Proliferation capacity and cytotoxic activity are mediated by functionally and phenotypically distinct virus-specific CD8 T cells defined by interleukin-7R{alpha} (CD127) and perforin expression

Molecular mechanisms underlying the modulation of T-cell proliferation and cytotoxicity by immobilized CCL21 and ICAM1

BACKGROUND

Adoptive cancer immunotherapy, using engineered T-cells, expressing chimeric antigen receptor or autologous tumor infiltrating lymphocytes became, in recent years, a major therapeutic approach for diverse types of cancer. However, despite the transformative potential of adoptive cancer immunotherapy, this field still faces major challenges, manifested by the apparent decline of the cytotoxic capacity of effector CD8+ T cells upon their expansion. To address these challenges, we have developed an ex vivo "synthetic immune niche" (SIN), composed of immobilized CCL21 and ICAM1, which synergistically induce an efficient expansion of antigen-specific CD8+ T cells while retaining, and even enhancing their cytotoxic potency.

METHODS

To explore the molecular mechanisms through which a CCL21+ICAM1-based SIN modulates the interplay between the proliferation and cytotoxic potency of antigen-activated and CD3/CD28-activated effector CD8+ T cells, we performed integrated analysis of specific differentiation markers via flow cytometry, together with gene expression profiling.

RESULTS

On day 3, the transcriptomic effect induced by the SIN was largely similar for both dendritic cell (DC)/ovalbumin (OVA)-activated and anti-CD3/CD28-activated cells. Cell proliferation increased and the cells exhibited high killing capacity. On day 4 and on, the proliferation/cytotoxicity phenotypes became radically "activation-specific"; The DC/OVA-activated cells lost their cytotoxic activity, which, in turn, was rescued by the SIN treatment. On longer incubation, the cytotoxic activity further declined, and on day7, could not be rescued by the SIN. SIN stimulation following activation with anti-CD3/CD28 beads induced a major increase in the proliferative phenotype while transiently suppressing their cytotoxicity for 2-3 days and fully regaining their killing activity on day 7. Potential molecular regulatory pathways of the SIN effects were identified, based on transcriptomic and multispectral imaging profiling.

CONCLUSIONS

These data indicate that cell proliferation and cytotoxicity are negatively correlated, and the interplay between them is differentially regulated by the mode of initial activation. The SIN stimulation greatly enhances the cell expansion, following both activation modes, while displaying high survival and cytotoxic potency at specific time points following stimulation, suggesting that it could effectively reinforce adoptive cancer immunotherapy.

Distinct association between chronic Epstein-Barr virus infection and T cell compartments from pediatric heart, kidney, and liver transplant recipients

Chronic Epstein-Barr virus (EBV) infection after pediatric organ transplantation (Tx) accounts for significant morbidity and mortality. The risk of complications, such as posttransplant lymphoproliferative disorders, in high viral load (HVL) carriers is the highest in heart Tx recipients. However, the immunologic signatures of such a risk have been insufficiently defined. Here, we assessed the phenotypic, functional, and transcriptomic profiles of peripheral blood CD8+/CD4+ T cells, including EBV-specific T cells, in 77 pediatric heart, kidney, and liver Tx recipients and established the relationship between memory differentiation and progression toward exhaustion. Unlike kidney and liver HVL carriers, heart HVL carriers displayed distinct CD8+ T cells with (1) up-regulation of interleukin-21R, (2) decreased naive phenotype and altered memory differentiation, (3) accumulation of terminally exhausted (TEX PD-1+T-bet-Eomes+) and decrease of functional precursors of exhausted (TPEX PD-1intT-bet+) effector subsets, and (4) transcriptomic signatures supporting the phenotypic changes. In addition, CD4+ T cells from heart HVL carriers displayed similar changes in naive and memory subsets, elevated Th1 follicular helper cells, and plasma interleukin-21, suggesting an alternative inflammatory mechanism that governs T cell responses in heart Tx recipients. These results may explain the different incidences of EBV complications and may help improve the risk stratification and clinical management of different types of Tx recipients.

A multivariate, quantitative assay that disentangles key kinetic parameters of primary human T cell function in vitro

Cell therapy is poised to play a larger role in medicine, most notably for immuno-oncology. Despite the recent success of CAR-T therapeutics in the treatment of blood tumors and the rapid progress toward improved versions of both CAR- and TCR-Ts, important analytical aspects of preclinical development and manufacturing of engineered T cells remain immature. One limiting factor is the absence of robust multivariate assays to disentangle key parameters related to function of engineered effector cells, especially in the peptide-MHC (pMHC) target realm, the natural ligand for TCRs. Here we describe an imaging-based primary T cell assay that addresses several of these limitations. To our knowledge, this assay is the first quantitative, high-content assay that separates the key functional parameters of time- and antigen-dependent T cell proliferation from cytotoxicity. We show that the assay sheds light on relevant biology of CAR- and TCR-T cells, including response kinetics and the influence of effector:target ratio.

IL-7Rαlow CD8+ T Cells from Healthy Individuals Are Anergic with Defective Glycolysis

Effector memory (EM) CD8⁺ T cells expressing lower levels of IL-7R α (IL-7Rα^low) from healthy individuals are partly compromised in vitro, but the identity of these cells has remained unclear. In this study, we demonstrate that human IL-7Rα^low EM CD8⁺ T cells are naturally occurring anergic cells in vivo and impaired in proliferation and IL-2 production but competent in IFN-γ and TNF-α production, a state that can be restored by IL-2 stimulation. IL-7Rα^low EM CD8⁺ T cells show decreased expression of GATA3 and c-MYC and are defective in metabolic reprogramming toward glycolysis, a process required for the proliferation of T cells. However, IL-7Rα^low EM CD8⁺ T cells can proliferate with TCR stimulation in the presence of IL-2 and IL-15, suggesting that these cells can be restored to normality or increased activity by inflammatory conditions and may serve as a reservoir for functional immunity.

sLeX Expression Delineates Distinct Functional Subsets of Human Blood Central and Effector Memory T Cells

Sialyl Lewis X (sLeX) regulates T cell trafficking from the vasculature into skin and sites of inflammation, thereby playing a critical role in immunity. In healthy persons, only a small proportion of human blood T cells express sLeX, and their function is not fully defined. Using a combination of biochemical and functional studies, we find that human blood sLeX+CD4+T cells comprise a subpopulation expressing high levels of Th2 and Th17 cytokines, chemokine receptors CCR4 and CCR6, and the transcription factors GATA-3 and RORγT. Additionally, sLeX+CD4+T cells exclusively contain the regulatory T cell population (CD127lowCD25high and FOXP3+) and characteristically display immune-suppressive molecules, including the coinhibitor receptors PD-1 and CTLA-4. Among CD8+T cells, sLeX expression distinguishes a subset displaying low expression of cytotoxic effector molecules, perforin and granzyme β, with reduced degranulation and CD57 expression and, consistently, marginal cytolytic capacity after TCR engagement. Furthermore, sLeX+CD8+T cells present a pattern of features consistent with Th cell-like phenotype, including release of pertinent Tc2 cytokines and elevated expression of CD40L. Together, these findings reveal that sLeX display is associated with unique functional specialization of both CD4+ and CD8+T cells and indicate that circulating T cells that are primed to migrate to lesional sites at onset of inflammation are not poised for cytotoxic function.

