Introduction In 2003 the results of the first two efficacy trials of candidate HIV-1 vaccines will be available. The first, the AIDSVAX B/B trial, was started in 1998 in the USA, Canada, Puerto Rico and the Netherlands. The trial will conclude in late 2002 with initial efficacy results available in the first quarter of 2003. The second, the AIDSVAX B/E trial, was started in Bangkok, Thailand in 1999 and will similarly have initial efficacy results available in late 2003. Each study is unique. The North American/European trial will determine the efficacy of AIDSVAX B/B, a bivalent subtype B gp120 vaccine using MN and GNE8 antigens, in preventing sexual transmission of HIV-1 in geographical areas where subtype B HIV is most prevalent. For this trial, 5108 men who have sex with men (MSM) and 309 high-risk women have volunteered. The Thailand trial will determine the efficacy of AIDSVAX B/E, a bivalent gp120 vaccine containing the MN and A244 envelope antigens from subtype B and subtype E viruses respectively, against blood-borne infection (Fig. 1). This trial involves 2545 injecting drug users (IDU), mostly heroin addicts, in Bangkok where both subtype B and subtype E HIV are prevalent [1].Fig. 1.: Vial of AIDSVAX B/E vaccine.The road from initial pre-clinical and clinical results to phase III efficacy trials has been long and difficult. The purpose of this paper is to review the lessons that have been learned through the experience of conducting the first phase III HIV vaccine efficacy trials. The VaxGen HIV-1 preventive vaccine—AIDSVAX The rationale for these recombinant gp120 envelope vaccines has been described in detail elsewhere [2]. Briefly, the design and manufacture of gp120 by recombinant DNA technology is similar to that of the licensed hepatitis B vaccine and the candidate herpesvirus type II vaccine. The evaluation of the safety and potential efficacy of these candidate HIV vaccines has, by necessity, also followed a development course similar to that of hepatitis B vaccine where the only susceptible animal model, for both viruses, is the chimpanzee. Pre-clinical studies of AIDSVAX showed impressive chimpanzee protection with minimal toxicity [3,4]. From chimpanzees, evaluation of the vaccine advanced to human studies. In these studies, essentially all recipients developed a robust immune response as judged by both binding and functional antibodies as well as skin-test positivity [1,5]. Evaluation of the safety of AIDSVAX has shown that both formulations have an acceptable safety profile with only mild injection site pain and tenderness being the most common adverse effect. AIDSVAX B/B and B/E vaccines are composed of rgp120/HIV-1 recombinant envelope glycoproteins produced by expression of the fusion proteins in genetically engineered Chinese hamster ovary cell lines. Based on complementary characteristics, two subtype B antigens, MN and GNE8, were selected for the B/B vaccine intended to cover the majority of subtype B HIV strains present in North America and Europe. The MN antigen is derived from a T-cell tropic or syncytium-inducing B subtype of HIV-1 and requires the CXCR4 receptor to bind to CD4 cells. The GNE8 antigen is macrophage tropic, non-syncytia inducing and requires the CCR5 receptor to bind to CD4 cells. Based on analysis of amino acid sequence, MN and GNE8 differ by approximately 15% and thus should cover around 80% of the subtype B viruses prevalent in North America and Europe. AIDSVAX B/E consists of the same MN antigen along with the A244 antigen which is derived from the CM244 subtype E strain of HIV. This latter virus is a primary macrophage-tropic, non-syncytia inducing and requires the CCR5 chemokine receptor to bind to CD4. Being from different HIV-1 subtypes, the amino acid sequences of these two antigens differ by 30% and should cover both subtypes B and E viruses which are prevalent in Thailand. The bivalent vaccines contain 300 μg of each antigen with 600 μg of alum adjuvant and are administered by intramuscular injection. AIDSVAX B/B and AIDSVAX B/E are currently being tested for protective efficacy and safety in randomized, placebo-controlled, double-blinded phase III trials in North America and Europe (VAX004), and in Thailand (VAX003). A total of seven immunizations with either bivalent vaccine are administered at months 0, 1, 6, 12, 18, 24, and 30. In VAX004, 5417 volunteers in North America and Europe at high risk of contracting HIV-1 via sexual transmission will be immunized with AIDSVAX B/B or placebo (2 : 1 ratio). And in VAX003, 2545 volunteers in Thailand at high risk of contracting HIV-1 via injecting drug use will be immunized with AIDSVAX B/E or placebo (1 : 1 ratio). These vaccines that are currently in phase III evaluation are derived from a long and arduous research and development path that started with the determination of the molecular structure of HIV by researchers at Genentech, Inc. in 1984 [6] (Fig. 2). Since that time, the antigens have been tested, rejected, restructured, and retested. Initial failed attempts to protect chimpanzees [7] resulted in the redesign of the HIV antigen selected for the vaccine altogether. Eventually, after showing that antibodies to gp120 inhibit binding of gp120 to CD4 cells [8], determination of the disulfide and carbohydrate structure of gp120 [9], and showing that monovalent gp120 makes neutralizing antibodies in humans [10], the effort proceeded. Multiple phase I/II clinical trials in humans were conducted to arrive at the optimal dosing and administration schedule. This development endeavor will have taken almost 20 years and has cost over $300 million dollars to complete. Although long and difficult, this process is not unlike that of many other vaccines that have been brought to licensure [11].Fig. 2.: Timeline for development of the phase III HIV vaccine trials.Social value of vaccines Although vaccines are well understood to be the key to controlling epidemic infectious diseases like