CD8(+) T-cell gamma interferon production specific for human immunodeficiency virus type 1 (HIV-1) in HIV-1-infected subjects

Genomic foundations of evolution and ocular pathogenesis in human adenovirus species D

Human adenovirus commonly causes infections of respiratory, gastrointestinal, genitourinary, and ocular surface mucosae. Although most adenovirus eye infections are mild and self-limited, specific viruses within human adenovirus species D are associated with epidemic keratoconjunctivitis (EKC), a severe and highly contagious ocular surface infection, which can lead to chronic and/or recurrent, visually disabling keratitis. In this review, we discuss the links between adenovirus ontogeny, genomics, immune responses, and corneal pathogenesis, for those viruses that cause EKC.

Normal Distribution of CD8+ T-Cell-Derived ELISPOT Counts within Replicates Justifies the Reliance on Parametric Statistics for Identifying Positive Responses

Accurate assessment of positive ELISPOT responses for low frequencies of antigen-specific T-cells is controversial. In particular, it is still unknown whether ELISPOT counts within replicate wells follow a theoretical distribution function, and thus whether high power parametric statistics can be used to discriminate between positive and negative wells. We studied experimental distributions of spot counts for up to 120 replicate wells of IFN-γ production by CD8+ T-cell responding to EBV LMP2A (426 - 434) peptide in human PBMC. The cells were tested in serial dilutions covering a wide range of average spot counts per condition, from just a few to hundreds of spots per well. Statistical analysis of the data using diagnostic Q-Q plots and the Shapiro-Wilk normality test showed that in the entire dynamic range of ELISPOT spot counts within replicate wells followed a normal distribution. This result implies that the Student t-Test and ANOVA are suited to identify positive responses. We also show experimentally that borderline responses can be reliably detected by involving more replicate wells, plating higher numbers of PBMC, addition of IL-7, or a combination of these. Furthermore, we have experimentally verified that the number of replicates needed for detection of weak responses can be calculated using parametric statistics.

Positioning of APOBEC3G/F mutational hotspots in the human immunodeficiency virus genome favors reduced recognition by CD8+ T cells

Due to constitutive expression in cells targeted by human immunodeficiency virus (HIV), and immediate mode of viral restriction upon HIV entry into the host cell, APOBEC3G (A3G) and APOBEC3F (A3F) have been considered primarily as agents of innate immunity. Recent bioinformatic and mouse model studies hint at the possibility that mutation of the HIV genome by these enzymes may also affect adaptive immunity but whether this occurs in HIV-infected individuals has not been examined. We evaluated whether APOBEC-mediated mutations within common HIV CD8⁺ T cell epitopes can potentially enhance or diminish activation of HIV-specific CD8⁺ T cells from infected individuals. We compared ex vivo activation of CD8⁺ T lymphocytes from HIV-infected individuals by wild type HIV peptide epitopes and synthetic variants bearing simulated A3G/F-induced mutations by measuring interferon-γ (IFN-γ) production. We found that A3G/F-induced mutations consistently diminished HIV-specific CD8⁺ T cell responses against the common epitopes we tested. If this reflects a significant trend in vivo, then adaptation by HIV to enrich sequences that are favored for mutation by A3G/F (A3G/F hotspots) in portions of its genome that encode immunogenic CD8⁺ T cell epitopes would favor CTL escape. Indeed, we found the most frequently mutated A3G motif (CCC) is enriched up to 6-fold within viral genomic sequences encoding immunodominant CD8⁺ T cell epitopes in Gag, Pol and Nef. Within each gene, A3G/F hotspots are more abundant in sequences encoding epitopes that are commonly recognized due to their HLA restriction. Thus, in our system, mutations of the HIV genome, mimicking A3G/F activity, appeared to abrogate or severely reduce CTL recognition. We suggest that the physiological significance of this potential effect in facilitating CTL escape is echoed in the adaptation of the HIV genome to enrich A3G/F hotspots in sequences encoding CTL epitopes that are more immunogenic at the population level.

