Antigen specificity of gammadelta T cells depends primarily on the flanking sequences of CDR3delta

Non-structure protein ORF1ab (NSP8) in SARS-CoV-2 contains potential γδT cell epitopes

Upon activation by the pathogen through T-cell receptors (TCRs), γδT cells suppress the pathogenic replication and thus play important roles against viral infections. Targeting SARS-CoV-2 via γδT cells provides alternative therapeutic strategies. However, little is known about the recognition of SARS-CoV-2 antigens by γδT cells. We discovered a specific Vγ9/δ2 CDR3 by analyzing γδT cells derived from the patients infected by SARS-CoV-2. Using a cell model exogenously expressing γδ-TCR established, we further screened the structural motifs within the CDR3 responsible for binding to γδ-TCR. Importantly, these sequences were mapped to NSP8, a non-structural protein in SARS-CoV-2. Our results suggest that NSP8 mediates the recognition by γδT cells and thus could serve as a potential target for vaccines.

Human and murine memory γδ T cells: Evidence for acquired immune memory in bacterial and viral infections and autoimmunity

γδ T cells are unconventional lymphocytes that could play a role in bridging the innate and adaptive immune system. Upon initial exposure to an antigen, some activated T cells become memory T cells that could be reactivated upon secondary immune challenge. Recently, subsets of γδ T cells with a restricted antigen repertoire and long-term persistence have been observed after clearance of viral and bacterial infections. These γδ T cells possess the hallmark ability of memory T cells to respond more strongly and proliferate to a higher extent upon secondary infection. Murine and primate models of Listeria monocytogenes and cytomegalovirus infection display these memory hallmarks and demonstrate γδ T cell memory responses. In addition, human and non-human primate infections with Mycobacterium tuberculosis, as well as non-human primate infection with monkeypox and studies on patients suffering from autoimmune disease (rheumatoid arthritis and multiple sclerosis) reveal memory-like responses corresponding with disease. Murine models of psoriatic disease (imiquimod) and parasite infections (malaria) exhibited shifts to memory phenotypes with repeated immune challenge. These studies provide strong support for the formation of immune memory in γδ T cells, and memory γδ T cells may have a widespread role in protective immunity and autoimmunity.

Preferential Infiltration of Unique Vγ9Jγ2-Vδ2 T Cells Into Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is clinically highly aggressive as a result of evolutionary dynamics induced by cross-talk between cancer cells and a heterogeneous group of immune cells in tumor microenvironment. The brain harbors limited numbers of immune cells with few lymphocytes and macrophages; thus, innate-like lymphocytes, such as γδ T cells, have important roles in antitumor immunity. Here, we characterized GBM-infiltrating γδ T cells, which may have roles in regulating the GBM tumor microenvironment and cancer cell gene expression. V(D)J repertoires of tumor-infiltrating and blood-circulating γδ T cells from four patients were analyzed by next-generation sequencing-based T-cell receptor (TCR) sequencing in addition to mutation and immune profiles in four GBM cases. In all tumor tissues, abundant innate and effector/memory lymphocytes were detected, accompanied by large numbers of tumor-associated macrophages and closely located tumor-infiltrating γδ T cells, which appear to have anti-tumor activity. The immune-related gene expression analysis using the TCGA database showed that the signature gene expression extent of γδ T cells were more associated with those of cytotoxic T and Th1 cells and M1 macrophages than those of Th2 cells and M2 macrophages. Although the most abundant γδ T cells were Vγ9Vδ2 T cells in both tumor tissues and blood, the repertoire of intratumoral Vγ9Vδ2 T cells was distinct from that of peripheral blood Vγ9Vδ2 T cells and was dominated by Vγ9Jγ2 sequences, not by canonical Vγ9JγP sequences that are mostly commonly found in blood γδ T cells. Collectively, unique GBM-specific TCR clonotypes were identified by comparing TCR repertoires of peripheral blood and intra-tumoral γδ T cells. These findings will be helpful for the elucidation of tumor-specific antigens and development of anticancer immunotherapies using tumor-infiltrating γδ T cells.

