HIV Peptides Research Articles

Vaccination with dendritic cells loaded with HIV-1 lipopeptides elicits broad T cell immunity and control of viral load in HIV infected patients

Background The DALIA trial tested the hypothesis that immunization with HIV peptide loaded Dendritic Cells (DC) may improve HIV immune responses and help to contain viral replication.

Alteration of HIV epitope processing and presentation by HIV protease inhibitors

Background Epitopes displayed by MHC-I come from the multistep degradation of proteins by intracellular peptidases such as proteasome and aminopeptidases or cathepsins in the exogenous pathway. We hypothesize that due to structural homologies HIV protease inhibitors (PIs) used in antiretroviral therapies may affect activities of cellular peptidases involved in epitope processing and may affect epitope presentation to immune cells. Methods Using a fluorogenic assay the effect of 5 HIV-1 PIs (Ritonavir, Saquinavir, Nelfinavir, Indinavir, Atazanavir) on proteasome, aminopeptidase and cathepsin activities was tested in PBMCs from at least 6 healthy donors. Using PBMC cytosol as a source of peptidases and HPLC and mass spectrometry to define and quantify the degradation products, the effect of HIV PIs on HIV peptide processing kinetics and HIV epitope half-life was assessed. Finally we assessed the impact of PIs on the endogenous processing and presentation of epitopes by infected cells to CD8 T cells using a fluorescence-based cytotoxicity assay. Results HIV PIs variably altered proteasome, post-proteasomal aminopeptidases and cathepsin activities. Depending on the PI, some activities were inhibited (from 1.1 to 5 folds, p<0.001), enhanced (1.2 to 9 folds, p<0.001), and others not changed. These PI-induced changes in protease activities modified HIV peptide processing patterns and HIV epitope intracellular half-life prior to MHC-I loading. Depending on the PI and the epitope the halflife was increased 1.5 fold (p<0.01) or decreased 1.3 fold (p<0.05). Furthermore HIV PI altered (from 2.2 fold decrease to 1.3 fold increase, p<0.01) the presentation of HIV epitopes and recognition by epitope-specific CD8 T cells. Conclusion These findings suggest that in HIV-infected patients an antiretroviral therapy including PIs might -by altering host proteases function- modify the pattern of epitope presentation, leading to the elicitation of additional CTL responses against HIV and potentially against other pathogens co-infecting HIV+ persons. This project was supported by NIH-NIAID grant R01A1084106.

36-OR

Aim HIV eludes immune responses that directly target the virus. Previous work in our lab showed that HIV-1 infection leads HLA to present distinct host peptides. We hypothesize that, in the absence of effective HIV-1-specific epitope recognition, host-specific ligands uniquely presented on infected cells can be therapeutically targeted to block transmission of the virus. Our aim is to characterize epitopes presented by the non-progressor/protection-associated allele B∗57:01 and to generate antibodies with potential for anti-viral activity. Methods We utilized sHLA and mass spectroscopy to characterize the endogenous B∗57:01 ligands presented by infected cells. The SUPT1 human T cell line expressing soluble B∗57:01 was infected with HIV-1 and HLA-bound peptides from infected and uninfected cells were comparatively analyzed by mass spectrophotometry. Unique upregulated host ligands were identified in a number of host metabolic pathways that interact with HIV-1. Results At least five host derived, B∗57:01-specific peptide ligands are highly upregulated and/or unique to HIV infected SUPT1 T cells. These epitopes are derived from host proteins involved in chromosome cohesion, ER resident protein retention, and interferon regulation as well as virus propagation. Conclusions HIV utilizes a number of immune evasion tactics, including diminished presentation of viral peptides by the class I HLA of infected cells. We therefore discovered several endogenous targets that distinguish HIV-infected cells from healthy cells. Having validated these targets as unique to infected cells, monoclonal antibodies known as T cell receptor mimics (TCRm) specific for these B∗57:01/ligand complexes will be tested for their ability to distinguish and target virus infected cells.