Safety, tolerability, and immunogenicity of repeated doses of dermavir, a candidate therapeutic HIV vaccine, in HIV-infected patients receiving combination antiretroviral therapy: results of the ACTG 5176 trial

BACKGROUND

HIV-specific cellular immune responses are associated with control of viremia and delayed disease progression. An effective therapeutic vaccine could mimic these effects and reduce the need for continued antiretroviral therapy. DermaVir, a topically administered plasmid DNA-nanomedicine expressing HIV (CladeB) virus-like particles consisting of 15 antigens, induces predominantly central memory T-cell responses.

METHODS

Treated HIV-infected adults (HIV RNA <50 and CD4 >350) were randomized to placebo or escalating DermaVir doses (0.1 or 0.4 mg of plasmid DNA at weeks 1, 7, and 13 in the low- and intermediate-dose groups and 0.8 mg at weeks 0, 1, 6, 7, 12, and 13 in the high-dose group), n = 5-6 evaluable subjects per group. Immunogenicity was assessed by a 12-day cultured interferon-γ enzyme-linked immunosorbent spot assay at baseline and at weeks 9, 17, and 37 using 1 Tat/Rev and 3 overlapping Gag peptide pools (p17, p24, and p15).

RESULTS

Groups were comparable at baseline. The study intervention was well tolerated, without dose-limiting toxicities. Most responses were highest at week 17 (4 weeks after last vaccination) when Gag p24 responses were significantly greater among intermediate-dose group compared with control subjects [median (IQR): 67,600 (5633-74,368) versus 1194 (9-1667)] net spot-forming units per million cells, P = 0.032. In the intermediate-dose group, there was also a marginal Gag p15 response increase from baseline to week 17 [2859 (1867-56,933), P = 0.06], and this change was significantly greater than in the placebo group [0 (-713 to 297), P = 0.016].

CONCLUSIONS

DermaVir administration was associated with a trend toward greater HIV-specific, predominantly central memory T-cell responses. The intermediate DermaVir dose tended to show the greatest immunogenicity, consistent with previous studies in different HIV-infected patient populations.

Natural killer cell inhibits human immunodeficiency virus replication in chronically infected immune cells

Natural killer (NK) cells are a crucial component of the host innate immune system. We investigated the noncytolytic anti-human immunodeficiency virus (HIV) activity of NK cells in chronically HIV-infected immune cells. Supernatants collected from NK cell cultures (both primary NK cells and NK cell lines, YTS and NK 92) inhibited HIV activation in peripheral blood mononuclear cells (PBMCs) from HIV-infected subjects. NK supernatants (NK SN) also suppressed tumor necrosis factor (TNF)-alpha-induced HIV activation in chronically infected cell lines (U1 and ACH-2 cells). The antibody to interferon (IFN)-gamma blocked NK SN-mediated anti-HIV effect, while the antibodies to CC-chemokines had no impact on NK SN-mediated HIV inhibition in U1 and ACH-2 cells. Investigation of mechanism(s) responsible for the NK action showed that NK SN inhibited TNF-alpha-mediated activation of HIV-long-terminal repeat (LTR), and upregulated the expression of signal transducer and activator of transcription (STAT)-1 and phosphorylated P38 mitogen-activated protein kinase (MAPK). The P38 MAPK inhibitor (SB 203580) blocked NK SN-mediated HIV inhibition. These data provide compelling evidence that NK cells have a critical role in controlling HIV activation in the reservoirs.

Activation of HIV type 1 specific cytotoxic T lymphocytes from semen by HIV type 1 antigen-presenting dendritic cells and IL-12

Seminal HIV-1-specific cytotoxic T lymphocytes (CTLs) could provide an important immune defense against local HIV-1 infection, and be important in impeding the spread of HIV-1 infection. In this study, we demonstrate that autologous blood-derived dendritic cells (DCs) loaded in vitro with synthetic HIV-1 peptides representing known CTL epitopes activated HLA class I restricted, anti-HIV-1 CTLs and interferon gamma responses in seminal CD8+ T cells from subjects with chronic HIV-1 infection on antiretroviral therapy. CTLs specific for the same HLA-restricted epitopes were detected in semen and blood of the same individuals by stimulation with peptide-loaded DCs. Anti-HIV-1 CTL responses from semen were enhanced by stimulation with DCs loaded with HIV-1 peptides and interleukin 12. Our results suggest that blood-derived DCs have HIV-1 antigen-presenting capacity for seminal CTL in HIV-1-infected subjects. The DC-T cell system can serve as a model for immunotherapy of HIV-1 infection in the local genital tract as well as systemic blood circulation.

