DC maturation and function are not altered by melanoma-derived immunosuppressive soluble factors

BACKGROUND

Although melanoma can elicit robust tumor antigen-specific immune responses, advanced melanoma is associated with immune tolerance. We have previously described several mechanisms of melanoma-induced immunosuppression, including the skewing of the immune response towards a Th2 cytokine profile and the induction of regulatory T cells. Since dendritic cells (DCs) are potentially important players that can direct other cells of the immune system towards a cytotoxic, humoral, or regulatory phenotype, we hypothesized that melanoma-produced factors directly affect the maturation and function of DCs, influencing the nature and magnitude of the resulting immune response.

MATERIALS AND METHODS

To test this hypothesis, immature myeloid-derived DCs (mdDCs) were derived with cytokines from CD14+ peripheral blood mononuclear cells (PBMCs) and exposed to 20% melanoma-conditioned media (MCM). After 2 d, the expression of maturation markers and the function of these mdDCs, measured by cytokine production, the amount of endocytosis, expression of the inhibitory molecule indoleamine 2,3-dioxygenase (IDO), and the ability to stimulate T cells were determined.

RESULTS

We found that incubation with MCM did not inhibit the expression of maturation markers or IDO, the production of cytokines, the amount of antigen uptake, or the ability to induce T cell proliferation in mixed-lymphocyte reactions by mdDC.

CONCLUSIONS

These results suggest that the immunosuppressive effects of melanoma-produced factors are independent of directly measurable changes in mdDC function or maturation in vitro.

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

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

Human intestinal lamina propria CD1c+ dendritic cells display an activated phenotype at steady state and produce IL-23 in response to TLR7/8 stimulation

Intestinal dendritic cells (DCs) play key roles in mediating tolerance to commensal flora and inflammatory responses against mucosal pathogens. The mechanisms by which intestinal "conditioning" influences human DC responses to microbial stimuli remain poorly understood. Infections with viruses, such as HIV-1, that target mucosal tissue result in intestinal epithelial barrier breakdown and increased translocation of commensal bacteria into the lamina propria (LP). It is unclear whether innate LP DC responses to concurrent viral and bacterial stimuli influence mucosal HIV-1 pathogenesis. In this study, direct ex vivo phenotype and in vitro constitutive cytokine production of CD1c+ DCs in human intestinal LP were compared with those in peripheral blood (PB). To evaluate innate responses to viral and bacterial stimuli, intracellular cytokine production by LP and PB DCs following stimulation with ligands for TLRs 2, 4, 5, and 7/8 was evaluated. At steady state, LP CD1c+ DCs expressed higher levels of activation markers (CD40, CD83, CD86, HLA-DR, and CCR7) than did PB CD1c+ DCs, and higher frequencies of LP CD1c+ DCs constitutively produced IL-6 and -10 and TNF-alpha. LP DCs had blunted cytokine responses to TLR4 ligand and TLR5 ligand stimulation relative to PB DCs, yet similarly produced IL-10 in response to TLR2 ligand. Only synthetic TLR7/8 ligand, a mimic of viral ssRNA, induced IL-23 production by LP CD1c+ DCs, and this proinflammatory cytokine response was synergistically enhanced following combined TLR7/8 and TLR4 stimulation. These findings highlight a potential mechanism by which viruses like HIV-1 may subvert homeostatic mechanisms and induce inflammation in the intestinal mucosa.

Impaired plasmacytoid dendritic cell maturation and differential chemotaxis in chronic hepatitis C virus: associations with antiviral treatment outcomes

BACKGROUND

Dendritic cell (DC) defects may contribute to chronicity in hepatitis C virus (HCV) infection and determine response to PEG-interferon and ribavirin therapy via poor T cell stimulation. Studies to date have produced inconsistent results regarding DC maturation and function: no large study has examined DCs before and after therapy.

AIMS

We examined if DC defects in maturation and chemotaxis are present by comparing therapeutic responders to non-responders.

METHODS

We analysed peripheral DCs of 64 HCV genotype 1-infected patients from the Virahep-C study 2 weeks before and 24 weeks after therapy. We used flow cytometry to enumerate plasmacytoid DC (pDC) and myeloid DCs (mDC) and quantify expression of chemokine receptors and maturation markers. Chemotaxis was measured with an in vitro assay.