CTL recognition of HIV‐1‐infected cells via cross‐recognition of multiple overlapping peptides from a single 11‐mer Pol sequence

It is known that overlapping HIV-1 peptides of different lengths can be presented by a given HLA class I molecule. However, the role of those peptides in CD8(+) T cells recognition of HIV-1-infected cells remains unclear. Here we investigated the recognition of overlapping 8-mer to 11-mer peptides of Pol 155-165 by HLA-B*54:01-restricted CD8(+) T cells. The analysis of ex vivo T cells using ELISPOT and tetramer binding assays showed that there were different patterns of CD8(+) T-cell responses to these peptides among chronically HIV-1-infected HLA-B*54:01(+) individuals, though the response to the 9-mer peptide was the strongest among them. CD8(+) T-cell clones with TCRs specific for the 9-mer, 10-mer, and/or 11-mer peptides effectively killed HIV-1-infected cells. Together, these results suggest that the 9-mer and 10-mer peptides could be predominantly presented by HLA-B*54:01, though it remains possible that the 11-mer peptide was also presented by this HLA allele. The present study demonstrates effective CD8(+) T-cell recognition of HIV-1-infected cells via presentation of multiple overlapping HIV-1 peptides and cross-recognition by the CD8(+) T cells.

Thrombocytopenia During Primary HIV-1 Infection Predicts the Risk of Recurrence During Chronic Infection

Thrombocytopenia During Primary HIV-1 Infection Predicts the Risk of Recurrence During Chronic Infection

Complexation of HIV derived peptides with carbosilane dendrimers

Dendrimers have been proposed as new carriers for selected HIV-1 peptides. This paper reports on the complexation behaviour of the three HIV-derived-peptides: Gp160, NH-EIDNYTNTIYTLLEE-COOH; P24, NH-DTINEEAAEW-COOH and Nef, NHGMDDPEREVLEWRFDSRLAF-COOH with second generation cationic carbosilane dendrimers (CBD) branched with carbonsilicon bonds (CBD-CS) or oxygensilicon bonds (CBD-OS). Studies on the formation of complexes between HIV peptides and CBDs by fluorescence polarization, zeta-potential, electrophoresis and transmission electron microscopy have shown that both studied dendrimers form complexes with HIV peptides. At a molar ratio of (2.5–3):1 (dendrimer:peptide), the complexes formed were in the size range of 180–275nm and with significant positive surface charge. The results suggest that interactions between dendrimers and HIV peptides have electrostatic nature due to the negative charge of peptides backbone and positive charge of dendrimer functional groups. Dendriplex stability depended on the type of studied dendrimers. Time of peptides release from the complexes ranged from 1 (CBD-OS) to ∼36 (CBD-CS)h. Basing on the obtained results, we propose that the water-soluble cationic carbosilane dendrimers can be considered for delivery of HIV peptides to dendritic cells.

Immune and Viral Correlates of “Secondary Viral Control” after Treatment Interruption in Chronically HIV-1 Infected Patients

Upon interruption of antiretroviral therapy, HIV-infected patients usually show viral load rebound to pre-treatment levels. Four patients, hereafter referred to as secondary controllers (SC), were identified who initiated therapy during chronic infection and, after stopping treatment, could control virus replication at undetectable levels for more than six months. In the present study we set out to unravel possible viral and immune parameters or mechanisms of this phenomenon by comparing secondary controllers with elite controllers and non-controllers, including patients under HAART. As candidate correlates of protection, virus growth kinetics, levels of intracellular viral markers, several aspects of HIV-specific CD4+ and CD8+ T cell function and HIV neutralizing antibodies were investigated. As expected all intracellular viral markers were lower in aviremic as compared to viremic subjects, but in addition both elite and secondary controllers had lower levels of viral unspliced RNA in PBMC as compared to patients on HAART. Ex vivo cultivation of the virus from CD4+ T cells of SC consistently failed in one patient and showed delayed kinetics in the three others. Formal in vitro replication studies of these three viruses showed low to absent growth in two cases and a virus with normal fitness in the third case. T cell responses toward HIV peptides, evaluated in IFN-γ ELISPOT, revealed no significant differences in breadth, magnitude or avidity between SC and all other patient groups. Neither was there a difference in polyfunctionality of CD4+ or CD8+ T cells, as evaluated with intracellular cytokine staining. However, secondary and elite controllers showed higher proliferative responses to Gag and Pol peptides. SC also showed the highest level of autologous neutralizing antibodies. These data suggest that higher T cell proliferative responses and lower replication kinetics might be instrumental in secondary viral control in the absence of treatment.

