Human CD8(+) T cells expressing HLA-DR and CD28 show telomerase activity and are distinct from cytolytic effector T cells

Transcriptomics reveals shared immunosuppressive landscapes in ventilator-associated lower respiratory tract infections (VA-LRTI) patients

BACKGROUND

Ventilator-associated pneumonia (VAP) represents a transitory status of immunoparalysis, and we hypothesized that ventilator-associated tracheobronchitis (VAT) could share also some degree of immune response to a respiratory infection.

RESEARCH DESIGN AND METHODS

A prospective observational study in five medical ICUs to evaluate immunological alterations of patients with VA-LRTI. Immunological gene expression profiles in the blood using whole transcriptome microarrays in the first 24 hours following diagnosis. The area under the receiver operating characteristic curve (AUROC) was used to assess the accuracy of mRNA levels to differentiate VA-LRTI and lack of infection. A principal component analysis (PCA) was employed for analyzing the impact of each genetic expression footprint variable in explaining the variance of the cohort.

RESULTS

There was overlapping between the three classes of patients encompassing gene expression levels of 8 genes (i.e. HLA, IL2RA, CD40LG, ICOS, CCR7, CD1C, CD3E). HLA-DRA was equally low among VAT and VAP patients characterizing immune depression, and significantly lower than the control group.

CONCLUSIONS

Our findings suggest that VAP and VAT are not so different regarding gene expression levels suggesting a degree of immunosuppression. Our results indicate a state of immunoparalysis in respiratory infections in critically ill patients.

The frequency of differentiated CD3+CD27-CD28- T cells predicts response to CART cell therapy in diffuse large B-cell lymphoma

Background

Chimeric antigen receptor T (CART) cell therapy targeting the B cell specific differentiation antigen CD19 has shown clinical efficacy in a subset of relapsed/refractory (r/r) diffuse large B cell lymphoma (DLBCL) patients. Despite this heterogeneous response, blood pre-infusion biomarkers predicting responsiveness to CART cell therapy are currently understudied.

Methods

Blood cell and serum markers, along with clinical data of DLBCL patients who were scheduled for CART cell therapy were evaluated to search for biomarkers predicting CART cell responsiveness.

Findings

Compared to healthy controls (n=24), DLBCL patients (n=33) showed significant lymphopenia, due to low CD3⁺CD4⁺ T helper and CD3^-CD56⁺ NK cell counts, while cytotoxic CD3⁺CD8⁺ T cell counts were similar. Although lymphopenic, DLBCL patients had significantly more activated HLA-DR⁺ (P=0.005) blood T cells and a higher frequency of differentiated CD3⁺CD27^-CD28^- (28.7 ± 19.0% versus 6.6 ± 5.8%; P<0.001) T cells. Twenty-six patients were infused with CART cells (median 81 days after leukapheresis) and were analyzed for the overall response (OR) 3 months later. Univariate and multivariate regression analyses showed that low levels of differentiated CD3⁺CD27^-CD28^- T cells (23.3 ± 19.3% versus 35.1 ± 18.0%) were independently associated with OR. This association was even more pronounced when patients were stratified for complete remission (CR versus non-CR: 13.7 ± 11.7% versus 37.7 ± 17.4%, P=0.001). A cut-off value of ≤ 18% of CD3⁺CD27^-CD28^- T cells predicted CR at 12 months with high accuracy (P<0.001). In vitro, CD3⁺CD8⁺CD27^-CD28^- compared to CD3⁺CD8⁺CD27⁺CD28⁺ CART cells displayed similar CD19⁺ target cell-specific cytotoxicity, but were hypoproliferative and produced less cytotoxic cytokines (IFN-γ and TNF-α). CD3⁺CD8⁺ T cells outperformed CD3⁺CD4⁺ T cells 3- to 6-fold in terms of their ability to kill CD19⁺ target cells.

Interpretation

Low frequency of differentiated CD3⁺CD27^-CD28^- T cells at leukapheresis represents a novel pre-infusion blood biomarker predicting a favorable response to CART cell treatment in r/r DLBCL patients.

Differences in immunophenotypes between myasthenia gravis patients with and without thyroid antibodies

INTRODUCTION/AIMS

Immunophenotypes are related to the therapeutic efficacy of specific immunomodulating agents in patients with myasthenia gravis (MG), but the relationship of immunophenotype to the presence or absence of thyroid antibodies is unknown. This study aims to evaluate differences in the immunophenotypes between MG patients with and without thyroid antibody (TAb) positivity to provide insight for future targeted immunotherapies.

METHODS

This retrospective observational study included 48 MG patients with acetylcholine receptor antibody (AchR-Ab), of which 15 (31.25%) were TAb positive. Ocular MG (OMG) was defined as ocular-only manifestations for the duration for which records were available. Peripheral lymphocyte subpopulations were measured by flow cytometry.

RESULTS

TAb positive patients appeared to have a higher prevalence of OMG than TAb negative patients (53.33% vs. 24.24%, P  = 0.048). Percentages of B cells (mean difference (MD) = 6.16, 95% confidence interval (CI): 1.91 to 10.40, P = 0.007) and CD8 + CD28+ cells (MD = 15.14, 95%CI: 5.17 to 25.11, P  = 0.013) were higher in TAb positive patients than those in TAb negative patients, while AChR-Ab titers (MD = -6.49 nmol/L, 95%CI: -9.29 to -3.70, P  < 0.001), percentages of T cells (MD = -6.43, 95%CI: -11.92 to -0.94, P = 0.023), CD3 + HLA-DR+ cells (MD = -6.47, 95%CI: -12.31 to -0.63, P  = 0.031) and CD8+ T cells (MD = -6.60, 95%CI: -9.86 to -3.34, P < 0.001) were lower.

DISCUSSION

The immunophenotypes of MG patients with and without TAb positivity were significantly different, suggesting that their sensitivity to immunotherapy may be different. Further studies focused on differences between TAb positive and TAb negative MG patients in their responses to specific immunotherapies are needed to support our exploratory findings. This article is protected by copyright. All rights reserved.

Tumor-infiltrating lymphocytes are functionally inactivated by CD90+ stromal cells and reactivated by combined Ibrutinib and Rapamycin in human pleural mesothelioma

Rationale: Despite evidence suggesting that the tumor microenvironment (TME) in malignant pleural mesothelioma (MPM) is linked with poor prognosis, there is a lack of studies that functionally characterize stromal cells and tumor-infiltrating lymphocytes (TILs). Here, we aim to characterize the stromal subsets within MPM, investigate their relationship to TILs, and explore the potential therapeutic targets.

Methods: We curated a core set of genes defining stromal/immune signatures expressed by mesenchymal cells within the TME using molecular analysis of The Cancer Genome Atlas (TCGA) MPM cohort. Stromal and immune profiles were molecularly characterized using flow cytometry, immunohistochemistry, microarray, and functionally evaluated using T cell-activation/expansion, coculture assays and drug compounds treatment, based on samples from an independent MPM cohort.

