Reappraising the Value of HIV-1 Vaccine Correlates of Protection Analyses

With the much-debated exception of the modestly reduced acquisition reported for the RV144 efficacy trial, HIV-1 vaccines have not protected humans against infection, and a vaccine of similar design to that tested in RV144 was not protective in a later trial, HVTN 702. Similar vaccine regimens have also not consistently protected nonhuman primates (NHPs) against viral acquisition. Conversely, experimental vaccines of different designs have protected macaques from viral challenges but then failed to protect humans, while many other HIV-1 vaccine candidates have not protected NHPs. While efficacy varies more in NHPs than humans, vaccines have failed to protect in the most stringent NHP model. Intense investigations have aimed to identify correlates of protection (CoPs), even in the absence of net protection. Unvaccinated animals and humans vary vastly in their susceptibility to infection and in their innate and adaptive responses to the vaccines; hence, merely statistical associations with factors that do not protect are easily found. Systems biological analyses, including artificial intelligence, have identified numerous candidate CoPs but with no clear consistency within or between species. Proposed CoPs sometimes have only tenuous mechanistic connections to immune protection. In contrast, neutralizing antibodies (NAbs) are a central mechanistic CoP for vaccines that succeed against other viruses, including SARS-CoV-2. No HIV-1 vaccine candidate has yet elicited potent and broadly active NAbs in NHPs or humans, but narrow-specificity NAbs against the HIV-1 isolate corresponding to the immunogen do protect against infection by the autologous virus. Here, we analyze why so many HIV-1 vaccines have failed, summarize the outcomes of vaccination in NHPs and humans, and discuss the value and pitfalls of hunting for CoPs other than NAbs. We contrast the failure to find a consistent CoP for HIV-1 vaccines with the identification of NAbs as the principal CoP for SARS-CoV-2.

Issues related to gay and bisexual men's acceptance of a future AIDS vaccine

The purpose of this study was to identify the salient issues related to getting a future AIDS vaccine among a high-risk group. In-depth interviews were conducted with 24 White and Black men who have sex with men (MSM). Participants reported that they would need information regarding the vaccine strategy, the clinical trials research, and vaccine attributes. A prerequisite for Black participants was the prior inclusion of Blacks in clinical trials. A high degree of safety and effectiveness, minimal side-effects, high-perceived risk, and affordable cost would promote vaccine acceptance. Barriers were low degree of safety and effectiveness, harsh side-effects, low-perceived risk, perception of a backlash effect, cost, and inconvenience. MSM may not readily get an AIDS vaccine unless they are provided with specific details and the benefits outweigh the costs. Researchers conducting HIV vaccine trials should provide information about the research and insure that samples represent Black men.

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.

A robust approach for the quantitation of viral concentration in an adenoviral vector-based human immunodeficiency virus vaccine by real-time quantitative polymerase chain reaction

A real-time quantitative polymerase chain reaction (PCR)-based method was developed to measure the concentration of recombinant adenoviral vector genomes in purified virus bulks and final container samples of monovalent and multivalent human immunodeficiency virus (HIV) adenoviral vector vaccine candidates. This method, referred to as the genome quantitation assay (GQA), was optimized through a rigorous approach for evaluating PCR detection chemistries, designing a robust assay format, and establishing a properly calibrated reference standard. In addition, the use of a simplified lysis procedure, automated liquid transfer system, and parallel-line data analysis contribute to an accurate, precise, reliable, and high-throughput assay procedure that can be used for process monitoring, final formulation, and release of vaccine products. A variance component analysis study indicated that the GQA typically produces results with an interassay precision of less than 10% relative standard deviation (RSD), allowing generation of final results (average of three runs) with associated interassay precision of 6% RSD or less. The precision, accuracy, specificity, and robustness of the GQA demonstrate its utility for analytical characterization of a wide variety of viral vector- and DNA plasmid- based vaccines or gene therapy products. In addition, we also evaluated the Adenovirus Reference Standard generated by the Adenovirus Reference Material Working Group in the GQA to provide a common point-of-reference for our analytical method.

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.

