Bi1_2009_Lecture24_full - In thinking about vaccines,...

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Unformatted text preview: In thinking about vaccines, recall that there are two arms of the adaptive immune response • Cellular (Cytotoxic T Lymphocyte or CTL) response -- works well for controlling (most) viral infections because viruses replicate intracellularly. Less adapted for controlling extracellular pathogens such as bacteria or protozoa. • Humoral (antibody-mediated) response -- works well for controlling extracellular pathogens. – Passive transfer of antibodies alone (e.g., mother to offspring) can protect against viral infection. – Neutralizing antibodies can prevent reinfection by some viruses (e.g., influenza). Vaccination • For most viruses, you are immune to reinfection by the same virus (e.g., chicken pox). • Immunization or vaccination: Process by which one is exposed to a live or inactivated virus, or to components of the virus, in order to establish a state of immunity. • Immunizations against smallpox introduced >1000 years ago. Variolation: introduce dried smallpox scabs into nose of an uninfected person, who then contracted a mild form of the disease but was immune to smallpox. – 1-2% died after variolation compared with 30% after smallpox. • Vaccination against smallpox introduced by Edward Jenner in 1796. Jenner infected a boy with cowpox (a live-attenuated virus), then exposed him to smallpox, which he failed to contract. – Jenner later experimented on other children, including his son. These sorts of experiments are illegal today. Clicker question Most vaccines today are given in the form of wholekilled virus or live-attenuated virus. Whole-killed virus vaccines induce _____ immunity. Live-attenuated virus vaccines induce ____ immunity. 1) 2) 3) 4) 5) cellular and humoral; cellular and humoral cellular; cellular humoral; humoral cellular; cellular and humoral humoral; cellular and humoral Polio vaccine has been very successful in the US • • Polio epidemics in 1950s affected >50,000 people in US. Salk vaccine is an inactivated virus given in a series of injections. The vaccine induces circulating antibodies, but no cellular immunity. Prevents spread of virus from gastrointestinal tract to the central nervous system, but doesn’t prevent infection of the gastrointestinal tract by the virus. Sabin vaccine is a live-attenuated virus given orally. Produces cellular immunity and circulating antibodies and prevents subsequent infection by wild-type virus. Worldwide use of Sabin vaccine has eradicated polio in the US and Americas. We will discuss both of these methodologies (whole-killed virus and liveattenuated virus approaches) as potential ways to make an HIV vaccine. • • Clicker question What chemical did Jonas Salk use to inactivate poliovirus to make the famous vaccine? 1) Formaldehyde 2) Polyethylene Glycol 3) Methanol 4) Ammonia Clicker question What chemical did Jonas Salk use to inactivate poliovirus to make the famous vaccine? 1) Formaldehyde 2) 3) 4) Polyethylene Glycol (in many things, including in Dr. Pepper: prevents over-foaming) Methanol Ammonia Clicker question How many American children contracted polio in 1955 because of an incompletely inactivated batch of poliovirus vaccine produced by Cutter Laboratories? 1) 10 2) 3) 100 20000 4) 40000 Source: Offit, PA (2005) The Cutter Incident, 50 years later. New England Journal of Medicine Clicker question How many American children contracted polio in 1955 because of an incompletely inactivated batch of poliovirus vaccine produced by Cutter Laboratories? 1) 10 2) 3) 100 20000 120,000 doses contained live virus, resulting in 40,000 cases of abortive polio (headache, stiff neck, fever, muscle weakness). 51 children were permanently paralyzed, 5 died; 113 family members were paralyzed, 5 died. 4) 40000 Source: Offit, PA (2005) The Cutter Incident, 50 years later. New England Journal of Medicine Cases of polio per year in US From Morbidity and Mortality Weekly Report (MMWR), Vol. 46, p. 79 (1997) Flu vaccines • WHO* specifies the contents of the vaccine each year to contain the most likely strains of viruses that will attack the next year. • Annually updated trivalent flu vaccine for 2008-2009 season consisted of H3N2, H1N1 and B influenza viruses. (But the vaccine H1N1 strain doesn’t confer protection to H1N1 swine flu.) • Viruses are grown in hens’ eggs. • Inactivated viruses are injected or live attenuated viruses are given as a nasal spray (not currently approved in children younger than 5). *World Health Organization Why we need an HIV vaccine: Anti-retroviral therapy hasn’t eradicated HIV • Anti-retroviral treatment regimens are complex, expensive, and can result in serious side effects. • Developing safe, effective and affordable vaccines that can prevent HIV infection in uninfected people is the best hope for controlling and/or ending the AIDS epidemic. • In 1984, Margaret Heckler (President Reagan’s Secretary of the Department of Health and Human Services) announced that the virus responsible for