Watson - vaccination Flashcards
In what ways are vaccines better than pharmaceuticals?
- comparatively successful and cost effective
Why is a HIV-1 vaccine needed?
- 16,000 new infections per day
- substantial economic impact (triple therapy v expensive)
- now a pandemic
- destruction of economies and human capital
- only treatment (no cure) w/ antiretrovirals, eg. AZT
When and how was immunity 1st observed?
- in ancient times when infection w/ particular disease makes indiv resistant to infection w/ same disease again
How was variolation used to treat smallpox?
- infection w/ mild case of smallpox protected from subsequent serious infection
- scratched on arm were inoculated w/ pus from pustule
- Jenner observed milkmaids often suffered from cowpox and were resistant to smallpox –> so deliberately infected people w/ pus from cowpox lesion
What is the principle of active immunisation?
- manipulating IS to gen persistent protective response against pathogens
- triggers immune response and safely mimics natural infection
- mobilising approp arms of IS and gen immunological memory (ideally life long)
What is passive immunisation?
- transfer of preformed antibodies (antisera)
What is natural passive immunity?
- occurs naturally by transfer of maternal antibodies across placenta to dev fetus
- provides protection against diphtheria, tetanus, streptococcus, rubella, mumps, poliovirus
What are indications for the use of artificial passive immunity?
- indivs w/ agammaglobulinemia (lack of IgG in plasma) –> treated w/ pooled human IgG
- exposure to disease that could cause complications –> eg. immunocompromised patient (HIV/chemo) exposed to measles or other pathogen
- when no time for active immunisation to give protection –> ie. pathogen w/ short incubation time
- when acute exposure, so danger of infection –> eg. to ebola
Where are anti-toxins and antivenins usually from?
- horse serum –> inject horse w/ enough to mount response but not to kill
For some pathogens what is the main hazard, when not 1° infection which can be eliminated by IS?
- effects of v potent toxins released by bacteria, eg. tetanus and botulinum
Why is difficult to achieve immunity to toxins/venoms?
- exposure to sufficient amount to stim IS would be lethal
What can be used as vaccines against toxins?
- deactivated toxin derivatives (toxoids)
- most commonly used is tetanus toxoid
What is the problem w/ using horse serum for anti-toxins/antivenins?
- can only use once
- as recognised as foreign 2nd time, causing anaphylactic shock
What are the adv of passive immunity?
- can quickly neutralise toxins and venoms
- conventional immune response may be too slow
- for highly virulent pathogen can prevent or limit infection
- if no vaccine, may be only treatment
- in some cases can use antibodies from surviving patients (certain level of risk)
What are the disadv of passive immunity?
- doesn’t activate immunological memory
- no LT protection
- poss of reaction to antisera if cross species
What are the aims of a perfect vaccine (active immunisation)?
- LT protection
- stim B and T cells and induce memory B and T cells
- stim protective high affinity IgG prod (and poss IgA)
- induce approp immune response
- safe
- stable and easy to transport
- should not rew repeated boosting (to reduce problems w/ patient compliance)
What is the aim of perfect vaccine dep on?
- nature of targeted pathogen (not history of disease)
- and importance of memory B cell response dep on nature of pathogen
What do B cells and antibodies generally recognise?
- shapes and structures
- not enough to determine if pot target is non self
What are the advs of live attenuated vaccines?
- sets up transient infection
- activation of full natural immune response
- prolonged contact w/ IS
- stim of memory response in B and T cells –> prolonged and comprehensive protection
- often only singe immunisation req (+ve in 3rd world)
Why do live attenuated vaccines often only req a single immunisation?
- vaccine able to replicate, so antigens released over time
- in contrast to single vaccination w/ antigenic extracts or inactivated organisms
What are the disadvs of live attenuated vaccines?
- immunocompromised patients (or other rare indivs) may become infected as result of immunisation
- complications –> eg. for live measles vaccine 1 per 1 mil post infection encephalomyelitis and occasionally can revert to virulent form (can cause serious outbreak in areas w/ poor sanitation)
- refrigeration and transport –> typically live organisms need to be refrigerated for stable storage, issue in remote areas
What are the advs of whole inactivated pathogen vaccines?
- no risk of infection
- storage less critical
- wide range of diff antigenic components present so good immune response poss
What are the disadvs of whole inactivated pathogen vaccines?
- tends to just activate humoral responses
- lack of T cell involvement
- w/o transient infection immune response can be quiet weak
- repeated booster vaccinations req
- adjuvants may be needed to increase immune response
- patient compliance can be issue (esp for multiple vaccinations)
What is the importance of the correct inactivation procedure?