Large-Scale HLA Tetramer Tracking of T Cells during Dengue Infection Reveals Broad Acute Activation and Differentiation into Two Memory Cell Fates

T cells play important multifaceted roles during dengue infection, and understanding their responses is important for defining correlates of protective immunity and identifying effective vaccine antigens. Using mass cytometry and a highly multiplexed peptide-HLA (human leukocyte antigen) tetramer staining strategy, we probed T cells from dengue patients-a total of 430 dengue and control candidate epitopes-together with key markers of activation, trafficking, and differentiation. During acute disease, dengue-specific CD8⁺ T cells expressed a distinct profile of activation and trafficking receptors that distinguished them from non-dengue-specific T cells. During convalescence, dengue-specific T cells differentiated into two major cell fates, CD57⁺ CD127^--resembling terminally differentiated senescent memory cells and CD127⁺ CD57^--resembling proliferation-capable memory cells. Validation in an independent cohort showed that these subsets remained at elevated frequencies up to one year after infection. These analyses aid our understanding of the generation of T cell memory in dengue infection or vaccination.

An altered cytotoxic program of CD8+ T-cells in HIV-infected patients despite HAART-induced viral suppression

Despite the suppression of viral replication induced by the highly active anti-retroviral therapy (HAART), an increased immune activation and inflammatory state persists in HIV-infected patients, contributing to lower treatment response and immune reconstitution, and development of non-AIDS conditions. The chronic activation and inflammation affect the functionality and differentiation of CD8+ T-cells, particularly reducing their cytotoxic capacity, which is critical in the control of HIV replication. Although previous studies have shown that HAART induce a partial immune reconstitution, its effect on CD8+ T-cells cytotoxic function, as well as its relationship with the inflammatory state, is yet to be defined. Here, we characterized the functional profile of polyclonal and HIV-specific CD8+ T cells, based on the expression of cell activation and differentiation markers, in individuals chronically infected with HIV, under HAART. Compared with seronegative controls, CD8+ T-cells from patients on HAART exhibited a low degranulation capacity (surface expression of CD107a), with consequent low secreted levels and high intracellular expression of granzyme B and perforin. This degranulation defect was particularly observed in those cells expressing the activation marker HLA-DR, which were further characterized as effector memory cells with high expression of CD57. The expression of CD107a, but not of granzyme B and perforin, in CD8+ T-cells from HIV-infected patients on HAART reached levels similar to those in seronegative controls when the treatment duration was higher than 25 months. In addition, the expression of CD107a was negatively correlated with the expression of exhaustion markers on CD8+ T-cells and the plasma inflammatory molecule sCD14. Thus, despite HAART-induced viral suppression, CD8+ T-cells from HIV-infected patients have an alteration in their cytotoxic program. This defect is associated with the cellular activation, differentiation and exhaustion state, as well as with the inflammation levels, and can be partially recovered with a long and continuous treatment.

Interferon gamma (IFN-γ) negative CD4+ and CD8+ T-cells can produce immune mediators in response to viral antigens

Evaluation of antigen-specific T-cell responses to viral antigens is frequently performed on IFN-γ secreting cells. However, T-cells are capable of producing many more functions than just IFN-γ, some of which, like Perforin, are associated with immune protection in HIV-1 disease elite controllers. We evaluated the extent of missed T-cell functions when IFN-γ secretion is used as a surrogate marker for further evaluation of T-cell functions. Intracellular cytokine staining assay and flow cytometry were used to assess peripheral blood mononuclear cells (PBMCs) from 31 HIV-infected ART-naive individuals for the extent to which gated CD4+ and CD8+ IFN-γ producing and non-producing T-cells also secreted IL-2, Perforin, and TNF-α functions. Similarly, the extent of missed virus-specific responses in IFN-γ ELISpot assay negative T-cells from 5 HIV-1 uninfected individuals was evaluated. Cells from HIV-infected individuals were stimulated with pooled consensus group M (Con M) peptides; and those from healthy individuals were stimulated with pooled adenovirus (Ad) peptides. Overall, frequencies of virus-specific IFN-γ secreting CD4+ and CD8+ cells were low. Proportions of IFN-γ negative CD4+ expressing IL-2, Perforin, or TNF-α to Con M were significantly higher (5 of 7 functional profiles) than the corresponding IFN-γ positive CD4+ (0 of 7) T-cell phenotype, p = 0.02; Fisher's Exact test. Likewise, proportions of CD8+ T-cells expressing other functions were significantly higher in 4 of the 7 IFN-γ negative CD8+ T-cells. Notably, newly stimulated Perforin, identified as Perforin co-expression with IL-2 or TNF-α, was significantly higher in IFN-γ negative CD8+ T-cell than in the positive CD8+ T-cells. Using SEB, lower responses in IFN-γ positive cells were most associated with CD4+ than CD8+ T-cells. These findings suggest that studies evaluating immunogenicity in response to HIV and Adenovirus viral antigens should not only evaluate T-cell responsiveness among IFN-γ producing cells but also among those T-cells that do not express IFN-γ.

Abnormal T Cell Frequencies, Including Cytomegalovirus-Associated Expansions, Distinguish Seroconverted Subjects at Risk for Type 1 Diabetes

We analyzed T cell subsets from cryopreserved PBMC obtained from the TrialNet Pathway to Prevention archives. We compared subjects who had previously seroconverted for one or more autoantibodies with non-seroconverted, autoantibody negative individuals. We observed a reduced frequency of MAIT cells among seroconverted subjects. Seroconverted subjects also possessed decreased frequencies of CCR4-expressing CD4 T cells, including a regulatory-like subset. Interestingly, we found an elevation of CD57+, CD28–, CD127–, CD27– CD8 T cells (SLEC) among seroconverted subjects that was most pronounced among those that progressed to disease. The frequency of these SLEC was strongly correlated with CMV IgG abundance among seroconverted subjects, associated with IA-2 levels, and most elevated among CMV+ seroconverted subjects who progressed to disease. Combined, our data indicate discrete, yet profound T cell alterations are associated with islet autoimmunity among at-risk subjects.

The Vast Universe of T Cell Diversity: Subsets of Memory Cells and Their Differentiation

The T cell receptor confers specificity for antigen recognition to T cells. By the first encounter with the cognate antigen, reactive T cells initiate a program of expansion and differentiation that will define not only the ultimate quantity of specific cells that will be generated, but more importantly their quality and functional heterogeneity. Recent achievements using mouse model infection systems have helped to shed light into the complex network of factors that dictate and sustain memory T cell differentiation, ranging from antigen load, TCR signal strength, metabolic fitness, transcriptional programs, and proliferative potential. The different models of memory T cell differentiation are discussed in this chapter, and key phenotypic and functional attributes of memory T cell subsets are presented, both for mouse and human cells. Therapeutic manipulation of memory T cell generation is expected to provide novel unique ways to optimize current immunotherapies, both in infection and cancer.

Cell-Mediated Immune Predictors of Vaccine Effect on Viral Load and CD4 Count in a Phase 2 Therapeutic HIV-1 Vaccine Clinical Trial

Background

In a placebo-controlled trial of the peptide-based therapeutic HIV-1 p24^Gag vaccine candidate Vacc-4x, participants on combination antiretroviral therapy (cART) received six immunizations over 18 weeks, followed by analytical treatment interruption (ATI) between weeks 28 and 52. Cell-mediated immune responses were investigated as predictors of Vacc-4x effect (VE) on viral load (VL) and CD4 count during ATI.