Broad HIV-1 neutralizing antibody response induced by heterologous gp140/gp145 DNA prime-vaccinia boost immunization

ObjectiveTo develop an effective HIV vaccine strategy that can induce cross-reactive neutralizing antibody. MethodsCodon-optimized gp140 and gp145 env genes derived from HIV-1cn54, a CRF07 B′/C recombinant strain, were constructed as DNA and recombinant Tiantan vaccinia (rTV) vaccines. The effect of heterologous immunization with gp140 and gp145 was tested in mice and guinea pigs. T cell responses were detected using the IFN-γ ELISPOT assay. A panel of primary isolates of clade B′ and B′/C HIV-1 and TZM-bl cells was used to determine the neutralizing activity of immunized sera. ResultsThe neutralizing antibodies (NAbs) induced by the heterologous immunogen immunization neutralized all HIV-1 B′ and B′/C primary isolates in the guinea pig model. Gp145 and gp140 heterologous prime-boost induced the best neutralizing antibody response with a broad neutralizing spectrum and the highest titer of 1:270 at 6 weeks after the last inoculation. However, the T cell response to HIV-1 peptides was significantly weaker than the gp145+gp145 homologous prime-boost. ConclusionsThis heterologous prime-boost immunization strategy could be used to design immunogen-generating broad neutralizing antibodies against genetic variance pathogens.

Characterization of regulatory and conventional T cell phenotype and function in HIV exposed seronegative subjects. (170.29)

Abstract The role of regulatory T cells (Tregs) in preventing or facilitating HIV infection remains unclear. To address this question, we analyzed samples from 129 HIV-exposed seronegative (HESN) individuals, divided into high and low exposure groups based on partner viral load. The two groups had comparable frequencies of Tregs, but in the higher exposure group there was a trend for increased expression of the Treg suppressive markers CD39 and CTLA4. CD4+ and CD8+ T cell activation was similar in the two groups. To assess T cell function, we measured the proliferation of T cells in response to four HIV peptide pools by a CFSE-based assay. Both low and high exposure groups showed a comparable percentage of CD4+ (12.7 % versus 9.7% respectively) and CD8+T cell proliferation (3.2% versus 4.9%). To assess the Treg suppressive function, we compared the proliferation of peripheral blood mononuclear cells (PBMCs) and Treg-depleted PBMCs in response to the peptide pools. In 41% of the samples that showed proliferation in response to at least one peptide, T reg depletion induced an increased proliferation of CD4+ T cells. The suppression was similar in high and low exposure groups. In the remaining samples, Treg depletion led to a decrease in CD4+ T cell proliferation. In conclusion, our study suggests that HESN can mount an HIV-specific T cell response and further, Treg can either suppress or assist this response, though the mechanism for this difference remains under investigation.

