Dietary gluten triggers concomitant activation of CD4+ and CD8+ αβ T cells and γδ T cells in celiac disease

Celiac disease is an intestinal autoimmune disease driven by dietary gluten and gluten-specific CD4⁺ T-cell responses. In celiac patients on a gluten-free diet, exposure to gluten induces the appearance of gluten-specific CD4⁺ T cells with gut-homing potential in the peripheral blood. Here we show that gluten exposure also induces the appearance of activated, gut-homing CD8⁺ αβ and γδ T cells in the peripheral blood. Single-cell T-cell receptor sequence analysis indicates that both of these cell populations have highly focused T-cell receptor repertoires, indicating that their induction is antigen-driven. These results reveal a previously unappreciated role of antigen in the induction of CD8⁺ αβ and γδ T cells in celiac disease and demonstrate a coordinated response by all three of the major types of T cells. More broadly, these responses may parallel adaptive immune responses to viral pathogens and other systemic autoimmune diseases.     

Cross-dressed CD8α+/CD103+ dendritic cells prime CD8+ T cells following vaccination

Activation of naïve cluster of differentiation (CD)8⁺ cytotoxic T lymphocytes (CTLs) is a tightly regulated process, and specific dendritic cell (DC) subsets are typically required to activate naive CTLs. Potential pathways for antigen presentation leading to CD8⁺ T-cell priming include direct presentation, cross-presentation, and cross-dressing. To distinguish between these pathways, we designed single-chain trimer (SCT) peptide–MHC class I complexes that can be recognized as intact molecules but cannot deliver antigen to MHC through conventional antigen processing. We demonstrate that cross-dressing is a robust pathway of antigen presentation following vaccination, capable of efficiently activating both naïve and memory CD8⁺ T cells and requires CD8α⁺/CD103⁺ DCs. Significantly, immune responses induced exclusively by cross-dressing were as strong as those induced exclusively through cross-presentation. Thus, cross-dressing is an important pathway of antigen presentation, with important implications for the study of CD8⁺ T-cell responses to viral infection, tumors, and vaccines.Professional antigen-presenting cells (APCs) are typically required to activate naïve cluster of differentiation (CD)8⁺ T cells, either by direct priming or cross-priming. In direct priming, infected (viral infection) or directly transfected (DNA vaccination) APCs synthesize the foreign antigen and use endogenous MHC class I pathways of antigen presentation to present antigen and prime CD8⁺ T cells. In cross-priming, APCs are able to capture, process, and present exogenous antigen onto MHC class I molecules through a process known as cross-presentation (1). Cross-priming has been shown to be an essential pathway for immunity to many viral infections and tumors. Although the pathways that lead to cross-presentation remain incompletely understood, increasing evidence suggests that only certain dendritic cell (DC) subsets are efficient in this process.Cross-dressing involves the transfer of intact MHC class I/peptide complexes between cells without the requirement for further processing, representing an alternative pathway of indirect antigen presentation (2, 3). Although cross-dressed DCs can activate memory CD8⁺ T cells following viral infection in vivo (4), it remains unclear whether cross-dressing can prime naïve CD8⁺ T-cell responses, what DC subtypes are required to prime CD8⁺ T cells by cross-dressing, and how robust this pathway is compared with traditional pathways of indirect antigen presentation. These questions must be addressed before the physiologic relevance of cross-dressing can be evaluated in context.To address these questions, we have taken advantage of Batf3-deficient mice and engineered MHC class I single chain trimer (SCT) constructs. Batf3^−/− mice have a selective loss of CD8α⁺ and CD103⁺ DCs, without abnormalities in other hematopoietic cell types or architecture (5). DCs from Batf3^−/− mice are deficient in cross-presentation, and cytotoxic T lymphocyte (CTL) responses to viral infection and syngeneic tumors are impaired in Batf3^−/− mice. Thus, Batf3^−/− mice represent a valuable model system to study cross-presentation, cross-dressing, and the role of CD8α⁺/CD103⁺ DCs following DNA or cellular vaccination. We have previously engineered completely assembled MHC class I SCT whereby all three components of the complex (heavy chain, β₂m, and peptide) are attached by flexible linkers (6). Through progressive molecular engineering, even peptides with low binding affinities can be successfully anchored in the peptide binding groove by a disulfide trap between the first linker and the heavy chain (7–9). Using these experimental tools, we demonstrate that cross-dressing is a robust pathway of antigen presentation following DNA and cellular vaccination, capable of priming naïve and memory CD8⁺ T cells. In addition, we demonstrate that CD8α⁺/CD103⁺ DCs are required to prime CTLs by cross-dressing.     