Methods

All analyses of week 28 responses and fold-changes relative to baseline considered per-protocol participants (Vacc-4x:placebo = 72:32) resuming cART after week 40. Linear regression models with interaction tests were used. VE was estimated as the Vacc-4x–placebo difference in log₁₀-transformed VL (VE^VL) or CD4 count (VE^CD4).

Findings

A lower fold-change of CD4+ T-cell proliferation was associated with VE^CD4 at week 48 (p = 0.036, multiplicity adjusted q = 0.036) and week 52 (p = 0.040, q = 0.080). A higher fold-change of IFN-γ in proliferation supernatants was associated with VE^VL at week 44 (p = 0.047, q = 0.07). A higher fold-change of TNF-α was associated with VE^VL at week 44 (p = 0.045, q = 0.070), week 48 (p = 0.028, q = 0.070), and week 52 (p = 0.037, q = 0.074). A higher fold-change of IL-6 was associated with VE^VL at week 48 (p = 0.017, q = 0.036). TNF-α levels (> median) were associated with VE^CD4 at week 48 (p = 0.009, q = 0.009).

Interpretation

These exploratory analyses highlight the potential value of investigating biomarkers in T-cell proliferation supernatants for VE in clinical studies.

•

Ex vivo CD4+ T-cell proliferation was predictive of Vacc-4x effect.

•

IFN-γ, TNF-α and IL-6 secretion in T-cell proliferation supernatants were predictive of Vacc-4x effect.

•

Such immune predictors could be utilized to mitigate risks associated with cART interruption towards HIV cure.

No immune correlates or predictors of therapeutic vaccine effect (i.e. a reduction in viral load compared to placebo on treatment interruption) for human immunodeficiency virus (HIV)-1 are known. We investigated a broad array of cytokines/chemokines produced in T-cell proliferation supernatants from a placebo-controlled clinical study of a therapeutic HIV vaccine. Although such supernatants do not provide cell type-specific readouts, the cytokines/chemokines studied included T-helper (Th)1, Th2, growth factor, immuno-modulatory and pro-inflammatory functions. Specifically, we found that, IFN-γ, TNF-α and IL-6 secretion correlated with vaccine effect, suggesting such supernatants could represent important sample material not previously considered for the identification of immune markers of vaccine effect.

Sequential Vacc-4x and romidepsin during combination antiretroviral therapy (cART): Immune responses to Vacc-4x regions on p24 and changes in HIV reservoirs

OBJECTIVES

The REDUC clinical study Part B investigated Vacc-4x/rhuGM-CSF therapeutic vaccination prior to HIV latency reversal using romidepsin. The main finding was a statistically significant reduction from baseline in viral reservoir measurements. Here we evaluated HIV-specific functional T-cell responses following Vacc-4x/rhuGM-CSF immunotherapy in relation to virological outcomes on the HIV reservoir.

METHODS

This study, conducted in Aarhus, Denmark, enrolled participants (n = 20) with CD4>500 cells/mm³ on cART. Six Vacc-4x (1.2 mg) intradermal immunizations using rhuGM-CSF (60 μg) as adjuvant were followed by 3 weekly intravenous infusions of romidepsin (5 mg/m²). Immune responses were determined by IFN-γ ELISpot, T-cell proliferation to p24 15-mer peptides covering the Vacc-4x region, intracellular cytokine staining (ICS) to the entire HIV^Gag and viral inhibition.

RESULTS

The frequency of participants with CD8+ T-cell proliferation assay positivity was 8/16 (50%) at baseline, 11/15 (73%) post-vaccination, 6/14 (43%) during romidepsin, and 9/15 (60%)post-romidepsin. Participants with CD8+ T-cell proliferation assay positivity post-vaccination showed reductions in total HIV DNA post-vaccination (p = 0.006; q = 0.183), post-latency reversal (p = 0.005; q = 0.183), and CA-RNA reductions post-vaccination (p = 0.015; q = 0.254). Participants (40%) were defined as proliferation 'Responders' having ≥2-fold increase in assay positivity post-baseline. Robust ELISpot baseline responses were found in 87.5% participants. No significant changes were observed in the proportion of polyfunctional CD8+ T-cells to HIV^Gag by ICS. There was a trend towards increased viral inhibition from baseline to post-vaccination (p = 0.08).

CONCLUSIONS

In this 'shock and kill' approach supported by therapeutic vaccination, CD8+ T-cell proliferation represents a valuable means to monitor functional immune responses as part of the path towards functional HIV cure.

Signaling Lymphocytic Activation Molecule Family Member 7 Engagement Restores Defective Effector CD8+ T Cell Function in Systemic Lupus Erythematosus

OBJECTIVE

Effector CD8+ T cell function is impaired in systemic lupus erythematosus (SLE) and is associated with a compromised ability to fight infections. Signaling lymphocytic activation molecule family member 7 (SLAMF7) engagement has been shown to enhance natural killer cell degranulation. This study was undertaken to characterize the expression and function of SLAMF7 on CD8+ T cell subsets isolated from the peripheral blood of SLE patients and healthy subjects.

METHODS

CD8+ T cell subset distribution, SLAMF7 expression, and expression of cytolytic enzymes (perforin, granzyme A [GzmA], and GzmB) on cells isolated from SLE patients and healthy controls were analyzed by flow cytometry. CD107a expression and interferon-γ (IFNγ) production in response to viral antigenic stimulation in the presence or absence of an anti-SLAMF7 antibody were assessed by flow cytometry. Antiviral cytotoxic activity in response to SLAMF7 engagement was determined using a flow cytometry-based assay.

RESULTS

The distribution of CD8+ T cell subsets was altered in the peripheral blood of SLE patients, with a decreased effector cell subpopulation. Memory CD8+ T cells from SLE patients displayed decreased amounts of SLAMF7, a surface receptor that characterizes effector CD8+ T cells. Ligation of SLAMF7 increased CD8+ T cell degranulation capacity and the percentage of IFNγ-producing cells in response to antigen challenge in SLE patients and healthy controls. Moreover, SLAMF7 engagement promoted cytotoxic lysis of target cells in response to stimulation with viral antigens.

CONCLUSION

CD8+ T cell activation in response to viral antigens is defective in SLE patients. Activation of SLAMF7 through a specific monoclonal antibody restores CD8+ T cell antiviral effector function to normal levels and thus represents a potential therapeutic option in SLE.

Identification of Autoantigen Epitopes in Alopecia Areata

Alopecia areata (AA) is believed to be a cell-mediated autoimmune hair loss disease. Both CD4 and cytotoxic CD8 T cells (CTLs) are important for the onset and progression of AA. Hair follicle (HF) keratinocyte and/or melanocyte antigen epitopes are suspected potential targets of autoreactive CTLs, but the specific epitopes have not yet been identified. We investigated the potential for a panel of known epitopes, expressed by HF keratinocytes and melanocytes, to induce activation of CTL populations in peripheral blood mononuclear cells. Specific synthetic epitopes derived from HF antigens trichohyalin and tyrosinase-related protein-2 induced significantly higher frequencies of response in AA CTLs compared with healthy controls (IFN-gamma secretion). Apoptosis assays revealed conditioned media from AA peripheral blood mononuclear cells stimulated with trichohyalin peptides elevated the expression of apoptosis markers in primary HF keratinocytes. A cytokine array revealed higher expression of IL-13 and chemokine ligand 5 (CCL5, RANTES) from AA peripheral blood mononuclear cells stimulated with trichohyalin peptides compared with controls. The data indicate that AA affected subjects present with an increased frequency of CTLs responsive to epitopes originating from keratinocytes and melanocytes; the activated CTLs secreted soluble factors that induced apoptosis in HF keratinocytes. Potentially, CTL response to self-antigen epitopes, particularly trichohyalin epitopes, could be a prognostic marker for human AA.

