Cytotoxic granule release dominates gag-specific CD4+ T-cell response in different phases of HIV infection

Cytotoxic CD4+ T cells in chronic viral infections and cancer

CD4+ T cells play an important role in immune responses against pathogens and cancer cells. Although their main task is to provide help to other effector immune cells, a growing number of infections and cancer entities have been described in which CD4+ T cells exhibit direct effector functions against infected or transformed cells. The most important cell type in this context are cytotoxic CD4+ T cells (CD4+ CTL). In infectious diseases anti-viral CD4+ CTL are mainly found in chronic viral infections. Here, they often compensate for incomplete or exhausted CD8+ CTL responses. The induction of CD4+ CTL is counter-regulated by Tregs, most likely because they can be dangerous inducers of immunopathology. In viral infections, CD4+ CTL often kill via the Fas/FasL pathway, but they can also facilitate the exocytosis pathway of killing. Thus, they are very important effectors to keep persistent virus in check and guarantee host survival. In contrast to viral infections CD4+ CTL attracted attention as direct anti-tumor effectors in solid cancers only recently. Anti-tumor CD4+ CTL are defined by the expression of cytolytic markers and have been detected within the lymphocyte infiltrates of different human cancers. They kill tumor cells in an antigen-specific MHC class II-restricted manner not only by cytolysis but also by release of IFNγ. Thus, CD4+ CTL are interesting tools for cure approaches in chronic viral infections and cancer, but their potential to induce immunopathology has to be carefully taken into consideration.

Analysis of Antigen-Specific T and B Cells for Monitoring Immune Protection Against SARS-CoV-2

Immunological memory is the basis of protection against most pathogens. Long-living memory T and B cells able to respond to specific stimuli, as well as persistent antibodies in plasma and in other body fluids, are crucial for determining the efficacy of vaccination and for protecting from a second infection by a previously encountered pathogen. Antigen-specific cells are represented at a very low frequency in the blood, and indeed, they can be considered "rare events" present in the memory T-cell pool. Therefore, such events should be analyzed with careful attention. In the last 20 years, different methods, mostly based upon flow cytometry, have been developed to identify such rare antigen-specific cells, and the COVID-19 pandemic has given a dramatic impetus to characterize the immune response against the virus. In this regard, we know that the identification, enumeration, and characterization of SARS-CoV-2-specific T and B cells following infection and/or vaccination require i) the use of specific peptides and adequate co-stimuli, ii) the use of appropriate inhibitors to avoid nonspecific activation, iii) the setting of appropriate timing for stimulation, and iv) the choice of adequate markers and reagents to identify antigen-specific cells. Optimization of these procedures allows not only determination of the magnitude of SARS-CoV-2-specific responses but also a comparison of the effects of different combinations of vaccines or determination of the response provided by so-called "hybrid immunity," resulting from a combination of natural immunity and vaccine-generated immunity. Here, we present two methods that are largely used to monitor the response magnitude and phenotype of SARS-CoV-2-specific T and B cells by polychromatic flow cytometry, along with some tips that can be useful for the quantification of these rare events. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Identification of antigen-specific T cells Basic Protocol 2: Identification of antigen-specific B cells.

Effective Treatment of Patients Experiencing Primary, Acute HIV Infection Decreases Exhausted/Activated CD4+ T Cells and CD8+ T Memory Stem Cells

Several studies have identified main changes in T- and B-lymphocyte subsets during chronic HIV infection, but few data exist on how these subsets behave during the initial phase of HIV infection. We enrolled 22 HIV-infected patients during the acute stage of infection before the initiation of antiretroviral therapy (ART). Patients had blood samples drawn previous to ART initiation (T0), and at 2 (T1) and 12 (T2) months after ART initiation. We quantified cellular HIV-DNA content in sorted naïve and effector memory CD4 T cells and identified the main subsets of T- and B-lymphocytes using an 18-parameter flow cytometry panel. We identified correlations between the patients’ clinical and immunological data using PCA. Effective HIV treatment reduces integrated HIV DNA in effector memory T cells after 12 months (T2) of ART. The main changes in CD4+ T cells occurred at T2, with a reduction of activated memory, cytolytic and activated/exhausted stem cell memory T (T_SCM) cells. Changes were present among CD8+ T cells since T1, with a reduction of several activated subsets, including activated/exhausted T_SCM. At T2 a reduction of plasmablasts and exhausted B cells was also observed. A negative correlation was found between the total CD4+ T-cell count and IgM-negative plasmablasts. In patients initiating ART immediately following acute/early HIV infection, the fine analysis of T- and B-cell subsets has allowed us to identify and follow main modifications due to effective treatment, and to identify significant changes in CD4+ and CD8+ T memory stem cells.

Patients Recovering from Severe COVID-19 Develop a Polyfunctional Antigen-Specific CD4+ T Cell Response

Specific T cells are crucial to control SARS-CoV-2 infection, avoid reinfection and confer protection after vaccination. We have studied patients with severe or moderate COVID-19 pneumonia, compared to patients who recovered from a severe or moderate infection that had occurred about 4 months before the analyses. In all these subjects, we assessed the polyfunctionality of virus-specific CD4+ and CD8+ T cells by quantifying cytokine production after in vitro stimulation with different SARS-CoV-2 peptide pools covering different proteins (M, N and S). In particular, we quantified the percentage of CD4+ and CD8+ T cells simultaneously producing interferon-γ, tumor necrosis factor, interleukin (IL)-2, IL-17, granzyme B, and expressing CD107a. Recovered patients who experienced a severe disease display high proportions of antigen-specific CD4+ T cells producing Th1 and Th17 cytokines and are characterized by polyfunctional SARS-CoV-2-specific CD4+ T cells. A similar profile was found in patients experiencing a moderate form of COVID-19 pneumonia. No main differences in polyfunctionality were observed among the CD8+ T cell compartments, even if the proportion of responding cells was higher during the infection. The identification of those functional cell subsets that might influence protection can thus help in better understanding the complexity of immune response to SARS-CoV-2.

Granzyme B+ CD4 T cells accumulate in the colon during chronic HIV-1 infection

Chronic HIV-1 infection results in the sustained disruption of gut homeostasis culminating in alterations in microbial communities (dysbiosis) and increased microbial translocation. Major questions remain on how interactions between translocating microbes and gut immune cells impact HIV-1-associated gut pathogenesis. We previously reported that in vitro exposure of human gut cells to enteric commensal bacteria upregulated the serine protease and cytotoxic marker Granzyme B (GZB) in CD4 T cells, and GZB expression was further increased in HIV-1-infected CD4 T cells. To determine if these in vitro findings extend in vivo, we evaluated the frequencies of GZB⁺ CD4 T cells in colon biopsies and peripheral blood of untreated, chronically infected people with HIV-1 (PWH). Colon and blood GZB⁺ CD4 T cells were found at significantly higher frequencies in PWH. Colon, but not blood, GZB⁺ CD4 T cell frequencies were associated with gut and systemic T cell activation and Prevotella species abundance. In vitro, commensal bacteria upregulated GZB more readily in gut versus blood or tonsil-derived CD4 T cells, particularly in inflammatory T helper 17 cells. Bacteria-induced GZB expression in gut CD4 T cells required the presence of accessory cells, the IL-2 pathway and in part, MHC Class II. Overall, we demonstrate that GZB⁺ CD4 T cells are prevalent in the colon during chronic HIV-1 infection and may emerge following interactions with translocated bacteria in an IL-2 and MHC Class II-dependent manner. Associations between GZB⁺ CD4 T cells, dysbiosis and T cell activation suggest that GZB⁺ CD4 T cells may contribute to gut HIV-1 pathogenesis.

