HIV-1-Specific Memory CD4+ T Cells Are Phenotypically Less Mature Than Cytomegalovirus-Specific Memory CD4+ T Cells

Low-level HIV-1 viremia affects T-cell activation and senescence in long-term treated adults in the INSTI era

BACKGROUND

Around 10% of people with HIV (PWH) exhibit a low-level viremia (LLV) under antiretroviral therapy (ART). However, its origin and clinical significance are largely unknown, particularly at viremias between 50 and 200 copies/mL and under modern ART based on integrase strand transfer inhibitors (INSTIs). Our aim was to characterize their poor immune response against HIV in comparison to individuals with suppressed viremia (SV) and non-HIV controls (NHC).

METHODS

Transversal observational study in 81 matched participants: 27 PWH with LLV, 27 PWH with SV, and 27 NHC. Activation (CD25, HLA-DR, and CD38) and senescence [CD57, PD1, and HAVCR2 (TIM3)] were characterized in peripheral T-cell subsets by spectral flow cytometry. 45 soluble biomarkers of systemic inflammation were evaluated by immunoassays. Differences in cell frequencies and plasma biomarkers among groups were evaluated by a generalized additive model for location, scale, and shape (GAMLSS) and generalized linear model (GLM) respectively, adjusted by age, sex at birth, and ART regimen.

RESULTS

The median age was 53 years and 77.8% were male. Compared to NHC, PWH showed a lower CD4+/CD8+ ratio and increased activation, senescence, and inflammation, highlighting IL-13 in LLV. In addition, LLV showed a downtrend in the frequency of CD8+ naive and effector memory (EM) type 1 compared to SV, along with higher activation and senescence in CD4+ and CD8+ EM and terminally differentiated effector memory RA+ (TEMRA) subpopulations. No significant differences in systemic inflammation were observed between PWH groups.

CONCLUSION

LLV between 50 and 200 copies/mL leads to reduced cytotoxic activity and T-cell dysfunction that could affect cytokine production, being unable to control and eliminate infected cells. The increase in senescence markers suggests a progressive loss of immunological memory and a reduction in the proliferative capacity of immune cells. This accelerated immune aging could lead to an increased risk of developing future comorbidities. These findings strongly advocate for heightened surveillance of these PWH to promptly identify potential future complications.

Mitochondrial disturbance related to increased caspase-1 of CD4+T cells in HIV-1 infection

BACKGROUND

In HIV-1 infection, more than 95% of CD4+T cells die of caspase-1 mediated pyroptosis. What governs the increased susceptibility of CD4+T cells to pyroptosis is poorly understood.

METHODS

Blood samples were obtained from 31 untreated HIV-infected patients (UNT), 29 antiretroviral therapy treated HIV-infected patients (ART), and 21 healthy control donors (HD). Plasma levels of IL-18 and IL-1β, caspase-1 expression, mitochondrial mass (MM) and mitochondrial fusion/fisson genes of CD4+T subsets were measured.

RESULTS

A significantly higher IL-18 level in plasma and MM level of CD4+T cells were found in HIV-infected patients (UNT and ART) compared to HD, and the MMhigh phenotype was manifested, related to increased caspase-1 expression. Moreover, the increased MM was more pronounced in the early differentiated and inactivated CD4+T cells. However, higher MM was not intrinsically linked to T cell differentiation disorder or excessive activation of the CD4+T cells. Mechanistically, the increased MM was significantly correlated with an elevated level of expression of the mitochondrial fusion gene mitofusin1.

CONCLUSION

An increase in MM was associated with heightened sensitivity of CD4+T cells to pyroptosis, even in early differentiated and inactivated CD4+T cells, in patients with HIV-1 infection, regardless of whether patients were on antiretroviral therapy or not. These new revelations have uncovered a previously unappreciated challenge to immune reconstitution with antiretroviral therapy.

Human Variation in DNA Repair, Immune Function, and Cancer Risk

DNA damage constantly threatens genome integrity, and DNA repair deficiency is associated with increased cancer risk. An intuitive and widely accepted explanation for this relationship is that unrepaired DNA damage leads to carcinogenesis due to the accumulation of mutations in somatic cells. But DNA repair also plays key roles in the function of immune cells, and immunodeficiency is an important risk factor for many cancers. Thus, it is possible that emerging links between inter-individual variation in DNA repair capacity and cancer risk are driven, at least in part, by variation in immune function, but this idea is underexplored. In this review we present an overview of the current understanding of the links between cancer risk and both inter-individual variation in DNA repair capacity and inter-individual variation in immune function. We discuss factors that play a role in both types of variability, including age, lifestyle, and environmental exposures. In conclusion, we propose a research paradigm that incorporates functional studies of both genome integrity and the immune system to predict cancer risk and lay the groundwork for personalized prevention.

Mapping the extent of heterogeneity of human CCR5+ CD4+ T cells in peripheral blood and lymph nodes

BACKGROUND

CD4 T cells that express the chemokine receptor, CCR5, are the most important target of HIV-1 infection, but their functions, phenotypes and anatomical locations are poorly understood. We aimed to use multiparameter flow cytometry to better define the full breadth of these cells.

METHODS

High-parameter fluorescence flow and mass cytometry were optimized to analyse subsets of CCR5 memory CD4 T cells, including CD25CD127 Tregs, CXCR3CCR6- Th1-like, CCR6CD161CXCR3- Th17-like, integrins α4ß7 gut-homing, CCR4 skin-homing, CD62L lymph node-homing, CD38HLA-DR activated cells, and CD27-CD28- cytotoxic T lymphocytes, in a total of 22 samples of peripheral blood, ultrasound-guided fine needle biopsies of lymph nodes and excised tonsils. CCR5 antigen-specific CD4 T cells were studied using the OX40 flow-based assay.

RESULTS

10-20% of CCR5 memory CD4 T cells were Tregs, 10-30% were gut-homing, 10-30% were skin-homing, 20-40% were lymph node-homing, 20-50% were Th1-like and 20-40% were Th17-like cells. Up to 30% were cytotoxic T lymphocytes in CMV-seropositive donors, including cells that were either CCR5Granzyme K or CCR5Granzyme B. When all possible phenotypes were exhaustively analysed, more than 150 different functional and trafficking subsets of CCR5 CD4 T cells were seen. Moreover, a small population of resident CD69Granzyme KCCR5 CD4 T cells was found in lymphoid tissues. CMV- and Mycobacterium tuberculosis-specific CD4 T cells were predominantly CCR5.

CONCLUSION

These results reveal for the first time the prodigious heterogeneity of function and trafficking of CCR5 CD4 T cells in blood and in lymphoid tissue, with significant implications for rational approaches to prophylaxis for HIV-1 infection and for purging of the HIV-1 reservoir in those participants already infected.

CD4⁺CD28null T lymphocytes resemble CD8⁺CD28null T lymphocytes in their responses to IL-15 and IL-21 in HIV-infected patients

HIV-infected individuals suffer from accelerated immunologic aging. One of the most prominent changes during T lymphocyte aging is the accumulation of CD28(null) T lymphocytes, mainly CD8(+) but also CD4(+) T lymphocytes. Enhancing the functional properties of these cells may be important because they provide antigen-specific defense against chronic infections. The objective of this study was to compare the responses of CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes from HIV-infected patients to the immunomodulatory effects of cytokines IL-15 and IL-21. We quantified the frequencies of CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes in peripheral blood from 110 consecutive, HIV-infected patients and 25 healthy controls. Patients showed increased frequencies of CD4(+)CD28(null) and CD8(+)CD28(null). Both subsets were positively correlated to each other and showed an inverse correlation with the absolute counts of CD4(+) T lymphocytes. Higher frequencies of HIV-specific and CMV-specific cells were found in CD28(null) than in CD28(+) T lymphocytes. Activation of STAT5 by IL-15 and STAT3 by IL-21 was higher in CD28(null) compared with CD28(+) T lymphocytes. Proliferation, expression of CD69, and IFN-γ production in CD28(null) T lymphocytes were increased after treatment with IL-15, and IL-21 potentiated most of those effects. Nevertheless, IL-21 alone reduced IFN-γ production in response to anti-CD3 stimulation but increased CD28 expression, even counteracting the inhibitory effect of IL-15. Intracytoplasmic stores of granzyme B and perforin were increased by IL-15, whereas IL-21 and simultaneous treatment with the 2 cytokines also significantly enhanced degranulation in CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes. IL-15 and IL-21 could have a role in enhancing the effector response of CD28(null) T lymphocytes against their specific chronic antigens in HIV-infected patients.

