Rapid whole blood analysis of virus-specific CD4 and CD8 T cell responses in persistent HIV infection

Assessment of immune functions and MRI disease activity in relapsing-remitting multiple sclerosis patients switching from natalizumab to fingolimod (ToFingo-Successor)

BACKGROUND

In light of the increased risk of progressive multifocal encephalopathy (PML) development under long-term treatment with the monoclonal antibody natalizumab which is approved for treatment of active relapsing remitting multiple sclerosis (RRMS), there is a clear need for alternative treatment options with comparable efficacy and reduced PML risk. One such option is fingolimod, a functional sphingosin-1-receptor antagonist that has been approved as first oral drug for treatment of active RRMS. However, the optimal switching design in terms of prevention of disease reoccurrence is still unknown. Moreover, potential additive effects of both drugs on immune functions, especially with regard to migration, have not yet been evaluated.

METHODS/DESIGN

This is an exploratory, open-label, monocentric, investigator-initiated clinical trial. Fifteen RRMS patients under stable treatment with natalizumab will receive one last natalizumab infusion followed by a wash-out period of 8 weeks before fingolimod treatment initiation for a period of 24 weeks. Disease activity under natalizumab and during switching will be closely monitored by assessment of relapse rate and disease severity as well as high-frequent high-resolution magnetic resonance imaging including quantitative diffusion tensor imaging. Immunological assays include longitudinal assessment of adhesion molecule expression, functional evaluation of the migratory capacity of immune cells in an in-vitro model of the blood-brain-barrier, and the quality of cellular antiviral immune responses.

DISCUSSION

Our trial represents the first detailed and longitudinal functional analysis of key immunological parameters in the process of switching from natalizumab and fingolimod, especially with regard to potential additive effects of both drugs on trafficking and immune surveillance. Moreover, our study will generate valuable information about even subtle disease exacerbations as consequence of natalizumab cessation, which will help to understand whether a switching protocol containing a wash-out period of 8 weeks before fingolimod treatment is appropriate in terms of disease stability.

Monitoring CD27 expression to evaluate Mycobacterium tuberculosis activity in HIV-1 infected individuals in vivo

The level of bacterial activity is only poorly defined during asymptomatic Mycobacterium tuberculosis (MTB) infection. The objective was to study the capacity of a new biomarker, the expression of the T cell maturation marker CD27 on MTB-specific CD4 T cells, to identify active tuberculosis (TB) disease in subjects from a MTB and HIV endemic region. The frequency and CD27 expression of circulating MTB-specific CD4 T cells was determined in 96 study participants after stimulation with purified protein derivative (PPD) using intracellular cytokine staining for IFNgamma (IFNγ). Subjects were then stratified by their TB and HIV status. Within PPD responders, a CD27⁻ phenotype was associated with active TB in HIV⁻ (p = 0.0003) and HIV⁺ (p = 0.057) subjects, respectively. In addition, loss of CD27 expression preceded development of active TB in one HIV seroconverter. Interestingly, in contrast to HIV⁻ subjects, MTB-specific CD4 T cell populations from HIV⁺ TB-asymptomatic subjects were often dominated by CD27⁻ cells. These data indicate that down-regulation of CD27 on MTB-specific CD4 T cell could be used as a biomarker of active TB, potentially preceding clinical TB disease. Furthermore, these data are consistent with the hypothesis that late, chronic HIV infection is frequently associated with increased mycobacterial activity in vivo. The analysis of T cell maturation and activation markers might thus be a useful tool to monitor TB disease progression.

Identification of human immunodeficiency virus-1 specific CD8+ and CD4+ T cell responses in perinatally-infected infants and their mothers

BACKGROUND

There are few data describing the specificity, breadth and magnitude of T cell responses to HIV-1 in infancy.

METHODS

HIV-specific CD8+ and CD4+ T cell responses to peptide pools representing Gag, Env, Pol, Nef and the regulatory regions (Reg) were simultaneously measured in 18 perinatally-infected infants and 14 of their chronically-infected mothers, using a whole blood interleukin-2 and interferon-gamma flow cytometric intracellular cytokine staining assay.