Results: We found that a high extracellular matrix (ECM)/stromal gene signature, a high ECM score, or the ratio of ECM to an immune activation gene signature are significantly associated with poor survival in the MPM cohort in TCGA. Analysis of an independent MPM cohort (n = 12) revealed that CD8+ and CD4+ TILs were characterized by PD1 overexpression and concomitant downregulation in degranulation and CD127. This coincided with an increase in CD90+ cells that overexpressed PD-L1 and were enriched for ECM/stromal genes, activated PI3K-mTOR signaling and suppressed T cells. Protein array data demonstrated that MPM samples with high PD-L1 expression were most associated with activation of the mTOR pathway. Further, to reactivate functionally indolent TILs, we reprogrammed ex vivo TILs with Ibrutinib plus Rapamycin to block interleukin-2-inducible kinase (ITK) and mTOR pathways, respectively. The combination treatment shifted effector memory (T_EM) CD8+ and CD4+ TILs towards T cells that re-expressed CD45RA (T_EMRA) while concomitantly downregulating exhaustion markers. Gene expression analysis confirmed that Ibrutinib plus Rapamycin downregulated coinhibitory and T cell signature pathways while upregulating pathways involved in DNA damage and repair and immune cell adhesion and migration.

Conclusions: Our results suggest that targeting the TME may represent a novel strategy to redirect the fate of endogenous TILs with the goal of restoring anti-tumor immunity and control of tumor growth in MPM.

T-lymphocyte subtyping: an early warning and a potential prognostic indicator of active cytomegalovirus infection in patients with sepsis

Cytomegalovirus (CMV) infection is very common in patients suffering from sepsis and may cause poor prognosis. To explore the relationship between immune status of patients with sepsis and CMV infection, we assessed T lymphocyte subtyping and other commonly used clinical parameters in patients with sepsis upon admission to the intensive care unit (ICU) and evaluated their potential impact on diagnosis and outcomes of active CMV infection. In our study, 82 of 599 patients with sepsis were diagnosed with active CMV infection. The 28-day mortality was higher in active CMV-infected than nonactive CMV-infected patients (20.7% versus 9.9%); 51of 82 active CMV-infected patients with sepsis were assessed to have CMV-DNA-negative conversion, while 31 were persistently positive for CMV DNA. Higher CD8⁺ CD28⁺ T-cell counts at presentation were associated with CMV-DNA-negative conversion and lower 28-day mortality. The CMV-DNA-negative conversion and 28-day mortality of active CMV-infected patients with sepsis could be predicted using cutoff values of 151 (74.5% sensitivity and 87.1% specificity) and 64.5 (52.9% sensitivity and 92.3% specificity) CD8⁺ CD28⁺ T cells mL^-1 at ICU admission, respectively. Higher CD8⁺ CD28⁺ T-cell count was significantly associated with active CMV infection, higher CMV-DNA-negative conversion and lower 28-day mortality, which may be a potential marker for early warning of active CMV infection and outcome prediction.

Myeloid antigen-presenting cell niches sustain antitumor T cells and license PD-1 blockade via CD28 costimulation

The mechanisms regulating exhaustion of tumor-infiltrating lymphocytes (TIL) and responsiveness to PD-1 blockade remain partly unknown. In human ovarian cancer, we show that tumor-specific CD8+ TIL accumulate in tumor islets, where they engage antigen and upregulate PD-1, which restrains their functions. Intraepithelial PD-1+CD8+ TIL can be, however, polyfunctional. PD-1+ TIL indeed exhibit a continuum of exhaustion states, with variable levels of CD28 costimulation, which is provided by antigen-presenting cells (APC) in intraepithelial tumor myeloid niches. CD28 costimulation is associated with improved effector fitness of exhausted CD8+ TIL and is required for their activation upon PD-1 blockade, which also requires tumor myeloid APC. Exhausted TIL lacking proper CD28 costimulation in situ fail to respond to PD-1 blockade, and their response may be rescued by local CTLA-4 blockade and tumor APC stimulation via CD40L.

Integrated longitudinal immunophenotypic, transcriptional and repertoire analyses delineate immune responses in COVID-19 patients

To understand how a protective immune response against SARS-CoV-2 develops over time, we integrated phenotypic, transcriptional and repertoire analyses on PBMCs from mild and severe COVID-19 patients during and after infection, and compared them to healthy donors (HD). A type I IFN-response signature marked all the immune populations from severe patients during the infection. Humoral immunity was dominated by IgG production primarily against the RBD and N proteins, with neutralizing antibody titers increasing post infection and with disease severity. Memory B cells, including an atypical FCRL5⁺ T-BET⁺ memory subset, increased during the infection, especially in patients with mild disease. A significant reduction of effector memory, CD8⁺ T cells frequency characterized patients with severe disease. Despite such impairment, we observed robust clonal expansion of CD8⁺ T lymphocytes, while CD4⁺ T cells were less expanded and skewed toward T_CM and T_H2-like phenotypes. MAIT cells were also expanded, but only in patients with mild disease. Terminally differentiated CD8⁺ GZMB⁺ effector cells were clonally expanded both during the infection and post-infection, while CD8⁺ GZMK⁺ lymphocytes were more expanded post-infection and represented bona fide memory precursor effector cells. TCR repertoire analysis revealed that only highly proliferating T cell clonotypes, which included SARS-CoV-2-specific cells, were maintained post-infection and shared between the CD8⁺ GZMB⁺ and GZMK⁺ subsets. Overall, this study describes the development of immunity against SARS-CoV-2 and identifies an effector CD8⁺ T cell population with memory precursor-like features.

T-cell exhaustion in HIV infection

The T‐cell response is central in the adaptive immune‐mediated elimination of pathogen‐infected and/or cancer cells. This activated T‐cell response can inflict an overwhelming degree of damage to the targeted cells, which in most instances leads to the control and elimination of foreign invaders. However, in conditions of chronic infection, persistent exposure of T cells to high levels of antigen results in a severe T‐cell dysfunctional state called exhaustion. T‐cell exhaustion leads to a suboptimal immune‐mediated control of multiple viral infections including the human immunodeficiency virus (HIV). In this review, we will discuss the role of T‐cell exhaustion in HIV disease progression, the long‐term defect of T‐cell function even in aviremic patients on antiretroviral therapy (ART), the role of exhaustion‐specific markers in maintaining a reservoir of latently infected cells, and exploiting these markers in HIV cure strategies.

