GeaerlJl SW'1fetY 139 SUllGICAL TECHNOLOGY INTERNATIONAL n

Liver Xenotransplantation IGNAZIO ROBERTO MARINO, MD, ANDREAS G. TZAKIS, MD

JOHN J. FUNG, MD, PHD, SATORU TODO, MD

HOWARD R. DOYLE, MD, RAFAEL MANEZ, MD

THOMAS E. STARZL, MD, PHD UNIVERSITY OF PITTSBURGH SCHOOL OF MEDICINE AND THE VETERANS ADMINISTRATION MEDICAL CENTER, PITTSBURGH, PENNSYLVANIA

DURING THE PAST 30 YEARS ORTHOTOPIC LIVER TRANSPLANTATION HAS BECOME A

highly successful form of surgical treatment.'-3 The significant advances

achieved in this field have led to an increased demand for organs and created a

wide gap between organ availability and organ supply.4

A wider availability of organs for transplantation would allow an expansionS rather

than a contraction of the indications for transplantation, and, at the same time a relax­

ation of the patient selection criteria.6,7 All these facts clearly justify the renewed

interest observed in the last decade in xenotransplantation.8

The original concept of xenografting, meaning the transplantation of cells, tissues,

or organs between different species, is so ancient that it is easily recognizable in Greek

and Roman mythology. The centaur Chiron,9 the teacher of Esculapius, and the

Chimera'o are legendary examples of discordant" xenogeneic creatures_

However, it is oruy during this century that scientists have been able to bring this idea

intO the clinical arena. The early efforts were prompted by the shortage of humans organs

at a time when there were few alternatives for treating end-stage organ failure. I H4

The first three attempts at whole organ xenotransplamanon were made in France and Germany between fanuary and April 1906 usmg a pig. a goat, and a rna~que as kidney donors. ll.13 None of these kidneys tunctloned because ot almost Immewate vascular thromboSIS, and the human reclpi­c:ntS died in less than 3 days. In a further ;mempt In 1923 by Neuhotl~ :l lamb was used as a kidney donor and the patlent wed atter <) days. Un February 16, 1963, Hitchcock of the Henneptn County Hospital to Minneapolis, transplanted the kidney ot a baboon to a 6S-year-old woman. The organ tuncuoned ior 4 dayS before ItS

. Hterv clotted. ls A few months bter on October H, 1 Y63, Reemtsma 01 Tulane UniversitY used a Rhesus monkey as a kid­nev donor tor a human reCIpient who sur-

vived 12 days. Then, Rcemtsma tried agam with a senes of 6 consecutive chimpanzee kidney gratts.11> One of these xenografts tunctloned for 270 days.

In December [963 and Tanuary 1964, SIX patients were transplanted uSing baboon kidneys at the University ot Colorado In Denver.18 All of these kid­neys worked Immewately and sustamed ,I dlalysls-iree liie tor 10 to 60 days. The patients were on heavy doses 01 aza­t hlOpnne and prednisone and in 4 of them St!PSIS was the leading cause ut Jeath, whIle relectlOn was maInly responsible tor the other two deaths . However, the relectlOn pathology was not qualitlyely dlifcrent trom that observed 10 allograrts.': s In [984, slmdar Immunopatholol/:lCal t!vents caused tat!-

AIded bv Re~arch Grants from the Veterans Ailirurusu~uon and Prolect Gram No. DK 29961 tram the

Liver Xeaotrampl4lJtatioa 140 MARINO, TZAXIS, FUNG, TODO, DOYLE, MANEZ, STARZL

ure of a baboon heart transplanted in a 2,200 gr neonate, known as Baby Fae,14 after 20 days, Despite heavy cyclosporine­sterOId immunosuppresslOn.

A pig kidney and a pig heart trans­planted respectlvelv by KusS26 and Ross2-1 in the '60s were hyperacutely rejected in d matter of minutes, clearly demonstrat­ing that the pig was not and will not be dn easy donor tor a human recipient.