RESULTS

HIV-specific CD8+ T cell responses were detected in all the infants aged 6 weeks and older (range 0.1-6.62%) and their mothers (range 0.1-4.89%). HIV-specific CD4+ T cell responses were detected in 33% of the infants (range 0.11-0.54%) and 73% of the mothers (range 0.16-0.84). CD8+ T cell responses in the mothers were almost equally spread between the variable (Nef, Reg and Env) and conserved proteins (Gag and Pol). Conversely, CD8+ T cell responses to the more variable proteins dominated in the perinatally-infected infants comprising 74% of the total response. Interestingly, mothers and infants shared responses to at least one peptide pool, whereas only one mother-infant pair shared a peptide pool targeted by CD4+ T cells. Two in-utero-infected infants tested at birth had CD8+ T cell responses, and one of them had an Env-specific CD4 T cell response.

CONCLUSION

Our observations that HIV-specific CD8+ and CD4+ T cell responses can be detected in perinatally-infected infants from 6 weeks of age and that CD8+ T cell responses predominantly target the variable proteins have important implications for HIV vaccine design.

Host CCL3L1 gene copy number in relation to HIV-1-specific CD4+ and CD8+ T-cell responses and viral load in South African women

HIV-specific T-cell responses play an important role in control of infection. Because CCL3 has immune modulatory and antiviral activities, we hypothesized that host CCL3 genotype (CCL3L1 gene duplications) would influence the development of effective HIV-specific immune responses. Copy numbers of CCL3L1 were determined for 71 HIV-infected women, and HIV-specific CD4 and CD8 T-cell responses to overlapping peptide pools spanning the HIV-1 subtype C genome were simultaneously measured by an interferon-gamma and interleukin-2 whole-blood flow cytometric assay. Host CCL3L1 copy number correlated negatively with viral load (r=-0.239, P=0.045), as did magnitudes of Gag CD4 (r=-0.362, P=0.002) and CD8 (r=-0.261, P=0.028) T-cell responses. Patients with a Gag CD4 response (P=0.002) or dominant Gag CD8 (P=0.006) response had significantly lower viral loads than those whose dominant response targeted another region of the genome, whereas a dominant Nef-specific CD8 T-cell response was associated with higher HIV viral load. CCL3L1 copy number greater than or equal to the population median of 5 was significantly associated with increased magnitude of CD4 Gag responses (P=0.017), and women who had CD4 and CD8 Gag-specific responses had significantly lower viral loads (P=0.004) and higher CCL3L1 copy number (P=0.015) than those women with only CD8 Gag-specific responses.

Estimation of human herpesvirus 8 prevalence in high-risk patients by analysis of humoral and cellular immunity

BACKGROUND

Immunocompromized individuals, such as patients with end-stage renal disease, transplant recipients, and HIV-infected patients, are at increased risk of acquiring human herpesvirus (HHV)-8 associated infectious complications. The prevalence of HHV-8 infection generally is determined by detection of immunoglobulin G. However, because serological assays differ greatly, estimations on the actual HHV-8 prevalence vary considerably.

METHODS

HHV-8-specific cellular and humoral immunity were analyzed in 128 controls, 73 patients on dialysis, 67 transplant recipients, and 69 HIV-infected patients with the use of flow cytometry and indirect immunofluorescence microscopy.

RESULTS

A higher seroprevalence (from 13.7% to 44.9%) was confirmed for all groups of immunocompromised individuals as compared with healthy controls (3.9%). Among immunocompetent individuals, as little as 12.5% had HHV-8 reactive T-cell frequencies greater than the detection limit. In line with a higher seroprevalence in immunosuppressed patients, HHV-8-specific T cells were detectable in 30.1% of dialysis patients, 20.9% of transplant recipients, and 24.6% of HIV-infected individuals. When combining the individual presence of either HHV-8-specific antibodies or T cells or both, the prevalence of HHV-8 infection approached 15.6% in healthy individuals and 41.1%, 40.3%, and 55.1% in dialysis patients, transplant recipients, and HIV-infected individuals, respectively.

CONCLUSIONS

The exclusive serological analysis considerably underestimates the prevalence of HHV-8 infection in all study groups. Thus, the combined quantitation of both humoral and cellular immunity may instead be a superior method to assign the individual HHV-8 status. Moreover, this study suggests that the relative contributions of humoral and cellular immunity in control of HHV-8 may be different depending on the type of immunodeficiency.

Maintenance of HIV-specific central and effector memory CD4 and CD8 T cells requires antigen persistence

The HIV-specific central and effector CD4 and CD8 memory T cell populations disappear from the peripheral blood of infected individuals under highly active antiretroviral therapy (HAART) with a mean half-life of 6.0 and 7.7 months, respectively. By contrast, cytomegalovirus (CMV)-specific responses are stable or increase. The striking quantitative differences between T cell memory to two persistent viral infections are instructive as to how antigen dosage contributes to the maintenance of antigen-specific memory T cell responses in humans.

