Human gammadelta T cells express a higher TCR/CD3 complex density than alphabeta T cells

Spatially resolved immune exhaustion within the alloreactive microenvironment predicts liver transplant rejection

Allograft rejection is common following clinical organ transplantation, but defining specific immune subsets mediating alloimmunity has been elusive. Calcineurin inhibitor dose escalation, corticosteroids, and/or lymphocyte depleting antibodies have remained the primary options for treatment of clinical rejection episodes. Here, we developed a highly multiplexed imaging mass cytometry panel to study the immune response in archival biopsies from 79 liver transplant (LT) recipients with either no rejection (NR), acute T cell-mediated rejection (TCMR), or chronic rejection (CR). This approach generated a spatially resolved proteomic atlas of 461,816 cells (42 phenotypes) derived from 96 pathologist-selected regions of interest. Our analysis revealed that regulatory (HLADR+ Treg) and PD1+ T cell phenotypes (CD4+ and CD8+ subsets), combined with variations in M2 macrophage polarization, were a unique signature of active TCMR. These data provide insights into the alloimmune microenvironment in clinical LT, including identification of potential targets for focused immunotherapy during rejection episodes and suggestion of a substantial role for immune exhaustion in TCMR.

Immune Regulatory Networks and Therapy of γδ T Cells in Liver Cancer: Recent Trends and Advancements

The roles of γδ T cells in liver cancer, especially in the potential function of immunotherapy due to their direct cytotoxic effects on tumor cells and secretion of important cytokines and chemokines, have aroused research interest. This review briefly describes the basic characteristics of γδ T cells, focusing on their diverse effects on liver cancer. In particular, different subtypes of γδ T cells have diverse or even opposite effects on liver cancer. We provide a detailed description of the immune regulatory network of γδ T cells in liver cancer from two aspects: immune components and nonimmune components. The interactions between various components in this immune regulatory network are dynamic and pluralistic, ultimately determining the biological effects of γδ T cells in liver cancer. We also integrate the current knowledge of γδ T-cell immunotherapy for liver cancer treatment, emphasizing the potential of these cells in liver cancer immunotherapy.

Mechanistically modeling peripheral cytokine dynamics following bispecific dosing in solid tumors

Bispecific antibodies exhibit proven clinical benefit, and many bispecifics are currently in clinical development for oncology. Cytokine release syndrome (CRS) is a common clinical adverse effect observed following CD3-based bispecific dosing. However, the pathophysiology of CRS is not fully understood, and no computational model mechanistically describing clinical cytokine dynamics following bispecific dosing in solid tumors exists. Here, a quantitative systems pharmacology (QSP) model describing peripheral clinical cytokine dynamics following bispecific dosing in solid tumors is presented. Using tebentafusp as a case study, a CD3-bispecific approved for uveal melanoma, the model successfully captures the dynamics of five cytokines. The QSP model was shown to predict observed phenomena, such as cytokine maximum concentration suppression using step-up dosing regimens and the importance of on-target off-tumor binding toward CRS and toxicity. Furthermore, the QSP model provides rationale for these biological phenomena based on dynamics of immune cell activation and desensitization in tumors and healthy tissues. Overall, the QSP model structure presented here serves as a basis to infer cytokine dynamics for other CD3-based bispecifics or tumor types by altering model parameters to capture the scenario of interest, supporting applications including dose selection, candidate nomination, and disease area selection.

Spatially resolved immune exhaustion within the alloreactive microenvironment predicts liver transplant rejection

Allograft rejection is a frequent complication following solid organ transplantation, but defining specific immune subsets mediating alloimmunity has been elusive due to the scarcity of tissue in clinical biopsy specimens. Single cell techniques have emerged as valuable tools for studying mechanisms of disease in complex tissue microenvironments. Here, we developed a highly multiplexed imaging mass cytometry panel, single cell analysis pipeline, and semi-supervised immune cell clustering algorithm to study archival biopsy specimens from 79 liver transplant (LT) recipients with histopathological diagnoses of either no rejection (NR), acute T-cell mediated rejection (TCMR), or chronic rejection (CR). This approach generated a spatially resolved proteomic atlas of 461,816 cells derived from 98 pathologist-selected regions of interest relevant to clinical diagnosis of rejection. We identified 41 distinct cell populations (32 immune and 9 parenchymal cell phenotypes) that defined key elements of the alloimmune microenvironment (AME), identified significant cell-cell interactions, and established higher order cellular neighborhoods. Our analysis revealed that both regulatory (HLA-DR+ Treg) and exhausted T-cell phenotypes (PD1+CD4+ and PD1+CD8+ T-cells), combined with variations in M2 macrophage polarization, were a unique signature of TCMR. TCMR was further characterized by alterations in cell-to-cell interactions among both exhausted immune subsets and inflammatory populations, with expansion of a CD8 enriched cellular neighborhood comprised of Treg, exhausted T-cell subsets, proliferating CD8+ T-cells, and cytotoxic T-cells. These data enabled creation of a predictive model of clinical outcomes using a subset of cell types to differentiate TCMR from NR (AUC = 0.96 ± 0.04) and TCMR from CR (AUC = 0.96 ± 0.06) with high sensitivity and specificity. Collectively, these data provide mechanistic insights into the AME in clinical LT, including a substantial role for immune exhaustion in TCMR with identification of novel targets for more focused immunotherapy in allograft rejection. Our study also offers a conceptual framework for applying spatial proteomics to study immunological diseases in archival clinical specimens.