Profiling the pattern of the human T-cell receptor γδ complementary determinant region 3 repertoire in patients with lung carcinoma via high-throughput sequencing analysis

γδ T cells function as sentinels in early host responses to infections and malignancies. Specifically, γδ T cells recognize tumor-associated stress antigens via T-cell receptor (TCR) γδ and play important roles in the antitumor immune response. In this study, we characterized the pattern of the human TCR γδ complementary determinant region 3 (CDR3) repertoire in patients with lung carcinoma (LC) via high-throughput sequencing. The results showed that the diversity of CDR3δ was significantly reduced, and that of CDR3γ was unchanged in LC patients compared with healthy individuals; in addition, LC patients shared significantly more CDR3δ sequences with each other than healthy individuals. The CDR3 length distribution and N-addition length distribution did not significantly differ between LC patients and healthy individuals. In addition, the CDR3 repertoire tended to use more Vδ2 and fewer Vδ1 germline gene fragments among LC patients. Moreover, we found a combination of four TCR γδ repertoire features that focus on CDR3δ and can be used as a biomarker for LC diagnosis. Our research suggests that the TCR γδ CDR3 repertoire changed in LC patients due to the antitumor immune response by γδ T cells in vivo, and these changes primarily focus on the amplification of certain tumor-specific CDR3δ clones among patients. This study demonstrates the role of γδ T cells from the TCR γδ CDR3 repertoire in tumor immunity and lays the foundation for elucidating the mechanism underlying the function of γδT cells in antitumor immunity.

Characterization of the diversity of T cell receptor γδ complementary determinant region 3 in human peripheral blood by Immune Repertoire Sequencing

γδ T cells function as sentinels in early host response to infections and malignancies. Although γδ T cells are regarded as innate immune cells and recognize antigens in a non-MHC restricted manner, they possess a huge diversity of complementary determinant region 3 (CDR3) of T cell receptor (TCR) generated by the rearrangement of germ-line gene V- (D) -J-C fragments. However, the detailed characteristics of the TCRγδ CDR3 repertoire remain unclear. A comprehensive analysis would answer fundamental questions about the diversity of the TCRγδ CDR3 repertoire and elucidate the mechanism underlying γδ T cell recognition of pathogens and tumor antigens. In this study, we used Immune Repertoire Sequencing (IR-SEQ) to analyze the diversity of TCRγδ CDR3 repertoires from 30 healthy donors. The results show that IR-SEQ had sufficient repeatability to analyze the TCRγδ CDR3 repertoire. The diversity of TCRγδ CDR3 repertoire is quite dispersed and individually different. The TCR δ chain (TRD) repertoire displayed more diversity and less sharing among individuals compared with TCR γ chain (TRG). To our knowledge, this is the first study to use IR-SEQ to characterize the repertoire of TCRγδ CDR3 in human peripheral blood γδ T cells by using IR-SEQ. Our findings provide a basic understanding of the diversity of TCRγδ repertoire in the physiological condition, which provides a clue to the underlying mechanism of γδ T cell recognition of pathogens and tumor antigens.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Characterization of complementary determinant region 3δ in human MutS homologue 2-specific γδ T cells

γδT cells function as sentinels in early host responses to infections and malignancies. Previously, we found ectopically expressed human MutS homologue 2 (hMSH2), recognized by γδT cells, triggered a γδT cell-mediated cytolysis to tumor cells. However, the characteristics of hMSH2-specific γδ Τ cells are not fully understood. In this study, we investigated the complementary determinant region (CDR) 3δ diversity of hMSH2-specific γδ T cells. We found that the CDR3δ sequences of hMSH2-specific γδ T cells displayed limited diversity, while the length and germline gene usage showed no differences compared with whole CDR3δ immune repertoire. There are more hydrophilic amino acids in P/N insert of hMSH2-specific γδ T cells including the more conserved amino acid at the position 97. Our results offer clues to understanding antigen recognition pattern of γδ T cells to stress-induced hMSH2 of tumor cells and also the mechanism of γδT cell-mediated tumor immune surveillance.