The Autographa californica nuclear polyhedrosis virus AcNPV induces functional maturation of human monocyte-derived dendritic cells

The initiation of an adaptive immune response is critically dependent on the activation of dendritic cells (DCs). Therefore, vaccination strategies targeting DCs have to ensure a proper presentation of the immunogen as well as an activation of DCs to accomplish their full maturation. Viral vectors can achieve gene delivery and a subsequent presentation of the expressed immunogen, however, the immunization efficiency may be hampered by an inhibition of DC activation. Here we report that the insect born Autographa californica nuclear polyhedrosis virus (AcNPV), which is already used for genetic immunization, is able to activate human monocyte-derived DCs. This activation induces the production of tumor necrosis factor alpha (TNF-alpha), an up-regulation of the surface molecules CD83, CD80, CD86, HLA-DR and HLA-I and increases the T cell stimulatory capacity of DCs. Thus, AcNPV represents a promising vector for vaccine trials.

Dominant ex vivo cross-stimulation of CD8+ T-cells with whole soluble gag protein in HIV-infected subjects

BACKGROUND

Soluble HIV proteins are often used to detect HIV-specific CD4+ T-helper cell responses in vitro. However, exogenous antigens can also indirectly stimulate CD8+ T-cells and thus complicate assessment of CD4+ T-cell responses.

OBJECTIVE

To analyze the extent of in vitro HIV-1 Gag p55 protein cross-stimulation to CD8+ T-cells in therapy-naive and highly active antiretroviral therapy (HAART)-treated HIV patients and to correlate this phenomenon with HIV disease progression.

METHODS

Gag protein-stimulated T-cell responses were measured in total and CD8-depleted peripheral blood mononuclear cells (PBMCs) by interferon (IFN)-gamma enzyme-linked immunosorbent spot (ELISPOT) assays in 20 therapy-naive and 60 HAART-treated HIV patients. Numbers of spot forming cells (SFCs) relative to CD4+ and CD8+ T-cell subsets were calculated. Gag protein-stimulated responses were correlated with markers of disease progression.

RESULTS

Stimulation of PBMC with HIV-1 Gag protein induced higher CD8+ T-cell responses than CD4+ T-cell responses in both therapy-naive and HAART-treated HIV patients (P < 0.001). Gag protein cross-stimulation of CD8+ T-cells was higher in therapy-naive than in HAART-treated HIV patients (P < 0.001). In HAART-treated HIV patients, we detected an inverse correlation between Gag protein cross-stimulation of CD8+ T-cells and the CD4 count (R = -0.311; P = 0.016). Depletion of CD14+ cells abrogated the responses, suggesting that Gag protein cross-stimulation of CD8+ T-cells depends on antigen processing and presentation by antigen-presenting cells (APCs).

CONCLUSIONS

HIV protein cross-presentation to CD8+ T-cells should be taken into account when detecting HIV-specific T-cell responses by stimulation of PBMCs with whole exogenous antigens.

Antigen-specific T cell responses: Determination of their frequencies, homing properties, and effector functions in human whole blood

Several prevalent and life-threatening agents enter the organism via the mucosa. In this case, a mucosal cellular immune response is essential for protection and is therefore considered the main objective of vaccination. The frequency of antigen-specific CD4+ and CD8+ T cells can be determined directly in human whole blood by a combination of surface marker and intracellular cytokine staining. Immune cells primed in the mucosal compartment also migrate through the blood and can be identified by expression of the gut-specific homing receptor alpha4beta7. Simultaneously, these lymphocytes can be functionally characterized regarding their differentiation status by analysis of CD45RO and CD27 expression and effector functions by measuring intracellular perforin or granzyme B content. Thus, the technique described in the paper is a powerful tool for clinical monitoring of the total cellular immune response to complex antigens during infection or vaccination.