Subsets of memory CD4+ T cell and bactericidal antibody response to Neisseria meningitidis serogroup C after immunization of HIV-infected children and adolescents

Meningococcal disease is endemic in Brazil, with periodic outbreaks and case fatality rates reach as high as 18 to 20% of cases. Conjugate vaccines against meningococci are immunogenic in healthy children. However, we have previously shown a poor bactericidal antibody response to a Men C conjugate vaccine in Brazilian HIV-infected children and adolescents after a single vaccine administration. The goal of the present work was to investigate associations between bactericidal antibody response induced by MenC vaccine and the frequency and activation profile (expression of CD38, HLA-DR and CCR5 molecules) of total CD4+ memory T cell sub-populations in HIV-1-infected children and adolescents. Responders to vaccination against MenC had a predominance (about 44%) of CD4+ TINTERMEDIATE subset followed by TTRANSITIONAL memory subset (23 to 26%). Importantly, CD4+ TINT frequency was positively associated with bactericidal antibody response induced by vaccination. The positive correlation persisted despite the observation that the frequency TINT CD38+HLA-DR+ was higher in responders. In contrast, CD4+ TCENTRAL MEMORY (TCM) subset negatively correlated with bactericidal antibodies. In conclusion, these data indicate that less differentiated CD+ T cells, like TCM may be constantly differentiating into intermediate and later differentiated CD4+ T cell subsets. These include CD4 TINT subset which showed a positive association with bactericidal antibodies.

CD45RA-Foxp3(low) non-regulatory T cells in the CCR7-CD45RA-CD27+CD28+ effector memory subset are increased in synovial fluid from patients with rheumatoid arthritis

Increased numbers of regulatory T (Treg) cells are found in synovial fluid from patients with rheumatoid arthritis (RASF) compared with peripheral blood. However, Treg cells in RASF have been shown to have a decreased capacity to suppress T cells. Here we phenotypically classified CD4+ T cells in RASF into six subsets based on the expression of CD45RA, CCR7, CD27 and CD28, and demonstrated that the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in synovial fluid compared with peripheral blood. In addition, the proportion of Foxp3+ Treg cells in the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in RASF. Furthermore, most of the Foxp3+ Treg cells in RASF were non-suppressive CD45RA-Foxp3(low) non-Treg cells, and the frequency of the non-Treg cells in the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in RASF. Our findings suggest that the pro-inflammatory environment in RA joints may induce the increase of CD45RA-Foxp3(low) non-Treg cells in synovial fluid.

In vivo identification and characterization of CD4⁺ cytotoxic T cells induced by virulent Brucella abortus infection

CD4⁺ T cells display a variety of helper functions necessary for an efficient adaptive immune response against bacterial invaders. This work reports the in vivo identification and characterization of murine cytotoxic CD4⁺ T cells (CD4⁺ CTL) during Brucella abortus infection. These CD4⁺ CTLs express granzyme B and exhibit immunophenotypic features consistent with fully differentiated T cells. They express CD25, CD44, CD62L ,CD43 molecules at their surface and produce IFN-γ. Moreover, these cells express neither the co-stimulatory molecule CD27 nor the memory T cell marker CD127. We show here that CD4⁺ CTLs are capable of cytolytic action against Brucella-infected antigen presenting cells (APC) but not against Mycobacterium-infected APC. Cytotoxic CD4⁺ T cell population appears at early stages of the infection concomitantly with high levels of IFN-γ and granzyme B expression. CD4⁺ CTLs represent a so far uncharacterized immune cell sub-type triggered by early immune responses upon Brucella abortus infection.

CD45RA-Foxp3(high) activated/effector regulatory T cells in the CCR7 + CD45RA-CD27 + CD28+central memory subset are decreased in peripheral blood from patients with rheumatoid arthritis

Human CD4+ T cells can be classified as either naïve, central memory (TCM), or effector memory (TEM) cells. To identify the CD4+ T cell subsets most important in the pathogenesis of rheumatoid arthritis (RA), we phenotypically defined human CD4+ T cells as functionally distinct subsets, and analyzed the distribution and characteristics of each subset in the peripheral blood. We classified CD4+ T cells into six novel subsets based on the expression of CD45RA, CCR7, CD27, and CD28. The CCR7 + CD45RA-CD27 + CD28+ TCM subset comprised a significantly smaller proportion of CD4+ T cells in RA patients compared to healthy controls. The frequency of TNF-α-producing cells in the CCR7-CD45RA-CD27 + CD28+ TEM subset was significantly increased in RA. Furthermore, within the CCR7 + CD45RA-CD27 + CD28+ TCM subset, which was decreased in periperal blood from RA, the proportions of total Foxp3+ Treg cells and CD45RA-Foxp3(high) activated/effector Treg cells were significantly lower in RA patients. Our findings suggest that the increased proportion of TNF-α-producing cells and the decreased proportion of CD45RA-Foxp3(high) activated/effector Treg cells in particular subsets may have critical roles in the pathogenesis of RA.

When Aging Reaches CD4+ T-Cells: Phenotypic and Functional Changes

Beyond midlife, the immune system shows aging features and its defensive capability becomes impaired, by a process known as immunosenescence that involves many changes in the innate and adaptive responses. Innate immunity seems to be better preserved globally, while the adaptive immune response exhibits profound age-dependent modifications. Elderly people display a decline in numbers of naïve T-cells in peripheral blood and lymphoid tissues, while, in contrast, their proportion of highly differentiated effector and memory T-cells, such as the CD28^null T-cells, increases markedly. Naïve and memory CD4+ T-cells constitute a highly dynamic system with constant homeostatic and antigen-driven proliferation, influx, and loss of T-cells. Thymic activity dwindles with age and essentially ceases in the later decades of life, severely constraining the generation of new T-cells. Homeostatic control mechanisms are very effective at maintaining a large and diverse subset of naïve CD4+ T-cells throughout life, but although later than in CD8 + T-cell compartment, these mechanisms ultimately fail with age.

CD27 expression discriminates porcine T helper cells with functionally distinct properties

Differentiation of porcine T helper cells is still poorly investigated, partly due to a lack of monoclonal antibodies (mAbs) specific for molecules involved in this process. Recently, we identified a mAb specific for porcine CD27 and showed that CD27 is expressed by all naïve CD8α- T helper cells but divides CD8α+ T helper cells into a CD27+ and a CD27- subset. In the present study, detailed phenotypical and functional analyses of these T-helper cell subpopulations were performed. Naïve CD8α-CD27+ T helper cells predominantly resided in various lymph nodes, whereas higher proportions of CD8α+CD27+ and CD8α+CD27- T helper cells were found in blood, spleen and liver. Both CD8α+CD27+ and CD8α+CD27- T helper cells were capable of producing IFN-γ upon in vitro polyclonal stimulation and antigen-specific restimulation. Experiments with sorted CD8α-CD27+, CD8α+CD27+ and CD8α+CD27- T-helper cell subsets following polyclonal stimulation revealed the lowest proliferative response but the highest ability for IFN-γ and TNF-α production in the CD8α+CD27- subset. Therefore, these cells resembled terminally differentiated effector memory cells as described in human. This was supported by analyses of CCR7 and CD62L expression. CD8α+CD27- T helper cells were mostly CCR7- and had considerably reduced CD62L mRNA levels. In contrast, expression of both homing-receptors was increased on CD8α+CD27+ T helper cells, which also had a proliferation rate similar to naïve CD8α-CD27+ T helper cells and showed intermediate levels of cytokine production. Therefore, similar to human, CD8α+CD27+ T helper cells displayed a phenotype and functional properties of central memory cells.

Impact of antigen specificity on CD4+ T cell activation in chronic HIV-1 infection

BACKGROUND

HIV infection induces chronic immune activation which is associated with accelerated disease progression; the causes of this activation, however, are incompletely understood. We investigated the activation status of CD4+ T cells specific for chronic herpes viruses and the non-persistent antigen tetanus toxoid (TT) in HIV positive and HIV negative donors to assess whether persistent infections contribute to chronic CD4+ T cell activation.