AIDS, they do not receive the same social, political, or financial support as do therapeutic agents. This contrast is exemplified by a variety of measurements. Consider the immense international activism over the past decade in the USA and more recently in developing countries protesting the lack and cost of anti-HIV therapeutic agents. Multiple activist groups and protest actions have resulted in the establishment of large public funds to help develop these antivirals and, later, to purchase them. The fact that over 20 anti-HIV therapeutic drugs have completed phase III studies and have been licensed attests to the success that has followed this high social valuation. Contrast this result to the lack of social activism and funds established for an HIV/AIDS vaccine. The scientific challenge of developing vaccines is certainly no greater than that posed by developing antiviral agents. Indeed, prior to the HIV/AIDS epidemic, the search for antiviral agents for other viruses seemed overwhelming. In contrast, multiple effective viral vaccines had been developed and were widely used. It has been different for AIDS. Since the beginning of the epidemic, a large number of antiviral therapeutic agents have entered phase III testing, and many have been subsequently licensed. In contrast, only one preventive HIV candidate vaccine, AIDSVAX, has thus far entered phase III testing. Why? We propose that this effect reflects the lack of social value currently given to vaccines in general and to HIV vaccines in particular—a difficult lesson for those attempting to develop them. Industry will follow social value. If society values a vaccine and there is a potential return on investment, industry can better accept the risk of the development costs. Like therapeutic drugs, hundreds of millions of dollars are required to bring a candidate vaccine through phase III testing. Without societal recognition of the impact of vaccines on disease prevention and the potential for profit incentives for industry, it has been very difficult to convince industry to invest the resources necessary to bring candidate vaccines forward. Lesson: To stimulate industry to invest in preventive vaccines, society must recognize the value that they deserve. Health care and public health officials must more effectively address this societal need and policy makers must establish funds and mechanisms to retain and stimulate industry involvement in vaccine development. Taking risk: government, activists and industry In the early 1990s the United States government, through the National Institutes of Health (NIH), worked with industry and shared some of the expenses of HIV vaccine development. In 1994, two envelope-based recombinant vaccines had completed phase II testing and met the government's criteria to advance to phase III trials. But at the time, a constellation of forces influenced the NIH to alter the phase III advancement criteria and a decision was made not to sponsor the phase III trials. The decision was based on political, financial, and scientific grounds. Although both vaccines had protected chimpanzees from large intravenous challenges of HIV-1, there was concern that the vaccines may not protect humans. The NIH formed a scientific committee that reviewed all of the data and advancement to phase In some activists concern was that support of a large vaccine study funds from of therapeutic drug research and development. In some were that of funds to support vaccine clinical trials the available for The of these two with the of some that a better candidate vaccine, a followed by a gp120 was around the the NIH with from committee to to not support the phase III trials This decision was a to vaccine development and industry with the that the was not a development Lesson: If the and to stimulate vaccine they must that can and the and both financial and political, which are required for the development of an HIV vaccine. for of Without VaxGen had to for to the millions of dollars to the of the vaccine and to the phase III trials. In the of or VaxGen to these many the potential to be adverse to But potential not vaccine on researchers to help in the this is will to with vaccine they invest in a vaccine the research and industry development is and not by the research The the process required to the research and the industry process required to a candidate for and are and the value of the research be for years it must advance through the of development a licensed many of the researchers these have no experience in the process of vaccine development and, do not the research and development. the years there have been many scientific or of the or a vaccine in the these have a vaccine that has protected a in one vaccine development experience and to the impact that or may have on the of volunteers in a phase III trial or to the who may be to the trial, the that candidate be the to an vaccine. public not can have adverse to studies and The of in the vaccine can be For are not a the fact that this is the only animal susceptible to HIV-1 and most the of HIV-1 infection in the by gp120 do not the fact that no of this as a of protection has been Indeed, from chimpanzees that were protected against a challenge not HIV-1 in the primary that was to protection of volunteers will the of volunteers for other the fact that many more are for studies Lesson: and must with and experience and not be by or the research of the Without from a scientific from of will be to the potential value of a and support industry to develop an effective HIV vaccine. in the and as is review some adverse of a vaccine VaxGen was in million dollars to bivalent vaccine and the phase III trials. A this process was the with the USA, and In contrast to the lack of vaccine development experience the and committee were and The by these most the and the were and the from these groups to the of the phase III studies. Lesson: can be in the of and review of trial to advance HIV vaccine