A subpopulation of CD24⁺ cells in colon cancer cell lines possess stem cell characteristics

Cancer stem cells (CSCs) have been shown to contribute to the resistance and relapse in a range of cancer types such as breast cancer and glioma. However, colon cancer stem cells remain poorly characterized. Here we reported that CD24+ subpopulation in colon cancer cell lines HCT116 and SW480 exhibited cancer stem cell-like characteristics. Using flow cytometry candidate CSCs markers were selected after initial screening of known CSCs markers from other types of cancer on colon cancer cell lines HCT116, SW480 and HT29. CD24 was expressed in the minority of bulk cell population of HCT116 and SW480 cell lines. Moreover, functional tests demonstrated that CD24+ cells exhibited enhanced chemotherapy-resistance, self-renewal and tumorigenic capacity both in vitro and in vivo, compared to CD24- subpopulations. These results suggest that CD24+ subpopulation in colon cancer cell lines HCT116 and SW480 exhibits CSCs like characteristics, and represents a nice model to study and develop effective strategies to overcome chemo-resistance and relapse of colon cancer.     

In vivo dynamics of T cell activation,proliferation, and death in HIV-1 infection: why are CD4+ but not CD8+ T cells depleted?

Deuterated glucose labeling was used to measure the in vivo turnover of T lymphocytes. A realistic T cell kinetic model, with populations of resting and activated T cells, was fitted to d-glucose labeling data from healthy and HIV-1-infected individuals before and after antiretroviral treatment. Our analysis highlights why HIV-1 infection, which increases the fraction of both CD4(+) and CD8(+) T lymphocytes that are proliferating (Ki67(+)), leads to CD4 but not CD8 depletion. We find that HIV-1 infection tends to increase the rates of death and proliferation of activated CD4(+) T cells, and to increase the rate at which resting CD4 T cells become activated, but does not increase the fraction of activated CD4(+) T cells, consistent with their preferential loss in HIV-1-infected individuals. In contrast, HIV-1 infection does not lead to an increase in proliferation or death rates of activated CD8(+) T cells, but did increase the fraction of activated CD8(+) T cells, consistent with these cells remaining in an activated state longer and undergoing more rounds of proliferation than CD4(+) T cells. Our results also explain why telomeres shorten in CD8(+) cells, but not in CD4(+) cells of HIV-1-infected patients, compared with age-matched controls.     

Recently primed CD8+ T cells entering the liver induce hepatocytes to interact with naïve CD8+ T cells in the mouse

Large number of T cells traffic through the liver. In order to examine the effects of such traffic on the phenotype of hepatocytes, we vaccinated mice using DNA vaccines encoding antigens with MHC class I-binding epitopes. Small numbers of activated CD8(+) T blasts (10(5)-10(6)/liver) changed the surface phenotype and cytokine expression profile of hepatocytes (HCs). HCs upregulate surface expression of major histocompatibility complex (MHC) class I molecules and CD1d but not MHC class II molecules Qa-1, CD80, CD86, CD54, or CD95; in addition, they expressed/secreted interleukin (IL)-10 and IL-4 but not IL-1, IL-6, IL-13, interferon (IFN)-gamma, tumor necrosis factor (TNF), IL-4, or IL-27 (i.e., they acquire the HC* phenotype). HCs* (but not HCs) induced specific activation, proliferation, and IFN-gamma, TNF, and IL-13 release of cocultured na?ve CD8(+) T cells. In contrast to the specific activation of na?ve CD8(+) T cells by dendritic cells (DCs), specific CD8(+) T cell activation by HC* was not down-modulated by IFN-alphabeta. Only recently activated CD8(+) T blasts (but not recently activated CD4(+) T blasts or activated cells of the innate immune system, including natural killer T [NKT] cells) induced the HC* phenotype that is prominent from day 10 to day 20 postvaccination (i.e., time points at which peak numbers of recently primed CD8(+) T blasts are found in the liver). In conclusion, recently activated CD8(+) T blasts that enter the liver postimmunization in small numbers can transiently modulate the phenotype of HC, allowing them to activate na?ve CD8(+) T cells with unrelated specificities.     

