Micro - 4th Asessment - Viral Immunization - 2007

Viral Immunization 4th Year Medical, 2006/2007 Prof. Widad Al-Nakib, FRCPath.

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Principle of Immunization • The principle of vaccination is to induce a "primed" state in the vaccinated subject so that, following exposure to a pathogen, a rapid secondary immune response is generated leading to the accelerated elimination of the organism and protection from clinical disease. Success depends on the generation of memory T and B cells and the presence in the serum of neutralizing antibody 2

What makes a Good Vaccine? 1. Ability to elicit the appropriate immune response for the particular pathogen: – Tuberculosis - cell mediated response – most bacterial and viral infections - antibody

2. Long term protection ideally life-long 3. Safety vaccine itself should not cause disease 4. Stable retain immunogenicity, despite adverse storage conditions prior to administration 5. Inexpensive 3

Different Types of Virus Vaccines • • • • • •

Live whole virus vaccines Killed whole virus vaccines Subunit vaccines;- purified or recombinant viral antigen Recombinant virus vaccines Anti-idiotype antibodies DNA vaccines 4

‘Kids Get Vaccinated’

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‘Teenagers Get Vaccinated’

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Live-Attenuated Viral Vaccines • Live virus vaccines are prepared from attenuated strains that are almost or completely devoid of pathogenicity but are capable of inducing a protective immune response. They multiply in the human host and provide continuous antigenic stimulation over a period of time, Primary vaccine failures are uncommon and are usually the result of inadequate storage or administration. Another possibility is interference by related viruses as is suspected in the case of oral polio vaccine in developing countries 7

Use of a Related Virus from Another Animal as Live Vaccines (Hetrologous Vaccines)

• Both cowpox virus and vaccinia virus are closely related to variola virus, the causitive agent of smallpox. The eighteenth centuary physician, Edward Jenner observed that milkmaids who had been infected with cowpox virus were immune to smallpox. Widespread use of vaccinia virus as a vaccine has lead to the world-wide eradication of smallpox. 8

Use of Partially Attenuated Virus by an Unnatural Route as a Live Vaccine • The virulence of the virus is often reduced when administered by an unnatural route. This principle is used in the immunization of military recruits against adult respiratory distress syndrome using enterically coated live adenovirus type 4, 7 and (21). 9

Passage of the Virus in an “Unnatural Host" or Host Cell as Live Vaccine • The major vaccines used in man and animals have all been prepared this way. After repeated passages, the virus is administered to the natural host. The initial passages are made in healthy animals or in primary cell cultures. There are several examples of this approach: the 17D strain of yellow fever was developed by passage in mice and then in chick embryos. Polioviruses were passaged in monkey kidney cells and measles in chick embryo fibroblasts. Human diploid cells are now widely used such as the WI-38 and MRC-5 10

Development of Temperature Sensitive Mutants as Live Vaccines • As previously described but passaging the virus under reduced temperature. • Good example; the live –attenuated polio virus vaccines

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Inactivated (Killed) Whole Virus Vaccines

• The virus is simply inactivated. The outer virion coat should be left intact but the replicative function should be destroyed. To be effective, non-replicating virus vaccines must contain much more antigen than live vaccines that are able to replicate in the host. Preparation of killed vaccines may take the route of heat or chemicals. The chemicals used include formaldehyde or beta- propiolactone. The traditional agent for inactivation of the virus is formalin. Excessive treatment can destroy immunogenicity whereas insufficient treatment can leave infectious virus capable of causing disease. 12

Live vs Killed Vaccines Feature

Live

Dead

Dose No. of doses Need for adjuvant

Low Single No

High Multiple Yes

Duration of immunity Antibody response

Many years

Short

IgG, IgA

IgG

CMI

Good

Poor

Reversion to virulence

Possible

Not possible 13

Potential Safety Problems • • • • • • •

Live vaccines Underattenuation Mutation leading to reversion to virulence Preparation instability Contaminating viruses in cultured cells Heat lability Should not be given to immunocompromized or pregnant patients 14

Potential Safety Problems • Killed vaccines • Incomplete inactivation • Increased risk of allergic reactions due to large amounts of antigen involved

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Present Problems with Vaccine Development Include Failure to grow large amounts of organisms in laboratory Crude antigen preparations often give poor protection. eg. Key antigen not identified Live vaccines of certain viruses can (1) induce reactivation, (2) be oncogenic in nature 16

Subunit Vaccines •

As the technology for growing viruses to high titres in cell cultures advanced, it became practicable to purify virus and viral antigens. It is now possible to identify the peptide sites encompassing the major antigenic sites of viral antigens, from which highly purified subunit vaccines can be produced. Increasing purification may lead to loss of immunogenicity, and this may necessitate coupling to an immunogenic carrier protein or adjuvant, such as an aluminum salt. Examples of purified subunit vaccines include the HA vaccines for influenza A and B, and HBsAg derived from the plasma of carriers 17

Recombinant Viral Proteins Vaccines • Virus proteins have been expressed in bacteria, yeast, mammalian cells, and viruses. E. Coli cells were first to be used for this purpose but the expressed proteins were not glycosylated, which was a major drawback since many of the immunogenic proteins of viruses such as the envelope glycoproteins, were glycosylated. Nevertheless, in many instances, it was demonstrated that the non-glycosylated protein backbone was just as immunogenic. Recombinant hepatitis B vaccine is the only recombinant vaccine licensed at present. 18

Synthetic Peptides • The best known example is foot and mouth disease, where protection was achieved by immunizing animals with a linear sequence of 20 aminoacids. Synthetic peptide vaccines would have many advantages. Their antigens are precisely defined and free from unnecessary components which may be associated with side effects. They are stable and relatively cheap to manufacture. Furthermore, less quality assurance is required. Changes due to natural variation of the virus can be readily accommodated, which would be a great advantage for unstable viruses such as influenza

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Anti-idiotype Antibodies Vaccines • The ability of anti-idiotype antibodies to mimic foreign antigens has led to their development as vaccines to induce immunity against viruses, bacteria and protozoa in experimental animals. Anti-idiotypes have many potential uses as viral vaccines, particularly when the antigen is difficult to grow or hazardous. They have been used to induce immunity against a wide range of viruses, including HBV, rabies 20

DNA Vaccines • Dubbed the new technology the "third revolution" in vaccine development—in par with the development of subunit vaccines. The first clinical trials using injections of DNA to stimulate an immune response against a foreign protein began for HIV in 1995. Four other clinical trials using DNA vaccines against influenza, herpes simplex virus, T-cell lymphoma, and an additional trial for HIV were started in 1996. • The technique that is being tested in humans involves the direct injection of plasmids - loops of DNA that contain genes for proteins produced by the organism being targeted for immunity. Once injected into the host's muscle tissue, the DNA is taken up by host cells, which then start expressing the foreign protein. The protein serves as an antigen that stimulate an immune responses and protective immunological memory 21

Adjuvants

• Used to potentiate the immune response • Functions to localize and slowly release antigen at or near the site of administration. • Functions to activate APCs to achieve effective antigen processing or presentation • Materials that have been used include;• Aluminum salts • Mineral oils • Mycobacterial products, eg. Freund's adjuvants 22

Immunostimulating Complexes (ISCOMS) • • • • • •

An alternative vaccine vehicle The antigen is presented in an accessible, multimeric, physically well defined complex Composed of adjuvant (Quil A) and antigen held in a cage like structure Adjuvant is held to the antigen by lipids Can stimulate CMI Mean diameter 35nm 23

‘Measles Attack’

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Measles Mumps Rubella (MMR) Vaccine • Live attenuated vaccines prepared in cell-cultures of human fibroblast given as part of the childhood vaccination program • Measles immunizations aimed at preventing the more serious complications of measles such as pneumonia in young children under 15 months of age in developing countries such as in Africa and measles encephalitis in well developed countries. • Mumps immunization is aimed at preventing the more serious complications of mumps including meningitis • Rubella immunization is aimed at preventing rubella infection in early pregnancy and hence congenital rubella syndrome. 25

‘Poliomyelitis’

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Polio Virus Vaccines • Two highly effective vaccines containing all 3 strains of poliovirus are in general use: • The killed virus vaccine (Salk, 1954) is used mainly in Sweden, Finland, Holland and Iceland. • The live attenuated oral polio vaccine (Sabin, 1957) has been adopted in most parts of the world; its chief advantages being: low cost, the fact that it induces mucosal immunity and the possibility that, in poorly immunized communities, vaccine strains might replace circulating wild strains and improve herd immunity. Against this is the risk of reversion to virulence (especially of types 2 and 3) and the fact that the vaccine is sensitive to storage under adverse conditions. • The inactivated Salk vaccine is recommended for children who are immunosuppressed 27

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Hepatitis B Virus Vaccines • Two vaccines are in current use: a serum derived vaccine and a recombinant vaccine. Both contain purified preparations of the hepatitis B surface protein. • The serum derived vaccine is prepared from hepatitis B surface protein, purified from the serum of hepatitis B carriers. This protein is synthesised in vast excess by infected hepatocytes and secreted into the blood of infected individuals.. • A second vaccine, produced by recombinant DNA technology, has since become available. Vaccine is administration to individuals who are at high risk of exposure to hepatitis B, namely: infants of hepatitis B carrier mothers, health care workers, homosexual men and intravenous drug abusers. 29

Hepatitis A Virus Vaccine • A vaccine for hepatitis A has been developed from formalin-inactivated, cell culture-derived virus. Two doses, administered one month apart, appear to induce high levels of neutralising antibodies. The vaccine is recommended for travellers to third world countries, and indeed all adults who are not immune to hepatitis A 30

