World's Vaccine Experts Meeting in Washington to Report New Progress in Vaccine Development
WASHINGTON, April 30 /PRNewswire/ -- Hundreds of the world's leading vaccine scientists are gathering today in Washington, D.C., for the Third Annual Conference on Vaccine Research to report new research on the ``new generation'' of vaccines for such dive
``We are seeing real progress in vaccine research, including exciting developments on vaccines to prevent HIV infection and some types of cancer,'' says William J. Martone, MD, senior executive director of the National Foundation for Infectious Diseases (NFID) and co-chair of the three-day conference. ``In addition, we are understanding how to make better use of some vaccines that are already available.''
Vaccines Against Human Papillomavirus Aim to Prevent Cervical Cancer
Compelling evidence shows sexually transmitted infection by certain human papillomaviruses (HPV) causes most cervical cancer, which one day may be vaccine-preventable, according to John T. Schiller, PhD, of the Laboratory of Cellular Oncology at the National Cancer Institute, who will present research at the conference.
``When most people think of sexually transmitted diseases, cancer does not readily come to mind,'' said Dr. Schiller, ``yet, if we can prevent genital HPV infection, we should be able to prevent most cases of cervical cancer.''
The basis of Dr. Schiller's vaccine research is virus-like particles, or VLPs. A VLP is the outer shell of the virus. Because it does not contain the genes of the virus, a VLP cannot cause infection. The HPV VLP consists only of the L1 major capsid protein.
A Phase I clinical trial has been conducted on an HPV type 16 (HPV16) VLP-based vaccine (HPV16 is found in about half of all cervical cancers). After 72 volunteers received a priming dose and two boosters of the HPV16 VLP-based vaccine, they demonstrated high levels of neutralizing antibodies, the mark of successful immunization.
A Phase II trial is now beginning at Johns Hopkins University School of Medicine in Baltimore. A vaccine efficacy trial is planned for Costa Rica, where the incidence of cervical cancer is higher than in the United States.
The L2 minor capsid protein accounts for a small portion of the HPV viral shell. Another vaccine under development is based on chiremic VLPs, in which other HPV proteins are linked to the L2 minor capsid protein and co-assembled into L1 VLPs. Injection of chimeric VLPs in mouse models resulted in strong antitumor responses.
``We hope to be able to prevent HPV infection by the HPV16 VLP-based vaccine,'' explained Dr. Schiller. ``The chimeric VLP vaccine might be able to eliminate any breakthrough infection that escaped antibody neutralization.''
If these vaccines prove safe and effective, Dr. Schiller foresees a way to prevent cervical cancer in future generations. ``Girls and boys could be vaccinated before they become sexually active. Although boys obviously do not get cervical cancer, they hopefully would receive the vaccine because HPV is sexually transmitted.''
Vaccine Offers Novel Approach to Help Smokers Kick the Habit
A solution for permanent smoking cessation may someday be available in the form of a vaccine, according to Ali Fattom, PhD, senior director of research at the biopharmaceutical company Nabi, who reported on preclinical (animal) studies with the NicVAX(TM) vaccine.
NicVAX is a nicotine conjugate vaccine. Because the nicotine molecule is too small to be recognized by the body's immune system, nicotine is bound, or conjugated, to a larger protein, a Pseudomonas toxoid. (Pseudomonas toxin can cause disease in humans. A toxoid, however, is a form that cannot cause disease.) The conjugated compound is recognized by the immune system and induces the formation of antibodies in animals given NicVAX.
When animals were immunized with NicVAX and then challenged with intravenously administered nicotine, their plasma retention of nicotine was 8.5 times higher than in control animals. In addition, nicotine distribution to the brain was 64% less than in control animals. These are exactly the effects that were sought.
Researchers believe that a vaccine that generates nicotine-specific antibodies capable of binding to nicotine in the blood and preventing nicotine from reaching the brain might prevent addiction and help smokers quit.
``Experience with other vaccines suggests that antibodies will probably remain in the circulation for several years,'' said Dr. Fattom. ``So a vaccinee who decides to light up a cigarette a year or two after quitting won't get a good feeling from smoking and probably won't have any desire to resume the habit.''