Regulation of CD8+ T-cell cytotoxicity in HIV-1 infection

Understanding the mechanisms involved in cellular immune responses against control of human immunodeficiency virus (HIV) infection is key to development of effective immunotherapeutic strategies against viral proliferation. Clear insights into the regulation of cytotoxic CD8+ T cells is crucial to development of effective immunotherapeutic strategies due to their unique ability to eliminate virus-infected cells during the course of infection. Here, we reviewed the roles of transcription factors, co-inhibitory molecules and regulatory cytokines following HIV infection and their potential significance in regulating the cytotoxic potentials of CD8+ T cells.

CD160-associated CD8 T-cell functional impairment is independent of PD-1 expression

Expression of co-inhibitory molecules is generally associated with T-cell dysfunction in chronic viral infections such as HIV or HCV. However, their relative contribution in the T-cell impairment remains unclear. In the present study, we have evaluated the impact of the expression of co-inhibitory molecules such as 2B4, PD-1 and CD160 on the functions of CD8 T-cells specific to influenza, EBV and CMV. We show that CD8 T-cell populations expressing CD160, but not PD-1, had reduced proliferation capacity and perforin expression, thus indicating that the functional impairment in CD160⁺ CD8 T cells may be independent of PD-1 expression. The blockade of CD160/CD160-ligand interaction restored CD8 T-cell proliferation capacity, and the extent of restoration directly correlated with the ex vivo proportion of CD160⁺ CD8 T cells suggesting that CD160 negatively regulates TCR-mediated signaling. Furthermore, CD160 expression was not up-regulated upon T-cell activation or proliferation as compared to PD-1. Taken together, these results provide evidence that CD160-associated CD8 T-cell functional impairment is independent of PD-1 expression.

T-cell immune response is regulated by a variety of molecules known as co-inhibitory receptors. The over expression of co-inhibitory receptors has been observed in several chronic viral infections such as HIV disease, and is found to be associated with severe T-cell dysfunction. Recent studies have demonstrated that the co-expression of several co-inhibitory receptors correlated with greater impairment of CD8 T cells. However, the relative contribution of individual co-inhibitory receptors to the regulation of T-cell functions remains unclear. In order to shed light on these issues, we have evaluated the influence of the expression of 3 major co-inhibitory receptors such as PD-1, 2B4 and CD160 on CD8 T-cell functions such as proliferation, cytokines production and expression of cytotoxic granules. We demonstrate that CD160-associated CD8 T-cell functional impairment is independent of PD-1 expression and that the blockade of CD160 signaling may partially restore CD8 T-cell functions.

Exhaustion of bacteria-specific CD4 T cells and microbial translocation in common variable immunodeficiency disorders

Common variable immunodeficiency (CVID) is characterized by abnormally low levels of antibodies in the blood and dysfunctional immune cells called CD4⁺ T cells. Perreau et al. now show evidence that bacteria-fighting CD4⁺ T cells in these patients are in a state of exhaustion due to a constant leakage of normal gut bacteria into the bloodstream, possibly due to insufficient antibody levels.

In the present study, we have investigated the functional profile of CD4 T cells from patients with common variable immunodeficiency (CVID), including production of cytokines and proliferation in response to bacteria and virus-derived antigens. We show that the functional impairment of CD4 T cells, including the reduced capacity to proliferate and to produce IFN-γ and IL-2, was restricted to bacteria-specific and not virus-specific CD4 T cells. High levels of endotoxins were found in the plasma of patients with CVID, suggesting that CD4 T cell dysfunction might be caused by bacterial translocation. Of note, endotoxemia was associated with significantly higher expression of programmed death 1 (PD-1) on CD4 T cells. The blockade of the PD-1–PD-L1/2 axis in vitro restored CD4 T cell proliferation capacity, thus indicating that PD-1 signaling negatively regulates CD4 T cell functions. Finally, we showed that intravenous immunoglobulin G (IVIG) treatment significantly reduced endotoxemia and the percentage of PD-1⁺ CD4 T cells, and restored bacteria-specific CD4 T cell cytokine production and proliferation. In conclusion, the present study demonstrates that the CD4 T cell exhaustion and functional impairment observed in CVID patients is associated with bacterial translocation and that IVIG treatment resolves bacterial translocation and restores CD4 T cell functions.

Functional avidity and IL-2/perforin production is linked to the emergence of mutations within HLA-B*5701-restricted epitopes and HIV-1 disease progression

Viral escape from HIV-1-specific CD8(+) T cells has been demonstrated in numerous studies previously. However, the qualitative features driving the emergence of mutations within epitopes are still unclear. In this study, we aimed to distinguish whether specific functional characteristics of HLA-B*5701-restricted CD8(+) T cells influence the emergence of mutations in high-risk progressors (HRPs) versus low-risk progressors (LRPs). Single-genome sequencing was performed to detect viral mutations (variants) within seven HLA-B*5701-restricted epitopes in Gag (n = 4) and Nef (n = 3) in six untreated HLA-B*5701 subjects followed from early infection up to 7 y. Several well-characterized effector markers (IFN-γ, IL-2, MIP-1β, TNF, CD107a, and perforin) were identified by flow cytometry following autologous (initial and emerging variant/s) epitope stimulations. This study demonstrates that specific functional attributes may facilitate the outgrowth of mutations within HLA-B*5701-restricted epitopes. A significantly lower fraction of IL-2-producing cells and a decrease in functional avidity and polyfunctional sensitivity were evident in emerging epitope variants compared with the initial autologous epitopes. Interestingly, the HRPs mainly drove these differences, whereas the LRPs maintained a directed and maintained functional response against emerging epitope variants. In addition, LRPs induced improved cell-cycle progression and perforin upregulation after autologous and emerging epitope variant stimulations in contrast to HRPs. The maintained quantitative and qualitative features of the CD8(+) T cell responses in LRPs toward emerging epitope variants provide insights into why HLA-B*5701 subjects have different risks of HIV-1 disease progression.

MART-1 peptide vaccination plus IMP321 (LAG-3Ig fusion protein) in patients receiving autologous PBMCs after lymphodepletion: results of a Phase I trial

Background

Immunotherapy offers a promising novel approach for the treatment of cancer and both adoptive T-cell transfer and immune modulation lead to regression of advanced melanoma. However, the potential synergy between these two strategies remains unclear.

Methods

We investigated in 12 patients with advanced stage IV melanoma the effect of multiple MART-1 analog peptide vaccinations with (n = 6) or without (n = 6) IMP321 (LAG-3Ig fusion protein) as an adjuvant in combination with lymphodepleting chemotherapy and adoptive transfer of autologous PBMCs at day (D) 0 (Trial registration No: NCT00324623). All patients were selected on the basis of ex vivo detectable MART-1-specific CD8 T-cell responses and immunized at D0, 8, 15, 22, 28, 52, and 74 post-reinfusion.