Yellow Fever Virus Vaccine • The 17D strain is a live attenuated vaccine developed in 1937. It is a highly effective vaccine which is administered to residents in the tropics and travellers to endemic areas. A single dose induces protective immunity to travellers and booster doses, every 10 years, are recommended for residents in endemic areas. 31

Rabies Virus Vaccine • No safe attenuated strain of rabies virus has yet been developed for humans. Vaccines in current use include: • The neurotissue vaccine - here the virus is grown in the spinal cords of rabbits, and then inactivated with beta-propiolactone. There is a high incidence of neurological complications following administration of this vaccine due to a hypersensitivity reaction to the myelin in the preparation and largely it has been replaced by • A human diploid cell culture-derived vaccine (also inactivated) which is much safer. 32

Rabies Virus Vaccines There are two situations where vaccine is given: a) Post-exposure prophylaxis, following the bite of a rabid animal: A course of 5-6 intramuscular injections, starting on the day of exposure. Hyperimmune rabies globulin may also administered on the day of exposure. b) Pre-exposure prophylaxis is used for protection of those whose occupation puts them at risk of infection with rabies; for example, vets, abbatoir and laboratory workers. This schedule is 2 doses one month apart ,and a booster dose one year later. (Further boosters every 2-3 years should be given if risk of exposure continues). 33

Influenza Virus Vaccine • Repeated infections with influenza virus are common due to rapid antigenic variation of the viral envelope glycoproteins. Antibodies to the viral neuraminidase and haemagglutinin proteins protect the host from infection. • However, because of the rapid antigenic variation, new vaccines, containing antigens derived from influenza strains currently circulating in the community, are produced every year. Surveillance of influenza strains now allows the inclusion of appropriate antigens for each season.The vaccines consist of partially purified envelope proteins of inactivated current influenza A and B strains. 34

Varicella-Zoster Virus Vaccine Alive attenuated strain of varicella zoster • virus has been developed. It is not licensed in in many countries for general use, but is used in some oncology unitsto protect immuno-compromised children who have not been exposed to wild-type varicella zoster virus. Such patients may develop severe, life threatening infections if infected with the wild type virus 35

Efficacy of Current Vaccines

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New Rotavirus Vaccines Licensed • Two new vaccines have recently been licensed • “Rotarix” (GlaxoSmithKline), monovalent, live, oral human 89-12 strain • “RotaTeq” (Merck), pentavalent, live, oral human-bovine reassortants

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Rotavirus Vaccine • Concern about the emergence of “new” serotypes and “reassortants” strains require constant monitoring and surveillance. • Updating of the new vaccine with the “new” strains could be important to maintain efficacy

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The ‘New’ HSV Vaccine is Efficacious in Reducing Genital Herpes in Susceptible Women

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The ‘New” HPV vaccines • Two ‘new’ vaccines against HPV have completed initial double blind –placebo controlled trials • ‘Bivalent’ recombinant vaccine (against HPV-16 & 18) (GlaxoSmithKline) • ‘Quadravalent’ recombinant vaccine (against HPV-16 & 18 and also HPV-6 &11 (Merck) • Both vaccines showed 90-100 % protection against persistent infections or disease caused by these HPV strains in women after follow-up of a period of over 2 years.

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Passive Immunization Passive immunisation is the transfer of immunity to a host by means of immunoglobulins (preformed antibodies). These immunoglobulins are typically prepared by cold ethanol fractionation as a 16% solution of gamma globulin from large pools of serum obtained from the blood donations of at least 1000 donors. Immunoglobulin from immune individuals can be used as prophylaxis to prevent viral infections in exposed, but non immune individuals. It works by binding to extra-cellular virions and preventing them from attaching to and entering susceptible cells. 41

Passive immunization "Normal" Immune globulin This is a pooled product, prepared from the serum of normal blood donors. It contains low titers of antibody to a wide range of human viruses. It is mainly used as prophylaxis against: • Hepatitis A virus infection, • Parvovirus infection, and • Enterovirus infections (in neonates). • HIV-infected babies.

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Passive Immunization Hyper-immune globulin Immunoglobulin may be prepared from the serum of selected individuals who have high titers of antibody to particular viruses. Examples include: • Zoster immune globulin Prevention of Varicella in immunocompromised children and neonates. • Human Rabies immune globulin Post-exposure prophylaxis in an individual who has been bitten by a rabid animal. • Hepatitis B immune globulin Non-immune individual who has been exposed to HBV. • RSV immune globulin Treatment of respiratory syncytial virus infections in the very 43 young.

Viral Vaccination Schedules- Kuwait Vaccination Schedule

Vaccine

2nd day after birth

HBV (I.M.)/OPV-1

2nd month

HBV/OPV-1

4th month

OPV-1,2,3

6th month

HBV/OPV-1,2,3/MMR

12 month

MMR (S.C.)

18 month

OPV-1,2,3

2.5 years

OPV

3.5-4 years

MMR

Adulthood

?Boosters

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