Loss of BAP1 expression is associated with an immunosuppressive microenvironment in uveal melanoma, with implications for immunotherapy development

Immunotherapy using immune checkpoint inhibitors (ICIs) induces durable responses in many metastatic cancers. Metastatic uveal melanoma (mUM), typically occurring in the liver, is one of the most refractory tumours to ICIs and has dismal outcomes. Monosomy 3 (M3), polysomy 8q, and BAP1 loss in primary uveal melanoma (pUM) are associated with poor prognoses. The presence of tumour-infiltrating lymphocytes (TILs) within pUM and surrounding mUM - and some evidence of clinical responses to adoptive TIL transfer - strongly suggests that UMs are indeed immunogenic despite their low mutational burden. The mechanisms that suppress TILs in pUM and mUM are unknown. We show that BAP1 loss is correlated with upregulation of several genes associated with suppressive immune responses, some of which build an immune suppressive axis, including HLA-DR, CD38, and CD74. Further, single-cell analysis of pUM by mass cytometry confirmed the expression of these and other markers revealing important functions of infiltrating immune cells in UM, most being regulatory CD8+ T lymphocytes and tumour-associated macrophages (TAMs). Transcriptomic analysis of hepatic mUM revealed similar immune profiles to pUM with BAP1 loss, including the expression of IDO1. At the protein level, we observed TAMs and TILs entrapped within peritumoural fibrotic areas surrounding mUM, with increased expression of IDO1, PD-L1, and β-catenin (CTNNB1), suggesting tumour-driven immune exclusion and hence the immunotherapy resistance. These findings aid the understanding of how the immune response is organised in BAP1 - mUM, which will further enable functional validation of detected biomarkers and the development of focused immunotherapeutic approaches. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Tracking Dye-Independent Approach to Identify and Isolate In Vitro Expanded T Cells

T cell proliferation is routinely identified in vitro using tracking dyes or through detecting intracellular upregulation of the nuclear protein, Ki-67. However, labeling with tracking dyes is cumbersome, associated with cellular toxicity, while Ki-67 cannot be used to identify and isolate viable T cells, and both techniques are incompatible with MACS technology. Here, we introduce a simple tool to identify and isolate in vitro T cell expansion that is tracking dye-independent and allows for sorting of viable T cells. We show that CD71, a transferrin receptor, and CD98, a heterodimer glycoprotein involved in both integrin signaling and amino-acid transport, are both highly upregulated on proliferating T cells upon in vitro stimulation, and that CD71 expression is maximal on the more recent progeny T cells, while CD98 upregulation remains stable across different generations of progeny T cells. Moreover, we demonstrate that the upregulation of CD71 and CD98 identifies CFSE^low T cells and provides further proof of the antigen-specificity of T cells identified by CD71 and CD98 dual upregulation based on tetramer staining. We further show that CD71 can be used to enrich for in vitro expanding T cells using MACS technology. In conclusion, we show that CD71 and CD98 can be used to identify and isolate expanded T cells following in vitro stimulation and that CD71 is an MACS-compatible alternative to tracking dyes or Ki-67 detection. © 2019 International Society for Advancement of Cytometry.

Neoepitope targets of tumour-infiltrating lymphocytes from patients with pancreatic cancer

BACKGROUND

Pancreatic cancer exhibits a poor prognosis and often presents with metastasis at diagnosis. Immunotherapeutic approaches targeting private cancer mutations (neoantigens) are a clinically viable option to improve clinical outcomes.

METHODS

3/40 TIL lines (PanTT26, PanTT39, PanTT77) were more closely examined for neoantigen recognition. Whole-exome sequencing was performed to identify non-synonymous somatic mutations. Mutant peptides were synthesised and assessed for antigen-specific IFN-γ production and specific tumour killing in a standard Cr51 assay. TIL phenotype was tested by flow cytometry. Lymphocytes and HLA molecules in tumour tissue were visualised by immunohistochemistry.

RESULTS

PanTT26 and PanTT39 TILs recognised and killed the autologous tumour cells. PanTT26 TIL recognised the KRASG12v mutation, while a PanTT39 CD4+ TIL clone recognised the neoepitope (GLLRYWRTERLF) from an aquaporin 1-like protein (gene: K7N7A8). Repeated stimulation of TILs with the autologous tumour cells line lead to focused recognition of several mutated targets, based on IFN-γ production. TILs and corresponding PBMCs from PanTT77 showed shared as well as mutually exclusively tumour epitope recognition (TIL-responsive or PBMC-responsive).

CONCLUSION

This study provides methods to robustly screen T-cell targets for pancreatic cancer. Pancreatic cancer is immunogenic and immunotherapeutic approaches can be used to develop improved, targeted therapies.

Flow cytometric discrimination of seven lineage markers by using two fluorochromes

Flow cytometry is the primary immunological technique used to analyze multiple parameters on complex cell populations. We present a staining method that identifies major human mononuclear lymphoid and myeloid populations (CD4⁺ and CD8⁺ T cells, γδ T cells, B cells, NK cells and monocytes), using only two fluorochromes and a minimal number of cells. Our approach increases the number of markers recordable on most flow cytometers allowing for a deeper and more comprehensive immunophenotyping.

Precursor Forms of Vitamin D Reduce HIV-1 Infection In Vitro

BACKGROUND

Although the anti-HIV-1 effects of vitamin D (VitD) have been reported, mechanisms behind such protection remain largely unexplored.

METHODS

The effects of two precursor forms (cholecalciferol/calciol at 0.01, 1 and 100 nM and calcidiol at 100 and 250 nM) on HIV-1 infection, immune activation, and gene expression were analyzed in vitro in cells of Colombian and Italian healthy donors. We quantified levels of released p24 by enzyme-linked immunosorbent assay, of intracellular p24 and cell-surface expression of CD38 and HLA-DR by flow cytometry, and mRNA expression of antiviral and immunoregulatory genes by real-time reverse transcription-polymerase chain reaction.

RESULTS

Cholecalciferol decreased the frequency of HIV-1-infected p24CD4 T cells and levels of p24 in supernatants in a dose-dependent manner. Moreover, the CD4CD38HLA-DR and CD4CD38HLA-DR subpopulations were more susceptible to infection but displayed the greatest cholecalciferol-induced decreases in infection rate by an X4-tropic strain. Likewise, cholecalciferol at its highest concentration decreased the frequency of CD38HLA-DR but not of CD38HLA-DR T-cell subsets. Analyzing the effects of calcidiol, the main VitD source for immune cells and an R5-tropic strain as the most frequently transmitted virus, a reduction in HIV-1 productive infection was also observed. In addition, an increase in mRNA expression of APOBEC3G and PI3 and a reduction of TRIM22 and CCR5 expression, this latter positively correlated with p24 levels, was noted.

CONCLUSIONS

VitD reduces HIV-1 infection in T cells possibly by inducing antiviral gene expression, reducing the viral co-receptor CCR5 and, at least at the highest cholecalciferol concentration, by promoting an HIV-1-restrictive CD38HLA-DR immunophenotype.