IL-7Rαlow memory CD8+ T cells are significantly elevated in patients with systemic lupus erythematosus

Objective. Human effector memory (EM) CD8(+) T cells include IL-7Rα(high) and IL-7Rα(low) cells with distinct cellular characteristics, including the expression of cytotoxic molecules. Both NK cells and the NK cell-associated molecule 2B4 that is expressed on CD8(+) T cells promote cytotoxicity. Here we analysed the expression of 2B4 on IL-7Rα(high) and IL-7Rα(low) EM CD8(+) T cells and its contribution to cytotoxicity. We also analysed the frequency of IL-7Rα(high) and IL-7Rα(low) EM CD8(+) T cells in patients with SLE or lupus and in healthy individuals given the potential role of cytotoxic CD8(+) T cells in the pathogenesis of lupus. Methods. We used flow cytometry to measure the expression of 2B4 on IL-7Rα(high) and IL-7Rα(low) EM CD8(+) T cells as well as the frequency of these cell populations in the peripheral blood of healthy individuals and patients with SLE. Also, 2B4-mediated cytotoxicity was quantitated in IL-7Rα(high) and IL-7Rα(low) EM CD8(+) T cells using target cells with CD48 antigen. Results. We found that IL-7Rα(high) EM CD8(+) T cells had higher levels of 2B4 expression compared with IL-7Rα(low) EM CD8(+) T cells. Triggering 2B4 enhanced the cytotoxic function of IL-7Rα(low) EM CD8(+) T cells against target cells. We also noticed that patients with SLE had an increased frequency of IL-7Rα(low) EM CD8(+) T cells that correlated with disease manifestation. Conclusion. Our findings show that SLE patients have increased IL-7Rα(low) EM CD8(+) T cells, possibly contributing to tissue damage through 2B4-mediated cytotoxicity.     

The dominant human conjunctival epithelial CD8αβ+ T cell population is maintained with age but the number of CD4+ T cells increases

The conjunctiva is a highly specialized ocular mucosal surface that, like other mucosa, houses a number of leukocyte populations. These leukocytes have been implicated in age-related inflammatory diseases such as dry-eye, but their phenotypic characteristics remain largely undetermined. Existing literature provides rudimentary data from predominantly immunohistochemical analyses of tissue sections, prohibiting detailed and longitudinal examination of these cells in health and disease. Using recovered cells from ocular surface impression cytology and flow cytometry, we examined the frequency of leukocyte subsets in human conjunctival epithelium and how this alters with age. Of the total CD45+ leukocyte population within the conjunctival epithelium, 87% [32–99] (median) [range] comprised lymphocytes, with 69% [47–90] identified as CD3 + CD56- T cells. In contrast to peripheral blood, the dominant conjunctival epithelial population was TCRαβ + CD8αβ + (80% [37–100]) with only 10% [0-56%] CD4+ cells. Whilst a significant increase in the CD4+ population was seen with age (r = 0.5; p < 0.01) the CD8+ population remained unchanged, resulting in an increase in the CD4:CD8 ratio (r = 0.5;p < 0.01). IFNγ expression was detectable in 18% [14–48] of conjunctival CD4+ T cells and this was significantly higher among older individuals (<35 years, 7[4–39] vs. >65 years, 43[20–145]; p < 0.05). The elevation of CD4+ cells highlights a potentially important age-related alteration in the conjunctival intra-epithelial leukocyte population, which may account for the vulnerability of the aging ocular surface to disease.     

β-Catenin in dendritic cells exerts opposite functions in cross-priming and maintenance of CD8+ T cells through regulation of IL-10