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.

Processing and presentation of exogenous HLA class I peptides by dendritic cells from human immunodeficiency virus type 1-infected persons

Dendritic cells (DCs) loaded with viral peptides are a potential form of immunotherapy of human immunodeficiency virus type 1 (HIV-1) infection. We show that DCs derived from blood monocytes of subjects with chronic HIV-1 infection on combination antiretroviral drug therapy have increases in expression of HLA, T-cell coreceptor, and T-cell activation molecules in response to the DC maturation factor CD40L comparable to those from uninfected persons. Mature DCs (mDCs) loaded with HLA A*0201-restricted viral peptides of the optimal length (9-mer) were more efficient at activating antiviral CD8(+) T cells than were immature DCs or peptide alone. Optimal presentation of these exogenous peptides required uptake and vesicular trafficking and was comparable in DCs derived from HIV-1-infected and uninfected persons. Furthermore, DCs from HIV-1-infected and uninfected persons had similar capacities to process viral peptides with C-terminal and N-terminal extensions through their proteasomal and cytosolic pathways, respectively. We conclude that DCs derived from HIV-1-infected persons have similar abilities to process exogenous peptides for presentation to CD8(+) T cells as those from uninfected persons. This conclusion supports the use of DCs loaded with synthetic peptides in immunotherapy of HIV-1 infection.

Statistical considerations for the design and analysis of the ELISpot assay in HIV-1 vaccine trials

Effector T lymphocyte responses are considered critical for controlling human immunodeficiency virus type-1 (HIV-1) infection. The enzyme-linked immunospot (ELISpot) assay has emerged as a primary means of assessing HIV-specific T cell responses, and the development of objective methods that distinguish positive and negative ELISpot responses while properly controlling the rate of false positives is critical. In this paper, we consider several statistical methods that are helpful in defining such a positive criterion. Simulation results under a variety of scenarios suggest that a permutation-based criterion using a resampling adjustment for multiple comparisons yields the desired false positive rate while remaining competitive with other potential criteria in terms of sensitivity. These results also provide guidance on the effect of the number of experimental and negative control replicate wells on assay sensitivity. Application of different potential positive criteria using ELISpot assay results from IFN-gamma-secreting T cells of HIV-1 seropositive and seronegative donors confirmed several of the results obtained under simulation. Our findings support the application of statistically-based positive criteria such as the permutation-based resampling approach in assessing HIV vaccine-induced T cell responses. Moreover, the proposed methods have potential utility in related HIV immunopathogenesis studies and in non-HIV clinical vaccine trials.

Cytokine flow cytometry: a multiparametric approach for assessing cellular immune responses to viral antigens

Considerable attention has been focused on CD8 and CD4 T cell responses as a major element of the cellular immune response to viral infections including human immunodeficiency virus (HIV) and hepatitis C virus (HCV). However, increasing evidence based on the recent introduction of more quantitative assays for measuring antigen-specific T cells has suggested that the role of these cells in the development of a protective immune response to a particular viral pathogen may be determined by a complex interplay of multiple virologic and cellular factors. Thus, measurements of only the frequencies of the T cell subsets participating in the response to viral pathogens may be an incomplete reflection of efficacy. In this review, we suggest that some measurable factors may influence the role of T cell immunity in conferring protection, including functional avidity, epitope breadth and specificity, proliferative capacity, cytokine repertoire, degree of anergy, and differentiation phenotype, as well as magnitude, of viral-specific CD4 and CD8 T cells. We suggest that automated cytokine flow cytometry (CFC) is an efficient approach to the measurement of the complex interplay of multiple immune parameters involved in immune protection. These ideas are discussed in the context of new developments in sample preparation and analysis automation.