The emerging roles of γδ T cells in cancer immunotherapy

Current cancer immunotherapies are primarily predicated on αβ T cells, with a stringent dependence on MHC-mediated presentation of tumour-enriched peptides or unique neoantigens that can limit their efficacy and applicability in various contexts. After two decades of preclinical research and preliminary clinical studies involving very small numbers of patients, γδ T cells are now being explored as a viable and promising approach for cancer immunotherapy. The unique features of γδ T cells, including their tissue tropisms, antitumour activity that is independent of neoantigen burden and conventional MHC-dependent antigen presentation, and combination of typical properties of T cells and natural killer cells, make them very appealing effectors in multiple cancer settings. Herein, we review the main functions of γδ T cells in antitumour immunity, focusing on human γδ T cell subsets, with a particular emphasis on the differences between Vδ1⁺ and Vδ2⁺ γδ T cells, to discuss their prognostic value in patients with cancer and the key therapeutic strategies that are being developed in an attempt to improve the outcomes of these patients.

Distinctive phenotype for HLA-E- versus HLA-A2-restricted memory CD8 αβT cells in the course of HCMV infection discloses features shared with NKG2C+CD57+NK and δ2-γδT cell subsets

The human cytomegalovirus (HCMV) triggers both innate and adaptive immune responses, including protective CD8⁺ αβT cells (CD8T) that contributes to the control of the infection. In addition to CD8T restricted by classical HLA class Ia molecules, HCMV also triggers CD8T recognizing peptides from the HCMV UL40 leader peptide and restricted by HLA-E molecules (HLA-E_UL40 CD8T). This study investigated the frequency, phenotype and functions of HLA-E_UL40 CD8T in comparison to the immunodominant HLA-A2_pp65 CD8T upon acute (primary or secondary infection) or chronic infection in kidney transplant recipients (KTR) and in seropositive (HCMV⁺) healthy volunteer (HV) hosts. The frequency of hosts with detected HLA-E_UL40 CD8T was similar after a primary infection (24%) and during viral latency in HCMV+ HV (26%) and equal to the frequency of HLA-A2_pp65 CD8T cells in both conditions (29%). Both CD8T subsets vary from 0.1% to >30% of total circulating CD8T according to the host. Both HLA-E_UL40 and HLA-A2_pp65 CD8T display a phenotype specific of CD8⁺ TEMRA (CD45RA⁺/CCR7^-) but HLA-E_UL40 CD8T express distinctive level for CD3, CD8 and CD45RA. Tim3, Lag-3, 4-1BB, and to a lesser extend 2B4 are hallmarks for T cell priming post-primary infection while KLRG1 and Tigit are markers for restimulated and long lived HCMV-specific CD8T responses. These cell markers are equally expressed on HLA-E_UL40 and HLA-A2_pp65 CD8T. In contrast, CD56 and PD-1 are cell markers discriminating memory HLA-E- from HLA-A2-restricted CD8T. Long lived HLA-E_UL40 display higher proliferation rate compared to HLA-A2_pp65 CD8T consistent with elevated CD57 expression. Finally, a comparative immunoprofiling indicated that HLA-E_UL40 CD8T, divergent from HLA-A2_pp65 CD8T, share the expression of CD56, CD57, NKG2C, CD158 and the lack of PD-1 with NKG2C⁺CD57+ NK and δ2^-γδT cells induced in response to HCMV and thus defines a common immunopattern for these subsets.