Immune Response to Viruses

Viruses are essentially, obligate intracellular parasites. They require a host to replicate their genetic material, spread to other cells, and eventually to other hosts. For humans, most viral infections are not considered lethal, regardless if at the cellular level, the virus can obliterate individual cells. Constant genomic mutations, (which can alter the antigenic content of viruses such as influenza or coronaviruses), zoonosis or immunosuppression/immunocompromisation, is when viruses achieve higher host mortality. Frequent examples of the severe consequenses of viral infection can be seen in children and the elderly. In most instances, the immune system will take a multifaceted approach in defending the host against viruses. Depending on the virus, the individual, and the point of entry, the immune system will initiate a robust response which involves multiple components. In this chapter, we expand on the total immune system, breaking it down to the two principal types: Innate and Adaptive Immunity, their different roles in viral recognition and clearance. Finally, how different viruses activate and evade different arms of the immune system.

CMV exposure drives long-term CD57+ CD4 memory T-cell inflation following allogeneic stem cell transplant

Donor and recipient cytomegalovirus (CMV) serostatus correlate with transplant-related mortality that is associated with reduced survival following allogeneic stem cell transplant (SCT). Prior epidemiologic studies have suggested that CMV seronegative recipients (R-) receiving a CMV-seropositive graft (D+) experience inferior outcomes compared with other serostatus combinations, an observation that appears independent of viral reactivation. We therefore investigated the hypothesis that prior donor CMV exposure irreversibly modifies immunologic function after SCT. We identified a CD4+/CD57+/CD27- T-cell subset that was differentially expressed between D+ and D- transplants and validated results with 120 patient samples. This T-cell subset represents an average of 2.9% (D-/R-), 18% (D-/R+), 12% (D+/R-), and 19.6% (D+/R+) (P < .0001) of the total CD4+ T-cell compartment and stably persists for at least several years post-SCT. Even in the absence of CMV reactivation post-SCT, D+/R- transplants displayed a significant enrichment of these cells compared with D-/R- transplants (P = .0078). These are effector memory cells (CCR7-/CD45RA+/-) that express T-bet, Eomesodermin, granzyme B, secrete Th1 cytokines, and are enriched in CMV-specific T cells. These cells are associated with decreased T-cell receptor diversity (P < .0001) and reduced proportions of major histocompatibility class (MHC) II expressing classical monocytes (P < .0001), myeloid (P = .024), and plasmacytoid dendritic cells (P = .0014). These data describe a highly expanded CD4+ T-cell population and putative mechanisms by which prior donor or recipient CMV exposure may create a lasting immunologic imprint following SCT, providing a rationale for using D- grafts for R- transplant recipients.

Clinical and ASOCT evaluations of 'bleb-sparing epithelial exchange' in paediatric and adult dysfunctional blebs over 5 years

PURPOSE

To evaluate the long-term outcome of 'bleb-sparing epithelial exchange' surgery for dysfunctional filtering blebs in paediatric and adult eyes.

METHODS

Patients who had undergone bleb revision ≥ 5 years back and were on regular follow-up were included. Age, ocular diagnosis, details of primary filtering surgery including mitomycin-C (MMC) usage, indication and year of bleb revision were recorded. After bleb revision, the mean intraocular pressure (IOP), glaucoma medications and best corrected visual acuity (BCVA) up to 5 years were noted. On last review, clinical details, bleb characteristics and swept source anterior segment tomographic (SSOCT) assessment of bleb were recorded. Comparative analysis of paediatric and adult eyes was performed.

MAIN OUTCOME MEASURES

Change in IOP and BCVA. 'Complete success' was defined as IOP ≥ 6 to ≤ 18mmHg without use of any topical glaucoma medications and 'Qualified success' when ≥ 1 topical glaucoma medication(s) was required.

RESULTS

A total of 51 eyes of 51 consecutive patients were studied, among which 22 were children. The mean duration between filtering surgery and bleb revision was 4.54 ± 1.53 years in paediatric and 6.48 ± 3.5 years in the adult group, p = 0.04. Children underwent trabeculotomy + trabeculectomy with 0.04% MMC, while adults underwent trabeculectomy with 0.02% MMC. The mean pre-revision IOP was 6.38 ± 2.80 and 6.51 ± 2.78 mmHg in the paediatric and adult group respectively, p = 0.86. At 3 months post-revision, it increased to 11.81 ± 3.48 and 12.75 ± 3.52 mmHg respectively (p < 0.001). At final review, mean IOP of paediatric group was 10.90 ± 2.59 and adult group was 11.86 ± 2.66 mmHg, p = 0.20. At 5 years, complete success was 68.18% and 72.41%, and qualified success was 31.87% and 27.59% in the former and latter group respectively, p = 0.49. No failures were seen. Kaplan-Meier probability at 5 years for IOP target ≤ 18, ≤ 15 and ≤ 12 in children was 95.45%, 63.64% and 50% and in adults 93.10%, 65.52% and 41.38% respectively. BCVA improved up to 1 year in paediatric group, with continued improvement in adults up to 3 years. SSOCT measured bleb height was 0.88 ± 0.37 and 1.32 ± 0.49mm in children versus adults (p = 0.006) and wall thickness, 0.35 ± 0.22 and 0.58 ± 0.24mm respectively, p = 0.008.

CONCLUSION

Bleb-sparing epithelial exchange is an equally safe and effective technique with good long-term success in both paediatric and adult dysfunctional blebs.

Anti-HIV potency of T-cell responses elicited by dendritic cell therapeutic vaccination

Identification and characterization of CD8+ and CD4+ T-cell epitopes elicited by HIV therapeutic vaccination is key for elucidating the nature of protective cellular responses and mechanism of the immune evasion of HIV. Here, we report the characterization of HIV-specific T-cell responses in cART (combination antiretroviral therapy) treated HIV-1 infected patients after vaccination with ex vivo-generated IFNα Dendritic Cells (DCs) loaded with LIPO-5 (HIV-1 Nef 66-97, Nef 116-145, Gag 17-35, Gag 253-284 and Pol 325-355 lipopeptides). Vaccination induced and/or expanded HIV-specific CD8+ T cells producing IFNγ, perforin, granzyme A and granzyme B, and also CD4+ T cells secreting IFNγ, IL-2 and IL-13. These responses were directed against dominant and subdominant epitopes representing all vaccine regions; Gag, Pol and Nef. Interestingly, IL-2 and IL-13 produced by CD4+ T cells were negatively correlated with the peak of viral replication following analytic treatment interruption (ATI). Epitope mapping confirmed that vaccination elicited responses against predicted T-cell epitopes, but also allowed to identify a set of 8 new HIV-1 HLA-DR-restricted CD4+ T-cell epitopes. These results may help to better design future DC therapeutic vaccines and underscore the role of vaccine-elicited CD4+ T-cell responses to achieve control of HIV replication.

Cytotoxic CD4+ T-cells during HIV infection: Targets or weapons?