Results

After immunization, a significant expansion of MART-1-specific CD8 T cells was measured in 83% (n = 5/6) and 17% (n = 1/6) of patients from the IMP321 and control groups, respectively (P < 0.02). Compared to the control group, the mean fold increase of MART-1-specific CD8 T cells in the IMP321 group was respectively >2-, >4- and >6-fold higher at D15, D30 and D60 (P < 0.02). Long-lasting MART-1-specific CD8 T-cell responses were significantly associated with IMP321 (P < 0.02). At the peak of the response, MART-1-specific CD8 T cells contained higher proportions of effector (CCR7⁻ CD45RA^+/−) cells in the IMP321 group (P < 0.02) and showed no sign of exhaustion (i.e. were mostly PD1⁻CD160⁻TIM3⁻LAG3⁻2B4^+/−). Moreover, IMP321 was associated with a significantly reduced expansion of regulatory T cells (P < 0.04); consistently, we observed a negative correlation between the relative expansion of MART-1-specific CD8 T cells and of regulatory T cells_. Finally, although there were no confirmed responses as per RECIST criteria, a transient, 30-day partial response was observed in a patient from the IMP321 group.

Conclusions

Vaccination with IMP321 as an adjuvant in combination with lymphodepleting chemotherapy and adoptive transfer of autologous PBMCs induced more robust and durable cellular antitumor immune responses, supporting further development of IMP321 as an adjuvant for future immunotherapeutic strategies.

Safety and efficacy of the peptide-based therapeutic vaccine for HIV-1, Vacc-4x: a phase 2 randomised, double-blind, placebo-controlled trial

BACKGROUND

Present combination antiretroviral therapy (cART) alone does not cure HIV infection and requires lifelong drug treatment. The potential role of HIV therapeutic vaccines as part of an HIV cure is under consideration. Our aim was to assess the efficacy, safety, and immunogenicity of Vacc-4x, a peptide-based HIV-1 therapeutic vaccine targeting conserved domains on p24(Gag), in adults infected with HIV-1.

METHODS

Between July, 2008, and June, 2010, we did a multinational double-blind, randomised, phase 2 study comparing Vacc-4x with placebo. Participants were adults infected with HIV-1 who were aged 18-55 years and virologically suppressed on cART (viral load <50 copies per mL) with CD4 cell counts of 400 × 10(6) cells per L or greater. The trial was done at 18 sites in Germany, Italy, Spain, the UK, and the USA. Participants were randomly assigned (2:1) to Vacc-4x or placebo. Group allocation was masked from participants and investigators. Four primary immunisations, weekly for 4 weeks, containing Vacc-4x (or placebo) were given intradermally after administration of adjuvant. Booster immunisations were given at weeks 16 and 18. At week 28, cART was interrupted for up to 24 weeks. The coprimary endpoints were cART resumption and changes in CD4 counts during treatment interruption. Analyses were by modified intention to treat: all participants who received one intervention. Furthermore, safety, viral load, and immunogenicity (as measured by ELISPOT and proliferation assays) were assessed. The 52 week follow-up period was completed in June, 2011. For the coprimary endpoints the proportion of participants who met the criteria for cART resumption was analysed with a logistic regression model with the treatment effect being assessed in a model including country as a covariate. This study is registered with ClinicalTrials.gov, number NCT00659789.

FINDINGS

174 individuals were screened; because of slow recruitment, enrolment stopped with 136 of a planned 345 participants and 93 were randomly assigned to receive Vacc-4x and 43 to receive placebo. There were no differences between the two groups for the primary efficacy endpoints in those participants who stopped cART at week 28. Of the participants who resumed cART, 30 (34%) were in the Vacc-4x group and 11 (29%) in the placebo group, and percentage changes in CD4 counts were not significant (mean treatment difference -5·71, 95% CI -13·01 to 1·59). However, a significant difference in viral load was noted for the Vacc-4x group both at week 48 (median 23,100 copies per mL Vacc-4x vs 71,800 copies per mL placebo; p=0·025) and week 52 (median 19,550 copies per mL vs 51,000 copies per mL; p=0·041). One serious adverse event, exacerbation of multiple sclerosis, was reported as possibly related to study treatment. Vacc-4x was immunogenic, inducing proliferative responses in both CD4 and CD8 T-cell populations.

INTERPRETATION

The proportion of participants resuming cART before end of study and change in CD4 counts during the treatment interruption showed no benefit of vaccination. Vacc-4x was safe, well tolerated, immunogenic, seemed to contribute to a viral-load setpoint reduction after cART interruption, and might be worth consideration in future HIV-cure investigative strategies.

FUNDING

Norwegian Research Council GLOBVAC Program and Bionor Pharma ASA.

Stemness of T cells and the hematopoietic stem cells: fate, memory, niche, cytokines

Stem cells are able to generate both cells that differentiate and cells that remain undifferentiated but potentially have the same developmental program. The prolonged duration of the protective immune memory for infectious diseases such as polio, small pox, and measles, suggested that memory T cells may have stem cell properties. Understanding the molecular basis for the life-long persistence of memory T cells may be useful to project targeted therapies for immune deficiencies and infectious diseases and to formulate vaccines. In the last decade evidence from different laboratories shows that memory T cells may share self-renewal pathways with bone marrow hematopoietic stem cells. In stem cells the intrinsic self-renewal activity, which depends on gene expression, is known to be modulated by extrinsic signals from the environment that may be tissue specific. These extrinsic signals for stemness of memory T cells include cytokines such as IL-7 and IL-15 and there are other cytokine signals for maintaining the cytokine signature (TH1, TH2, etc.) of memory T cells. Intrinsic and extrinsic pathways that might be common to bone marrow hematopoietic stem cells and memory T lymphocytes are discussed and related to self-renewal functions.

Immunological assessment of influenza vaccines and immune correlates of protection

Influenza vaccines remain the primary public health tool in reducing the ever-present burden of influenza and its complications. In seeking more immunogenic, more effective and more broadly cross-protective influenza vaccines, the landscape of influenza vaccines is rapidly expanding, both in near-term advances and next-generation vaccine design. Although the first influenza vaccines were licensed over 60 years ago, the hemagglutination-inhibition antibody titer is currently the only universally accepted immune correlate of protection against influenza. However, hemagglutination-inhibition titers appear to be less effective at predicting protection in populations at high risk for severe influenza disease; older adults, young children and those with certain medical conditions. The lack of knowledge and validated methods to measure alternate immune markers of protection against influenza remain a substantial barrier to the development of more immunogenic, broadly cross-reactive and effective influenza vaccines. Here, the authors review the knowledge of immune effectors of protection against influenza and discuss assessment methods for a broader range of immunological parameters that could be considered in the evaluation of traditional or new-generation influenza vaccines.

From "truly naïve" to "exhausted senescent" T cells: when markers predict functionality

The study of T cell biology has been accelerated by substantial progress at the technological level, particularly through the continuing advancement of flow cytometry. The conventional approach of observing T cells as either T helper or T cytotoxic is overly simplistic and does not allow investigators to clearly identify immune mechanisms or alterations in physiological processes that impact on clinical outcomes. The complexity of T cell sub-populations, as we understand them today, combined with the immunological and functional diversity of these subsets represent significant complications for the study of T cell biology. In this article, we review the use of classical markers in delineating T cell sub-populations, from "truly naïve" T cells (recent thymic emigrants with no proliferative history) to "exhausted senescent" T cells (poorly proliferative cells that display severe functional abnormalities) wherein the different phenotypes of these populations reflect their disparate functionalities. In addition, since persistent infections and chronological aging have been shown to be associated with significant alterations in human T cell distribution and function, we also discuss age-associated and cytomegalovirus-driven alterations in the expression of key subset markers.