Abstract 3508: Zoledronate induce expansion of glypican-3 (GPC3) peptide specific cytotoxic T lLymphocytes sufficient for adoptive cancer immunotherapy

Abstract BACKGROUND Glypican-3 (GPC3) is an onco-fetal antigen which is overexpressed in human hepatocellular carcinoma (HCC), and is only expressed in the placenta and embryonic liver among normal tissues. Previously, we completed a phase I clinical trial of HLA-A2-restricted GPC3144-152 (FVGEFFTDV) and A24-restricted GPC3298-306 (EYILSLEEL) peptide vaccine in 33 patients with advanced HCC. This clinical trial of GPC3-derived peptide vaccine showed the vaccination to be safe, and indicates many immunological responses. To develop more efficient immunotherapy, we investigated large scale expansion of GPC3 peptide specific CTLs for adoptive immunotherapy. PURPOSE In this study, we investigated the efficiency of new method to induce expansion of GPC3 peptide specific CTLs. METHODS Treatment of human peripheral blood mononuclear cells (PBMCs) with zoledronate is a method that enables large-scale γδ T cell expansion. To induce expansion of GPC3 peptide specific CTLs and γδ T cells, the PBMCs of patients vaccinated with GPC3 peptide were cultured with GPC3 peptide and zoledronate for 14 days. We used CD8+ and CD8− cells that isolated from cultured cells using CD8 microbeads at day 14 as a effector cells. GPC3 peptide specificity and cytotoxic activity of CTLs were analysed by Dextramer assay, cytotoxicity assay and IFN-γ ELISPOT assay. We used human liver cancer cell line SK-Hep-1 (GPC3−, HLA-A*02:01/24:02) and a human GPC3 gene transfectant, SK-Hep-1 [[Unsupported Character - &amp;#8260;]] hGPC3 (GPC3+, HLA-A*02:01/24:02) as target cells. T2 (HLA-A*02:01, TAP−) was pulsed with GPC3 peptide or HIV peptide at room temperature for 1h. To evaluate antitumor activity in vivo, we inoculated SK-Hep-1/hGPC3 and SK-Hep-1/vec cells at the right flank of NOD/SCID mice. We injected the CD8+, CD8− or all cells as effector cells intravenously. RESULTS The expansion of Lymphocytes from a few PBMCs of vaccinated patients with advanced HCC using zoledronate yields cell numbers sufficient for adoptive transfer. The rate of increase of GPC3 specific CTLs was approximate 490 to 170,000-fold, whereas the rate of increase of total cell number was approximate 13 to 1,000-fold. These CD8+ cells including CTLs showed GPC3 specific cytotoxicity against SK-Hep-1/hGPC3 and T2 pulsed with GPC3 peptide, but not against SK-Hep-1/vec and T2 pulsed with HIV peptide, whereas CD8− cells including γδ T cells showed cytotoxicity against SK-Hep-1/hGPC3 and SK-Hep-1/vec while did not show GPC3 specificity. Furthermore, adoptive cell transfer of CD8+ cells, CD8− cells and total cells after expansion significantly inhibited tumor growth in NOD/SCID mouse model. CONCLUSION This study indicates that zoledronate is useful to large-scale expand antigen-specific CTLs and γδ T cells for adoptive immunotherapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3508. doi:1538-7445.AM2012-3508

Frequent and strong antibody-mediated natural killer cell activation in response to HIV-1 Env in individuals with chronic HIV-1 infection.

Natural killer (NK) cells play a critical role in the control of HIV-1 infection, and NK cells that respond to HIV-1 peptides have been recently described. However, the mechanisms by which NK cells recognize HIV-1 antigens are not fully understood. We investigated NK cell activation in response to HIV-1 peptides during early and chronic HIV-1 clade B infection using a whole-blood assay and multiparameter flow cytometry. Antibody-mediated NK cell activation in response to HIV-1 peptides was not detected in HIV-1-uninfected individuals. In contrast, 79% of individuals with chronic infection and 22% of individuals with early infection had detectable gamma interferon (IFN-γ) NK cell responses to HIV-1 antigens (P < 0.00001). IFN-γ- and tumor necrosis factor alpha (TNF-α)-producing NK cells most frequently targeted Env gp120 (median of 4% and range of 0 to 31% of all NK cells). NK cells rarely targeted other HIV-1 proteins such as Gag, Pol, and Nef. Antibody-mediated NK cell responses to peptides mapped predominantly to Env protein, required the presence of plasma or plasma IgG, and resulted in lower CD16 expression on NK cells, suggesting an antibody-mediated activation of NK cells. Further studies are needed to assess the consequences of these antibody-mediated NK cell responses for HIV-1 disease progression and vaccine-induced protection from infection.