development. These should high in the the of the and can be the viral of protection vaccine to phase III the of the of HIV-1 vaccine development has been viral the of the of the virus and the need for a the vaccine candidate and the viruses in the being entered phase III trials. VaxGen has taken the and has that this is have that both by HIV CXCR4 and should be the monovalent MN subtype B gp120 vaccine and two bivalent AIDSVAX B/B for the North American/European study and AIDSVAX B/E for the Thailand study [2]. do not vaccine protection may by or drug or type or of immune response are necessary for vaccine For this are conducting trials in the risk groups of and to determine of makes a and immune response by a variety of and to determine the of It is only through efficacy trial results that immune of protection can be Lesson: of the to will be candidate vaccines clinical should use trials to to advance vaccine development. If the need for a vaccine the financial, and scientific one must and the data the trial To the efficacy of an HIV vaccine, of at risk for HIV infection are required to the will at a of the VaxGen the two phase III studies was that the the study or it to a that determination of efficacy was not and who had to in studies and that the and available. Indeed, multiple studies of both and the risk of these in the of concern these studies was a vaccine trial was in these for vaccine trials and, they they with the of a The concern was given that the volunteers are to at receive seven vaccine or placebo have at and multiple and and over a trial Consider the of a effort that was in of volunteers only to have a high the data in vaccine there were data available that that a was experience with the hepatitis B vaccine trials that the of of volunteers was and that were experience showed that be and that the was In data had been the of conducting vaccine trials studies by the Health the for and and the Bangkok showed that had a high of that they be followed over time, and that they for a vaccine trial These studies of the of infection in the of and of high-risk to in vaccine and the this the number of volunteers required for a study be the process of conducting these studies as and for in and for the success of phase III Lesson: studies well in advance of efficacy trials is the large of resources to a trial need data to that the trial is The data by and studies were very to those of and large efficacy trials. In as are and research are a of This to be key in developing and general study a of was it was far to that as the studies. with for success in Thailand was the and of the and vaccine to advance the of HIV vaccine in the of United States was to VaxGen in Thailand. and Thailand with the development of a National for HIV which a and an through which candidate vaccines be from research to To that trials be conducted with the scientific and were along with to and of HIV vaccine trials. This was by international Indeed, the AIDSVAX B/E trial was reviewed by no than or the for HIV of the Thailand National the of the Thailand of the Bangkok the the for and the for the of and the Although this review of the first international phase III trial was necessary by VaxGen to the international scientific that this trial was being Lesson: health be a and of vaccine development in support of public The of those to advance vaccine trials in the of In the of an by establish review of the international Although the international review and process has that the Thailand trial is conducted the scientific and design A HIV vaccine is one that either infection disease infection For the primary prevention of one must have an that volunteers from For AIDSVAX, this has been as a can HIV infection antibodies to multiple from the envelope with the more DNA or vaccine of the which may antigens from multiple HIV infection from immune response to the vaccine may present For the prevention or of has the beginning of the AIDSVAX trials. that time, the was to use were to as to the clinical of But as the years have data have that the of virus in the of well with disease studies to clinical to follow volunteers for a it must be that evaluation of for efficacy may be from the of primary efficacy evaluation to the required for of the Lesson: studies data for the and clinical disease We have with the use of to for HIV infection the course of efficacy trials. as HIV vaccine more by the of other viral antigens, volunteers from volunteers may difficult. We have also learned that the primary and can be as and that one has to for the fact that the primary of prevention of infection will be the data to prevention of disease will available. This fact has for the of and determination of In it is in the evaluation of candidate HIV vaccines to the effect of prevention of infection and the public health of or the of disease in the who also the of there was concern that 300 women and not be the trials or the number of to in vaccine that the AIDSVAX trials the of trial experience that many are to for HIV vaccine trials. they trial an to do to help the It is to that the for the North American/European trials have in different geographical have on have on the general to the and have on to the In it was more as the is of and a high of HIV infection as as of those in Lesson: were of high-risk who to after trials were and trials can be of vaccine trial on the of volunteers who will the In large the key to this success on the and of the and to establish a with each This to the to a study that arduous over In there are other that can to the North study the USA and the course of the the study to have a high of of the volunteers in this study have with some two or the of has almost all volunteers to be to study In Thailand the has been In Bangkok, of is with approximately in or This fact has establishment of a the health of the Bangkok and the Bangkok of that be in or the of volunteers and to the either from or other Lesson: and are of