RESULTS

Pre-treatment frequencies of pDCs and mDCs were significantly lower in HCV patients than controls and successful therapy normalised pDCs. Levels of CXCR3 and CXCR4 on pDCs were higher at baseline compared to normal controls and decreased with therapy. Pre-therapy levels of co-stimulatory marker CD40 and the maturation marker CD83 were higher in pDCs of patients chronically infected with HCV compared to normal patients, and levels of both markers dropped significantly with therapy in the SVR+ group only. Other maturation markers (CD86 and CCR7) were not elevated suggesting a partially activated phenotype. Baseline chemotaxis of pDCs to CXCL12 and CXCL10 predicted failure of antiviral response and correlated with the histological activity index inflammation score.

CONCLUSIONS

Plasmacytoid DC defects exist in chronic HCV and successful antiviral therapy normalises many phenotypic and functional abnormalities.

Evidence for dendritic cell-dependent CD4(+) T helper-1 type responses to commensal bacteria in normal human intestinal lamina propria

Reactivity of lamina propria (LP) T cells to commensal bacteria has been demonstrated in animal models of inflammatory bowel disease (IBD) and in humans with IBD, but few studies have evaluated the function of such cells in normal individuals. LP mononuclear cells (LPMC) were disaggregated from healthy human intestinal tissue and cultured with heat-killed commensal and pathogenic bacteria. CD3(+)CD4(+) IFN-gamma-producing (Th1) cells reactive to commensal bacteria were demonstrated at frequencies ranging from 0.05 to 2.28% in LPMC. Bacteria-specific Th1 responses were inhibited by anti-HLA-DR antibodies and chloroquine exposure, were enriched in LP relative to peripheral blood, and expressed effector memory cell markers. Bacteria-specific CD4(+) T cell proliferation in vitro was dependent on the presence of LP dendritic cells (DCs), which produced pro-inflammatory cytokines upon bacterial exposure. These results suggest that bacteria-reactive DCs and CD4(+) T cells in normal LP have substantial pro-inflammatory potential that is revealed upon disaggregation in vitro.

Increased survival from stage IV melanoma associated with fewer regulatory T Cells

BACKGROUND

Melanoma often elicits a profound immune response, and this response has been exploited by various immune therapies. These immunotherapies ultimately fail, however, and advanced melanoma is uniformly fatal, suggesting the development of an immune escape mechanism. In this study, markers of immune escape including regulatory T cells (T(regs)), dendritic cells (DCs), and TGF-beta were evaluated in 14 Stage IV melanoma patients and correlated with survival.

MATERIALS AND METHODS

Peripheral blood mononuclear cells were isolated from Stage IV melanoma patients and analyzed for T(regs) and DCs by flow cytometry using fluorescent CD3, CD4, CD25, Lin, HLA-DR, CD11c, and CD123 antibodies. Serum TGF-beta levels were evaluated by ELISA from these patients. Clinical data were extracted from the patients' medical records.

RESULTS

Stage IV melanoma patients with shorter survival (less than 24 mo) had a significantly higher proportion of T(regs) than those with longer survival (15% versus 8%, respectively, P = 0.004). The numbers of DCs and the serum TGF-beta levels were not significantly different in these two groups. There was an inverse relationship between the percentage of T(regs) and survival, although this did not reach statistical significance (r = -0.35, P = 0.22). There was also an inverse relationship between peripheral T(regs) and DCs. When patients were divided into groups of greater than or less than 7% T(regs), the number of total DCs was higher in the patients with fewer T(regs) than in those with more T(regs), but this did not reach statistical significance (16,535 versus 12,126 total DCs/mL, P = 0.52).

CONCLUSIONS

In Stage IV melanoma patients, a high percentage of T(regs) appears to be associated with shorter survival. The inverse relationship of the number of DCs and T(regs) in these patients may provide an insight to the origin of this observation.

Configurational and conformational classification of pyranose sugars

Automated cluster analysis is used to examine the conformation and configuration of pyranose sugars. Previous findings on this issue are confirmed, importantly from an analysis that requires no prior knowledge of the significant factors determining the conformational classification. The findings on the conformations adopted in the crystalline solid state are found to be different to existing quantum chemical calculations performed for D-glucose in the gas phase, but consistent with empirically determined conformations in the solution state. The use of this clustering analysis in studying chirality in the determined structures is discussed, as is the ability of this type of method to examine higher dimensions within the metric multi-dimensional scaling formalism.