The Vγ9Vδ2 T Cell Antigen Receptor and Butyrophilin-3 A1: Models of Interaction, the Possibility of Co-Evolution, and the Case of Dendritic Epidermal T Cells

Most circulating human gamma delta T cells are Vγ9Vδ2 T cells. Their hallmark is the expression of T cell antigen receptors (TCR) whose γ-chains show a Vγ9-JP (Vγ2-Jγ1.2) rearrangement and are paired with Vδ2-containing δ-chains, a dominant TCR configuration, which until recently seemed to occur in primates only. Vγ9Vδ2 T cells respond to phosphoantigens (PAg) such as (E)-4-Hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), which is produced by many pathogens and isopentenyl pyrophosphate (IPP), which accumulates in certain tumors or cells treated with aminobisphosphonates such as zoledronate. A prerequisite for PAg-induced activation is the contact of Vγ9Vδ2 T cells with cells expressing butyrophilin-3 A1 (BTN3A1). We will first critically review models of how BTN3 might act in PAg-mediated Vγ9Vδ2 T cell activation and then address putative co-evolution of Vγ9, Vδ2, and BTN3 genes. In those rodent and lagomorphs used as animal models, all three genes are lost but a data-base analysis showed that they emerged together with placental mammals. A strong concomitant conservation of functional Vγ9, Vδ2, and BTN3 genes in other species suggests co-evolution of these three genes. A detailed analysis was performed for the new world camelid alpaca (Vicugna pacos). It provides an excellent candidate for a non-primate species with presumably functional Vγ9Vδ2 T cells since TCR rearrangements share features characteristic for PAg-reactive primate Vγ9Vδ2 TCR and proposed PAg-binding sites of BTN3A1 have been conserved. Finally, we analyze the possible functional relationship between the butyrophilin-family member Skint1 and the γδ TCR-V genes used by murine dendritic epithelial T cells (DETC). Among placental mammals, we identify five rodents, the cow, a bat, and the cape golden mole as the only species concomitantly possessing potentially functional homologs of murine Vγ3, Vδ4 genes, and Skint1 gene and suggest to search for DETC like cells in these species.

γδ T cells are involved in acute HIV infection and associated with AIDS progression

Background

Early diagnosis is vital to HIV control. γδ T cells play critical roles in viral infections, but their activation in acute HIV infected patients and follow up to 18 months has not been described.

Methods

Changes in γδ T cells, including subsets, function and activation, in treated and untreated acutely HIV-infected patients (n = 79) were compared by cytotoxicity assay and flow cytometry with healthy controls (n = 21) at month 0, 6, 12 and 18.

Results

In acutely HIV-infected patients, Vδ1 cell proportion was elevated (P = 0.027) with Vδ2 population reduced (P = 0.002). Effector and central memory γδ T cell factions were decreased (P = 0.006 and P = 0.001, respectively), while proportion of terminal γδ T cells increased (P = 0.002). γδ T cell cytotoxicity was compromised over time. Fraction of IL-17-producing cells increased (P = 0.008), and IFN-γ-producing cells were unaffected (P = 0.115). Elevation of a microbial translocation marker, sCD14, was associated with γδ T cell activation (P = 0.001), which increased in a time-dependent manner, correlating with CD4/CD8 T cell activation set-points and CD4 counts. Antiretroviral therapy did not affect these changes.

Conclusions

γδ T cell subpopulation and functions change significantly in acute HIV infection and over time. Early γδ T cell activation was associated with CD4/CD8 T cell activation set-points, which predict AIDS progression. Therefore, γδ T cell activation represents a potential surrogate marker of AIDS progression.

Generation of human neutralizing monoclonal antibodies against the 2009 pandemic H1N1 virus from peripheral blood memory B lymphocytes

The 2009 H1N1 influenza pandemic demonstrated the significance of a global health threat to human beings. Although pandemic H1N1 vaccines have been rapidly developed, passive serotherapy may offer superior immediate protection against infections in children, the elderly and immune-compromised patients during an influenza pandemic. Here, we applied a novel strategy based on Epstein-Barr virus (EBV)-immortalized peripheral blood memory B cells to screen high viral neutralizing monoclonal antibodies (MAbs) from individuals vaccinated with the 2009 pandemic H1N1 vaccine PANFLU.1. Through a massive screen of 13 090 immortalized memory B-cell clones from three selected vaccinees, seven MAbs were identified with both high viral neutralizing capacities and hemagglutination inhibition (HAI) activities against the 2009 pandemic H1N1 viruses. These MAbs may have important clinical implications for passive serotherapy treatments of infected patients with severe respiratory syndrome, especially children, the elderly and immunodeficient individuals. Our successful strategy for generating high-affinity MAbs from EBV-immortalized peripheral blood memory B cells may also be applicable to other infectious or autoimmune diseases.