Rapid perturbation in viremia levels drives increases in functional avidity of HIV-specific CD8 T cells

The factors determining the functional avidity and its relationship with the broad heterogeneity of antiviral T cell responses remain partially understood. We investigated HIV-specific CD8 T cell responses in 85 patients with primary HIV infection (PHI) or chronic (progressive and non-progressive) infection. The functional avidity of HIV-specific CD8 T cells was not different between patients with progressive and non-progressive chronic infection. However, it was significantly lower in PHI patients at the time of diagnosis of acute infection and after control of virus replication following one year of successful antiretroviral therapy. High-avidity HIV-specific CD8 T cells expressed lower levels of CD27 and CD28 and were enriched in cells with an exhausted phenotype, i.e. co-expressing PD-1/2B4/CD160. Of note, a significant increase in the functional avidity of HIV-specific CD8 T cells occurred in early-treated PHI patients experiencing a virus rebound after spontaneous treatment interruption. This increase in functional avidity was associated with the accumulation of PD-1/2B4/CD160 positive cells, loss of polyfunctionality and increased TCR renewal. The increased TCR renewal may provide the mechanistic basis for the generation of high-avidity HIV-specific CD8 T cells. These results provide insights on the relationships between functional avidity, viremia, T-cell exhaustion and TCR renewal of antiviral CD8 T cell responses.

CD8 T cells directed against virus are complex and functionally heterogeneous. One relevant component of CD8 T cells is their functional avidity which reflects their sensitivity to cognate antigens, i.e. how prone T cells are to respond when they encounter low doses of antigens. In patients with chronic and established HIV infection, we observed that the sensitivity of HIV-specific CD8 T cells was not different between patients with progressive or non-progressive disease. In contrast, the sensitivity of HIV-specific CD8 T cells was significantly lower in patients with early and recent HIV infection. Furthermore, CD8 T cells of high avidity were preferentially associated with a state of functional impairment known as exhaustion. Of interest, some patients treated with antiretroviral therapy during acute infection spontaneously interrupted their treatment and experienced a rebound of virus. In these patients, the avidity of HIV-specific CD8 T cells increased and this increase was associated to stronger cell exhaustion and greater renewal of the population of antiviral CD8 T cells, thus potentially providing the mechanistic basis for the generation of high-avidity CD8 T cells. Overall, our data suggest that rapid perturbation in viremia levels drove increases in the functional avidity of HIV-specific CD8 T cells.

Lack of Mycobacterium tuberculosis-specific interleukin-17A-producing CD4+ T cells in active disease

Protective immunity to Mycobacterium tuberculosis (Mtb) is commonly ascribed to a Th1 profile; however, the involvement of Th17 cells remains to be clarified. Here, we characterized Mtb-specific CD4(+) T cells in blood and bronchoalveolar lavages (BALs) from untreated subjects with either active tuberculosis disease (TB) or latent Mtb infection (LTBI), considered as prototypic models of uncontrolled or controlled infection, respectively. The production of IL-17A, IFN-γ, TNF-α, and IL-2 by Mtb-specific CD4(+) T cells was assessed both directly ex vivo and following in vitro antigen-specific T-cell expansion. Unlike for extracellular bacteria, Mtb-specific CD4(+) T-cell responses lacked immediate ex vivo IL-17A effector function in both LTBI and TB individuals. Furthermore, Mtb-specific Th17 cells were absent in BALs, while extracellular bacteria-specific Th17 cells were identified in gut biopsies of healthy individuals. Interestingly, only Mtb-specific CD4(+) T cells from 50% of LTBI but not from TB subjects acquired the ability to produce IL-17A following Mtb-specific T-cell expansion. Finally, IL-17A acquisition by Mtb-specific CD4(+) T cells correlated with the coexpression of CXCR3 and CCR6, currently associated to Th1 or Th17 profiles, respectively. Our data demonstrate that Mtb-specific Th17 cells are selectively undetectable in peripheral blood and BALs from TB patients.

Combination of immune and viral factors distinguishes low-risk versus high-risk HIV-1 disease progression in HLA-B*5701 subjects

HLA-B*5701 is the host factor most strongly associated with slow HIV-1 disease progression, although rates can vary within this group. Underlying mechanisms are not fully understood but likely involve both immunological and virological dynamics. The present study investigated HIV-1 in vivo evolution and epitope-specific CD8(+) T cell responses in six HLA-B*5701 patients who had not received antiretroviral treatment, monitored from early infection for up to 7 years. The subjects were classified as high-risk progressors (HRPs) or low-risk progressors (LRPs) based on baseline CD4(+) T cell counts. Dynamics of HIV-1 Gag p24 evolution and multifunctional CD8(+) T cell responses were evaluated by high-resolution phylogenetic analysis and polychromatic flow cytometry, respectively. In all subjects, substitutions occurred more frequently in flanking regions than in HLA-B*5701-restricted epitopes. In LRPs, p24 sequence diversity was significantly lower; sequences exhibited a higher degree of homoplasy and more constrained mutational patterns than HRPs. The HIV-1 intrahost evolutionary rate was also lower in LRPs and followed a strict molecular clock, suggesting neutral genetic drift rather than positive selection. Additionally, polyfunctional CD8(+) T cell responses, particularly to TW10 and QW9 epitopes, were more robust in LRPs, who also showed significantly higher interleukin-2 (IL-2) production in early infection. Overall, the findings indicate that HLA-B*5701 patients with higher CD4 counts at baseline have a lower risk of HIV-1 disease progression because of the interplay between specific HLA-linked immune responses and the rate and mode of viral evolution. The study highlights the power of a multidisciplinary approach, integrating high-resolution evolutionary and immunological data, to understand mechanisms underlying HIV-1 pathogenesis.

Low perforin expression of early differentiated HCV-specific CD8+ T cells limits their hepatotoxic potential

BACKGROUND & AIMS

Perforin plays a central role in the immunopathogenesis of different viral infections. However, its role in hepatitis C virus (HCV) infection has not been fully understood. Here, we analyzed two closely related questions: first, is CD8+ T cell-mediated killing of HCV-replicating human hepatoma cells mediated by perforin? Second, if so, do HCV-specific CD8+ T cells obtained from chronically HCV infected patients express and upregulate perforin?

METHODS

Susceptibility of HCV-replicating human hepatoma cells to the cytotoxic pathway was tested in vitro by addition of perforin substitute streptolysin O and granzyme B and by co-culture experiments with a perforin-expressing HCV-specific CD8+ T cell clone in the presence of perforin or caspase inhibitors. HCV-specific CD8+ T cells were obtained and analyzed for perforin expression and differentiation markers ex vivo from 12 chronically infected patients and 12 patients with resolved HCV infection.