Programmed death 1 expression on HIV-specific CD4+ T cells is driven by viral replication and associated with T cell dysfunction

Functional impairment of HIV-specific CD4(+) T cells during chronic HIV infection is closely linked to viral replication and thought to be due to T cell exhaustion. Programmed death 1 (PD-1) has been linked to T cell dysfunction in chronic viral infections, and blockade of the PD-1 pathway restores HIV-specific CD4(+) and CD8(+) T cell function in HIV infection. This study extends those findings by directly examining PD-1 expression on virus-specific CD4(+) T cells. To investigate the role of PD-1 in HIV-associated CD4(+) T cell dysfunction, we measured PD-1 expression on blood and lymph node T cells from HIV-infected subjects with chronic disease. PD-1 expression was significantly higher on IFN-gamma-producing HIV-specific CD4(+) T cells compared with total or CMV-specific CD4(+) T cells in untreated HIV-infected subjects (p = 0.0001 and p < 0.0001, respectively). PD-1 expression on HIV-specific CD4(+) T cells from subjects receiving antiretroviral therapy was significantly reduced (p = 0.007), and there was a direct correlation between PD-1 expression on HIV-specific CD4(+) T cells and plasma viral load (r = 0.71; p = 0.005). PD-1 expression was significantly higher on HIV-specific T cells in the lymph node, the main site of HIV replication, compared with those in the blood (p = 0.0078). Thus, PD-1 expression on HIV-specific CD4(+) T cells is driven by persistent HIV replication, providing a potential target for enhancing the functional capacity of HIV-specific CD4(+) T cells.

Mitochondrial DNA identification of game and harvested freshwater fish species

The use of DNA in forensics has grown rapidly for human applications along with the concomitant development of bioinformatics and demographic databases to help fully realize the potential of this molecular information. Similar techniques are also used routinely in many wildlife cases, such as species identification in food products, poaching and the illegal trade of endangered species. The use of molecular techniques in forensic cases related to wildlife and the development of associated databases has, however, mainly focused on large mammals with the exception of a few high-profile species. There is a need to develop similar databases for aquatic species for fisheries enforcement, given the large number of exploited and endangered fish species, the intensity of exploitation, and challenges in identifying species and their derived products. We sequenced a 500bp fragment of the mitochondrial cytochrome b gene from representative individuals from 26 harvested fish taxa from Ontario, Canada, focusing on species that support major commercial and recreational fisheries. Ontario provides a unique model system for the development of a fish species database, as the province contains an evolutionarily diverse array of freshwater fish families representing more than one third of all freshwater fish in Canada. Inter- and intraspecific sequence comparisons using phylogenetic analysis and a BLAST search algorithm provided rigorous statistical metrics for species identification. This methodology and these data will aid in fisheries enforcement, providing a tool to easily and accurately identify fish species in enforcement investigations that would have otherwise been difficult or impossible to pursue.

CD4+ T cell targeting of human immunodeficiency virus type 1 (HIV-1) peptide sequences present in vivo during chronic, progressive HIV-1 disease

We previously detected HIV-1 Gag-specific CD4+ T cells recognizing reference strain viral epitopes in subjects with progressive, chronic infection. To test whether these CD4+ T cells persist in vivo by failing to recognize autologous HIV-1 epitopes, we compared autologous plasma HIV-1 p24 nucleotide sequences with targeted HXB.2 strain Gag p24 CD4+ T cell epitopes in nine chronically infected, untreated subjects. In five responding subjects, 10 of 26 HXB.2 strain p24 peptides targeted by CD4+ T cells exactly matched autologous plasma viral sequences. Four subjects with plasma viral loads >100,000 copies/mL had no measurable p24-specific CD4+ T cell responses despite carrying HIV-1 strains that matched HXB.2 sequences at predicted epitopes. These results show that HIV-1-specific CD4+ T cells can persist in chronic HIV-1 infection despite recognition of epitopes present in vivo. However, with high-level in vivo HIV-1 replication, CD4+ T cells targeting autologous HIV-1 may be non-responsive or absent.

