Key issues for a potential human immunodeficiency virus vaccine

Prospects for prophylactic and therapeutic vaccines against hepatitis C virus

Natural cross-protective immunity is induced after spontaneous clearance of primary hepatitis C virus (HCV) infection. Although this suggests that effective prophylactic vaccines against HCV are possible, there are still several areas that require further study. Current data indicate that, at best, vaccine-induced immunity may not completely prevent HCV infection but rather prevent persistence of the virus. However, this may be an acceptable goal, because chronic persistence of the virus is the main cause of pathogenesis and the development of serious liver conditions. Therapeutic vaccine development is also highly challenging; however, strategies have been pursued in combination with current or new treatments in an effort to reduce the costs and adverse effects associated with antiviral therapy. This review summarizes the current state of HCV vaccines and the challenges faced for future development and clinical trial design.

Further progress on defining highly conserved immunogenic epitopes for a global HIV vaccine: HLA-A3-restricted GAIA vaccine epitopes

Two major obstacles confronting HIV vaccine design have been the extensive viral diversity of HIV-1 globally and viral evolution driven by escape from CD8(+) cytotoxic T-cell lymphocyte (CTL)-mediated immune pressure. Regions of the viral genome that are not able to escape immune response and that are conserved in sequence and across time may represent the "Achilles' heel" of HIV and would be excellent candidates for vaccine development. In this study, T-cell epitopes were selected using immunoinformatics tools, combining HLA-A3 binding predictions with relative sequence conservation in the context of global HIV evolution. Twenty-seven HLA-A3 epitopes were chosen from an analysis performed in 2003 on 10,803 HIV-1 sequences, and additional sequences were selected in 2009 based on an expanded set of 43,822 sequences. These epitopes were tested in vitro for HLA binding and for immunogenicity with PBMCs of HIV-infected donors from Providence, Rhode Island. Validation of these HLA-A3 epitopes conserved across time, clades, and geography supports the hypothesis that epitopes such as these would be candidates for inclusion in our globally relevant GAIA HIV vaccine constructs.

Lessons drawn from recent HIV vaccine efficacy trials

A safe and effective HIV vaccine is needed to curtail the US and global epidemics. However, the search for one has been elusive despite more than 25 years of focused research. Results from the RV144 Thai efficacy trial have renewed hope that a vaccine may protect against HIV acquisition. We can draw several scientific and operational lessons from RV144 and other recent tests-of-concept efficacy trials. Here we describe how trial results, some unexpected, highlight the fundamental role these clinical studies play in HIV vaccine discovery. These trials also teach us that transparency in data analysis and results dissemination can yield substantial rewards and that efforts to engage communities, particularly those most heavily affected by the epidemic, are needed to augment research literacy and trial recruitment. Future efficacy trial designs may incorporate novel, partially effective prevention strategies. Although greater in size and complexity, these trials may offer unique opportunities to explore synergies with vaccines under study.

HIV vaccine acceptability: a systematic review and meta-analysis

OBJECTIVE

To conduct a systematic review of the literature to examine HIV vaccine acceptability and factors impacting acceptability of future HIV vaccines.

DESIGN

Systematic review and meta-analysis of peer-reviewed articles that assessed HIV vaccine acceptability.

METHODS

We used a comprehensive search strategy across multiple electronic databases to locate original quantitative or qualitative studies that examined rates or correlates of HIV vaccine acceptability. We conducted meta-analysis on studies reporting correlates or predictors of HIV vaccine acceptability.

RESULTS

Twenty studies (n=7576) reported HIV vaccine acceptability ranging from 37.2 to 94.0 on a 100-point scale; weighted mean acceptability =65.6 (SD=21.1). Eleven studies compared HIV vaccine acceptability at high (80-95%) efficacy (mean =73.8; SD=9.2) versus moderate (50%) efficacy (mean =40.4; SD=20.2). Among 13 studies (n=5023) included in meta-analysis, efficacy and non 'risk group' membership had medium effect sizes, and pragmatic obstacles, cost, perceived susceptibility to HIV infection, side effects/safety concerns, fear of vaccines, perceived vaccine benefits, duration of protection, and ethnicity had small effect sizes on HIV vaccine acceptability.

CONCLUSION

Public health strategies to promote the benefits of partial efficacy HIV vaccines and accurate HIV risk perceptions, and to dispel vaccine fears, along with structural interventions to subsidize vaccine costs and facilitate access, may increase future HIV vaccine uptake and, in turn, the effectiveness of HIV vaccines in controlling the epidemic.

Are young injection drug users ready and willing to participate in preventive HCV vaccine trials?