Engineering γδ T Cells: Recognizing and Activating on Their Own Way

Adoptive cell therapy (ACT) with engineered T cells has emerged as a promising strategy for the treatment of malignant tumors. Among them, there is great interest in engineered γδ T cells for ACT. With both adaptive and innate immune characteristics, γδ T cells can be activated by γδ TCRs to recognize antigens in a MHC-independent manner, or by NK receptors to recognize stress-induced molecules. The dual recognition system enables γδ T cells with unique activation and cytotoxicity profiles, which should be considered for the design of engineered γδ T cells. However, the current designs of engineered γδ T cells mostly follow the strategies that used in αβ T cells, but not making good use of the specific characteristics of γδ T cells. Therefore, it is no surprising that current engineered γδ T cells in preclinical or clinical trials have limited efficacy. In this review, we summarized the patterns of antigen recognition of γδ T cells and the features of signaling pathways for the functions of γδ T cells. This review will additionally discuss current progress in engineered γδ T cells and provide insights in the design of engineered γδ T cells based on their specific characteristics.

A Quantitative Systems Pharmacology Model of T Cell Engager Applied to Solid Tumor

Cancer immunotherapy has recently drawn remarkable attention as promising results in the clinic have shown its ability to improve the overall survival, and T cells are considered to be one of the primary effectors for cancer immunotherapy. Enhanced and restored T cell tumoricidal activity has shown great potential for killing cancer cells. Bispecific T cell engagers (TCEs) are a growing class of molecules that are designed to bind two different antigens on the surface of T cells and cancer cells to bring them in close proximity and selectively activate effector T cells to kill target cancer cells. New T cell engagers are being investigated for the treatment of solid tumors. The activity of newly developed T cell engagers showed a strong correlation with tumor target antigen expression. However, the correlation between tumor-associated antigen expression and overall response of cancer patients is poorly understood. In this study, we used a well-calibrated quantitative systems pharmacology (QSP) model extended to bispecific T cell engagers to explore their efficacy and identify potential biomarkers. In principle, patient-specific response can be predicted through this model according to each patient's individual characteristics. This extended QSP model has been calibrated with available experimental data and provides predictions of patients' response to TCE treatment.

T Cell Reprogramming Against Cancer

Advances in academic and clinical studies during the last several years have resulted in practical outcomes in adoptive immune therapy of cancer. Immune cells can be programmed with molecular modules that increase their therapeutic potency and specificity. It has become obvious that successful immunotherapy must take into account the full complexity of the immune system and, when possible, include the use of multifactor cell reprogramming that allows fast adjustment during the treatment. Today, practically all immune cells can be stably or transiently reprogrammed against cancer. Here, we review works related to T cell reprogramming, as the most developed field in immunotherapy. We discuss factors that determine the specific roles of αβ and γδ T cells in the immune system and the structure and function of T cell receptors in relation to other structures involved in T cell target recognition and immune response. We also discuss the aspects of T cell engineering, specifically the construction of synthetic T cell receptors (synTCRs) and chimeric antigen receptors (CARs) and the use of engineered T cells in integrative multifactor therapy of cancer.

A Translational Quantitative Systems Pharmacology Model for CD3 Bispecific Molecules: Application to Quantify T Cell-Mediated Tumor Cell Killing by P-Cadherin LP DART®

CD3 bispecific antibody constructs recruit cytolytic T cells to kill tumor cells, offering a potent approach to treat cancer. T cell activation is driven by the formation of a trimolecular complex (trimer) between drugs, T cells, and tumor cells, mimicking an immune synapse. A translational quantitative systems pharmacology (QSP) model is proposed for CD3 bispecific molecules capable of predicting trimer concentration and linking it to tumor cell killing. The model was used to quantify the pharmacokinetic (PK)/pharmacodynamic (PD) relationship of a CD3 bispecific targeting P-cadherin (PF-06671008). It describes the disposition of PF-06671008 in the central compartment and tumor in mouse xenograft models, including binding to target and T cells in the tumor to form the trimer. The model incorporates T cell distribution to the tumor, proliferation, and contraction. PK/PD parameters were estimated for PF-06671008 and a tumor stasis concentration (TSC) was calculated as an estimate of minimum efficacious trimer concentration. TSC values ranged from 0.0092 to 0.064 pM across mouse tumor models. The model was translated to the clinic and used to predict the disposition of PF-06671008 in patients, including the impact of binding to soluble P-cadherin. The predicted terminal half-life of PF-06671008 in the clinic was approximately 1 day, and P-cadherin expression and number of T cells in the tumor were shown to be sensitive parameters impacting clinical efficacy. A translational QSP model is presented for CD3 bispecific molecules, which integrates in silico, in vitro and in vivo data in a mechanistic framework, to quantify and predict efficacy across species.

