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Flashcards in lecture 21 Deck (24)
1

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?)

2

What are transplantation statistics?

- UK:
-- '92 - '95 1700 transplants/year
-- waiting list grew from 4,000 to 5,000

- USA:
-- 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

3

Why do transplants?

costs
- dialysis $40,000
- kidney transplant $30,000 in first year
- $8,000 per year

improved quality of life

4

Why is there a shortage of donors?

- decrease in road accidents
- family permission less
- not suitable (age, disease, etc)
- time factor
- greater demand

5

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

6

What were patient attitudes towards xenografts?

131 renal patients:
- 51% would accept xenograft
- 39% unsure, wanted more information
- 10% unacceptable

7

Why did we revisit xenografts?

- molecular biology
- transgenesis/animal cloning

8

What are problems with xenografts?

- physiological
- ethical
- biological
- infection
- immunological

9

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

10

What are ethical considerations of xenografts?

- emotional
- conservation

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)

11

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)

12

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

13

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

14

What is hyperacute rejection?

- antibody
- antigen
- complement
- immediate
- clots
- loss of vascular endothelium
- haemmhorage and oedema
- not unique to xenografts
- e.g. mis-match blood transfusion

15

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

16

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

17

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

pancreatic islets
- destroyed by anti-pig antibodies
- protected by expression of CD46

18

How can you use ES cells?

- get rid of the antigen in mice
- can't use ES cells of pigs

19

What are Gal o/o pigs?

- cloned pigs
- reported by 4 groups
- Gal- survive >150 days
- HAR/DXR solved

20

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

21

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

22

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

23

What are unsolved problems of xenografts?

- organ compatibility
- delayed xenograft rejection
- retrovirus infection
- cellular immunity/immunosuppression
- tolerance induction
- other carbohydrate antigens
- further genetic engineering

24

What are the important points re: xenografts?

- the pig is the most suitable animal for donor
- hyperacute rejection entirely due to Ab, Ag and C'
- antigen negative pigs cloned
- more genetic engineering required