Trials to evaluate the efficacy of preventive HCV vaccines will need participation from high risk HCV seronegative injection drug users (IDUs). To guide trial planning, we assessed willingness of young IDU in San Francisco to participate in HCV vaccine efficacy trials and evaluate knowledge of vaccine trial concepts: placebo, randomization and blinding. During 2006 and 2007, a total of 67 participants completed the survey. A substantial proportion (88%) would definitely (44%) or probably (44%) be willing to participate in a randomized trial, but knowledge of vaccine trial concepts was low. Reported willingness to participate in an HCV vaccine trial decreased with increasing trial duration, with 67% of participants surveyed willing to participate in a trial of 1 year duration compared to 43% of participants willing to participate in a trial of 4 years duration. Willingness to enroll in HCV vaccine trials was higher in young IDU than reported by most at-risk populations in HIV vaccine trials. Educational strategies will be needed to ensure understanding of key concepts prior to implementing HCV vaccine trials.

Global reduction of cervical cancer with human papillomavirus vaccines: insights from the hepatitis B virus vaccine experience

Background: Worldwide, prophylactic vaccines against two major human cancers are now commercially available: hepatitis B virus (HBV) vaccines (first licensed in 1982) against primary hepatocellular carcinoma and human papillomavirus (HPV) vaccines (first licensed 2006) against cervical cancer. Initial implementation strategies for HBV vaccination were not successful in preventing disease in the community: it took 15 years for significant global reduction in the burden of this disease. Methods: We compare and contrast HBV vaccine experiences to challenges for successful global HPV vaccination strategies, and make recommendations accordingly. Results: Lessons from HBV immunisation for successful outcomes with HPV immunisation showed that several factors need to be met: (i) the engagement of key stakeholders in all aspects of planning and delivery of HPV vaccine strategies; (ii) understanding the specific characteristics of targeted population groups; (iii) global cooperation and support with WHO recommendations; (iv) Government supported mass immunization programs and cooperation between public and private entities; (v) affordable HPV vaccines for some regions; (vi) culturally appropriate and diverse public education programs in targeted health promotion strategies; (vii) pro-active health providers and parents in encouraging adolescents to undertake HPV vaccination; and (vii) eventual immunisation of infants. Conclusions: The key to success will be affordable, readily deliverable HPV vaccines to young girls as universal campaigns.

Blood and seminal plasma HIV-1 RNA levels among HIV-1-infected injecting drug users participating in the AIDSVAX B/E efficacy trial in Bangkok, Thailand

BACKGROUND

We investigated effects of vaccination with AIDSVAX B/E HIV-1 candidate vaccine on blood and seminal plasma HIV-1 RNA viral loads (BVL and SVL, respectively) in vaccine recipients (VRs) and placebo recipients (PRs) who acquired infection.

METHODS

Linear mixed models were fitted for repeated measurements of BVL. Generalized estimating equations were used to assess the difference in SVL detectability between VRs and PRs.

RESULTS

A total of 196 participants became HIV-1 infected during the trial. Thirty-two (16%) became infected with HIV-1 subtype B and 164 (84%) with HIV-1 subtype CRF01_AE. Per protocol-specified analysis, there were no differences in BVL levels between VRs and PRs. When stratified by HIV-1-infecting subtype, vaccination with AIDSVAX B/E was initially associated with higher BVL among HIV-1 CRF01_AE-infected VRs compared with HIV-1 CRF01_AE-infected PRs; however, this difference did not persist over time. HIV-1 subtype B-infected VRs had slightly higher BVL levels and were more likely to have detectable SVL during the follow-up period than HIV-1 subtype B-infected PRs.

CONCLUSIONS

Subtle differences in BVL and SVL were detected between VRs and PRs. These results may help to further understand the dynamics between HIV-1 vaccination, HIV-1-infecting subtypes, and subsequent viral expression in different body compartments.

A small dose of HIV? HIV vaccine mental models and risk communication

Existing knowledge and beliefs related to HIV vaccines provide an important basis for the development of risk communication messages to support future HIV vaccine dissemination. This study explored HIV vaccine mental models among adults from segments of the population disproportionately affected by HIV/AIDS. Nine focus groups were conducted with participants (N = 99; median age = 33 years; 48% female; 22% African American, 44% Latino, and 28% white) recruited from needle exchange sites, public clinics, and gay community centers in Los Angeles. Data were analyzed using narrative thematic analysis and Ethnograph qualitative software. Mental models of HIV vaccines included live virus, side effects, complete protection (100% efficacy, lifetime protection, reduced anxiety about HIV/AIDS), and "high-risk groups." HIV vaccine risk communication to counter undue fears of vaccine-induced infection and side effects and to mitigate exaggerated expectations of a "magic bullet" may be vital to the effectiveness of first-generation HIV vaccines in controlling the AIDS epidemic.