Classically, CD4⁺ T-cells have been referred as cytokine-producing cells and important players in immune responses by providing soluble factors that potentiate several effector immune functions. However, it is now evident that CD4⁺ T-cells can also elaborate cytotoxic responses, inducing apoptosis of target cells. Cytotoxic CD4⁺ T cells (CD4⁺ CTLs), exhibit cytolytic functions that resemble those of CD8⁺ T-cells; in fact, there is evidence suggesting that they may have a role in the control of viral infections. In this article, we discuss the role of CD4⁺ CTLs during HIV infection, where CD4⁺ CTLs have been associated with viral control and slow disease progression. In addition, we address the implication of CD4⁺ CTLs in the context of antiretroviral therapy and the partial reconstitution of CD8⁺ T-cells effector function.

HIV-specific T-cell Responses and Generalized Activation in HIV-1 Infected Long-term Non-progressors and Progressors from South India

Background:

Anti-viral cytokine expressions by cytotoxic T-cells and lower activation rates have been reported to correlate with suppressed HIV replication in long-term non-progressors (LTNP). Immune mechanisms underlying disease non-progression in LTNP might vary with HIV-1 subtype and geographical locations.

Objective:

This study evaluates cytokine expression and T-cells activation in relation to disease non-progression in LTNP.

Methods:

HIV-1 Subtype C infected LTNP (n=20) and progressors (n=15) were enrolled and flowcytometry assays were performed to study HIV-specific CD8 T-cells expressing IL-2, IFN-γ, TNF-α and MIP-1β against gag and env peptides. CD4+ T-cell activation was evaluated by surface expression of HLADR and CD38.

Results:

Proportions of cytokines studied did not differ significantly between LTNP and progressors, while contrasting correlations with disease progression markers were observed in LTNP. CD4+ T-cell activation rates were significantly lower in LTNP compared to progressors which indicate the potential role of T-cell activation rates in disease non-progression in LTNP.

Conclusion:

LTNP and progressors showed similar CD8+ T-cell responses, but final conclusions can be drawn only by comparing multiple immune factors in larger LTNP cohort with HIV-1 infected individuals at various levels of disease progression. A possible role of HIV-1 subtype variation and ethnic differences in addition to host-genetic and viral factors cannot be ruled out.

Cancer neoantigens targeted by adoptive T cell transfer: private no more

Effector T cell responses directed toward cancer neoantigens mediate tumor regression following checkpoint blockade or adoptive T cell immunotherapy, but are generally "private", thus requiring considerable effort for their identification. In this issue of the JCI, Malekzadeh et al. show that a fraction of patients with epithelial cancers mount antigen-specific T cell responses to "hot spot" p53 mutations that in some cases are shared among patients. This work suggests that other genes frequently mutated in human cancer can be immunogenic, thus offering a rapid way to screen for cancer neoantigens that can be targeted by subsequent T cell-based therapies.

Recovery of effective HIV-specific CD4+ T-cell activity following antiretroviral therapy in paediatric infection requires sustained suppression of viraemia

Background:

The success of increasing access to antiretroviral therapy (ART) in paediatric HIV infection prompts the question of the potential for eradication of HIV infection in this age group. ‘Shock-and-kill’ HIV cure approaches, currently in development, may depend upon an effective antiviral T-cell response to eradicate virus-infected cells.

Method:

We here investigate the ability of HIV-infected children receiving ART from early childhood (median 24 months’ age) to generate effective HIV-specific CD4⁺ and CD8⁺ T-cell immune responses that would facilitate future immune-based cure therapies.

Results:

Initial analysis of ART-naive HIV-infected children demonstrated that maintenance of normal-for-age absolute CD4⁺ T-cell counts was strongly linked to high IL-2 production and polyfunctional HIV-specific CD4⁺ T-cell responses (P < 0.0001 in each case). Low viral load was, similarly, strongly associated with markedly low IFN-γ and high IL-2 HIV-specific CD4⁺ T-cell responses (P < 0.0001). In children receiving ART, establishment of this immune profile (high IL-2 and low IFN-γ HIV-specific T-cell production) was strongly related to the duration of viraemic suppression. Failure to suppress viraemia on ART, and even the successful suppression of viraemia interrupted by the occurrence of transient viraemia of more than 1000 HIV copies/ml, was associated with an immune profile of high IFN-γ and low IL-2 HIV-specific T-cell responses and low polyfunctionality.

Conclusion:

These data are consistent with recovery of functional CD4⁺ T-cell responses in ART-treated children, in contrast to relative lack of CD4⁺ T-cell function recovery described in ART-treated adults. However, the challenges of achieving long-term suppression of viraemia in ART-treated children through adolescence remain daunting.

HIV-Specific CD8 T Cells Producing CCL-4 Are Associated With Worse Immune Reconstitution During Chronic Infection

BACKGROUND

Immunological nonresponse represents the Achilles heel in the combination antiretroviral therapy (cART) effectiveness, and increases risk of clinical events and death. CD8 T cells play a crucial role in controlling HIV replication, and polyfunctional HIV-specific CD8 T cells have been associated with nonprogressive HIV infection. However, the possible role of polyfunctional CD8 T cells in predicting posttreatment immune reconstitution has not yet been explored. The aim of this study was to identify functional markers predictive of immunological response to cART in chronic HIV-infected patients.

METHODS

A cohort of chronic HIV-infected individuals naive to cART were enrolled in the ALPHA study. CD4/CD8 T-cell subsets, their differentiation/activation, as well as susceptibility to apoptosis were analyzed before and after 12 months of cART. Moreover, CD8 T cells polyfunctional response after HIV antigenic stimulation was also assessed.

RESULTS

Results showed a significant correlation between worse CD4 T-cell restoration and low frequency of naive CD4 T cells, high frequency of effector memory CD4 T cells, and high susceptibility to apoptosis of CD4 T cells all before cART. Moreover, CD8 functional subsets expressing total C-C motif chemokine ligand 4 (CCL-4) or in combination with CD107a and interferon gamma (IFNγ) were negatively associated with immune reconstitution.

CONCLUSIONS

In conclusion, our study shows that a more differentiated phenotype of CD4 T cells and CCL-4-producing CD8 T cells could represent valuable predictors of worse immune reconstitution. These parameters may be used as tools for identifying patients at risk of immunological failure during cART and eventually represent the basis for innovative therapeutic strategies.

Decrease of CD69 levels on TCR Vα7.2+CD4+ innate-like lymphocytes is associated with impaired cytotoxic functions in chronic hepatitis B virus-infected patients

Hepatitis B virus (HBV) infection is a major cause of chronic liver disease that may progress to liver cirrhosis and hepatocellular carcinoma. Host immune responses represent the key determinants of HBV clearance or persistence. Here, we investigated the role of the early activation marker, CD69 and effector cytokines, granzyme B (GrB) and IFN-γ in the exhaustion of innate-like TCR Vα7.2⁺CD4⁺T cells, in 15 individuals with chronic HBV (CHB) infection where six were HBV DNA⁺ and nine were HBV DNA^-. The percentage of cytokine-producing T cells and MAIT cells were significantly perturbed in HBV patients relative to healthy controls (HCs). The intracellular expression of GrB and IFN-γ was significantly reduced in MAIT cells derived from HBV-infected patients as compared to HCs, and the levels correlated with the percentage and levels [mean fluorescence intensity (MFI)] of CD69 expression. The total expression of CD69 (iMFI) was lower in CHB patients as compared to HCs. The frequency of CD69⁺ cells correlated with the levels of cytokine expression (MFI), particularly in CHB patients as compared to HCs. In summary, the polyfunctionality of peripheral T cells was significantly reduced among CHB patients, especially in the TCR Vα7.2⁺CD4⁺T cells, and the levels of cytokine expression correlated with functional cytokine levels.