THE ANTIPROLIPE.R.ATIVE DRUGS 1

Sir Peter Medawar, in 1969, stated that: "A new solution IS therefore called for: the use at heterografts - that is to say, of grafts transplanted from lower animals into man. Of the use of heterografts I can say only thiS: that In the laboratory we dre achievmg greater success with grafts between species today than we achieved With gratts Wltrun l5 years ago. We shall sohl: the problem by usmg heterografts one dav 1t we try hard enough, and maybe

in less than l5 years". 27 However, the laboratory work performed at different institutions in the following 15-20 years did not bring particularly encouragmg results in further clinical trials. In May 1992 the results of a study performed in Pittsburgh by Dr. Noriko M~ase et al,28 were discussed at the meeting of the American Society of Transplant Surgeons in Chicago. Murase's work clearly showed, in a hamster-to-rat xenotrans­plant model, that when FKS06 treatment was combined with either of two "antiproliferatlve" drugs that" suppress purine iRS 614431 or pyrimidine (Brequmarl ribonucleotide synthesis for the first two post-transplant weeks, indefinite survival under continued FKS06 alone was routinely achievable, The use of cyclophosphamide, an alkylat­ing agent with conSiderable B cell specI­ficity,29,30 allowed simHar consistent chrornc survival after either heart or liver xcnotransplantauon. Parncularly signili.-

BLOOD GROUP AND DEMOGRAPHICAL DUA OF TIlE 1

flltST CASES OF IWIOON-'J'O.HUMAN LIVER XENOGJtUT

Tabl.t.

ABO IIIAIIOOI'Il

AIO PA11EII'I' DIAGNOSIS IP.4.l1IJI(O DATA

A 35y male Hcpalllis B

02y male flcpalllis B

PUYlOUS .... OOMlNJU. SURGERY

sple ..... omy

XENOGRAFr SURVlVJU. DAn (DAYS)

h/"1JJ/'12 70

1/10/93 26

cant was the fact that a single large dose of cyclophosphamide, given 10 days before the xenotransplant, allowed suc­cess ill almost 100% of the animals with daily admlnIstratIon of FKS06 only. When cyclophosphamide had been used in the past for kidney and intestinal transplants in the dog, there was no pro­longation of graft survival, or else the effect was a minor one.J1 .33 The dog may have been an mappropriate model to

evaluate cyclophosphamide for human immunosuppression.J1.33 How-ever, the successful use of this drug by Santos et a1.34,35 in bone marrow grafts, and by other authors in a few cases of clinical kidney transplantation,J6,37 prompted its use at the UniversIty of Colorado in a series of liver and kidney transplant patients, as the baseline for chronic ther­apy, in combination With prednisone and horse antilymphocyte globulin,J8,39 Later, a more extensive report was pub­lished agam by the Denver group.oW This previous clinical use of cyclophos­phamide as an effectlve drug 10 trans­plant patients appeared to lustify its use in clinical xenograft trials,28

Clinical Trial On rune 28, 1992, and on fanuary 10, 1993, two patients aged 35 and 62 years respectively, suffering from end stage liver disease related to hepatitis B virus (HBVI underwent a liver xenotransplanta­tion (Table 1). The chosen donor was the baboon Papio cynocephalus. Theoretical· ly, at least.3 arumal-human combinatIons

Figurw 2. BI~n liver XlltlClll'llllplentldlon

Case 2. ChoIqiognm performed on pcIIt-opennmt

day 18.1IIIougII1IIe indwelling bilia/Y c:adIeI8r pieced and exwiorized IllIIIe time at IIIe 1UIlJIIY. The arrow showslh. choledocftoj.junOSlOllly on • ",WI .... \'

bo_lloop. Th. bili.ry clllhlllltr pl.cld in Case 2 .IIOWIId f1IIIIine coIlec8oa DIllie bil. during 1M poli­

o .... coune.. (Nom: Marino IR. Tzakia AG. fung

JJ. Todo S. DoyI. HR. SIarzI TE: XenohpianID .. co: .... ieIIza elinica. In: II TrapianID Iii fegaID (Df 0" Amico. N Baai. Idsl pp. 26!12111. MIIIOII. Milaa. Italy, .mUsed ~ ... miuioa~