Tumorigenicity assessments of Per.C6 cells and of an Ad5-vectored HIV-1 vaccine produced on this continuous cell line

PER.C6, a cell line derived from human embryonic retinal cells transformed with the Adenovirus Type 5 (Ad5) E1A and E1B genes, is used to produce E1-deleted Ad5 vectors such as the MRKAd5 HIV-1 gag vaccine. While whole, live PER.C6 cells are capable of growing as tumours when transplanted subcutaneously into immunodeficient nude mice at a high dosage, the process for vaccine production includes filtration steps and other methods which effectively preclude contamination by intact viable substrate cells. However, because of the neoplastic nature of this cell line, we carried out a series of investigations to assess the tumorigenic risk posed by residuals from the cell substrate in a vaccine. To address concerns about transmission of oncogenic DNA, we demonstrated that purified PER.C6 cellular DNA does not induce tumours in newborn hamsters or nude mice. To address concerns about other potential residuals, including hypothetical adventitious tumour viruses, we demonstrated that a PER.C6 cell lysate and a MRKAd5 HIV-1 gag vaccine produced on PER.C6 cells do not induce tumours in newborn hamsters or newborn rats. These results, in conjunction with the wide panel of viral safety tests performed on these cells, support the safety of the PER.C6 as a cell substrate for vaccine production.

Approaches to the release of a master cell bank of PER.C6 cells; a novel cell substrate for the manufacture of human vaccines

At Merck and Co. we have developed a recombinant E1 deficient adenovirus type 5 vaccine vector for HIV-1 and have adopted the PER.C6 cell line as a cell substrate for the manufacture of this vector for Phase I and II clinical trials. The PER.C6 cell line was developed at Crucell by the transfection of human primary embryonic retinoblasts with a transgene of E1 constructed with a minimum of E1 coding sequences to preclude homologous recombination generating replication-competent adenovirus, between E1 sequences in PER.C6 and adenovirus vectors with E1 deletions of the same molecular coordinates. We have developed a Master Cell Bank (MCB) of PER.C6 cells under serum-free conditions of suspension culture from a vial of PER.C6 cells obtained from Crucell. This MCB has been released according to an extensive panel of testing for the detection of adventitious viral agents, including assays for sterility and mycoplasma, in vivo and in vitro assays for the detection of viruses of human, bovine and porcine origin, replication competent adenoviruses, sensitive PERT assays for the detection of RT in supernatants of co-cultivations, electron microscopy and a panel of PCR-based assays for specific human and animal viruses. This MCB has been used for the manufacture of vaccine vector supporting a number of IND submissions for Phase I clinical trials over a three-year period during which the panel of PCR testing applied to the MCB has been judiciously expanded. Advances in QPCR technology, liquid handling systems, and more recently mass spectrometry offer the possibility that very broad panels of primers and probes capable of the detection of all known human viruses can be applied routinely to support the release of biologicals for human clinical trials. The impact of this breadth of testing on the continued reliance of classical in vivo and in vitro assays for adventitious viruses is clearly an emerging issue worthy of serious debate.

European Union and EDCTP strategy in the global context: Recommendations for preventive HIV/AIDS vaccines research

The European Commission (EC) has strong commitments and recognises the need to continue to ensure that HIV/AIDS research efforts receive global attention. The EC is facing this challenge in a global context and has made substantial investments together with European Developing Countries Clinical Trial Partnership (EDCTP) to formulate a program for the accomplishment of a scientific strategic plan promoting the European/African HIV vaccine development approach. The EC and EDCTP has convened a number of meetings by experts in basic and clinical virology, immunology, epidemiology, as well as industrial and regulatory representatives. The remit of the committee of experts was to define (1) objective criteria for selection of HIV candidates; (2) to determine criteria for selection of sites for clinical trials in Europe and Africa. The resulting consensus paper will guide the EC and EDCTP in developing HIV vaccine strategy and recommendations.

Understanding what makes a good versus a bad vaccine

The majority of the HIV vaccines under development are aimed at stimulating T cell responses. Therefore, it is critical to delineate the factors regulating the generation of the T cell responses and to develop strategies maximizing vaccine-induced T cell responses. The identification of these factors and the delineation of the kinetics of the generation of vaccine-induced immune responses have been hard to investigate, due to the limited number of precursor naive antigen-specific T cells. To overcome these obstacles, Estcourt and collaborators have developed an elegant strategy that consists of an in vivo mouse model employing transfer of naive CFSE-labeled TCR-transgenic T lymphocytes into syngeneic nontransgenic recipients prior to vaccination. Using this model, the authors demonstrate that the dose, the route of administration and the type of vaccine determine the magnitude, the dissemination and the kinetics of vaccine-induced T cell responses. Furthermore, the mouse model of Estcourt and collaborators may represent the basis for the development of powerful in vivo experimental strategies to evaluate vaccine candidates.