RESULTS

HCV-replicating human hepatoma cells were susceptible to cytotoxic killing in vitro and a dominant role of perforin in HCV-specific CD8+ T cell-mediated cytolysis was observed. However, HCV-specific CD8+ T cells obtained ex vivo from chronically HCV infected patients expressed only low levels of perforin and showed an impaired ability to upregulate perforin. This was tightly linked to the distinct differentiation stage of HCV-specific CD8+ T cell differentiation ex vivo since early and intermediate differentiated HCV-specific CD8+ T cells only showed weak perforin expression in contrast to late differentiated CD8+ T cells that displayed strong perforin expression.

CONCLUSIONS

Our results suggest that perforin plays a dominant role in CD8+ T cell-mediated lysis of HCV-replicating human hepatoma cells but that lysis may be limited in human chronic viral infection by the low perforin expression of early/intermediate differentiated HCV-specific CD8+ T cells.

Characteristics of alloreactive T cells measured before renal transplantation

Several assays to measure pre-existing allospecific T cell immunity in renal transplant candidates have been developed in the past years. In 46 patients, we used flow cytometry-based mixed lymphocyte culture to measure the precursor frequency and phenotype of alloreactive T cells before renal transplantation, using donor-specific or third-party cells for allostimulation. Allostimulation induced up-regulation of co-stimulatory molecules, chemokine receptors relevant for migration of T cells into the graft and effector proteins. Recipients prone for acute rejection had a higher precursor frequency of alloreactive CD8(+) T cells and a lower percentage of interleukin (IL)-7Rα expressing alloreactive CD8(+) T cells than non-rejectors. These data point to quantitative and qualitative differences between T cells of patients who will experience acute cellular rejection episodes from those who will not.

HLA-B7-restricted EBV-specific CD8+ T cells are dysregulated in multiple sclerosis

It was hypothesized that the EBV-specific CD8(+) T cell response may be dysregulated in multiple sclerosis (MS) patients, possibly leading to a suboptimal control of this virus. To examine the CD8(+) T cell response in greater detail, we analyzed the HLA-A2-, HLA-B7-, and HLA-B8-restricted EBV- and CMV-specific CD8(+) T cell responses in a high number of MS patients and control subjects using tetramers. Content in cytolytic granules, as well as cytotoxic activity, of EBV- and CMV-specific CD8(+) T cells was assessed. We found that MS patients had a lower or a higher prevalence of HLA-A2 and HLA-B7, respectively. Using HLA class I tetramers in HLA-B7(+) MS patients, there was a higher prevalence of MS patients with HLA-B*0702/EBV(RPP)-specific CD8(+) T cells ex vivo. However, the magnitude of the HLA-B*0702/EBV(RPP)-specific and HLA-B*0702/CMV(TPR)-specific CD8(+) T cell response (i.e., the percentage of tetramer(+) CD8(+) T cells in a study subject harboring CD8(+) T cells specific for the given epitope) was lower in MS patients. No differences were found using other tetramers. After stimulation with the HLA-B*0702/EBV(RPP) peptide, the production of IL-2, perforin, and granzyme B and the cytotoxicity of HLA-B*0702/EBV(RPP)-specific CD8(+) T cells were decreased. Altogether, our findings suggest that the HLA-B*0702-restricted viral (in particular the EBV one)-specific CD8(+) T cell response is dysregulated in MS patients. This observation is particularly interesting knowing that the HLA-B7 allele is more frequently expressed in MS patients and considering that EBV is associated with MS.

Positive and negative regulation of cellular immune responses in physiologic conditions and diseases

The immune system has evolved to allow robust responses against pathogens while avoiding autoimmunity. This is notably enabled by stimulatory and inhibitory signals which contribute to the regulation of immune responses. In the presence of a pathogen, a specific and effective immune response must be induced and this leads to antigen-specific T-cell proliferation, cytokines production, and induction of T-cell differentiation toward an effector phenotype. After clearance or control of the pathogen, the effector immune response must be terminated in order to avoid tissue damage and chronic inflammation and this process involves coinhibitory molecules. When the immune system fails to eliminate or control the pathogen, continuous stimulation of T cells prevents the full contraction and leads to the functional exhaustion of effector T cells. Several evidences both in vitro and in vivo suggest that this anergic state can be reverted by blocking the interactions between coinhibitory molecules and their ligands. The potential to revert exhausted or inactivated T-cell responses following selective blocking of their function made these markers interesting targets for therapeutic interventions in patients with persistent viral infections or cancer.

Anti-gamma interferon antibodies enhance the immunogenicity of recombinant adenovirus vectors

Vaccination for eliciting antigen-specific memory CD8(+) T cells may be facilitated by manipulating the pleiotropic effects of gamma interferon (IFN-γ). We assessed strategies for modulating the contribution of IFN-γ during the development of antigen-specific cytotoxic T lymphocyte (CTL) populations. We first showed that recombinant IFN-γ suppressed antigen expression in vitro from a recombinant adenovirus (rAd) vector in a dose-dependent manner and that addition of an anti-IFN-γ antibody (Ab) eliminated this suppression. Consistent with these in vitro findings, we found that HIV-1 envelope (Env)-specific CTL responses were higher in IFN-γ-knockout (GKO) mice than in wild-type mice following immunization with rAd. Since these observations suggested that IFN-γ might suppress rAd-induced CTL development, we assessed the ability of anti-IFN-γ Ab administration to augment rAd-elicited CTL in vivo. In fact, blockage of IFN-γ activity by monoclonal Ab administration was associated with elevated levels of interleukin 7 receptor alpha chain-positive (IL-7Rα(+)) Env-specific CTL populations postboost. These observations illustrate the utility of an anti-IFN-γ Ab for potentiating rAd immunizations to effect quantitative and qualitative changes in the effector and memory CTL populations.

Living in a house of cards: re-evaluating CD8+ T-cell immune correlates against HIV

The Merck STEP and the Thai RV144 human immunodeficiency virus (HIV) vaccine trials confirmed that we still have a long way to go before developing a prophylactic HIV vaccine. The main issue at hand is that we have yet to identify an immunological correlate of protection against HIV. While many question the T-cell-based approach towards vaccine development, it is likely that T cells will be a necessary part of any vaccine strategy. CD8(+) T cells remain an attractive option because of their ability to specifically recognize and eliminate virally infected host cells. In this review, we recapitulate the evidence for CD8(+) T cells as an immunological correlate against HIV, but more importantly, we assess the means by which we evaluate their antiviral capacity. To achieve a breakthrough in the domain of T-cell-based HIV vaccine development, it has become abundantly clear that we must overhaul our system of immune monitoring and come up with a 'rational' tactic to evaluate the efficacy of HIV-specific CD8(+) T cells.

Qualitative features of the HIV-specific CD8+ T-cell response associated with immunologic control

PURPOSE OF REVIEW

Over the past 2 years, a clearer picture has emerged regarding the properties of HIV-specific CD8+ T cells associated with immunologic control of HIV replication. These properties represent a potential mechanism by which rare patients might control HIV replication in the absence of antiretroviral therapy. This review addresses the background and recent findings that have lead to our current understanding of these mechanism(s).

RECENT FINDINGS

Patients with immunologic control of HIV are not distinguished by targeted specificities, or greater numbers or breadth of their HIV-specific CD8+ T-cell response. For this reason, recent work has focused greater attention on qualitative features of this response. The qualitative features most closely associated with immunologic control of HIV are related to the granule-exocytosis-mediated elimination of HIV-infected CD4 T cells. The ability of HIV-specific CD8+ T cells to increase their contents of proteins known to mediate cytotoxicity, such as granzyme B and perforin, appears to be a critical means by which HIV-specific cytotoxic capacity is regulated.