Vitamin D modulates the expression of HLA-DR and CD38 after in vitro activation of T-cells

OBJECTIVE

Vitamin D (VitD) is an anti-inflammatory hormone; however, some evidence shows that VitD may induce the expression of activation markers, such as CD38 and HLA-DR. We explored its effect on the expression of these markers on CD4+ and CD8+ T-cells in vitro, and their potential correlations in vivo.

MATERIALS AND METHODS

CD38 and HLA-DR expression was measured by flow cytometry in PHA/IL-2-activated mononuclear cells cultured under VitD precursors: three cholecalciferol (10-11M, 10-9M, 10-7M; n=11) and two calcidiol (40 ng/mL, 80 ng/mL; n=9) concentrations. The correlation between the expression of these markers in freshly isolated blood cells and serum levels of calcidiol was also explored (n=10).

RESULTS

Cholecalciferol at 10-7M increased the proportion of CD4+ CD38+ and CD8+ CD38+ cells, and decreased CD8+HLA-DR+ cells. As co-expression, it increased the CD38+HLA-DR- and decreased CD38-HLA-DR+ subpopulations in both CD4+ and CD8+ T-cells, and decreased CD4+CD38-HLA-DR- and CD8+ CD38+HLA-DR+; whereas both calcidiol concentrations decreased the proliferation of CD38-HLA-DR- and CD38-HLA-DR+ subpopulations. Both forms of VitD increased the number of CD38 molecules per cell. In contrast, there was a positive but non-significant correlation between serum calcidiol levels and the expression of CD38 and HLA-DR in CD4+ and CD8+ T-cells.

CONCLUSION

Although no significant correlations were observed in vivo in healthy subjects, VitD treatment in vitro modulated immune activation by increasing the expression of CD38 and decreasing the proliferation of HLA-DR+ and resting cells, which may correlate with improved effector and decreased proliferative capabilities. These results highlight the potential use of VitD as therapeutic strategy in immune disorders.

Potential role for HIV-specific CD38-/HLA-DR+ CD8+ T cells in viral suppression and cytotoxicity in HIV controllers

Background

HIV controllers (HIC) are rare HIV-1-infected patients who exhibit spontaneous viral control. HIC have high frequency of CD38⁻/HLA-DR⁺ HIV-specific CD8⁺ T cells. Here we examined the role of this subset in HIC status.

Materials and Methods

We compared CD38⁻/HLA-DR⁺ CD8⁺ T cells with the classical CD38⁺/HLA-DR⁺ activated phenotype in terms of 1) their activation status, reflected by CD69, CD25, CD71, CD40 and Ki67 expression, 2) functional parameters: Bcl-2 expression, proliferative capacity, and IFN-γ and IL-2 production, and 3) cytotoxic activity. We also investigated how this particular profile is generated.

Results

Compared to CD38⁺/HLA-DR⁺ cells, CD38⁻/HLA-DR⁺ cells exhibited lower expression of several activation markers, better survival capacity (Bcl-2 MFI, 367 [134–462] vs 638 [307–747], P = 0.001), higher frequency of polyfunctional cells (15% [7%–33%] vs 21% [16%–43%], P = 0.0003), greater proliferative capacity (0-fold [0–2] vs 3-fold [2]–[11], P = 0.007), and higher cytotoxicity in vitro (7% [3%–11%] vs 13% [6%–22%], P = 0.02). The CD38⁻/HLA-DR⁺ profile was preferentially generated in response to low viral antigen concentrations.

Conclusions

These data highlight the role of CD38⁻/HLA-DR⁺ HIV-specific CD8⁺ T cell cytotoxicity in HIC status and provide insights into the mechanism by which they are generated. Induction of this protective CD8⁺ subset may be important for vaccine strategies.

Density of tumor-infiltrating FOXP3+ T cells as a response marker for induction chemoradiotherapy and a potential prognostic factor in patients treated with trimodality therapy for locally advanced non-small cell lung cancer

PURPOSE

To examine the relationship between the density of tumor-infiltrating T cell subpopulations and the pathological response to induction chemoradiotherapy (CRT) in patients with locally advanced NSCLC, and to assess the impact of T cell density on patient prognosis.

METHODS

A total of 64 patients with c-stages IIA-IIIB NSCLC who underwent induction CRT followed by R0 surgery were enrolled. Tumor-infiltrating T cells expressing either FOXP3 or CD8 were detected by immunohistochemical staining.

RESULTS

Mean numbers of tumor-infiltrating FOXP3+ T cells were 39.9 for patients with minor pathological responses (n = 9), 18.4 for those with major pathological responses (n = 25), and 12.9 for those with complete pathological responses (n = 30; P &lt;0.001). The number of CD8+ T cells was not associated with pathological responses. Patients with lower FOXP3+ T cell densities showed better survival, although the difference was not statistically significant.

CONCLUSION

Our study demonstrated that the density of tumor-infiltrating FOXP3+ T cells indicated the degree of response for induction CRT and prognosis in patients treated with trimodality therapy for locally advanced NSCLC, suggesting that FOXP3+ T cells may be target for adjunct immunotherapy.

Enhanced cytotoxicity and decreased CD8 dependence of human cancer-specific cytotoxic T lymphocytes after vaccination with low peptide dose

In mice, vaccination with high peptide doses generates higher frequencies of specific CD8+ T cells, but with lower avidity compared to vaccination with lower peptide doses. To investigate the impact of peptide dose on CD8+ T cell responses in humans, melanoma patients were vaccinated with 0.1 or 0.5 mg Melan-A/MART-1 peptide, mixed with CpG 7909 and Incomplete Freund's adjuvant. Neither the kinetics nor the amplitude of the Melan-A-specific CD8+ T cell responses differed between the two vaccination groups. Also, CD8+ T cell differentiation and cytokine production ex vivo were similar in the two groups. Interestingly, after low peptide dose vaccination, Melan-A-specific CD8+ T cells showed enhanced degranulation upon peptide stimulation, as assessed by CD107a upregulation and perforin release ex vivo. In accordance, CD8+ T cell clones derived from low peptide dose-vaccinated patients showed significantly increased degranulation and stronger cytotoxicity. In parallel, Melan-A-specific CD8+ T cells and clones from low peptide dose-vaccinated patients expressed lower CD8 levels, despite similar or even stronger binding to tetramers. Furthermore, CD8+ T cell clones from low peptide dose-vaccinated patients bound CD8 binding-deficient tetramers more efficiently, suggesting that they may express higher affinity TCRs. We conclude that low peptide dose vaccination generated CD8+ T cell responses with stronger cytotoxicity and lower CD8 dependence.