I •

possibly qualified for this xenouansplan­tatlOn attempt. The Rhesus monkey-to­human. the baboon-to-human. and the chimpanzee-to-human. The Rhesus mon­key had been used in 1963 by Reemtsma for an heterotopIc lollipop kidney trans­plant. The Rhesus kidneys were aggres­sively relected in a few days. 16 The use of the baboon at the University of Colorado allowed a dialysIs free survival of the ure­mic patient for up to 60 days, and only two of the 6 patients transplanted died from reiection. The chimpanzee was used at Tulane University agam by Dr. Reemtsma and one of his patients lived for mne months WIthout dialvsls, and succumbing only to an acute illness of undetermined etIOlogy (probably pneu­montal. Consequentlv, on the baSIS of the preVIOUS experience the chimpanzee could seem the best possible donor. I fowever, It IS an endangered species and 111 the LJ .5. onl y hetween 25 and 50 chim­panzees per ve:u would be avadable for ,til biomedical research, Including that In the Important frelds of hepatitis and AIDS' I :\Iso, It has been calculated that

only 70 chimpanzees could be available world wide as organ donors. 42 The use of chimpanzees would further Jeopardize this species without solving the organ shortage problem.

The baboon. thus, appeared to be the only possible donor choice, and the liver seemed to be the organ to use in the clin­ical trial, because its relative resistance to humoral rejectlOn. 4"49

The pharmacological cocktail used for the prevention and the control of relec­tion was made by "old" immunosuppres­sants (sterOids, cyclophosphamide and Prostoglandin E 1),1,2.29·35.38.40.44 . .10 and "new" immunosuppressants (FKS061.51

Donor Surveillance and Selection The baboons for the donor selection were provided by the Southwest Foundation for Research and Education (SFREI, San :\monio, Texas, who also proVided the haboons for the prevIOus Denver senes of haboon-to-human renal xenotransplanta­tlon.l~ All of the baboons involved m the donor selectIOn process were PaplO cyno­(cphalus, and were born In the U.S.A. at

General Surgery SURGICAL TECHNOLOGY INTERNATIONAL 11 141

SFRE.S2 Baboons have weakly expressed A, B, and AB blood types on all celis, and wtll rarely have type a blood group/53 but ABO incompatibility did not influence the outcome in previous human xenograft trials (1,18). Thus, ABO match m baboon-to-human xenotransplantation IS desirable but not mandatory. However, both of our patients had ABO compatible donors: A to A in Case 1, and B to B in Case 21Table 11.

The conventIOnal lymphocytotoxic cross match of the recipient sera to their Jonor lymphocytes was positive in both cases but negative after dithiothreltol treatment. During the selection process the baboons underwent a complete bio­chemical and infectious disease work-up. This work-up was performed at the Virus Reference Laboratory of SFRE and includ­e d screening for retroviruses I STLV, HTLV, SIV, SRV1, SRV2, SRVS, HIV1, HIV2, and foamy virus I, Herpes viruses ,SA8, HSV, BVirus, rCMV, hCMV, EBV, Jnd VZVI, and hepatitiS viruses IHBV, HAV, Jnd HCV), Marburg Virus, cncephalomyocarditis virus, lympho-

I V & Ofal Oral

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Figure 3. Clinical course atter baboon-to-human liver transplant Casa 1. SM. SolumedrolJE {methylprednisolona,; PGE_ prostaglandin E,; Bx. liver biopsy; AST. aspanate aminotnlnsferese: ALT. alanine eminotransfenlse; Alk Ph, alka­line phosphatase.lfrom: Starz! TE. fung J. Tzakis A. Todo S. Demetris AJ. Manno IR. Doyle H. Zeevi A. Wany V, Michaels M. Kusne S. Ruden WA. Trucco M: Baboon to human liver tnlnsplantallon. lancet 341(88311:6571. 1993. Used by 08nn1SSlon./

Figure 4. Clinical course atter baboon-Io-human liver transplant Case 2. SM, SolumedrolJE (methylprednisolone); PGE. prostaglandin E,; Bx. liver biopsy: AST. aspanate amlRotransferese: ALT, alanine aminotransferase: WBC. while blood cell count. tfrom: Stanl TE. Tzakis A. Fung JJ, Todo S, Marino IR. Demelns AJ: Human liver xenotnlnsplantallon. Xeno. 1ft press. Used by peml1s­sion.'

Liver XenotrllnspidDtDtion 142 MARINO, TZAKIS, rUNG, TODO, DOYLE, MANEZ, STARZL

chorIomeningitis ViruS, and hemorrhagic fever virus. The animals were also screened for tuberculosis and toxoplas­mosIs and blood and stool cultures were obtained.

