A recombinant vaccinia virus based ELISPOT assay detects high frequencies of Pol-specific CD8 T cells in HIV-1-positive individuals

T cell perturbations persist for at least 6 months following hospitalization for COVID-19

COVID-19 is being extensively studied, and much remains unknown regarding the long-term consequences of the disease on immune cells. The different arms of the immune system are interlinked, with humoral responses and the production of high-affinity antibodies being largely dependent on T cell immunity. Here, we longitudinally explored the effect COVID-19 has on T cell populations and the virus-specific T cells, as well as neutralizing antibody responses, for 6-7 months following hospitalization. The CD8⁺ TEMRA and exhausted CD57⁺ CD8⁺ T cells were markedly affected with elevated levels that lasted long into convalescence. Further, markers associated with T cell activation were upregulated at inclusion, and in the case of CD69⁺ CD4⁺ T cells this lasted all through the study duration. The levels of T cells expressing negative immune checkpoint molecules were increased in COVID-19 patients and sustained for a prolonged duration following recovery. Within 2-3 weeks after symptom onset, all COVID-19 patients developed anti-nucleocapsid IgG and spike-neutralizing IgG as well as SARS-CoV-2-specific T cell responses. In addition, we found alterations in follicular T helper (TFH) cell populations, such as enhanced TFH-TH2 following recovery from COVID-19. Our study revealed significant and long-term alterations in T cell populations and key events associated with COVID-19 pathogenesis.

Cytomegalovirus-Specific T Cell Epitope Recognition in Congenital Cytomegalovirus Mother-Infant Pairs

Background: Congenital cytomegalovirus (cCMV) infection is the most common infection acquired before birth and from which about 20% of infants develop permanent neurodevelopmental effects regardless of presence or absence of symptoms at birth. Viral escape from host immune control may be a mechanism of CMV transmission and infant disease severity. We sought to identify and compare CMV epitopes recognized by mother-infant pairs. We also hypothesized that if immune escape were occurring, then one pattern of longitudinal CD8 T cell responses restricted by shared HLA alleles would be maternal loss (by viral escape) and infant gain (by viral reversion to wildtype) of CMV epitope recognition. Methods: The study population consisted of 6 women with primary CMV infection during pregnancy and their infants with cCMV infection. CMV UL83 and UL123 peptides with known or predicted restriction by maternal MHC class I alleles were identified, and a subset was selected for testing based on several criteria. Maternal or infant cells were stimulated with CMV peptides in the IFN-γ ELISpot assay. Results: Overall, 14 of 25 (56%; 8 UL83 and 6 UL123) peptides recognized by mother-infant pairs were not previously reported as CD8 T cell epitopes. Of three pairs with longitudinal samples, one showed maternal loss and infant gain of responses to a CMV epitope restricted by a shared HLA allele. Conclusions: CD8 T cell responses to multiple novel CMV epitopes were identified, particularly in infants. Moreover, the hypothesized pattern of CMV immune escape was observed in one mother-infant pair. These findings emphasize that knowledge of paired CMV epitope recognition allows exploration of viral immune escape that may operate within the maternal-fetal system. Our work provides rationale for future studies of this potential mechanism of CMV transmission during pregnancy or clinical outcomes of infants with cCMV infection.

The immunologic dominance of an epitope within a rationally designed poly-epitope vaccine is influenced by multiple factors

INTRODUCTION

CD4⁺ T cells are essential for inducing optimal CD8⁺ T cell and antibody-producing B cell responses and maintaining their long-term immunological memory. Therefore, CD4⁺ T cells are a critical component in HIV vaccine development. Due to enormous viral gene variation and significant human host genetic diversity, HIV vaccines may need to be custom-made for different countries.

METHODS

Previously, we designed a CD4⁺ T cell vaccine based on Chinese HIV isolates and HLA-DR alleles using bioinformatics tools and predicted that 20 epitopes could cover 98.1% of the Chinese population. In vivo testing of the poly-epitope antigen in mice only activated specific T cells for some epitopes. To elucidate the mechanism of the observed differential immunogenicity, we examined poly-epitope antigen processing and presentation using in vitro and in vivo analytical methods.

RESULTS

Enzymatic digestion indicated that all 20 epitopes comprising the poly-epitope antigen could be liberated, but MHC II binding assays showed that neither binding affinity nor dissociation rate was associated with the magnitude of T cell immune responses elicited by each peptide epitope in vaccinated mice. Mass spectrometry analysis of MHC II-bound peptides suggested that the abundance of endogenously processed peptides bound to MHC II molecules was significantly associated with the relative immunodominance of these epitopes.

CONCLUSION

These results provide a new rationale for improving the design and testing of poly-epitope vaccines for HIV and other diseases.

Emergence of CD4+ and CD8+ Polyfunctional T Cell Responses Against Immunodominant Lytic and Latent EBV Antigens in Children With Primary EBV Infection

Long term carriers were shown to generate robust polyfunctional T cell (PFC) responses against lytic and latent antigens of Epstein-Barr virus (EBV). However, the time of emergence of PFC responses against EBV antigens, pattern of immunodominance and difference between CD4+ and CD8+ T cell responses during various stages of EBV infection are not clearly understood. A longitudinal study was performed to assess the development of antigen-specific PFC responses in children diagnosed to have primary symptomatic (infectious mononucleosis [IM]) and asymptomatic (AS) EBV infection. Evaluation of IFN-γ secreting CD8+ T cell responses upon stimulation by HLA class I-specific peptides of EBV lytic and latent proteins by ELISPOT assay followed by assessment of CD4+ and CD8+ PFC responses upon stimulation by a panel of overlapping EBV peptides for co-expression of IFN-γ, TNF-α, IL-2, perforin and CD107a by flow cytometry were performed. Cytotoxicity of T cells against autologous lymphoblastoid cell lines (LCLs) as well as EBV loads in PBMC and plasma were also determined. Both IM and AS patients had elevated PBMC and plasma viral loads which declined steadily during a 12-month period from the time of diagnosis whilst decrease in the magnitude of CD8+ T cell responses toward EBV lytic peptides in contrast to increase toward latent peptides was shown with no significant difference between those of IM and AS patients. Both lytic and latent antigen-specific CD4+ and CD8+ T cells demonstrated polyfunctionality (defined as greater or equal to three functions) concurrent with enhanced cytotoxicity against autologous LCLs and steady decrease in plasma and PBMC viral loads over time. Immunodominant peptides derived from BZLF1, BRLF1, BMLF1 and EBNA3A-C proteins induced the highest proportion of CD8+ as well as CD4+ PFC responses. Diverse functional subtypes of both CD4+ and CD8+ PFCs were shown to emerge at 6–12 months. In conclusion, EBV antigen-specific CD4+ and CD8+ PFC responses emerge during the first year of primary EBV infection, with greatest responses toward immunodominant epitopes in both lytic and latent proteins, correlating to steady decline in PBMC and plasma viral loads.

Differences in Evolution of HIV-1 Subtype C Reverse Transcriptase Between Children and Adults Likely Explained by Maturity of Cytotoxic T-Lymphocyte Responses

In this study HIV-1 subtype C-infected adults demonstrated higher purifying selection on their viral populations in reverse transcriptase (RT) than infected children. This difference is likely explained by more mature cytotoxic T-lymphocyte responses in adults, which may have implications for the development of drug resistance in the RT region.

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.

