Human immunodeficiency virus-infected patients receiving highly active antiretroviral therapy maintain activated CD8+ T cell subsets as a strong adaptive immune response to cytomegalovirus

HIV-Specific CD8(+) T Lymphocytes in Blood of Long-Term HIV-Infected Hemophilia Patients

Hemophilia patients infected with human immunodeficiency virus (HIV) 30 years ago show increased proportions of activated CD8⁺DR⁺ blood lymphocytes. We hypothesized that this might indicate a cellular immune response directed against HIV and might be the reason for long-term clinical stability of these patients. CD8⁺ peripheral blood lymphocytes (PBL) reactive with six HIV and two cytomegalovirus (CMV) pentamers were determined in heparinized whole blood. Additional lymphocyte subsets as well as plasma cytokines and HIV-1 load were studied. Long-term HIV-infected hemophilia patients with (n=15) or without (n=33) currently detectable HIV-1 load in the plasma showed higher proportions of CD8⁺ lymphocytes reactive with HIV (p<0.001) and CMV pentamers (p=0.010) than healthy individuals. The cellular anti-HIV response tended to be stronger and more polyclonal in patients during periods of viral replication than in patients with retroviral quiescence (p=0.077). Anti-HIV CD8⁺ lymphocyte responses were strongest in patients with high counts of activated CD8⁺DR⁺ T (r=0.353; p=0.014) and low CD19⁺ B lymphocyte counts (r=−0.472; p=0.001). Patients with or without HIV-1 viral load showed normal Th1 and Th2 plasma cytokine levels and high plasma interleukin-6 (versus healthy controls, p=0.001) and tumor necrosis factor-α (p=0.020). Hemophilia patients who have been living with HIV for more than 30 years showed a polyclonal CD8⁺ T-cell response against HIV and CMV. This cellular antiviral immune response was strongest during periods of HIV-1 replication and remained detectable during periods of HIV-1 quiescence. We hypothesize that the consistent cellular anti-HIV-1 response in combination with highly active antiretroviral therapy ensures stability and survival of these chronically HIV-1–infected hemophilia patients.

HIV RNA suppression and immune restoration: can we do better?

HAART has significantly changed the natural history of HIV infection: patients receiving antiretrovirals are usually able to control viremia, even though not all virological responders adequately recover their CD4+ count. The reasons for poor immune restoration are only partially known and they include genetic, demographic and immunologic factors. A crucial element affecting immune recovery is immune activation, related to residual viremia; indeed, a suboptimal virological control (i.e., low levels of plasma HIV RNA) has been related with higher levels of chronic inflammation and all-cause mortality. The sources of residual viremia are not yet completely known, even though the most important one is represented by latently infected cells. Several methods, including 2-LTR HIV DNA and unspliced HIV RNA measurement, have been developed to estimate residual viremia and predict the outcome of antiretroviral therapy. Considering that poor immunologic responders are exposed to a higher risk of both AIDS-related and non-AIDS-related diseases, there is a need of new therapeutic strategies, including immunomodulators and drugs targeting the latent viral reservoirs, in order to face residual viremia but also to “drive” the host immunologic responses.

Immune reconstitution under antiretroviral therapy: the new challenge in HIV-1 infection

Although highly active antiretroviral therapy has enabled constant progress in reducing HIV-1 replication, in some patients who are "aviremic" during treatment, the problem of insufficient immune restoration remains, and this exposes them to the risk of immune deficiency-associated pathologies. Various mechanisms may combine and account for this impaired immunologic response to treatment. A first possible mechanism is immune activation, which may be because of residual HIV production, microbial translocation, co-infections, immunosenescence, or lymphopenia per se. A second mechanism is ongoing HIV replication. Finally, deficient thymus output, sex, and genetic polymorphism influencing apoptosis may impair immune reconstitution. In this review we will discuss the tools at our disposal to identify the various mechanisms at work in a given patient and the specific therapeutic strategies we could propose based on this etiologic diagnosis.