Fighting Viral Infections and Virus-Driven Tumors with Cytotoxic CD4+ T Cells

CD4+ T cells have been and are still largely regarded as the orchestrators of immune responses, being able to differentiate into distinct T helper cell populations based on differentiation signals, transcription factor expression, cytokine secretion, and specific functions. Nonetheless, a growing body of evidence indicates that CD4+ T cells can also exert a direct effector activity, which depends on intrinsic cytotoxic properties acquired and carried out along with the evolution of several pathogenic infections. The relevant role of CD4+ T cell lytic features in the control of such infectious conditions also leads to their exploitation as a new immunotherapeutic approach. This review aims at summarizing currently available data about functional and therapeutic relevance of cytotoxic CD4+ T cells in the context of viral infections and virus-driven tumors.

Cytotoxic CD4 T Cells-Friend or Foe during Viral Infection?

CD4 T cells with cytotoxic function were once thought to be an artifact due to long-term in vitro cultures but have in more recent years become accepted and reported in the literature in response to a number of viral infections. In this review, we focus on cytotoxic CD4 T cells in the context of human viral infections and in some infections that affect mice and non-human primates. We examine the effector mechanisms used by cytotoxic CD4 cells, the phenotypes that describe this population, and the transcription factors and pathways that lead to their induction following infection. We further consider the cells that are the predominant targets of this effector subset and describe the viral infections in which CD4 cytotoxic T lymphocytes have been shown to play a protective or pathologic role. Cytotoxic CD4 T cells are detected in the circulation at much higher levels than previously realized and are now recognized to have an important role in the immune response to viral infections.

Th1 and Th17 proinflammatory profile characterizes invariant natural killer T cells in virologically suppressed HIV+ patients with low CD4+/CD8+ ratio

INTRODUCTION

Scanty data exist on the phenotype and functionality of invariant natural killer T (iNKT) cells in HIV-infected (HIV+) patients.

METHODS

By flow cytometry, we studied iNKT cells from 54 HIV+ patients who started combined antiretroviral therapy and had undetectable viral load for more than 1 year. Twenty-five maintained a CD4/CD8 ratio less than 0.4, whereas 29 reached a ratio more than 1.1; 32 age-matched and sex-matched patients were healthy controls (CTR).

RESULTS

Patients with low ratio had lower percentage of CD4 iNKT cells compared with patients with high ratio and higher CD8 iNKT cell percentage; double-negative iNKT cells were lower in HIV+ patients compared with CTR. Patients with low ratio had higher percentage of CD4 and double-negative iNKT cells expressing CD38 and HLA-DR compared with patients with high ratio. CD4 iNKT cells expressing PD-1 were higher in patients with CD4/CD8 ratio less than 0.4, whereas double-negative iNKT cells expressing PD-1 were lower compared with patients with ratio more than 1.1. Patients with low ratio had higher CD4 iNKT cells producing IL-17, CD8 iNKT cells producing IFN-γ, TNF-α or IFN-γ and TNF-α, and double-negative iNKT cells producing IL-17 or IL-17 and IFN-γ compared with CTR. Activated CD4 (or CD8) T cells correlated with activated CD4 (or CD8) iNKT cells, as well as the percentages of CD4 (or CD8) T cells expressing PD-1 was correlated to that of CD4 (or CD8) iNKT cells expressing PD-1.

CONCLUSION

Low CD4/CD8 ratio despite effective combined antiretroviral therapy is associated with altered iNKT cell subsets, enhanced activation, and prominent Th1/Th17 proinflammatory profile.

Conditions for the generation of cytotoxic CD4(+) Th cells that enhance CD8(+) CTL-mediated tumor regression

Adoptive cell therapies (ACTs) using tumor-reactive T cells have shown clinical benefit and potential for cancer treatment. While the majority of the current ACT are focused on using CD8⁺ cytotoxic T lymphocytes (CTL), others have shown that the presence of tumor-reactive CD4⁺ T helper (Th) cells can greatly enhance the anti-tumor activity of CD8⁺ CTL. However, difficulties in obtaining adequate numbers of CD4⁺ Th cells through in vitro expansion can limit the application of CD4 Th cells in ACT. This study aims to optimize the culture conditions for mouse CD4 T cells to provide basic information for animal studies of ACT using CD4 T cells. Taking advantage of the antigen-specificity of CD4⁺ Th cells from OT-II transgenic mice, we examined different methodologies for generating antigen-specific CD4⁺ Th1 cells in vitro. We found that cells grown in complete advanced-DMEM/F12 medium supplemented with low-dose IL-2 and IL-7 induced substantial cell expansion. These Th cells were Th1-like, as they expressed multiple Th1-cytokines and exhibited antigen-specific cytotoxicity. In addition co-transfer of these CD4⁺ Th1-like cells with CD8⁺ CTL significantly enhanced tumor regression, leading to complete cure in 80% of mice bearing established B16-OVA. These observations indicate that the CD4⁺ Th1-like cells generated using the method we optimized are functionally active to eliminate their target cells, and can also assist CD8⁺ CTL to enhance tumor regression. The findings of this study provide valuable data for further research into in vitro expansion of CD4⁺ Th1-like cells, with potential applications to cancer treatment involving ACT.

A novel SIV gag-specific CD4(+)T-cell clone suppresses SIVmac239 replication in CD4(+)T cells revealing the interplay between antiviral effector cells and their infected targets

To study CD4(+)T-cell suppression of AIDS virus replication, we isolated nine rhesus macaque SIVGag-specific CD4(+)T-cell clones. One responding clone, Gag68, produced a typical cytotoxic CD8(+)T-cell response: induction of intracellular IFN-γ, MIP-1α, MIP-1β, and CD107a degranulation. Gag68 effectively suppressed the spread of SIVmac239 in CD4(+)T cells with a corresponding reduction of infected Gag68 effector cells, suggesting that CD4(+)effectors need to suppress their own infection in addition to their targets to be effective. Gag68 TCR cloning and gene transfer into CD4(+)T cells enabled additional experiments with this unique specificity after the original clone senesced. Our data supports the idea that CD4(+)T cells can directly limit AIDS virus spread in T cells. Furthermore, Gag68 TCR transfer into CD4(+)T-cell clones with differing properties holds promise to better understand the suppressive effector mechanisms used by this important component of the antiviral response using the rhesus macaque model.

Analysis of inflammasomes and antiviral sensing components reveals decreased expression of NLRX1 in HIV-positive patients assuming efficient antiretroviral therapy

OBJECTIVE

Few studies have investigated the importance of different components of the inflammasome system and of innate mitochondrial sensing (IMS) pathways in HIV infection and its treatment. We analysed the expression of several components of the inflammasome and of the IMS in HIV-positive patients taking successful combination antiretroviral therapy (cART).