Recent studies have demonstrated that β-catenin in DCs serves as a key mediator in promoting both CD4⁺ and CD8⁺ T-cell tolerance, although how β-catenin exerts its functions remains incompletely understood. Here we report that activation of β-catenin in DCs inhibits cross-priming of CD8⁺ T cells by up-regulating mTOR-dependent IL-10, suggesting blocking β-catenin/mTOR/IL-10 signaling as a viable approach to augment CD8⁺ T-cell immunity. However, vaccination of DC–β-catenin^−/− (CD11c-specific deletion of β-catenin) mice surprisingly failed to protect them against tumor challenge. Further studies revealed that DC–β-catenin^−/− mice were deficient in generating CD8⁺ T-cell immunity despite normal clonal expansion, likely due to impaired IL-10 production by β-catenin^−/− DCs. Deletion of β-catenin in DCs or blocking IL-10 after clonal expansion similarly led to reduced CD8⁺ T cells, suggesting that β-catenin in DCs plays a positive role in CD8⁺ T-cell maintenance postclonal expansion through IL-10. Thus, our study has not only identified mTOR/IL-10 as a previously unidentified mechanism for β-catenin–dependent inhibition of cross-priming, but also uncovered an unexpected positive role that β-catenin plays in maintenance of CD8⁺ T cells. Despite β-catenin’s opposite functions in regulating CD8⁺ T-cell responses, selectively blocking β-catenin with a pharmacological inhibitor during priming phase augmented DC vaccine-induced CD8⁺ T-cell immunity and improved antitumor efficacy, suggesting manipulating β-catenin signaling as a feasible therapeutic strategy to improve DC vaccine efficacy.As the initiators of antigen-specific immune responses, dendritic cells (DCs) play a central role in regulating both T-cell immunity and tolerance (1). β-Catenin, a major component in Wnt signaling pathway, has emerged as a key factor in DC differentiation and function (2). Previous studies have shown that β-catenin regulates DC-mediated CD4⁺ T-cell responses and promotes CD4⁺ T-cell tolerance in murine models of autoimmune diseases (3, 4). Consistently, activation of β-catenin in DCs has recently been shown to suppress CD8⁺ T-cell immunity in a DC-targeted vaccine model (5), suggesting that β-catenin in DCs might similarly serve as a tolerizing signal that shifts the balance between CD8⁺ T-cell immunity and tolerance. Although the underlying mechanisms of how β-catenin mediates CD8⁺ T-cell tolerance remain largely unclear, we have shown that activation of β-catenin in DCs genetically or induced by tumors suppresses CD8⁺ T-cell immunity by inhibiting cross-priming (5). Exploiting their ability to potentiate host effector and memory CD8⁺ T-cell responses, DC vaccines have emerged as a leading strategy for cancer immunotherapy (6). However, one major obstacle for their success is host DC-mediated immunosuppression (7–9). Given that cross-priming plays a major role in generating antitumor CD8⁺ T-cell immunity (7, 10), activation of β-catenin in DCs might be a key mechanism for tumors to achieve immunosuppression. Thus, manipulating β-catenin function in cross-priming might be a viable approach to overcome DC-mediated immunosuppression and improve DC vaccine efficacy. However, The underlying mechanisms of how β-catenin in DCs achieves immunosuppression, in particular how β-catenin negatively regulates cross-priming to suppress CD8⁺ T-cell immunity, remain poorly understood.Although the mechanisms for DC-mediated priming of antitumor CD8⁺ T cells through cross-presentation remain incompletely understood, DC subsets, DC maturation status and cytokines have been shown to possibly affect their capacity in cross-priming (7, 10, 11). Although the role of cytokines in cross-priming has not been directly tested, cytokines as “signal 3” have been shown in principal to play a critical role in priming and effector differentiation of antitumor CD8⁺ T cells (12). β-Catenin in DCs has been shown to play a critical role in regulating cytokine induction (3, 4), thus suggesting that β-catenin might regulate DC cytokine production to achieve its effects on cross-priming.In this report we have identified mTOR/IL-10 signaling as a mechanism for β-catenin–dependent inhibition of cross-priming. Activation of β-catenin in DCs inhibited cross-priming of CD8⁺ T cells by up-regulating mTOR-dependent IL-10, and blocking mTOR or IL-10 led to restored cross-priming by β-catenin^active DCs. Surprisingly, mice with DC-specific deletion of β-catenin (DC–β-catenin^−/− mice) exhibited reduced antitumor immunity upon vaccination, despite the fact that deletion of β-catenin in DCs abrogated tumor-induced inhibition of cross-priming. Further studies showed that DC–β-catenin^−/− mice were deficient in generating CD8⁺ T-cell immunity despite normal clonal expansion, and β-catenin in DCs was required to maintain primed CD8⁺ T cells postclonal expansion. Thus, β-catenin in DCs exerts negative and positive functions in cross-priming and maintenance of CD8⁺ T cells, respectively. Importantly, we have demonstrated blocking β-catenin selectively at priming phase as a feasible strategy to improve DC vaccine efficacy.     

