HIV-1 infections with multiple founders are associated with higher viral loads than infections with single founders.

Given the variation in the HIV-1 viral load (VL) set point across subjects, as opposed to a fairly stable VL over time within an infected individual, it is important to identify the characteristics of the host and virus that affect VL set point. Although recently infected individuals with multiple phylogenetically linked HIV-1 founder variants represent a minority of HIV-1 infections, we found--n two different cohorts--hat more diverse HIV-1 populations in early infection were associated with significantly higher VL 1 year after HIV-1 diagnosis.

HIV Vaccine Trials Network: activities and achievements of the first decade and beyond.

The HIV Vaccine Trials Network (HVTN) is an international collaboration of scientists and educators facilitating the development of HIV/AIDS preventive vaccines. The HVTN conducts all phases of clinical trials, from evaluating experimental vaccines for safety and immunogenicity, to testing vaccine efficacy. Over the past decade, the HVTN has aimed to improve the process of designing, implementing and analyzing vaccine trials. Several major achievements include streamlining protocol development while maintaining input from diverse stakeholders, establishing a laboratory program with standardized assays and systems allowing for reliable immunogenicity assessments across trials, setting statistical standards for the field and actively engaging with site communities. These achievements have allowed the HVTN to conduct over 50 clinical trials and make numerous scientific contributions to the field.

Optimization and qualification of an 8-color intracellular cytokine staining assay for quantifying T cell responses in rhesus macaques for pre-clinical vaccine studies.

Vaccination and SIV challenge of macaque species is the best animal model for evaluating candidate HIV vaccines in pre-clinical studies. As such, robust assays optimized for use in nonhuman primates are necessary for reliable ex vivo measurement of immune responses and identification of potential immune correlates of protection. We optimized and qualified an 8-color intracellular cytokine staining assay for the measurement of IFNγ, IL-2, and TNF from viable CD4 and CD8 T cells from cryopreserved rhesus macaque PBMC stimulated with peptides. After optimization, five laboratories tested assay performance using the same reagents and PBMC samples; similar results were obtained despite the use of flow cytometers with different configurations. The 8-color assay was then subjected to a pre-qualification study to quantify specificity and precision. These data were used to set positivity thresholds and to design the qualification protocol. Upon completion of the qualification study, the assay was shown to be highly reproducible with low inter-aliquot, inter-day, and inter-operator variability according to the qualification criteria with an overall variability of 20-40% for each outcome measurement. Thus, the 8-color ICS assay was formally qualified according to the ICH guidelines Q2 (R1) for specificity and precision indicating that it is considered a standardized/robust assay acceptable for use in pre-clinical trial immunogenicity testing.

Magnitude and breadth of the neutralizing antibody response in the RV144 and Vax003 HIV-1 vaccine efficacy trials.

BACKGROUND: A recombinant canarypox vector expressing human immunodeficiency virus type 1 (HIV-1) Gag, Pro, and membrane-linked gp120 (vCP1521), combined with a bivalent gp120 protein boost (AIDSVAX B/E), provided modest protection against HIV-1 infection in a community-based population in Thailand (RV144 trial). No protection was observed in Thai injection drug users who received AIDSVAX B/E alone (Vax003 trial). We compared the neutralizing antibody response in these 2 trials. METHODS: Neutralization was assessed with tier 1 and tier 2 strains of virus in TZM-bl and A3R5 cells. RESULTS: Neutralization of several tier 1 viruses was detected in both RV144 and Vax003. Peak titers were higher in Vax003 and waned rapidly in both trials. The response in RV144 was targeted in part to V3 of gp120.vCP1521 priming plus 2 boosts with gp120 protein was superior to 2 gp120 protein inoculations alone, confirming a priming effect for vCP1521. Sporadic weak neutralization of tier 2 viruses was detected only in Vax003 and A3R5 cells. CONCLUSION: The results suggest either that weak neutralizing antibody responses can be partially protective against HIV-1 in low-risk heterosexual populations or that the modest efficacy seen in RV144 was mediated by other immune responses, either alone or in combination with neutralizing antibodies.

Genetic impact of vaccination on breakthrough HIV-1 sequences from the STEP trial.