Posttrial HIV vaccine adoption: concerns, motivators, and intentions among persons at risk for HIV

BACKGROUND

Suboptimal uptake of existing vaccines, potential obstacles specific to HIV/AIDS stigma and mistrust, and marked health disparities suggest that it is vital to investigate consumer concerns, motivations, and adoption intentions regarding posttrial HIV vaccines before a vaccine is publicly available.

METHOD

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 7 high-risk venues in Los Angeles using purposive venue-based sampling. A semistructured interview guide elicited concerns, motivators, and adoption intentions regarding hypothetical U.S. Food and Drug Administration-approved HIV vaccines. Data were analyzed using narrative thematic analysis and Ethnograph qualitative software.

RESULTS

Concerns included vaccine efficacy, vaccine-induced infection, vaccine-induced HIV seropositivity, side effects, cost/access, trustworthiness, and relationship issues. Motivators included protection against HIV infection and the ability to safely engage in unprotected sex. Participants expressed reluctance to adopt partial efficacy vaccines and likelihood of increased sexual risk behaviors in response to vaccine availability.

CONCLUSION

Tailored interventions to facilitate uptake of future U.S. Food and Drug Administration-approved HIV vaccines and to prevent risk behavior increases may be vital to the effectiveness of vaccines in controlling the AIDS pandemic.

Biologic and genetic characterization of a panel of 60 human immunodeficiency virus type 1 isolates, representing clades A, B, C, D, CRF01_AE, and CRF02_AG, for the development and assessment of candidate vaccines

A critical priority for human immunodeficiency virus type 1 (HIV-1) vaccine development is standardization of reagents and assays for evaluation of immune responses elicited by candidate vaccines. To provide a panel of viral reagents from multiple vaccine trial sites, 60 international HIV-1 isolates were expanded in peripheral blood mononuclear cells and characterized both genetically and biologically. Ten isolates each from clades A, B, C, and D and 10 isolates each from CRF01_AE and CRF02_AG were prepared from individuals whose HIV-1 infection was evaluated by complete genome sequencing. The main criterion for selection was that the candidate isolate was pure clade or pure circulating recombinant. After expansion in culture, the complete envelope (gp160) of each isolate was verified by sequencing. The 50% tissue culture infectious dose and p24 antigen concentration for each viral stock were determined; no correlation between these two biologic parameters was found. Syncytium formation in MT-2 cells and CCR5 or CXCR4 coreceptor usage were determined for all isolates. Isolates were also screened for neutralization by soluble CD4, a cocktail of monoclonal antibodies, and a pool of HIV-1-positive patient sera. The panel consists of 49 nonsyncytium-inducing isolates that use CCR5 as a major coreceptor and 11 syncytium-inducing isolates that use only CXCR4 or both coreceptors. Neutralization profiles suggest that the panel contains both neutralization-sensitive and -resistant isolates. This collection of HIV-1 isolates represents the six major globally prevalent strains, is exceptionally large and well characterized, and provides an important resource for standardization of immunogenicity assessment in HIV-1 vaccine trials.

The private demand for an AIDS vaccine in Thailand

A contingent valuation survey of Thai adults revealed that private demand for a hypothetical AIDS vaccine that is safe, has no side effects, and lasts 10 years, rises with income, the lifetime risk of HIV infection and vaccine efficacy, and declines with vaccine price and respondent's age. Demand for both high (95%) and low (50%) efficacy AIDS vaccines is substantial. Nearly 80% of adults would agree to be vaccinated with a free vaccine. Government will have an important role to ensure that those at highest risk of HIV infection with low incomes have access to the vaccine and to reinforce other safe preventive behavior to prevent reductions in condom use.

