cell repertoire of nine T1D patients, four type 2 diabetes (T2D) patients, and six nondiabetic controls. The diversity of the T cell repertoire in T1D patients was significantly decreased in comparison with T2D patients (P=7.0E−08 for CD4+ T cells, P=1.4E−04 for CD8+ T cells) and nondiabetic controls (P=2.7E−09 for CD4+ T cells, P=7.6E−06 for CD8+ T cells). Moreover, T1D patients had significantly more highly-expanded T cell clones than T2D patients (P=5.2E−06 for CD4+ T cells, P=1.9E−07 for CD8+ T cells) and nondiabetic controls (P=1.7E−07 for CD4+ T cells, P=3.3E−03 for CD8+ T cells). Furthermore, we identified a group of highly-expanded T cell receptor clones that are shared by more than two T1D patients. Although further validation in larger cohorts is needed, our data suggest that T cell receptor diversity measurements may become a valuable tool in investigating diabetes, such as using the diversity as an index to distinguish different types of diabetes.

SY 17-3 ROLE OF CMV INDUCED T CELL SENESCENCE IN THE PATHOPHYSIOLOGY OF CARDIOVASCULAR DISEASE

Abstract Immunosenescence, defined as the age-associated dysregulation and dysfunction of the immune system, is characterized by impaired protective immunity and decreased efficacy of vaccines. Immunosenescence affects both the innate and adaptive immune systems; however, the most notable changes are in T cell immunity and include thymic involution, the collapse of T cell receptor (TCR) diversity, an imbalance in T cell populations, and the clonal expansion of senescent T cells. An increasing number of immunological, clinical and epidemiological studies suggest that persistent Cytomegalovirus (CMV) infection is associated with accelerated aging of the immune system and T cell immunosenescence especially. T cell responses to CMV are restricted to a limited number of immunodominant epitopes, as compared to responses to other chronic or persistent viruses. This response results in progressive, prolonged expansion of CMV-specific T cells, termed 'memory inflation'. The expanded CMV-specific T cell population is extraordinarily large and is more prominent in the elderly. CMV-specific senescent T cells have the ability to produce large quantities of proinflammatory cytokines and cytotoxic mediators; thus, they have been implicated in the pathogenesis of many chronic inflammatory diseases. Recently, an increasing body of evidence has suggested that senescent T cells also have pathogenic potential in cardiovascular diseases, such as hypertension, heart failure, and myocardial infarction, underscoring the detrimental roles of these cells in various chronic inflammatory responses. In this presentation, we will discuss the general features of age-related alterations in T cell immunity and the possible roles of CMV induced T cell senescence in the pathophysiology of cardiovascular disease.

T cell repertoire following kidney transplantation revealed by high-throughput sequencing

Delayed T cell recovery and restricted T cell receptor (TCR) diversity after kidney transplantation are associated with increased risks of infection and malignancy. Technical challenges limit the faithful measurement of TCR diversity after kidney transplantation. In this study, we used a combination of multiplex-PCR, Illumina sequencing and IMGT/HighV-QUEST to directly assess millions of TCRs per individual before and at two time points after kidney transplantation (1days and 7days after transplantation) in a cohort of 10 patients compared to a normal control (NC) group (n=10). We identified the most commonly observed CDR3 length, VD indel length, and DJ indel length in transplantation group and normal group. In addition, we found that the TCR repertoire diversity of transplantation groups was relatively lower compared to NC group. T cell depletion in Post-1 group can be observed, which resulted in the altered distribution characteristics of clonotype abundance. A modest proportion of high abundance clones were shared among the pre-1 group, post-1 group and post-7 group, and it did not exist in the NC group, which exhibited a signature of antigen selection. Moreover, our results also demonstrated that various TRBV expression increased and some public sequences at different time points after kidney transplantation, which may provide biomarkers to monitor the immune status of transplant patients.

T cell receptor diversity in the human thymus.