CD8+ cell noncytotoxic anti-HIV response: restoration by HAART in the late stage of infection

Highly active antiretroviral therapy (HAART) is currently the best HIV infection management strategy. However, its effects on the CD8+ T cell noncytotoxic anti-HIV response (CNAR) are not well known. We investigated if HAART has different effects on CNAR in patients at the intermediate and late stages of HIV infection. Untreated healthy HIV-infected subjects with a mean CD4+ T cell count of 606 cells/microl were examined as a reference group. Plasma viral load, CD4+ T cell count, and CNAR activity were measured at baseline and regular intervals for at least 48 weeks following initiation of HAART. Baseline CNAR activity in all subjects correlated inversely with viral load and directly with CD4 T+ cell counts. The level of CNAR in the latestage group was significantly lower than in the intermediate-stage and the healthy reference group (p < 0.01). Following initiation of HAART, substantial increases in CD4+ T cell counts and decreases in viral loads were observed in both groups, indicating treatment success. CNAR activity was found to be increased significantly during HAART, but only in the late-stage group (p < 0.01). This increase in CD8+ cell function was seen within 4 weeks of treatment initiation and resulted in levels of CNAR activity almost equal to those observed in the healthy reference subjects. Our findings suggest a beneficial effect on CNAR in those individuals with reduced activity, typically in late-stage infection.

Frequency, proliferation, and activation of human memory T cells induced by a nonhuman adenovirus

Multiple human adenovirus (HAd) infections during childhood generate a memory T-cell (T(M)) response, which is the primary defense against HAd-induced morbidity. This cellular memory creates a conundrum for the potential clinical use of HAd-derived vectors: vector-mediated gene transfer is efficient in immunologically naïve mammals but will be compromised by memory immunity when using vectors derived from ubiquitous human pathogens. The potential lack of cellular and humoral memory is one reason we developed vectors from canine adenovirus serotype 2 (CAV-2). Here, we assayed human peripheral blood mononuclear cells for a T(M) response that could be stimulated by CAV-2 virion and individual capsid proteins. We found that less than half of the donors harbored a proliferating T(M) response directed against the CAV-2 virion (versus >85% against HAd5) in spite of a conserved antigenic Adenoviridae epitope in the CAV-2 hexon. When CAV-2 induced proliferation, it was 2.3- to >10-fold lower than HAd5 depending on the assay. The primary proliferating cells appeared to be memory (CD45RO+) CD4+ lymphocytes, differentiated into Th1 gamma interferon-producing cells, with a frequency that was up to 66-fold lower than that obtained for HAd5. We also compared CAV-2 to prototype HAd from five of the six human species and found that CAV-2-induced cellular proliferation was similar to that found with rare HAd serotypes. Individual CAV-2 capsid proteins also induced less proliferation than their HAd5 homologues. Our data suggest that CAV-2 vectors may be safer (i.e., less immunogenic) for gene transfer but are not without a theoretical risk in a subset of potential patients.

Recombinant HIV-1 Pr55gag virus-like particles: potent stimulators of innate and acquired immune responses

Several previous reports have clearly demonstrated the strong effectiveness of human immunodeficiency virus (HIV) Gag polyprotein-based virus-like particles (VLP) to stimulate humoral and cellular immune responses in complete absence of additional adjuvants. Yet, the mechanisms underlying the strong immunogenicity of these particulate antigens are still not very clear. However, current reports strongly indicate that these VLP act as "danger signals" to trigger the innate immune system and possess potent adjuvant activity to enhance the immunogenicity of per se only weakly immunogenic peptides and proteins. Here, we review the current understanding of how various particle-associated substances and other impurities may contribute to the observed immune-activating properties of these complex immunogens.

Gut-homing (alpha(4)beta(7)(+)) Th1 memory responses after inactivated poliovirus immunization in poliovirus orally pre-immunized donors

Mucosal infections are prevented by a specialized local immune system. Immune cells of this compartment can also be found in the blood and are characterized by the expression of mucosa-specific homing molecules. Here, the cellular immune responses after inactivated poliovirus immunization (IPV) in poliovirus orally pre-immunized donors were investigated. Subcutaneous IPV induced a transient increase in the proliferative response against poliovirus antigen and in the number of poliovirus-specific CD4(+) T cells in the blood of the vaccinees. These cells were characterized to be of the effector memory type (CD45RA(-)/CD45RO(+)/CCR7(-)/CD27(+)) and expressed the homing molecule alpha(4)beta(7), indicating their origin from the gut. Together these data show the recurrence of gut-derived poliovirus-specific cells upon IPV and evaluate the whole-blood assay as a powerful tool for monitoring the success of a vaccination.

Tuberculin skin testing underestimates a high prevalence of latent tuberculosis infection in hemodialysis patients

BACKGROUND

Identification of latent Mycobacterium tuberculosis infection in hemodialysis patients is hampered by reduced sensitivity of the established tuberculin skin test. We investigated whether in vitro quantitation of purified protein derivative (PPD)-specific T cells using a rapid 6-hour assay may represent an alternative approach for detecting latent infection.

METHODS

One hundred and twenty-seven hemodialysis patients and 218 control patients (blood donors, health care workers, and control patients) were analyzed. Specific T cells toward PPD and early secretory antigenic target-6 (ESAT-6), a protein expressed in Mycobacterium tuberculosis but absent from M. bovis bacillus Calmette-Guerin (BCG) vaccine strains, were flow cytometrically quantified from whole blood, and results were compared with skin testing.

RESULTS

Compared to blood donors, a high proportion of both health care workers (48.6%) and hemodialysis patients (53.5%) had PPD-specific Th1-type CD4 T-cell reactivity with similar median frequencies of PPD-specific T cells (0.17%; 0.06-3.75% vs. 0.26%; 0.06-4.12%, respectively). In contrast, skin test reactivity was significantly reduced in hemodialysis patients. Whereas 85.7% of control patients with PPD reactivity in vitro were skin test-positive, the respective percentage among hemodialysis patients was 51.4% (P= 0.007). Among individuals with PPD reactivity in vitro, approximately 50% had T cells specific for ESAT-6.

CONCLUSION

Unlike the skin test, measurement of PPD reactivity by in vitro quantitation of PPD-specific T cells was unaffected by uremia-associated immunosuppression. This whole-blood assay may thus be a valuable alternative to skin testing, and detection of ESAT-6-specific T cells could moreover allow distinction of latent M. tuberculosis infection from BCG-induced reactivity to PPD. The assay is well suited for clinical use and may facilitate targeting of preventative therapy in high-risk individuals.

Extensive MHC class I-restricted CD8 T lymphocyte responses against various yeast genera in humans

The human cellular immune response against 14 distantly related yeast species was analyzed by intracellular cytokine staining of lymphocytes after ex vivo stimulation of whole blood. While the CD4 T cell response was marginal, extensive MHC class I-restricted CD8 T cell responses were detected against a number of species including spoiling, environmental and human pathogenic yeasts. The yeast-specific CD8 T cells expressed interferon-gamma but lacked expression of CD27 and CCR7, indicating that they were end-differentiated effector memory cells. Mainly intact yeast cells rather than spheroplasts were able to induce cytokine expression in T cells demonstrating that the dominant immunogens were located in the yeast cell wall. Together these data underline the importance of the cellular immune response in protecting humans against yeast and fungal infections. And, from another perspective, recombinant yeast suggests itself as a potential vaccine candidate to efficiently induce antigen-specific CD8 T cell responses.

Dissociation of CD4+ cell counts from viral load and association with immune complexes in HIV+ hemophilia patients

OBJECTIVE

We have postulated that the host autoimmune response regulates and mediates CD4 depletion during HIV infection by opsonization of circulating CD4(+) lymphocytes carrying autoreactive immune complexes (IC) consisting of complement-fixing IgM and IgG, and during advanced stages of HIV disease of IgM/ IgG/gp120 complexes. In this retrospective study, we investigated whether HIV causes CD4 depletion by direct cytotoxicity or indirectly by induction of a host autoimmune response.

PATIENTS AND METHODS

In 1996, 12 HIV(+) hemophilia patients were converted to highly active antiretroviral therapy (HAART), while 10 other patients were maintained on conventional antiretroviral treatment and another 11 patients refused to be treated with antiretroviral drugs. The host immune response of these 33 HIV(+) patients was studied during the periods of minimum viral replication (Interval 1), subsequent rise in viral replication with strong replication dynamic (Interval 2), and maximum viral replication (Interval 3). The patients were categorized into three groups according to viral load (VL). Group A: patients with low level VL (n=10) showed a modest increase from <80 to <4 log 10 HIV-1 RNA copies per milliliter plasma during the observation period; Group B: patients with medium level VL (n=12) showed a stronger increase from <80 to >4 log 10 copies per milliliter plasma; and Group C: patients with high level VL (n=11) consistently had a median of >4 log 10 copies per milliliter plasma, during Intervals 1-3, with the exception of one patient who during Interval 2 had 4800 copies per milliliter. Blood lymphocyte subpopulations, proportions of CD4(+) blood lymphocytes coated with IgM, IgG, C3d and/or gp120, in vitro responses to mitogens and pooled allogeneic stimulator cells, as well as numbers of HIV-1 RNA copies per milliliter plasma were measured.