Psoriasis patients are enriched for genetic variants that protect against HIV-1 disease.

An important paradigm in evolutionary genetics is that of a delicate balance between genetic variants that favorably boost host control of infection but which may unfavorably increase susceptibility to autoimmune disease. Here, we investigated whether patients with psoriasis, a common immune-mediated disease of the skin, are enriched for genetic variants that limit the ability of HIV-1 virus to replicate after infection. We analyzed the HLA class I and class II alleles of 1,727 Caucasian psoriasis cases and 3,581 controls and found that psoriasis patients are significantly more likely than controls to have gene variants that are protective against HIV-1 disease. This includes several HLA class I alleles associated with HIV-1 control; amino acid residues at HLA-B positions 67, 70, and 97 that mediate HIV-1 peptide binding; and the deletion polymorphism rs67384697 associated with high surface expression of HLA-C. We also found that the compound genotype KIR3DS1 plus HLA-B Bw4-80I, which respectively encode a natural killer cell activating receptor and its putative ligand, significantly increased psoriasis susceptibility. This compound genotype has also been associated with delay of progression to AIDS. Together, our results suggest that genetic variants that contribute to anti-viral immunity may predispose to the development of psoriasis.

Design of highly potent HIV fusion inhibitors based on artificial peptide sequences

Specific interactions were introduced between an artificial heptad repeat peptide template and HIV-1 gp41 for fusion inhibitor design, using a structure based rational design strategy. The designed peptides are nonhomologous with naturally occurring peptide and protein sequences, specifically interact with HIV-1 gp41, and show strong anti-HIV activity.

A novel self-assembled nanoparticle vaccine with HIV-1 Tat49-57/HPV16 E749-57 fusion peptide and GM-CSF DNA elicits potent and prolonged CD8+ T cell-dependent anti-tumor immunity in mice

Peptide-based vaccines derived from the E7 protein of human papillomavirus (HPV) type 16 were developed to induce effective T cell responses against established cervical cancer, but have met with limited clinical success. It is necessary to develop novel peptide-based strategies to substantially improve the immune response against HPV16-related cancer. In this study, we aimed to design a novel peptide-based self-assembled nanoparticle HPV16 vaccine by combining the cell-penetrating peptide HIV-1 Tat(49-57) that was fused with the HPV16 E7(49-57) cytotoxic T lymphocyte (CTL) epitope and the granulocyte-macrophage colony stimulating factor (GM-CSF) gene, and to investigate how it improves the immune response and the therapeutic outcome ex vivo and in vivo. Nanoparticles were prepared and identified by transmission electron microscopy (TEM), gel retardation and DNase I protection assays. This type of vaccine formulation formed the 20-80 nm nanoparticles, and greatly improved epitope-specific immunity both ex vivo and in vivo. Importantly, this vaccine type was associated with decreased tumor growth and enhanced long-term survival in the prophylactic and therapeutic mouse models. The underlying mechanisms were determined to involve priming of enhanced frequency of CD8(+) memory T subtype cells. These results suggest that the nanoparticle Tat-E7/pGM-CSF represents a promising novel approach to enhance the potency of peptide-based cervical cancer vaccines, and this vaccine design strategy may act as a useful reference for research of virus-associated diseases and specific tumor immunotherapies.