Detection of high frequencies of HIV-1 cross-subtype reactive CD8 T lymphocytes in the peripheral blood of HIV-1-infected Kenyans

OBJECTIVES

To quantitate rapidly the frequency of HIV-1 subtype-specific and broadly HIV-1 cross-subtype-reactive CD8 T cells in the peripheral blood of HIV-1-infected individuals from a geographical region of multiple subtype endemicity.

METHODS

Autologous B-lymphoblastoid cell lines infected with recombinant vaccinia-viruses expressing gag, env and nef gene products from HIV-1 subtypes A-H were used as antigen-presenting cells to stimulate CD8 T cells from cryopreserved peripheral blood mononuclear cells. Cross-subtype and subtype-specific CD8 cell responses were assessed by flow cytometry for the upregulation of IFN-gamma gene expression in specifically activated CD8 T cells.

RESULTS

Strikingly high frequencies of circulating CD8 T cells (up to 11.3% of peripheral CD8 T cells) with specificity for HIV-1 were detectable using this methodology. Both subtype-specific and broadly cross-subtype-reactive CD8 T cells were detected as assessed by IFN-gamma production after stimulation. The pattern of cross-subtype reactivity appeared to be random when the results were assessed as a population, but analysis of the full-length sequence of the infecting virus for each individual showed some skewing of the CD8 cell response towards the infecting subtype.

CONCLUSION

High frequencies of HIV-1 cross-subtype-reactive peripheral CD8 T cells can be detected in individuals from a multiple subtype endemic region, providing an incentive for vaccine advancement in such locations. The future assessment of the subtype specificity of cellular immune responses requires full-length sequencing of the infecting virus in conjunction with a comprehensive analysis of phenotypic and functional parameters.

Cross-clade T lymphocyte-mediated immunity to HIV type 1: implications for vaccine design and immunodetection assays

Identifying immunodominant regions of HIV-1 that are recognized by CD8(+) T lymphocytes in infected individuals may be important for the design and evaluation of candidate HIV-1 vaccines, particularly for developing countries. In this study, cryopreserved peripheral blood mononuclear cells (PBMCs) from 15 chronically HIV-1-infected U.S. volunteers were screened for HIV-1 Gag-specific T lymphocyte interferon gamma production in an enzyme-linked immunospot (ELISpot) assay matrix format, using overlapping HIV-1 subtype A, B, and C Gag peptide pools. In the initial matrix screen, responses to HIV-1 subtype B Gag were detected in 11 of 15 (73%) of seropositive individuals and in none of 4 HIV-1-seronegative controls. There were differences in both the breadth and magnitudes of the responses observed in the matrix assay. Responses varied in breadth, ranging from broad responses (more than four peptides) of moderate magnitude (<100 spot-forming cells [SFCs]/10(5) PBMCs) to narrowly focused (two or fewer peptides), more potent responses (>150 SFC/10(5) PBMCs). Responses to A, B, and C clade peptides of HIV-1 Gag revealed that all responders to subtype B peptides were also found to recognize corresponding peptides from at least one of the other clades. The ability to recognize cross-clade peptides with one or two amino acid substitutions relative to the B clade peptide was both peptide and patient dependent. Overall, our results show that the ELISpot matrix algorithm described here may be an efficient approach for characterizing cross-clade CD8(+) T cell responses in either seropositive individuals or in seronegative HIV-1 vaccine recipients.

The ELISPOT assay: an easily transferable method for measuring cellular responses and identifying T cell epitopes

Characterization of human leukocyte antigen (HLA) class I restricted epitopes derived from viral pathogens is imperative for formulating therapeutic interventions, as well as for vaccine design and monitoring. Sensitive, easy and cost-effective assays that measure the frequency of antigen-specific T lymphocytes are crucial for evaluating and improving vaccines and therapies. This paper reviews the ELISPOT technique that allows for quantifying HIV-specific T lymphocytes at the single cell level from peripheral blood by detection of antigen-induced cytokine secretion. The assay can be used successfully to quantify T cell immune responses in humans infected with different pathogens and to assess T cell immunogenicity of vaccines in phase I/II and III clinical trials. This review focuses on the ELISPOT methodology and discusses how it can be standardized and potentially used by multiple international laboratories attached to clinical trial sites.