A diverse T cell receptor (TCR) repertoire is essential for adaptive immune responses and is generated by somatic recombination of TCRα and TCRβ gene segments in the thymus. Previous estimates of the total TCR diversity have studied the circulating mature repertoire, identifying 1 to 3×10(6) unique TCRβ and 0.5×10(6) TCRα sequences. Here we provide the first estimate of the total TCR diversity generated in the human thymus, an organ which in principle can be sampled in its entirety. High-throughput sequencing of samples from four pediatric donors detected up to 10.3×10(6) unique TCRβ sequences and 3.7×10(6) TCRα sequences, the highest directly observed diversity so far for either chain. To obtain an estimate of the total diversity we then used three different estimators, preseq and DivE, which measure the saturation of rarefaction curves, and Chao2, which measures the size of the overlap between samples. Our results provide an estimate of a thymic repertoire consisting of 40 to 70×10(6) unique TCRβ sequences and 60 to 100×10(6) TCRα sequences. The thymic repertoire is thus extremely diverse. Moreover, extrapolation of the data and comparison with earlier estimates of peripheral diversity also suggest that the thymic repertoire is transient, with different clones produced at different times.

Recent Thymic Emigrants and Chronic Salmonellosis: How New T Cells Combat an Old Infection

Abstract Typhoid fever, caused by infection with Salmonella bacteria affects approximately 21 million people annually, killing nearly 200,000 and yet the immunological response to this infection is poorly understood. Recent thymic emigrants (RTEs) are the youngest subset of peripheral T cells, which are known to differ in how they functionally contribute to the naïve T cell pool. This distinctive cell population is known to contribute to the maintenance of T cell receptor diversity in the peripheral T cell pool, but their involvement in combating chronic bacterial infections, such as typhoid fever, has not been explored. In the present study, we hypothesized that RTEs are essential contributors to the CD4 T cell response during persistent Salmonella Typhimurium (ST) infection, which predominantly relies on helper T cell immunity to control bacteria. Here, we show that thymectomy of adult mice prior to oral infection with ST leads to increased mortality in addition to significantly increased bacterial burdens in the spleen, mesenteric lymph nodes and liver 30 days post-infection compared to sham surgical controls, suggesting Salmonella-specific RTEs may contribute to bacterial clearance. Surprisingly, thymectomized animals also demonstrated expanded numbers of peripheral Salmonella-specific T cells, compared to control animals, implying that these existing cells are somehow incapable of controlling infection in the absence of RTEs. The results of this study provide insight into how new pathogen-specific T cells leaving the thymus participate in combatting a persistent bacterial infection.

Interim Analysis of an Observational Study Assessing T Cell Receptor Diversity As an Early Predictor of NRM in Cord Blood Transplant Recipients

Interim Analysis of an Observational Study Assessing T Cell Receptor Diversity As an Early Predictor of NRM in Cord Blood Transplant Recipients

Molecular and immunological characterization of DNA ligase IV deficiency

DNA ligase IV (LIG4) deficiency is an extremely rare autosomal recessive primary immunodeficiency disease caused by the LIG4 mutation. To date, fewer than 30 cases of patients have been reported worldwide. No reversion mutations have been previously identified in LIG4. This study enrolled seven Chinese patients with LIG4 deficiency who presented with combined immunodeficiency, microcephaly, and growth retardation. One patient (P1) acquired non-Hodgkin lymphoma. Four patients had impaired T cell proliferation function and skewed T cell receptor diversity. Five novel mutations in LIG4 and a potential hotspot mutation (c.833G>T; p.R278L) in the Chinese population were identified. TA cloning analysis of T cells, NK cells, granulocytes, and oral mucosa cells in P6 revealed wild-type clones and clones that contained both maternally and paternally inherited mutations, indicating possible somatic reversion which need further investigation since no functional or protein assays were possible for all the patients died and no cell lines were available.