Distinct phenotype and function of circulating Vδ1+ and Vδ2+ γδT-cells in acute and chronic hepatitis B

Hepatitis B virus (HBV) persists with global and virus-specific T-cell dysfunction, without T-cell based correlates of outcomes. To determine if γδT-cells are altered in HBV infection relative to clinical status, we examined the frequency, phenotype and function of peripheral blood Vδ1⁺ and Vδ2⁺γδT-cells by multi-parameter cytometry in a clinically diverse North American cohort of chronic hepatitis B (CHB), acute hepatitis B (AHB) and uninfected control subjects. We show that circulating γδT-cells were comprised predominantly of CD3^hiCD4^- Vδ2⁺γδT-cells with frequencies that were 2–3 fold higher among Asian than non-Asian Americans and inversely correlated with age, but without differences between CHB, AHB and control subjects. However, compared to control subjects, CHB was associated with increased Tbet^hiEomes^dim phenotype in Vδ2⁺γδT-cells whereas AHB was associated with increased Tbet^hiEomes^dim phenotype in Vδ1⁺γδT-cells, with significant correlations between Tbet/Eomes expression in γδT-cells with their expression of NK and T-cell activation and regulatory markers. As for effector functions, IFNγ/TNF responses to phosphoantigens or PMA/Ionomycin in Vδ2⁺γδT-cells were weaker in AHB but preserved in CHB, without significant differences for Vδ1⁺γδT-cells. Furthermore, early IFNγ/TNF responses in Vδ2⁺ γδT-cells to brief PMA/Ionomycin stimulation correlated inversely with serum ALT but not HBV DNA. Accordingly, IFNγ/TNF responses in Vδ2⁺γδT-cells were weaker in patients with CHB with hepatitis flare compared to those without hepatitis flares, and this functional deficit persisted beyond clinical resolution of CHB flare. We conclude that circulating γδT-cells show distinct activation and differentiatiation in acute and chronic HBV infection as part of lymphoid stress surveillance with potential role in clinical outcomes.

We examined circulating γδT-cells in a North American cohort with chronic hepatitis B (CHB) and acute hepatitis B (AHB) compared to uninfected control subjects. While frequencies and composition of circulating γδT-cells were preserved in AHB and CHB, γδT-cells showed distinct and innate phenotypes based on the expression of Tbet/Eomes in association with various NK/T-cell markers. Notably, IFNγ/TNF responses to phosphoantigens and PMA/Ionomycin were preserved in CHB, but weaker in AHB compared to uninfected control subjects, in association with NKG2A/CD94 but not PD1. Furthermore, early IFNγ/TNF responses in Vδ2⁺ γδT-cells to brief PMA/Ionomycin stimulation showed significant inverse correlations with serum alanine aminotransferase, a measure of hepatocellular injury, and were persistently deficient in CHB subjects with hepatitis flare compared to those without such flares. Finally, Vδ2⁺ γδT-cells were significantly enriched for Tbet^hiEomes^dim phenotype in associations with their expression of NK and T-cell activation and regulatory markers, suggesting a role for Tbet in γδT-cell differentiation and function. We conclude that circulating γδT-cells show distinct activation and differentiation in acute and chronic HBV infection as part of lymphoid stress surveillance with potential role in clinical outcomes.

A novel antibody-TCR (AbTCR) platform combines Fab-based antigen recognition with gamma/delta-TCR signaling to facilitate T-cell cytotoxicity with low cytokine release

The clinical use of genetically modified T-cell therapies has led to unprecedented response rates in leukemia and lymphoma patients treated with anti-CD19 chimeric antigen receptor (CAR)-T. Despite this clinical success, FDA-approved T-cell therapies are currently limited to B-cell malignancies, and challenges remain with managing cytokine-related toxicities. We have designed a novel antibody-T-cell receptor (AbTCR) platform where we combined the Fab domain of an antibody with the γ and δ chains of the TCR as the effector domain. We demonstrate the ability of anti-CD19-AbTCR-T cells to trigger antigen-specific cytokine production, degranulation, and killing of CD19-positive cancer cells in vitro and in xenograft mouse models. By using the same anti-CD19 binding moiety on an AbTCR compared to a CAR platform, we demonstrate that AbTCR activates cytotoxic T-cell responses with a similar dose-response as CD28/CD3ζ CAR, yet does so with less cytokine release and results in T cells with a less exhausted phenotype. Moreover, in comparative studies with the clinically validated CD137 (4-1BB)-based CAR, CTL019, our anti-CD19-AbTCR shows less cytokine release and comparable tumor inhibition in a patient-derived xenograft leukemia model.