Comprehensive screening for human immunodeficiency virus type 1 subtype-specific CD8 cytotoxic T lymphocytes and definition of degenerate epitopes restricted by HLA-A0207 and -C(W)0304 alleles

For this report, the rapid identification and characterization of human immunodeficiency virus type 1 (HIV-1)-derived broadly cross-subtype-reactive CD8 cytotoxic T lymphocyte (CTL) epitopes were performed. Using a gamma interferon (IFN-gamma) Elispot assay-based approach and a panel of recombinant vaccinia viruses expressing gag, env, pol, and nef genes representing the seven most predominant subtypes and one circulating recombinant form of HIV-1, the subtype specificity and cross-subtype reactivity of a CD8 response were directly measured from circulating peripheral blood mononuclear cells (PBMC). Enhanced sensitivity of detection of CD8 responses from cryopreserved PBMC was achieved using autologous vaccinia virus-infected B-lymphoblastoid cell lines as supplemental antigen-presenting cells. Of eleven subjects studied, six exhibited broadly cross-subtype-reactive CD8-mediated IFN-gamma production (at least seven of eight subtypes recognized) to at least one major gene product from HIV-1. Screening of subjects showing broadly cross-subtype-specific responses in the vaccinia virus-based enzyme-linked immunospot (Elispot) assay using a panel of overlapping peptides resulted in the identification of cross-subtype responses down to the 20-mer peptide level in less than 3 days. Three subjects showed broad cross-subtype reactivity in both the IFN-gamma Elispot assay and the standard chromium release cytotoxicity assay. Fine mapping and HLA restriction analysis of the response from three subjects demonstrated that this technique can be used to define epitopes restricted by HLA-A, -B, and -C alleles. In addition, the ability of all three epitopes to be processed from multiple subtypes of their parent proteins and presented in the context of HLA class I molecules following de novo synthesis is shown. While all three minimal epitopes mapped here had previously been defined as HIV-1 epitopes, two are shown to have novel HLA restriction alleles and therefore exhibit degenerate HLA binding capacity. These findings provide biological validation of HLA supertypes in HIV-1 CTL recognition and support earlier studies of cross-subtype CTL responses during HIV-1 infection.

Ex vivo detection and enumeration of human antigen-specific CD8+ T lymphocytes using antigen delivery by a recombinant vaccinia expression vector and intracellular cytokine staining

We describe an intracellular cytokine staining, flow cytometry based technique for quantitative and qualitative assessment of CD8+ T lymphocyte-mediated antigen specific immune responses. This adaptation of the technique first described by Suni et al. [J. Immunol. Methods, 212 (1998) 89; Cytometry, 40 (2000) 60] utilises a recombinant vaccinia expression vector to deliver the test antigen to the MHC class I processing pathway. This allows the measurement of antigen-specific CD8+ T cell responses in human subjects, irrespective of HLA type, and un-restricted to responses directed against a single peptide epitope. This method offers an advantage over the ELISPOT methods because the cells producing cytokine in the assay can be readily phenotyped, and it permits the simultaneous analysis of multiple cytokines. Finally, this technique does not require the prior establishment of autologous transformed B cell lines from patients/subjects.

HIV antigens can induce TGF-beta(1)-producing immunoregulatory CD8+ T cells

HIV-infected individuals may progressively lose both HIV-specific and unrelated CTL responses despite the high number of circulating CD8+ T cells. In this study, we report that approximately 25% of HIV+ donors produced TGF-beta(1) in response to stimulation with HIV proteins or peptides. The production of TGF-beta(1) was sufficient to significantly reduce the IFN-gamma response of CD8+ cells to both HIV and vaccinia virus proteins. Ab to TGF-beta reversed the suppression. We found the source of the TGF-beta(1) to be predominantly CD8+ cells. Different peptide pools stimulated TGF-beta(1) and IFN-gamma in the same individual. The TGF-beta(1) secreting cells have distinct peptide specificity from the IFN-gamma producing cells. This represents an important mechanism by which an HIV-specific response can nonspecifically suppress both HIV-specific and unrelated immune responses.