Anti-EGFR mAb cetuximab therapy increases T cell receptor (TCR) diversity in the peripheral blood and focuses TCR richness in the tumor microenvironment

T cell receptor (TCR) recognition of tumor antigen is essential for effective antitumor immunity. The immune system`s ability to respond to a broad spectrum of antigens requires a sophisticated selection of various TCR. So far, little is known about the role of TCR richness and clonality in the immune response to the EGFR-specific mAb, cetuximab. Therefore, we investigated differences in TCR sequences between HPV+ and HPV- patients, as well as differences in sequence characteristics between T cells of peripheral blood mononuclear cells (PBMC) and tumor infiltrating lymphocytes (TIL). Additionally, we were able to investigate the TCR richness and clonality in samples pre- and post-treatment in a clinical single agent cetuximab trial.

NK cell function and receptor diversity in the context of HCV infection.

Hepatitis C virus (HCV) infects over 170 million people in the world. While a minority of individuals are able to naturally clear this hepatotropic virus using their immune system, most people go on to develop a lifetime chronic infection that can result in severe liver pathology, potentially leading to liver cirrhosis and hepatic cellular carcinoma. Investigations into acute immune responses and spontaneous clearance of the virus are severely hampered by difficulties in identification of relevant patient cohorts. While the role for the adaptive immune response in viral clearance is well established, it is becoming clear that the innate immune system also impacts on HCV outcome. The innate immune response to infection is likely to influence the type of adaptive immune response that develops and will ultimately influence if the virus is cleared or develops into a chronic infection. Natural Killer (NK) cells are lymphocytes that have important anti-viral functions including direct cytotoxicity of infected cells and the production of inflammatory cytokines, e.g., IFN-γ. They are generally considered to be cells of the innate immune system, although there is increasing evidence that NK cells adapt and persist in response to particular viral infections. NK cells are altered in patients with acute and chronic HCV infection. There is increasing evidence from both cellular and genetic studies that NK cells modulate HCV outcome. This review will describe and discuss the current experimental and clinical evidence of a role for NK cells in HCV infection and describe recent discoveries that are likely to play a role in future research.

Commentary: "Can Selective MHC Downregulation Explain the Specificity and Genetic Diversity of NK Cell Receptors?".

GENERAL COMMENTARY article Front. Immunol., 31 August 2015Sec. NK and Innate Lymphoid Cell Biology Volume 6 - 2015 | https://doi.org/10.3389/fimmu.2015.00444

T cell senescence and cardiovascular diseases.

Age-related changes in the immune system, commonly termed "immunosenescence," contribute to deterioration of the immune response and fundamentally impact the health and survival of elderly individuals. Immunosenescence affects both the innate and adaptive immune systems; however, the most notable changes are in T cell immunity and include thymic involution, the collapse of T cell receptor(TCR) diversity, an imbalance in T cell populations, and the clonal expansion of senescent T cells. Senescent T cells have the ability to produce large quantities of proinflammatory cytokines and cytotoxic mediators; thus, they have been implicated in the pathogenesis of many chronic inflammatory diseases. Recently, an increasing body of evidence has suggested that senescent T cells also have pathogenic potential in cardiovascular diseases, such as hypertension, atherosclerosis, and myocardial infarction, underscoring the detrimental roles of these cells in various chronic inflammatory responses. Given that cardiovascular disease is the number one cause of death worldwide, there is great interest in understanding the contribution of age-related immunological changes to its pathogenesis. In this review, we discuss general features of age-related alterations in T cell immunity and the possible roles of senescent T cells in the pathogenesis of cardiovascular disease.

Peripheral T cell receptor diversity is associated with clinical outcomes following ipilimumab treatment in metastatic melanoma.