Control of human cytomegalovirus infection in patients infected with human immunodeficiency virus by high levels of specific CD8+ T-cells

A new technique was used to simultaneously determine human cytomegalovirus (HCMV)-specific CD4(+) and CD8(+) T-cells in highly active anti-retroviral therapy (HAART)-naive and HAART-treated patients infected with human immunodeficiency virus (HIV). HIV-infected patients with HCMV infection, but without HCMV disease, showed low numbers of HCMV-specific CD4(+) cells and high numbers of CD8(+) T-cells, both before and during HAART. HIV-infected patients with HCMV disease had no HCMV-specific CD4(+) T-cells and extremely low levels of CD8(+) T-cells. Resolution of disease during HAART was associated with rescue of specific CD4(+) T-cells and a large increase in the specific CD8(+) T-cell count. Thus, HAART does not completely restore the normal immune function. In HIV-infected patients, sustained control of HCMV infection requires high frequencies of specific CD8(+) T-cells.

Regulatory T cells generated during cytomegalovirus in vitro stimulation of mononuclear cells from HIV-infected individuals on HAART correlate with decreased lymphocyte proliferation

HIV-infected patients fail to fully recover cell-mediated immunity despite HAART. To identify regulatory factors, we studied the phenotype and function of in vitro cytomegalovirus (CMV)-stimulated T cells from HAART recipients. CFSE-measured proliferation showed CD4+ and CD8+ cells dividing in CMV-stimulated cultures. Compared with healthy controls, CMV-stimulated lymphocytes from HAART recipients had lower 3H-thymidine incorporation; lower IFNgamma and TNFalpha production; higher CD4+ CD27- CD28- and CD8+ CD27- CD28- frequencies; lower CD4+ CD25hi; and higher FoxP3 expression in CD8+ CD25hi cells. CMV-specific proliferation correlated with higher IFNgamma, TNFalpha and IL10 levels and higher CD4+ perforin+ and CD8+ perforin+ frequencies. Decreased proliferation correlated with higher CD4+ CD27- CD28- frequencies and TGFbeta1 production, which also correlated with each other. Anti-TGFbeta1 neutralizing antibodies restored CMV-specific proliferation in a dose-dependent fashion. In HIV-infected subjects, decreased proliferation correlated with higher CMV-stimulated CD8+ CD25hi frequencies and their FoxP3 expression. These data indicate that FoxP3- and TGFbeta1-expressing regulatory T cells contribute to decreased immunity in HAART recipients.

In vitro expansion of polyclonal T-cell subsets for adoptive immunotherapy by recombinant modified vaccinia Ankara

OBJECTIVE

Adoptive cellular therapy of cytomegalovirus (CMV)-specific T cells in allogeneic hematopoietic stem cell transplantation (HSCT) patients is a promising approach for controlling CMV viremia and its morbidity. We sought to develop a clinically suitable strategy to dually expand infusible CD8(+) and CD4(+) T-cell subsets specific for CMV.

METHODS

Polyclonal CMV T-cell lines were generated using peripheral blood mononuclear cell (PBMCs) treated with synthetic single-stranded CpG motif-containing oligodeoxynucleotides (ODNs) and infected with recombinant (r) modified vaccinia Ankara (MVA) expressing CMV antigens. Cultures derived from 12 healthy CMV-positive donors were analyzed using chromium release and lymphoproliferation assays, intracellular staining for interferon-gamma (IFN-gamma), and HLA tetramers.

RESULTS

A 3-day incubation with a combination of ODN 2006 and 2216 was found to reproducibly generate a highly rMVA infectable population of PBMCs with concomitant high expression of CMV antigens. CpG ODN-treated autologous PBMCs infected with rMVA elicited a 30-fold average expansion of both CMV-specific CD4(+) and CD8(+) T cells in 10 days. The enriched T-cell populations showed minimal alloreactivity, high levels of CMV-specific HLA class I tetramer binding, cytotoxic activity, and IFN-gamma production from both CD8(+) and CD4(+) T cells.

CONCLUSIONS

The ability to quickly produce autologous professional antigen-presenting cells, capable of stimulating clinically useful amounts of CMV-specific CD4(+) and CD8(+) T-cell lines, enhances the attractiveness of using rMVA for immunotherapeutic interventions to manage HSCT-related CMV disease.

