3.6: Vaccines

active immunity

• getting the disease or getting vaccinated activates the immune response

• Strong T and B cell memory

• Cons- getting the disease may be dangerous, likely need boosters

Passive immunity

• someone else’s antibodies are transferred to help you (from mother or therapy)

• no memory—> short term

• IgG mediated protection

why do we vaccinate

1. protect ourselves from life-threatening infections

2. achieve herd immunity

herd immunity

most of the population is vaccinated, so spread of contagious disease is contained, fewer people come into contact with the germ

antigen

the part of a vaccine that trains your immune system

adjuvant

an immune system booster

preservatives

prevent the vaccine from going bad after opening

stabilizers

prevent the vaccine from sticking to the vial

surfactants

keep the vaccine an even mixture

residuals

small amounts of the substances used in the manufacturing of the vaccine

diluent

liquid that dilutes the vaccine to the proper dosage

critical features of vaccines (6)

1. safe- vaccine must not cause illness or death

2. protective- protect against illness resulting from exposure to pathogen

3. gives sustained protection- protection from illness must last several years

4. induce neutralizing antibodies- block pathogens from infecting cells

5. induces protective T cells- intracellular pathogens need T cell response

6. practical considerations- cost per dose, biological stability, ease of administration, few side effects

neutralization

antibodies bind to pathogens or the toxins they produce preventing them from ebing able to infect or cause disease

opsonization

antibodies bind to the surface of pathogens and flag them for destruction through the complement system or phagocytosis

antibody-dependent cell cytotoxicity

antibodies can also bind to pathogen proteins on the surface of infected cells and trigger degranulation of NK cells to poke holes in pathogen

IgM

dominated the initial antibody response following infection or vaccination

IgG

generated after IgM but quickly becomes more abundant in the blood, binds more strongly to antigens and dominates the overall antibody response to vaccination

Types of vaccines

1. whole cell (attenuated and inactivated)

2. viral vector (replicating and non-replicating)

3. subunit (protein, conjugate, toxoid)

4. nucleic acid (DNA and RNA)

Live attenuated vaccines

• contain live pathogens that are produced by selecting or creating strains that still produce a strong enough immune response but do not cause disease

• either eliminate genes that cause disease or temperature sensitive variants

• contain the whole pathogen so the immune system reacts strongly and induced long-lived immune memory

• immunocompromised individuals shouldn’t receive vaccine

how live attenuated vaccines work

1. live attenuated delivered via syringe

2. vaccine virus enters cells and releases code to replicate itself

3. code is read and cell makes more of virus

4. viral elements made that makes cell sick are too weak to cause disease and released

5. replicated virions are taken in by APC

whole cell inactivated vaccines

• live pathogen is killed

• when vaccine is given, the inactivated pathogen is strong enough to create an immune response but can’t cause disease

• multiple does are needed to build up enough immunity for protection

• easy and inexpensive to make

How does inactivated vaccine work

1. inactivated vaccine delivered by syringe

2. vaccine virus or bacteria taken up by APC

3. vaccine is chopped up into pieces (antigens)

4. Antigens displayed on cell surface to be recognized by immune cells

5. Immune helper cells trigger response

6. body creates army of B cells to produce antibodies against virus/bacteria

7. antibodies bind to virus or bacteria and prevent entry into cells

8. antibody levels fade with time and usually additional shots are needed

viral vector vaccines

• non pathogenic viruses carry the genetic code of an antigen from a pathogen to host cells

• target antigen is transcribed and translated into protein which triggers the body’s immune response

• trigger strong immune response

• one dose and maybe a booster are sufficient

• most time and cost to make

how viral vector vaccines work

1. viral vector vaccine delivered via syringe

2. viral vector fuses with host cell membrane releasing genetic code

3. instructions/code are read and host cell makes target protein

4. protein is broken down

5. fragement is presented on cell surface for immune cells to respond

subunit vaccines

• proteins or polysaccharide targets from pathogen mimic the surface of pathogens

• stuck/conjugated to a protein that elicits a strong immune response

• stimulate B and T cells and generate T cell dependent immunity

• do not contain any organism so they don’t cause infection

• larger does and boosters are necessary

How polysaccharide and conjugate vaccines work

1. vaccine released into body

2. vaccine taken up by APC and displayed as an antigen

3. immune helper cells identify antigen and trigger immune response

toxoid vaccines

• use inactivated toxins (toxoids) from a pathogen to induce antibodies and neutralize the toxins rather than target the bacteria itself

• boosters required

how toxoid vaccines work

1. toxoid vaccine released into the body

2. toxoids cannot bind to cells as toxins do

3. toxoids can trigger the similar immune response as bacterial toxins

4. taken up my and APC

mRNA Vaccines

• mRNA is encapsulated in nanoparticles that elicit an immune response

• nanoparticles fuse w host cells and pathogen proteins are translated from the mRNA

• protein triggers an immune response that includes the generation of antibodies that recognize the protein

• vaccinated individual has an established population of antibody secreting and memory B cells that can protect just as if the person were exposed naturally to the pathogen

how do mRNA vaccines work

1. nanoparticle RNA delivered via syringe

2. capsule fuses with cell membrane releasing genetic code

3. code is read by host cell and makes the target protein

4. cell presents new peptides on surface to be found by immune cells

adjuvant

a substance that enhances the immune response to an antigen that typically induced a weak or non-specific response

• mixture= antigen and adjuvants are mixed in a solution

• conjugate= antigen and adjuvant are bound together

pros of adjuvants (8)

• makes vaccine more cost effective

• effective innate immune signals, including danger signals

• good immuno-stimulating capacity

• high specific antibody production

• antigen-specific clonal expansion

• generation of cytotoxic T Cells

• long-lasting adaptive immune response

• makes antigen more potent