BackgroundIpilimumab improves overall survival in a subset of patients with metastatic melanoma. Peripheral blood T cell receptor (TCR) repertoire diversity has been associated with favorable outcomes in patients with cancer, but its relevance as a biomarker for ipilimumab outcomes remains unknown.FindingsIn this pilot study, we analyzed the pre-treatment peripheral blood TCR repertoire in 12 patients with metastatic melanoma who received ipilimumab at 3 mg/kg (clinical benefit, n = 4; no clinical benefit, n = 8). TCR diversity was evaluated using a polymerase chain reaction assay which measures TCR combinatorial diversity between V and J genes from genomic DNA. TCR repertoire diversity was studied through richness (observed V-J rearrangements) and evenness (similarity between the frequencies of specific V-J rearrangements). The Wilcoxon rank sum test was used to compare patients with clinical benefit and those without. Association with benefit in a dichotomized analysis was assessed through a Fisher’s exact test. Overall survival was studied through log-rank analysis.There was a significant difference in richness (p = 0.033) and evenness (p = 0.028) between patients with and without clinical benefit. Dichotomized analysis showed that none of the patients with low richness (n = 0/5, p = 0.081) nor low evenness (n = 0/7, p = 0.01) achieved clinical benefit. There were no significant differences in overall survival.ConclusionsIn this small group of patients, baseline TCR diversity in the peripheral blood was associated with clinical outcomes. Further investigation is ongoing in larger cohorts of patients to explore these preliminary findings and determine whether TCR diversity can be used as a predictive biomarker in cancer immunotherapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s40425-015-0070-4) contains supplementary material, which is available to authorized users.

Can Selective MHC Downregulation Explain the Specificity and Genetic Diversity of NK Cell Receptors?

Natural killer (NK) cells express inhibiting receptors (iNKRs), which specifically bind MHC-I molecules on the surface of healthy cells. When the expression of MHC-I on the cell surface decreases, which might occur during certain viral infections and cancer, iNKRs lose inhibiting signals and the infected cells become target for NK cell activation (missing-self detection). Although the detection of MHC-I deficient cells can be achieved by conserved receptor-ligand interactions, several iNKRs are encoded by gene families with a remarkable genetic diversity, containing many haplotypes varying in gene content and allelic polymorphism. So far, the biological function of this expansion within the NKR cluster has remained poorly understood. Here, we investigate whether the evolution of diverse iNKRs genes can be driven by a specific viral immunoevasive mechanism: selective MHC downregulation. Several viruses, including EBV, CMV, and HIV, decrease the expression of MHC-I to escape from T cell responses. This downregulation does not always affect all MHC loci in the same way, as viruses target particular MHC molecules. To study the selection pressure of selective MHC downregulation on iNKRs, we have developed an agent-based model simulating an evolutionary scenario of hosts infected with herpes-like viruses, which are able to selectively downregulate the expression of MHC-I molecules on the cell surface. We show that iNKRs evolve specificity and, depending on the similarity of MHC alleles within each locus and the differences between the loci, they can specialize to a particular MHC-I locus. The easier it is to classify an MHC allele to its locus, the lower the required diversity of the NKRs. Thus, the diversification of the iNKR cluster depends on the locus specific MHC structure.

Longitudinal analysis of peripheral blood T cell receptor diversity in patients with systemic lupus erythematosus by next-generation sequencing.