Inhibition of allogeneic cytotoxic T cell (CD8+) proliferation via polymer-induced Treg (CD4+) cells

T cell-mediated immune rejection remains a barrier to successful transplantation. Polymer-based bioengineering of cells may provide an effective means of preventing allorecognition and the proliferation of cytotoxic (CD8⁺) T lymphocytes (CTL). Using MHC-disparate murine splenocytes modified with succinimidyl valerate activated methoxypoly(ethylene glycol) [SVA-mPEG] polymers, the effects of leukocyte immunocamouflage on CD8⁺ and CD4⁺ alloproliferation and T regulatory (Treg) cell induction were assessed in a mixed lymphocyte reaction (MLR) model. Polymer-grafting effectively camouflaged multiple leukocyte markers (MHC class I and II, TCR and CD3) essential for effective allorecognition. Consequent to the polymer-induced immunocamouflage of the cell membrane, both CD8⁺ and CD4⁺ T cell alloproliferation were significantly inhibited in a polymer dose-dependent manner. The loss of alloproliferation correlated with the induction of Treg cells (CD4⁺CD25⁺Foxp3⁺). The Tregs, surprisingly, arose primarily via differentiation of naive, non-proliferating, CD4⁺ cells. Of biologic importance, the polymer-induced Treg were functional and exhibited potent immunosuppressive activity on allogeneic CTL proliferation. These results suggest that immunocamouflage-mediated attenuation of alloantigen-TCR recognition can prevent the tissue destructive allogeneic CD8⁺ T cell response, both directly and indirectly, through the generation/differentiation of functional Tregs. Immunocamouflage induced tolerance could be clinically valuable in attenuating T cell-mediated transplant rejection and in the treatment of autoimmune diseases.

STATEMENT OF SIGNIFICANCE

While our previous studies have demonstrated that polymer-grafting to MHC disparate leukocytes inhibits CD4⁺ cell proliferation, the effects of PEGylation on the alloproliferation of CD8⁺ cytotoxic T cells (CTL) was not examined. As shown here, PEGylation of allogeneic leukocytes prevents the generation of the CTL response responsible for acute rejection. The loss of CTL proliferation is consequent to the polymer-based attenuation of allorecognition and the induction of T regulatory cells (Tregs). Interestingly, the Tregs are primarily generated via the differentiation of non-proliferating naive T cells. Importantly, the Tregs are functional and effectively induce a tolerogenic environment when transferred to an alloresponsive environment. The use of polymer-modified leukocytes provides a unique approach to effectively maximize the biologic production of functional Tregs both in vitro and in vivo. By using this approach it may be possible to attenuate unwanted alloresponses (e.g., graft rejection) or to treat autoimmune diseases.

Activated skin γδ T-cells regulate T-cell infiltration of the wound site after burn

Burn induces an immunopathological response involving multiple immune cell types that includes γδ T-cells. Nonetheless, the role of γδ T-cells at the wound site after burn is not clearly defined. Wild type and γδ T-cell receptor deficient (δ TCR(-/-)) mice were subjected to a major burn or sham procedure. At 1-7 d thereafter, skin samples were collected and T-cell populations analyzed. The majority of T-cells in the skin of sham mice were γδ T-cells. After burn, however, an increase in the total T-cells was observed at the wound site and these cells were predominantly αβ T-cells. Their influx was γδ T-cell dependent, as it was markedly reduced in injured δ TCR(-/-) mice. Burn wound γδ T-cells were activated with increased expression of TLRs and CD69. In contrast, the infiltrating αβ T-cells TLR and CD69 expressions were attenuated after burn. Thus, burn is associated with of γδ T-cell activation at the injury site, which initiates a massive infiltration of the wound with αβ T-cells that likely facilitate the transition from the inflammatory to the proliferative phase of healing.

Human CD3γ, but not CD3δ, haploinsufficiency differentially impairs γδ versus αβ surface TCR expression

Background

The T cell antigen receptors (TCR) of αβ and γδ T lymphocytes are believed to assemble in a similar fashion in humans. Firstly, αβ or γδ TCR chains incorporate a CD3δε dimer, then a CD3γε dimer and finally a ζζ homodimer, resulting in TCR complexes with the same CD3 dimer stoichiometry. Partial reduction in the expression of the highly homologous CD3γ and CD3δ proteins would thus be expected to have a similar impact in the assembly and surface expression of both TCR isotypes. To test this hypothesis, we compared the surface TCR expression of primary αβ and γδ T cells from healthy donors carrying a single null or leaky mutation in CD3G (γ^+/−) or CD3D (δ^+/−, δ^+/leaky) with that of normal controls.