METHODS

We enrolled 20 HIV-positive patients under cART, who achieved viral suppression since at least 10 months and 20 age and sex-matched healthy donors. By RT-PCR, using peripheral blood mononuclear cells (PBMCs), we quantified the mRNA expression of 16 genes involved in inflammasome activation and regulation (AIM2, NAIP, PYCARD, CASP1, CASP5, NLRP6, NLRP1, NLRP3, TXNIP, BCL2, NLRC4, PANX1, P2RX7, IL-18, IL-1β, SUGT1) and eight genes involved in IMS (MFN2, MFN1, cGAS, RIG-I, MAVS, NLRX1, RAB32, STING).

RESULTS

Compared with controls, HIV-positive patients showed significantly lower mRNA levels of the mitochondrial protein NLRX1, which plays a key role in regulating apoptotic cell death; main PBMC subpopulations behave in a similar manner. No differences were observed in the expression of inflammasome components, which however showed complex correlations.

CONCLUSION

The decreased level of NLRX1 in HIV infection could suggest that the virus is able to downregulate mechanisms linked to triggering of cell death in several immune cell types. The fact that HIV-positive patients did not show altered expression of inflammasome components, nor of most genes involved in IMS, suggests that the infection and/or the chronic immune activation does not influence the transcriptional machinery of innate mechanisms able to trigger inflammation at different levels.

Reliable and accurate CD4+ T cell count and percent by the portable flow cytometer CyFlow MiniPOC and "CD4 Easy Count Kit-Dry", as revealed by the comparison with the gold standard dual platform technology

Background

An accurate and affordable CD4+ T cells count is an essential tool in the fight against HIV/AIDS. Flow cytometry (FCM) is the “gold standard” for counting such cells, but this technique is expensive and requires sophisticated equipment, temperature-sensitive monoclonal antibodies (mAbs) and trained personnel. The lack of access to technical support and quality assurance programs thus limits the use of FCM in resource-constrained countries. We have tested the accuracy, the precision and the carry-over contamination of Partec CyFlow MiniPOC, a portable and economically affordable flow cytometer designed for CD4+ count and percentage, used along with the “CD4% Count Kit-Dry”.

Materials and Methods

Venous blood from 59 adult HIV+ patients (age: 25–58 years; 43 males and 16 females) was collected and stained with the “MiniPOC CD4% Count Kit-Dry”. CD4+ count and percentage were then determined in triplicate by the CyFlow MiniPOC. In parallel, CD4 count was performed using mAbs and a CyFlow Counter, or by a dual platform system (from Beckman Coulter) based upon Cytomic FC500 (“Cytostat tetrachrome kit” for mAbs) and Coulter HmX Hematology Analyzer (for absolute cell count).

Results

The accuracy of CyFlow MiniPOC against Cytomic FC500 showed a correlation coefficient (CC) of 0.98 and 0.97 for CD4+ count and percentage, respectively. The accuracy of CyFlow MiniPOC against CyFlow Counter showed a CC of 0.99 and 0.99 for CD4 T cell count and percentage, respectively. CyFlow MiniPOC showed an excellent repeatability: CD4+ cell count and percentage were analyzed on two instruments, with an intra-assay precision below ±5% deviation. Finally, there was no carry-over contamination for samples at all CD4 values, regardless of their position in the sequence of analysis.

Conclusion

The cost-effective CyFlow MiniPOC produces rapid, reliable and accurate results that are fully comparable with those from highly expensive dual platform systems.

Successful treatment of HIV-1 infection increases the expression of a novel, short transcript for IL-18 receptor α chain

: The importance of interleukin (IL)-18 in mediating immune activation during HIV infection has recently emerged. IL-18 activity is regulated by its receptor (IL-18R), formed by an α and a β chain, the IL-18-binding protein, and the newly identified shorter isoforms of both IL-18R chains. We evaluated gene expression of the IL-18/IL-18R system in peripheral blood mononuclear cells from HIV+ patients. Compared with healthy donors, IL-18 expression decreased in patients with primary infection. The IL-18Rα short transcript expression was strongly upregulated by successful highly active antiretroviral therapy. HIV progression and its treatment can influence the expression of different components of the complex IL-18/IL-18R system.

Modulation of polyfunctional HIV-specific CD8 T cells in patients responding differently to antiretroviral therapy

Antiretroviral therapy allows a restoration of immune cell homeostasis associated with a normal immune competence. Our goal was to analyze the modulation of polyfunctional HIV-specific CD8+ T-cell responses during antiretroviral therapy. HIV-infected individuals were divided into four groups according to CD4+ cell count and viral load at the moment of recruitment. Whole blood was stimulated with a pool of CD8-specific HIV-antigens to assess cytokine/chemokine production and cytotoxicity activity by using flow cytometry. The groups show different modulation in HIV-specific CD8+ T-cell responses. In particular, immunological failure showed different distributions of polyfunctional HIVspecific CD8+ responses, mainly due to an increase of cells producing CD107alpha/IFNgamma/IL-2/MIP-1beta. Our results indicate that this particular 4+ functional subset is a possible correlate of immunological failure. Considering the complexity of interactions among HAART, immune system and HIV, work is in progress to find correlates of therapy efficacy.

Vaccination with Gag, Vif, and Nef gene fragments affords partial control of viral replication after mucosal challenge with SIVmac239

Broadly targeted cellular immune responses are thought to be important for controlling replication of human and simian immunodeficiency viruses (HIV and SIV). However, eliciting such responses by vaccination is complicated by immunodominance, the preferential targeting of only a few of the many possible epitopes of a given antigen. This phenomenon may be due to the coexpression of dominant and subdominant epitopes by the same antigen-presenting cell and may be overcome by distributing these sequences among several different vaccine constructs. Accordingly, we tested whether vaccinating rhesus macaques with "minigenes" encoding fragments of Gag, Vif, and Nef resulted in broadened cellular responses capable of controlling SIV replication. We delivered these minigenes through combinations of recombinant Mycobacterium bovis BCG (rBCG), electroporated recombinant DNA (rDNA) along with an interleukin-12 (IL-12)-expressing plasmid (EP rDNA plus pIL-12), yellow fever vaccine virus 17D (rYF17D), and recombinant adenovirus serotype 5 (rAd5). Although priming with EP rDNA plus pIL-12 increased the breadth of vaccine-induced T-cell responses, this effect was likely due to the improved antigen delivery afforded by electroporation rather than modulation of immunodominance. Indeed, Mamu-A*01(+) vaccinees mounted CD8(+) T cells directed against only one subdominant epitope, regardless of the vaccination regimen. After challenge with SIVmac239, vaccine efficacy was limited to a modest reduction in set point in some of the groups and did not correlate with standard T-cell measurements. These findings suggest that broad T-cell responses elicited by conventional vectors may not be sufficient to substantially contain AIDS virus replication.

IMPORTANCE

Immunodominance poses a major obstacle to the generation of broadly targeted, HIV-specific cellular responses by vaccination. Here we attempted to circumvent this phenomenon and thereby broaden the repertoire of SIV-specific cellular responses by vaccinating rhesus macaques with minigenes encoding fragments of Gag, Vif, and Nef. In contrast to previous mouse studies, this strategy appeared to minimally affect monkey CD8(+) T-cell immundominance hierarchies, as seen by the detection of only one subdominant epitope in Mamu-A*01(+) vaccinees. This finding underscores the difficulty of inducing subdominant CD8(+) T cells by vaccination and demonstrates that strategies other than gene fragmentation may be required to significantly alter immunodominance in primates. Although some of the regimens tested here were extremely immunogenic, vaccine efficacy was limited to a modest reduction in set point viremia after challenge with SIVmac239. No correlates of protection were identified. These results reinforce the notion that vaccine immunogenicity does not predict control of AIDS virus replication.

