Vaccination is the simplest, safest and most effective way to prevent many diseases. Vaccines for many viral diseases are routinely given to children and adults in all countries of the world. These vaccines, including smallpox, polio and measles vaccines, are both cheap and effective. Yet former Surgeon General C. Everett Koop told the American public not to expect a vaccine for HIV before the end of the century, and Margaret Johnston, PhD, who spearheads the new International AIDS Vaccine Initiative (IAVI), told the XI International Conference on AIDS in Vancouver that current research and development efforts are unlikely to yield an effective vaccine for 6 more years. What is holding back research? Where are the candidate vaccines that were so widely publicized in the early 1990s?
Drug companies have backed away from HIV vaccine research for the last several years for a number of reasons. The failure of envelope glycoprotein (gp) 120 subunit vaccines to neutralize primary isolates of the virus (strains of HIV taken from the blood of infected individuals, rather than developed in the laboratory) led to a pivotal decision in June 1994 not to pursue wide-scale vaccine trials in the United States. In response, biotechnology and pharmaceutical companies reduced their commitment to vaccine research and development. Genentech, where vaccine researcher Donald Francis, MD, for years has championed wider testing of his gp120 vaccine candidate, created a smaller, vaccine-focused company named Genenvax, then backed away from AIDS vaccine research in general. Merck and Repligen suspended work on their candidate vaccine in 1994. And MicroGeneSys, maker of a controversial baculovirus-grown subunit gp 160 vaccine candidate, ceased further vaccine research when that ! candidate failed to demonstrate positive effect in clinical studies.
The focus of vaccine testing then shifted to the developing world. In Thailand, increasing infection rates created the political will to test candidate vaccines that certainly will not be 100% effective. However, it is felt that even a modest rate of protection would have a major impact on diminishing new infections. A wide-scale study of a Genenvax vaccine candidate is slated for Thailand in 1997. Later this year, a Chiron gp120 subunit vaccine candidate based on the subtype of HIV prevalent in Thai land will enter Phase I testing.
Primary concerns regarding the development of a vaccine intended for wide use in developing countries are low cost and ease of administration. A cheap and easily administered vaccine is considered the only possible means of containing burgeoning infections in most third world nations. Unfortunately, potential vaccine makers have chosen to direct their research and development efforts elsewhere, fearing potential financial losses.
Also of concern is the huge variability of HIV, both in infected individuals (more than 660 variants are known) and in infected populations (subtypes or clades). HIV-1 has been classified in 2 groups, M and O; 9 subtypes have been identified within group M, and only a few in group O. Subtypes in a group differ genetically from one another by about 30%. A successful HIV vaccine would need to elicit immunity to all the HIV subtypes to which a vaccinee may be exposed.
Two major initiatives to bolster vaccine research were revealed at the Vancouver conference. The director of the Office of AIDS Research at the U.S. National Institutes of Health, William Paul, MD, announced an increased allocation of funds for research on vaccines and a "restructured, redirected vaccine research program." Moreover, efforts by Seth Berkley at the Rockefeller Foundation in New York to raise $600 million over 7 years to fund the IAVI have borne fruit. IAVI, incorporated in January 1996, now has $5 million in its coffers for its first year of operation. Under the leadership of scientific director Johnston, formerly deputy director of the Division of AIDS, IAVI will support vaccine research and development in areas where there are currently gaps. IAVI also plans to work with the World Bank, governments, private industry, funders and regulatory agencies to increase investment in vaccine research and development. Perhaps the most important mission of IAVI is to foster the creation of coordinated global vaccine efforts to make vaccines that can be effectively and cheaply used in the developing world.