Results

Although the partial reduction in the intracellular availability of CD3γ or CD3δ proteins was comparable as a consequence of the mutations, surface TCR expression measured with anti-CD3ε antibodies was significantly more decreased in γδ than in αβ T lymphocytes in CD3γ^+/− individuals, whereas CD3δ^+/− and CD3δ^+/leaky donors showed a similar decrease of surface TCR in both T cell lineages. Therefore, surface γδ TCR expression was more dependent on available CD3γ than surface αβ TCR expression.

Conclusions

The results support the existence of differential structural constraints in the two human TCR isotypes regarding the incorporation of CD3γε and CD3δε dimers, as revealed by their discordant surface expression behaviour when confronted with reduced amounts of CD3γ, but not of the homologous CD3δ chain. A modified version of the prevailing TCR assembly model is proposed to accommodate these new data.

Effective flow cytometric phenotyping of cells using minimal amounts of antibody

Here we introduce a modified antibody staining method that uses up to 80% less antibody for flow cytometry. We demonstrate this method for the detection of antigens expressed at high, moderate, or low levels in mouse and rat lymphocytes as well as mouse mammary epithelial cells. We obtained reproducibly accurate results for the detection of up to seven parameters for activation induced-proliferation, cell cycle analysis, and phenotyping of cell-surface and intracellular antigens.

Analyses of the PRF1 gene in individuals with hemophagocytic lymphohystiocytosis reveal the common haplotype R54C/A91V in Colombian unrelated families associated with late onset disease

Familial hemophagocytic lymphohistiocytosis (FHL), is a rare autosomal recessive disorder characterized by an impairment of cytotoxic cells and uncontrolled activation of macrophages. This study presents the first description of four patients with FHL type 2 in Latin America. Patient 1 fulfilled the disease diagnostic criteria since 2 months of age, whereas patients 2, 3 and 4 exhibited the typical manifestations of the disease only later in their childhood. The PRF1 genetic analysis in these patients revealed two previously reported mutations: L17fsx50 and R54C. Interestingly, seven out of the 8 alleles evaluated here in patients carried the haplotype R54C/A91V, suggesting that this is a highly frequent FHL type 2 allele in Colombia. This haplotype confers residual cytotoxic function leading to late onset disease. Therefore, this report highlights the remarkable complexity of FHL diagnostic, emphasizing the importance of the genetic characterization of the disease.

Potential selective advantage mechanism for polymorphic genetics in celiac disease

Celiac Disease is a common cause of morbidity in the developed world but its etiology is still unknown. Considering that Celiac Disease was first documented in Scandinavian Europe, a population exposed to a high fat diet, perhaps the polymorphic genetics of the disease provides balanced polymorphism against this environmental stimulus. Celiac Disease has been associated with higher levels of the T cell receptor (TCR)γδ, receptors that have played a greater role in recognizing microbial lipids. Furthermore, obesity has been associated with lower levels of CD-3 expression while Celiac Disease has been associated with an up regulation of this molecule. These finding might help to describe a balance polymorphism that exists in Celiac Disease as well as an etiological factor that lead to the development of the disease.

Variability of CD3 membrane expression and T cell activation capacity

BACKGROUND

AlphabetaT cells have a wide distribution of CD3 membrane density. The aim of this article was to evaluate the significance of the CD3 differential expression on T cell subsets. Analysis was performed on healthy donors and renal transplant patients by flow cytometry. The results obtained are: (1) CD3 expression was widely distributed (CV = 38.3 +/- 3.1 to 43 +/- 2.3%). (2) The CD4, CD8, CD45 and forward scatter were similarly distributed. (3) The diversity of CD3 expression was directly related to the clonotypes: gamma9, non gamma9 from gammadeltaT cells and Vbeta clonotype from alphabetaT cells (e.g., Vbeta3FITC 7,980 +/- 1,628 Vbeta8PE: Vbeta20-FITC 11,768 +/- 1,510). (4) Using a computer simulation, we could confirm differential kinetics of T cell activation according to the initial parameters. Finally, in vitro activation was significantly higher on Vbeta8 and Vbeta9 (high CD3) compared with Vbeta2 and Vbeta3 (low CD3, P = 0.040-0.0003). In conclusion, T cells have highly heterogeneous CD3 expression, possibly predetermined and with clear functional significance.

A practical approach to the flow cytometric detection and diagnosis of T-cell lymphoproliferative disorders

The flow cytometric analysis of T-cell malignancies is difficult due to the heterogeneity of T-cells and the lack of convenient methods to detect T-cell clonality. Neoplastic T-cells are most often detected by their altered level of surface antigen expression, and detection requires an extensive knowledge of the phenotype of normal T-lymphocytes. This review focuses on the methods to distinguish malignant T-cells from their normal counterparts and the phenotypic features of the T-cell lymphoproliferative disorders.

Immunophenotypic attributes of benign peripheral blood gammadelta T cells and conditions associated with their increase

CONTEXT

In comparison to alphabeta T cells, little is known about the immunophenotype of healthy peripheral blood gammadelta T cells or about conditions associated with expansion of this usually minor T-cell subset.

OBJECTIVE

To study the immunophenotype of increased nonneoplastic peripheral blood gammadelta T cells and to determine clinical conditions associated with this laboratory finding.

DESIGN

Flow cytometric T-cell phenotyping studies performed on 352 consecutive peripheral blood specimens were reviewed, and 62 cases (18%) in which gammadelta T cells comprised either more than 5% of the total lymphocytes or had an absolute count of more than 200 cells per muL or both, were studied further. Clinical data were available from 36 cases.

RESULTS

The gammadelta T cells often had an immunophenotype distinct from the alphabeta T cells, with differences in CD5 expression as the most common (n = 17), followed by differences in CD3 (n = 6) and CD7 (n = 3). CD16 coexpression by the gammadelta T cells was also frequent (n = 20). In 28 (78%) of 36 cases, there were one or more associated conditions: infection/inflammatory disease (n = 18), autoimmune disease (n = 9), lymphoproliferative disorder (n = 6), and splenectomy (n = 3).

CONCLUSIONS

Circulating gammadelta T cells are immunophenotypically distinct from alphabeta T cells, and mild increases in these cells are not uncommon and may be associated with immune system activation and splenectomy. Recognition of this phenomenon is important because reactive gammadelta T cells can exhibit distinctive immunophenotypic features that are also encountered in neoplastic conditions, such as T-cell large granular lymphocytic leukemia.

Both percentage of gammadelta T lymphocytes and CD3 expression are reduced during septic shock

OBJECTIVE

The mechanisms involved during sepsis-induced immunosuppression are far from being extensively established. The objective of the present study was to investigate whether two characteristics of T cells were altered in this situation: the percentage of circulating gammadelta T lymphocytes and the level of CD3 expression on T lymphocytes.

DESIGN

Observational study.

SETTING

Adult intensive care units in a university hospital.

PATIENTS

Patients with septic shock (n = 21) and healthy individuals (n = 21).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In patients, we first observed the decreased percentage of gammadelta T lymphocytes in peripheral blood (1% [0.7-3.1], median [interquartile range]) in comparison with healthy individuals (3.5% [2.1-4.8]). Regarding CD3, we measured a highly significant decrease of its expression on both alphabeta and gammadelta T lymphocytes from patients (p < .005), whereas the CD3 mean fluorescence intensities ratio (gammadelta/alphabeta) was not affected: 2.2 [2.1-2.4] and 2.1 [1.9-2.3] in healthy individuals and septic patients, respectively. The magnitude in the decrease of CD3 expression was thus similar in alphabeta and gammadelta cells, suggesting a common down-regulation mechanism for both T-cell lineages.

CONCLUSIONS

Combined with a reduced percentage of monocytes expressing human leukocyte antigen-DR, a reduced CD3 expression may be involved in the failure of antigen presentation depicted after septic shock, whereas the diminished percentage of circulating gammadelta T cells could be partly responsible for the elevated incidence of secondary infections. These two observations constitute additional pieces of the complex puzzle of sepsis-induced immunosuppression.