Activation of NK Cells by ADCC Antibodies and HIV Disease Progression

Antibody-dependent cellular cytotoxicity (ADCC) is of considerable interest as an immune response that may facilitate the control of HIV infection. We studied ADCC responses prospectively in a cohort of 79 HIV-positive subjects followed up for a mean of 2.3 years without antiretroviral therapy. We used a novel assay of the ability of ADCC to activate natural killer (NK) cells, either from the same HIV-positive subject or from a healthy blood donor. We found that ADCC responses to either gp140 Env protein or HIV peptide pools were common in HIV-positive subjects when NK cells from the HIV-positive subject were used but did not correlate with markers of HIV disease progression. In contrast, ADCC responses to whole gp140 Env protein were strongly associated with a slower decline in CD4 T-cell loss when healthy donor NK cells were used as effectors. Our data had implications for induction of the most effective ADCC responses by HIV vaccines.

Development and preclinical safety evaluation of a new therapeutic HIV-1 vaccine based on 18 T-cell minimal epitope peptides applying a novel cationic adjuvant CAF01

Therapeutic immunization of HIV-1-infected individuals with or without anti-retroviral therapy is a new promising disease prevention. To induce a new cytotoxic T CD8 lymphocyte (CTL) immunity during chronic HIV-1 infection 15 infrequently targeted but conserved HLA-supertype binding CTL epitopes from Gag, Pol, Nef, Env, Vpu and Vif were identified. The 15 T CD8 and three T CD4 helper peptides were GMP synthesised and formulated with a new adjuvant CAF01 which is a synthetic two-component liposomic adjuvant comprising the quaternary ammonium dimethyl-dioctadecyl-ammonium (DDA) and the immune modulator trehalose 6,6′-dibehenate (TDB). Using IFN-γ ELISPOT assay, T-cell immune induction by the vaccine was found to both CD4 and CD8 T-cell restricted peptides in HLA-A2 transgenic mice. Comprehensive toxicity studies of the CAF01 adjuvant-alone and together with different vaccines showed that CAF01 when tested at human dose levels was safe and well tolerated with only local inflammation at the site of injection and no systemic reactions. No pharmacological safety issues were observed in Beagle dogs. The HIV-1 vaccine toxicity study in the Göttingen Minipig ® showed no systemic toxicity from five repetitive i.m. injections, each with a 2-week interval, of either the 18 HIV-1 peptide antigen solution (AFO18) or the AFO18–CAF01, in which the 18 HIV-1 peptides were formulated with the CAF01 adjuvant. Distinct inflammatory responses were observed in the injected muscles of the AFO18–CAF01 vaccine treated animals as a result of the immune stimulating effect of the adjuvant on the vaccine. The results of the toxicity studies provide optimism for phase I clinical trials evaluating the therapeutic HIV-1 T-cell vaccination approach using multiple subdominant minimal epitope peptides applying the novel cationic adjuvant CAF01.

Synthesis, gp120 binding and anti-HIV activity of fatty acid esters of 1,1-linked disaccharides

Inspired by the anti-human immunodeficiency virus (HIV) activity of analogues of β-galactosylceramide (GalCer), a set of mono- and di-saccharide fatty acid esters were designed as GalCer mimetics and their binding to the V3 loop peptide of HIV-1 and anti-HIV activity evaluated. 1,1-linked Gal-Man and Glu-Man disaccharides with an ester on the Man subunit bound the V3 loop peptide and inhibited HIV infectivity in single round infection assays with the TZM-bl cell line. IC50’s were in the 50μM range with no toxicity to the cells at concentrations up to 200μM. These compounds appear to inhibit virus entry at early steps in viral infection since they were inactive if added post viral entry. Although these compounds were found to bind to the V3 loop peptide of gp120, it is not clear that this interaction is responsible for their anti-HIV activity because the relative binding affinity of closely related analogues did not correlate with their antiviral behavior. The low cytotoxicity of these 1,1-linked disaccharide fatty acid esters, combined with the easy accessibility to structurally diverse analogues make these molecules attractive leads for new topical anti-viral agents.

