Lecture 26. Prevention and Control -- Vaccines Flint et al., chapter 19, pp. 703 - 725

How do we acquire immunity? HOW LONG LASTING??? aby from other human beings - a few weeks to a few months IgG from mom 3-6months used for: botulism diphtheria hepatitis measles rabies snake/spiders bites

Passive Immunity in Infants

Artificial Passive Immunity Gamma globulin Ig’s from pooled blood of at least 1,000 human donors variable content non-specific Specific immune globulin (SIG) higher titers of specific antibodies Antisera and antitoxins of animal origin

Antibody and effector T-cells are the basis of protective immunity Primary infection stimulates an initial immune response. A second infection is “inapparant” because it provokes no symptoms. However, it does re-stimulate and fine tune the immune response. Years later, memory B- and T-cells can become reactivated upon infection, protecting the individual from disease

Artificial Active Immunity Vaccination (Immunization) exposing a person to material that is antigen but NOT pathogenic. Regardless of the nature of the immunizing substance, the mechanism of active immunization is the same: When administred, the immune system recognizes it as foreign and produces antibodies or cytotoxic Tcells or both AND memory cells. The immune response is the same as the one that occurs during the course of a disease. The disease doesn’t occur because whole organisms aren’t used or (if whole orgare used) they have been weaked so that they are no longer virulent.

History of Vaccination: Smallpox Smallpox killed or maimed 10% of humankind. Killed > 300,000,000 people in the 20th century alone Ancient Chinese history: a once in a lifetime disease. 11th century China and India: “Variolation” Scratch a healthy person with pus from infected person If they don’t die, they are immune for life

Vaccination May 14, 1796, Edward Jenner Noted that milkmaids got cowpox, but not smallpox. Injected pus from a cowpox lesion under the skin of a child Waited 2 weeks Deliberately infected the child with smallpox. The boy survived (Today, Jenner would be majorly sued, would lose his license, be put on trial, get a good lawyer, write a book, and do the talk show circuit…Just like Michael Jackson’s doctor!)

History of Vaccination Despite Jenner’s success, it took 100 years til the next vaccine. 1881, Louis Pasteur: coined the word Vaccine. Used dried spinal cord from rabid rabbit to create a rabies vaccine. Also developed vaccines to fowl cholera and anthrax July 6, 1885: 9 year old Joseph Meister who was badly bitten by a rabid dog. Although Pasteur was not a licensed physician and faced legal risks, the boy would most certainly have died without treatment like many before him. Pasteur decided to treat the boy nevertheless and inoculated Joseph with rabies vaccine that had been tested only on dogs previously. The risk paid off and the boy recovered dramatically.

Large scale vaccination programs Fig. 19.1 Dramatic improvements in public health. Nobody in this room has had… Smallpox, Polio, Measles, Chickenpox Mumps, Rubella …Because of vaccination Smallpox is the only human disease to ever be eradicated

Characteristics of a good vaccine Safe Few side effects Give long lasting, appropriate protection Low in cost Stable with long shelf life (no special storage requirements) Easy to administer Inexpensive Public must see more benefit than risk

Types of vaccines whole agent subunit recombinant individual parts alone

Whole agent vaccines -- Killed using heat or formaldehyde Killed virus Live virus epitopes epitopes Problem: These microbes are dead! Living organisms, b/c they replicate in the body, usually elicit a more robust immune response and are more likely than killed organisms to cause production of memory cells. Living organism provide longer stimulation of the immune system. Despite this limitation, there have been a number of effective killed microbe vaccines Inactivated polio vaccine (Salk) Influenza (Classic)

Whole agent vaccines -- Attenuated attenuated - a process that lessens the virulence of a microbe Attenuation is usually achieved by modfying the growth conditions or manipulating microbial genes in a way that eliminates virulence factors. Attenuation methods include long-term cultivation, selection of mutant strains that grow at lower (or higher) temperatures, passage of the microbe through unnatural hosts or tissue culture TB vaccine was obtained after 13 years of subculturing an agent of bovine TB oral polio vaccine (Sabin), MMR (measles, mumps, rubella) Influenza -- Flumist TM

Vaccines stimulate immune memory Killed virus vaccine requires multiple doses (booster shots) to adequately stimulate a protective immune response Live virus vaccines replicate in the host. No requirement for boosters.

Attenuation of viruses by passage through non-human cells Pathogenic virus isolated from patient, grown in human cells Infect monkey cells with cultured virus Virus acquires many mutations that allow it to grow well in monkey cells Mutations make the virus unable to grow well in human cells  Vaccine candidate 1 2 3 4

Advantages for live vaccines multiply like natural organism require fewer doses and boosters long-lasting Disadvantages for live vaccines special storage back mutation side effects side effects - both live and dead whole cell vaccines

Live attenuated Sabin oral poliovirus vaccine

Construction of recombinant attenuated virus Isolate virus Clone genome Isolate virulence gene Mutate or delete virulence gene Resulting virus is Viable Immunogenic Not virulent Can be used as a vaccine

Subunit vaccines Single antigen or mixture of antigens Safer (cannot reproduce) However, often less effective than whole agent vaccines Can be costly Always require boosters Provide an alternative to whole microbes vaccines in cases where the Whole microbes are toxic. Subunit vaccines have two drawbacks. COST: it is much more expensive to extract and purify isolated antigens than to use intact microbes. BOOSTERS: must be administered more than once to mimic the repeated stimulation of the immune system by a living organism. Their safety has made them very popular.

Overcoming Subunit vaccine problems Multiple doses - booster shots Use adjuvants prolongs stimulation of immune response works by trapping the antigens in a chemical complex and releases them slowly DTp - p was killed bacteria for whooping cough (Bordetella pertussis) aP - acellular pertussis is now a toxoid - as effective as killed whole cells Usually require a series of injections (boosters) b/c cannot replicate - THIS IS A PROBLEM!!

Vaccine delivery systems and adjuvants ISCOMS as peptide delivery systems Fig. 19.9

Recombinant vaccines Genetic engineering approach Hepatitis B Vaccina or adenovirus alteration Hep BA second vaccine, produced by recombinant DNA technology, has since become available. Previously, vaccine administration was restricted to individuals who were at high risk of exposure to hepatitis B, namely: infants of hepatitis B carrier mothers, health care workers, homosexual men and intravenous drug abusers. However, hepatitis B has been targetted for eradication , and since 1995 the vaccine has been included in the universal childhood immunization schedule. Three doses are given; at 6, 10, and 14 weeks of age. As with any killed viral vaccines, a booster will be required at some interval (not yet determined, but about 5 years) to provide protection in later life from hepatitis B infection as a venereal disease. Another strategy to make a bacterial vaccine is to use part of the sugar coating (or polysaccharide) of the bacteria. Protection against infection by certain bacteria is based on immunity to this sugar coating. However, because young children don't make a very good immune response to the sugar coating alone, the coating is linked to a harmless protein (this is called a "conjugated polysaccharide" vaccine). The haemophilus influenzae B (or Hib) and pneumococcal vaccines are made this way.

Create a recombinant plasmid containing a gene encoding a specific antigen. Engineer in sequences Enabling it to be expressed in humans Passaged through bacteria Introduce it into humans Let the human cells produce the antigen Present it to T-cells Provoke immune response DNA vaccines

Representative results of DNA vaccine trials