Human dendritic cell interactions with whole recombinant yeast: implications for HIV-1 vaccine development

Defects in number and function of dendritic cells (DCs) have been observed during HIV-1 infection, so therapeutic HIV-1 vaccine approaches that target or activate DCs may improve vaccine immunogenicity. To determine the potential of recombinant Saccharomyces cerevisiae yeast as an HIV-1 vaccine, we investigated interactions between yeast and human DCs. Yeast induced direct phenotypic maturation of monocyte-derived DCs (MDDCs) and enriched blood myeloid DCs (mDCs), but only indirectly matured blood plasmacytoid DCs (pDCs). Yeast-pulsed MDDCs and blood mDCs produced inflammatory cytokines and stimulated strong allo-reactive T cell proliferation. Both blood DC subsets internalized yeast, and when pulsed with yeast recombinant for HIV-1 Gag protein, both stimulated in vitro expansion of Gag-specific CD8+ memory T cells. These results suggest that S. cerevisiae yeast have potent adjuvant effects on human DCs. Furthermore, recombinant yeast-derived antigens are processed by human blood DCs for MHC class-I cross-presentation. These DC-targeting characteristics of yeast suggest that it may be an effective vaccine vector for induction of HIV-1-specific cellular immune responses.

Functional and phenotypic characterization of CD57+CD4+ T cells and their association with HIV-1-induced T cell dysfunction

HIV-1 replication is associated with reduced or absent HIV-1-specific CD4+ T cell proliferation and skewing of HIV-1-specific CD4+ T cells toward an IFN-gamma-producing, CCR7- phenotype. The CCR7- T cell population is heterogeneous and can be subdivided based on the expression of CD57. Although CD57 expression on CD8+ T cells is associated with proliferation incompetence and replicative senescence, less is known about the function of CD57-expressing CD4+ T cells. In this study, the frequency, phenotype, and function of CD57+CD4+ T cells were evaluated in 25 HIV-1-infected subjects and 10 seronegative controls. CD57+CD4+ T cells were found to be proliferation incompetent, even after strong mitogen stimulation. Percentages of CD4+ T cells that expressed CD57 were significantly higher in untreated HIV-1-infected subjects than in HIV-1-seronegative donors, and CD57 expression did not normalize in subjects receiving at least 6 mo of effective antiretroviral therapy. CD57 was predominately expressed on the CCR7- fraction of the CD4+ T cell compartment and accounted for the majority of cells in the CCR7-CD45RA+ population from untreated HIV-1-infected subjects. HIV-1-specific CD4+ T cells producing only IFN-gamma had the highest expression of CD57, whereas few cells producing IL-2 alone expressed CD57. These findings further define a novel population of proliferation-incompetent CD4+ T cells that are generated in the presence of chronic Ag exposure. A better understanding of the generation and persistence of CD57+ T cells in HIV-1 infection could provide important insights into the immunopathogenesis of this disease.

HIV-1-Specific CD4+ T-Cell Responses Are Not Associated With Significant Viral Epitope Variation in Persons With Persistent Plasma Viremia

OBJECTIVES

To determine whether increased sequence variation occurs in regions of endogenous HIV-1 targeted by HIV-1-specific CD4 T cells. The presence of increased variation would be suggestive of immune evasion by HIV-1.

DESIGN

We performed a cross-sectional study of untreated HIV-1-infected subjects measuring HIV-1-specific interferon (IFN)-gamma-secreting CD4 T-cell responses against epitopes in Gag p17 and p24 and concurrent endogenous plasma HIV-1 RNA epitope sequence variation.

METHODS

CD8- depleted IFNgamma enzyme-linked immunospot assays were used to identify regions of HIV-1 Gag recognized by CD4 T cells. Reverse transcriptase polymerase chain reaction and TA cloning were used to sequence endogenous plasma HIV-1 virus and identify variants.

RESULTS

CD4 T-cell epitopes in Gag p17 and p24 were identified in 5 individuals, and concurrent sequence information on endogenous HIV-1 was obtained in 4 of these individuals. Endogenous plasma HIV-1 RNA sequencing revealed no intrapatient amino acid sequence variation through identified epitopes.

CONCLUSIONS

In these chronically infected viremic subjects, circulating IFNgamma-secreting CD4 T-cell responses were directed against epitope sequences found in the predominant strain of endogenous circulating plasma HIV-1, suggesting that escape from CD4 T-cell responses is not a common process in vivo.