A novel antibody-like TCRγδ-Ig fusion protein exhibits antitumor activity against human ovarian carcinoma

TCRγ9δ2(OT3) is a tumor-specific TCR with an unique complementarity-determining region 3 (CDR3) sequence, referred to as OT3, in its δ2 chain. This region was identified in tumor-infiltrating lymphocytes (TILs) from human ovarian epithelial carcinoma. We demonstrated that TCRγ9δ2(OT3)-Fc, a fusion protein composed of the complete extracellular domains of the γ9 and δ2 chains linked to the Fc domains of human IgG1, exhibited successful binding to multiple human carcinoma cell lines. In vitro, TCRγ9δ2(OT3)-Fc mediated cell killing via antibody-dependent cellular cytotoxicity (ADCC) in a dose-dependent manner. In vivo, TCRγ9δ2(OT3)-Fc significantly inhibited tumor growth and enhanced survival in human ovarian carcinoma xenograft models. Our findings suggest that the TCRγ9δ2(OT3)-Fc fusion protein possesses both the antigen-recognition properties of TCR γδ and the Fc-mediated effector functions of the antibody.

Comparative biology of γδ T cell function in humans, mice, and domestic animals

γδ T cells are a functionally heterogeneous population and contribute to many early immune responses. The majority of their activity is described in humans and mice, but the immune systems of all jawed vertebrates include the γδ T cell lineage. Although some aspects of γδ T cells vary between species, critical roles in early immune responses are often conserved. Common features of γδ T cells include innate receptor expression, antigen presentation, cytotoxicity, and cytokine production. Herein we compare studies describing these conserved γδ T cell functions and other, potentially unique, functions. γδ T cells are well documented for their potential immunotherapeutic properties; however, these proposed therapies are often focused on human diseases and the mouse models thereof. This review consolidates some of these studies with those in other animals to provide a consensus for the current understanding of γδ T cell function across species.

γδ-T cells: an unpolished sword in human anti-infection immunity

γδ-T cells represent a small population of immune cells, but play an indispensable role in host defenses against exogenous pathogens, immune surveillance of endogenous pathogenesis and even homeostasis of the immune system. Activation and expansion of γδ-T cells are generally observed in diverse human infectious diseases and correlate with their progression and prognosis. γδ-T cells have both 'innate' and 'adaptive' characteristics in the immune response, and their anti-infection activities are mediated by multiple pathways that are under elaborate regulation by other immune components. In this review, we summarize the current state of the literature and the recent advancements in γδ-T cell-mediated immune responses against common human infectious pathogens. Although further investigation is needed to improve our understanding of the characteristics of different γδ-T cell subpopulations under specific conditions, γδ-T cell-based therapy has great potential for the treatment of infectious diseases.

Ectopically expressed human tumor biomarker MutS homologue 2 is a novel endogenous ligand that is recognized by human γδ T cells to induce innate anti-tumor/virus immunity

Human (h) MutS homologue 2, a nuclear protein, is a critical element of the DNA mismatch repair system. Our previous studies suggest that hMSH2 might be a protein ligand for TCRγδ. Here, we show that hMSH2 is ectopically expressed on a large panel of epithelial tumor cells. We found that hMSH2 interacts with both TCRγδ and NKG2D and contributes to Vδ2 T cell-mediated cytolysis of tumor cells. Moreover, recombinant human MSH2 protein stimulates the proliferation and IFN-γ secretion of Vδ2 T cells in vitro. Finally, hMSH2 expression is induced on the cell surface of Epstein-Barr virus-transformed lymphoblastoid cell lines, and the induction increases the sensitivity of these lymphoblastoid cell lines to γδ T cell-mediated cytolysis. Our data suggest that hMSH2 functions as a tumor-associated or virus infection-related antigen recognized by both Vδ2 TCR and NKG2D, and it plays a role in eliciting the immune responses of γδ T cells against tumor- and virus-infected cells. The recognition of ectopic surface-expressing endogenous antigen by TCRγδ and NKG2D may be an important mechanism of innate immune response to carcinogenesis and viral infection.