IntroductionT cells play an important role in the pathogenesis of systemic lupus erythematosus (SLE). Clonal expansion of T cells correlating with disease activity has been observed in peripheral blood (PB) of SLE subjects. Recently, next-generation sequencing (NGS) of the T cell receptor (TCR) β loci has emerged as a sensitive way to measure the T cell repertoire. In this study, we utilized NGS to assess whether changes in T cell repertoire diversity in PB of SLE patients correlate with or predict changes in disease activity.MethodsTotal RNA was isolated from the PB of 11 SLE patients. Each subject had three samples, collected at periods of clinical quiescence and at a flare. Twelve age-matched healthy controls (HC) were used for reference. NGS was used to profile the complementarity-determining region 3 (CDR3) of the rearranged TCR β loci.ResultsRelative to the HC, SLE patients (at quiescence) demonstrated a 2.2-fold reduction in repertoire diversity in a given PB volume (P <0.0002), a more uneven distribution of the repertoire (Gini coefficient, HC vs SLE, P = 0.015), and a trend toward increased percentage of expanded clones in the repertoire (clone size >1.0 %, HC vs SLE, P = 0.078). No significant correlation between the overall repertoire diversity and clinical disease activity was observed for most SLE patients with only two of eleven SLE patients showing a decreasing trend in repertoire diversity approaching the flare time point. We did not observe any overlap of CDR3 amino acid sequences or a preferential Vβ or Jβ gene usage among the top 100 expanded clones from all SLE patients. In both HC and SLE, the majority of the expanded clones were remarkably stable over time (HC = 5.5 ±0.5 months, SLE = 7.2 ±2.4 months).ConclusionsA significant decrease in T cell repertoire diversity was observed in PB of SLE patients compared to HC. However, in most SLE patients, repertoire diversity did not change significantly with increases in disease activity to a flare. Thus, without a priori knowledge of disease-specific clones, monitoring TCR repertoire in PB from SLE patients is not likely to be useful to predict changes in disease activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-015-0655-9) contains supplementary material, which is available to authorized users.

Determining the contribution of antigen-specific, CD4+ recent thymic emigrants to Salmonella persistence in vivo (LYM5P.661)

Abstract Typhoid fever, caused by infection with Salmonella bacteria affects approximately 21 million people annually, killing nearly 200,000. Recent thymic emigrants (RTEs) are the youngest subset of peripheral T cells, which are known to differ in how they functionally contribute to the naïve T cell pool. This distinctive cell population is known to contribute to the maintenance of T cell receptor diversity in the peripheral T cell pool, but their involvement in combating chronic bacterial infections, such as typhoid fever, has not been explored. In the present study, we hypothesized that RTEs are essential contributors to the CD4 T cell response during persistent Salmonella Typhimurium (ST) infection, which predominantly relies on helper T cell immunity to control bacteria. Here, we show that thymectomy of adult mice prior to oral infection with ST led to significantly increased bacterial burdens in the spleen, mesenteric lymph nodes and liver 30 days post-infection compared to sham surgical controls, suggesting Salmonella-specific RTEs may contribute to bacterial clearance. Surprisingly, existing peripheral Salmonella-specific T cells also increased significantly in number, implying that these cells are somehow incapable of controlling infection in the absence of RTEs. The results of this study provide insight into how new pathogen-specific T cells leaving the thymus participate in combatting a persistent bacterial infection.

T cell receptor diversity evaluation to predict patient response to ipilimumab in metastatic melanoma

T cell receptor diversity evaluation to predict patient response to ipilimumab in metastatic melanoma

Quantitative Assessment of T Cell Repertoire Recovery after Double Unit Cord Blood Transplantation Demonstrates Early T Cell Diversity and Correlation Between CMV Reactivation and CD8 Clonal Domimance