Both Paplo cvnocephalus donors were healthy and found to be antibody poSitive for foamy ViruS, EBV, CMV, and Simian agent 8. In addition the donor to the first patient had VZV antlbodies. The donor/reclplent weights were 25.8170 Kg In Case 1 and 35.8/80.4 Kg in Case 2.~4,SS

Donor and Recipient Operations The donor operation for the liver harvest­ing from the two baboons was performed according to our donor standard tech­nique SA The donor and recipient opera­tions were performed in two different tlperatlng rooms, With the donor opera­tions starting sltghtiy after the reCipient llperatlOns to minimiZe the cold ische'mta time II J 7 minutes In Case l. Jnd 231 I11lnutes In Case 21. The haboon donor livers were prescrved with the Universltv ot WisconSin solution.

Both bahoon-to-human liver xeno­transplantatiOnS were performed uSing a piggyback technlque,.i7 ~lnd a venovenous bypass,.ix ~I mOllification of the standard techmque for orthotopIC liver transplan­tation described .10 years ago.·i~ SpeCifically due to the small size ot the donor livers 1(,(JOg ami 4S0g, respective Iv In C.lse j .1Ilt! l~.lse 21, and the Size dis­crepancy hetween the reCipient and the donor ycssds. the reCipient'S nght hepat· IL veins werc cltlsed With a runnIng ,uturc, .llld the d'll1lH upper cava was ,IIJastomosni cnd·(O·c:nd to an adequate dltt tJShllll1cd uSing the reCIpients l111d­dk and ktt i1ep'lllc veins. The donor cdl' .IL .IXIS was .1l1.1stoll1osed end·w·end to the reClpl!.:nt Cl)llllllOn hepatic artery 111

l=JSC j .• 1I1d el1l!·((1·'lJe on the supra cdl-

ac reCipient aorta in Case 2, by interposi­tion of a donor carotid graft. The donor portal vein was anastomosed on the stump of the reCipient left portal vein in Case I, while the size match allowed a direct porta-to-porta anastomosis in Case 2. The liver reperfused promptly and um­formly (Figure II in both cases. The post­reperluslOn biopsies showed a good liver architecture, With a moderate degree of sinusoidal neutrophilic aggregates. The biliary reconstruction, with a Roux-en- Y choledochoielunostomy in both cases. However, in Case 2 an indwelling biliary catheter was placed at the time of the operation and extenonzed. This catheter i Figure 2) allowed routine collection of the bile during the post-operative course of the second patient.

Postoperative Course The ImmunosuppressIOn was based on the use ot 4 drugs: cyclophosphamide, FKS06, methylprednisolone and PGE I. Doses and routes of administration are reported in Figure J and 4. Cyclophos­phamide was started 2 days before the xenotransplants, and was given for 56/70 days In Case I and 10126 days in Case 2, .It a dose ranging from 0.07 to 10.6 mg/kg/day. FKS06 was started the same day of the xenografts and, except for high· er doses given during the nrst '2 postoper­.1tlVe weeks 111 Case l, the doses were Within standard therapeutic r:Inges. Detailed descnptlOns of the immunosup­pressive drug doses and of their blood lev­els have been recently reported else­\\! here.·i~.'i:;'w

Some ot the dcmographlc charactens­(ICS ot the .2 patients are shown In Table l. l\oth patients had end-stage chroniC .H:tlVe hepatitis caused by hepatitis II virus IHBVI. The eYldcnce that the haboon liver would be resistant to the

HBVS4 that reinfects most al!ografts under comparable circumstance61 pro­moted the selection of these two candi­dates who had already been refused human liver transplantation at other Institutions. Some dIfferences between the two patients could have impacted on the efficacy of perioperative immune modulation. The second patient was nearly twice as old and far more frail than the first patient. Also, the second patient did not have a splenectomy, and the spleen was removed on day postoperative 4. The first patient underwent splenecto­my in 1989 after a motorcycle accident. Both patients were immunocompetent at the time of the xenograft, although the first also had an HIV infectionY Both patients were in stage 3 coma during the 24 hours preceding the surgery. The first patient woke promptly, was extubated Jfter 17 hours, and was eating and walk­in~ within S days. He had an almost nor­mal bilirubm for the malonty of the 70 days of sumval (Figure 31. He also spent almost 30 days 10 a regular ward. The second patlent, by contrast, remained lctenc IFigure 4), and comatose and was mechanically ventilated for the 26 days of survival. Both patients suffered from hypoalbuminemia and received frequent albumin mfusion. s4,ss The first patient went into renal failure on postoperative dav 21, whIle the second patient became ~Inuric immedi:ltely after sur~ery.