RESULTS

Sequential analysis of VL, IC load on CD4(+) blood lymphocytes and CD4 counts showed that an increasing VL was not associated with CD4 depletion, when the proportion of IC-coated circulating CD4(+) blood lymphocytes remained stable. When, CD4 counts and IC load were analyzed during corresponding intervals of retroviral replication in the three patient groups, a higher VL was associated with lower CD4 counts only when the IC load (IgG or gp120/IgG) on CD4(+) lymphocytes was higher as well.

CONCLUSION

These data suggest that HIV regulates and mediates CD4 depletion in part by the induction of autoreactive ICs against CD4(+) lymphocytes, especially complement-fixing autoreactive IgG and gp120/IgG complexes.

Specific activation of CMV-primed human T lymphocytes by cytomegalovirus pp65 expressed in fission yeast

Threatening virus infections constantly illustrate the growing need for novel vaccines that specifically induce efficient T cell-mediated immune responses. In this study, we used a human whole blood assay to determine the activation of antigen-specific human T lymphocytes by a viral antigen of human cytomegalovirus (HCMV). The major HCMV tegument protein pp65, recombinantly expressed in fission yeast (Schizosaccharomyces pombe), specifically activated antigen-specific CD4- and CD8-positive memory T cells in blood of HCMV seropositive donors. Moreover, the immune response against recombinant pp65, in particular that of CD8 class I major histocompatibility complex-restricted cytotoxic T cells, was similar to the response against the intact HCMV. Since fission yeast cells per se did not activate a significant number of human T lymphocytes ex vivo, the system described here might represent a novel approach in vaccine development as well as in the identification of vaccine candidates directly from human whole blood.

Immunity to human immunodeficiency virus (HIV) in children with chronic HIV infection receiving highly active antiretroviral therapy

Our objective was to describe the CD4-mediated human immunodeficiency virus (HIV)-specific cell-mediated immunity (CMI) and its virologic and immunologic correlates in children with chronic HIV infection on highly active antiretroviral therapy (HAART). Twelve HIV-infected children on stable antiretroviral therapy with a median level of CD4+ lymphocytes (CD4%) of 25.5% and a median viral load (VL) of 786 HIV RNA copies/ml were enrolled in this study. Nine of these children were also cytomegalovirus (CMV) seropositive. Blood mononuclear cells, stimulated with HIV and CMV antigens, were used to measure lymphocyte proliferation and to enumerate gamma interferon (IFN-gamma)-producing CD4+ cells. HIV CMI and CMV CMI were detected in similar proportions of patients and correlated with each other, although the HIV responses were less robust. HIV lymphocyte proliferation significantly increased with lower HIV VL and showed a trend to increase with higher CD4% and longer time on HAART. The in vitro IFN-gamma response to HIV or CMV was not affected by CD4%, VL, or HAART. Pediatric patients with established HIV infection on HAART frequently exhibit HIV CMI despite undetectable HIV replication. We concluded that the association between HIV CMI and CMV CMI indicates that the same factors govern responsiveness to either antigen.

Frequencies of ex vivo-activated human immunodeficiency virus type 1-specific gamma-interferon-producing CD8+ T cells in infected children correlate positively with plasma viral load

HIV-specific CD8+ T cells are critical in controlling human immunodeficiency virus (HIV) replication. We present the evaluation of a gamma-interferon (IFN-gamma)-based enzyme linked immunospot (ELISPOT) assay for the quantification of HIV-specific CD8+ T cells from HIV-infected children. We studied 20 HLA-A*0201-positive HIV-infected children. The IFN-gamma production in response to stimulation with two HLA-A*0201-restricted immunodominant CD8 epitopes (SLYNTVATL [SL9] in Gag and ILKEPVHGV [IV9] in Pol) was tested using the ELISPOT assay. The results were compared to labeling with the corresponding tetramers. Among the 20 children, 18 had detectable responses against the SL9 and/or the IV9 epitope using the ELISPOT assay (medians, 351 and 134 spot-forming cells/10(6) peripheral blood mononuclear cells, respectively). Comparison of results from the tetramer and ELISPOT assays suggests that only a fraction of HIV-specific CD8+ T cells were able to produce IFN-gamma. Most importantly, we found that the frequencies of IFN-gamma-producing CD8+ T cells were positively correlated with the viral load whereas the frequencies of tetramer-binding CD8+ T cells were not. The high sensitivity of the ELISPOT assay and the fact that this functional assay provided information different from that of tetramer labeling support its use for measurement of HIV-specific CD8+ T cells. In conclusion, our results show that the ex vivo-activated IFN-gamma-producing HIV-specific CD8+ T-cell subset is dependent upon continuous antigenic stimulation.