METHODS

Untreated HIV+ patients and healthy, aged matched controls were recruited and activation levels assessed and compared between cells specific for persistent and non-persistent antigens. Activation levels on antigen-specific CD4+ T cells were measured by intracellular cytokine staining following in vitro stimulation with various recall antigens (CMV, EBV, HSV, VZV and TT) in conjunction with cell surface phenotyping.

RESULTS

Activation levels of herpes virus-specific CD4+ T cell populations, assessed by co-expression of CD38 and HLA-DR, were significantly elevated in HIV+ individuals compared to normal controls and compared to TT-specific responses. In contrast, we found similar levels of activation of TT-specific CD4+ T cells in HIV+ and HIV- donors.

CONCLUSIONS

These results show a disparate distribution of immune activation within CD4+ T cell populations depending on their specificity and suggest that the elevated level of immune activation that characterizes chronic HIV infection may be influenced by the persistence of other antigens.

T-cell subset distribution in HIV-1-infected patients after 12 years of treatment-induced viremic suppression

OBJECTIVE

Residual immune activation and skewed T cell maturation may contribute to excess comorbidity and mortality in successfully treated HIV-infected patients, and long-term effects of combination antiretroviral therapy (cART) on immune reconstitution remain a debated issue. Quantitative T cell reconstitution and activation and its association with residual viremia in patients with 12 years of viremic suppression were investigated.

DESIGN

Blood samples collected cross-sectionally from 71 HIV-infected patients with cART-induced viremic suppression through 12 years were compared with samples from 16 healthy controls.

METHODS

Several different subsets of naive, memory, and activated T cells were analyzed in fresh whole blood by 6-color flowcytometry, and ultrasensitive quantification of HIV RNA was performed.

RESULTS

HIV-infected patients had lower absolute and relative CD4 T cell counts and higher absolute and relative CD8 T cell counts than controls. HIV-infected patients had lower concentrations of naive CD4 cells than controls, but proportions were similar. HIV-infected patients had higher concentrations of CD8 T cells than controls in all the examined subsets but only a higher proportion of CD8 cells in the intermediately differentiated and activated subsets. Residual viremia did not correlate to proportions of naive CD4, CD4 recent thymic emigrants, or activated CD8 T cells.

CONCLUSIONS

This study demonstrated some degree of T cell imbalance even after 12 years of successful cART. Large longitudinal studies are needed to establish whether these discrete changes have clinical relevance.

Expansion of activated memory CD4+ T cells affects infectivity of CCR5-tropic HIV-1 in humanized NOD/SCID/JAK3null mice

Humanized mice reconstituted with human hematopoietic cells have been developed as an experimental animal model for human immunodeficiency virus type 1 (HIV-1) infection. Myeloablative irradiation is usually performed to augment the engraftment of donor hematopoietic stem cells (HSCs) in recipient mice; however, some mouse strains are susceptible to irradiation, making longitudinal analysis difficult. We previously attempted to construct humanized NOD/SCID/JAK3^null (hNOJ) mice, which were not irradiated prior to human HSC transplantation. We found that, over time, many of the reconstituted CD4⁺ T cells expanded with an activated effector memory phenotype. Therefore, the present study used hNOJ mice that were irradiated (hNOJ (IR+)) or not (hNOJ (IR−)) prior to human HSC transplantation to examine whether the development and cellularity of the reconstituted CD4⁺ T cells were influenced by the degree of chimerism, and whether they affected HIV-1 infectivity. Indeed, hNOJ (IR+) mice showed a greater degree of chimerism than hNOJ (IR−) mice. However, the conversion of CD4⁺ T cells to an activated effector memory phenotype, with a high percentage of cells showing Ki-67 expression, occurred in both hNOJ (IR+) and hNOJ (IR−) mice, probably as a result of lymphopenia-induced homeostatic expansion. Furthermore, when hNOJ (IR+) and hNOJ (IR−) mice, which were selected as naïve- and memory CD4⁺ T cell subset-rich groups, respectively, were infected with CCR5-tropic HIV-1 in vivo, virus replication (as assessed by the plasma viral load) was delayed; however, the titer subsequently reached a 1-log higher level in memory-rich hNOJ (IR−) mice than in naïve-rich hNOJ (IR+) mice, indicating that virus infectivity in hNOJ mice was affected by the different status of the reconstituted CD4⁺ T cells. Therefore, the hNOJ mouse model should be used selectively, i.e., according to the specific experimental objectives, to gain an appropriate understanding of HIV-1 infection/pathogenesis.

In vitro HIV-1 LTR integration into T-cell activation gene CD27 segment and the decoy effect of modified-sequence DNA

Integration into the host genome is an essential step in the HIV-1 life cycle. However, the host genome sequence that is favored by HIV-1 during integration has never been documented. Here, we report that CD27, a T cell activation gene, includes a sequence that is a target for in vitro HIV-1 cDNA integration. This sequence has a high affinity for integrase, and the target nucleotides responsible for this higher affinity were identified using a crystal microbalance assay. In experiments involving a segment of the CD27 gene, integration converged in the target nucleotides and flanking sequence DNA, indicating that integration is probably dependent upon the secondary structure of the substrate DNA. Notably, decoy modified CD27 sequence DNAs in which the target nucleotides were replaced suppressed integration when accompanying the original CD27 sequence DNA. Our identified CD27 sequence DNA is useful for investigating the biochemistry of integrase and for in vitro assessment of integrase-binding inhibitors.

HIV-1 infection alters CD4+ memory T-cell phenotype at the site of disease in extrapulmonary tuberculosis

HIV-1-infected people have an increased risk of developing extrapulmonary tuberculosis (TB), the immunopathogenesis of which is poorly understood. Here, we conducted a detailed immunological analysis of human pericardial TB, to determine the effect of HIV-1 co-infection on the phenotype of Mycobacterium tuberculosis (MTB)-specific memory T cells and the role of polyfunctional T cells at the disease site, using cells from pericardial fluid and blood of 74 patients with (n=50) and without (n=24) HIV-1 co-infection. The MTB antigen-induced IFN-γ response was elevated at the disease site, irrespective of HIV-1 status or antigenic stimulant. However, the IFN-γ ELISpot showed no clear evidence of increased numbers of antigen-specific cells at the disease site except for ESAT-6 in HIV-1 uninfected individuals (p=0.009). Flow cytometric analysis showed that CD4⁺ memory T cells in the pericardial fluid of HIV-1-infected patients were of a less differentiated phenotype, with the presence of polyfunctional CD4⁺ T cells expressing TNF, IL-2 and IFN-γ. These results indicate that HIV-1 infection results in altered phenotype and function of MTB-specific CD4⁺ T cells at the disease site, which may contribute to the increased risk of developing TB at all stages of HIV-1 infection.

NKG2D expression in CD4+ T lymphocytes as a marker of senescence in the aged immune system

Human aging is characterized by changes in the immune system which have a profound impact on the T-cell compartment. These changes are more frequently found in CD8+ T cells, and there are not well-defined markers of differentiation in the CD4+ subset. Typical features of cell immunosenescence are characteristics of pathologies in which the aberrant expression of NKG2D in CD4+ T cells has been described. To evaluate a possible age-related expression of NKG2D in CD4+ T cells, we compared their percentage in peripheral blood from 100 elderly and 50 young adults. The median percentage of CD4+ NKG2D+ in elders was 5.3% (interquartile range (IR): 8.74%) versus 1.4% (IR: 1.7%) in young subjects (p < 0.3 × 10(-10)). CD28 expression distinguished two subsets of CD4+ NKG2D+ cells with distinct functional properties and differentiation status. CD28+ cells showed an immature phenotype associated with high frequencies of CD45RA and CD31. However, most of the NKG2D+ cells belonged to the CD28(null) compartment and shared their phenotypical properties. NKG2D+ cells represented a more advanced stage of maturation and exhibited greater response to CMV (5.3 ± 3.1% versus 3.4 ± 2%, p = 0.037), higher production of IFN-γ (40.56 ± 13.7% versus 24 ± 8.8%, p = 0.015), lower activation threshold and reduced TREC content. Moreover, the frequency of the CD4+ NKG2D+ subset was clearly related to the status of the T cells. Higher frequencies of the NKG2D+ subset were accompanied with a gradual decrease of NAIVE and central memory cells, but also with a higher level of more differentiated subsets of CD4+ T cells. In conclusion, CD4+ NKG2D+ represent a subset of highly differentiated T cells which characterizes the senescence of the immune system.

Altered phenotype of regulatory T cells associated with lack of human immunodeficiency virus (HIV)-1-specific suppressive function

Mechanisms by which CD4+ regulatory T cells (T(regs)) mediate suppression of virus-specific responses remain poorly defined. Adenosine, mediated via CD39 and CD73, has been shown to play a role in the action of murine T(regs) . In this study we investigate the phenotype of T(regs) in the context of human immunodeficiency virus (HIV)-1 infection, and the function of these cells in response to HIV-1-Gag and cytomegalovirus (CMV) peptides. Phenotypic data demonstrate a decrease in forkhead box transcription factor 3 (FoxP3+) T(reg) numbers in the peripheral blood of HIV-1+ individuals compared to healthy controls, which is most pronounced in those with high HIV-1 RNA plasma load. Due to aberrant expression of CD27 and CD127 during HIV-1 disease, these markers are unreliable for T(reg) identification. The CD3+ CD4+ CD25(hi) CD45RO+ phenotype correlated well with FoxP3 expression in both the HIV-1+ and seronegative control cohorts. We observed expression of CD39 but not CD73 on T(regs) from HIV-1+ and healthy control cohorts. We demonstrate, through T(reg) depletion, the suppressive potential of T(regs) over anti-CMV responses in the context of HIV-1 infection; however, no recovery of the HIV-1-specific T cell response was observed indicating a preferential loss of HIV-1-specific T(reg) function. We propose that before immunotherapeutic manipulation of T(regs) is considered, the immunoregulatory profile and distribution kinetics of this population in chronic HIV-1 infection must be elucidated fully.

Alteration of CD8+ T cell effector diversity during HIV-1 infection with discordant normalization in effective antiretroviral therapy

BACKGROUND

Although the impairment of HIV-specific T lymphocytes is evident during chronic HIV-infection, it is unclear whether the increased CD8+ T cells associates with either selective or overall change of effector functional phenotype. Instead of study on HIV-specific T cells only, analyzing bulk T cell populations represent a neglected area of T cell impairment, which go far beyond HIV-specific T cells.

METHODS

In this study, we determined the diversity of CD8+ T cells in term of cytolytic molecule expression (perforin, granzyme A, and granzyme B) and cytokine production ability (IFN-gamma, TNF-alpha, and IL-2) using intracellular staining and flow cytometry technique. The results were compared between healthy individuals, untreated, and antiretroviral therapy (ART) treated HIV infected patients.

RESULTS

We demonstrated the presence of four different subsets of CD8+ T cells that expressed different combinations of cytolytic molecules. We also identified seven different subsets of cytokine producing cells based on different combination of IFN-gamma, TNF-alpha, and IL-2. Results showed significant alterations of these cell subsets that expressed different combination of cytolytic effector molecules or cytokines in HIV infected patients. Furthermore, cytolytic molecule expressing cell subsets are not normalized in effective ART treated patients, whereas the selective population of cytokine producing cells returned to normal value.

CONCLUSIONS

The effector diversity of CD8+ T cells changed in HIV infected patients. Although effective ART altered functional diversity of these cells, long-term suppression of viral replication may be required to normalize the selected CD8+ T cell effector phenotype in HIV infected patients.

Altered T cell differentiation associated with loss of CD27 and CD28 in HIV infected Indian individuals

BACKGROUND

HIV-1 infection is associated with depletion of naïve T cell subsets and skewed T cell differentiation and maturation, leading to accumulation of T cells at intermediate and end stages of differentiation. CD27 and CD28 expression have been utilized in assessing these population subsets.

METHODS

We characterized T cell subsets based on expression of CD45RA, CCR7, CD27, and CD28 and compared these subsets in HIV-1 infected Indian subjects and uninfected controls.

RESULTS

HIV-1 infection was associated with an increase in effector and memory T cell subsets and a concomitant decrease in naïve T cells. HIV-1 infected subjects showed accumulation of intermediate CD8 T cell (CD27+CD28-) differentiation subsets, whereas CD4 T cells progressed to late stage differentiation (CD27-CD28-). These subsets were negatively associated with CD4 T cell counts and positively associated with plasma viremia. CD57, an immunosenescence marker, was also increased on T cell subsets from HIV-1 infected individuals. Antiretroviral therapy resulted in partial restoration of differentiation status.

CONCLUSION

Persistent HIV-1 replication and chronic immune activation, along with altered cytokine secretion profile, lead to impaired T cell differentiation and maturation. Detailed understanding of factors associated with differentiation defects in HIV-1 infected Indian individuals will strongly assist in Indian HIV-1 vaccine efforts and add to our knowledge of HIV-1 subtype C pathogenesis.

CCR2 identifies a stable population of human effector memory CD4+ T cells equipped for rapid recall response

Because T cells act primarily through short-distance interactions, homing receptors can identify colocalizing cells that serve common functions. Expression patterns for multiple chemokine receptors on CD4(+) T cells from human blood suggested a hierarchy of receptors that are induced and accumulate during effector/memory cell differentiation. We characterized CD4(+)CD45RO(+) T cells based on expression of two of these receptors, CCR5 and CCR2, the principal subsets being CCR5(-)CCR2(-) (∼70%), CCR5(+)CCR2(-) (∼25%), and CCR5(+)CCR2(+) (∼5%). Relationships among expression of CCR5 and CCR2 and CD62L, and the subsets' proliferation histories, suggested a pathway of progressive effector/memory differentiation from the CCR5(-)CCR2(-) to CCR5(+)CCR2(-) to CCR5(+)CCR2(+) cells. Sensitivity and rapidity of TCR-mediated activation, TCR signaling, and effector cytokine production by the subsets were consistent with such a pathway. The subsets also showed increasing responsiveness to IL-7, and the CCR5(+)CCR2(+) cells were CD127(bright) and invariably showed the greatest response to tetanus toxoid. CCR5(+)CCR2(+) cells also expressed the largest repertoire of chemokine receptors and migrated to the greatest number of chemokines. By contrast, the CCR5(+)CCR2(-) cells had the greatest percentages of regulatory T cells, activated/cycling cells, and CMV-reactive cells, and were most susceptible to apoptosis. Our results indicate that increasing memory cell differentiation can be uncoupled from susceptibility to death, and is associated with an increase in chemokine responsiveness, suggesting that vaccination (or infection) can produce a stable population of effector-capable memory cells that are highly enriched in the CCR5(+)CCR2(+) subset and ideally equipped for rapid recall responses in tissue.

Role of CD4+ cytotoxic T lymphocytes in the control of viral diseases and cancer

Our knowledge on the physiological role of CD4(+) T lymphocytes has improved in the last decade: available data convincingly demonstrate that, besides the 'helper' activity, CD4(+) T cells may be also endowed with lytic properties. The cytotoxic function of these effector cells has a relevant role in the control of pathogenic infections and in mediating antitumor immune responses. On these bases, several immunotherapeutic approaches exploiting the cytotoxic properties of CD4(+) T cells are under investigation. This review summarizes available data supporting the functional and therapeutic relevance of cytotoxic CD4(+) T cells, with a particular focus on Epstein-Barr virus (EBV)-related disorders.

No difference in Gag and Env immune-response profiles between vaccinated and non-vaccinated rhesus macaques that control immunodeficiency virus replication

Recent advances in human immunodeficiency virus (HIV) vaccine design have resulted in induction of strong CD4 T-cell proliferative and polyfunctional cytokine responses, which are also characteristic for long-term non-progressing (LTNP) HIV-infected individuals. However, limited information is available on the persistence of these responses after infection. Results from studies in non-human primates indicate that vaccine-induced immune responses are partially maintained upon viral infection and differ from the responses seen in non-vaccinated animals that typically progress to disease. However, it is unclear how these partially preserved responses compare to immune responses that are acquired naturally by LTNP animals. In this study, immune-response profiles were compared between vaccinated animals that, upon SHIV₈₉.₆ challenge, became infected but were able to control virus replication, and a group of animals having spontaneous control of this viral infection. Both groups were found to develop very similar immune responses with regard to induction of CD4 and CD8 T-cell polyfunctional cytokine responses, proliferative capacity and cytotoxic capacity, as measured by a standard ₅₁Cr release assay and more direct ex vivo and in vivo CTL assays. Hence, vaccinated animals that become infected, but control infection, appear to establish immune responses that are similar to those elicited by long-term non-progressors.