Isolation and characterization of human antigen-specific TCR alpha beta+ CD4(-)CD8- double-negative regulatory T cells

Down-regulation of immune responses by regulatory T (Treg) cells is an important mechanism involved in the induction of tolerance to allo-antigens (Ags). Recently, a novel subset of Ag-specific T-cell receptor (TCR)alpha beta+ CD4(-)CD8- (double-negative [DN]) Treg cells has been found to be able to prevent the rejection of skin and heart allografts by specifically inhibiting the function of antigraft-specific CD8+ T cells. Here we demonstrate that peripheral DN Treg cells are present in humans, where they constitute about 1% of total CD3+ T cells, and consist of both naive and Ag-experienced cells. Similar to murine DN Treg cells, human DN Treg cells are able to acquire peptide-HLA-A2 complexes from antigen-presenting cells by cell contact-dependent mechanisms. Furthermore, such acquired peptide-HLA complexes appear to be functionally active, in that CD8+ T cells specific for the HLA-A2-restricted self-peptide, Melan-A, became sensitive to apoptosis by neighboring DN T cells after acquisition of Melan-A-HLA-A2 complexes and revealed a reduced proliferative response. These results demonstrate for the first time that a sizable population of peripheral DN Treg cells, which are able to suppress Ag-specific T cells, exists in humans. DN Treg cells may serve to limit clonal expansion of allo-Ag-specific T cells after transplantation.

Immune-enhancing effects of growth hormone-releasing hormone delivered by plasmid injection and electroporation

Growth hormone-releasing hormone (GHRH) is a hypothalamic hormone with both direct and indirect functions in the maintenance of immune status under physiological and pathological conditions. In this study, 52 Holstein heifers were evaluated for the effects of a plasmid-mediated GHRH treatment on their immune function and on the morbidity and mortality of treated animals. In the third trimester of pregnancy, 32 heifers received 2.5 mg of a myogenic GHRH-expressing plasmid by intramuscular injection followed by electroporation, while 20 heifers were used as controls. No adverse effects were associated with either the plasmid delivery or GHRH expression. At 18 days after plasmid administration, GHRH-treated animals had increased numbers of CD2(+) alphabeta T-cells (P < 0.004), CD25(+)CD4(+) cells (P < 0.0007), and CD4(+)CD45R(+) cells (P < 0.016) compared to controls. These increases were maintained long term after treatment and correlated with plasmid expression. At 300 days post-GHRH therapy, CD45R(+)/CD45R0(-) naïve lymphocytes were significantly increased in frequency (P < 0.05). Natural killer lymphocytes (CD3(-)CD2(+)) were also increased. As a consequence of improved health status, body condition scores of treated animals improved (3.55 vs. 3.35, P < 0.0001). Hoof pathology was also reduced with treatment. The mortality of heifers was decreased (3% vs. 20% in controls, P < 0.003). Collectively, these results indicate that the myogenic GHRH plasmid can be successfully electrotransferred into a 500-kg mammal and expressed for prolonged periods of time, ensuring physiological levels of GHRH. The plasmid injection followed by electroporation could prove an efficient method for the systemic production of therapeutic proteins and may provide a useful means for basic research in relevant animal models.

Response of bovine gammadelta T cells to activation through CD3

Since the T cell receptor of gammadelta T cells is associated with CD3 molecules, it is a reasonable postulate that signal transduction through CD3 would occur in gammadelta T cells as it does in alphabeta T cells. However, while a small percentage of bovine gammadelta T cells divided in cultures of peripheral blood mononuclear cells (PBMCs) in response to stimulation by anti-CD3 monoclonal antibody (mAb) the majority of viable gammadelta T cells at the end of the culture period had not. This was assessed by carboxyfluorescein succinimidyl ester (CFSE) loading of cells and flow cytometric analysis here and previously [Res. Vet. Sci. 69 (2000) 275]. When intracytoplasmic staining for interferon-gamma (IFN-gamma) was also used here to assess activation through CD3, a small proportion of gammadelta T cells (approximately 14%) produced IFN-gamma during the first 4 h of culture and by 72 h of culture that number had doubled. By comparison, a much larger proportion of CD4 and CD8 T cells stimulated with anti-CD3 mAb divided and although the percentage of CD4 and CD8 T cells that produced IFN-gamma at 4 h was similar to that of gammadelta T cells, by 72 h the majority of CD4 and CD8 T cells were IFN-gamma(+). Addition of IL-2 did not increase the proportion of gammadelta T cells that responded to anti-CD3 stimulation by cell division. To test the hypothesis that gammadelta T cells were inhibited from responding by other mononuclear cell populations within PBMC, monocytes were removed from the PBMC or gammadelta T cells were purified by magnetic-bead sorting. Only a small distinct population of the sorted cells underwent multiple cell divisions in response to anti-CD3 mAb and removal of monocytes resulted in only a moderate increase in gammadelta T cell replication. The anti-CD3 mAb stimulation system may provide a useful system to evaluate the difference in the requirements for activation and clonal expansion for gammadelta T cells versus alphabeta T cells.