Dominance of virus-specific CD8 T cells in human primary cytomegalovirus infection

Cellular immune responses are of high importance in initiating and maintaining immunity against virus infections. Whereas the cellular immune response during persistent cytomegalovirus (CMV) infection is well assessable, the individual contribution of CD4 and CD8 T cell responses during primary infection has not been described. A novel whole-blood assay, which relies on the flow-cytometric detection of antigen-induced cytokine expression, was used to characterize CMV-specific CD4 and CD8 T cell responses during primary infection of CMV seronegative recipients of a renal allograft from a CMV seropositive donor. These T cell responses were compared with long-term CMV-positive patients with known history of transplantation-related seroconversion. Results were further correlated to CMV load and serum IgG and IgM. The long-term seroconverted patients consistently showed a dominant CMV-specific CD4 T cell response (median frequencies: CD4, 1.12% [range, 0.35 to 8.10%] versus CD8 0.13% [range, <0.05 to 0.55%]). In contrast, during primary infection, the cellular immune response is strongly dominated by CMV-specific CD8 T cells (median peak frequencies: CD4, 1.24% [range, 0.21 to 1.60%] versus CD8, 2.47% [range, 1.34 to 6.67%]). Upon receipt of ganciclovir, viral load as well as CMV-specific CD8 responses decreased. The frequency of the respective CD4 T cells fluctuated during decrease of CMV load and became dominant over CMV-specific CD8 T cell responses. These results are consistent with the view of an effective direct antiviral activity of CD8 T cells, which is most critical during periods of high viremia. Later on during persistent infection, CD4 T cells dominate the immune response to support the state of antiviral immunity.

The fraction of perforin-expressing HIV-specific CD8 T cells is a marker for disease progression in HIV infection

OBJECTIVE

Perforin is an important component of the death machinery of cytotoxic T cells (CTL). To evaluate functional differences between HIV- and cytomegalovirus (CMV)-specific CTL of coinfected patients, the frequencies of the respective perforin-expressing T cells were analysed in a rapid whole blood assay.

METHODS

Whole blood of HIV- and CMV-infected individuals was specifically stimulated by HIV-1 Pr55(gag) or complete CMV antigen, and activation-induced intracellular cytokine and perforin expression in CD8 T cells was analysed by flow cytometry.

RESULTS

Perforin-expressing HIV-1- and CMV-specific CD8 T cells can be quantified simultaneously. Within a patient, the frequency of such HIV-specific CD8 T cells in peripheral blood was lower than the frequency of the respective CMV-specific cells. The number of the perforin-expressing HIV-specific CD8 T cells inversely correlated with the peripheral blood CD4 T cell count.

CONCLUSIONS

The differential fractions of perforin-expressing virus-specific CD8 T cells in HIV and CMV double infection might be caused by differences in priming and trafficking to or from replication sites. However, without knowing the underlying mechanism, the fraction of perforin-expressing HIV-specific CD8 T cells provides another surrogate marker for disease progression.

Sustained high frequencies of specific CD4 T cells restricted to a single persistent virus

Replication of cytomegalovirus (CMV) is largely controlled by the cellular arm of the immune response. In this study the CMV-specific CD4 T-cell response was characterized in a cohort of apparently healthy individuals. In 11% of all individuals, extremely high frequencies, between 10 and 40%, were found. High-level frequencies of CMV-specific CD4 T cells persisted over several months and were not the result of an acute infection. Specific T cells were oligoclonal and were phenotypically and functionally characterized as mature effector cells, with both cytokine-secreting and proliferative potential. These high-level frequencies do not seem to compromise the immune response towards heterologous infections, and no signs of immunopathology were observed. Whereas a large temporary expansion of virus-specific T cells is well known to occur during acute infection, we now show that extremely high frequencies of virus-specific T cells may continuously exist in chronic CMV infection without overtly compromising the remaining protective immunity.