Critical role of γ4 chain in the expression of functional Vγ4Vδ1 T cell receptor of gastric tumour-infiltrating γδT lymphocytes

Vγ4Vδ1 T cell receptor (TCRγ4δ1)-expressing γδT cells were the most dominant subset in gastric tumour-infiltrating γδT cells (γδTIL) we recently analyzed. To study the essential roles of γ and δ chains in assembly and function of TCRγ4δ1, we sequenced and constructed them into lentiviral vectors for the reconstitution of TCRγ4δ1 using different modalities of transduction. We were able to efficiently reconstitute TCRγ4δ1 with functional activities when both γ4 and δ1 chains are coexpressed in TCR-negative J.RT3-T3.5 cells. However, the expression of δ1 chain is greatly diminished when γ4 expression is absent, suggesting that the coexpressing γ4 is critical in maintaining the folding and stability of δ1 product. To functionally study the reconstituted TCRγ4δ1, we examined the cytolytic activity of TCRγ4δ1-reconstituted J.RT3-T3.5 cells and cytokine secretion and found the receptors are fully functional, but their functionality also requires the presence of γ4. Our results demonstrated that γ4 is critical for the stability of δ1 and the function of TCRγ4δ1.

CDR3δ -grafted γ9δ2T cells mediate effective antitumor reactivity

Adoptive cell-transfer therapy (ACT) has been reported to suppress growing tumors and to overcome tumor escape in animal models. As a candidate ACT effector, γ9δ2T cells can be activated and expanded in vitro and in vivo and display strong antitumor activity against colorectal, lung, prostate, ovarian and renal cell carcinomas. However, it is difficult to obtain a large enough number of γδT cells to meet the need for immunotherapy that can overcome the cancer patients' immune suppressive tumor microenvironment. In previous studies, our lab confirmed that γ9δ2T cells recognized tumor cells via the CDR3δ region of the γδ-T-cell receptor (TCR). We constructed full-length human peripheral blood mononuclear cell (PBMC)-derived γ9 and δ2 chains in which the CDR3 region was replaced by an ovarian epithelial carcinoma (OEC)-derived CDR3. We transferred the CDR3δ-grafted γ9δ2TCR into peripheral blood lymphocytes (PBLs) to develop genetically modified γ9δ2T cells. In vitro studies have shown that these CDR3δ-grafted γ9δ2T cells can produce cytokines after stimulation with tumor cell extracts and exhibit cytotoxicity towards tumor cells, including human OEC and cervical adenocarcinoma. CDR3δ-grafted γ9δ2T cells adoptively transferred into nude mice bearing a human OEC cell line demonstrated significant antitumor effects. These results indicate that CDR3δ-grafted γ9δ2T cells might be candidates for clinical tumor immunotherapy.

γδ T cells response to Mycobacterium tuberculosis in pulmonary tuberculosis patients using preponderant complementary determinant region 3 sequence

BACKGROUND & OBJECTIVES

The unique immunological functions of γδ T lymphocytes to contribute immunity against Mycobacterium tuberculosis attracted interest of researchers. However, little is known about the specificity of γδ Τ cell in tuberculosis patients and the lack of exact tuberculosis antigen recognized by γδ T cells limited its application. The analysis of complementary determinant region (CDR)3 sequence characteristic in γδ T cells of tuberculosis patients would contribute to understand the distribution specificity of γδ T cell. In present study, we investigated the diversity of the γ9/δ2 T cell immunorepertoire and analysed the specificity of the expressed CDR3 in pulmonary tuberculosis patients.