Introduction: Double-unit cord blood transplantation (DCBT) is a viable therapy for adults with high-risk hematologic malignancies who lack an adult donor. However, lack of transfer of memory T cells in the graft is associated with an increased risk of viral infections. To study immune reconstitution, we recently described a novel method that combines 5′ rapid amplification of complementary DNA ends (RACE) PCR and deep sequencing to quantify T cell receptor (TCR) diversity after allogeneic hematopoietic stem cell transplant (van Heijst, Nat Med 2013). In that study, we showed that recipients of DCBT recover TCR diversity comparable to healthy donors by 12 months. We now report results of a prospective analysis of CD4+ and CD8+ T cell repertoire recovery in DCBT recipients and correlation with clinical outcomes.Methods: We prospectively collected samples from 33 DCBT recipients. The median age was 45 years (range 26-71), 18 (55%) were CMV seropositive, and the majority (n = 17, 52%) had non-European ancestry. Diagnoses included 20 (61%) acute leukemias and 13 (39%) lymphomas. Conditioning was myeloablative (n=1, 3%), reduced intensity (n=28, 85%), or non-myeloablative (n=4, 12%), and all patients received GVHD prophylaxis with cyclosporine-A and mycophenolate mofetil and no ATG. Patients received double-unit CB grafts (4-6/6 HLA-A,-B antigen, -DRB1 allele donor-recipient matched); this was supplemented with haploidentical CD34-selected PBSC in 18 patients. The 66 units had a median donor-recipient HLA-allele match of 6/8 (range 3-8). Infused total nucleated cell doses were 2.3 (1.7-3.3) and 1.9 (1.3-2.5) for the larger and smaller units, respectively. Samples were collected from the DCB grafts, recipient day+21 bone marrow, and peripheral blood at days +30, 60, 90, 120, 180 and 365 post-transplant. TCR-β sequences from each sample were amplified and sequenced using the Illumina/MiSeq sequencing platform after isolation of CD4+ and CD8+ T cells. TCR abundances were assessed at the level of clonotype and TCR diversity was calculated using inverse Simpson index.Results: Of the 33 patients, long-term samples were obtained in 25 patients, short-term samples (≤ day 100) in 6 patients who died early after DCBT, and no samples other than the graft for 2 patients. The remainder of the results focuses on 25 patients with complete samples. As previously shown, there is a 1-2-log increased diversity in CD4+ vs. CD8+ T cells (Figure). Furthermore, median CD4+ steady-state diversity is achieved early by day 60. In contrast, there is a higher rate of clonal dominance in CD8+ compared to CD4+ T cells (24/25 vs. 11/25, p=0.0001 by Fisher test). Several patterns of clonal dominance were observed, including two main patterns in CD8+ T cells. In 7/24 patients, clonal dominance is established by day 60 and persists throughout, whereas in 12/24 patients, clonal dominance fluctuates throughout follow-up. In CD4 +T cells, where less dominance is observed, a similar distribution is seen, though prolonged clonal dominance is rare. Interestingly, some of the dominant clones can be detected in the graft and are present in the day 21 marrow sample. Persistent clonal dominance in CD8+ T cells was seen 6/9 patients with CMV reactivation, whereas ongoing fluctuation was seen in 9/12 patients without CMV reactivation. In 2 patients with fluctuating clones who reactivated CMV, 1 had low level and the other a late viremia. In contrast, no link to a specific pattern was observed in patients with HHV6 viremia or acute GVHD. Finally, when we assessed similarity in clonal distribution between time points, there was more similarity in CD8+ than CD4+ T cells.Conclusions: This novel deep TCR repertoire sequencing provides a quantitative picture of T cell recovery after DCBT and supports the following: 1) separate analysis of CD4+ and CD8+ T cell populations is critical given different patterns of recovery in T cell subsets; 2) there is significant turnover in CD4+ clones but with overall limited dominance, whereas there is less turnover in CD8+ clones; 3) although the grafts contain predominantly naïve T cells, the clonal evolution of CD8+ T cells strongly suggests generation of virus-specific T cells that control viral infection; and 4) CMV appears to be an important driver of CD8+ T cell clonal expansion after CBT. Ongoing analyses are correlating immune recovery with cord blood unit dominance as well as the biology of GVHD and relapse. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Reduction of T cell receptor diversity in NOD mice prevents development of type 1 diabetes but not Sjögren's syndrome.