HIV vaccine acceptability among communities at risk: the impact of vaccine characteristics

HIV vaccines offer the best long-term hope of controlling the AIDS pandemic; yet, the advent of HIV vaccines will not ensure their acceptability. We conducted a cross-sectional survey (n=143), incorporating conjoint analysis, to assess HIV vaccine acceptability among participants recruited using multi-site (n=9), venue-based sampling in Los Angeles. We used a fractional factorial experimental design to construct eight hypothetical HIV vaccines, each with seven dichotomous attributes. The acceptability of each vaccine was assessed individually and then averaged across participants. Next, the impact of each attribute on vaccine acceptability was estimated for each participant using ANOVA and then analyzed across participants. Acceptability of the eight hypothetical HIV vaccines ranged from 33.2 (S.D. 34.9) to 82.2 (S.D. 31.3) on a 0-100 scale; mean=60.0 (S.D. 21.9). Efficacy had the greatest impact on acceptability (22.7; CI: 18.5-27.1; p<0.0001), followed by cross-clade protection (12.5; CI: 8.7-16.3, p<0.0001), side effects (11.5; CI: 7.4-15.5; p<0.0001), and duration of protection (6.1; CI: 3.2-9.0; p<.0001). Route of administration, number of doses and cost were not significant. Low acceptability of "partial efficacy" vaccines may present obstacles to future HIV vaccine dissemination. Educational and social marketing interventions may be necessary to ensure broad HIV vaccine uptake.

Early markers of HIV-1 disease progression in a prospective cohort of seroconverters in Bangkok, Thailand: implications for vaccine trials

BACKGROUND

Some candidate HIV-1 vaccines may not prevent HIV-1 infection but may alter the course of disease. Surrogate endpoints based on early laboratory makers in HIV-1-infected persons who are antiretroviral therapy (ART)-naive will be useful for evaluating vaccine efficacy in slowing disease progression (VEp). We examined pretreatment HIV-1 viral loads and CD4 cell counts in recent HIV-1 seroconverters to inform selection of these endpoints.

METHODS

We studied 130 newly HIV-1-infected injection drug users identified from a prospective cohort of initially uninfected persons in Bangkok during 1995 through 1998. We analyzed trends in HIV-1 viral loads and CD4 cell counts as well as progression to the surrogate endpoint, defined as 2 consecutive CD4 cell counts of fewer than 350 cells/mm, during 24 months after the first HIV-1 seropositive (FP) visit.

RESULTS

Median HIV-1 RNA copies/mL with interquartile ranges were 43,693 (14,320-94,767) at the FP visit, 46,924 (16,273-104,314) at 6 months, 28,446 (11,292-54,325) at 12 months, and 18,080 (8713-54,059) at 18 months. HIV-1 viral loads at the FP visit and at 18 months were positively correlated (r = 0.53, P < 0.0001). Of 130 participants, 12% reached the surrogate endpoint by 6 months, 16% by 12 months, and 27% by 18 months. In Cox regression analyses, HIV-1 viral loads of more than 50,000 copies/mL at the FP visit (hazard ratio [HR] = 2.3, 95% confidence interval [CI]: 1.1-4.8) and first CD4 cell count of 500 or fewer cells/mm (HR = 7.6, 95% CI: 3.2-17.6) were independently associated with faster progression to the surrogate endpoint.

CONCLUSIONS

Participants with high HIV-1 RNA levels and low CD4 cell counts close to the time of seroconversion were more likely to experience early immunologic progression. Approximately one quarter of seroconverters reached the surrogate immunologic endpoint within 18 months of their FP visit and before starting ART, suggesting the utility of this endpoint for analyses of VEp in some ongoing and planned HIV-1 vaccine efficacy trials.

Challenges for HIV vaccine dissemination and clinical trial recruitment: if we build it, will they come?

HIV vaccine availability does not guarantee uptake. Given suboptimal uptake of highly efficacious and already accessible vaccines in the United States, low vaccine coverage in the developing world, and the expectation that initial HIV vaccines will be only partially efficacious, the public health community will face formidable challenges in disseminating U.S. Food and Drug Administration (FDA)-approved HIV vaccines. HIV/AIDS stigma, fear of vaccine- induced HIV infection, social side effects of testing HIV-positive, and mistrust of government and research present additional obstacles to HIV vaccine dissemination. Increased risk behaviors because of HIV vaccine availability can undermine the effectiveness of partially efficacious vaccines in reducing HIV incidence. HIV vaccine efficacy trials also face significant challenges in recruitment of sufficient volunteers and possible increases in risk behaviors due to trial participation. Planning and designing interventions to facilitate successful recruitment for large-scale phase 3 efficacy trials is a vital step towards U.S. FDA-approved HIV vaccines. Rather than despair in the face of momentous HIV vaccine dissemination challenges, or presume unrealistically that vaccine uptake will ensue automatically and that risk behavior increases will not occur, let us deem the estimated 10-year window to an approved HIV vaccine as an opportunity to investigate and confront these challenges. A consumer research agenda founded on social marketing principles is needed to facilitate the design of empirically-based interventions tailored to the unique needs and preferences of specific segments of consumers. Social marketing interventions may increase future HIV vaccine uptake and clinical trial participation, and mitigate increases in HIV risk behaviors.