Measuring HIV vaccine efficacy

Some HIV vaccine candidates have a potential VE I (vaccine efficacy for infectiousness) type effect, which tends to reduce the viral load and may reduce infectiousness of an infected individual. In general, the efficacy of this kind of vaccine is very difficult to assess because it requires information on contacts of vaccinated infected individuals, and current methods to estimate VE I rely on the time elapsed between infections of an individual and his/her sexual partner, thus making infection of the sexual partner necessary to assess the efficacy. To avoid behavioural changes that may affect the estimates, HIV status is kept undisclosed to participants, which raises many ethical questions. Here we present a method that allows immediate notification of HIV status to both members of a couple, reducing the risk of infection when one of them has not been infected and allowing immediate medical treatment. The method allows for estimation of any VE I and VE S (vaccine efficacy for susceptibility) effect, and it is robust to the most common situations found in these type of studies, namely: differential risk of participants, staggered enrollment and small sample sizes.

Hemagglutinating virus of Japan protein is efficient for induction of CD4+ T-cell response by a hepatitis B core particle-based HIV vaccine

By using the hepatitis B core (HBc) protein gene as a carrier, HIV-1 env V3 gene was inserted into the carrier gene, and the HIV gene was expressed inside a chimeric HIV-HBc particle (HIV-HBc), which was a unique candidate for induction of HIV-specific CTL activity. This was seen significantly in mice without the need of an adjuvant, because other responses specific for the HIV peptide such as T-cell proliferation and antibody production were not induced. However, when hemagglutinating virus of Japan (HVJ) protein was incorporated into an anionic liposome containing HIV peptide (HIV-HVJ-liposome) and was used as a booster immunization in HIV-HBc primed animals, the HIV-specific T-cell response and enhanced CTL activity were clearly induced in consecutively immunized animals. Furthermore, the HIV-specific humoral immune response was also induced and a neutralization activity was detected in the immune sera. Thus, when an HIV peptide antigen is expressed inside the virus like a particle of HBc, it can induce both cellular and humoral immunities when an HVJ-HIV-liposome, but not an HIV-liposome, is inoculated as the booster antigen. The HVJ-stimulated splenocytes secreted IL-18 and IL-12 to synergistically enhance the secretion of IFN-gamma in vitro. These findings suggest that the HVJ protein is effective at inducing the HIV-specific immunities, if used as part of a booster antigen in the consecutive immunization regimen.

[Clinical trials in "developing" countries: is there a special "Third World" ethic?]

With increasing frequency, clinical trials are carried through in countries of the "third world". In particular, recent studies aimed at establishing the efficacy of new AIDS therapies, or AIDS vaccines, applied lower ethical standards than those formulated by the Declaration of Helsinki of the World Medical Association, and accepted in the US and internationally,--although American researchers and institutions were involved in these studies. The paper reconstructs the controversies following the publication of these studies, and analyses the conditions for the existence of such double standards of research ethics. Particular attention is given to the concept of informed consent and the difficulties to put it into practice in different cultural contexts.

Particle-based vaccines for HIV-1 infection

The use of live-attenuated viruses as vaccines has been successful for the control of viral infections. However, the development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge. HIV infects cells of the immune system and results in a severe immunodeficiency. In addition, the ability of the virus to adapt to immune pressure and the ability to reside in an integrated form in host cells present hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes from different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immunity, however, a live-attenuated vaccine for HIV is problematic. The possibility of a live-attenuated vaccine to revert to a pathogenic form or recombine with a wild-type or defective virus in an infected individual is a drawback to this approach. Therefore, these vaccines are currently only being tested in non-human primate models. Live-attenuated vaccines are effective in stimulating immunity, however challenged animals rarely clear viral infection and the degree of attenuation directly correlates with the protection of animals from disease. Another particle-based vaccine approach for HIV involves the use of virus-like particles (VLPs). VLPs mimic the viral particle without causing an immunodeficiency disease. HIV-like particles (HIV-LP) are defined as self-assembling, non-replicating, nonpathogenic, genomeless particles that are similar in size and conformation to intact virions. A variety of VLPs for both HIV and SIV are currently in pre-clinical and clinical trials. This review focuses on the current knowledge regarding the immunogenicity and safety of particle-based vaccine strategies for HIV-1.