SUMMARY

Investigation from multiple groups has now focused upon HIV-specific CD8+ T-cell granule-exocytosis-mediated cytotoxicity as a correlate of immunologic control of HIV. In the near future, a more detailed understanding of the qualities associated with immunologic control may provide critical insights regarding the necessary features of a response that should be stimulated by immunotherapies or T-cell-based vaccines.

Early and prolonged antiretroviral therapy is associated with an HIV-1-specific T-cell profile comparable to that of long-term non-progressors

BACKGROUND

Intervention with antiretroviral treatment (ART) and control of viral replication at the time of HIV-1 seroconversion may curtail cumulative immunological damage. We have therefore hypothesized that ART maintenance over a very prolonged period in HIV-1 seroconverters could induce an immuno-virological status similar to that of HIV-1 long-term non-progressors (LTNPs).

METHODOLOGY/PRINCIPAL FINDINGS

We have investigated a cohort of 20 HIV-1 seroconverters on long-term ART (LTTS) and compared it to one of 15 LTNPs. Residual viral replication and reservoirs in peripheral blood, as measured by cell-associated HIV-1 RNA and DNA, respectively, were demonstrated to be similarly low in both cohorts. These two virologically matched cohorts were then comprehensively analysed by polychromatic flow cytometry for HIV-1-specific CD4(+) and CD8(+) T-cell functional profile in terms of cytokine production and cytotoxic capacity using IFN-γ, IL-2, TNF-α production and perforin expression, respectively. Comparable levels of highly polyfunctional HIV-1-specific CD4(+) and CD8(+) T-cells were found in LTTS and LTNPs, with low perforin expression on HIV-1-specific CD8(+) T-cells, consistent with a polyfunctional/non-cytotoxic profile in a context of low viral burden.

CONCLUSIONS

Our results indicate that prolonged ART initiated at the time of HIV-1 seroconversion is associated with immuno-virological features which resemble those of LTNPs, strengthening the recent emphasis on the positive impact of early treatment initiation and paving the way for further interventions to promote virological control after treatment interruption.

EBV-specific CD8+ T cells from asymptomatic pediatric thoracic transplant patients carrying chronic high EBV loads display contrasting features: activated phenotype and exhausted function

Serial EBV load monitoring of clinically asymptomatic pediatric thoracic organ transplant patients has identified three groups of children who exhibit undetectable (<100 copies/ml), chronic low (100-16,000 copies/ml), or chronic high (>16,000 copies/ml) EBV loads in peripheral blood. Chronic high EBV load patients have a 45% rate of progression to late-onset posttransplant lymphoproliferative disorders. In this article, we report that asymptomatic patients carrying EBV loads (low and high) expressed increased frequencies of EBV-specific CD8(+) T cells, as compared with patients with undetectable EBV loads. Although patients with low viral load displayed EBV-specific CD8(+) T cells with moderate signs of activation (CD38(+/-)/CD127(+/-)), programmed death 1 upregulation and effective IFN-γ secretion, high EBV load carriers showed significant CD38(+) upregulation, features of cellular exhaustion (programmed death 1(+)/CD127(-)) accompanied by a decline in IFN-γ release. Immunopolarization of EBV-specific CD8(+) T cells was skewed from the expected type 1 (IFN-γ) toward type 0 (IFN-γ/IL-5) in patients, and Tr1 (IL-10) in high load carriers. These results indicate the importance of chronic EBV load and of the levels of antigenic pressure in shaping EBV-specific memory CD8(+) T cells. Concomitant phenotypic and functional EBV monitoring is critical for identifying the complex "functional" versus "exhausted" signature of EBV-specific CD8(+) T cells, with implications for immunologic monitoring in the clinic.

CD8+ T-cell differentiation in chronic HCV infection

HCV has the tendency to persist in the majority of infected patients despite the presence of virus-specific CD8+ T-cell responses. The HCV-specific CD8+ T-cell pool consists of heterogenous subsets that can be elegantly distinguished by CD127 expression. Indeed, HCV-specific CD8+ T cells with high levels of CD127 expression are characterized by features consistent with memory differentiation, while HCV-specific CD8+ T cells with low levels of CD127 expression display an exhausted phenotype characterized by the coexpression of PD-1 and other inhibitory receptors. In this article, the current knowledge about the phenotypes and differentiation profiles of HCV-specific CD8+ T cells is summarized. Clearly, the differentiation of HCV-specific CD8+ T cells in chronic HCV infection results from complex virus–host interactions, and both viral and immunological factors shape the HCV-specific CD8+ T-cell pool.

Programmed Death-1 expression on Epstein Barr virus specific CD8+ T cells varies by stage of infection, epitope specificity, and T-cell receptor usage

BACKGROUND

Programmed Death-1 (PD-1) is an inhibitory member of the CD28 family of molecules expressed on CD8+ T cells in response to antigenic stimulation. To better understand the role of PD-1 in antiviral immunity we examined the expression of PD-1 on Epstein-Barr virus (EBV) epitope-specific CD8+ T cells during acute infectious mononucleosis (AIM) and convalescence.

METHODOLOGY/PRINCIPAL FINDINGS

Using flow cytometry, we observed higher frequencies of EBV-specific CD8+ T cells and higher intensity of PD-1 expression on EBV-specific CD8+ T cells during AIM than during convalescence. PD-1 expression during AIM directly correlated with viral load and with the subsequent degree of CD8+ T cell contraction in convalescence. Consistent differences in PD-1 expression were observed between CD8+ T cells with specificity for two different EBV lytic antigen epitopes. Similar differences were observed in the degree to which PD-1 was upregulated on these epitope-specific CD8+ T cells following peptide stimulation in vitro. EBV epitope-specific CD8+ T cell proliferative responses to peptide stimulation were diminished during AIM regardless of PD-1 expression and were unaffected by blocking PD-1 interactions with PD-L1. Significant variability in PD-1 expression was observed on EBV epitope-specific CD8+ T cell subsets defined by V-beta usage.

CONCLUSIONS/SIGNIFICANCE

These observations suggest that PD-1 expression is not only dependent on the degree of antigen presentation, but also on undefined characteristics of the responding cell that segregate with epitope specificity and V-beta usage.

Diversity in CD8(+) T cell function and epitope breadth among persons with genital herpes

CD8(+) T cells are known to be important in clearing herpes simplex virus (HSV) infections. However, investigating the specific antiviral mechanisms employed by HSV-2-specific T cell populations is limited by a lack of reagents such as CD8(+) T cell epitopes and specific tetramers. Using a combination of intracellular cytokine staining flow cytometry and ELISpot methods, we functionally characterized peripheral HSV-2-specific CD8(+) T cells from peripheral blood mononuclear cell (PBMC) that recognize 14 selected HSV-2 open-reading frames (ORFs) from 55 HSV-2 seropositive persons; within these ORFs, we subsequently identified more than 20 unique CD8(+) T cell epitopes. CD8(+) T cells to HSV-2 exhibited significant heterogeneity in their functional characteristics, proliferation, production of inflammatory cytokines, and potential to degranulate ex vivo. The diversity in T cell response in these ex vivo assessments offers the potential of defining immune correlates of HSV-2 reactivation in humans.