Human dendritic cells infected with the nonpathogenic Mopeia virus induce stronger T-cell responses than those infected with Lassa virus

The events leading to death in severe cases of Lassa fever (LF) are unknown. Fatality seems to be linked to high viremia and immunosuppression, and cellular immunity, rather than neutralizing antibodies, appears to be essential for survival. We previously compared Lassa virus (LV) with its genetically close but nonpathogenic homolog Mopeia virus (MV), which was used to model nonfatal LF. We showed that strong and early activation of antigen-presenting cells (APC) may play a crucial role in controlling infection. Here we developed an in vitro model of dendritic-cell (DC)-T-cell coculture in order to characterize human T-cell responses induced by MV- or LV-infected DCs. Our results show very different responses to infection with LV and MV. MV strongly and durably stimulated CD8(+) and CD4(+) T cells, showing early and high activation, a strong proliferative response, and acquisition of effector and memory phenotypes. Furthermore, robust and functional CD4(+) and CD8(+) cytotoxic T lymphocytes (CTL) were generated. LV, however, induced only weak memory responses. Thus, this study allows an improved understanding of the pathogenesis and immune mechanisms involved in the control of human LV.

Profile of a serial killer: cellular and molecular approaches to study individual cytotoxic T-cells following therapeutic vaccination

T-cell vaccination may prevent or treat cancer and infectious diseases, but further progress is required to increase clinical efficacy. Step-by-step improvements of T-cell vaccination in phase I/II clinical studies combined with very detailed analysis of T-cell responses at the single cell level are the strategy of choice for the identification of the most promising vaccine candidates for testing in subsequent large-scale phase III clinical trials. Major aims are to fully identify the most efficient T-cells in anticancer therapy, to characterize their TCRs, and to pinpoint the mechanisms of T-cell recruitment and function in well-defined clinical situations. Here we discuss novel strategies for the assessment of human T-cell responses, revealing in part unprecedented insight into T-cell biology and novel structural principles that govern TCR-pMHC recognition. Together, the described approaches advance our knowledge of T-cell mediated-protection from human diseases.

Therapeutic immunization with HIV-1 Tat reduces immune activation and loss of regulatory T-cells and improves immune function in subjects on HAART

Although HAART suppresses HIV replication, it is often unable to restore immune homeostasis. Consequently, non-AIDS-defining diseases are increasingly seen in treated individuals. This is attributed to persistent virus expression in reservoirs and to cell activation. Of note, in CD4⁺ T cells and monocyte-macrophages of virologically-suppressed individuals, there is continued expression of multi-spliced transcripts encoding HIV regulatory proteins. Among them, Tat is essential for virus gene expression and replication, either in primary infection or for virus reactivation during HAART, when Tat is expressed, released extracellularly and exerts, on both the virus and the immune system, effects that contribute to disease maintenance. Here we report results of an ad hoc exploratory interim analysis (up to 48 weeks) on 87 virologically-suppressed HAART-treated individuals enrolled in a phase II randomized open-label multicentric clinical trial of therapeutic immunization with Tat (ISS T-002). Eighty-eight virologically-suppressed HAART-treated individuals, enrolled in a parallel prospective observational study at the same sites (ISS OBS T-002), served for intergroup comparison. Immunization with Tat was safe, induced durable immune responses, and modified the pattern of CD4⁺ and CD8⁺ cellular activation (CD38 and HLA-DR) together with reduction of biochemical activation markers and persistent increases of regulatory T cells. This was accompanied by a progressive increment of CD4⁺ T cells and B cells with reduction of CD8⁺ T cells and NK cells, which were independent from the type of antiretroviral regimen. Increase in central and effector memory and reduction in terminally-differentiated effector memory CD4⁺ and CD8⁺ T cells were accompanied by increases of CD4⁺ and CD8⁺ T cell responses against Env and recall antigens. Of note, more immune-compromised individuals experienced greater therapeutic effects. In contrast, these changes were opposite, absent or partial in the OBS population. These findings support the use of Tat immunization to intensify HAART efficacy and to restore immune homeostasis.

Comparison of anti-CD3 and anti-CD28-coated beads with soluble anti-CD3 for expanding human T cells: differing impact on CD8 T cell phenotype and responsiveness to restimulation

Background

The ability to expand virus- or tumor-specific T cells without damaging their functional capabilities is critical for success adoptive transfer immunotherapy of patients with opportunistic infection or tumor. Careful comparisons can help identify expansion methods better suited for particular clinical settings and identify recurrent deficiencies requiring new innovation.

Methods

We compared the efficacy of magnetic beads coated with anti-CD3 and anti-CD28 (anti-CD3/CD28 beads), and soluble anti-CD3 plus mixed mononuclear cells (designated a rapid expansion protocol or REP) in expanding normal human T cells.

Results

Both anti-CD3/CD28 beads and soluble anti-CD3 promoted extensive expansion. Beads stimulated greater CD4 cell growth (geometric mean of 56- versus 27-fold (p < 0.01) at day 21) but both stimulated similar CD8 expansion (189- versus 186-fold). Phenotypically, bead-treated CD4 and CD8 T cells and anti-CD3-treated CD4 cells typically assumed an effector/effector memory phenotype by day 14. By comparison, a subset of anti-CD3-treated CD8 cells, derived from naïve cells, retained much greater expression of CD45RA, CD27 and CCR7, than matched bead-treated cells despite comparable expansion. These cells were clearly distinguishable from CD45RA+ terminally differentiated effector cells by the presence of CD27, the absence of CD57 and their inability to produce cytokines after stimulation. When used to expand previously stimulated cells, anti-CD3 plus autologous MNCs produced much less antigen-induced cell death of CD8 cells and significantly more CD8 expansion than beads.

Conclusions

Anti-CD3/CD28 beads are highly effective for expanding CD4 cells, but soluble anti-CD3 has significant potential advantages for expanding CD8 T cells, particularly where preservation of phenotypically "young" CD8 cells would be desirable, or where the T cells of interest have been antigen-stimulated in vitro or in vivo in the recent past.

Relationship between regulatory T cells and immune activation in human immunodeficiency virus-infected patients interrupting antiretroviral therapy

Persistent immune activation plays a central role in driving Human Immunodeficiency Virus (HIV) disease progression. Whether CD4+CD25+ regulatory T cells (Tregs) are harmful by suppressing HIV-specific immune responses and/or beneficial through a decrease in immune activation remains debatable. We analysed the relationship between proportion and number of regulatory T cells (Tregs) and immune activation in HIV-infected patients interrupting an effective antiretroviral therapy (ART). Twenty-five patients were included in a substudy of a prospective multicenter trial of treatment interruption (TI) (ANRS 116). Proportions and numbers of Tregs and the proportion of activated CD4 and CD8 T cells were assessed at baseline and month 12 (M12) of TI. Specific anti-HIV CD4 and CD8 responses were investigated at baseline and M12. Non parametric univariate analyses and multivariate linear regression models were conducted. At baseline, the proportion of Tregs negatively correlated with the proportion of HLA-DR⁺CD8⁺T cells (r = −0.519). Following TI, the proportion of Tregs increased from 6.3% to 7.2% (p = 0.029); absolute numbers of Tregs decreased. The increase in the proportion of HLA-DR⁺CD38⁺CD8⁺T cells was significantly related to the increase in proportion of Tregs (p = 0.031). At M12, the proportion of Tregs did not negatively correlate with CD8 T-cell activation. Nevertheless, Tregs retain a suppressive function since depletion of Treg-containing CD4⁺CD25⁺ cells led to an increase in lymphoproliferative responses in most patients studied. Our data suggest that Tregs are efficient in controlling residual immune activation in patients with ART-mediated viral suppression. However, the insufficient increase in the proportion and/or the decrease in the absolute number of Tregs result in a failure to control immune activation following TI.