- so that vaccine is safe
- also doesn’t decrease immunogenicity of pathogen
How are pathogens inactivated for vaccines?
- heat treatment not preferred as can alt conformation of target antigens
- modern approaches can exploit DNA tech to remove genes that control virulence, but leave genes for infection intact
What are the 3 major types of subunit vaccines currently in use?
- inactivated exotoxins (toxoids)
- capsular polysaccharides
- recomb microbial antigens
What are bacterial exotoxins responsible for, and how can they be used as a vaccine?
- symptoms of disease caused by no. important pathogens
- eg. diphtheria toxin inhibits translation by inactivating EF2
- eg. tetanus toxin causes uncontrolled contraction of voluntary muscles
- use toxoid = heat treated or chem modified to eliminate toxicity
What are capsular polysaccharides and what is their role?
- highly polar, hydrophilic cell surface polymers consisting of oligosaccharide repeating units
- main antigens involved in protective immunity to encapsulated bacteria
- may interfere w/ bacterial interactions w/ phagocytes by blocking opsonisation
How can purified proteins be used as subunit vaccines?
- cultivation of pathogen and subsequent processing to purify single component (eg. toxoids)
How can recomb proteins be used as subunit vaccines?
- cloning and expression of single gene in recomb host –> eg. subunit vaccine comprised of hep B surface proteins
- virus coat proteins expressed in yeast and spontaneously assemble in virus like patches
What is a conjugate vaccine and what issue do they solve (type of subunit vaccine)?
- in some cases target antigen (eg. CPS) may only stim weak T cell response
- would decrease induction of immunological memory, so CPS can be chem conjugated to 2nd antigen (freq, but not necessarily from same organism)
- immunisation w/ this conjugate vaccine can then stim B and T cell responses
What are the advs of subunit vaccines?
- safer as only portions of pathogen used
- no risk of infection
- easier to store and preserve
What are the disadvs of subunit vaccines?
- immune response less powerful than live attenuated
- repeat vaccines needed
- adjuvants have to choose subunit that elicit response in widest range of subjects (MHC difference?)
What is the aim of DNA vaccines?
- transiently express genes from pathogens in host cells and gen immune response similar to natural infection, leading to B and T cell memory responses
Do only B and T cells take up DNA from a DNA vaccine?
- other cell types may too, eg. antigen presenting cells (follicular dendritic cells)
What proof of the principle of DNA vaccines is there, and is this enough?
- immune responses in animals obtained using genes from variety of infectious agents, inc influenza, hep B, HIV, rabies
- in some cases protective response resulted
- but too little known about how they lead to immune response –> poss side effects? what adjuvants could be useful?
What are the advs of DNA vaccines?
- don’t req complex storage and transportation
- delivery can be simple and adaptable to widespread vaccination programmes –> DNA gun
What are the disadvs of DNA vaccines?
- as w/ “killed” vaccines and subunit vaccines, no transient infection
- only likely to prod mild immune response and req subsequent boosting
What is the aim of recomb vector vaccines, and how do they work?
- imitate effects of transient infection w/ pathogen, but using non-pathogenic organism
- genes for major pathogen antigens introd into non-pathogenic or attenuated MO and introd into host
- viral or bacterial
What are the advs of recomb vector vaccines?
- create ideal stimulus to IS
- prod immunological memory
- flexible –> diff components can be engineered in
- safe (relative to live attenuated pathogen)
What are the disadvs of recomb vector vaccines?
- req refrigeration for transport
- can cause illness in compromised indivs
- immune response can negate effectiveness
What is the aim of using synthetic peptides as vaccines?
- prod peptides that inc immunodominant B cell epitopes and can stime memory T cell dev
What are the difficulties w/ using synthetic peptides as vaccines?
- knowledge of MHC presentation of peptides essential
- peptides can be stimulatory or suppressive
- most B cell epitopes are conformational
What are adjuvants?
- essentially any substance added to vaccine to stim IS
- can inc whole killed orgs, toxoids, proteins (as in conjugate vaccines), chemicals (aluminium salts, oil emulsions)
How do aluminium salts act as adjuvants, and is this the same as other adjuvants?
- may extend half life of immunogen in site of injection (depot effect)
- mechanisms can vary
What is the issue w/ using chemicals as adjuvants?
- can cause irritation and inflam
How do toxoids and whole killed orgs act as adjuvants?
- trigger IS and send out “danger signals”
What is the role of adjuvants?
- act as delivery system and immune stimulators
- essentially trigger innate IS
What are some eg.s of adjuvants used in humans?
- alum
- oil/water emulsions
- detoxified bacterial lipopolysaccharide
- more recently, toll-like receptor agonists
What is often the downside of high efficiency adjuvants?
- can be accompanied by safety hazards –> risk of inapprop immune responses and chronic inflam
What did evo of the cell membrane lead to?
- definition of self and non-self
- and war w/ viruses
How is AIDS transmitted?
- through blood and bodily fluids
- or perinatal
What is the origin of HIV-1?
- evolved from related lentivirus in monkeys (SIV)
When do viruses usually cause the most problems?
- when they cross species
What is the role of the TM glycoprotein on cell surface of HIV-1?
- req attachment point to get into cell
Why would passive immunisation not help against HIV?
- integrates into host genome and can be dormant when integrated for long periods
Why is HIV not recognised as foreign?
- packaged and secreted out of infected host cells, so has human membrane
What happens when HIV is activated?
- prod many copies by reverse transcriptase
- billions per day
What are the characteristics of the HIV genome?
- ds RNA
- dense and efficient
- accessory proteins all enhance ability to rep
What part of the HIV genome is the target for vaccines, why?
- envelope protein
- stop it getting into cells in the 1st place
What does expression of envelope protein of HIV involve, and what can be used to combat this?
- expressed and cleaved by protease into 2 subunits (gp41 and gp120)
- form structure that is key to life cycle
- protease inhibitors used to break life cycle
What happens during the HIV infection process?
- fusion w/ membrane via gp120/gp41 “spike”
- interacts w/ CD4 and accessory proteins CCR5 (chemokine receptor)
- target cells are CD4 T cells, macrophages, dendritic cells
- reverse transcrip of genome from RNA to cDNA
- migration to nucleus and integration into host genome
- expression of viral proteins
- gen of viral RNA genome and encapsulation
- expression of envelope protein and cleavage
- secretion of mature virions from cell surface
Why cant HIV infect some people, and why could these people be useful?
- mutant CCR5
- could be good source of antibodies against HIV
What are the effects of HIV infection for cells?
- increased apoptosis of infected cells
- targeting of infected cells by CD8 killer cells
What is the pathology of HIV/AIDS?
- acute phase = CD4 T cells depleted by cytotoxic T cells
- initially CD4 cells recover as evades IS
- chronic slow depletion of CD4 T cells, due to generalised immune activation and loss of ability to prod new CD4 T cells
- when CD4 cell levels fall below critical level, IS is compromised
- get opportunistic infections w/ rare pathogens and cancers
Are antibodies for HIV/AIDS present in patients, and what do they show?
- yes, but don’t prevent infection or progression
- but show level of infection
What makes HIV so adapted to evading IS?
- accessory mols –> nef, vif, vpu, vpr
What is the role of nef in HIV?
- stabilises interaction between CD4 and AP2
- AP2 is another adaptor for clathrin
- by similar mechanism surface CD4 misdirected to endolysomal compartment and degraded
- assists viral release as CD4 would tether nascent viral to surface via gp41/gp120 interaction
What are the roles of vif/vpu/vpr in HIV?
- subvert cellular ubiquitination system to neutralise anti-viral responses –> act as adaptors to cause E3 to target viral defense proteins
Why is HIV so difficult to eradicate?
- attacks cells of IS
- accessory proteins downreg immune response
- can be dormant for long periods –> evading IS and creating ‘reservoir’ of virus that can later re-establish infection
Why is there such a need for a HIV vaccine?
- big impact on communities
- > 1% of worlds pop now infected
- 1 of handful of devastating world pandemics
What does triple therapy involve using?
- inhibitors of membrane fusion/infection
- inhibitors if reverse transcriptase
- inhibitors of integration
- protease inhibitors
What evidence is there for the possibility of a HIV vaccine?
- “long term non-progressors” and natural immunity exist
- experiments w/ pre-formed antibody (passive immunisation) showed infection could be prevented
- pre-infection w/ less virulent HIV-2 confers some protection against HIV
- possess antibodies w/ broad neutralising activity against many strains
- target gp120 stalk and block infection
What are “LT natural progressors”?
- people who carried HIV for long periods (30+ yrs) w/o dev AIDS
How could broad neutralising antibodies be used against HIV?
- can be cleaved from LT supporessor patients and expressed in recomb form (a kind of passive immunisation)
In theory is a HIV vaccine poss?
- not infectious (on av takes over 200 exposures to cause infections)
- infection often by 1 virion or v small no.
- so theoretically vaccination could present infection and/or progression
What are the aims of a HIV vaccine?
- cause humoral responses –> B cell vaccines
- route is purified recomb subunits and repeated doses
What were early vaccine trials for HIV, and were they effective?
- inactivated virus and attenuated virus –> not really pursued
- subunits –> purified recomb proteins (gp120, gp41, gp160)
- subunits expressed in recomb viral vectors
- all proved ineffective –> patient gen antibodies but infection and progression not prevented
What are the features of HIV that hinder immune responses?
- high genetic variability
- immunodominance and cryptic epitopes
- immunosuppressive factors
How does HIV exhibit genetic variability?
- exists in series of related variants or clades
- high genetic variability, even w/in indivs
- new variants constantly emerging as virus rep –> due to error prone rep by reverse transcriptase
- allows evo selection w/in infected indiv –> observed as resistance to antiviral drugs freq arises w/ AZT and other therapies
Does infection w/ HIV prevent subsequent infections, and what are the implications of this?
- no, still get subsequent superinfections w/ other variants
- so patients either fail to dev neutralising antibody or cellular immune response
- or HIV mutated and evades IS
- after initial small scale infection remains in IS and begins prolif (≈ 1 bil virions/day)
- created conditions for natural selection to gen novel variants
What is a key target for preventing infection w/ HIV?
- env “spike” –> trimer of membrane spanning gp41 in complex w/ gp120
- gp120 has recognition sites for CD4 and CCR5
- blocking these sites w/ antibody can sterically inhibit binding of CD4 and infection
- non-progressors target this site
What is the main problem w/ targeting CD4 and CCR5 binding sites?
- not exposed to IS
- transiently exposed as result of CD4 binding and conformational changes
- these epitopes masked, so not easily targeted by IS
- Ig too large to access these sites
What are further problems with targeting CD4 and CCR5 binding sites?
- gp120 features no. solvent exposed peptide loops that are highly variable
- these are preferred immunodominant targets for B cell responses = decoys
- adaptive IS is not “intelligent”
What is sterilising immunity?
- stopping infection from occurring in 1st place
Should a HIV vaccine cause sterilising or non-sterilising immunity?
- rate of infection must be decreased
- decreased viral load could decrease rate of transmission
- strategy must shift to decrease spread
- elimination may be impossible
What is the potential of non-progressors?
- discovery of neutralising B cell epitopes by screening these people?
- isolate patient sera who have broad neutralising activity and determine corresponding epitopes
What is the challenge, now we know natural neutralising antibodies for HIV do exist?
- to make immunogen that would elicit same antibody response in subjects receiving vaccine
- titer of neutralising antibody correlates w/ protection so req high levels
- likely that protection will req both neutralising antibody and cytotoxic T cell responses
What are the future trends for dev a HIV vaccine?
- exploit natural non-progressors
- clone their antibodies
- broadly neutralising
- use in passive immunisation approach to decrease viral load
- decrease viremia and halt transmission
What features of HIV make dev vaccine problematic?
- vaccines mimic natural immunity against reinfection → but don’t see recovery
- most vaccines protect from disease, not infection, but if infects too late, due to latency
- can’t use whole killed or live attenuated which are most effective
- most vaccines protect from pathogens encountered infreq, but daily for those at high risk
- most vaccines protect from infection through mucosal surfaces of resp/GI tract, but through UG
Why can’t we use live attenuated or killed vaccines for HIV?
- attenuated too dangerous
- killed lose immuno-characteristics so doesn’t gen approp Ab
What are the issues with T cell vaccines for HI?
- difficult in immunocompromised patients as can establish widespread lethal infection
- unlikely to target latent reservoir
What are the options in terms of what a HIV vaccine could do, and how could these be studied?
- prevent infection (stim B cell and gen Ab) → look at no. new infections in vaccinated group comp to control
- delaying progression (stop immune depletion/prog to AIDS) → viral load tests, comp those infected after receiving vaccine to those infected w/o vaccine
- blocking transmission (decrease viral load) → look at if rates of infection decrease after vaccine and comp pops where vaccine available, to those where its not
What recent dev has there been for a target for HIV vaccine?
- density spikes on env quite sparse (14/virion)
- hard for Ab to bind 2 spikes sim
- found in some infected appear to be polyreactive Abs –> bind glycoprot w/ 1 arm and unknown surface Ag w/ other
- aim = artificially make these