Complement opsonization of HIV-1 results in a different intracellular processing pattern and enhanced MHC class I presentation by dendritic cells

Induction of optimal HIV-1-specific T-cell responses, which can contribute to controlling viral infection in vivo, depends on antigen processing and presentation processes occurring in DCs. Opsonization can influence the routing of antigen processing and pathways used for presentation. We studied antigen proteolysis and the role of endocytic receptors in MHC class I (MHCI) and II (MHCII) presentation of antigens derived from HIV-1 in human monocyte-derived immature DCs (IDCs) and mature DCs, comparing free and complement opsonized HIV-1 particles. Opsonization of virions promoted MHCI presentation by DCs, indicating that complement opsonization routes more virions toward the MHCI presentation pathway. Blockade of macrophage mannose receptor (MMR) and β7-integrin enhanced MHCI and MHCII presentation by IDCs and mature DCs, whereas the block of complement receptor 3 decreased MHCI and MHCII presentation. In addition, we found that IDC and MDC proteolytic activities were modulated by HIV-1 exposure; complement-opsonized HIV-1 induced an increased proteasome activity in IDCs. Taken together, these findings indicate that endocytic receptors such as MMR, complement receptor 3, and β7-integrin can promote or disfavor antigen presentation probably by routing HIV-1 into different endosomal compartments with distinct efficiencies for degradation of viral antigens and MHCI and MHCII presentation, and that HIV-1 affects the antigen-processing machinery.

Defining ELISpot cut-offs from unreplicated test and control wells

In the absence of replication of wells, empirical criteria for enzyme-linked immunospot (ELISpot) positivity use fixed differences or ratios between spot forming units (SFU) counts between test and control. We propose an alternative approach which first identifies the optimally variance-stabilizing transformation of the SFU counts, based on the Bland-Altman plot of the test and control wells. The second step is to derive a positivity threshold from the difference in between-plate distribution functions of the transformed test and control SFU counts. This method is illustrated using 1309 assay results from a cohort study of influenza in Vietnam in which some, but not all, of the peptide pools have clear tendencies for SFU counts to be higher in test than control wells.

Use of interferon-γ enzyme-linked immunospot assay to characterize novel T-cell epitopes of human papillomavirus

A protocol has been developed to overcome the difficulties of isolating and characterizing rare T cells specific for pathogens, such as human papillomavirus (HPV), that cause localized infections. The steps involved are identifying region(s) of HPV proteins that contain T-cell epitope(s) from a subject, selecting for the peptide-specific T cells based on interferon-γ (IFN-γ) secretion, and growing and characterizing the T-cell clones (Fig. 1). Subject 1 was a patient who was recently diagnosed with a high-grade squamous intraepithelial lesion by biopsy and underwent loop electrical excision procedure for treatment on the day the T cells were collected(1). A region within the human papillomavirus type 16 (HPV 16) E6 and E7 proteins which contained a T-cell epitope was identified using an IFN- g enzyme-linked immunospot (ELISPOT) assay performed with overlapping synthetic peptides (Fig. 2). The data from this assay were used not only to identify a region containing a T-cell epitope, but also to estimate the number of epitope specific T cells and to isolate them on the basis of IFN- γ secretion using commercially available magnetic beads (CD8 T-cell isolation kit, Miltenyi Biotec, Auburn CA). The selected IFN-γ secreting T cells were diluted and grown singly in the presence of an irradiated feeder cell mixture in order to support the growth of a single T-cell per well. These T-cell clones were screened using an IFN- γ ELISPOT assay in the presence of peptides covering the identified region and autologous Epstein-Barr virus transformed B-lymphoblastoid cells (LCLs, obtained how described by Walls and Crawford)(2) in order to minimize the number of T-cell clone cells needed. Instead of using 1 x 10(5) cells per well typically used in ELISPOT assays(1,3), 1,000 T-cell clone cells in the presence of 1 x 10(5) autologous LCLs were used, dramatically reducing the number of T-cell clone cells needed. The autologous LCLs served not only to present peptide antigens to the T-cell clone cells, but also to keep a high cell density in the wells allowing the epitope-specific T-cell clone cells to secrete IFN-γ. This assures successful performance of IFN-γ ELISPOT assay. Similarly, IFN- γ ELISPOT assays were utilized to characterize the minimal and optimal amino acid sequence of the CD8 T-cell epitope (HPV 16 E6 52-61 FAFRDLCIVY) and its HLA class I restriction element (B58). The IFN- γ ELISPOT assay was also performed using autologous LCLs infected with vaccinia virus expressing HPV 16 E6 or E7 protein. The result demonstrated that the E6 T-cell epitope was endogenously processed. The cross-recognition of homologous T-cell epitope of other high-risk HPV types was shown. This method can also be used to describe CD4 T-cell epitopes(4).

Analyzing cellular immunity to AAV in a canine model using ELISPOT assay

Adeno-associated viral (AAV) vector-mediated gene transfer represents a promising gene replacement strategy for treating various genetic diseases. One obstacle in using viral-derived vectors for in vivo gene delivery is the development of host immune responses to the vector. Recent studies have demonstrated cellular immune responses specific to capsid proteins of various AAV serotypes in animal models and in human trials for different diseases. We developed a canine-specific ELISPOT assay to detect such immunity in dogs received AAV treatment. Here, we describe in detail the use of a constructed panel of overlapping peptides spanning the entire VP1 sequence of AAV capsid protein to detect specific T-cell responses in peripheral blood in dogs following intramuscular injection of AAV. This high-throughput method allows the identification of T-cell epitopes without the need for large cell numbers and the need for major histocompatibility complex molecule-matched cell lines.

Protective role of cytotoxic T lymphocytes in filovirus hemorrhagic fever

Infection with many emerging viruses, such as the hemorrhagic fever disease caused by the filoviruses, Marburg (MARV), and Ebola virus (EBOV), leaves the host with a short timeframe in which to mouse a protective immune response. In lethal cases, uncontrolled viral replication and virus-induced immune dysregulation are too severe to overcome, and mortality is generally associated with a lack of notable immune responses. Vaccination studies in animals have demonstrated an association of IgG and neutralizing antibody responses against the protective glycoprotein antigen with survival from lethal challenge. More recently, studies in animal models of filovirus hemorrhagic fever have established that induction of a strong filovirus-specific cytotoxic T lymphocyte (CTL) response can facilitate complete viral clearance. In this review, we describe assays used to discover CTL responses after vaccination or live filovirus infection in both animal models and human clinical trials. Unfortunately, little data regarding CTL responses have been collected from infected human survivors, primarily due to the low frequency of disease and the inability to perform these studies in the field. Advancements in assays and technologies may allow these studies to occur during future outbreaks.

Use of replication restricted recombinant vesicular stomatitis virus vectors for detection of antigen-specific T cells

Detection of antigen-specific T cells at the single-cell level by ELISpot or flow cytometry techniques employing intracellular cytokine staining (ICS) is now an indispensable tool in many areas of immunology. When precisely mapped, optimal MHC-binding peptide epitopes are unknown, these assays use antigen in a variety of forms, including recombinant proteins, overlapping peptide sets representing one or more target protein sequences, microbial lysates, lysates of microbially-infected cells, or gene delivery vectors such as DNA expression plasmids or recombinant vaccinia or adenoviruses expressing a target protein of interest. Here we introduce replication-restricted, recombinant vesicular stomatitis virus (VSV) vectors as a safe, easy to produce, simple to use, and highly effective vector for genetic antigen delivery for the detection of human antigen-specific helper and cytotoxic T cells. To demonstrate the broad applicability of this approach, we have used these vectors to detect human T cell responses to the immunodominant pp65 antigen of human cytomegalovirus, individual segments of the yellow fever virus polyprotein, and to various influenza proteins.