METHODS

The total RNA in peripheral blood mononuclear cell of 50 pulmonary tuberculosis patients and 10 healthy controls was extracted. The polymerase chain reaction was used to specifically amplify the CDR3 region of γ9 and δ2 chain. The PCR products were ligated into the pGEM-T easy vector. The plasmid DNA was sequenced using the ABI3700 and the T7 primer.

RESULTS

Our findings showed that predominant CDR3 sequence of δ2 chain in pulmonary tuberculosis patients was CACDTLVSTDKLIFGKG. The sequence specifically exists in almost all pulmonary tuberculosis patients. The conserved hydrophobic acid residue in 97 positions is present in the γδ T cell reactive to M. tuberculosis. The length of δ2 CDR3 in pulmonary tuberculosis patients has no relation with the disease progress.

INTERPRETATION & CONCLUSIONS

Our results suggest that γδ T cells appear to use CDR3 sequence to recognise M. tuberculosis antigen. γδ T cells reactive to M. tuberculosis were diverse and polyclonal.

Flanking V and J sequences of complementary determining region 3 of T cell receptor (TCR) δ1 (CDR3δ1) determine the structure and function of TCRγ4δ1

The γδ T cell receptor (TCR) differs from immunoglobulin and αβ TCR in its overall binding mode. In human, genes δ1, δ2, and δ3 are used for TCRδ chains. Previously, we have studied antigen binding determinants of TCRδ2 derived from dominant γδ T cells residing in peripheral blood. In this study we have investigated the critical determinants for antigen recognition and TCR function in TCRδ1 originated from gastric tumor-infiltrating γδ T lymphocytes using three independent experimental strategies including complementary determining region 3 (CDR3) of TCRδ1 (CDR3δ1)-peptide mediated binding, CDR3δ1-grafted TCR fusion protein-mediated binding, and TCRγ4δ1- and mutant-expressing cell-mediated binding. All three approaches consistently showed that the conserved flanking V and J sequences but not the diverse D segment in CDR3δ1 determine the antigen binding. Most importantly, we found that mutations in the V and J regions of CDR3δ1 also abolish the assembly of TCR and TCR-CD3 complexes in TCRγ4δ1-transduced J.RT3-T3.5 cells. Together with our previous studies on CDR3δ2 binding, our finding suggests that both human TCRδ1 and TCRδ2 recognize antigen predominately via flanking V and J regions. These results indicate that TCRγδ recognizes antigens using conserved parts in their CDR3, which provides an explanation for a diverse repertoire of γδTCRs only recognizing a limited number of antigens.

Generation of human regulatory gammadelta T cells by TCRgammadelta stimulation in the presence of TGF-beta and their involvement in the pathogenesis of systemic lupus erythematosus

As a component of the innate immune cell population, γδ T cells are involved in tumor immunosurveillance and host defense against viral invasion. In this study, we demonstrated a novel function of human γδ T cells as regulatory cells by detecting their suppressive effect on the proliferation of autologous naive CD4(+) T cells. These regulatory γδ T cells (γδ Tregs) could be generated in vitro by stimulating with anti-TCRγδ in the presence of TGF-β and IL-2. Similar to CD4(+)Foxp3(+) Tregs, γδ Tregs also expressed Foxp3. Additionally, they primarily belonged to the Vδ1 subset with a CD27(+)CD25(high) phenotype. Furthermore, these γδ Tregs showed an immunoregulatory activity mainly through cell-to-cell contact. Importantly, this γδ regulatory population decreased in the peripheral blood of systemic lupus erythematosus patients, suggesting a potential mechanism in understanding the pathogenesis of systemic lupus erythematosus.

A novel strategy to screen Bacillus Calmette-Guérin protein antigen recognized by γδ TCR

Background

Phosphoantigen was originally identified as the main γδ TCR-recognized antigen that could activate γδ T cells to promote immune protection against mycobacterial infection. However, new evidence shows that the γδ T cells activated by phosphoantigen can only provide partial immune protection against mycobacterial infection. In contrast, whole lysates of Mycobacterium could activate immune protection more potently, implying that other γδ TCR-recognized antigens that elicit protective immune responses. To date, only a few distinct mycobacterial antigens recognized by the γδ TCR have been characterized.