Preventive Vaccine Candidates
The AIDS Vaccine Evaluation Group (AVEG), sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), has conducted 25 clinical studies of candidate HIV vaccines, involving more than 1,900 seronegative adults. A table of completed, current and planned trials is shown below. Results of AVEG 201, the only study in Phase II, were reported at the Vancouver conference. A total of 296 adult heterosexuals, gay or bisexual men and intravenous drug users received either 600 mg of the recombinant gp120 MN vaccine candidate (made by Genenvax) in alum adjuvant, MF-59 adjuvant alone or alum alone, or 50 micrograms of the recombinant gp120 SF2 vaccine candidate in MF-59 adjuvant (made by Chiron Biocene). Comparisons of neutralizing antibody were made between the groups, and it was concluded that 4 rather than 3 immunizations may be the optimal dosing schedule to elicit antibody responses. The participants in the study did not increase their risk behaviors because they were in a vaccine study. Also reported were the results of Phase I/II trials of a "prime/boost" strategy employing a recombinant canarypox vaccine candidate designated ALVAC-HIVgp160 (Virogenetics/Pasteur Merieux) as the prime followed by the Chiron Biocene gp120 candidate as the boost. The strategy has proven safe and capable of inducing not only neutralizing antibodies, but also cytotoxic lymphocyte responses in vaccinees. This shows that the humoral and cell-mediated (B-cell and T-cell) types of immunity can be induced by intramuscular injection of the 2 candidate vaccines. Different doses and dosing schedules were compared. Participants were vaccinated at baseline, 1 or 2 months later, 6 or 9 months later, and 12 months later. Ten participants received 106 50% tissue culture infectious doses of ALVAC-HIVgp160 alone while 9 also received 50 micrograms of Chiron's gp120; 18 received 107 50% tissue culture infectious doses of ALVAC-HIVgp160 alone while 29 also received 50 micrograms of Chiron's gp! 120; and 9 participants received only 50 micrograms of Chiron's gp120.
Those participants who received prime/boost developed antibodies that could neutralize both the MN and SF2 strains of HIV. The 4-dose schedule appeared to be better than the 3-dose schedule, and a current study will assess if even higher doses enhance the immune responses that were found.
AIDS Vaccine Evaluation Group Completed, Current and Planned Vaccine Trials
-Product: gp160 IIIB Sponsor*: MicroGeneSys Number of volunteers: 128
-Product: gp160 IIIB and MN Sponsor*: Immuno-AG Number of volunteers: 159
-Product: gp 120 (yeast) Sponsor*: Biocene Number of volunteers: 78
-Product: gp 120 IIIB Sponsor*: Genentech Number of volunteers: 28
Live pox virus envelope:
-Product: Vaccinia -env envelope boosts Sponsor*: Bristol-Myers Number of volunteers: 217
-Product: Vaccinia-env(gag)pol Sponsor*: Therion Number of volunteers: 14
-Product: gp 120 MN Sponsor*: Genentech Number of volunteers: 211
-Product: gp 120 SF2 Sponsor*: Biocene Number of volunteers: 205
-Product: gp120 (new formulation) Sponsor*: Biocene Number of volunteers: 30
-Product: gp120 + novel adjuvants Sponsor*: Genentech/Biocene Number of volunteers: 311
Live pox envelope:
-Product: Canarypox env gp120 Sponsor*: PMC/Biocene Number of volunteers: 131
-Product: Low-dose canarypox env/gag gp120 Sponsor*: PMC/Biocene Number of volunteers: 76
-Product: V3 peptide Sponsor*: UBI Number of volunteers: 137 Method: intramuscular, intramuscular + oral
-Product: p24 virus-like particle Sponsor*: British Biotech Number of volunteers: 36 Method: intramuscular + mucosal
Live pox envelope:
-Product: High dose canarypox env/gag gp120 Sponsor*: PMC/Biocene
-Product: Canarypox env/gag mucosal Sponsor*: PMC
-Product: Canarypox env/gag/pol gp120 Sponsor*: PMC/Biocene
-Product: Number of volunteers: Sponsor*: Therion
-Product: T-B peptide Sponsor*: Lederle
-Product: Pseudovirion Sponsor*: PMC
-Product: Salmonella gp160 Sponsor*: University of Maryland
*Sponsors: MicroGeneSys, Wallingford CT, USA Immuno-AG, Vienna, Austria Biocene, Emeryville, CA, USA Genentech, South San Francisco, CA, USA Bristol-Myers, Wallingford, CT, USA PMC (Pasteur Murieux Connaught), Swiftwater, PA, USA UBI (United Biomedical, Inc.) Hauppauge, NY, USA British Biotech, Ltd., Cambridge, UK Lederle/Praxis, Rochester, NY, USA University of Maryland, Baltimore, MD, USA.