Cytomegalovirus immune reconstitution occurs in recipients of allogeneic hematopoietic cell transplants irrespective of detectable cytomegalovirus infection

The question of when immune reconstitution of cytomegalovirus (CMV)-specific CD8 T cells occurs after hematopoietic cell transplantation and, more specifically, to which CMV targets this immunity is likely to be directed remains poorly understood. The dependence of immune reconstitution on CMV reactivation is even less clear. To better understand these events, 44 CMV-seropositive HLA-A*0201 subjects were followed up at approximately days 40, 90, 120, 150, 180, and 360 after hematopoietic cell transplantation for CMV immunity as measured by 2 types of assays: (1) an HLA-A*0201 tetramer-binding assay for both CMV pp65 (pp65) and immediate-early 1 (IE-1) or (2) intracellular cytokine interferon gamma responses induced by pp65 or IE-1-derived peptides. To verify the reliability of IE-1-specific assays relative to the pp65-based assays, a pilot study first compared the development of IE-1-specific immunity in a subgroup by using multiple HLA-A*0201-restricted peptides, and then these recipients were followed up for 1 year for immunologic function and for CMV infection. The IE-1-specific response occurred to each of the 3 HLA-A*0201-restricted peptides studied (IE-1-256, -297, and -316), and there was no predominant IE peptide response. However, the immunodominant HLA-A*0201-restricted pp65 peptide was recognized significantly more frequently than these IE-1 peptides. When this was compared with the occurrence of CMV infection, the overall immune reactivity, as measured by the mean or median number of CD8+ T cells reactive to either pp65 or IE-1 peptides by intracellular cytokine or tetramer binding assay, was not significantly different in those with and without CMV infection. For patients who demonstrated reconstituted immunity to CMV at 1 year, all were reconstituted by 6 months, and the timing of the first observed immune reactivity to either of the pp65 or the IE peptides was not different in those with and without detectable CMV infection.

Reduced type 1 and type 2 cytokines in antiviral memory T helper function among women coinfected with HIV and HCV

Bias in cytokine responses has been proposed as a contributing mechanism to pathogenesis in persistent HIV or hepatitis C virus (HCV) infections. We investigated whether coinfection with HCV modifies the profile of antigen-specific cytokine secretion in women persistently infected with HIV compared to women with single HIV or HCV infection. The T helper response to HIV, HCV and cytomegalovirus (CMV) as a positive viral control was dominated by type 1 cytokines (interleukin- [IL] 2, interferon- [IFN] gamma and tumor necrosis factor- [TNF] alpha), with IFN-gamma as the most abundantly secreted. IL-4, IL-5 and IL-10 were low in healthy controls and patients. Robust CMV-specific responses contrasted with curtailed HCV-specific responses in HCV-infected women. The overall anti-viral profile was dominated by Th1 cytokines even in coinfected women but both type 1 and type 2 responses were reduced in HIV-infected women and more extensively in women with HCV/HIV coinfection.

Assessment of cellular immunity to human cytomegalovirus in recipients of allogeneic stem cell transplants

Effective reconstitution of cellular immunity following hematopoietic stem cell transplantation (HCT) is thought to be important for protection from the morbidity caused by cytomegalovirus (CMV) reactivation and disease. This review critically discusses current methods for assessment of CMV-specific cellular immune responses, with emphasis on flow cytometry-based methodologies such as MHC-I and MHC-II tetramer staining and intracellular cytokine assays. The advantages and weaknesses of these assays are considered in comparison to traditional immunologic techniques. Application of these newer methodologies has provided insight into the dynamics of the levels of CMV-specific CD4(+) and CD8(+) T-lymphocytes following HCT, and into the sources and diversity of these cells. Data from preliminary clinical studies suggest that CMV-specific CD8(+) T-lymphocyte levels greater than 1 x 10(7)/L of peripheral blood may correlate with protection from CMV disease. Studies on the functional phenotypes of CMV-specific CD8(+) T-lymphocytes such as cytokine production, degranulation, and cytotoxicity have indicated that these cells are heterogeneous with regard to these properties. Future research will focus on establishing whether any of these immunologic assays will serve as a correlate of protection and inform as to which patients are at high risk for CMV reactivation and disease. Identification of an informative assay may allow its incorporation into standard clinical practice for monitoring HCT patients.

Assessment of human cytomegalovirus specific T cell immunity in human immunodeficiency virus infected patients in different disease stages following HAART and in long-term non-progressors

T cell immunity to human cytomegalovirus (HCMV) was assessed in HAART-treated HIV-1 infected patients (9 asymptomatic, CDC group A; and 22 symptomatic, CDC group B), and in eight HIV-1 long term non-progressors. Patients were either prospectively or cross-sectionally examined for CD4(+) T cell counts, HIV RNA load, HCMV leukoDNAemia, HCMV DNA in urine, lymphoproliferative response (LPR) to HCMV and phytohemagglutinin (PHA), and cytokine secretion (IFN-gamma and IL-4) by HCMV-stimulated peripheral blood mononuclear cell (PBMC) cultures. No patient either progressed to clinical AIDS or developed HCMV active infection during the study period. Twenty-nine patients responded to HAART, though 12 patients failed to recover the LPR to HCMV over the study period (three from CDC group A and nine from CDC group B). In contrast to healthy control individuals, most patients displaying positive LPRs LPRs to HCMV had unstable responses. Sustained LPRs to HCMV were significantly associated with high pre-HAART nadir CD4(+) T cell counts. Long-term suppression of HIV viremia correlated with recovery of LPR to HCMV. Sequential PBMC cultures from most patients secreted IFN-gamma (but not IL-4) at normal levels upon HCMV stimulation, irrespective of the pre-HAART nadir CD4(+) T cell counts and CDC group to which patients belonged. Failure to reconstitute IFN-gamma response was associated with very low pre-HAART nadir CD4(+) T cell counts. Control of HCMV infection in the cohort was associated with either recovery or maintenance of IFN-gamma response rather than with reconstitution of LPR to HCMV. A LPR to HCMV was absent in three out of eight long term non-progressors; contrarily, all patients showed preserved IFN-gamma responses.

Cytomegalovirus infection in the era of HAART: fewer reactivations and more immunity

The incidence of cytomegalovirus (CMV) disease, once the most common and highly feared viral complication of AIDS, has dramatically decreased with the advent of highly active antiretroviral therapy (HAART). HAART-associated changes in the epidemiology of CMV disease resulted from the increase in CMV-specific immune responses coupled with the decrease in CMV reactivation. However, CMV disease continues to afflict HIV-infected patients on HAART when CD4+ cell counts fail to rise above 100 cells/mm(3) and when reconstitution of normal CMV-specific immune responses does not occur. The latter scenario may lead to recurrent or de novo CMV end-organ disease, or to the recently described CMV immune recovery vitritis. HAART-associated immune reconstitution offers unique opportunities to investigate the virological and immunological correlates of protection against CMV disease. Although the full extent of CMV-specific immune reconstitution has not been defined thus far, CMV-specific interferon-gamma production has been shown to be significantly associated with protection against CMV reactivation and recurrent disease.

Retinal and extraocular cytomegalovirus end-organ disease in HIV-infected patients in Europe: a EuroSIDA study, 1994-2001

This multicentre prospective cohort study by the EuroSIDA study group was designed to determine the factors affecting the incidence of cytomegalovirus (CMV) end-organ disease (CMVD) and the rate of survival after diagnosis in patients with AIDS during the years 1994-2001. This period includes two eras, the pre-HAART era and the HAART era, because HAART affects the natural history of HIV infection, especially with respect to opportunistic infections, including CMV infection. Clinical and laboratory data were collected from the charts of 8,556 patients in 63 AIDS clinics in Europe. A total of 707 patients had CMVD at recruitment and at follow-up: 449 with retinitis (CMVR), 190 with extraocular CMV disease (EOCMVD), and 58 with both. Of the cases of EOCMVD, 66% involved the gastrointestinal tract and 17% the central nervous system. Of patients with a CD4+ count of < or =200 mm(-3) initially, 1.8% on HAART developed CMVD within a 24-month period, as compared to 11.1% on dual therapy and 14.3% without treatment (P<0.0001). There were highly significant differences in survival according to the calendar year (P<0.0001), with mortality declining from 79% during the years 1994-1995 to 42% in 2000-2001. The incidence of death after any CMVD was 28.4 per 100 patient-years of follow-up. Median survival of CMVR patients and EOCMVD patients was 11 and 7 months, respectively, the prognosis being better among patients with gastrointestinal rather than neurological CMVD. The initiation of HAART was associated with a 37% decrease in mortality (P<0.05). Eighteen percent of all deaths were caused by EOCMVD itself. This study describes a decline in the incidence and mortality of CMVR and EOCMVD during the HAART era of the HIV epidemic. It furthermore serves as a reminder of the importance of EOCMVD as a cause of morbidity and mortality in AIDS in the pre-HAART era.