We analyzed HIV-1 genome sequences from 68 newly infected volunteers in the STEP HIV-1 vaccine trial. To determine whether the vaccine exerted selective T cell pressure on breakthrough viruses, we identified potential T cell epitopes in the founder sequences and compared them to epitopes in the vaccine. We found greater distances to the vaccine sequence for sequences from vaccine recipients than from placebo recipients. The most significant signature site distinguishing vaccine from placebo recipients was Gag amino acid 84, a site encompassed by several epitopes contained in the vaccine and restricted by human leukocyte antigen (HLA) alleles common in the study cohort. Moreover, the extended divergence was confined to the vaccine components of the virus (HIV-1 Gag, Pol and Nef) and not found in other HIV-1 proteins. These results represent what is to our knowledge the first evidence of selective pressure from vaccine-induced T cell responses on HIV-1 infection in humans.

Magnitude and breadth of a nonprotective neutralizing antibody response in an efficacy trial of a candidate HIV-1 gp120 vaccine.

BACKGROUND: A candidate vaccine consisting of human immunodeficiency virus type 1 (HIV-1) subunit gp120 protein was found previously to be nonprotective in an efficacy trial (Vax004) despite strong antibody responses against the vaccine antigens. Here we assessed the magnitude and breadth of neutralizing antibody responses in Vax004. METHODS: Neutralizing antibodies were measured against highly sensitive (tier 1) and moderately sensitive (tier 2) strains of HIV-1 subtype B in 2 independent assays. Vaccine recipients were stratified by sex, race, and high versus low behavioral risk of HIV-1 acquisition. RESULTS: Most vaccine recipients mounted potent neutralizing antibody responses against HIV-1(MN) and other tier 1 viruses. Occasional weak neutralizing activity was detected against tier 2 viruses. The response against tier 1 and tier 2 viruses was significantly stronger in women than in men. Race and behavioral risk of HIV-1 acquisition had no significant effect on the response. Prior vaccination had little effect on the neutralizing antibody response that arose after infection. CONCLUSIONS: Weak overall neutralizing antibody responses against tier 2 viruses is consistent with a lack of protection in this trial. The magnitude and breadth of neutralization reported here should be useful for identifying improved vaccines.

Tiered categorization of a diverse panel of HIV-1 Env pseudoviruses for assessment of neutralizing antibodies.

The restricted neutralization breadth of vaccine-elicited antibodies is a major limitation of current human immunodeficiency virus-1 (HIV-1) candidate vaccines. In order to permit the efficient identification of vaccines with enhanced capacity for eliciting cross-reactive neutralizing antibodies (NAbs) and to assess the overall breadth and potency of vaccine-elicited NAb reactivity, we assembled a panel of 109 molecularly cloned HIV-1 Env pseudoviruses representing a broad range of genetic and geographic diversity. Viral isolates from all major circulating genetic subtypes were included, as were viruses derived shortly after transmission and during the early and chronic stages of infection. We assembled a panel of genetically diverse HIV-1-positive (HIV-1(+)) plasma pools to assess the neutralization sensitivities of the entire virus panel. When the viruses were rank ordered according to the average sensitivity to neutralization by the HIV-1(+) plasmas, a continuum of average sensitivity was observed. Clustering analysis of the patterns of sensitivity defined four subgroups of viruses: those having very high (tier 1A), above-average (tier 1B), moderate (tier 2), or low (tier 3) sensitivity to antibody-mediated neutralization. We also investigated potential associations between characteristics of the viral isolates (clade, stage of infection, and source of virus) and sensitivity to NAb. In particular, higher levels of NAb activity were observed when the virus and plasma pool were matched in clade. These data provide the first systematic assessment of the overall neutralization sensitivities of a genetically and geographically diverse panel of circulating HIV-1 strains. These reference viruses can facilitate the systematic characterization of NAb responses elicited by candidate vaccine immunogens.

Simultaneous Evaluation of the Magnitude and Breadth of a Left and Right Censored Multivariate Response, with Application to HIV Vaccine Development.

Both the magnitude and breadth of neutralization against multiple strains of virus are main endpoints for comparing antibody-based HIV-1 vaccine candidates in Phase I and II trials, and are key markers to be evaluated in vaccine efficacy trials as immune correlates of protection against HIV-1 infection. More generally, consideration of both magnitude and breadth is encountered when there is interest in comparing quantitative multivariate response data between groups. In this paper, we discuss two approaches to simultaneously evaluating the magnitude and breadth of a multivariate response. We suggest methods for the summarization and group comparison of multivariate response data that are subject to left and/or right censoring. Applications to data from a phase III clinical trial (Vax004) are discussed. Simulation-based sample size calculations and power analyses of the described methods also are presented.