Regulation of virus-specific CD4+ T cell function by multiple costimulatory receptors during chronic HIV infection

Elevated expression of inhibitory receptors on virus-specific T cells has been implicated as a mechanism by which viruses evade host immune surveillance. Blockade of these pathways during chronic infection leads to increased T cell function and improved immune control of viral replication. To explore the association between costimulatory receptors and HIV replication, we examined the expression of programmed death 1 (PD-1), CTLA-4, T cell Ig domain and mucin domain 3 (TIM-3), and CD28 on HIV-specific CD4(+) T cells from HIV-infected subjects. Greater than 30% of HIV-specific CD4(+) T cells from untreated subjects coexpressed PD-1, CTLA-4, and TIM-3, whereas <2% of CMV- or varicella-zoster virus-specific CD4(+) T cells expressed all three receptors. Coexpression of all three inhibitory receptors on HIV-specific CD4(+) T cells was more strongly correlated with viral load compared with the expression of each receptor individually. Suppression of HIV replication with antiretroviral therapy was associated with decreased expression of all three inhibitory receptors on HIV-specific CD4(+) T cells. Surprisingly, a high percentage of HIV-specific CD4(+) T cells that expressed inhibitory receptors also coexpressed CD28. In vitro blockade of PD-1 binding concurrent with stimulation through CD28 synergistically increased HIV-specific CD4(+) T cell proliferation to a greater extent than did either alone. These findings indicate that HIV-specific CD4(+) T cell responses during chronic infection are regulated by complex patterns of coexpressed inhibitory receptors and that the synergistic effect of inhibitory receptor blockade and stimulation of costimulatory receptors could be used for therapeutic augmentation of HIV-specific CD4(+) T cell function.

A steady state of CD4+ T cell memory maturation and activation is established during primary subtype C HIV-1 infection

The functional integrity of CD4(+) T cells is crucial for well-orchestrated immunity and control of HIV-1 infection, but their selective depletion during infection creates a paradox for understanding a protective response. We used multiparameter flow cytometry to measure activation, memory maturation, and multiple functions of total and Ag-specific CD4(+) T cells in 14 HIV-1- and CMV- coinfected individuals at 3 and 12 mo post HIV-1 infection. Primary HIV-1 infection was characterized by elevated levels of CD38, HLA-DR, and Ki67 in total memory and Gag-specific CD4(+) and CD8(+) T cells. In both HIV-infected and 15 uninfected controls, the frequency of activated cells was uniformly distributed among early differentiated (ED; CD45RO(+)CD27(+)), late differentiated (CD45RO(+)CD27(-)), and fully differentiated effector (CD45RO(-)CD27(-)) memory CD4(+) T cells. In HIV-1-infected individuals, activated CD4(+) T cells significantly correlated with viremia at 3 mo postinfection (r = 0.79, p = 0.0007) and also harbored more gag provirus DNA copies than nonactivated cells (p = 0.04). Moreover, Gag-specific ED CD4(+) T cells inversely associated with plasma viral load (r = -0.87, p < 0.0001). Overall, we show that low copy numbers of gag provirus and plasma RNA copies associated with low CD4 activation as well as accumulation of ED HIV-specific CD4(+) memory. Significant positive correlations between 3 and 12 mo activation and memory events highlighted that a steady state of CD4(+) T cell activation and memory maturation was established during primary infection and that these cells were unlikely to be involved in influencing the course of viremia in the first 12 mo of HIV-1 infection.

Regulatory function of cytomegalovirus-specific CD4+CD27-CD28- T cells

CMV infection is characterized by high of frequencies of CD27-CD28- T cells. Here we demonstrate that CMV-specific CD4+CD27-CD28- cells are regulatory T cells (TR). CD4+CD27-CD28- cells sorted from CMV-stimulated PBMC of CMV-seropositive donors inhibited de novo CMV-specific proliferation of autologous PBMC in a dose-dependent fashion. Compared with the entire CMV-stimulated CD4+ T-cell population, higher proportions of CD4+CD27-CD28- TR expressed FoxP3, TGFbeta, granzyme B, perforin, GITR and PD-1, lower proportions expressed CD127 and PD1-L and similar proportions expressed CD25, CTLA4, Fas-L and GITR-L. CMV-CD4+CD27-CD28- TR expanded in response to IL-2, but not to CMV antigenic restimulation. The anti-proliferative effect of CMV-CD4+CD27-CD28- TR significantly decreased after granzyme B or TGFbeta inhibition. The CMV-CD4+CD27-CD28- TR of HIV-infected and uninfected donors had similar phenotypes and anti-proliferative potency, but HIV-infected individuals had higher proportions of CMV-CD4+CD27-CD28- TR. The CMV-CD4+CD27-CD28- TR may contribute to the downregulation of CMV-specific and nonspecific immune responses of CMV-infected individuals.

Effect of lentivirus encoding HIV-1 Nef-U3 shRNA on the function of HIV-specific memory CD4(+) T cells in patients with chronic HIV-1 infection

OBJECTIVE

To determine whether HIV-1-specific CD4 T cells with proliferative capacity are eliminated or functionally defective because of HIV-1 reactivation.

DESIGN

The loss of proliferative capacity by HIV-1-specific CD4 T cells compromises the host's ability to maintain protective immunity against HIV-1 and is a hallmark of disease progression. We used a recombinant lentivirus encoding an HIV-specific short hairpin (sh)RNA (Lenti shNef366) with known HIV-inhibitory activity to analyze the functional state of HIV-1-specific CD4 T cells.

METHODS

T lymphocytes from untreated chronically HIV-infected patients with documented high viral loads (above 10 000 HIV-RNA) were transduced with Lenti shNef366, and the proliferation, differentiation, and cytokine production of HIV-specific CD4 T cells were analyzed.

RESULTS

Lenti shNef366 restored the proliferation of HIV p24-specific CD4 T cells in eight of 12 patients tested, affecting primarily CD27 or CD28 CD4 T cells that were at an intermediate stage of differentiation. Although cytokine production by CD4 T cells remained poor after transduction with Lenti shNef366, improved proliferative capacity was associated with significantly higher levels of expression of CD107a.

CONCLUSION

In chronic stages of HIV-1 infection with high levels of HIV replication, proliferation-competent HIV-specific CD4 T cells in an intermediate stage of differentiation are present but are exquisitely and strongly impaired. Blocking HIV reactivation may restore a key functional property of memory T cells.

Autocrine production of beta-chemokines protects CMV-Specific CD4 T cells from HIV infection

Induction of a functional subset of HIV-specific CD4⁺ T cells that is resistant to HIV infection could enhance immune protection and decrease the rate of HIV disease progression. CMV-specific CD4⁺ T cells, which are less frequently infected than HIV-specific CD4⁺ T cells, are a model for such an effect. To determine the mechanism of this protection, we compared the functional response of HIV gag-specific and CMV pp65-specific CD4⁺ T cells in individuals co-infected with CMV and HIV. We found that CMV-specific CD4⁺ T cells rapidly up-regulated production of MIP-1α and MIP-1β mRNA, resulting in a rapid increase in production of MIP-1α and MIP-1β after cognate antigen stimulation. Production of β-chemokines was associated with maturational phenotype and was rarely seen in HIV-specific CD4⁺ T cells. To test whether production of β-chemokines by CD4⁺ T cells lowers their susceptibility to HIV infection, we measured cell-associated Gag DNA to assess the in vivo infection history of CMV-specific CD4⁺ T cells. We found that CMV-specific CD4⁺ T cells which produced MIP-1β contained 10 times less Gag DNA than did those which failed to produce MIP-1β. These data suggest that CD4⁺ T cells which produce MIP-1α and MIP-1β bind these chemokines in an autocrine fashion which decreases the risk of in vivo HIV infection.