Immunological approaches for HIV therapy

The induction of a Th-1 polarized immune response is believed to be advantageous when designing immunologic approaches for HIV therapy. DNA vaccines represent one of the best immunologic strategies capable of inducing such a response. From conception to clinical application it is now possible to rationally design DNA vaccines based on reliable experimental data, thus a systemic approach to the development of new and the enhancement of existing vaccine immunogens is now possible. The addition of adjuvants may also increase immunogenicity and depending on the choice of adjuvant, polarize the immune response. Other important factors in the formulation of a successful vaccine are the selection of administration route, heterologous or homologous prime/boost schedules, and the feasibility of the eventual clinical application. This review will summarize recently developed preventive and therapeutic vaccines, and carefully evaluate the advantages and potential risks for Human Immunodeficiency Virus (HIV) infected patients. Finally, the concept of "autovaccination" will be defined as it represents the basis for the development of our innovative therapeutic antigen presenting cell targeted HIV vaccine. DermaVir is the first topical vaccine, in combination with antiretroviral therapy, to demonstrate immunological and clinical benefits in a relevant animal model (chronically infected rhesus macaques).

Immune responses in baboons vaccinated with HIV-2 genetic expression libraries

Immunization using genetic expression libraries may be an improvement over conventional DNA immunization using a single gene because more epitopes are simultaneously presented to the immune system. In this study, we evaluated the effectiveness of an HIV-2 vaccine made from a genomic expression library in baboons. We found that HIV-2 expression library immunization induced HIV-2-specific memory responses but low levels of CD8+ cell anti-viral responses and neutralizing antibodies. After intravenous virus challenge using a homologous pathogenic variant, HIV-2UC2/9429, viral loads were similar in the HIV-2-immunized and control baboons. We conclude that although immunization using HIV-2 expression libraries induces immune responses, this approach does not provide protection in baboons against intravenous challenge with HIV-2.

Scientific considerations for the regulation and clinical evaluation of HIV/AIDS preventive vaccines: report from a WHO-UNAIDS Consultation 13-15 March 2001, Geneva, Switzerland

The consultation was jointly organized by the WHO-UNAIDS HIV Vaccine Initiative and the Quality Assurance and Safety of Biologicals Team of the World Health Organization (WHO). Thirty-four experts from 16 developed and developing countries attended the meeting, bringing together expertise from academic institutions, clinical trial centres, national and international regulatory authorities. Representatives of major pharmaceutical companies were also invited. The primary objective of the meeting was to identify gaps that need to be addressed from regulatory perspective to ensure appropriate progress of HIV vaccine development from basic research to human trials, licensing and future application, with a special focus on needs of developing countries. As a result of discussions, the following priority needs were identified and recommendations were made in order to establish an appropriate regulatory framework for the development and evaluation of preventive HIV/AIDS vaccines, which were divided in two main areas: (a) standardization and control of candidate HIV/AIDS vaccines, and (b) approaches to the conduct of clinical trials of candidate HIV/AIDS vaccines.

Lipopeptide vaccines--yesterday, today, and tomorrow

Peptide-based vaccines offer several potential advantages over the conventional whole proteins (or whole gene, in the case of genetic immunisation) in terms of purity and a high specificity in eliciting immune responses. However, concerns about toxic adjuvants, which are critical for immunogenicity of synthetic peptides, still remain. Lipopeptides, a form of peptide vaccine, discovered more then a decade ago, are currently under intensive investigation because they can generate comprehensive immune responses, without the use of adjuvants. In this review, we address the past of lipopeptide vaccines, highlight the progress made toward their optimisation, and stress future challenges and issues related to their synthesis, formulation, and delivery. In particular, the recent development of mucosal application of lipopeptide vaccines may present an ideal strategy against many pathogens that infect mucosal surfaces.

Willingness to volunteer in future preventive HIV vaccine trials: issues and perspectives from three U.S. communities

This study examined perceived risks, benefits, and desired information related to willingness to volunteer in preventive HIV vaccine trials.

SAMPLE

Purposive sampling was used to select 90 participants among injecting drug users (Philadelphia, PA, U.S.A.); gay men (San Francisco, CA, U.S.A.); and black Americans (Durham, NC, U.S.A.).

METHODS

A qualitative interview guide elicited perceived benefits, risks, and desired information relating to trial participation. Themes were developed from the transcribed texts and from freelists.

RESULTS

Stated willingness to volunteer in a preventive HIV vaccine trial was similar across the three communities. Eight perceived benefits were reported, including self-benefits, altruism, and stopping the spread of AIDS. Seven perceived risks were reported, including negative side effects and vaccine safety issues, contracting HIV from the vaccine, and social stigmatization. Participants voiced the desire for eight types of information about issues relating to trust and confidentiality in the research process, health complications and later assistance, and vaccine trial methodology.