Effect of ageing on CMV-specific CD8 T cells from CMV seropositive healthy donors

BACKGROUND

Ageing is associated with changes in the immune system with substantial alterations in T-lymphocyte subsets. Cytomegalovirus (CMV) is one of the factors that affect functionality of T cells and the differentiation and large expansions of CMV pp65-specific T cells have been associated with impaired responses to other immune challenges. Moreover, the presence of clonal expansions of CMV-specific T cells may shrink the available repertoire for other antigens and contribute to the increased incidence of infectious diseases in the elderly. In this study, we analyse the effect of ageing on the phenotype and frequency of CMV pp65-specific CD8 T cell subsets according to the expression of CCR7, CD45RA, CD27, CD28, CD244 and CD85j.

RESULTS

Peripheral blood from HLA-A2 healthy young, middle-aged and elderly donors was analysed by multiparametric flow cytometry using the HLA-A*0201/CMV pp65(495-504) (NLVPMVATV) pentamer and mAbs specific for the molecules analysed. The frequency of CMV pp65-specific CD8 T cells was increased in the elderly compared with young and middle-aged donors. The proportion of naïve cells was reduced in the elderly, whereas an age-associated increase of the CCR7(null) effector-memory subset, in particular those with a CD45RA(dim) phenotype, was observed, both in the pentamer-positive and pentamer-negative CD8 T cells. The results also showed that most CMV pp65-specific CD8 T cells in elderly individuals were CD27/CD28 negative and expressed CD85j and CD244.

CONCLUSION

The finding that the phenotype of CMV pp65-specific CD8 T cells in elderly individuals is similar to the predominant phenotype of CD8 T cells as a whole, suggests that CMV persistent infections contributes to the age-related changes observed in the CD8 T cell compartment, and that chronic stimulation by other persistent antigens also play a role in T cell immunosenescence. Differences in subset distribution in elderly individuals showing a decrease in naive and an increase in effector-memory CD8 T cells may be relevant in the age-associated defective immune response.

Infection of CD8+CD45RO+ memory T-cells by HIV-1 and their proliferative response

CD8+ T-cells are involved in controlling HIV-1 infection by eliminating infected cells and secreting soluble factors that inhibit viral replication. To investigate the mechanism and significance of infection of CD8+ T-cells by HIV-1 in vitro, we examined the susceptibility of these cells and their subsets to infection. CD8+ T-cells supported greater levels of replication with T-cell tropic strains of HIV-1, though viral production was lower than that observed in CD4+ T-cells. CD8+ T-cell infection was found to be productive through ELISA, RT-PCR and flow cytometric analyses. In addition, the CD8+CD45RO+ memory T-cell population supported higher levels of HIV-1 replication than CD8+CD45RA+ naïve T-cells. However, infection of CD8+CD45RO+ T-cells did not affect their proliferative response to the majority of mitogens tested. We conclude, with numerous lines of evidence detecting and measuring infection of CD8+ T-cells and their subsets, that this cellular target and potential reservoir may be central to HIV-1 pathogenesis.

Imbalances in circulating lymphocyte subsets in Hu antibody associated paraneoplastic neurological syndromes

In paraneoplastic neurological syndromes (PNS) associated with small cell lung cancer (SCLC) and Hu antibodies, neuron-specific Hu antigens expressed by the tumour hypothetically trigger an immune response that cross-reacts with Hu antigens in the nervous system, resulting in tumour suppression and neuronal damage. To gain more insight into the hypothesized cell-mediated immune pathogenesis of these syndromes, we analysed the circulating lymphocyte subsets in untreated patients with SCLC, PNS and Hu antibodies (n = 18), SCLC without PNS (n = 19) and controls (n = 29) using flow cytometry. SCLC patients with PNS had a variety of imbalances within their circulating lymphocyte subsets as compared with SCLC patients without PNS and healthy controls: (i) a lymphopenia of the major subsets (i.e. B, CD4+ and CD8+ T lymphocytes); (ii) increased proportions of activated CD4+ and CD8+ T cells; (iii) reduced numbers of terminally differentiated effector CD8+ T cells and cells with a cytotoxic T-cell phenotype (CD56+ and CD57+). Although indirect, our data provide further support for the involvement of T cells in the pathogenesis of Hu antibody associated PNS.

Assessing ageing of individual T lymphocytes: mission impossible?

Effector T lymphocytes are the progeny of a limited number of antigen-specific precursor cells and it has been estimated that clonotypic human T cells may expand million fold on their way reaching high cell numbers that are sufficient for immune protection. Moreover, memory T cell responses are characterized by repetitive expansion of antigen-specific T cell clonotypes, and limitations in the proliferative capacity could lead to immune senescence. Because telomeres progressively shorten as a function of cell division, telomere length is a powerful indicator of the replicative in vivo history of human T lymphocytes. In this review, we summarize observations made over the last decade on telomere length dynamics of well-defined T cell populations derived from healthy donors and patients with infectious disease or cancer. We focus on T cell differentiation, T cell ageing, and natural and vaccine induced immune responses. We also discuss the scientific evidence for in vivo replicative senescence of antigen-specific T cells, and evaluate the available methods for measuring telomere lengths and telomerase activity, and their potential and limitations to increase our understanding of T cell physiology.

Four functionally distinct populations of human effector-memory CD8+ T lymphocytes

In humans, the pathways of memory and effector T cell differentiation remain poorly defined. We have dissected the functional properties of ex vivo effector-memory (EM) CD45RA-CCR7- T lymphocytes present within the circulating CD8+ T cell pool of healthy individuals. Our studies show that EM T cells are heterogeneous and are subdivided based on differential CD27 and CD28 expression into four subsets. EM(1) (CD27+CD28+) and EM(4) (CD27-CD28+) T cells express low levels of effector mediators such as granzyme B and perforin and high levels of CD127/IL-7Ralpha. EM(1) cells also have a relatively short replicative history and display strong ex vivo telomerase activity. Therefore, these cells are closely related to central-memory (CD45RA-CCR7+) cells. In contrast, EM(2) (CD27+CD28-) and EM(3) (CD27-CD28-) cells express mediators characteristic of effector cells, whereby EM(3) cells display stronger ex vivo cytolytic activity and have experienced larger numbers of cell divisions, thus resembling differentiated effector (CD45RA+CCR7-) cells. These data indicate that progressive up-regulation of cytolytic activity and stepwise loss of CCR7, CD28, and CD27 both characterize CD8+ T cell differentiation. Finally, memory CD8+ T cells not only include central-memory cells but also EM(1) cells, which differ in CCR7 expression and may therefore confer memory functions in lymphoid and peripheral tissues, respectively.