Inclusion of adolescents in preventive HIV vaccine trials: public health policy and research design at a crossroads.

The search for a safe effective HIV vaccine has been a centerpiece of HIV research for almost 2 decades. More than 60 clinical HIV vaccine trials have been conducted to date. Several promising candidate HIV vaccines are in advanced clinical development. To date, however, no trial has included adolescents, one of the most important target groups for any preventive HIV vaccine. To license a vaccine for use in this age group, efficacy data or, at a minimum, bridging safety and immunogenicity data in this population are needed. To accomplish this, several critical issues and special challenges in the development and implementation of HIV vaccine trials in adolescents must be addressed, including regulatory considerations, potential differentials in safety and immunogenicity, alternative trial design strategies, recruitment and retention challenges, community involvement models, and approaches to informed consent/assent. This article examines these issues and proposes specific next steps to facilitate the routine inclusion of this high-priority population in preventive HIV vaccine trials as early and seamlessly as possible.

Identification of cross-neutralization determinants by GAP analysis: a mutational behavior approach.

Antigenic variation, which is the result of amino acid substitution and genetic evolution, poses a major challenge in the development of vaccines against pathogens with unstable genomes, such as HIV-1 and Influenza. Thus, it is highly important to characterize the relationship of genetic evolution, antigenic variation and positional mutation (GAP) from the perspective of vaccine development. For this purpose, we introduce an automatic and simple GAP analysis approach, which is based on the fundamental concept of "mutational behavior" in genomic research, to predict the specificity-determining positions in protein families. This approach identifies cross-neutralization determinants by mutational behavior correlation to antigenic and genetic changes. Correlated mutation analysis and structure mapping further refine the cross-neutralization determinants. The usability of this approach is confirmed by analysis of an Influenza H3N2 cross-reactive dataset.

HIV-1 CTL-based vaccine immunogen selection: antigen diversity and cellular response features.

Much of the current effort in HIV-1 vaccine design is directed at achieving T-cell immunity that will result in enough immunological memory to contain HIV-1 infection after acquisition. However, antigenic diversity, plus a lack of understanding of HIV-1 vaccine immunology, have hindered the development of a globally effective cytotoxic T-lymphocyte (CTL)-based vaccine. Cellular response, in using a finite immune system to recognize an infinite number of potential pathogens, exhibits a series of parsimonious features. These features are considered critical in modulating HIV-1 vaccine multiple specificities. We took the features into consideration when the potential epitope coverage (E(c)) to circulating strains by current vaccine strategies was analyzed. Based on these analyses, several approaches are proposed to enhance the breadth of vaccine responses and, hence, the potential protective efficacy.

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

BACKGROUND: A goal of T-cell HIV vaccines is to define the correlation between a vaccine-induced immune response and protection from HIV infection. We conducted a phase 2 trial to determine if a canarypox vaccine candidate (vCP1452) administered with rgp120 subunit protein would "qualify" for a trial to define a correlate of efficacy. METHODS: A total of 330 healthy volunteers were enrolled into 4 groups: 120 received vCP1452 alone (0, 1, 3, and 6 months), 120 received vCP1452 with 2 different regimens of rgp120 coadministration, and 90 received placebo. HIV-specific antibody responses were measured by enzyme-linked immunoassay (ELISA) and neutralizing activity. T-cell responses were measured by chromium release and interferon-gamma (IFNgamma) enzyme-linked immunospot (ELISpot) assay. RESULTS: Significant neutralizing antibody responses to the HIV MN strain were detected in all vaccine groups, with net responses ranging from 57% (95% confidence interval [CI]: 40% to 71%) to 94% (95% CI: 85% to 99%). Net cumulative HIV-specific CD8 IFNgamma ELISpot assay responses were 13% (95% CI: -1% to 26%) for recipients of vCP1452 alone and 16% (95% CI: 2% to 29%) for recipients of vCP1452 plus rgp120. CONCLUSIONS: Overall, the HIV-specific CD8 cytotoxic T lymphocyte (CTL) response was not sufficient to qualify the regimen for a subsequent trial designed to detect an immune correlate of protection requiring a minimum CD8 CTL frequency of 30%.