Correlation of HIV-specific immunity, viral control, and diversification following planned multiple exposures to autologous HIV in a pediatric population

Repeated controlled exposure to autologous virus was previously shown to result in increased CD8 T lymphocyte response to HIV antigens and accompanying reduction in viremia. We attempted to see if this immunity contributed to virologic control by correlating the immune response with quasispecies envelope diversification, an indicator of immune selection. The greatest diversification was seen in those with the greatest reduction in viremia but was unrelated to the frequency of Env-specific gamma interferon-producing cells. There was a trend toward correlation between the response to multiple HIV antigens and diversification.

Rapid progressing allele HLA-B35 Px restricted anti-HIV-1 CD8+ T cells recognize vestigial CTL epitopes

Background

The HLA-B*35-Px allele has been associated with rapid disease progression in HIV-1 infection, in contrast to the HLA-B*35-Py allele.

Methodology/Principal Findings

Immune responses to two HLA-B*35 restricted HIV-1 specific CTL epitopes and their variants were followed longitudinally during early HIV-1 infection in 16 HLA-B*35+ individuals. Subjects expressing HLA-B*35-Px alleles showed no difference in response to the consensus epitopes compared to individuals with HLA-B*35-Py alleles. Surprisingly, all the HLA-B*35-Px+ individuals responded to epitope-variants even in the absence of a consensus response. Sequencing of the viral population revealed no evidence of variant virus in any of the individuals.

Conclusions/Significance

This demonstrates a novel phenomenon that distinguishes individuals with the HLA-B*35-Px rapid progressing allele and those with the HLA-B*35-Py slower progressing allele.

Determination of rubella virus-specific cell-mediated immunity using IFN gamma-ELISpot

Immunity to rubella virus (RV) is conventionally determined by measuring specific immunoglobulin G (IgG). However, several individuals may be considered immune despite undetectable antibody levels. In the present study RV-specific interferon-gamma (IFN gamma)-ELISpot and rubella-IgG-ELISA were compared in 75 young adults aged between 20 and 30 years. In a subgroup, not only rubella-like particles (RLP), but also HPV77 rubella vaccine derived antigen was used in IFN gamma-ELISpot. The results from both, ELISA and ELISpot were independent of previous encounter to RV (vaccination, exanthematous disease, or childhood infection). There was no difference between RLP and RV vaccine antigen in IFN gamma-ELISpot response, and there was no correlation between IFN gamma-ELISpot and RV-specific IgG levels. IFN gamma-producing cells were found in 78.7% of all tested persons, and 83.8% of them were positive in ELISA. In almost all individuals seronegative for RV antibody, IFN gamma-producing cells were detected. Considering both humoral and cell-mediated immune responses, a positive RV immune reaction was seen in 98.6%. The results indicate that the IFN gamma-ELISpot can provide valuable additional information in seronegative individuals.

Co-immunization with IL-15 enhances cellular immune responses induced by a vif-deleted simian immunodeficiency virus proviral DNA vaccine and confers partial protection against vaginal challenge with SIVmac251

Simian immunodeficiency virus (SIV) infection of rhesus macaques is a valuable animal model for human immunodeficiency virus (HIV)-1 vaccine development. Our laboratory recently described the immunogenicity and limited efficacy of a vif-deleted SIVmac239 proviral DNA (SIV/CMVDelta vif) vaccine. The current report characterizes immunogenicity and efficacy for the SIV/CMVDelta vif proviral DNA vaccine when co-inoculated with an optimized rhesus interleukin (rIL)-15 expression plasmid. Macaques co-inoculated with rIL-15 and SIV/CMVDelta vif proviral plasmids showed significantly improved SIV-specific CD8 T cell immunity characterized by increased IFN-gamma ELISPOT and polyfunctional CD8 T cell responses. Furthermore, these animals demonstrated a sustained suppression of plasma virus loads after multiple low dose vaginal challenges with pathogenic SIVmac251. Importantly, SIV-specific cellular responses were greater in immunized animals compared to unvaccinated controls during the initial 12 weeks after challenge. Taken together, these findings support the use of IL-15 as an adjuvant in prophylactic anti-HIV vaccine strategies.

Quantifying HIV-1-specific CD8 (+) T-cell responses using ELISPOT and cytokine flow cytometry

Since the initial description and characterization of the agent that causes AIDS, human immunodeficiency virus (HIV-1), numerous research groups have characterized immune responses to this virus. Much effort has been directed towards identifying potential correlates of protection that may be useful for the development of vaccines and immunotherapies. In addition, several investigations have focused on comparing patients with rapid vs. slow disease progression profiles in an attempt to identify the characteristics of a "successful" immune response. Although many gaps remain in our understanding of the host-pathogen relationship, great progress has been made during the past 20 years in elucidating the adaptive, cell-mediated response to HIV-1. These investigations have benefited in recent years from the development of new approaches to the analysis of antigen-specific CD8+ T-cell function, notably the ELISPOT assay and cytokine flow cytometry. This chapter provides simple protocols for these two methods.

Determination of specific CD4 and CD8 T cell epitopes after AAV2- and AAV8-hF.IX gene therapy

The application of AAV2 or AAV8 vectors for delivery of human coagulation factor IX (hF.IX) is a promising gene therapy for hemophilia B. One major limitation of this therapy is the development of antibodies and a cytotoxic T lymphocyte (CTL) response against both the vector capsid and the transgene. We determined the class I and class II MHC peptide epitopes for AAV2, AAV8, and hF.IX after administration of AAV-2-hF.IX or AAV8-hF.IX in H2(b) (C57BL/6), H2(d) (BALB/c), or H2(k) (C3H) strains of mice. The results indicate that the AAV2 capsid peptide AA(373-381), the AAV8 capsid peptide AA(50-58), and the hF.IX transgene peptide AA(311-319) can elicit a CTL response as indicated by an IFN-gamma ELISPOT assay and an in vivo CTL assay. Furthermore, a strong H2(k) MHC II-restricted Th1 response can be elicited in C3H mice by the AAV8 capsid peptide AA(126-140) and the hF.IX peptide AA(108-122), whereas a strong Th2 response can be elicited by the AAV2 peptide AA(475-489). These results show that specific CTL responses are generated to both AAV capsid epitopes and hF.IX epitopes after injection of AAV-hF.IX, and MHC class II epitopes derived from AAV-hF.IX promote development of either Th1 or Th2 cells.

Effects of recombinant human growth hormone on HIV-1-specific T-cell responses, thymic output and proviral DNA in patients on HAART: 48-week follow-up

BACKGROUND

Efficacious immune-based therapy in treated chronic HIV-1 infection requires the induction of virus-specific CD4+ T cells and subsequent maturation and maintenance of specific memory CD8+ T cells. Concomitant daily administration of recombinant human growth hormone (rhGH) with highly active antiretroviral therapy (HAART) was used in chronically infected patients with lipodystrophy in an attempt to reconstitute these virus-specific T-cell responses.