Attenuated poxviruses generate clinically relevant frequencies of CMV-specific T cells

Immunotherapeutic approaches to limit cytomegalovirus (CMV) morbidity and mortality after hematopoietic stem cell transplants (HSCTs) are currently under investigation as alternatives to antiviral drugs. In this context, we have inserted full-length and ubiquitin-modified CMV phosphoprotein 65 (pp65), phosphoprotein 150 (pp150), and immediate early protein 1 (IE1) immunodominant antigens into the virulent Western Reserve strain of vaccinia virus (VV) and the highly attenuated strain, modified vaccinia Ankara (MVA). Recombinant (r) VV or rMVA stimulated vigorous expansion of CMV-specific CD8+ T cells in CMV-positive donor peripheral blood mononuclear cells (PBMCs), which showed minimal alloreactivity and high levels of HLA tetramer binding, cytokine production, and cytotoxicity. Ubiquitinated antigens had a profound effect when expressed in VV. Single antigen rMVA expressing pp65 or IE1, either ubiquitin-modified or native, stimulated both cytotoxic T lymphocyte (CTL) populations to be expanded up to 500-fold in a 60-mL blood draw from the same donor. This result demonstrates the clinical feasibility of simultaneously amplifying multiple CMV-CTL populations. Transgenic HLA A2.1 (HHD II) mice, immunized with the same rMVA as used with human PBMCs, produced a robust cytotoxic response to both CMV pp65 and IE1. The specificity of the vigorous immunologic response to rMVA, both in vitro and in vivo, makes them candidates for clinical evaluation in the context of adoptive immunotherapy for hematopoietic stem cell transplant (HSCT) recipients or donor vaccination.

Posterior segment manifestations of HIV/AIDS

The ocular posterior segment manifestations of AIDS may be divided into four categories: retinal vasculopathy, unusual malignancies, neuro-ophthalmologic abnormalities, and opportunistic infections. Microvasculopathy is the most common manifestation. Opportunistic infections, particularly cytomegalovirus retinitis and progressive outer retinal necrosis, are the most likely to result in visual loss due to infection or subsequent retinal detachment. Diagnosis and treatment are guided by the particular conditions and immune status of the patient.

Immunization with Th-CTL fusion peptide and cytosine-phosphate-guanine DNA in transgenic HLA-A2 mice induces recognition of HIV-infected T cells and clears vaccinia virus challenge

We evaluated immunogenicity of a novel Th-CTL fusion peptide composed of the pan DR Th epitope and a CTL epitope derived from HIV-pol in two transgenic HLA-A*0201/K(b) mouse models. The immunogenicity of peptides of this structure is highly dependent on coadministered cytosine-phosphate-guanine DNA. Initial evaluations of peptide-specific immunity are based on results of chromium release assay, intracellular cytokine, and tetramer staining. Significant cytotoxic T cell responses are found upon a single immunization with as low as 0.1 nmol both peptide and cytosine-phosphate-guanine DNA. Splenocytes from immunized mice recognize naturally processed HIV-pol expressed from vaccinia virus (pol-VV). Translation of immunologic criteria into more relevant assays was pursued using systemic challenge of immunized mice with pol-VV. Only mice receiving both peptide and DNA together successfully cleared upward of 6 logs of virus from ovaries, compared with controls. Challenge with pol-VV by intranasal route of intranasal immunized mice showed a significant reduction in the levels of VV in lung compared with naive mice. A convincing demonstration of the relevance of these vaccines is the robust lysis of HIV-infected Jurkat T cells (JA2/R7/Hyg) by immune splenocytes from peptide- and DNA-immunized mice. This surprisingly effective immunization merits consideration for clinical evaluation, because it succeeded in causing immune recognition and lysis of cells infected with its target virus and reduction in titer of highly pathogenic VV.

HIV, 'an evolving species'. Roles of cellular activation and co-infections

Each small variation of the genome of a species can be preserved if it is useful for the survival of the species in a given environment. Within this framework, the finality of the biological cycle of HIV consists in a search for harmony (biological coherence) with man, which is to say a stable condition. Cellular activation appears to be the strategy developed by HIV in order to achieve this coherence. The price of this strategy is the AIDS. The first contact between HIV and immune system appears to determine the subsequent clinical outcome and the future of HIV. Lymphocytic activation varies during the course of the vital cycle of HIV. For each individual, this lymphocytic activation depends on both the HLA repertoire acquired during thymic ontogenesis and the antigenic experience before and after HIV infection. Thus intercurrent infections alter the immune condition of the organism and influence the outcome of HIV. We described a synthetic analysis of the effects of HIV on the surface protein expression and the cellular activation pathways which should provide insights in the evolutionary relationship between HIV and man and should permit to do a more physiological therapeutic approach.