The who's who of T-cell differentiation: human memory T-cell subsets

Following antigen encounter and subsequent resolution of the immune response, a single naïve T cell is able to generate multiple subsets of memory T cells with different phenotypic and functional properties and gene expression profiles. Single-cell technologies, first and foremost flow cytometry, have revealed the complex heterogeneity of the memory T-cell compartment and its organization into subsets. However, a consensus has still to be reached, both at the semantic (nomenclature) and phenotypic level, regarding the identification of these subsets. Here, we review recent developments in the characterization of the heterogeneity of the memory T-cell compartment, and propose a unified classification of both human and nonhuman primate T cells on the basis of phenotypic traits and in vivo properties. Given that vaccine studies and adoptive cell transfer immunotherapy protocols are influenced by these recent findings, it is important to use uniform methods for identifying and discussing functionally distinct subsets of T cells.

Incomplete normalization of regulatory t-cell frequency in the gut mucosa of Colombian HIV-infected patients receiving long-term antiretroviral treatment

INTRODUCTION

To evaluate the effect of late initiation of HAART and poor immune reconstitution on the frequency of regulatory T-cells (Treg) in the peripheral blood and gut of HIV-infected patients, we studied Colombian HIV-infected patients who had been on suppressive HAART for at least one year. They had undetectable viremia but were either immunological responders (HIR); (CD4 counts >500 cells/µl) or non-immunological responders (NIR); (CD4 T-cell count <300 cells/µl). Untreated HIV-infected patients and uninfected controls from the same region were also evaluated.

METHODS

Frequency and phenotype of regulatory T-cells (Treg) were analyzed in gut biopsies and blood samples. The functional effect of Treg depletion on CMV and HIV responses was determined. Markers of immune activation and circulating LPS levels were quantified.

RESULTS

Untreated patients exhibited high Treg frequency in PBMC and gut, and their Treg express high levels of CTLA-4 and PD-1. Although HAART significantly decreased mucosal Treg frequency, it did not normalize it in any of the treated groups (HIR and NIR patients). Treg normalization was observed in the blood of HIR patients following HAART, but did not occur in NIR patients. Treg from HIV-infected patients (treated or not) suppressed HIV and hCMV-specific T-cells from gut and blood. Plasma LPS levels and percentage of HLA-DR+CD38+ T-cells were significantly elevated in all infected groups compared to controls.

CONCLUSIONS

These findings suggest that control of viral replication is not sufficient to normalize gut Treg frequency in patients, independent of their response to HAART. Furthermore, persistence of functional Treg in the gut appears to be associated with the failure of HAART to repair mucosal damage.

Cytometry, immunology, and HIV infection: three decades of strong interactions

Flow cytometry (FCM) has been extensively used to investigate immunological changes that occur from infection with the human immunodeficiency virus (HIV). This review describes some of the most relevant cellular and molecular changes in the immune system that can be detected by FCM during HIV infection. Finally, it will be discussed how this technology has facilitated the understanding not only of the biology of the virus but also of the mechanisms that the immune system activates to fight HIV and is allowing to monitor the efficacy of antiretroviral therapy.

Expanding roles for CD4 T cells and their subpopulations in tumor immunity and therapy

The importance of CD4 T cells in orchestrating the immune system and their role in inducing effective T cell-mediated therapies for the treatment of patients with select established malignancies are undisputable. Through a complex and balanced array of direct and indirect mechanisms of cellular activation and regulation, this functionally diverse family of lymphocytes can potentially promote tumor eradication, long-term tumor immunity, and aid in establishing and/or rebalancing immune cell homeostasis through interaction with other immune cell populations within the highly dynamic tumor environment. However, recent studies have uncovered additional functions and roles for CD4 T cells, some of which are independent of other lymphocytes, that can not only influence and contribute to tumor immunity but paradoxically promote tumor growth and progression. Here, we review the recent advances in our understanding of the various CD4 T cell lineages and their signature cytokines in disease progression and/or regression. We discuss their direct and indirect mechanistic interplay among themselves and with other responding cells of the antitumor response, their potential roles and abilities for "plasticity" and memory cell generation within the hostile tumor environment, and their potentials in cancer treatment and immunotherapy.

T cell activation but not polyfunctionality after primary HIV infection predicts control of viral load and length of the time without therapy

Objective

Immune changes occurring after primary HIV infection (PHI) have a pivotal relevance. Our objective was to characterize the polyfunctionality of immune response triggered by PHI, and to characterize immune activation and regulatory T cells, correlating such features to disease progression.

Patients and Methods

We followed 11 patients experiencing PHI for 4 years. By polychromatic flow cytometry, we studied every month, for the first 6 months, T lymphocyte polyfunctionality after cell stimulation with peptides derived from HIV-1 gag and nef. Tregs were identified by flow cytometry, and T cell activation studied by CD38 and HLA-DR expression.

Results

An increase of anti-gag and anti-nef CD8+ specific T cells was observed 3 months after PHI; however, truly polyfunctional T cells, also able to produce IL-2, were never found. No gross changes in Tregs were present. T lymphocyte activation was maximal 1 and 2 months after PHI, and significantly decreased in the following period. The level of activation two months after PHI was strictly correlated to the plasma viral load 1 year after infection, and significantly influenced the length of period without therapy. Indeed, 80% of patients with less than the median value of activated CD8+ (15.5%) or CD4+ (0.9%) T cells remained free of therapy for >46 months, while all patients over the median value had to start treatment within 26 months.

Conclusions

T cell activation after PHI, more than T cell polyfunctionality or Tregs, is a predictive marker for the control of viral load and for the time required to start treatment.

CD8+ and CD4+ cytotoxic T cell escape mutations precede breakthrough SIVmac239 viremia in an elite controller

Background

Virus-specific T cells are critical components in the containment of immunodeficiency virus infections. While the protective role of CD8+ T cells is well established by studies of CD8+ T cell-mediated viral escape, it remains unknown if CD4+ T cells can also impose sufficient selective pressure on replicating virus to drive the emergence of high-frequency escape variants. Identifying a high frequency CD4+ T cell driven escape mutation would provide compelling evidence of direct immunological pressure mediated by these cells.

Results

Here, we studied a SIVmac239-infected elite controller rhesus macaque with a 1,000-fold spontaneous increase in plasma viral load that preceded disease progression and death from AIDS-related complications. We sequenced the viral genome pre- and post-breakthrough and demonstrate that CD8+ T cells drove the majority of the amino acid substitutions outside of Env. However, within a region of Gag p27^CA targeted only by CD4+ T cells, we identified a unique post-breakthrough mutation, Gag D205E, which abrogated CD4+ T cell recognition. Further, we demonstrate that the Gag p27^CA-specific CD4+ T cells exhibited cytolytic activity and that SIV bearing the Gag D205E mutation escapes this CD4+ T cell effector function ex vivo.