CONCLUSIONS

In this study, many benefits as well as risks of preventive HIV vaccine trial participation were cited. Scientists conducting preventive HIV vaccine trials need to address community perceptions of risks and provide information about the research if trial enrollment is to be diverse and successful.

Comparison of competing risks failure time methods and time-independent methods for assessing strain variations in vaccine protection

In a preventive vaccine efficacy trial of a vaccine for a genotypically and phenotypically diverse pathogen, it is important to assess if and how vaccine protection against infection or disease varies with characteristics of the exposing pathogen. Gilbert, Self and Ashby developed statistical methods for this problem when the outcome data are counts of the number of vaccinated and unvaccinated trial participants infected by each pathogen strain. However, in many vaccine trials time-to-case information is available, and the extent to which this information improves investigation of differential vaccine protection is unclear. We describe how cause-specific proportional hazards models and other popular competing risks failure time techniques can be applied to this problem. This includes new results on the assumptions required for these methods to give valid inferences about strain-specific vaccine efficacy, and a comparison of theoretical and finite-sample properties between these methods and the time-independent methods. Theoretical considerations, a cholera vaccine trial example, and an extensive simulation study of a human immunodeficiency virus type 1 (HIV-1) vaccine trial show that information about failure times does not appreciably improve estimation or testing unless the pathogen has a high attack rate and the relative prevalence of pathogen strains shifts substantially during the trial follow-up period. An important implication is that practically optimal evaluation of strain-specific vaccine efficacy in HIV-1 vaccine trials will not require knowledge of infection times.

AIDS and Africa

Africa is dying. As much of the world turns its back, and a powerful spokesman in Africa insists that HIV is not the cause of AIDS, unimaginable numbers of young Africans are condemned to an early death. Public opinion in the West, meanwhile, turns its back on the catastrophe. 'The victims are distant blacks in an alien culture. They simply don't concern us.' This reprehensible attitude has all but excluded the tragedy from the UK media.

A simple vaccination model with multiple endemic states

A simple two-dimensional SIS model with vaccination exhibits a backward bifurcation for some parameter values. A two-population version of the model leads to the consideration of vaccination policies in paired border towns. The results of our mathematical analysis indicate that a vaccination campaign &phi; meant to reduce a disease's reproduction number R(&phi;) below one may fail to control the disease. If the aim is to prevent an epidemic outbreak, a large initial number of infective persons can cause a high endemicity level to arise rather suddenly even if the vaccine-reduced reproduction number is below threshold. If the aim is to eradicate an already established disease, bringing the vaccine-reduced reproduction number below one may not be sufficient to do so. The complete bifurcation analysis of the model in terms of the vaccine-reduced reproduction number is given, and some extensions are considered.

Simulation studies of phase III clinical trials to test the efficacy of a candidate HIV-1 vaccine

One question of particular importance in phase III HIV vaccine trials is the choice of efficacy measure (EM) to validly and precisely estimate the true vaccinal efficacy. Traditional EMs, based on hazard rate ratio (HRR) or cumulative incidence ratio (CIR) are time-sensitive to mode of vaccine action and population heterogeneities. Through Monte-Carlo simulation, the performance of HRR and CIR based EMs are examined across different trial designs and vaccine and population characteristics. A new EM based on log-spline hazard regression (HARE) is proposed. Given that vaccinal properties (mode of action, time-lag, waning) are unknown a priori, appropriate selection of EM is problematic, and HRR and CIR can be unreliable to estimate the true maximum efficacy of candidate products. Non-random sexual mixing can exacerbate biases in HRR and CIR. HARE can offer valid estimation across different modes of vaccine action and in presence of frailty effects, contrary to its traditional counterparts. Our simulation studies highlight the weaknesses of widely used EMs while offering guidelines for trial design and suggesting new avenues for statistical analysis.