Non-obese diabetic (NOD) mice are well-established models of independently developing spontaneous autoimmune diseases, Sjögren’s syndrome (SS) and type 1 diabetes (T1D). The key determining factor for T1D is the strong association with particular MHCII molecule and recognition by diabetogenic T cell receptor (TCR) of an insulin peptide presented in the context of I-Ag7 molecule. For SS the association with MHCII polymorphism is weaker and TCR diversity involved in the onset of the autoimmune phase of SS remains poorly understood. To compare the impact of TCR diversity reduction on the development of both diseases we generated two lines of TCR transgenic NOD mice. One line expresses transgenic TCRβ chain originated from a pathogenically irrelevant TCR, and the second line additionally expresses transgenic TCRαmini locus. Analysis of TCR sequences on NOD background reveals lower TCR diversity on Treg cells not only in the thymus, but also in the periphery. This reduction in diversity does not affect conventional CD4+ T cells, as compared to the TCRmini repertoire on B6 background. Interestingly, neither transgenic TCRβ nor TCRmini mice develop diabetes, which we show is due to lack of insulin B:9–23 specific T cells in the periphery. Conversely SS develops in both lines, with full glandular infiltration, production of autoantibodies and hyposalivation. It shows that SS development is not as sensitive to limited availability of TCR specificities as T1D, which suggests wider range of possible TCR/peptide/MHC interactions driving autoimmunity in SS.

T cell receptor diversity evaluation to predict patient response to Ipilimumab in metastatic melanoma

Meeting abstracts Ipilimumab blocks the immunologic checkpoint cytotoxic T lymphocyte antigen-4 (CTLA-4) and improves overall survival in patients with metastatic melanoma. Since only a subset of patients achieves benefit from ipilimumab, biomarkers that can predict patient outcome are needed. CTLA

Vδ2neg γ δ T Cells, a Multi-Reactive Tissue Subset: from Innate to Adaptive Altered-Self Surveillance

Human  T cells are usually considered to contribute to fast-acting local immune responses. Their somewhat limited T cell receptor (TCR) diversity implies that large subsets of  T cells share the capacity to respond to the same restricted set of antigens, rather than showing the fine specificity toward extremely diverse antigens, as is characteristic of  T cells. This has been well demonstrated for V 9V 2 T cells, particularly in non-human primate models. However, much less is known about the other subsets of  T cells, herein collectively called V 2 neg  T cells. Most of these cells express the V 1 chain, some express the V 3 chain, and very few express the four remaining V chains (V 4 to V 8). All these V chains can be associated with any of the six V chains (V 2, 3, 4, 5, 8, 9). V 2 neg  T cells are mainly located in epithelial tissues and the spleen, and are barely found in the circulation in normal physiological conditions. This tissue localization has limited their analysis. Establishment of murine models is difficult since murine and human  T cell populations vary greatly. For example, the equivalent of murine dendritic epithelial  T cells (DETC) does not exist in humans, and conversely, the equivalent of human V 9V 2 T cells is present only in primates. Therefore, human V 2 neg  T cells have mostly been examined during pathological situations where their circulating levels are increased. Like V 9V 2 T cells, V 1 and V 3 T cells have been shown to be involved in widely diverse pathological contexts, such as infection, cancer, auto-immunity, and inflammation. This suggests that  T cells respond to a variety of altered microenvironments induced by these situations. It is acknowledged that  T cells can recognize ubiquitous stress-induced conserved antigens in their native form, and altered-self or foreign ligands presented on non-polymorphic molecules in total independence of classical MHC molecules. Since V 2 neg  T cells can recognize broadly distributed antigens and are localized at the interface with the outer environment within epithelial tissues, V 2 neg  T cells can act as a first line of defense in the surveillance of body integrity and microorganism infections. Nevertheless, V 2 neg  T cells can also display effector/memory phenotypes similar to conventional MHC-restricted  T cells. This suggests an ability to mount long-lasting anamnestic immunity similar to conventional  T cells. Here, we will review what is currently known about V 2 neg  T cells highlighting the pathological situations where they expand. We will also discuss what is known concerning the cellular and molecular mechanisms of their activation and their effector functions.