causing AIDS had been identified, and that a vaccine would be ready for testing within two years. •We still don’t have a vaccine. Why? “CD4” means CD4 T cells; “CTL” means CD8 cytotoxic T lymphocytes; “VLP” means virus-like particle Pantello and Koup, 2004, Nature Medicine 10: 806-810 Pantello and Koup, 2004, Nature Medicine 10: 806-810 Traditional approach to an HIV vaccine: whole-killed virus Problems: • Safety issues: are the viruses really dead? • Production of strain-specific responses: would need to inject a mixture of MANY different killed HIVs. • A big problem: gp120 is shed from HIV, so what is being injected isn’t a form to which the host will make effective neutralizing antibodies. • Another big problem: where do you get the HIV to kill and then inject? Answer: grow in cells in the lab, but laboratory strains are antigenically different than primary HIV isolates. Future research needs (from • Identify HIV isolate(s) that retain sufficient envelope glycoprotein to effectively mimic wild-type HIV and generate a strong, protective immune response. • Develop and test inactivation procedures that will retain antigenic integrity of the envelope glycoprotein. • Develop cells and culture methods that will permit largescale production of primary HIV isolates. • Develop alternative methods that can circumvent some of the safety and technical concerns posed by manufacturing and then inactivating infectious HIV virions. Live-attenuated virus approach to making an HIV vaccine • Initial optimism because live SIV with a deletion in the Nef gene* caused no disease in macaques and protected against initial infection by wild-type** SIV. • However, Nef-deletion mutants only slow disease progression, but don’t abrogate it completely • Adult macaques eventually showed immune dysfunction and 18% developed AIDS. • This vaccine shows limited or no cross protection against infection by other strains of SIV. • Live-attenuated HIV vaccines have not been tested in humans due to safety concerns. • Long-term growth of live-attenuated viruses would be done in culture, but laboratory strains of HIV are antigenically different than primary isolates. *Nef down-regulates surface expression class I MHC molecules and CD4 **Wild-type: A normal, non-mutant form of a macromolecule, cell or organism Possible vaccine approaches • Induction of antibodies by injection with whole-killed virus or viral proteins. • Induction of antibodies and cellular immunity using live-attenuated virus. • Induction of only cellular immunity (cytotoxic T lymphocyte (CTL) responses) by inducing expression of viral proteins. transient expression of proteins encoded by introduced genes. Peptides derived from these proteins are presented by MHC class I proteins to CD8 CTLs. • Note that these sorts of vaccines can never prevent infection because T cells do not recognize or kill free viruses. A strong anti-HIV CTL response, however, has the potential to reduce or eliminate virally-infected cells and therefore greatly reduce viral load. • DNA vaccines -- injection of purified DNA, usually into muscle, results in DNA vaccines: Possible HIV Vaccine Strategies • Peptide vaccines • Recombinant subunit protein vaccines – gp120, gp41, or gp160 produced by genetic engineering • Live vector vaccines – non-HIV viruses engineered to carry HIV genes • Virus-like particle vaccines – non-infectious HIV containing one or more HIV genes • DNA vaccines – HIV genes inserted into plasmids • Combinations of vaccines –Prime-boost regimens (e.g., DNA vaccine followed by injection of recombinant protein) • Current HIV Vaccine trials: – Merck’s HIV vaccine • Merck V520 ad5 vaccine -- a live attenuated virus designed to produce cellular and humoral immunity • Note HIV genes derived from only one HIV strain – Three stretches of HIV genome (from HIV gag, pol and nef genes) – Shell from adenovirus type 5 (normally causes cold symptoms) • Virus was replication incompetent -- could infect cells, but couldn’t produce more virus -Vaccine cannot cause HIV infection. STEP trial • 1500 volunteers (high-risk for HIV infection) in Americas and Australia recruited in December 2004. 3000 volunteers by March 2007. –62% male, Average age = 29 • Trial stopped in September 2007. – Vaccine conferred no protective effects against HIV infection and no effect on course of infection. – More infections in vaccine recipients (49) than placebo (33). • Much analysis now to figure out what went wrong. – Is difference in infection rates significant? – Did adenovirus immunity increase infection risk? Is there any hope for an antibody-based therapeutic approach against HIV given that people don’t normally make broadly neutralizing antibodies against HIV? • HIV rapidly mutates so that antibodies are no longer effective. • HIV spike proteins are covered with carbohydrates, which are poorly or non-immunogenic. • Antibodies are too big to access some regions of the HIV spike. Burton, Dennis R. et al. (2005) Proc. Natl. Acad. Sci. USA 102, 14943-14948 ...
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