HIV controllers exhibit potent CD8 T cell capacity to suppress HIV infection ex vivo and peculiar cytotoxic T lymphocyte activation phenotype

Some rare HIV-1-infected individuals, referred to as HIV controllers (HIC), have persistently undetectable plasma viral load in the absence of therapy. This control of HIV-1 replication has been associated with a strong, multifunctional specific CD8(+) T cell response. However, no direct link between this immune response and the control of viremia has so far been provided. We investigated parameters of specific CD8(+) T cell response and in vitro susceptibility to HIV-1 infection in 11 HIC. We found high frequencies of HIV-specific CD8(+) T cells. Interestingly, these cells expressed the activation marker HLA-DR but not CD38. This unique phenotype differentiates HIV-specific CD8(+) T cells from HIC and noncontroller subjects and likely reflects a high potential to expand upon exposure to antigen and a capacity to exert effector functions. Accordingly, although CD4(+) T cells from HIC were fully susceptible to HIV-1 superinfection, their CD8(+) T cells effectively suppressed HIV-1 infection. Remarkably, this potent anti-HIV activity was observed without prior stimulation of CD8(+) T cells. This activity was not mediated by secreted inhibitory factors but was due to the elimination of infected CD4(+) T cells and was observed only with autologous CD4(+) T cells, indicating an HLA-restricted cytotoxic mechanism. This constitutive antiviral capacity of CD8(+) T cells could account for the control of viral replication in HIC.

Ex vivo characterization of human CD8+ T subsets with distinct replicative history and partial effector functions

After antigenic challenge, naive T lymphocytes enter a program of proliferation and differentiation during the course of which they acquire effector functions and may ultimately become memory cells. In humans, the pathways of effector and memory T-cell differentiation remain poorly defined. Here we describe the properties of 2 CD8+ T-lymphocyte subsets, RA+CCR7-27+28+ and RA+CCR7-27+28-, in human peripheral blood. These cells display phenotypic and functional features that are intermediate between naive and effector T cells. Like naive T lymphocytes, both subsets show relatively long telomeres. However, unlike the naive population, these T cells exhibit reduced levels of T-cell receptor excision circles (TRECs), indicating they have undergone additional rounds of in vivo cell division. Furthermore, we show that they also share effector-type properties. At equivalent in vivo replicative history, the 2 subsets express high levels of Fas/CD95 and CD11a, as well as increasing levels of effector mediators such as granzyme B, perforin, interferon gamma, and tumor necrosis factor alpha. Both display partial ex vivo cytolytic activity and can be found among cytomegalovirus-specific cytolytic T cells. Taken together, our data point to the presence of T cells with intermediate effector-like functions and suggest that these subsets consist of T lymphocytes that are evolving toward a more differentiated effector or effector-memory stage.

T-cell homeostasis in breast cancer survivors with persistent fatigue

Approximately 30% of women successfully treated for breast cancer suffer persistent fatigue of unknown origin. Recent studies linking inflammatory processes to central nervous system-mediated fatigue led us to examine cellular immune system status in 20 fatigued breast cancer survivors and 19 matched non-fatigued breast cancer survivors. Fatigued survivors, compared with non-fatigued survivors, had statistically significantly increased numbers of circulating T lymphocytes (mean 31% increase, 95% confidence interval [CI] = 6% to 56%; P =.015 by two-sided analysis of variance [ANOVA]), with pronounced elevation in the numbers of CD4+ T lymphocytes (mean 41% increase, 95% CI = 15% to 68%; P =.003 by two-sided ANOVA) and CD56+ effector T lymphocytes (mean 52% increase, 95% CI = 4% to 99%; P =.027 by two-sided ANOVA). These changes were independent of patient demographic and treatment characteristics. Absolute numbers of B cells, natural killer cells, granulocytes, and monocytes were not altered. The increased numbers of circulating T cells correlated with elevations in the level of serum interleukin 1 receptor antagonist (for CD3+ cells, r =.56 and P =.001; for CD3+/CD4+ cells, r =.68 and P<.001, by Spearman rank correlation). Results of this study suggest that persistent fatigue in breast cancer survivors might be associated with a chronic inflammatory process involving the T-cell compartment. These results require confirmation in a larger study that is specifically designed to address this hypothesis.

Regulation of HLA-DR and co-stimulatory molecule expression on natural killer T cells by granulocyte-macrophage colony-stimulating factor

A subset of mononuclear cells present in most tissues coexpresses receptors of both natural killer (NK) and T cells. Although linked to antiviral immunity, the function of these putative NKT cells is uncertain. We present evidence that human CD56+ DR- NKT cells exhibit hybrid adaptive and innate immune functions. These cells spontaneously lysed tumour cell targets and upon engagement of T-cell antigen receptors secreted the cytokines interferon-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF). Conversely, GM-CSF treatment transformed the NKT cells into dendritic cells, inducing rapid expression of HLA-DR and the co-stimulatory molecules CD80 and CD86. The ability to stimulate tetanus toxoid-specific responses from naïve T cells was acquired within 3 days of activating CD56+ NKT cells with GM-CSF. These results suggest a potential role for NKT cells in the initiation and control of primary immunity during the acute phase of infection.

CD8+CD28- T cells: certainties and uncertainties of a prevalent human T-cell subset

Human peripheral blood CD8+ T cells comprise cells that are in different states of differentiation and under the control of complex homeostatic processes. In a number of situations ranging from chronic inflammatory conditions and infectious diseases to ageing, immunodeficiency, iron overload and heavy alcohol intake, major phenotypic changes, usually associated with an increase in CD8+ T cells lacking CD28 expression, take place. CD8+CD28- T cells are characterized by a low proliferative capacity to conventional stimulation in vitro and by morphological and functional features of activated/memory T cells. Although the nature of the signals that give origin to this T-cell subset is uncertain, growing evidence argues for the existence of an interplay between epithelial cells, molecules with the MHC-class I fold and CD8+ T cells. The possibility that the generation of CD8+CD28- T cells is the combination of TCR/CD3zeta- and regulatory factor-mediated signals as a result of the sensing of modifications of the internal environment is discussed.

The activatory receptor 2B4 is expressed in vivo by human CD8+ effector alpha beta T cells

The membrane receptor 2B4 is a CD2 family member that is involved in lymphocyte activation. A fraction of human CD8+ alphabeta T cells up-regulate 2B4 in vivo, and here we demonstrate that this correlates with the acquisition of effector cell properties such as granzyme B and perforin expression, rapid IFN-gamma production, and down-regulation of the lymph node homing chemokine receptor CCR7. In PBLs from healthy donors, cytomegalovirus-specific effector T cells were 2B4 positive, whereas naive melanoma Ag (Melan-A/melanoma Ag recognized by T cells-1)-specific T cells were 2B4 negative. In melanoma patients, Melan-A-specific T cells up-regulated 2B4 in parallel with in vivo differentiation. This occurred in PBLs after vaccination with Melan-A peptides and in tumor-infiltrated lymph nodes, likely through disease-associated activation of Melan-A-specific T cells. Thus, 2B4 expression correlates with CD8+ T cell differentiation in vivo.

Role of CD28-B7 interactions in generation and maintenance of CD8 T cell memory

Although the role of CD28-B7 interaction in the activation of naive T cells is well established, its importance in the generation and maintenance of T cell memory is not well understood. In this study, we examined the requirement for CD28-B7 interactions in primary T cell activation and immune memory. Ag-specific CD8 T cell responses were compared between wild-type (+/+) and CD28-deficient (CD28(-/-)) mice following an acute infection with lymphocytic choriomeningitis virus (LCMV). During the primary response, there was a substantial activation and expansion of LCMV-specific CD8 T cells in both +/+ and CD28(-/-) mice. However, the magnitude of the primary CD8 T cell response to both dominant and subdominant LCMV CTL epitopes was approximately 2- to 3-fold lower in CD28(-/-) mice compared with +/+ mice; the lack of CD28-mediated costimulation did not lead to preferential suppression of CD8 T cell responses to the weaker subdominant epitopes. As seen in CD28(-/-) mice, blockade of B7-mediated costimulation by CTLA4-Ig treatment of +/+ mice also resulted in a 2-fold reduction in the anti-LCMV CD8 T cell responses. Loss of CD28/B7 interactions did not significantly affect the generation and maintenance of CD8 T cell memory; the magnitude of CD8 T cell memory was approximately 2-fold lower in CD28(-/-) mice as compared with +/+ mice. Further, in CD28(-/-) mice, LCMV-specific memory CD8 T cells showed normal homeostatic proliferation in vivo and also conferred protective immunity. Therefore, CD28 signaling is not necessary for the proliferative renewal and maintenance of memory CD8 T cells.

EBV-specific CD8+ T cell memory: relationships between epitope specificity, cell phenotype, and immediate effector function

EBV infection in humans induces CD8+ T cell memory to viral epitopes derived from both lytic and latent cycle Ags. We have analyzed the relationship between the phenotype and function of the memory pool of T cells specific for these Ags. Lytic epitope-specific populations were heterogeneous in terms of CD45RO/RA and CD28 expression, whereas latent epitope-specific populations were uniformly CD45RO+ and CD28+, consistent with the higher antigenic challenge from lytic epitopes driving some memory cells toward a CD45RA+, CD28- phenotype. However, both types of memory population showed immediate epitope-specific cytotoxicity and type 1 cytokine production in ex vivo assays. Cytotoxic function was not associated with preactivated T cells, as EBV-specific populations were negative for activation markers such as CD69 or CD38, nor could cytotoxic function be ascribed to CD27- or CD56+ subsets, as such cells were not detected in EBV-specific memory. Furthermore, cytotoxicity was not limited to CD45RA+ and/or CD28- fractions, but also was observed in CD45RO+, CD28+ populations in lytic and latent epitope-specific memory. Cytokine (IFN-gamma, TNF-alpha) responses, measured by intracytoplasmic staining after peptide stimulation, also were detectable in CD45RO+ and RA+ subsets as well as CD28+ and CD28- subsets. Of other markers that were heterogeneous in both lytic and latent epitope populations, CCR7 gave the best discrimination of functionality; thus, CCR7+ cells consistently failed to give an IFN-gamma or TNF-alpha response, whereas many CCR7- cells were responsive. Our data are consistent with effector functions having a broad distribution among phenotypically distinct subsets of "effector memory" cells that have lost the CCR7 marker.

Ex vivo analysis of tumor antigen specific CD8+ T cell responses using MHC/peptide tetramers in cancer patients

The development of soluble tetrameric MHC/peptide complexes has opened the possibility to directly identify and monitor antigen-specific CD8+ T cells in different clinical situations. This represents a technological breakthrough for the field of cell-mediated immunity. For example, the direct identification and enumeration of tumor-specific CD8+ T cells at the tumor site and in blood has recently provided compelling evidence that strong anti-tumoral responses naturally occur in some cancer patients. Moreover, the use of tetramers plays an essential role in the design of vaccination protocols aimed at inducing a strong and protective CD8+ T cell-mediated anti-tumoral response in cancer patients. The monitoring of antigen-specific T cell responses elicited by various peptide-based vaccines tested in phase I clinical trials clearly indicates that tumor-specific CD8+ T cells can be activated effectively at least in some cancer patients. Thus, multiparameter monitoring of antigen-specific T cell responses that combines ex vivo tetramer staining with various phenotyping and functional assays provides a novel approach to assess the functional potential of tumor-specific T lymphocytes and may also facilitate the optimization of vaccination protocols.

Ex vivo IFN-gamma secretion by circulating CD8 T lymphocytes: implications of a novel approach for T cell monitoring in infectious and malignant diseases

To elucidate the functional heterogeneity of Ag-specific T lymphocyte populations, we combined labeling of lymphocytes with MHC/peptide tetramers and a cell surface affinity matrix for IFN-gamma. Magnetic cell sorting of IFN-gamma-positive lymphocytes allowed the selective enrichment and identification of live Ag-specific cytokine-secreting cells by flow cytometry. Naive, memory, and effector Ag-specific populations were evaluated in healthy HLA-A2 individuals. Significant fractions of influenza- and CMV-specific cells secreted IFN-gamma upon challenge with cognate peptide, consistent with an effector/memory status. The sensitivity of the approach allowed the detection of significant numbers of CMV-specific IFN-gamma-secreting cells ex vivo (i.e., without Ag stimulation). This was not apparent when using previously described assays, namely, ELISPOT or intracellular IFN-gamma staining (cytospot). CD8+ T cells specific for the melamoma-associated Ag Melan-A/MART-1 did not produce IFN-gamma upon challenge with cognate peptide, reminiscent with their naive functional state in healthy individuals. In contrast, CD45RA(low) Melan-A/MART-1 tumor-specific cells from three of three melanoma patients presented levels of activity similar to those found for influenza- or CMV virus-specific lymphocytes, compatible with a functional differentiation into competent effector/memory T lymphocytes in vivo. Notably, a sizable fraction of Melan-A/MART-1-specific cells from a patient secreted IFN-gamma ex vivo following peptide-based vaccination. Thus, the high sensitivity of the assay provides a valuable tool to monitor effector T cell responses in different clinical situations.