Frequency of beryllium-specific, central memory CD4+ T cells in blood determines proliferative response

Beryllium exposure can lead to the development of beryllium-specific CD4+ T cells and chronic beryllium disease (CBD), which is characterized by the presence of lung granulomas and a CD4+ T cell alveolitis. Studies have documented the presence of proliferating and cytokine-secreting CD4+ T cells in blood of CBD patients after beryllium stimulation. However, some patients were noted to have cytokine-secreting CD4 T cells in blood in the absence of beryllium-induced proliferation, and overall, the correlation between the 2 types of responses was poor. We hypothesized that the relative proportion of memory T cell subsets determined antigen-specific proliferation. In most CBD patients, the majority of beryllium-specific CD4+ T cells in blood expressed an effector memory T cell maturation phenotype. However, the ability of blood cells to proliferate in the presence of beryllium strongly correlated with the fraction expressing a central memory T cell phenotype. In addition, we found a direct correlation between the percentage of beryllium-specific CD4+ T(EM) cells in blood and T cell lymphocytosis in the lung. Together, these findings indicate that the functional capability of antigen-specific CD4+ T cells is determined by the relative proportion of memory T cell subsets, which may reflect internal organ involvement.

Human immunodeficiency virus type 1 (HIV-1)-specific CD4+ T cells that proliferate in vitro detected in samples from most viremic subjects and inversely associated with plasma HIV-1 levels

Diminished in vitro proliferation of human immunodeficiency virus type 1 (HIV-1)-specific CD4+T cells has been associated with HIV-1 viremia and declining CD4+ T-cell counts during chronic infection. To better understand this phenomenon, we examined whether HIV-1 Gag p24 antigen-induced CD4+ T-cell proliferation might recover in vitro in a group of subjects with chronic HIV-1 viremia and no history of antiretroviral therapy (ART). We found that depletion of CD8+ cells from peripheral blood mononuclear cells (PBMC) before antigen stimulation was associated with a 6.5-fold increase in the median p24-induced CD4+ T-cell proliferative response and a 57% increase in the number of subjects with positive responses. These p24-induced CD4+ T-cell proliferative responses from CD8-depleted PBMC were associated with expansion of the numbers of p24-specific, gamma interferon (IFN-gamma)-producing CD4+ T cells. Among the 20 viremic, treatment-naive subjects studied, the only 5 subjects lacking proliferation-competent, p24-specific CD4+ T-cell responses from CD8-depleted PBMC showed plasma HIV-1 RNA levels > 100,000 copies/ml. Furthermore, both the magnitude of p24-induced CD4+ T-cell proliferative responses from CD8-depleted PBMC and the frequency of p24-specific, IFN-gamma-producing CD4+ T cells expanded from CD8-depleted PBMC were associated inversely with plasma HIV-1 RNA levels. Therefore, proliferation-competent, HIV-1-specific CD4+ T cells that might help control HIV-1 disease may persist during chronic, progressive HIV-1 disease except at very high levels of in vivo HIV-1 replication.

Recognition of variant HIV-1 epitopes from diverse viral subtypes by vaccine-induced CTL

Recognition by CD8(+) T lymphocytes (CTL) of epitopes that are derived from conserved gene products, such as Gag and Pol, is well documented and conceptually supports the development of epitope-based vaccines for use against diverse HIV-1 subtypes. However, many CTL epitopes from highly conserved regions within the HIV-1 genome are highly variable, when assessed by comparison of amino acid sequences. The TCR is somewhat promiscuous with respect to peptide binding, and, as such, CTL can often recognize related epitopes. In these studies, we evaluated CTL recognition of five sets of variant HIV-1 epitopes restricted to HLA-A*0201 and HLA-A*1101 using HLA transgenic mice. We found that numerous different amino acid substitutions can be introduced into epitopes without abrogating their recognition by CTL. Based on our findings, we constructed an algorithm to predict those CTL epitopes capable of inducing responses in the HLA transgenic mice to the greatest numbers of variant epitopes. Similarity of CTL specificity for variant epitopes was demonstrated for humans using PBMC from HIV-1-infected individuals and CTL lines produced in vitro using PBMC from HIV-1-uninfected donors. We believe the ability to predict CTL epitope immunogenicity and recognition patterns of variant epitopes can be useful for designing vaccines against multiple subtypes and circulating recombinant forms of HIV-1.