Natural Killer Cell Responses to HIV-1 Peptides are Associated With More Activating KIR Genes and HLA-C Genes of the C1 Allotype

What characterizes individuals whose natural killer (NK) cells are able to respond to HIV-1 peptides is not known. The association between NK cell responses and KIR gene profiles and HLA-B and HLA-C alleles was investigated among 76 HIV-1-infected women in South Africa previously categorized as responders (n = 39) or nonresponders (n = 37) to HIV-1 peptide pools in a whole blood intracellular cytokine assay. Viral load was significantly lower and CD4 T-cell counts higher among responders compared with nonresponders (P = 0.023 and P = 0.030, respectively). Possession of one HLA-C1 allele associated with increased magnitude of NK cell responses to Env (P = 0.031) and significantly decreased viral load (P = 0.027) compared with its absence. There was a trend to increased possession of KIR2DL3+HLA-C1 in responders (71.8% vs 51.4%, P = 0.098) and decreased possession of KIR2DL3/2DL3+C2C2 (2.6% vs 16.2%, P = 0.053). A total of 64.1% of responders versus 32.4% of nonresponders had 13 or more KIR genes (P = 0.0067). Notably, the 13-KIR gene containing the Bx21 genotype (has eight inhibitory and three activating genes KIR2DS2, 2DS4, 2DS5) showed substantially higher representation among the responders (28.2% vs 2.6%, P = 0.001). A significantly higher proportion of responders had both KIR2DS2 and KIR2DS5 compared with either gene alone (72.4% vs 37%; P = 0.015). At least one HLA-C1 allele together with 13 or more KIR genes was associated with NK cell responsiveness (48.7% vs 13.5%; P = 0.001). NK cell responses to HIV-1 peptides are more likely to occur among individuals with a genotype supporting a more activating NK cell phenotype and who possess at least one HLA-C1 allele.

An immunological comparison between lipidated and non-lipidated multivalent HIV-1 peptides representing Gp120 and Gag hypervariable regions

Despite the extensive efforts towards development of an effective HIV vaccine, major challenges surrounding vaccine design still exist. We have previously developed a unique multivalent HIV-1 candidate vaccine representing hypervariable Gp120 and Gag regions. This candidate vaccine was able to induce a broad cell-mediated immune response in HLA-A2.1 mice and non-human primates against HIV-1 subtypes A–F. Herein, the reactivity of each hypervariable peptide mixture within our candidate peptide vaccine was further characterized to optimize the final vaccine formulation for the future clinical studies. The binding of each hypervariable region to sera from HIV-infected individuals demonstrated a strong reactivity between the antibodies and hypervariable regions. In addition, 15 groups of mice were immunized with adjuvant alone or each individual peptide mixture (lipidated or non-lipidated) to evaluate the ability of each variable region to induce humoral and cellular immune responses against HIV-1. A reactive HIV-1 specific immune response was detected among the immunized groups; however, mice receiving the Gag hypervariable regions demonstrated the highest frequency of cell-mediated immune responses.

Variable HIV peptide stability in human cytosol is critical to epitope presentation and immune escape

Induction of virus-specific CD8⁺ T cell responses is critical for the success of vaccines against chronic viral infections. Despite the large number of potential MHC-I-restricted epitopes located in viral proteins, MHC-I-restricted epitope generation is inefficient, and factors defining the production and presentation of MHC-I-restricted viral epitopes are poorly understood. Here, we have demonstrated that the half-lives of HIV-derived peptides in cytosol from primary human cells were highly variable and sequence dependent, and significantly affected the efficiency of cell recognition by CD8⁺ T cells. Furthermore, multiple clinical isolates of HLA-associated HIV epitope variants displayed reduced half-lives relative to consensus sequence. This decreased cytosolic peptide stability diminished epitope presentation and CTL recognition, illustrating a mechanism of immune escape. Chaperone complexes including Hsp90 and histone deacetylase HDAC6 enhanced peptide stability by transient protection from peptidase degradation. Based on empirical results with 166 peptides, we developed a computational approach utilizing a sequence-based algorithm to estimate the cytosolic stability of antigenic peptides. Our results identify sequence motifs able to alter the amount of peptide available for loading onto MHC-I, suggesting potential new strategies to modulate epitope production from vaccine immunogens.