Q.785. What is Xenotransplantation (Xt.)?
﴾﴾ VII. Xenotransplantation. ﴿﴿
Q.785. What is Xenotransplantation (Xt.)?
Possible sources of xenografts
are: non-human
primates & non-primates, especially the pig. Sp. benefits
é
using swine xenografts include:[availability in unlimited No., organs
of appropriate size, and a limited risk of transmitting
infection]. There’re significant hurdles to successful
application of Xt., which include: [Immunological
resp. of recipient agst the graft, physiological limitations of the
graft, infection & ethical considerations]. Powerful immunologic
reactions: [hyper.Ac,
Ac. vascular, cellular & ch. Rj.].
Specific measures unique to Xt. have been utilized in the attempt to
over-come these issues. If biologic hurdles are overcome, kidney Xt. could be used for select populations. These may incl. presensitized
individuals, young infants é kidney failure, and others.
Q.786. What is the future
approach?
A.
Xt. may appear in a step-wise
fashion. As porcine
tissue
are
available in:
1)
Porcine livers: currently used as devices
for ttt. of fulminant hepatic
failure.
2)
Porcine skin is used for ttt. of
burns.
3)
Porcine cells are Tx. into ptn. é
Parkinson's dis.
& unremitting pain.
Furthermore, Tx. of porcine hepatocytes
& islet cells
may soon be undertaken. Fr. these clinical activities, information will emerge
concerning the immune resp. to Xt. &
risks of infection. It cn be anticipated that a next step will be "bridge" transplants, in which a porcine kidney, heart, or liver are implanted
to provide temporary
support until more definitive ttt can be available. It’s difficult to
envision how & under which conditions porcine kidney can be used as clinical bridge.
Bridge transplants
will provide important information about manifestation & control of the vascular
responses to Xt.. Only when these responses are effectively
controlled over a period of months is it likely that the porcine
kidney will be used as a permanent xenogeneic transplant.
Q.787. What are the possible future indications?
A. If the biological
hurdles to R. Xt
are overcome, the next critical😎question is which ptns é R. dis. wd be most
suitable
to
receive Xt. This’s esp. challenging because R.Tx., unlike Tx. of other
organs, is not
necessarily life-saving because DX is readily available in most countries.
On the other hand, Xt might be esp. appealing as the cost cd eventually be
lower than that in other procedures . In addition, Xt might be preferred
in certain medical settings:
(1) Presensitized ptn.: Xt may be initially considered for a limited No. of subjects
who’re pre-sensitized to multiple
potential donors and are therefore less
likely to receive an allograft. In this setting, successful performance of Xt assu-mes tht
anti-HLA A.B. do not cross-react é porcine Mj
histocompatibility Ag.(SLA) (2)Infants: R. Xt may be appropriate for young
infants é R.F. in whom DX is very difficult
to perform. Such infants are also difficult
to Tx. because of mism-atch in size between adult kidney & infant. A xenograft
cd be used in selected cases to
allow infant to grow to a size that’s more optimal for alloTx.. (3) Hyperoxaluria : Iry
hyperoxaluria may be suitable candidates because conventional Tx. experience in
these ptns has been relatively disappointing. R. oxalosis 🠞loss of the graft
occ. in many patients. (4) HIV: HIV+ve
ptn. é R.F. may be candidates for Xt, since many Tx. centers exclude
such ptns However, given the long-term
survival of some HIV-+ve ptn. with current therapy, a network of centers in the U.S. has been
created where feasibility of transplanting these ptns is being evaluated in a systematic
manner. Other Tx. programs are
considering Tx. of HIV ptns on an individual basis.
Q.788. What are the barriers to xenotransplantation? 💢💢
A. There’re signif. hurdles to successful
application of Xt., wch incl.:
1) Infection.
2) Ethical considerations.
3) Physiological limitations of
the graft.
4) Immunological responses of recipient against the graft.
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