Effects of sustained HIV-1 plasma viremia on HIV-1 Gag-specific CD4+ T cell maturation and function

An in vitro proliferative defect has been observed in HIV-1-specific CD4(+) T cells from infected subjects with high-level plasma HIV-1 viremia. To determine the mechanism of this defect, HIV-1 Gag-specific CD4(+) T cells from treated and untreated HIV-1-infected subjects were analyzed for cytokine profile, proliferative capacity, and maturation state. Unexpectedly high frequencies of HIV-1-specific, IL-2-producing CD4(+) T cells were measured in subjects with low or undetectable plasma HIV-1 loads, regardless of treatment status, and IL-2 frequencies correlated inversely with viral loads. IL-2-producing CD4(+) T cells also primarily displayed a central memory (T(Cm); CCR7(+)CD45RA(-)) maturation phenotype, whereas IFN-gamma-producing cells were mostly effector memory (T(Em), CCR7(-)CD45RA(-)). Among Gag-specific, IFN-gamma-producing CD4(+) T cells, higher T(Em) frequencies and lower T(Cm) frequencies were observed in untreated, high viral load subjects than in subjects with low viral loads. The percentage of HIV-1 Gag-specific CD4(+) T(Cm) correlated inversely with HIV-1 viral load and directly with Gag-specific CD4(+) T cell proliferation, whereas the opposite relationships were observed for HIV-1-specific CD4(+) T(Em). These results suggest that HIV-1 viremia skews Gag-specific CD4(+) T cells away from an IL-2-producing T(Cm) phenotype and toward a poorly proliferating T(Em) phenotype, which may limit the effectiveness of the HIV-1-specific immune response.

Development of a DNA vaccine designed to induce cytotoxic T lymphocyte responses to multiple conserved epitopes in HIV-1

Epitope-based vaccines designed to induce CTL responses specific for HIV-1 are being developed as a means for addressing vaccine potency and viral heterogeneity. We identified a set of 21 HLA-A2, HLA-A3, and HLA-B7 restricted supertype epitopes from conserved regions of HIV-1 to develop such a vaccine. Based on peptide-binding studies and phenotypic frequencies of HLA-A2, HLA-A3, and HLA-B7 allelic variants, these epitopes are predicted to be immunogenic in greater than 85% of individuals. Immunological recognition of all but one of the vaccine candidate epitopes was demonstrated by IFN-gamma ELISPOT assays in PBMC from HIV-1-infected subjects. The HLA supertypes of the subjects was a very strong predictor of epitope-specific responses, but some subjects responded to epitopes outside of the predicted HLA type. A DNA plasmid vaccine, EP HIV-1090, was designed to express the 21 CTL epitopes as a single Ag and tested for immunogenicity using HLA transgenic mice. Immunization of HLA transgenic mice with this vaccine was sufficient to induce CTL responses to multiple HIV-1 epitopes, comparable in magnitude to those induced by immunization with peptides. The CTL induced by the vaccine recognized target cells pulsed with peptide or cells transfected with HIV-1 env or gag genes. There was no indication of immunodominance, as the vaccine induced CTL responses specific for multiple epitopes in individual mice. These data indicate that the EP HIV-1090 DNA vaccine may be suitable for inducing relevant HIV-1-specific CTL responses in humans.

Diverse repertoire of HIV-1 p24-specific, IFN-gamma-producing CD4+ T cell clones following immune reconstitution on highly active antiretroviral therapy