BETA thanks Patricia Fast, MD, PhD, for permission to reprint this chart.
Laboratory and Animal Studies
Considerable interest has been generated by the news shared at the international AIDS conference by Robert Gallo, MD, of the Institute of Human Virology in Baltimore. Gallo and Paolo Lusso, MD, of the San Raffaele Scientific Institute, described 3 chemokines (pro-inflammatory chemicals made by the immune system) that may play an important role in the way that HIV infects cells. These chemokines, according to Daniel Zagury, MD, at the Pierre and Marie Curie University in Paris, are more highly concentrated in HIV positive non-progressors. Gallo argues that a strategy that can artificially boost the chemokines (MIP-1a, MIP-1b and RANTES) or down-regulate their receptors (designated cysteine-cysteine chemokine receptor 5, CKR5) might protect against infection with HIV. The theory is so far untested, but warrants closer scrutiny and research.
Several vaccine researchers have been pursuing "naked DNA" approaches to vaccine development. Over the last 3 years, DNA vaccines have increasingly been constructed and tested for HIV, as well as hepatitis B, tuberculosis and influenza. Upon injection, DNA vaccines apparently incorporate their genetic material into cells near the site of injection and begin producing their gene products (proteins) more efficiently than was predicted by tissue culture experiments. DNA vaccines can be simply and cheaply produced in large quantities, and are free of contaminants. Further, this type of vaccine remains very stable by comparison with other vaccine modalities, increasing the likelihood that they can be transported and utilized anywhere in the world.
Intramuscular injections of DNA expressing either gp120 or gp160 have been found to induce significant titers both of neutralizing antibody (a strong humoral response) and cytotoxic T-lymphocytes (cellular immunity). According to a research team headed by Britta Wahren, MD, of the Karolinska Institute in Stockholm, Sweden, immune responses to DNA that expresses regulatory genes of HIV are stronger than the responses to DNA based on HIV structural genes. Still, both types of genes may be needed to bring forth the wide immune response to HIV challenge that may be necessary to protect people from infection. Naked DNA vaccines are now established as players in the field of HIV vaccine candidates, despite the fact that little is known about the mechanisms by which they activate immune responses.
A collaboration between the University of Pennsylvania and Apollon, Inc. of Malvern, PA, funded by a $4.2 million grant from NIAID, has yielded a DNA vaccine candidate that expresses the envelope glycoprotein and rev protein of HIVMN. The first clinical study of this vaccine candidate demonstrated the safety of 3 doses (30, 100 and 300 micrograms) in 15 asymptomatic HIV positive volunteers. The volunteers received 3 intramuscular injections each at 10-week intervals. No trends were noted in CD4 or CD 8 cell counts or viral load. This study is the precursor to more elaborate planned studies; it is thought that the immunogen may be useful as both a therapeutic and prophylactic vaccine for HIV.
The most positive news in pre-clinical research on vaccines is data from a study of an attenuated (weakened) version of simian immunodeficiency virus (SIV) in monkeys. The vaccine was made by deleting the nef gene and injecting it, followed by a challenge that consisted of high intravenous doses of a lethal strain of SIV different from the one from which the vaccine was made. While the monkeys were protected from infection, control animals were not. Asakura Yusuke, PhD, and colleagues from Yokohama University in Japan, who constructed the DNA, saw production of nef-specific cytotoxic lymphocytes and no pathogenesis in vaccinated monkeys.
Burt Dorman, PhD, of Acrogen in Oakland, CA, believes that a whole inactivated (killed) HIV vaccine candidate would be likely to generate wide-ranging immune responses and might be as successful in reducing HIV infection rates as the killed polio vaccine was 4 decades ago. Dorman's team has proposed to identify appropriate strains of HIV, inactivate them, and test them in pre-clinical settings. This research has not been done because of the many attendant concerns that a vaccine based on whole HIV, if incompletely inactivated, could lead to infection, and because of the associated liability concerns. However, about one-third of all currently used viral vaccines are based on "whole-killed" technology.
The proposal to identify and perform rigorous scientific testing on whole-killed HIV vaccine candidates is currently the first proposal to be reviewed by the Scientific Advisory Committee (SAC) of the IAVI. The SAC is enthusiastic about advancing the concept of whole-killed HIV or another particle design to Phase I studies. The SAC additionally felt that an approach to distinguish between the vaccine strain of the virus and other HIV in an infected vaccinee needs to be conceptualized before initiating development of a whole-killed virus. This concern is shared by many potential HIV vaccine trial volunteers, who worry that health insurance and employment may be out of reach if a vaccinee cannot be distinguished from a person with active HIV infectio n. Correlates of Protection An effective preventive vaccine would have to protect people from transmission of HIV by 2 very distinct routes: intravenous and sexual. Sexual transmission can be further divided into transmission through oral, rectal and vaginal mucosal surfaces. Can a single vaccine candidate protect against challenge by both intravenous and sexual routes of transmission? Recently published information shows that immunization that protects monkeys from SIV injected directly into a vein does not protect against vaginal challenge. This finding suggests that mucosal immunity differs from systemic immunity, and supports the creation and testing of hybrid combinations of vaccine candidates to induce immune protection from infection by both intravenous and sexual routes of transmission.
These differences in transmission and in probable means of protection help to highlight the importance of finding out what exactly does protect people against HIV infection. Many researchers have attempted to find correlations between various blood cells, cytokines and other factors and protection against HIV infection by studying people who are at risk for HIV infection, are frequently exposed to it, and yet never seroconvert.
Progress in answering this central question has been very slow. Studies done at Chiang Mai University in Thailand and in Zambia reveal that there are no apparent differences in CD4 cell counts, CD8 cell counts or CD4/CD8 percentages between people who are at risk but do not seroconvert and people who do. Furthermore, levels of MIP-1a, MIP-1b and RANTES (the cytokines recently described by Gallo), beta 2 microglobulin and neopterin levels do not illuminate any fundamental differences between the groups. The Chiang Mai University study did detect a statistically significant difference in levels of natural killer (NK) cells, but this was the first report of such a difference and needs to be independently validated. In summary, according to the National Institute of Allergy and Infectious Diseases, "whether a natural protective state against HIV can exist remains unknown."
Much depends on public support for the development of an effective HIV vaccine. The current lack of interest in HIV vaccine research at pharmaceutical companies advances the field of vaccine research too slowly. On the other hand, current efforts to attract more research and development funding may offset the current lull. There are now only 4 major pharmaceutical companies that make vaccines. Private funding may help open up the field and bring more bright investigators into the crusade. With more investigators, the chance of a new, unusual idea changing the landscape of vaccine research increases, but the means to develop an effective HIV vaccine may already be in hand. Whole-killed vaccine candidates have not been made (the technology is now 40 years old) and no vaccine candidate has yet advanced to wide-scale (Phase III) testing.
It is hoped that surveys of the preparedness of potential vaccine study volunteers to participate in HIV vaccine trials, such as the survey currently underway at the Center for AIDS Prevention Studies at the University of California in San Francisco, will identify stumbling blocks and highlight the concerns of AIDS-affected communities. It is clear that not enough research is being devoted to this critically important area of AIDS research, and that fundamental changes in funding research and development coupled with community involvement will help.
Mark Bowers is Managing Editor of Treatment Publications at the San Francisco AIDS Foundation.
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