METHODS

Individuals with chronic HIV-1 infection on HAART were enrolled on a randomized, double-blinded, placebo-controlled study to receive rhGH therapy. We assessed HIV-1-specific proliferative CD4+ and interferon-gamma (IFN-gamma)-producing CD8+ T-cell responses, quantified thymic output and proviral HIV-1 DNA at the following time points: baseline; after 12 weeks of rhGH therapy; at 24 weeks, after randomization into three groups [placebo weeks 12-24 (Group A), alternate-day dosing weeks 12-24 (Group B), and twice-per-week dosing weeks 12-24 (Group C)]; and at 48 weeks after all patients had received HAART alone for the final 24 weeks.

RESULTS

We found significant increases in both proliferative CD4+ and IFN-gamma-producing CD8+ HIV-1-specific T-cell responses after daily administration of rhGH. This increase was focused on HIV-1 Gag-specific T-cell responses. Following subsequent randomisation into different dosing regimens, HIV-1-specific proliferative CD4+ T-cell responses declined in patients receiving less frequent dosing of rhGH, while virus-specific IFN-gamma-producing CD8+ T-cell responses were maintained for longer periods of time. There was no significant change in thymic output and the cell-associated HIV-1 DNA remained stable in most patients. An increased anti-HIV-1 Nef-specific CD4+ T-cell proliferative response was correlated to a decrease in proviral load, and an increased HIV-1 Gag-specific IFN-gamma-producing CD8+ T-cell response correlated with an increase in proviral load.

CONCLUSION

The implication of these data is that daily dosing of rhGH with HAART, in addition to improving HIV-1-associated lipodystrophy, may reverse some of the T-lymphocyte dysfunction seen in most treated HIV-1-positive patients, in a dose-dependent manner. Such immune-based therapeutic strategies used in treated, chronic HIV-1 infection may enable the induction of virus-specific CD4+ T cells essential for the subsequent 'kick-start' and expansion of virus-specific CD8+ T cells.

TRIAL REGISTRATION

GH in Lipoatrophy IMP22350.

Generation of HIV-1-specific CD8+ cell responses following allogeneic hematopoietic cell transplantation

This study tested whether donor-derived HIV-specific immune responses could be detected when viral replication was completely suppressed by the continuous administration of highly active antiretroviral therapy (HAART). A regimen of fludarabine and 200 cGy total body irradiation was followed by infusion of allogeneic donor peripheral blood cells and posttransplantation cyclosporine and mycophenolate mofetil. Viral load, lymphocyte counts, and HIV-1-specific CD8(+) cell immune responses were compared before and after hematopoietic cell transplantation (HCT). Uninterrupted administration of HAART was feasible during nonmyeloablative conditioning and after HCT. The HIV RNA remained undetectable and no HIV-associated infections were observed. CD8(+) T-cell responses targeting multiple epitopes were detected before HCT. After HCT a different pattern of donor-derived HIV-specific CTL responses emerged by day +80, presumably primed in vivo. We conclude that allogeneic HCT offers the unique ability to characterize de novo HIV-1-specific immune responses. This clinical trial was registered at ClinicalTrials.gov (identifier: NCT00112593).

Immunization with an HIV-1 immunogen induces CD4+ and CD8+ HIV-1-specific polyfunctional responses in patients with chronic HIV-1 infection receiving antiretroviral therapy

Development of polyfunctional T lymphocyte responses is critical in the immunological response against HIV-1. Fifty-four HIV-1 infected patients receiving antiretroviral treatment (ART) and immunization with an HIV-1 immunogen or placebo, periodically every 3 months throughout a period of 36 months, were evaluated for the purposes of analysing the development of HIV-1-specific CD4+ and CD8+ responses. A significant increase of proliferating and IFN-gamma producing CD8+ HIV-1-specific T cells, of HIV-1-specific precursor frequencies for CD8+ and for CD4+ T cells and of Gag/pol-specific memory CTL precursors (CTLp) was observed in the immunogen group in comparison to placebo. IL-2 intracellular expression and IFN-gamma and TNF-alpha co-expression in HIV-1-specific CD8+ T cells were also substantially increased in the immunized group. A negative correlation between viral load and CD3+CD4+CFSElow HIV-1-specific lymphoproliferative response and frequency of Gag/pol-specific CTLp was solely observed in the HIV-1 immunogen group. Long-term immunization in patients receiving ART helps to develop HIV-1-specific polyfunctional T cell responses.

Planned multiple exposures to autologous virus in HIV type 1-infected pediatric populations increases HIV-specific immunity and reduces HIV viremia

We tested to determine if planned multiple exposures to autologous HIV in pediatric patients with HIV-1 infection will induce cellular immunity that controls viremia. A prospective multicenter study of aviremic pediatric patients on highly active antiretroviral therapy who underwent progressively longer antiretroviral treatment interruptions in cycles starting with 3 days, increasing by 2 days in length each consecutive cycle, was conducted. Eight individuals became viremic and reached Cycle 13 or greater with an "off-therapy" interval of >or=27 days. HIV-specific interferon-gamma (IFN-gamma) production to inactivated HIV and vaccinia vectors expressing gag, env, nef, and pol increased (>10-fold) from baseline in six of eight subjects. The HIV-specific lymphoproliferative response as measured by the median stimulation index (SI) increased in the treatment group from 1 at baseline to 16, 12, 4, and 3 at Cycles 7, 10, 13, and 17, respectively. Median plasma RNA levels peaked at Cycle 7 (4.45 log) and declined to levels <10(4) cp/ml after Cycle 10 (4.1, 3.5, and 3.4 at Cycles 10, 13, and 17). In a subset of five patients who reached Cycle 17, HIV-specific IFN-gamma frequencies were 4- to 30-fold higher and median RNA levels were 0.32-2.10 (median 1.3) log lower than at comparable days off treatment at Cycle 8 (17 days off therapy). A second group of children, not undergoing drug interruption, did not develop significant increases in either HIV-specific IFN-gamma production or SI. Increased HIV-specific immune responses and decreased HIV RNA were seen in those children who have had >10 cycles of antiretroviral discontinuations of increasing durations acting as autologous virus vaccinations. Other studies may have failed due to an insufficient number of exposures to HIV; most of the studies had fewer than six drug interruptions.

Vaccination of rhesus macaques with a vif-deleted simian immunodeficiency virus proviral DNA vaccine

Studies in non-human primates, with simian immunodeficiency virus (SIV) and simian/human immunodeficiency virus (SHIV) have demonstrated that live-attenuated viral vaccines are highly effective; however these vaccine viruses maintain a low level of pathogenicity. Lentivirus attenuation associated with deletion of the viral vif gene carries a significantly reduced risk for pathogenicity, while retaining the potential for virus replication of low magnitude in the host. This report describes a vif-deleted simian immunodeficiency virus (SIV)mac239 provirus that was tested as an attenuated proviral DNA vaccine by inoculation of female rhesus macaques. SIV-specific interferon-gamma enzyme-linked immunospot responses of low magnitude were observed after immunization with plasmid containing the vif-deleted SIV provirus. However, vaccinated animals displayed strong sustained virus-specific T cell proliferative responses and increasing antiviral antibody titers. These immune responses suggested either persistent vaccine plasmid expression or low level replication of vif-deleted SIV in the host. Immunized and unvaccinated macaques received a single high dose vaginal challenge with pathogenic SIVmac251. A transient suppression of challenge virus load and a greater median survival time was observed for vaccinated animals. However, virus loads for vaccinated and unvaccinated macaques were comparable by twenty weeks after challenge and overall survival curves for the two groups were not significantly different. Thus, a vif-deleted SIVmac239 proviral DNA vaccine is immunogenic and capable of inducing a transient suppression of pathogenic challenge virus, despite severe attenuation of the vaccine virus.