Partial restoration of cytokine profile despite reconstitution of cytomegalovirus-specific cell-mediated immunity in human immunodeficiency virus-infected patients during highly active antiretroviral treatment

We reconstituted cytomegalovirus (CMV)-specific T-cell responses in human immunodeficiency virus-1-positive, CMV-positive patients receiving highly active antiretroviral treatment (HAART). We used several combinations of functionality parameters to determine the degree of T-lymphocyte reconstitution obtained during 1 year of treatment. Untreated patients displayed CMV-specific cytotoxic T-lymphocyte (CTL) activity despite the absence of CMV-specific lymphoproliferative responses (LPRs) and despite the fact that interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) were not secreted. The absence of LPRs, IFN-gamma and IL-2 before antiretroviral treatment suggests that CMV-specific immunity was deregulated despite the high CD4+ T-cell counts presented by our cohort, which are critical to the reactivation of CMV disease. After 6 months of HAART, CTL activity had increased compared with the baseline, as had the levels of secreted IFN-gamma and LPR. However, the levels of specific IL-2 produced did not change during therapy, and no specific IL-2 was detected during the follow-up period. Taken together, our findings suggest that 1 year of HAART led to the recovery of some, but not all, CMV-specific responses in our cohort of patients.

Preclinical development of an adjuvant-free peptide vaccine with activity against CMV pp65 in HLA transgenic mice

Epitope vaccines have shown promise for inducing cellular immune responses in animal models of infectious disease. In cases where cellular immunity was augmented, peptide vaccines composed of covalently linked minimal cytotoxic T-lymphocyte (CTL) and T-helper (T(H)) epitopes generally showed the most efficacy. To address a clinical vaccine strategy for cytomegalovirus (CMV) in the context of HCT (hematopoietic cell transplantation), we observed that linking the synthetically derived pan-DR epitope peptide (PADRE) or one of several tetanus T(H) epitopes to the immunodominant human leukocyte antigen (HLA) A*0201-restricted CTL epitope from CMV-pp65 to create a fusion peptide caused robust cytotoxic cellular immune responses in HLA A*0201/K(b) transgenic mice. Significantly, the fusion peptides are immunogenic when administered in saline solution by either subcutaneous or intranasal routes. CpG-containing single-stranded DNA (ss-oligodeoxynucleotide [ODN]) added to the fusion peptides dramatically up-regulated immune recognition by either route. Notably, target cells that either expressed full-length pp65 protein from vaccinia viruses or were sensitized with the CTL epitope encoded in the vaccine were recognized by splenic effectors from immunized animals. Visualization of murine peptide-specific CTL by flow cytometry was accomplished using an HLA A*0201 tetramer complexed with the pp65(495-503) CTL epitope. T(H)-CTL epitope fusion peptides in combination with CpG ss-ODN represent a new strategy for parenteral or mucosal delivery of vaccines in a safe and effective manner that has applicability for control or prophylaxis of infectious disease, especially in situations such as vaccination of donors or recipients of HCT, where highly inflammatory adjuvants are not desired.

Correlates of antiviral immune restoration in acute and chronic HIV type 1 infection: sustained viral suppression and normalization of T cell subsets

Highly active antiretroviral therapy (HAART) has suppressed viral replication and facilitated normalization of T cell subsets, resulting in restoration of immunity against opportunistic pathogens. Induction of full immune restoration in chronically infected individuals, including HIV-specific helper T cell responses, is considered a priority, particularly if immunological control of HIV is to be achieved. Regimens containing dual protease inhibitors (PIs) have provided greater suppression of viremia than single-PI regimens. We therefore conducted a prospective analysis of factors associated with immune restoration after 3 years of therapy in two cohorts of acutely and chronically HIV-infected patients, comparing dual- versus single-PI regimens. Earlier and more durable returns of p24-specific proliferation were demonstrated in patients receiving dual-PI compared with single-PI regimens. Individuals with restored p24 responses had larger reductions in total HIV-specific cytotoxic T lymphocytes (CTLs) associated with stronger viral suppression, but Gag-specific CTLs remained higher, demonstrating that Gag-specific helper T cell responses were a critical component of functional immune restoration. On examination of clinical factors associated with immune restoration, we demonstrated that decreasing activation of CD8+ T cells (%CD8+ CD38+) and increasing proportions of CD4+ T cells were independently associated with restoration of p24 responses. Minimal immune activation, resulting from maximal suppression of viral replication, was required for long-term restoration and maintenance of Gag-specific T cell responses. This study uniquely demonstrates that dual-PI regimens are superior in achieving these levels of virological control and immune restoration in both chronic and acute infection, compared with single-PI or non-PI regimens.