HIV infection results in a significant loss of CD4⁺ T cells, particularly HIV-specific CD4⁺ T cells. In contrast to this, CMV-specific CD4⁺ T cells persist in large numbers, even in individuals with AIDS. We compared the functional profile of HIV-specific and CMV-specific CD4⁺ T cells and found that unlike HIV-specific CD4⁺ T cells, CMV-specific CD4⁺ T cells rapidly produce MIP-1β when stimulated with cognate antigen. CMV specific CD4⁺ T cells also produce another β chemokine when stimulated with cognate antigen, MIP-1α. Addition of both of these chemokines to in vitro incubations protects CD4⁺ T cells from HIV infection. To determine if the production of these two chemokines could protect the CD4⁺ T cells that produce them in vivo, we analyzed peripheral blood cells from HIV infected individuals and separated CMV-specific CD4⁺ T cells that produced MIP-1β from CMV-specific CD4⁺ T cells that did not. We found that cells that produced MIP-1β were less frequently infected with HIV than those that did not produce MIP-1β. These data, and recent advances in vaccine design, suggest that it may be possible to design a vaccine in which vaccine-induced HIV-specific CD4⁺ T cells are less susceptible to infection than those usually produced during HIV infection.

CD8dim and NKG2D expression defines related subsets of CD4+ T cells in HIV-infected patients with worse prognostic factors

CD4 T lymphocytes expressing CD8dim (DP: CD4 CD8dim) or NKG2D represent cytotoxic effector populations, which have been involved in viral infections and chronic diseases. The frequency of DP cells was analyzed by flow cytometry in 300 consecutive HIV-infected patients and 50 healthy controls. NKG2D expression and memory/effector markers in CD4 T cells were also studied, in addition to virologic and genetic factors involved in DP T-cell expansion. HIV-infected patients showed a significantly higher frequency of DP cells than controls, mainly in patients with advanced disease. Expansion of DP cells was related to NKG2D appearance in CD4 T cells and was predicted by CD4 CD28null T-cell levels. Cells expressing CD8dim and NKG2D cells are closely related populations with a similar pattern of surface markers, perforin expression, and responses to activation. We also found that these subsets seem to share an ontogenic relationship and TcR oligoclonality. In this way, cytomegalovirus infection and certain HLA alleles, such as DR7, conditioned the expansion of DP cells. Their common ontogenic origin and oligoclonality, possibly due to repeated encounters with the same antigen, could result in a limitation of the repertoire of responder cells and in a worse prognosis of HIV infection.

Interleukin-7 receptor signaling is deficient in CD4+ T cells from HIV-infected persons and is inversely associated with aging

Loss of interleukin-7 (IL-2) receptor expression has been described in T lymphocytes from persons with human immunodeficiency virus (HIV) infection, potentially contributing to perturbations in T cell homeostasis. We investigated IL-7 receptor signaling by measuring signal transducer and activator of transcription 5 (STAT5) phosphorylation in CD4+ T cell subsets from HIV-infected persons. We determined that CD45RA- memory cell subsets (both CD27+ and CD27-) displayed the most robust immediate responses to IL-7, whereas naive CD4+ T cells sustained the signal most efficiently. Memory CD4+ T cells with a terminal phenotype (CD45RA+CD27-) responded poorly to IL-7 stimulation. Defects in signaling were observed in cells from viremic HIV-infected persons and were especially pronounced in CD45RA-CD27- memory subset. Although CD127 expression was diminished for T cells from HIV-infected persons, it was not directly related to IL-7 receptor signaling function. Instead, age was inversely related to IL-7 signaling in cells from both HIV-infected viremic subjects and healthy control subjects. Thus, HIV infection results in impaired IL-7 responsiveness, especially in memory CD4+ T cells, and this defect is likely compounded by aging.

Immunodominant HIV-1 Cd4+ T cell epitopes in chronic untreated clade C HIV-1 infection

Background

A dominance of Gag-specific CD8+ T cell responses is significantly associated with a lower viral load in individuals with chronic, untreated clade C human immunodeficiency virus type 1 (HIV-1) infection. This association has not been investigated in terms of Gag-specific CD4+ T cell responses, nor have clade C HIV-1–specific CD4+ T cell epitopes, likely a vital component of an effective global HIV-1 vaccine, been identified.

Methodology/Principal Findings

Intracellular cytokine staining was conducted on 373 subjects with chronic, untreated clade C infection to assess interferon-gamma (IFN-γ) responses by CD4+ T cells to pooled Gag peptides and to determine their association with viral load and CD4 count. Gag-specific IFN-γ–producing CD4+ T cell responses were detected in 261/373 (70%) subjects, with the Gag responders having a significantly lower viral load and higher CD4 count than those with no detectable Gag response (p<0.0001 for both parameters). To identify individual peptides targeted by HIV-1–specific CD4+ T cells, separate ELISPOT screening was conducted on CD8-depleted PBMCs from 32 chronically infected untreated subjects, using pools of overlapping peptides that spanned the entire HIV-1 clade C consensus sequence, and reconfirmed by flow cytometry to be CD4+ mediated. The ELISPOT screening identified 33 CD4+ peptides targeted by 18/32 patients (56%), with 27 of the 33 peptides located in the Gag region. Although the breadth of the CD4+ responses correlated inversely with viral load (p = 0.015), the magnitude of the response was not significantly associated with viral load.

Conclusions/Significance

These data indicate that in chronic untreated clade C HIV-1 infection, IFN-γ–secreting Gag-specific CD4+ T cell responses are immunodominant, directed at multiple distinct epitopes, and associated with viral control.

Engineering a stable and selective peptide blocker of the Kv1.3 channel in T lymphocytes

Kv1.3 potassium channels maintain the membrane potential of effector memory (T(EM)) T cells that are important mediators of multiple sclerosis, type 1 diabetes mellitus, and rheumatoid arthritis. The polypeptide ShK-170 (ShK-L5), containing an N-terminal phosphotyrosine extension of the Stichodactyla helianthus ShK toxin, is a potent and selective blocker of these channels. However, a stability study of ShK-170 showed minor pH-related hydrolysis and oxidation byproducts that were exacerbated by increasing temperatures. We therefore engineered a series of analogs to minimize the formation of these byproducts. The analog with the greatest stability, ShK-192, contains a nonhydrolyzable phosphotyrosine surrogate, a methionine isostere, and a C-terminal amide. ShK-192 shows the same overall fold as ShK, and there is no evidence of any interaction between the N-terminal adduct and the rest of the peptide. The docking configuration of ShK-192 in Kv1.3 shows the N-terminal para-phosphonophenylalanine group lying at the junction of two channel monomers to form a salt bridge with Lys(411) of the channel. ShK-192 blocks Kv1.3 with an IC(50) of 140 pM and exhibits greater than 100-fold selectivity over closely related channels. After a single subcutaneous injection of 100 microg/kg, approximately 100 to 200 pM concentrations of active peptide is detectable in the blood of Lewis rats 24, 48, and 72 h after the injection. ShK-192 effectively inhibits the proliferation of T(EM) cells and suppresses delayed type hypersensitivity when administered at 10 or 100 microg/kg by subcutaneous injection once daily. ShK-192 has potential as a therapeutic for autoimmune diseases mediated by T(EM) cells.

Phenotype and function of human T lymphocyte subsets: consensus and issues

In recent years, a tremendous effort has been devoted to the detailed characterization of the phenotype and function of distinct T cell subpopulations in humans, as well as to their pathway(s) of differentiation and role in immune responses. But these studies seem to have generated more questions than definitive answers. To clarify issues related to the function and differentiation of T cell subsets, one session of the MASIR 2008 conference was dedicated to this topic. Several points of consensus and discord were highlighted in the work presented during this session. We provide here an account of these points, including the relative heterogeneity of T cell subpopulations during infections with distinct pathogens, the relationship between phenotypic and functional T cell attributes, and the pathway(s) of T cell differentiation. Finally, we discuss the problems which still limit general agreement.

Standardization and optimization of multiparameter intracellular cytokine staining

Intracellular cytokine staining (ICS) is a common method for rapid quantitation of cytokine-producing antigen-specific T cells. T cell production of IFNgamma in particular, and more recently IL-2 as well, is often taken as a measure of vaccine immunogenicity in experimental vaccine trials. As more fluorochromes become available for use in ICS and other applications detecting intracellular markers, the selection of optimal fluorochrome combinations becomes correspondingly more complicated. Additionally, as more sophisticated flow cytometers become available, more attention is being paid to potential result variability from one instrument to another. This review summarizes an oral presentation given at MASIR 2008, January 30-Feb 1, 2008, in La Plagne, France. We focus on issues associated with multiparameter (>four color) flow cytometry, including matching antibody specificities with available fluorochromes and techniques to optimize fluorochrome combinations. We examine issues specific to intracellular staining as well as broader topics such as instrument setup, experimental controls, sample management, and analysis of multiparameter data sets. Particular emphasis is placed on the use of lyophilized cells, antibodies, beads, peptides, etc. (collectively known as "lyoplates"), which can decrease experiment-to-experiment variability as well as processing time. Most clinical trials compile results from multiple testing sites, using data that was acquired on-site in each location. We present data from two different ongoing multi-laboratory standardization studies, one involving 15 laboratories and one involving nine. We identify issues of variability and, where possible, offer solutions.

Detection of polyfunctional Mycobacterium tuberculosis-specific T cells and association with viral load in HIV-1-infected persons

BACKGROUND

The human immunodeficiency virus type 1 (HIV-1) epidemic is associated with a significant increase in the incidence of tuberculosis (TB); however, little is known about the quality of Mycobacterium tuberculosis (MTB)-specific cellular immune responses in coinfected individuals.

METHODS

A total of 137 HIV-1-positive individuals in Durban, South Africa, were screened with the use of overlapping peptides spanning Ag85A, culture filtrate protein 10 (CFP-10), early secretory antigen target 6 (ESAT-6), and TB10.4, in an interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) assay. Intracellular cytokine staining for MTB-specific production of IFN-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-2 was performed, as was ex vivo phenotyping of memory markers on MTB-specific T cells.

RESULTS

A total of 41% of subjects responded to ESAT-6 and/or CFP-10, indicating the presence of latent MTB infection. The proportion of MTB-specific IFN-gamma(+)/TNF-alpha(+) CD4(+) cells was significantly higher than the proportion of IFN-gamma(+)/IL-2(+) CD4(+) cells (P = .0220), and the proportion of MTB-specific IL-2-secreting CD4 cells was inversely correlated with the HIV-1 load (P = .0098). MTB-specific CD8 T cells were predominately IFN-gamma(+)/TNF-alpha(+)/IL-2(-). Ex vivo memory phenotyping of MTB-specific CD4 and CD8 T cells indicated an early to intermediate differentiated phenotype for the population of effector memory cells.

CONCLUSIONS

Polyfunctional MTB-specific CD4 and CD8 T cell responses are maintained in the peripheral blood of HIV-1-positive individuals, in the absence of active disease, and the functional capacity of these responses is affected by HIV-1 disease status.

Multifunctional T-cell characteristics induced by a polyvalent DNA prime/protein boost human immunodeficiency virus type 1 vaccine regimen given to healthy adults are dependent on the route and dose of administration

A phase I clinical vaccine study of a human immunodeficiency virus type 1 (HIV-1) vaccine regimen comprising a DNA prime formulation (5-valent env and monovalent gag) followed by a 5-valent Env protein boost for seronegative adults was previously shown to induce HIV-1-specific T cells and anti-Env antibodies capable of neutralizing cross-clade viral isolates. In light of these initial findings, we sought to more fully characterize the HIV-1-specific T cells by using polychromatic flow cytometry. Three groups of participants were vaccinated three times with 1.2 mg of DNA administered intradermally (i.d.; group A), 1.2 mg of DNA administered intramuscularly (i.m.; group B), or 7.2 mg of DNA administered i.m. (high-dose group C) each time. Each group subsequently received one or two doses of 0.375 mg each of the gp120 protein boost vaccine (i.m.). Env-specific CD4 T-cell responses were seen in the majority of participants; however, the kinetics of responses differed depending on the route of DNA administration. The high i.m. dose induced the responses of the greatest magnitude after the DNA vaccinations, while the i.d. group exhibited the responses of the least magnitude. Nevertheless, after the second protein boost, the magnitude of CD4 T-cell responses in the i.d. group was indistinguishable from those in the other two groups. After the DNA vaccinations and the first protein boost, a greater number of polyfunctional Env-specific CD4 T cells (those with > or = 2 functions) were seen in the high-dose group than in the other groups. Gag-specific CD4 T cells and Env-specific CD8 T cells were seen only in the high-dose group. These findings demonstrate that the route and dose of DNA vaccines significantly impact the quality of immune responses, yielding important information for future vaccine design.

Cytotoxic human CD4(+) T cells

The induction of adaptive immune responses critically depends on helper signals provided by CD4(+) T cells. These signals not only license antigen presenting cells (APC) to activate naïve CD8(+) T cells leading to the formation of vast numbers of cytotoxic T lymphocytes but also support the differentiation of B cells into immunoglobulin-secreting plasma cells. Next to these helper functions, a subpopulation of CD4(+) T cells can also directly function as effector cells by executing cytotoxicity in a peptide-specific and MHC class II-restricted manner. Cytotoxic CD4(+) T cells may function in combating pathogens but additionally their presence has been associated with autoimmune disease and vascular damage. On the contrary, the induction of cytotoxic CD4(+) T cells may be a future target for vaccine strategies.

Virus-specific interleukin-17-producing CD4+ T cells are detectable in early human immunodeficiency virus type 1 infection

T(H)-17 cells have been shown to play a role in bacterial defense, acute inflammation, and autoimmunity. We examined the role of interleukin 17 (IL-17) production in human immunodeficiency virus type 1 (HIV-1) infection. Both HIV-1- and cytomegalovirus (CMV)-specific IL-17-producing CD4(+) T cells were detectable in early HIV-1 infection but were reduced to nondetectable levels in chronic and nonprogressive HIV-1 infection. IL-17-producing CMV-specific cells were not detected in blood from HIV-1-uninfected normal volunteers. Virus-specific T(H)-17 cells could coexpress other cytokines and could express CCR4 or CXCR3. Although the etiology of these cells has yet to be established, we propose that microbial translocation may induce them.

Phenotypic analysis of human CD4+ T cells specific for immediate-early 63 protein of varicella-zoster virus

Open reading frame 63 of varicella-zoster Virus (VZV) encodes an immediate early (IE) phosphoprotein (IE63) that is believed to be important for viral infectivity and establishing latency. Evidence suggests that VZV-specific T cells are crucial in the control of viral replication; however, data addressing the existence of IE63 protein-specific CD4+ T cells are limited. Using IFN-gamma immunosorbent assays, we identified high frequencies of responses to overlapping peptides spanning the IE63 protein both ex vivo and after in vitro restimulation in healthy VZV-seropositive individuals. We identified a commonly recognised epitope, restricted by HLA-DRB1*1501, which was naturally processed and presented by keratinocytes. We proceeded to investigate the frequency and phenotype of the epitope-specific CD4+ T cells using HLA class II tetrameric complexes. Epitope-specific CD4+ T cells were detectable ex vivo and showed a mixed central and effector-memory differentiation phenotype, with a significant proportion showing evidence of recent activation and rapid effector function. In summary these data implicate persistent low-level or recurrent VZV antigen exposure in healthy immune donors and are compatible with a role for IE63-specific CD4+ T cells in the control of viral reactivation.

Ex vivo analysis of human T lymphotropic virus type 1-specific CD4+ cells by use of a major histocompatibility complex class II tetramer composed of a neurological disease-susceptibility allele and its immunodominant peptide

HLA-DRB1*0101 is associated with susceptibility to human T lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Here, we used a synthetic tetramer of DRB1*0101 and its epitope peptide to analyze HTLV-1-specific CD4(+) T cells ex vivo. The frequency of tetramer(+)CD4(+) T cells was significantly greater in patients with HAM/TSP than in healthy HTLV-1 carriers (HCs) at a given proviral load and correlated with HTLV-1 tax messenger RNA expression in HCs but not in patients with HAM/TSP. These cells displayed an early to intermediate effector memory phenotype and were preferentially infected by HTLV-1. T cell receptor gene analyses of 2 unrelated DRB1*0101-positive patients with HAM/TSP showed similar Vbeta repertoires and amino acid motifs in complementarity-determining region 3. Our data suggest that efficient clonal expansion of virus-specific CD4(+) T cells in patients with HAM/TSP does not simply reflect higher viral burden but rather reflects a rapid turnover caused by preferential infection and/or in vivo stimulation by major histocompatibility complex-peptide complexes.

Sensitive gene expression profiling of human T cell subsets reveals parallel post-thymic differentiation for CD4+ and CD8+ lineages

The differentiation of CD4(+) or CD8(+) T cells following priming of naive cells is central in the establishment of the immune response against pathogens or tumors. However, our understanding of this complex process and the significance of the multiple subsets of differentiation remains controversial. Gene expression profiling has opened new directions of investigation in immunobiology. Nonetheless, the need for substantial amount of biological material often limits its application range. In this study, we have developed procedures to perform microarray analysis on amplified cDNA from low numbers of cells, including primary T lymphocytes, and applied this technology to the study of CD4 and CD8 lineage differentiation. Gene expression profiling was performed on samples of 1000 cells from 10 different subpopulations, defining the major stages of post-thymic CD4(+) or CD8(+) T cell differentiation. Surprisingly, our data revealed that while CD4(+) and CD8(+) T cell gene expression programs diverge at early stages of differentiation, they become increasingly similar as cells reach a late differentiation stage. This suggests that functional heterogeneity between Ag experienced CD4(+) and CD8(+) T cells is more likely to be located early during post-thymic differentiation, and that late stages of differentiation may represent a common end in the development of T-lymphocytes.

Association between the HLA haplotype and the TCR-Vbeta repertoire of anti-hCMV specific memory T-cells in immunocompetent healthy adults

BACKGROUND

Despite the key role of memory T-cells specific for human cytomegalovirus (hCMV) in protecting against hCMV-reinfection early after immunodeficiency episodes, the precise characterization and definition of the essential components of a protective CD4 T-cell response still remain to be established.

METHODS

We analyzed by flow cytometry hCMV-specific immune responses driven by peripheral blood antigen-presenting cells (APC) and CD4 memory T-cells at both the cellular and soluble levels, and their cooperation in priming and sustaining the effector function of specific CD8 T cells in adult healthy individuals using a hCMV whole viral lysate stimulatory model.

RESULTS

Overall, activated T-cells showed a heterogeneous phenotype, with a marked predominance of CD45RA(-)/CCR7(+/-) memory CD4(+) T-cells. Despite this, cytoplasmic expression of granzyme B was found in both the CD45RA(+)/effector and CD45RA(-)/memory T-cell compartments of the two major CD4(+) and CD8(+) activated T-cell subpopulations, further confirming the presence of circulating antigen experienced cytotoxic CD4(+) T cells in hCMV-seropositive individuals. Moreover, we observed that both CD4(+) and CD8(+) hCMV-specific T-cells included relatively restricted numbers of TCR-Vbeta family members. Interestingly, we found a significant association between some HLA Class II and Class I haplotypes and the presence of specifically expanded TCR-Vbeta clones of anti-hCMV T cells.

CONCLUSIONS

These results indicate that hCMV-specific memory T-cells are phenotypically heterogeneous, their TCR-Vbeta repertoire shaped through the interaction between hCMV epitopes and the HLA haplotype.

Loss of T cell responses following long-term cryopreservation

Although cryopreservation of peripheral blood mononuclear cells (PBMC) is a commonly used technique, the degree to which it affects subsequent functional studies has not been well defined. Here we demonstrate that long-term cryopreservation has detrimental effects on T cell IFN-gamma responses in human immunodeficiency virus (HIV) infected individuals. Long-term cryopreservation caused marked decreases in CD4(+) T cell responses to whole proteins (HIV p55 and cytomegalovirus (CMV) lysate) and HIV peptides, and more limited decreases in CD8(+) T cell responses to whole proteins. These losses were more apparent in cells stored for greater than one year compared to less than six months. CD8(+) T cell responses to peptides and peptide pools were well preserved. Loss of both CD4(+) and CD8(+) T cell responses to CMV peptide pools were minimal in HIV-negative individuals. Addition of exogenous antigen presenting cells (APC) did not restore CD4(+) T cell responses to peptide stimulation and partially restored T cell IFN-gamma responses to p55 protein. Overnight resting of thawed cells did not restore T cell IFN-gamma responses to peptide or whole protein stimulation. A selective loss of phenotypically defined effector cells did not explain the decrement of responses, although cryopreservation did increase CD4(+) T cell apoptosis, possibly contributing to the loss of responses. These data suggest that the impact of cryopreservation should be carefully considered in future vaccine and pathogenesis studies. In HIV-infected individuals short-term cryopreservation may be acceptable for measuring CD4(+) and CD8(+) T cell responses. Long-term cryopreservation, however, may lead to the loss of CD4(+) T cell responses and mild skewing of T cell phenotypic marker expression.

MHC class II tetramer guided detection of Mycobacterium tuberculosis-specific CD4+ T cells in peripheral blood from patients with pulmonary tuberculosis

Novel diagnostic tools are needed to diagnose latent infection and to provide biologically meaningful surrogate markers to define cellular immune responses against Mycobacterium tuberculosis (MTB). Interferon gamma-based assays have recently been developed in addition to the more than 100-year-old tuberculin skin test (TST) for the immune diagnosis of MTB in blood. The advent of soluble MHC/peptide tetramer molecules allows to objectively enumerate antigen-specific T cells. We identified novel MHC class II-restricted MTB epitopes and used HLA-DR4 tetrameric complexes to visualize ex vivo CD4(+) T cells directed against the antigens Ag85B and the 19-kDa lipoprotein, shared between MTB and other Mycobacterium species, and CD4(+) T cells which recognize the MTB-associated ESAT-6 antigen. MTB-reactive CD4(+) T cells reside predominantly in the CD45RA(+) CD28(+) and CD45(-) CD28(+) T-cell subset and recognize naturally processed and presented MTB epitopes. HLA-DR4-restricted, Ag85B or ESAT-6-specific CD4(+) T cells show similar dynamics over time in peripheral blood mononuclear cells (PBMC) when compared with CD8(+) T cells directed against the corresponding HLA-A2-presented MTB epitopes in patients with pulmonary MTB infection and subsequent successful therapy. This was not found to be true for T-cell responses directed against the 19-kDa lipoprotein. The dissection of the cellular immune response in M. tuberculosis infection will enable novel strategies for monitoring MTB vaccine candidates and to gauge CD4(+) T cells directed against MTB.

Memory CD4+ T-lymphocyte loss and dysfunction during primary simian immunodeficiency virus infection

It has long been appreciated that CD4+ T lymphocytes are dysfunctional in human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV)-infected individuals, and it has recently been shown that HIV/SIV infections are associated with a dramatic early destruction of memory CD4+ T lymphocytes. However, the relative contributions of CD4+ T-lymphocyte dysfunction and loss to immune dysregulation during primary HIV/SIV infection have not been fully elucidated. In the current study, we evaluated CD4+ T lymphocytes and their functional repertoire during primary SIVmac251 infection in rhesus monkeys. We show that the extent of loss of memory CD4+ T lymphocytes and staphylococcal enterotoxin B-stimulated cytokine production by total CD4+ T lymphocytes during primary SIVmac251 infection is tightly linked in a cohort of six rhesus monkeys to set point plasma viral RNA levels, with greater loss and dysfunction being associated with higher steady-state viral replication. Moreover, in exploring the mechanism underlying this phenomenon, we demonstrate that the loss of functional CD4+ T lymphocytes during primary SIVmac251 infection is associated with both a selective depletion of memory CD4+ T cells and a loss of the functional capacity of the memory CD4+ T lymphocytes that escape viral destruction.

The role of cytokines which signal through the common gamma chain cytokine receptor in the reversal of HIV specific CD4(+) and CD8(+) T cell anergy

Background

HIV specific T cells are putatively anergic in vivo. IL-2, a member of a class of cytokines that binds to receptors containing the common gamma chain (γc) has been shown to reverse anergy. We examined the role of γc cytokines in reversing HIV specific T cell anergy.

Methods

PBMC from untreated HIV-infected individuals were briefly exposed to a panel of γc cytokines, and frequencies of gag specific T cells were enumerated by intracellular IFN-γ flow cytometry.

Results

Of the γc cytokines, brief exposure to IL-2, IL-15, or combined IL-15/IL-7 significantly enhanced (range 2–7 fold) the CD4⁺ and CD8⁺ T cell IFN-γ responses to HIV gag, with IL-15 giving the greatest enhancement. The effects of cytokines were not due to enhanced proliferation of pre-existing antigen specific cells, but were due to a combination of enhanced cytokine production from antigen specific T cells plus activation of non-epitope specific T cells.

Conclusions

These observations support the notion that a significant number of HIV specific T cells are circulating in an anergic state. IL-2, IL-7 and particularly IL-15 as an immune modulator to reverse HIV-1 specific T cell anergy should be investigated, with the caveat that non-specific activation of T cells may also be induced.