HIV-specific CD8+ T cells: serial killers condemned to die?

An increasing body of evidence supports a key role for cytotoxic CD8+ T cells (CTL) in controlling HIV infection. Although a vigorous HIV-specific CD8+ T cell response is raised during the primary infection, these cells ultimately fail to control virus and prevent disease progression. The failure of CTL to control HIV infection has been attributed to a number of strategies HIV employs to evade the immune system. Recently, intrinsic defects in the CTL themselves have been proposed to contribute to the failure of CTL to control HIV. HIV-specific CD8+ T cells differ in their effector/memory phenotype from other virus-specific CD8+ T cells indicating that their differentiation status differs. This altered differentiation may affect effector functions as well as homing properties of these cells. Other studies have indicated that activation of HIV-specific CTL may be impaired and this contributes to their dysfunction. The effector function of these CTL may also be affected. There are conflicting reports about their ability to kill, whereas IFNgamma production does not appear to be impaired in these cells. In this review we focus on recent work indicating that apoptosis may be an important mechanism through which HIV evades the CTL response. In particular, HIV-specific CD8+ T cells are highly susceptible to CD95/Fas-induced apoptosis. This leads to the hypothesis that virus-specific cytotoxic T cells can be eliminated upon binding CD95L/FasL on HIV-infected cells. Understanding the intrinsic defects of CTL in HIV infection could lead to new therapeutic strategies and optimized vaccination protocols that enhance the HIV-specific cytotoxic response.     

Associations of circulating CXCR3–PD-1+CD4+T cells with disease activity of systemic lupus erythematosus

Abstract

Objectives: Which helper CD4⁺ T cell subset contributes to autoantibodies generation and severity of end-organ involvement in lupus patients remains to be explored. Our research aims to investigate the roles of circulating Tfh (cTfh) cell subsets and corresponding CXCR5^– Th cells in lupus patients and their correlation with SLE disease activity index 2000 (SLEDAI).

Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from blood of systemic lupus erythematosus (SLE) patients as well as healthy donors. The proportion of Th cell subsets classified from cell surface markers (CD45RO, CXCR5, CXCR3, CCR6, PD-1, ICOS, and CCR7) is detected by flow cytometry.

Results: We found no difference in the frequency of CD45RO⁺CXCR5⁺CD4⁺ T cells between SLE patients and health controls. As previously reported, SLE patients showed an increase in the percentage of CXCR5⁺PD-1⁺, CXCR5⁺ICOS⁺PD-1⁺ and CXCR5⁺CCR7^loPD-1^hi cTfh subset, however, none of these populations had correlation with SLEDAI. Therefore, we further investigated the CXCR5^– subsets, and surprisingly we found that the frequency of CXCR3^–PD-1⁺ subset was correlated with SLEDAI, ds-DNA IgG, anti-nucleosome antibody, C3, and C4 independent of CXCR5. Consistently, CXCR3^–PD-1⁺CD45RO⁺CD4⁺T cells expressed factors associated with B-cell-help for the autoantibody production.

Conclusion: CXCR3^–PD-1⁺CD4⁺T cells are a sensitive indicator to assess SLE disease activity and might contribute B cell help and the generation of autoantibodies in patients.     

Characterization of naïve, memory and effector CD8+ T cells: effect of age

Aging is associated with progressive decline in T cell functions and increased frequency of infections, autoimmune phenomenon, and cancer. Memory T cells rapidly acquire effector functions to kill infected and malignant cells and/or inhibit their replication. Recently, memory T cells have been further classified into central and effector memory T cells (and early and intermediate T cells by some investigators). In aging, memory T cells are accumulated; however, these subpopulations of memory and effector T cells have not been fully characterized and changes in central memory and effector memory T cells in aged humans have not been described. In this article, we have further defined na?ve, central memory, effector memory, and effector CD8+ T cells in humans and their changes in aged humans.     