HIV vaccines

In summary, the development of HIV vaccines has progressed from simple first-generation env subunit vaccines to second-generation vaccines containing multiple subunits. Vaccines with epitopes for CMI and Ab responses have broadened the immune response and the potential efficacy of these vaccines. It is hoped that newer technologies including the development of adjuvants, new types of vaccines, such as naked DNA, and new delivery systems, such as liposomes, will evoke stronger immune responses with longer duration. Improved schedules for dosing and combinations of HIV vaccines may result in longer lasting immune responses. A phase III trial is anticipated to begin within the next 2 years. After a temporary lull, the outlook for HIV vaccine development is being met once again with strong enthusiasm and encouragement for the future.

A Markov model for measuring vaccine efficacy for both susceptibility to infection and reduction in infectiousness for prophylactic HIV vaccines

We use a discrete-time non-homogeneous Markov chain to model data from augmented human immunodeficiency virus (HIV) vaccine trials. For this design, the study population consists of primary participants some of whom have steady sexual partners who are also enrolled to augment the trial. The state space consists of the infection status of primary participants without steady partners and the infection status of both persons in the steady partnerships. The transition probabilities are functions of the two parameters: vaccine efficacy for susceptibility (VES) and infectiousness (VEI). We use likelihood methods to estimate VES and VEI from time-to-event data. We then use stochastic simulations to explore the bias and precision of the estimators under various plausible conditions for HIV vaccine trials. We show that both the VES and VEI are estimable with reasonable precision for the conditions that may exist for planned HIV vaccine trials. We show that exams conducted every six months will likely provide sufficient information to estimate the VE parameters accurately, and that there is little gain in precision for more frequent exams. Finally, we show that joint estimation of the VES and VEI will likely be feasible in a currently planned HIV vaccine trial among injecting drug users in Bangkok, Thailand, if one augments the information about the primary participants in the trial with information about their steady sexual partners.

Safety and immunogenicity of a recombinant HIV type 1 glycoprotein 160 boosted by a V3 synthetic peptide in HIV-negative volunteers

The safety and the immunogenicity of a recombinant hybrid envelope glycoprotein MN/LAI (rgp160) followed by booster injections of a V3 (MN) linear peptide were evaluated in HIV-negative adults at low risk for HIV infection. Volunteers received either rgp160 in alum at 0, 1, and 6 months (group A), rgp160 at 0 and 1 months followed by V3 at 3 and 6 months formulated in alum (group B), or in Freund's incomplete adjuvant (FIA) (group C). Local and systemic reactions were mild to moderate and resolved within the first 72 hr after immunization. No significant biological changes (routine tests and autoantibodies) were observed. One month after the last injection in either group, neutralizing antibodies (NAs) against the HIV-1 MN isolate were detected in 4 of 5 (A), 7 of 10 (B), and 10 of 10 (C) subjects with significantly higher geometric mean titers in the latter group. Four of nine sera with the highest NA titers against MN weakly cross-neutralized the HIV-1 SF2 isolate; none had NA against the HIV-1 LAI strain or against a North American primary isolate. Specific lymphocyte T cell proliferation to rgp160 was detected in 92% of the subjects after the second injection of rgp160 and in 80% of them 12 months after the first injection. A weak and short-lived envelope-specific CD(4+)-mediated cytotoxic lymphocyte activity was detected at certain time points in few subjects. This prime-boost vaccine approach using rgp160 followed by a V3 peptide was safe in humans, and was able to elicit high levels of neutralizing antibodies and a strong and persistent T cell lymphoproliferative response to rgp160 and to V3. However, the neutralization response was restricted to the homologous HIV-1 strain and little env-specific cytotoxic activity was induced.

Statistical issues in the design of HIV vaccine trials

HIV vaccine trials present significant challenges related to trial endpoints, vaccine efficacy measurement, and the role of nonvaccine interventions. Infection is a valid endpoint for detecting sterilizing immunity. But if the vaccine prevents AIDS without preventing infection, infection may be a misleading surrogate. Appropriate endpoints must be defined for other mechanisms of vaccine action. Direct, indirect, behavioral, and biological effects all determine vaccine efficacy. False security among HIV-vaccine recipients may make negative behavioral effects an important component of vaccine performance. Both biological potency and a more comprehensive program effectiveness should be measured. These goals may require unblinded designs or community randomization. Nonvaccine interventions are currently the only HIV-prevention strategy. Support for larger scale implementation requires more rigorous evaluation that is less dependent on self-reported behavioral changes. The vaccine trial cohorts provide a unique opportunity to cost-effectively evaluate behavioral interventions.