Methodology/Principal Findings

In the present study, we established a new approach to screen epitopes or protein antigens recognized by the γδ TCR using Bacillus Calmette-Guérin- (BCG-) specific γ TCR transfected cells as probes to pan a 12-mer random-peptide phage-displayed library. Through binding assays and functional analysis, we identified a peptide (BP3) that not only binds to the BCG-specific γδ TCR but also effectively activates γδ T cells isolated from human subjects inoculated with BCG. Importantly, the γδ T cells activated by peptide BP3 had a cytotoxic effect on THP-1 cells infected with BCG. Moreover, the oxidative stress response regulatory protein (OXYS), a BCG protein that matches perfectly with peptide BP3 according to bioinformatics analysis, was confirmed as a ligand for the γδ TCR and was found to activate γδ T cells from human subjects inoculated with BCG.

Conclusions/Significance

In conclusion, our study provides a novel strategy to identify epitopes or protein antigens for the γδ TCR, and provides a potential means to screen mycobacterial vaccines or candidates for adjuvant.

Mechanisms underlying γδ T-cell subset perturbations in SIV-infected Asian rhesus macaques

T cells that express the γδ T-cell receptor, which recognize microbial or stress-induced antigens, represent a minority of blood T cells but constitute a major proportion of intraepithelial lymphocytes in the gastrointestinal mucosa. As microbial products have been shown to translocate from the gastrointestinal tract into circulation in chronically HIV/Simian immunodeficiency virus (SIV)-infected individuals, we conducted a study of Vδ1 and Vδ2 T-cell frequency, phenotype, and function in blood, spleen, lymph nodes, gastrointestinal mucosa, and bronchoalveolar lavage of uninfected and chronically SIVsmE543-infected rhesus macaques (RMs). We found: (1) SIV-associated inversion of Vδ1/Vδ2 T cells occurs in blood and in several tissues; (2) γδ T cells are not infected by SIV in vivo; (3) the Vδ1/Vδ2 inversion involves expansion of Vδ1 T cells; (4) expanded Vδ1 T cells are phenotypically and functionally different from Vδ1 T cells from uninfected RMs; and (5) the stimulus underlying expansion of Vδ1 T cells appears to be microbial translocation. These data highlight the importance of microbial translocation-induced immune activation in chronically infected individuals and provide new insights into an immune dysregulation phenomenon that is a hallmark of HIV/SIV infection. These findings may lead to novel therapeutic interventions that improve the immune responses against microbial antigens, and thus, decrease microbial translocation-induced immune activation.

The recognition of gammadelta TCR to protein antigen does not depend on the hydrophobic I97 residue of CDR3delta

The crystal structure analysis demonstrated that the hydrophobic amino acid residue (isolecuine/leucine/valine) at conserved position 97 of Vdelta2 TCR plays an important role in recognizing the non-peptide antigen. But its importance to protein antigen remains unclear until now. In the present study, we focus on the role of hydrophobic amino acid residue at conserved position 97 of Vdelta2 TCR in complementarity determining region (CDR)3delta-mediated binding to protein antigen. We employed CDR3delta peptide and membrane-engineered gammadelta TCR as detecting molecules with mutated 97 hydrophobic amino acid residue in CDR3delta (nominated as OT10), a Vdelta2 CDR3 sequence derived from tumor infiltrating lymphocytes in ovarian epithelial carcinoma (OEC). Binding assays revealed that OT10 peptide and membrane-engineered gammadelta TCR (gammadelta TCR transfected cells with OT10 sequence) could bind specifically ovarian tumor cell line (SKOV3). The mutant analysis indicated that any amino acid substitution at position deltaI97 could abolish the response of the transfected cells to iso-butylamine, a known non-peptide antigen of gammadelta T cells. But amino acid substitution of isoleucine at position delta97 did not change the responsiveness of gammadelta TCR transfected cell to protein antigen. Our data suggested that a mechanism other than non-peptide antigen might mediate the recognition of Vdelta2gammadelta T cells for protein antigen. This finding may provide a possibility that gammadelta TCR recognize different ligands in diversity manners.