Conclusions

Cumulatively, these results confirm the importance of virus specific CD8+ T cells and demonstrate that CD4+ T cells can also exert significant selective pressure on immunodeficiency viruses in vivo during low-level viral replication. These results also suggest that further studies of CD4+ T cell escape should focus on cases of elite control with spontaneous viral breakthrough.

HIV controllers maintain a population of highly efficient Th1 effector cells in contrast to patients treated in the long term

HIV controllers are rare individuals who spontaneously control HIV replication in the absence of antiretroviral therapy. To identify parameters of the CD4 response that may contribute to viral control rather than merely reflect a persistently low viremia, we compared the T helper profiles in two groups of patients with more than 10 years of viral suppression: HIV controllers from the Agence Nationale de Recherche sur le SIDA et les Hépatites Virales (ANRS) CO18 cohort (n = 26) and efficiently treated patients (n = 16). Cells specific for immunodominant Gag and cytomegalovirus (CMV) peptides were evaluated for the production of 10 cytokines and cytotoxicity markers and were also directly quantified ex vivo by major histocompatibility complex (MHC) class II tetramer staining. HIV controller CD4(+) T cells were characterized by a higher frequency of gamma interferon (IFN-γ) production, perforin(+)/CD107a(+) expression, and polyfunctionality in response to Gag peptides. While interleukin 4 (IL-4), IL-17, and IL-21 production did not differ between groups, the cells of treated patients produced more IL-10 in response to Gag and CMV peptides, pointing to persistent negative immunoregulation after long-term antiretroviral therapy. Gag293 tetramer-positive cells were detected at a high frequency (0.12%) and correlated positively with IFN-γ-producing CD4(+) T cells in the controller group (R = 0.73; P = 0.003). Tetramer-positive cells were fewer in the highly active antiretroviral therapy (HAART) group (0.04%) and did not correlate with IFN-γ production, supporting the notion of a persistent immune dysfunction in HIV-specific CD4(+) T cells of treated patients. In conclusion, HIV controllers maintained a population of highly efficient Th1 effectors directed against Gag in spite of a persistently low antigenemia, while patients treated in the long term showed a loss of CD4 effector functions.

Imbalanced production of cytokines by T cells associates with the activation/exhaustion status of memory T cells in chronic HIV type 1 infection

Chronic HIV-1 infection is characterized by immune cell dysfunctions driven by chronic immune activation. Plasma HIV-1 viral load (VL) is closely correlated with disease progression and the level of immune activation. However, the mechanism by which the persistent presence of HIV-1 damages immune cells is still not fully understood. To evaluate how HIV-1 affects disruption of T cell-mediated immune responses during chronic HIV-1 infection we determined the functional profiles of T cells from subjects with chronic HIV-1 infection. We measured the capacity of peripheral blood mononuclear cells (PBMCs) to produce 25 specific cytokines in response to nonspecific T cell stimulation, and found that the capacity to produce Th-1-related cytokines (MIP-1α, MIP-1β, RANTES, IFN-γ, and MIG), sIL-2R, and IL-17, but not Th-2-related cytokines, was inversely correlated with plasma VL. The capacities to produce these cytokines were interrelated; notably, IL-17 production had a strong direct correlation with production of MIP-1α, MIP-1β, RANTES, and IFN-γ. In both CD4(+) and CD8(+) T cells, dysfunctional production of cytokines was associated with T cell activation (CD38 expression) and exhaustion (PD-1 and/or CTLA-4 expression) status of memory subsets. Although the capacity to produce these cytokines was recovered soon after multiple log(10) reduction of plasma viral levels by antiretroviral therapy, memory CD8(+) T cells remained activated and exhausted after prolonged virus suppression. Our data suggest that HIV-1 levels directly affect the ability of memory T cells to produce specifically Th1- and Th17-related cytokines during chronic HIV-1 infection.

The Thai phase III trial (RV144) vaccine regimen induces T cell responses that preferentially target epitopes within the V2 region of HIV-1 envelope

The Thai HIV phase III prime/boost vaccine trial (RV144) using ALVAC-HIV (vCP1521) and AIDSVAX B/E was, to our knowledge, the first to demonstrate acquisition efficacy. Vaccine-induced, cell-mediated immune responses were assessed. T cell epitope mapping studies using IFN-γ ELISPOT was performed on PBMCs from HIV-1-uninfected vaccine (n = 61) and placebo (n = 10) recipients using HIV-1 Env peptides. Positive responses were measured in 25 (41%) vaccinees and were predominantly CD4(+) T cell-mediated. Responses were targeted within the HIV Env region, with 15 of 25 (60%) of vaccinees recognizing peptides derived from the V2 region of HIV-1 Env, which includes the α(4)β(7) integrin binding site. Intracellular cytokine staining confirmed that Env responses predominated (19 of 30; 63% of vaccine recipients) and were mediated by polyfunctional effector memory CD4(+) T cells, with the majority of responders producing both IL-2 and IFN-γ (12 of 19; 63%). HIV Env Ab titers were higher in subjects with IL-2 compared with those without IL-2-secreting HIV Env-specific effector memory T cells. Proliferation assays revealed that HIV Ag-specific T cells were CD4(+), with the majority (80%) expressing CD107a. HIV-specific T cell lines obtained from vaccine recipients confirmed V2 specificity, polyfunctionality, and functional cytolytic capacity. Although the RV144 T cell responses were modest in frequency compared with humoral immune responses, the CD4(+) T cell response was directed to HIV-1 Env and more particularly the V2 region.

Immunological advantages of everolimus versus cyclosporin A in liver-transplanted recipients, as revealed by polychromatic flow cytometry

Several immunosuppressive drugs with different mechanisms of action are available to inhibit organ rejection after transplant. We analyzed different phenotypic and functional immunological parameters in liver-transplanted patients who received cyclosporin A (CsA) or Everolimus (Evr). In peripheral blood mononuclear cells (PBMC) from 29 subjects receiving a liver transplant and treated with two different immunosuppressive regimens, we analyzed T cell activation and differentiation, regulatory T cells (Tregs) and Tregs expressing homing receptors such as the chemokine receptor CXCR3. T cell polyfunctionality was studied by stimulating cells with the superantigen staphylococcal enterotoxin B (SEB), and measuring the simultaneous production of interleukin (IL)-2 and interferon (IFN)-γ, along with the expression of a marker of cytotoxicity such as CD107a. The analyses were performed by polychromatic flow cytometry before transplantation, and at different time points, up to 220 days after transplant. Patients taking Evr had a higher percentage of total CD4⁺ and naïve CD4⁺ T cells than those treated with CsA; the percentage of CD8⁺ T cells was lower, but the frequency of naïve CD8⁺ T cells higher. Patients taking Evr showed a significantly higher percentage of Tregs, and Tregs expressing CXCR3. After stimulation with SEB, CD8⁺ T cells from Evr-treated patients displayed a lower total response, and less IFN-γ producing cells. The effects on the immune system, such as the preservation of the naïve T cell pool and the expansion of Tregs (that are extremely useful in inhibiting organ rejection), along with the higher tolerability of Evr, suggest that this drug can be safely used after liver transplantation, and likely offers immunological advantages.