CD95-mediated apoptosis in naïve, central and effector memory subsets of CD4+ and CD8+ T cells in aged humans

Aging is associated with a decrease in naïve (T_N) and central memory (T_CM), and an accumulation of effector memory (T_EM and T_EMRA) T cell subsets. Previously, we have demonstrated an increased sensitivity of T_N and T_CM CD4+ and CD8+ T cells in aging to TNF-α-induced apoptosis. In this investigation, we examined whether similar differential sensitivity is applicable to CD95-mediated apoptosis. We show that T_N and T_CM CD4+ and CD8+ T cells from aged subjects are significantly more sensitive to CD95-mediated apoptosis. Increased apoptosis is associated with increased activation of caspase-8 and caspase-3. Both caspase-8 and caspase-3 inhibitors blocked CD95-mediated apoptosis and activation of caspase-8 and caspase-3 in T_N and T_CM CD4+ and CD8+ T cells. No significant difference was observed in apoptosis or in activation of caspase-8 and caspase-3 in T_EM and T_EMRA CD4+ and CD8+ T cells between young and aged subjects; both populations were relatively and comparably resistant to CD95-mediated apoptosis and caspase activation. No correlation was observed between the sensitivity/resistance of any of the subsets of CD4+ or CD8+T cells to CD95-mediated apoptosis and the expression of CD95. Our data suggest that increased CD95-mediated apoptosis of T_N and T_CM CD8+ and CD4+ T cells may play a role in their decline in human aging.     

Interleukin-10 expression: is there a neglected contribution of CD8+ T cells in rheumatoid arthritis joints?

OBJECTIVE: To search for RA specific processes among T cell accumulation, T cell activation, or cytokine expression in CD4+ and CD8+ synovial fluid (SF) T cells. METHODS: Flow cytometry of CD4+, CD8+, CD45RA+, CD45RO+, CD69 double or triple stained peripheral blood (PB) and SF T cells. IL-2, IL-10, and IFN-gamma expression was determined in PMA + ionomycin stimulated T cells on the single cell level. Concentrations of secreted IL-2, IL-4, IL-10, and IFN-gamma were quantified in the sera and synovial fluids by enzyme linked immunosorbent assay (ELISA). RESULTS: A preferential recruitment of CD45RO+ memory T cells was found for CD4+ helper T cells, and in similar also for CD8+ suppressor T cells. An elevated CD69 expression was detected in memory, but also in CD45RA+ naive CD4+ and CD8+ SF T cells, whilst IL-2 expression was only demonstrable in a minor proportion of T cells populations. Preferential recruitment of memory T cells, but incomplete activation of naive and memory, CD4+ and CD8+ T cells were in similar found in RA and control patients. In RA but not in the control patients, a relevant proportion of CD4+ and CD8+ PB and SF T cells expressed IL-10 and IFN-gamma. High concentrations of IL-10, that were correlated with the amounts of secreted TNF-alpha, were only detected in RA joints. CONCLUSION: Memory and naive T cell state of CD4+ and CD8+ T cell accumulates in the joints, and early T cell activation occur in similar patterns in RA and control patients. High IL-10 SF concentrations in contrast, and elevated percentages of IFN-gamma and IL-10 expressing CD4+ and CD8+ T cells in the PB and SF were characteristic for RA. Here, CD8+ T cells may contribute to high IL-10 concentrations in RA joints.     

Quantification of lymph node transit times reveals differences in antigen surveillance strategies of na?ve CD4+ and CD8+ T cells

Naïve T cells continually recirculate between blood and secondary lymphoid organs, scanning dendritic cells (DC) for foreign antigen. Despite its importance for understanding how adaptive immune responses are efficiently initiated from rare precursors, a detailed quantitative analysis of this fundamental process has not been reported. Here we measure lymph node (LN) entry, transit, and exit rates for naïve CD4⁺ and CD8⁺ T cells, then use intravital imaging and mathematical modeling to relate cell–cell interaction dynamics to population behavior. Our studies reveal marked differences between CD4⁺ vs. CD8⁺ T cells. CD4⁺ T cells recirculate more rapidly, homing to LNs more efficiently, traversing LNs twice as quickly, and spending ∼1/3 of their transit time interacting with MHCII on DC. In contrast, adoptively transferred CD8⁺ T cells enter and leave the LN more slowly, with a transit time unaffected by the absence of MHCI molecules on host cells. Together, these data reveal an unexpectedly asymmetric role for MHC interactions in controlling CD4⁺ vs. CD8⁺ T lymphocyte recirculation, as well as distinct contributions of T cell receptor (TCR)-independent factors to the LN transit time, exposing the divergent surveillance strategies used by the two lymphocyte populations in scanning for foreign antigen.     