HIV-1 Ag-specific CD4(+) T cell proliferative responses in human subjects with advanced, untreated HIV-1 disease are often weak or undetectable. Conversely, HIV-1-specific CD4(+) T cell proliferation is occasionally detected following suppression of HIV-1 replication with highly active antiretroviral therapy (HAART). These observations suggest that unchecked HIV-1 replication may lead to depletion or dysfunction of HIV-1-specific CD4(+) T cells, and that these defects may be partially corrected by viral suppression and subsequent immune reconstitution. However, the impact of this immune reconstitution on the repertoire of HIV-1-specific CD4(+) T cells has not been thoroughly evaluated. To examine the HIV-1-specific CD4(+) T cell repertoire in this clinical setting, we established HIV-1 p24-specific CD4(+) T cell clones from a successfully HAART-treated subject whose pretreatment peripheral CD4 count was 0 cells/ micro l. Eleven different p24-specific CD4(+) T cell clonotypes were distinguished among 13 clones obtained. Most clones produced both IFN-gamma and IL-4 upon Ag stimulation. Clones targeted eight distinct epitopes that varied in their conservancy among HIV-1 strains, and responses were restricted by one of three MHC II molecules. Clones showed a range of functional avidities for both protein and peptide Ags. Additional studies confirmed that multiple HIV-1 p24-derived epitopes were targeted by IFN-gamma-producing CD4(+) cells from subjects first treated with HAART during advanced HIV-1 disease (median, 4.5 peptides/subject; range, 3-6). These results suggest that in HAART-treated subjects whose peripheral CD4(+) T cell pools were once severely depleted, the HIV-1-specific CD4(+) T cell repertoire may include a diverse array of clonotypes targeting multiple HIV-1 epitopes.

Influence of plasma viremia on defects in number and immunophenotype of blood dendritic cell subsets in human immunodeficiency virus 1-infected individuals

Dendritic cells (DCs) are postulated to be involved in transmission of human immunodeficiency virus (HIV) type 1 to T cells and in stimulation of HIV-1-specific cell-mediated immunity. Blood DCs have been categorized as myeloid (mDC) and plasmacytoid (pDC) subsets, on the basis of differences in phenotype and function. Blood DC subset numbers and expression of costimulatory molecules and HIV-1 coreceptors on DCs were measured in the blood of treated and untreated HIV-1-infected subjects and uninfected control subjects. Absolute numbers of mDCs and pDCs were lower in HIV-1-infected subjects than in control subjects, most significantly in those with active HIV-1 replication. Increased surface expression of costimulatory molecules was observed on both DC subsets in subjects with HIV-1 viremia. Highly active antiretroviral therapy suppression of plasma viremia resulted in increases in blood DC numbers and decreases in DC costimulatory molecule expression. These findings further define the impact of HIV-1 replication on blood DC subsets in vivo.

Discordance between frequency of human immunodeficiency virus type 1 (HIV-1)-specific gamma interferon-producing CD4(+) T cells and HIV-1-specific lymphoproliferation in HIV-1-infected subjects with active viral replication

One hallmark of uncontrolled, chronic human immunodeficiency virus type 1 (HIV-1) infection is the absence of strong HIV-1-specific, CD4(+) T-cell-proliferative responses, yet the mechanism underlying this T helper (Th)-cell defect remains controversial. To better understand the impact of HIV-1 replication on Th-cell function, we compared the frequency of CD4(+) Th-cell responses based on production of gamma interferon to lymphoproliferative responses directed against HIV-1 proteins in HIV-1-infected subjects with active in vivo viral replication versus those on suppressed highly active antiretroviral therapy (HAART). No statistically significant differences in the frequencies of cytokine-secreting, HIV-1-specific CD4(+) T cells between the donor groups were found, despite differences in viral load and treatment status. However, HIV-1-specific lymphoproliferative responses were significantly greater in the subjects with HAART suppression than in subjects with active viral replication. Similar levels of HIV-1 RNA were measured in T-cell cultures stimulated with HIV-1 antigens regardless of donor in vivo viral loads, but only HIV-1-specific CD4(+) T cells from subjects with HAART suppression proliferated in vitro, suggesting that HIV-1 replication in vitro does not preclude HIV-1-specific lymphoproliferation. This study demonstrates a discordance between the frequency and proliferative capacity of HIV-1-specific CD4(+) T cells in subjects with ongoing in vivo viral replication and suggests that in vivo HIV-1 replication contributes to the observed defect in HIV-1-specific CD4(+) T-cell proliferation.

Recombinant yeast as a vaccine vector for the induction of cytotoxic T-lymphocyte responses

There is currently a need to develop safe and effective vaccines for the induction of cellular, in particular cytotoxic T-lymphocyte-mediated, protective immune responses. This review focuses on the challenges presented by such an endeavor, current strategies for the induction of such responses, and the relatively new idea that recombinant yeast may represent an ideal vaccine vector for the induction of cellular immune responses.