conducting a If the and to the of volunteers will be to the study and the to determine the efficacy of the vaccine will be social the advancement of AIDSVAX phase III there were those who potential that a study The two vaccine trial may and volunteers experience or other social on in a trial or testing tested for HIV of the the potential for risk were taken in the and of volunteers in the phase III studies to that volunteers understood the of and the of the trial, and that they should not protection from For other social the of were made available to help potential that may trial In were established to these potential that an and the potential for social the both studies, have been that trial has not resulted in a number of social as of or or In social have been very with the majority being to by or to volunteers have in the In these have to volunteers in the VaxGen trials are and risk the risk has in both AIDSVAX studies, most in Thailand where and had not been as as in North America and Europe. it must be that a and effective preventive HIV vaccine risk and must be and in with vaccine potential social the of is not a with a gp120 vaccine. of the of gp120 in the virus for AIDSVAX the of high If the is it is very to from HIV infection by testing. Lesson: is in HIV vaccine trials. in of potential and social in the design of the study has to address and to that the study is not the social that were vaccine safety Although pre-clinical animal toxicity studies and clinical phase and phase II studies showed no of clinical adverse of AIDSVAX, the number of to be given the phase III trials be greater and the of an as adverse effect was To the potential to vaccine, all adverse of to the vaccine are In of at the injection site is are and for the The the the of in the vaccine to that in the placebo The is is more prevalent in the vaccine In the potential of is the that the vaccine to infection or disease infection has To these the is with of viral and CD4 cell for those who are and placebo and to there is potential to vaccine. In all the has that there is no for these Lesson: In studies with large trial as trials with volunteers followed over the number of adverse is and the effort required to and is For both trials as of 1 2002 adverse have been the have that the of vaccine and placebo recipients not safety the effort required to the of each is large and to be for in studies. The effort required and value through These phase III efficacy trials have been immense in of the of and data For the two trials almost have been to over potential trial volunteers in to the have been made by the volunteers where almost have been and million which be high and the of the of 1). This effort not have been the of the volunteers and the who have been to the search for an effective HIV vaccine. has been the value of with the the National and the the Bangkok Evaluation and the Bangkok these VaxGen has from the of clinical and and and research results will far gp120 HIV will very data on of and for trial risk and HIV-1 in North America and of HIV to and many other data that can advance HIV vaccine in the of the two phase III HIV vaccine efficacy Although phase III efficacy trials with HIV vaccine are they can and should be as as to and to the of developing an effective HIV vaccine. This effort can be through industry, and will be In the it is that both of these phase III trials will be and the initial results made For the first time, data from HIV vaccine trials will available to the scientific of of AIDSVAX efficacy these trials will the of protection by different of that bind to the in the envelope for each of the subtypes in of from placebo and AIDSVAX recipients will a better of the of HIV subtype and potential protection by as and in in envelope sequences of HIV the impact of in of risk on of and the potential impact of an HIV vaccine on the of HIV infection will also available. Lesson: efficacy trials are a not an to developing an effective vaccine. can be learned from the results of the VaxGen phase III trials in 2003. It is that this type of data have been available and that no phase III HIV vaccine results will be available at the as the of both efficacy have and challenges success only an to a more difficult If efficacy of gp120 is in the scientific and public health and the will be and an HIV vaccine to be widely available the at an Although there is in the more this is not The licensure establishment of will at years to complete. In and for vaccine use must be for vaccine administration that and on HIV prevention must be and mechanisms must be established to developing countries with vaccine purchase and with a and available HIV vaccine, years of to bring HIV prevention by vaccine to a But efficacy is not We must not has been learned through these trials to advance HIV vaccine development. We must not a result be as a This in be a to trials. The AIDSVAX phase III trials will bring for HIV vaccine development. Lesson: of phase III trial has been and will be learned from these trials. results years of to manufacture the vaccine in large establish and for vaccine use and and mechanisms to it to the at an The first HIV vaccine efficacy trials will conclude in early 2003. as the industry in this have learned many lessons that can be in the to support the development of an HIV vaccine, it is gp120 or a to be tested 2). are developed and by this be by industry To the of a and effective HIV vaccine for those in industry, clinical and research of both public and are The of the USA, with of other to with international and the the for and to that in developing countries who are the most by the epidemic are a effective and HIV and for conducting HIV vaccine efficacy VaxGen the of volunteers in and for and which had made these phase III trials The Bangkok Evaluation and the study of for and on these the National Institutes of Health and the for and Thailand Genentech, the VaxGen and and and for in the AIDSVAX trials.