Identification of non-naïve CD4+CD45RA+ T cell subsets in adult allogeneic haematopoietic cell transplant recipients

The study of thymic-dependent pathways of T cell reconstitution in T cell replete haematopoietic cell transplant (HCT) recipients in previous studies was complicated by the transfer of na?ve CD4(+)CD45RA(+) T cells with the stem cell graft. However, direct quantification of thymic output has been enabled by measurement of T cell receptor excision circles (TREC). We analysed T cell reconstitution using T cell phenotyping and TREC quantification in 12 T cell-replete HCT recipients 6-53 years of age during the first 12 months post transplant. We have identified a novel subpopulation of CD4(+)CD45RA(+) T cells in the peripheral blood of these HCT recipients with expansions of this subset being more pronounced in older recipients. The recovery of classical na?ve CD4(+)CD45RA(+) T cells was dependent on thymic output whereas this novel CD4(+)CD45RA(+) subpopulation arose independently of thymic output and displayed effector function and phenotype. These results suggest that CD4(+)CD45RA(+) effector populations exist, similar to the CD8(+)CD45RA(+) effector subset, and that the CD45RA antigen should not be used alone to define na?ve CD4(+) T cells when monitoring T cell reconstitution in T cell replete HCT recipients. Furthermore, these results raise important questions regarding the role of the thymus in regulating T cell homeostasis in older HCT recipients and normal individuals.     

Expansion of CD4+CD25+ regulatory T cells from cord blood CD4+ cells using the common ��-chain cytokines (IL-2 and IL-15) and rapamycin

Rapamycin has important roles in the modulation of regulatory T cells. We tried to expand CD4(+)CD25(+) regulatory T cells (Treg cells) from umbilical cord blood (CB) CD4-positive cells using interleukin (IL)-15 or IL-2 with transforming growth factor (TGF)-β and rapamycin. We were able to obtain more than 500-fold expansion of CD4(+)CD25(+) cells from CB CD4(+) cells using IL-15 and TGF-β with rapamycin. These expanded CD4(+)CD25(+) cells expressed forkhead box P3 (FoxP3) mRNA at a level about 100-fold higher and could suppress allogeneic mixed lymphocyte culture (MLC) by more than 50%. Early after rapamycin stimulation, CB CD4(+) cells showed increased expression of FoxP3 and a serine/threonine kinase Pim2 and sustained expression of negative phosphoinositide 3-kinase regulator phosphatase and tensin homolog deleted on chromosome 10 (PTEN). On the other hand, CD4(+)CD25(+) cells expanded with rapamycin for 8 days showed much higher levels of FoxP3 mRNA expression and decreased expression of PTEN. A comparison of IL-15 stimulation and IL-2 stimulation showed slightly higher efficiency of IL-15 for expansion of CD4(+)CD25(+) cells, and for FoxP3 expression, IL-15 also showed significantly higher efficacy for inhibition of MLC. The combination of the common γ-chain cytokine IL-15, TGF-β, and rapamycin may be a useful means for expanding Treg cells. Pim2 expression early after stimulation with rapamycin may be important for conferring rapamycin resistance for growth of Treg cells. IL-15 is not less useful than IL-2 for expansion of Treg cells.     

TNF-alpha-induced apoptosis in human naïve and memory CD8+ T cells in aged humans

Recently, human CD8+ T cells have been divided into naïve, central memory (T_CM), and two types of effector memory cells (T_EM and T_EMRA), which are phenotypically identified by a set of cell surface molecules. In this investigation, we have compared the relative sensitivity of these subsets to TNF-α-induced apoptosis in young and aged humans. Our data show increased sensitivity of naïve and T_CM CD8+ T cells from aged humans to TNF-α-induced apoptosis as compared to young subjects. Both T_EM and T_EMRA CD8+ T cells from young and aged subjects were relatively resistant to TNF-α-induced apoptosis and no significant difference was observed between young and aged subjects. Increased apoptosis of naïve and T_CM CD8+ T cells in aged humans was associated with increased activation of caspase-8 and caspase-3 as compared to young subjects. There was no difference in the expression of TNFR-I or TNFR-II on any of the four subpopulations of CD8+ T cells between young and aged subjects. These data suggest that increased TNF-α-induced apoptosis of naïve and T_CM CD8+ T cells may play a role in the deficiency of naïve and T_CM CD8+ T cells in human aging. However, apoptosis does not appear to play a major role in increased accumulation of effector memory CD8+ T cells during human aging.