Cytotoxic CD4 T cells in antiviral immunity

CD4 T cells that acquire cytotoxic phenotype and function have been repeatedly identified in humans, mice, and other species in response to many diverse pathogens. Since CD4 cytotoxic T cells are able to recognize antigenic determinants unique from those recognized by the parallel CD8 cytotoxic T cells, they can potentially contribute additional immune surveillance and direct effector function by lysing infected or malignant cells. Here, we briefly review much of what is known about the generation of cytotoxic CD4 T cells and describe our current understanding of their role in antiviral immunity. Furthering our understanding of the many roles of CD4 T cells during an anti-viral response is important for developing effective vaccine strategies that promote long-lasting protective immunity.

CD4+ T-cell differentiation, regulatory T cells and gag-specific T lymphocytes are unaffected by CD4-guided treatment interruption and therapy resumption

OBJECTIVES

Despite limiting exposure to antiretroviral drugs, structured treatment interruptions can influence multiple aspects of T-cell immunity, particularly those regarding CD4(+) T lymphocytes. We evaluated the impact of CD4-guided treatment interruption (CD4-GTI) and treatment resumption on regulatory T cells (Tregs), T-lymphocyte activation, differentiation and polyfunctional gag-specific response.

METHODS

Patients were analyzed just prior to treatment interruption, at 2 and 6 months after treatment interruption, just prior to treatment resumption and at 2 and 6 months after treatment resumption. Thawed peripheral blood mononuclear cells were stained immediately for phenotype analysis or stimulated with HIV-gag peptides and analyzed by polychromatic flow cytometry.

RESULTS

Treatment interruption resulted in a CD4(+) cell count decrease and plasma viral load (pVL) increase, but did not preclude a good immune reconstitution and a complete suppression of pVL after treatment resumption. Treatment interruption did not influence CD4(+) T-cell differentiation and Treg subsets. During treatment interruption, gag-specific CD4(+) T cells were not lost, although the frequency of HIV-specific CD8(+) cells increased. Most gag-specific CD4(+) T cells were potentially cytotoxic (CD107a(+)) and were not influenced by pVL or by HAART. Most helper (CD154(+)) gag-specific CD4(+) T lymphocytes did not produce interferon-γ or interleukin-2.

CONCLUSION

CD4-GTI did not cause depletion of memory cells, Tregs or HIV-specific CD4(+) cells and, on the contrary, could induce HIV-specific responses. If guided by CD4(+) T-cell count, treatment interruption does not provoke irreversible immune damages.

Increased plasma levels of extracellular mitochondrial DNA during HIV infection: a new role for mitochondrial damage-associated molecular patterns during inflammation

HIV infection is characterized by a chronic inflammatory state. Recently, it has been shown that mitochondrial DNA (mtDNA) released from damaged or dead cells can bind Toll like receptor-9 (TLR9), an intracellular receptor that responds to bacterial or viral DNA molecules. The activation of TLR9 present within monocytes or neutrophils results in a potent inflammatory reaction, with the production of proinflammatory cytokines. We measured plasma levels of mtDNA in different groups of HIV(+) patients, i.e., those experiencing an acute HIV infection (AHI), long term non progressors (LTNP), late presenters (LP) taking antiretroviral therapy for the first time, and healthy controls. We found that in AHI and LP mtDNA plasma levels were significantly higher than in healthy individuals or in LTNP. Plasma mtDNA levels were not correlated to peripheral blood CD4(+) T cell count, nor to markers of immune activation, but had a significant correlation with plasma viral load, revealing a possible role for mtDNA in inflammation, or as a biomarker of virus-induced damage.

SPICE: exploration and analysis of post-cytometric complex multivariate datasets

Polychromatic flow cytometry results in complex, multivariate datasets. To date, tools for the aggregate analysis of these datasets across multiple specimens grouped by different categorical variables, such as demographic information, have not been optimized. Often, the exploration of such datasets is accomplished by visualization of patterns with pie charts or bar charts, without easy access to statistical comparisons of measurements that comprise multiple components. Here we report on algorithms and a graphical interface we developed for these purposes. In particular, we discuss thresholding necessary for accurate representation of data in pie charts, the implications for display and comparison of normalized versus unnormalized data, and the effects of averaging when samples with significant background noise are present. Finally, we define a statistic for the nonparametric comparison of complex distributions to test for difference between groups of samples based on multi-component measurements. While originally developed to support the analysis of T cell functional profiles, these techniques are amenable to a broad range of datatypes.

Polyfunctional analysis of Gag and Nef specific CD8+ T-cell responses in HIV-1 infected Indian individuals

Polyfunctional CD8+ T-cells have been described as most competent in controlling viral replication. We studied the impact of antigen persistence on the polyfunctional immune responses of CD8+ T-lymphocytes to HIV Gag and Nef peptides and polyclonal stimuli in 40 ART naïve HIV infected individuals and analyzed the alterations in T-cell functionality in early and late stages of infection. Significantly elevated level of global response and polyfunctional profile of CD8+ T-cells were observed to polyclonal stimulation, than HIV specific antigens in chronically infected individuals. However no key differences were observed in CD8+ T-cell functional profile in any of the 15 unique subsets for Gag and Nef specific antigens. The subjects in early stage of infection (defined as a gap of 6 months or less between seroconversion and enrolment and with no apparent clinical symptoms) had a higher degree of response functionality (4+ or 3+ different functions simultaneously) than in the late stage infection (defined as time duration since seroconversion greater than 6 months). The data suggest that persistence of antigen during chronic infection leads to functional impairment of HIV specific responses.

Cytolytic CD4(+) T cells in viral immunity

It is generally believed that the role of CD4(+) T cells is to coordinate the different arms of the adaptive immune system to shape an effective response against a pathogen and regulate nonessential or deleterious activities. However, a growing body of evidence suggests that effector CD4(+) T cells can directly display potent antiviral activity themselves. The presence of cytolytic CD4(+) T cells has been demonstrated in the immune response to numerous viral infections in both humans and in animal models and it is likely that they play a critical role in the control of viral replication in vivo. This article describes the current research on virus-specific cytolytic CD4(+) T cells, with a focus on HIV-1 infection and the implications that this immune response has for vaccine design.

Transient and persistent effects of IL-15 on lymphocyte homeostasis in nonhuman primates

Interleukin-15 (IL-15) is a cytokine with potential therapeutic application in individuals with cancer or immunodeficiency to promote natural killer (NK)- and T-cell activation and proliferation or in vaccination protocols to generate long-lived memory T cells. Here we report that 10-50 μg/kg IL-15 administered intravenously daily for 12 days to rhesus macaques has both short- and long-lasting effects on T-cell homeostasis. Peripheral blood lymphopenia preceded a dramatic expansion of NK cells and memory CD8 T cells in the circulation, particularly a 4-fold expansion of central memory CD8 T cells and a 6-fold expansion of effector memory CD8 T cells. This expansion is a consequence of their activation in multiple tissues. A concomitant inverted CD4/CD8 T-cell ratio was observed throughout the body at day 13, a result of preferential CD8 expansion. Expanded T- and NK-cell populations declined in the blood soon after IL-15 was stopped, suggesting migration to extralymphoid sites. By day 48, homeostasis appears restored throughout the body, with the exception of the maintenance of an inverted CD4/CD8 ratio in lymph nodes. Thus, IL-15 generates a dramatic expansion of short-lived memory CD8 T cells and NK cells in immunocompetent macaques and has long-term effects on the balance of CD4(+) and CD8(+) T cells.