Pathways utilized by dendritic cells for binding, uptake, processing and presentation of antigens derived from HIV-1

The outcome following HIV infection depends on the nature and durability of the HIV-specific T cell response induced initially. The activation of protective T cell responses depends upon dendritic cells (DC), antigen-presenting cells which have the capacity to process and present viral antigens. DC pulsed with aldrithiol-2-inactivated HIV and delivered in vivo were reported to induce immune responses and promote virologic control in chronically HIV-1-infected subjects. To gain an understanding of this phenomenon, we characterized the steps involved in the presentation of antigens derived from aldrithiol-2-treated vs. infectious HIV-1 by DC. Antigen presentation, on both MHC class I and II, was independent of DC-specific ICAM-3-grabbing integrin, DEC-205 and macrophage mannose receptor, C-type lectins expressed by the DC. Inhibitor studies showed that presentation on MHC class I was dependent on viral fusion in a CD4/coreceptor-dependent manner, both at the cell surface and within endosomes, and access to the classical endosomal processing pathway. MHC class II presentation of HIV-associated antigens was dependent on active endocytosis, probably receptor-mediated, and subsequent degradation of virions in acidified endosomes in the DC. Our study brings forth new facts regarding the binding, uptake, and processing of chemically inactivated virions leading to efficient antigen presentation and should aid in the design of more effective HIV vaccines.

Development of a whole blood intracellular cytokine staining assay for mapping CD4(+) and CD8(+) T-cell responses across the HIV-1 genome

A whole blood peptide mapping intracellular cytokine staining (ICS) assay was developed that allows the direct comparison, at the individual peptide level, of CD4(+) and CD8(+) T-cell responses that span every encoded protein, in patients infected with HIV-1. Whole blood samples from HIV-1 infected patients were stimulated with overlapping synthetic peptides spanning nine subtype C HIV-1 gene regions (Gag, Pol, Nef, Env, Tat, Rev, Vif, Vpu, Vpr). Following stimulation and permeabilization, cells were stained with fluorochrome labelled antibodies to CD3, CD8 (CD4(+) cells were defined as CD8 negative cells), and IL-2 and IFN-gamma. A total of 396 overlapping peptides were arranged in pools with a matrix design which allowed the identification of individual peptide responses from multiple pool responses. HIV-1 infected patients screened using this method showed a broad range of peptide responses across the entire HIV-1 genome with CD8 T-cell responses being higher in frequency in magnitude than CD4(+) T-cell responses. The advantages of this whole blood ICS assay include the following: (1) the response to all potential HIV-1 epitopes across the genome can be examined, (2) the responding cell type can be monitored in the same reaction, and (3) considerably less blood is required than would be necessary if peripheral blood mononuclear cells (PBMC) were first isolated prior to peptide stimulation.

Rational peptide selection to detect human immunodeficiency virus type 1-specific T-cell responses under resource-limited conditions

Understanding human immunodeficiency virus type 1 (HIV-1)-specific cytotoxic T-lymphocyte responses is important for the development of vaccines and therapies. We describe a novel method for the rational selection of peptides that target stable regions of the HIV-1 genome, rich in epitopes specifically recognized by the study population. This method will be of particular use under resource/sample-limited conditions.

Evaluation of aldrithiol-2-inactivated preparations of HIV type 1 subtypes A, B, and D as reagents to monitor T cell responses

The development of HIV vaccines is an urgent priority and there is need to generate reagents representing multiple subtypes that can be used to screen HIV-1-specific responses. We used Aldrithiol-2 (AT-2), a mild oxidizing reagent, to eliminate the infectivity of HIV while maintaining its structure and ability to be processed for presentation to T cells. Inactivated subtype A, B, and D viruses were evaluated for their ability to stimulate T cell responses in PBMC samples from 18 U.S. subjects infected with HIV-1 subtype B and 32 Ugandan subjects infected with subtypes A and D or recombinants AC and AD. Five HIV-1-negative samples were also analyzed. T cell responses to AT-2-inactivated viral isolates were monitored by interferon-gamma (IFN-gamma) intracellular cytokine secretion (ICS) analysis; matched microvesicle preparations served as negative controls. Among the 18 subtype B infected subjects, 39% had CD3(+) CD4 (+) IFN-gamma responses and 67% had CD3(+) CD8(+) IFN-gamma responses. Of the 32 Ugandan subjects, 34% demonstrated CD3(+) CD4(+) IFN-gamma responses and 78% demonstrated CD3(+) CD8(+) IFN-gamma responses. Both subtype-specific and cross-reactive responses were observed. Responses to the AT-2 viruses tended to be lower in magnitude than those detected by a set of overlapping gag peptides. Robust lymphoproliferative responses to AT-2 viruses were seen in a subset of subjects. In conclusion, AT-2-inactivated HIV-1 virions stimulated both CD4 and CD8 HIV-1-specific responses and may provide an additional reagent for screening HIV-1-specific responses in HIV seropositives and vaccinees.

Detection of human papillomavirus type 16-specific T lymphocytes by a recombinant vaccinia virus-based enzyme-linked immunospot assay

Cell-mediated immunity, particularly that induced by T cells, is thought to have a key role in controlling infection. The enzyme-linked immunospot (ELISPOT) assay has been successfully adapted to detect T-cell immune response to a variety of pathogens. However, it still remains a challenge to detect antigen-specific T cells when the numbers of circulating cells are low, such as in a local cervical infection caused by genital human papillomavirus (HPV). The goal of this study was to develop a protocol for enhanced detection of HPV-specific CD8(+) T cells by examining a number of the variables involved in performing an ELISPOT assay. Since blood samples consistently positive for HPV-specific T cells are difficult to obtain, previously described human papillomavirus type 16 (HPV16) E6 52-61 (FAFRDLCIVY)-specific T-cell clone cells (13) seeded in peripheral blood mononuclear cells from an HLA-B57-positive blood donor were used. The variables examined were the amounts of primary and secondary anti-gamma interferon antibodies, amounts of antigen-presenting monocytes and recombinant vaccinia virus expressing the HPV16 E6 protein, and amounts of exogenous cytokines added (recombinant human interleukin-2 [rhIL-2] and rhIL-7). The amounts of antigen-presenting monocytes, followed by the concentration of exogenous rhIL-2, had the most pronounced and significant effects in enhancing sensitivity of the ELISPOT assay. Blood samples from six patients being monitored for abnormal Pap smear results and from 12 healthy volunteers were examined using the enhanced conditions.

Phase 2 study of an HIV-1 canarypox vaccine (vCP1452) alone and in combination with rgp120: negative results fail to trigger a phase 3 correlates trial

BACKGROUND

A goal of T-cell HIV vaccines is to define the correlation between a vaccine-induced immune response and protection from HIV infection. We conducted a phase 2 trial to determine if a canarypox vaccine candidate (vCP1452) administered with rgp120 subunit protein would "qualify" for a trial to define a correlate of efficacy.

METHODS

A total of 330 healthy volunteers were enrolled into 4 groups: 120 received vCP1452 alone (0, 1, 3, and 6 months), 120 received vCP1452 with 2 different regimens of rgp120 coadministration, and 90 received placebo. HIV-specific antibody responses were measured by enzyme-linked immunoassay (ELISA) and neutralizing activity. T-cell responses were measured by chromium release and interferon-gamma (IFNgamma) enzyme-linked immunospot (ELISpot) assay.