According to Dr. Fattom, a Phase I/II trial in humans to study safety and immunogenicity of the vaccine is planned for later this year or early next year. Both smokers and nonsmokers will be enrolled in the trial to be conducted at the University of Minnesota. This effort is a collaboration of Nabi, the University of Minnesota, Hennepin County Medical Center in Minneapolis, and the University of Houston at Clear Lake, Texas.
Human Trials Proceeding to Evaluate Vaccines Against AIDS
Ever since human immunodeficiency virus (HIV) was recognized as the cause of AIDS, researchers have been hoping to develop a vaccine to protect against HIV infection. Vaccine development is complicated by the existence of many subtypes of related HIV viruses. The viruses are clustered in five families called clades and designated A, B, C, D and E.
Clade B is the most common form found in the Americas, Western Europe and Australia and is transmitted predominantly by homosexual contact. Clade E is the most common in Southeast Asia and the eastern Pacific Rim, where HIV-infected people tend to be drug users. Clades A, C and D are typically found in Africa, where HIV is mainly transmitted by heterosexual contact. Clade C is the most common form in sub-Saharan Africa and is spreading rapidly in India and China.
Because of these differences, more than one vaccine formulation may be needed to protect the world's population against HIV infection. The California company VaxGen has designed two formulations of its AIDSVAX vaccine. Both of its trials are randomized, double-blind, placebo-controlled studies -- the gold standard for testing medical treatment. More than 7,000 patients at risk for HIV infection have been enrolled in these studies.
The first study is with AIDSVAX B/B, a bivalent vaccine containing two viruses of the B clade: MN, which affects about 60% of North Americans infected with HIV, and GNE8. This vaccine or placebo is being administered to 5,415 women and homosexual men in 61 sites in the United States, Canada, Puerto Rico and the Netherlands. The second study, with AIDSVAX B/E, is designed for 2,500 intravenous drug users in Bangkok, Thailand, and is targeted for clade E and the MN variant of clade B.
``With a bivalent vaccine targeted for two clades, or virus types, we are hoping to provide better protection for a larger number of people,'' said John G. Curd, MD, senior vice president of VaxGen. ``If the vaccine proves to be effective, we will have a paradigm for making AIDS vaccines for other parts of the world.'' The company already has plans to develop a vaccine formulation for clades A, C and D.
In both trials, the study subjects, who do not have HIV but are at risk for infection, receive counseling to reduce their risk. A month after being given either vaccine or placebo, the volunteers receive a second dose. They get a third dose after another 5 months and then boosters every 6 months for up to 30 months. Neither the study subject, clinician, nor VaxGen knows whether the injection contains vaccine or placebo.
Safety of the vaccines is assessed every 6 months. An interim analysis for efficacy is scheduled for late 2001. If the analysis does not show sufficient statistical power to determine efficacy definitively, VaxGen will proceed as planned and complete the trials at the end of 2002.
``We already have results,'' Dr. Curd said. ``and have found thousands of people who are willing to enroll, who can give informed consent to participate in these studies and who are continuing to come for the periodic visits.''
A Unique Conference
The Third Annual Conference on Vaccine Research is a noncommercial scientific forum that brings together specialists from diverse disciplines such as microbiology, immunology, epidemiology, and public health.
The vaccine conference is jointly sponsored by eight prestigious groups: the National Foundation for Infectious Diseases, the Centers for Disease Control and Prevention, the National Institute of Allergy and Infectious Diseases, the International Society for Vaccines, the United States Department of Agriculture, the Center for Biologics Evaluation and Research of the Food and Drug Administration, the Albert B. Sabin Vaccine Institute at Georgetown University and the World Health Organization.
The conference is funded, in part, through unrestricted educational grants from Aventis Pasteur, Becton Dickinson and Company, Chiron Corporation, Glaxo Wellcome, Inc., King /Monarch Pharmaceuticals, Medeva Pharmaceuticals, Merck Vaccine Division, North American Vaccines, Inc., SmithKline Beecham Pharmaceuticals, and Wyeth-Lederle Vaccines.
For additional information about the conference:
See the National Foundation for Infectious Diseases website: