Flashcards in lecture 21 Deck (24)
How many cadaveric donors/solid organ transplants do we have compared to patients on the waiting list?
- 1998 - 2004: always much high numbers on the waiting list than transplants that occur
~ 1800 patients waiting for a transplant
- 700 patients get transplants
- 200 cadaveric donors (this doesn't match up)
- before about 1978 there wasn't really a waiting list, ~ 500 translplants
- 1978 waiting list appears and increass exponentially
- number of transplants rises but plateaus
- 1978 was when the technique for immunosuppression was approved (cyclosporin?)
What are transplantation statistics?
-- '92 - '95 1700 transplants/year
-- waiting list grew from 4,000 to 5,000
-- 45,000 patients waiting for transplants
-- <6,000 cadaveric donors = 20,000 organs
no way for supply to meet the demand
~10-15% chance of dying while waiting for an organ, not unique to australia
Why do transplants?
- dialysis $40,000
- kidney transplant $30,000 in first year
- $8,000 per year
improved quality of life
Why is there a shortage of donors?
- decrease in road accidents
- family permission less
- not suitable (age, disease, etc)
- time factor
- greater demand
What are possible solutions to this shortage?
- increase donors
-- e.g. donor games
-- getting older so not necessarily the solution
- artificial organs
- stem cells --> organs/tissue
- animal as donors: xenografts
-- first transplantations were chimpanzee kidneys to human
What were patient attitudes towards xenografts?
131 renal patients:
- 51% would accept xenograft
- 39% unsure, wanted more information
- 10% unacceptable
Why did we revisit xenografts?
- molecular biology
- transgenesis/animal cloning
What are problems with xenografts?
What are physiological problems of xenografts?
- size e.g. can't use a mouse (too small) or a horse (too big), maybe a kangaroo? but we use sheep/pig
- complexity of function
e.g. sheep regulate insulin by glucose AND fatty acids --> not the same
What are ethical considerations of xenografts?
e.g. chimps etc are probably the best immunologically speaking, but people have issues with taking organs from this animal, cf pig
considerations for use of pigs:
- food (as long as people are willing to slaughter pigs for food, they should be able to be used for donating organs)
- insulin (major source of insulin for diabetics)
- heparin (anticoagulant)
- heart valves (used to replace broken valves in humans)
- breeding (a forerunner for genetic manipulation)
What are biological considerations of xenografts?
- adaptability to captivity
-- pigs breed well in captivity
-- primates breed poorly in captivity
- litter size
-- pigs: 10
-- primates: 1
- pig husbandry relatively easy
- gnotobiotic pigs available (germ designed/germ free)
What are infectious considerations of xenografts?
- primates: potential source of infection, especially viruses
- pigs: lower potential source for infection
- human viruses could infect primates, but not pigs
What are immunological problems associated with xenografts?
- hyperacute rejection: antibody causes immediate graft loss
- delayed xenograft rejection: macrophages/NK cells
- cell mediated rejection: T cells
What is hyperacute rejection?
- loss of vascular endothelium
- haemmhorage and oedema
- not unique to xenografts
- e.g. mis-match blood transfusion
Do we have an 'anti-pig' antibody?
- yes: normal, present in all humans
- IgM, IgG, IgA
- 1-2% of all Ig
- >95% to Gal-alpha (1,3) Gal
What is the xenoantigen?
- Gal-alpha (1,3) Gal
- present on many different molecules
- expressed in most tissues
- alpha 1,3, galactosyltransferase
- GKO: mice, pigs
How has transgenesis played a role in xenotransplantation?
CD46 transgenic pigs:
- ubiquitously expressed human complement regulator
- renal transplants to non-immunosuppressed baboons
-- >72 hr (normal <1hr)
-- histologically normal
- destroyed by anti-pig antibodies
- protected by expression of CD46
How can you use ES cells?
- get rid of the antigen in mice
- can't use ES cells of pigs
What are Gal o/o pigs?
- cloned pigs
- reported by 4 groups
- Gal- survive >150 days
- HAR/DXR solved
What pig transplantations have occured?
pig heart transplants
- baboons (n=8)
- anti-CD154 mAb, mycophenolate mofetil, and methylprednisolone
- no HAR
- graft survival extended to between 2 and 6 mo
- thrombotic microangiopathy
pig kidney transplantation
- baboons (n=11)
- tolerance induction, including thymectomy, splenectomy, T-cell depletion, anti-CD154 monoclonal antibody and mycophenolate mofetil, with or without low-dose steroids
- no HAR
- graft survival extended to 83 days (now more than 160)
- thrombotic microangiopathy
pig kidney transplantation 2
- baboons (n=3)
- no immunosuppression
- no HAR
- graft survival extended to 4 days
- antibody and C' deposition, platelet deposition, perivascular infiltrate
- intravascular coagulopathy
pancreatic islets: more than a year
looking a blocking costimulation
What are some factors to consider in transgenesis?
- microinjection --> 1%
- xeno transgenes
-- DAF 1992
-- DAF + CD59 1998
-- CD46 2000
ie. 1-2 genes in 10 years
= 100 year programme unless SMGT
- nuclear transfer 0.5% : Gal knock out (some groups claim up to 10% in pigs... more in mice)
- retrovirus: Lenti virus in mice
What is sperm mediated gene transfer?
- collection of ejaculate from male, mixed with DNA (and appropriate buffers)
- artificially inseminated females
- could use this to create multi-transgenic pigs
What are unsolved problems of xenografts?
- organ compatibility
- delayed xenograft rejection
- retrovirus infection
- cellular immunity/immunosuppression
- tolerance induction
- other carbohydrate antigens
- further genetic engineering