RESULTS

Significant neutralizing antibody responses to the HIV MN strain were detected in all vaccine groups, with net responses ranging from 57% (95% confidence interval [CI]: 40% to 71%) to 94% (95% CI: 85% to 99%). Net cumulative HIV-specific CD8 IFNgamma ELISpot assay responses were 13% (95% CI: -1% to 26%) for recipients of vCP1452 alone and 16% (95% CI: 2% to 29%) for recipients of vCP1452 plus rgp120.

CONCLUSIONS

Overall, the HIV-specific CD8 cytotoxic T lymphocyte (CTL) response was not sufficient to qualify the regimen for a subsequent trial designed to detect an immune correlate of protection requiring a minimum CD8 CTL frequency of 30%.

A dual color ELISPOT method for the simultaneous detection of IL-2 and IFN-gamma HIV-specific immune responses

The single color IFN-gamma ELISPOT assay has become a standard for assessing HIV-specific immune responses in HIV-infected subjects. However, recent data suggests that single cytokine detection for immune monitoring of HIV-infected individuals may not be sufficient to fully describe virus-specific immune responses. Here, we have designed and validated a dual color ELISPOT assay capable of detecting both IL-2 and IFN-gamma secreting cells simultaneously in response to HIV antigens. We found that a cell input number of 200,000 cells/well provided a good balance between limited availability of cells due to blood volume restrictions and ability to detect all cytokine secretion patterns. The simultaneous detection of IL-2 and IFN-gamma resulted in a decreased magnitude of IFN-gamma but not IL-2 responses. Measures of intra- and inter-assay variability for the dual color ELISPOT assay were comparable to that seen for single cytokine ELISPOT assay with coefficients of variation below 20% for IL-2, IFN-gamma and dual secretion. Although CD8+ T cells mediated most HIV-specific responses in infected subjects, CD4+ T cells mediated responses to HIV were also detected. Features of this assay such as high throughput, cell number requirement and cytokine choice should make this assay a valuable tool for screening for HIV-specific immune responses in several clinically relevant settings.

Tenofovir treatment augments anti-viral immunity against drug-resistant SIV challenge in chronically infected rhesus macaques

BACKGROUND

Emergence of drug-resistant strains of human immunodeficiency virus type 1 (HIV-1) is a major obstacle to successful antiretroviral therapy (ART) in HIV-infected patients. Whether antiviral immunity can augment ART by suppressing replication of drug-resistant HIV-1 in humans is not well understood, but can be explored in non-human primates infected with simian immunodeficiency virus (SIV). Rhesus macaques infected with live, attenuated SIV develop robust SIV-specific immune responses but remain viremic, often at low levels, for periods of months to years, thus providing a model in which to evaluate the contribution of antiviral immunity to drug efficacy. To investigate the extent to which SIV-specific immune responses augment suppression of drug-resistant SIV, rhesus macaques infected with live, attenuated SIVmac239Deltanef were treated with the reverse transcriptase (RT) inhibitor tenofovir, and then challenged with pathogenic SIVmac055, which has a five-fold reduced sensitivity to tenofovir.

RESULTS

Replication of SIVmac055 was detected in untreated macaques infected with SIVmac239Deltanef, and in tenofovir-treated, naïve control macaques. The majority of macaques infected with SIVmac055 experienced high levels of plasma viremia, rapid CD4+ T cell loss and clinical disease progression. By comparison, macaques infected with SIVmac239Deltanef and treated with tenofovir showed no evidence of replicating SIVmac055 in plasma using allele-specific real-time PCR assays with a limit of sensitivity of 50 SIV RNA copies/ml plasma. These animals remained clinically healthy with stable CD4+ T cell counts during three years of follow-up. Both the tenofovir-treated and untreated macaques infected with SIVmac239Deltanef had antibody responses to SIV gp130 and p27 antigens and SIV-specific CD8+ T cell responses prior to SIVmac055 challenge, but only those animals receiving concurrent treatment with tenofovir resisted infection with SIVmac055.

CONCLUSION

These results support the concept that anti-viral immunity acts synergistically with ART to augment drug efficacy by suppressing replication of viral variants with reduced drug sensitivity. Treatment strategies that seek to combine immunotherapeutic intervention as an adjunct to antiretroviral drugs may therefore confer added benefit by controlling replication of HIV-1, and reducing the likelihood of treatment failure due to the emergence of drug-resistant virus, thereby preserving treatment options.

Prime-boost immunization with DNA, recombinant fowlpox virus and VLP(SHIV) elicit both neutralizing antibodies and IFNgamma-producing T cells against the HIV-envelope protein in mice that control env-bearing tumour cells

Different primings with DNA and fowlpox virus (FP) recombinants or FP alone were used in a pre-clinical trial to evaluate and compare immunogenicity and efficacy against HIV/SHIV. Three immunization regimens were tested in three groups of mice in which the SIV gag/pol and HIV-1 env transgenes were separately expressed by DNA and FP vectors, followed by VLP(SHIV) boosting. All of the protocols were effective in eliciting homologous neutralizing antibodies, although the mice immunized with DNA followed by FP recombinants or DNA+FP recombinants showed both high titres of neutralizing antibodies and high frequencies of env-specific IFNgamma-producing T lymphocytes. Vaccine efficacy, as demonstrated by growth control of env-expressing tumours, was obtained in both of these two groups of mice. These results establish a preliminary profile for the combined use of these recombinant vectors in protocols to be tested in the SHIV-macaque model of HIV-1 infection.

An adaptation of recombinant vaccinia-based ELISPOT and intracellular cytokine staining for a comparative measurement of cellular immune responses in HIV-1 and HIV-2 infections in West Africa

An efficient and quantitative tool for rapid assessment of human immunodeficiency virus (HIV)-induced cellular immune responses is important for resource-limited settings, such as in sub-Saharan Africa. Modifications are required to previously reported methods for evaluating ex-vivo antigen-specific cellular responses based on direct recombinant vaccinia virus (rVV) stimulation of peripheral blood mononuclear cells (PBMCs) by enzyme linked immunosorbent assay (ELISPOT) and by flow cytometry intracellular cytokine assay (ICA). We made such modifications in order to detect specific responses and compared quantitative cellular immune responses in HIV-1 and HIV-2 infected Gambians. The sensitivity of the rVV-based ELISPOT assay was on average 1.25 interferon (IFN)-gamma spot forming cells (SFC) per 50 000 PBMCs specific for either infection, and 5 IFN-gamma-secreting CD8+ T cells/50 000 in the ICA. The level of IFN-gamma SFC detected by ELISPOT and by ICA were correlated (P < 0.02). ICA detected pol-specific responses in 88% and 67% of HIV-1 and HIV-2 subjects, respectively, and gag-specific responses in more than 80% of both infections. Lower proportions of responders were obtained with ELISPOT, for which pol responses were present in 60% of HIV-1 and 46% of HIV-2 infected patients, and gag responses in 55% and 69%, respectively. The assays did not show any significant difference in cellular immune responses between HIV-1 and HIV-2 infected subjects with CD4% >or= 20%. These outcomes are comparable with results obtained using standard techniques and thus this method is a suitable, rapid and less expensive assessment of cellular immunity.

Time dependence of protective post-exposure prophylaxis with human monoclonal antibodies against pathogenic SHIV challenge in newborn macaques

In a primate model of postnatal virus transmission, we have previously shown that 1 h post-exposure prophylaxis (PEP) with a triple combination of neutralizing monoclonal antibodies (nmAbs) conferred sterilizing protection to neonatal macaques against oral challenge with pathogenic simian-human immunodeficiency virus (SHIV). Here, we show that nmAbs can also partially protect SHIV-exposed newborn macaques against infection or disease, when given as 12 or 24 h PEP, respectively. This work delineates the potential and the limits of passive immunoprophylaxis with nmAbs. Even though 24 h PEP with nmAbs did not provide sterilizing immunity to neonatal monkeys, it contained viremia and protected infants from acute disease. Taken together with our results from other PEP studies, these data show that the success of passive immunization depends on the nmAb potency/dose and the time window between virus exposure and start of immunotherapy.

Evaluation of the interlaboratory concordance in quantification of human immunodeficiency virus-specific T cells with a gamma interferon enzyme-linked immunospot assay

The gamma interferon (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay is a reference method for the ex vivo monitoring of antigen-specific T cells and a primary tool for assessing clinical trials of human immunodeficiency virus (HIV) or cancer vaccines. Four experienced laboratories in Paris compared their results with this method by exchanging frozen blood samples from eight HIV-seronegative and eight HIV-seropositive subjects. Each laboratory measured the IFN-gamma-producing cells specific for HIV, Epstein-Barr virus, cytomegalovirus, and influenza using the same set of peptides and the same ELISPOT reader but its own ELISPOT technique. The cutoff values for positive responses (50 or 100 spot-forming cells/10(6) peripheral blood mononuclear cells over background) were consistent with the binomial statistic criterion. The global qualitative concordance, as assessed by the kappa index, ranged from 0.38 to 0.92, that is, moderate to excellent, and was better for non-HIV 9-mer peptide pools than for HIV 15-mer peptide pools. The interlaboratory coefficient of variation for the frequency of virus-specific T cells was 18.7% (data are expressed on a log scale). Clustering analysis of HIV-positive subjects showed qualitative agreement for ELISPOT results from all four laboratories. Overall, the good interlaboratory qualitative concordance of IFN-gamma ELISPOT assays with only the peptide source and ELISPOT reader in common suggests that a qualitative comparison of interlaboratory findings is feasible. Nonetheless, a single set of standard operating procedures should be used in multicenter trials to improve standardization.

HIV-1-specific CD4+ T cell responses in chronically HIV-1 infected blippers on antiretroviral therapy in relation to viral replication following treatment interruption

The impact of transient viral load blips on anti-HIV-1 immune responses and on HIV-1 rebound following treatment interruption (TI) is not known. Clinical and immunological parameters were measured during 40 weeks of antiretroviral therapy (ART) and following TI in an observational cohort of 16 chronically HIV-1-infected subjects with or without observed viral load blips during ART. During therapy, blips in seven subjects were associated with higher anti-HIV-1 (p24) CD4+ T cell lymphoproliferative responses (p = 0.04), without a significant difference in T cell activation or total anti-HIV-1 CD8+ T cell interferon-gamma (IFN-gamma) responses when compared to nine matched non-blippers. Therapy interruption resulted in a significantly higher viral rebound in blippers by 8 week despite retention of higher lymphoproliferative p24 responses (p = 0.01) and a rise in CD3+ T cell activation (p = 0.04) and anti-HIV-1 CD8+ T cell responses in blippers by week 4 when compared to non-blippers. Past week 4 of interruption, therapy re-initiation criteria were also met by a higher frequency in blippers by week 14 (p < 0.04) with no difference between groups by week 24. These data support that blippers have higher anti-HIV lymphoproliferative responses while on ART but experience equal to higher viral rebound as compared to matched non-blippers upon TI.

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.

Helminth infection suppresses T-cell immune response to HIV-DNA-based vaccine in mice

A number of HIV-1 vaccines are in various phases of clinical trials and many more are in the developmental pipeline. Vaccines are especially needed for developing countries where morbidity and mortality due to HIV/AIDS is most severe, the prevalence of HIV infection is highest, and its incidence is often still rising dramatically. Individuals living in these regions are often infected with one or more helminth parasites which systemically bias the immune system towards Th2-type as well as drive immune anergy. The goal of this study was to develop a multi-T-cell epitope DNA-based vaccine for HIV-1 subtype C and to determine the impact of helminth infection on the immune response to this vaccine. We found that vaccination of naïve mice with the multi-epitope vaccine, designated TD158, induced a strong HIV-1C-specific T-cell immune response, and that the addition of the Igkappa leader sequence to the TD158 vaccine construct significantly increased the frequencies of IFN-gamma secreting CD8+ T cells. However, the TD158 vaccine specific response of mice infected with the human helminth Schistosoma mansoni was significantly suppressed. The impact of schistosome infection on suppressing the virus-specific immune response was the same whether mice were vaccinated with the TD158 vaccine or with the Igkappa enhanced TD158. The results of this study suggest that helminth infection may pose a serious problem for vaccination with the DNA-based HIV-1 vaccine in developing country populations, and that the prevalence of helminth infections in the vaccine cohorts should be taken into account for HIV-1 vaccine trial design.

Statistical evaluation of HIV vaccines in early clinical trials

The HIV pandemic is a pressing threat to global public health; HIV vaccine development is critical. Clinical evaluation of HIV vaccine candidates differs from the standard therapeutics trial framework primarily due to the fact that healthy individuals are studied. We present an early stage evaluation program developed for the HIV Vaccine Trials Network (HVTN) motivated by characteristics unique to the vaccine setting. The program consists of 3 prototypical stages (Phase I, Ib, II) that provide a unified yet flexible approach to the safety and immunogenicity evaluation of diverse vaccine regimens. The goal of these early trials is to narrow the number of candidate vaccines to the most promising candidates worthy of further study in efficacy trials.

CD8 T cell effector maturation in HIV-1-infected children

HIV-1 infection generates maturational responses in overall CD4 and CD8 T cell populations in adults, with elevated expression of lytic effector molecules perforin and granzyme B, and reduced expression of CCR7 and CD45RA. Here, we have found that these marked effects were significantly less pronounced in children, both in terms of the skewed CCR7/CD45RA expression profile as well as the increased perforin expression. Similar to adults, HIV-specific CD8 cells in children were largely CD27+ CD45RA- and lacked perforin. However, one pediatric subject with late-stage infection displayed robust expansion of Gag 77-85-specific CD8 T cells which were perforin+ and lytic, but lacked expression of CD27 and IFNgamma. Our data indicate that the T cell effector maturation induced by HIV-1 infection is markedly weaker in children as compared to adults. The data also suggest, however, that the perforin-deficient state of HIV-specific CD8 T cells in children may be reversible.

Detection of T lymphocytes specific for human endogenous retrovirus K (HERV-K) in patients with seminoma

Human endogenous retrovirus K (HERV-K) is distinctive among the retroviruses that comprise about 8% of the human genome in that multiple HERV-K proviruses encode full-length viral proteins, and many HERV-K proviruses formed during recent human evolution. HERV-K gag proteins are found in the cytoplasm of primary tumor cells of patients with seminoma. We identified HERV-K-specific T cells in patients with a past history of seminoma using the interferon-gamma ELISPOT assay and an MHC-HERV-K peptide-specific tetramer. A minority of apparently healthy subjects without evident germ cell tumors also made HERV-K-specific T cell responses. In summary, we detected T cell reactivity to HERV-K peptides in both past seminoma patients and a minority of apparently healthy controls.

Cross-clade CD8(+) T-cell responses with a preference for the predominant circulating clade

Human immunodeficiency virus (HIV) genetic diversity is a major impediment to the design of a successful vaccine. Even if an HIV vaccine is proven effective, it remains to be seen whether this protection will extend to inter-clade, intra-clade, and recombinant strains. We used recombinant vaccinia-based interferon gamma (IFN) Elispot assays to test the inter-clade crossreactivity of clades A, B, C, and D HIV Env in two cohorts of HIV-infected Kenyans. Despite the tremendous diversity in this HIV protein, a substantial proportion of multi-clade responses were observed. Although these multi-clade responses correlated well with each other in regression analyses, clade A responses were seen at a higher frequency and at greater relative magnitudes in a proportion of these patients, when compared to the other three clades. Epitope mapping indicates CD8(+) T cell recognition of conserved regions of Env, accounting for the high degree of cross-reactivity but not the clade A preference. A better understanding of cross-clade CD8(+) T cell responses to HIV may help to predict whether a successful vaccine could be used to stop geographically and genetically distinct HIV epidemics.

Evaluation of CD8+ T-cell and antibody responses following transient increased viraemia in rhesus macaques infected with live, attenuated simian immunodeficiency virus

In vivo depletion of CD8+ T cells results in an increase in viral load in macaques chronically infected with simian immunodeficiency virus (SIVmac239deltanef). Here, the cellular and humoral immune responses associated with this transient period of enhanced viraemia in macaques infected with SIVmac239deltanef were characterized. Fourteen days after in vivo CD8+ T-cell depletion, two of six macaques experienced a 1-2 log10 increase in anti-gp130 and p27 antibody titres and a three- to fivefold increase in gamma interferon-ecreting SIV-specific CD8+ T cells. Three other macaques had modest or no increase in anti-gp130 antibodies and significantly lower titres of anti-p27 antibodies, with minimal induction of functional CD8+ T cells. Four of the five CD8-depleted macaques experienced an increase in neutralizing antibody titres to SIVmac239. Induction of SIV-specific immune responses was associated with increases in CD8+ T-cell proliferation and fluctuations in the levels of signal-joint T-cell receptor excision circles in peripheral blood cells. Five months after CD8+ T-cell depletion, only the two high-responding macaques were protected from intravenous challenge with pathogenic SIV, whilst the remaining animals were unable to control replication of the challenge virus. Together, these findings suggest that a transient period of enhanced antigenaemia during chronic SIV infection may serve to augment virus-specific immunity in some, but not all, macaques. These findings have relevance for induction of human immunodeficiency virus (HIV)-specific immune responses during prophylactic and therapeutic vaccination and for immunological evaluation of structured treatment interruptions in patients chronically infected with HIV-1.

Combined megaplex TCR isolation and SMART-based real-time quantitation methods for quantitating antigen-specific T cell clones in mycobacterial infection

Despite recent advances in measuring cellular immune responses, the quantitation of antigen-specific T cell clones in infections or diseases remains challenging. Here, we employed combined megaplex TCR isolation and SMART-based real-time quantitation methods to quantitate numerous antigen-specific T cell clones using limited amounts of specimens. The megaplex TCR isolation covered the repertoire comprised of recombinants from 24 Vbeta families and 13 Jbeta segments, and allowed us to isolate TCR VDJ clonotypic sequences from one or many PPD-specific IFNgamma-producing T cells that were purified by flow cytometry sorting. The SMART amplification technique was then validated for its capacity to proportionally enrich cellular TCR mRNA/cDNA for real-time quantitation of large numbers of T cell clones. SMART amplified cDNA was shown to maintain relative expression levels of TCR genes when compared to unamplified cDNA. While the SMART-based real-time quantitative PCR conferred a detection limit of 10(-5) to 10(-6) antigen-specific T cells, the clonotypic primers specifically amplified and quantitated the target clone TCR but discriminated other clones that differed by >or=2 bases in the DJ regions. Furthermore, the combined megaplex TCR isolation and SMART-based real-time quantiation methods allowed us to quantitate large numbers of PPD-specific IFNgamma-producing T cell clones using as few as 2 x 10(6) PBMC collected weekly after mycobacterial infection. This assay system may be useful for studies of antigen-specific T cell clones in tumors, autoimmune and infectious diseases.

Seroconversion following nonoccupational postexposure prophylaxis against HIV

BACKGROUND

The efficacy of antiretroviral postexposure prophylaxis (PEP) against infection with human immunodeficiency virus (HIV) following occupational exposures has prompted the use of PEP after nonoccupational exposures. There are, however, important differences between occupational and nonoccupational exposures, and the effectiveness of PEP following nonoccupational exposure is unknown. We sought to describe the occurrence and circumstances of HIV seroconversion following nonoccupational PEP.

METHODS

HIV uninfected individuals reporting potential sexual or injection drug use exposures to HIV in the preceding 72 h received a 28-day regimen of antiretroviral therapy and counseling in a nonrandomized trial. The level of HIV antibody was measured 12 weeks after PEP initiation.

RESULTS

Of 877 exposed subjects, 702 were evaluable 12 weeks after exposure. Seroconversion was detected in 7 subjects (1%; 95% confidence interval, 0.4%-2%). Three seroconverters reported having no exposures after PEP initiation and, thus, probably represent evidence of chemoprophylactic failure. In the other 4 subjects, additional exposures to HIV after PEP initiation or detection of HIV RNA in plasma specimens obtained at baseline precluded determination of the source of seroconversion. No exposure source was available to assess genetic concordance with the seroconverter's virus.

CONCLUSIONS

As for occupational exposure, PEP is not completely effective in preventing HIV infection following nonoccupational exposure. Therefore, primary prevention remains essential. In contrast to the occupational setting, the potential source of exposure is rarely available for testing in the nonoccupational setting, and exposures are often not isolated. Thus, it is often impossible to determine whether seroconversion resulted from failure of PEP or from other exposures, posing difficulties for future comparative studies seeking to evaluate the effectiveness of PEP.

Sustained CD8+ T-cell responses induced after acute parvovirus B19 infection in humans

Murine models have suggested that CD8+ T-cell responses peak early in acute viral infections and are not sustained, but no evidence for humans has been available. To address this, we longitudinally analyzed the CD8+ T-cell response to human parvovirus B19 in acutely infected individuals. We observed striking CD8+ T-cell responses, which were sustained or even increased over many months after the resolution of acute disease, indicating that CD8+ T cells may play a prominent role in the control of parvovirus B19 and other acute viral infections of humans, including potentially those generated by live vaccines.

A vaccinia-based elispot assay for detection of CD8+ T cells from HIV-1 infected children

HIV-specific CD8+ T lymphocytes participate in the control of viral replication in infected patients. These responses are of low intensity in young infants and are decreased by antiretroviral therapy. In the present study, we report on a recombinant Vaccinia virus (rVV)-based Elispot assay for the detection of HIV-specific CD8+ T cells immediately after isolation of peripheral blood mononuclear cells (PBMC). The rVV-based assay was highly sensitive; 48 out of 50 children had a positive response against the rVV encoding HIV Env-Gag-Pol antigen. Interferon-gamma was produced by CD8+ T cells, and CD14+/15+ cells were the main cell subset presenting antigens expressed by rVV. We observed that the cell input per well had a critical influence on the sensitivity of the assay. Results from the ex vivo Elispot assay correlated poorly with those of the 51Cr release assay performed after expansion of PBMC in vitro; thus, both assays gave information on different subsets and/or functions of the HIV-specific T cell response.