30 - using viruses as tools in research and medicine

Question 1

properties of viruses that we can exploit

Answer 1

• they trigger an immune response
• they are a natural gene-delivery vehicle
• many viruses have a cytopathic (killing) effect
• viruses possess potent mechanisms for gene expression

Question 2

principle of vaccination

Answer 2

1) patient is inoculated with antigen (vaccine)

2) induced a primary immune response - a ‘primed’ state
• population of memory B and T cells
• neutralising antibody

3) on following exposure to pathogen there is a rapid response
• rapid eradication or control of pathogen
• no clinical symptoms
• mimics a natural infection

Question 3

types of vaccines

Answer 3

live

killed whole virus

subunit vaccines

Question 4

live vaccines

Answer 4

heterologous - closely related virus but less virulent (eg. vaccinia)

attenuated - weakened (eg. MMR)

if immunocompromised live viruses are too dangerous for some people

Question 5

killed whole virus vaccines

Answer 5

gives a good immune response

e.g. Salk vaccine - original polio virus

Question 6

subunit vaccines

Answer 6

vaccinate with just the immunogenic viral proteins rather than whole virus

purified from virus (e.g. influenza A)

recombinant proteins (e.g. HBV, HPV)

Question 7

generating the right kind of response

Answer 7

live vaccines infect cells and induce both antibody and cell mediated immune response

killed and subunit vaccines only induce antibody response
• cell mediated response is often critical in anti-viral immune response
• can only get cell-mediated response if theres replication of the virus

Question 8

why is it not always possible to make live vaccines?

Answer 8

viruses can’t be cultured - can put genes into a virus that can be cultured instead

virus can’t be attenuated to a safe level

live recombinant viral vaccines are a potential solution

Question 9

what is attenuation?

Answer 9

a process where we grow a virulent virus thats normally propagated in human cells by passing it in an alternative species of cell until it adapts

as a result, virus looses its ability to grow in human cells and its infectivity and virulence decreases

we can do this by recombinant DNA technology

Question 10

what is virotherapy?

Answer 10

using viruses to correct problems

Question 11

viral vectors in research

Answer 11

in vitro - in test tube / tissue culture
• express protein not normally expressed
• deliver siRNA (short-interfering) - a method of blocking expression of a specific gene

in vivo - in the live animal
• to create transgenic animals

Question 12

viruses as vectors in gene therapy

Answer 12

viruses are useful vectors in recombinant DNA technology

a viral vector is used to deliver a gene into a cell

viruses can be engineering to carry novel genes

Question 13

what are adenoviruses?

Answer 13

small viruses that are easy to manipulate - we know how to control their expression
• can insert new gene into viral DNA
• can use these to infect cells that may have defective proteins

Question 14

gene therapy using viral vectors

Answer 14

to deliver a functioning gene to cells which have a faulty gene - gene therapy

Question 15

oncolytic therapy using viral vectors

Answer 15

target cancer cells specifically and killing them leaving other cells unharmed

Question 16

bacteriophages

Answer 16

viruses that target bacterial cells in an infection

Question 17

what are the 2 approaches to gene therapy?

Answer 17

ex vivo - cells are removed from the body, the gene introduced and the cells retuned

in vivo - the replacement gene in introduced directly into the body via a gene vector or virus

Question 18

what are CAR-T?

Answer 18

chimeric antigen receptor T cells

modifies immune response so it attacks cancer cells

Question 19

advantages of using viral vectors

Answer 19

• targets specific cells
• protects nucleic acids en-route to target cells
• delivers genes into cytoplasm or nucleus of target cells
• gene expression can be transient or permanent

Question 20

disadvantages of using viral vectors

Answer 20

prior exposure may mean immunity attacking the virus

may work once but not again

Question 21

advantages of oncolytic virotherapy

Answer 21

combination of other cancer treatments - synergistic interaction

enhanced anti tumour efficacy

selective replication in tumour cells

direct oncolysis and immune-mediated anticancer effect

alternative killing mechanisms

Question 22

disadvantages of oncolytic virotherapy

Answer 22

resistant cancer cells

antiviral immune response

limited replication and spreading

Question 23

whats the difference between oncolytic and oncogenic viruses?

Answer 23

oncolytic viruses destroy tumour cells

oncogenic viruses promote development of tumour cells

Question 24

what is phage therapy?

Answer 24

use of virus (bacteriophage) to kill bacteria

Question 25

advantages of phage therapy

Answer 25

effective and quick

specific to a bacterium

can evolve and adapt to resistance

self-amplify until all bacteria re dead

Question 26

disadvantages of phage therapy

Answer 26

lysis of gram negative bacteria - release of endotoxins - sepsis

theoretical potenital to transfer DNA between bacteria - antibiotic resistance