Dressed to kill? A review of why antiviral CD8 T lymphocytes fail to prevent progressive immunodeficiency in HIV-1 infection

CD8 T cells play an important role in protection and control of HIV-1 by direct cytolysis of infected cells and by suppression of viral replication by secreted factors. However, although HIV-1-infected individuals have a high frequency of HIV-1-specific CD8 T cells, viral reservoirs persist and progressive immunodeficiency generally ensues in the absence of continuous potent antiviral drugs. Freshly isolated HIV-specific CD8 T cells are often unable to lyse HIV-1-infected cells. Maturation into competent cytotoxic T lymphocytes may be blocked during the initial encounter with antigen because of defects in antigen presentation by interdigitating dendritic cells or HIV-infected macrophages. The molecular basis for impaired function is multifactorial, due to incomplete T-cell signaling and activation (in part related to CD3zeta and CD28 down-modulation), reduced perforin expression, and inefficient trafficking of HIV-specific CD8 T cells to lymphoid sites of infection. CD8 T-cell dysfunction can partially be corrected in vitro with short-term exposure to interleukin 2, suggesting that impaired HIV-specific CD4 T helper function may play a significant causal or exacerbating role. Functional defects are qualitatively different and more severe with advanced disease, when interferon gamma production also becomes compromised.

Restoration of anti-human immunodeficiency virus type 1 (HIV-1) responses in CD8+ T cells from late-stage patients on prolonged antiretroviral therapy by stimulation in vitro with HIV-1 protein-loaded dendritic cells

We demonstrate that dendritic cells loaded in vitro with human immunodeficiency virus type 1 (HIV-1) protein-liposome complexes activate HLA class I-restricted anti-HIV-1 cytotoxic T-lymphocyte and gamma interferon (IFN-gamma) responses in autologous CD8+ T cells from late-stage HIV-1-infected patients on prolonged combination drug therapy. Interleukin-12 enhanced this effect through an interleukin-2- and IFN-gamma-mediated pathway. This suggests that dendritic cells from HIV-1-infected persons can be engineered to evoke stronger anti-HIV-1 CD8+ T-cell reactivity as a strategy to augment antiretroviral therapy.

Anti-human immunodeficiency virus type 1 (HIV-1) CD8(+) T-lymphocyte reactivity during combination antiretroviral therapy in HIV-1-infected patients with advanced immunodeficiency

The long-term efficacy of combination antiretroviral therapy may relate to augmentation of anti-human immunodeficiency virus type 1 (HIV-1) CD8(+) T-cell responses. We found that prolonged treatment of late-stage HIV-1-infected patients with a protease inhibitor and two nucleoside reverse transcriptase inhibitors failed to restore sustained, high levels of HIV-1-specific, HLA class I-restricted, cytotoxic-T-lymphocyte precursors and gamma interferon (IFN-gamma) production by CD8(+) T cells. In some patients, particularly those initiating three-drug combination therapy simultaneously rather than sequentially, there were early, transient increases in the frequency of anti-HIV-1 CD8(+) T cells that correlated with decreases in HIV-1 RNA and increases in T-cell counts. In the other patients, HIV-1-specific T-cell functions either failed to increase or declined from baseline during triple-drug therapy, even though some of these patients showed suppression of plasma HIV-1 RNA. These effects of combination therapy were not unique to HIV-1 specific T-cell responses, since similar effects were noted for CD8(+) T cells specific for the cytomegalovirus pp65 matrix protein. The level and breadth of CD8(+) cell reactivity to HLA A*02 HIV-1 epitopes, as determined by IFN-gamma production and HLA tetramer staining after combination therapy, were related to the corresponding responses prior to treatment. There was, however, a stable, residual population of potentially immunocompetent HIV-1-specific T cells remaining after therapy, as shown by tetramer staining of CD8(+) CD45RO(+) cells. These results indicate that new strategies will be needed to target residual, immunocompetent HIV-1-specific CD8(+) T cells to enhance the effectiveness of antiretroviral therapy in patients with advanced immunodeficiency.