Characterization of cytotoxic function of CMV-pp65-specific CD8+ T-lymphocytes identified by HLA tetramers in recipients and donors of stem-cell transplants

BACKGROUND

Human cytomegalovirus (CMV) is a ubiquitous herpesvirus that is an important complication of bone marrow and allogeneic stem-cell transplant (HSCT). CD8 T-lymphocytes have an important role in immunity against CMV, but correlation between antigen-specific subpopulations of these cells and protection are still unclear.

METHODS

Flow analysis with fluorescently-conjugated human leukocyte antigen (HLA) class I tetramers (Tet) was used to investigate levels of CMV-specific CD8 T-lymphocytes in peripheral blood monocyte cells (PBMC) samples from HSCT donors and recipients and their ability to produce interferon (IFN)-gamma on stimulation with either CMV antigenic peptide or nonspecific mitogenic stimulation. Chromium release assays were used to evaluate ex vivo CMV-specific cytotoxicity associated with the PBMC samples.

RESULTS

Use of Tet in conjunction with fluorescently conjugated anti-T-cell receptor (TCR) beta-chain variable (Vbeta) monoclonal antibodies indicated that the Vbeta repertoires associated with Tet cells seen in two HSCT recipients were similar to the Vbeta repertoires of the Tet cells in their HSCT donors. Significant ex vivo cytotoxicity against peptide-loaded targets was measured from several recipient samples after transplant. However, PBMC from the HSCT donors, even when containing populations of CMV-specific Tet cells capable of secreting IFN-gamma in response to peptide stimulation, possessed no ex vivo CMV-specific cytotoxicity.

CONCLUSIONS

We hypothesize that in the setting of the reconstituting immune system of HSCT recipients, CMV reactivation may stimulate a functional change in CMV-specific CD8 T-lymphocytes, rendering them able to directly lyse target cells presenting CMV antigens without in vitro stimulation. These findings have important implications for development of vaccines designed to induce protective cellular immunity to CMV in transplant recipients.

Characterization of CD8(-) HLA class I/epitope tetrameric complexes binding T cells

Antigen-specific CD8-expressing T cells play a crucial role in the host's defense against viral disease and malignancy. Epitope-specific CD8(+)T cell responses to malignant and viral disease can be accurately measured using tetramers (tHLA) of HLA class I molecules loaded with antigenic peptides. In addition, tHLA have been used to evaluate immune responses to antigen-specific immunization. tHLA bind specifically to complementary T-cell receptor (TCR) structures on the surface of T cells expressing the CD8 coreceptor. Surprisingly, however, CD8(-) cells binding tHLA are often observed. This study uses four-color flow cytometry to show that HLA-A*0201-tHLA-stained CD8(-) cells can be divided into two subsets: 87% represent B-lymphocytes (CD19(+), CD45RA(+), HLA-DR(+), and CD20(+)), and 13% represent T-helper cells (CD3(+), CD4(+), CD45RA(+), and CD27(+)). This phenomenon is not HLA-restricted because it could be observed even in peripheral blood mononuclear cells (PBMC) from a non HLA-A*0201-expressing healthy donor. In addition, no T-cell receptor was detected on the B-lymphocytes. Retrospective enumeration of vaccine-induced CD8(-) tHLA cells in 243 PBMC samples from 36 patients with melanoma undergoing peptide vaccination revealed that tHLA staining is not dependent on immunization status or the presence of CD8(+) tHLA(+) T cells. These findings, suggest that the nonspecific binding of tHLA to non-TCR-expressing T cells requires a careful interpretation of results and further steps in preparation of sample for tHLA-based sorting of epitope specific T cells.