PaplO cynoccph:llus normally produce elevated kvels of factor VII and low Iev­t.:ls of factors IX and XI, as compared t humans. C0agulatlon pranles were dOlh In both rl:Clplents preoperatively and sev· eral tllnes postoperatlvelv. Our results, reported elsewhere,',2 demonstrated that (he baboon's coagulation pattern was .lcqulfed by the patient after liver xenografung. This fact, however, did not

Figure 5. Baboon-Io-human liver uanspllRt Case t. CT scan of Ihl abdomen periormed on posloperauV8 dlY 24. Thl CT-calcuilled liver volume was 1,555ce. The willie Insert shows Ihe onginll volume of Ihe baboon liver on Ihe "au fti .h. t",n~nj.nI16OOccl.

Figure 6. Baboon-to-humin liver transpllnt Case 2. CT scan of Ihe abdomen performed on posloper.llve dlY 14. The CT-celeulated livlr volume wll 1.741cc. The while inse" shows Ihl onginal volume of Ihl baboon liver on lite day of lIIe transplant 145Occl.

aitect the clottmg ability of the patients. Dunng their postoperative courses the

patients underwent several liver biopsies \6 in patient 1 and 8 in patient 2. includ­mg the autopsv specimens\. Only the bIOpsy obtamed from the first patIent on the 12th postoperative day had signs of mild focal cellular relection. while no eVIdence of cellular reiection was detect­t:d In anv ot the other biopSies from eIther patlent:'~:i5.6.3 No evidence of HEV remtectlon was detectable bv immunoperoxidase staining in the liver tissue at anv time In the two patients.

!loth baboon li vers underwent a dra­matlcal regeneration after the xenograft. with tnpling or quadrupling the organ volume withIn the first month. Figure 5 and 6 show the change In size ot the liv­as alter the xenografts. calculated by CT ,can. with the standard method routmely used in our liver panents.64

The rour drug ImmunosuppressIve cocktaIl IFK506. methylprednisolone. PGE I. and cvclophosphamidel prevented these twO liver xenografts from being destroved bv cellular as well as humoral releCtion. The role played by cyclophos­phamIde and other" antiproliferattve" drugs m the Murase's cxperiments lB

reported above. was largely conrl.rmed by thIS clinical tnal.

The «Iuse of death was diffuse sub­arachnOId hemorrhage and left uncal brain stem hermatlon. secondary to an)?)OInva­,lye aspergillosis ill Case 1, artd sepsIs trom penronltls III Case 2. DetaIls at the necrop­-Ies have been reponed elsewhere.5-+,·"

IMMUNOLOGIC AND

METABOLIC QUESTIONS

The liver. 111 the hamster-to-rat xcnogrJIt model, demonstrated a umque .lbtlltv til resIst n':lectlon more than '1ther ()rgans~S, .md was also found to be ,lll1e [0 ~dllcld other concomltantlv transrlan[ed organs trom relectIon."·' \Is(), IIH: liver can resIst the attack 01

:'retormed xeno;lnubodles.'" The devat­c·d l111101l11t ot dendritic cells and other ""lie thSUe icukocvtes ;lllie to leave . c tL111splJnted organ and tnduce svs­

'lIC llllcrochllTIenSm makcs the ltver 'l1unOllH.!ICldlv rrtvdcgcd. The rro-

,iLtI011 (}[ thIS ceil chlmensm IS. tn tJct. . :le hJ'IS "I lIr"Jn trJnsplant accq1tance lild tll!crancc ,r, Cr.:ll chImerIsm was ;'rOVl'1l III (ile Tlrst r;ltlent. where h.lbolln ll:"-J t\ was (Ound 111 manv organs .it necropsv, lllciud111g the heart. lung, kidney .111\1 j vmrh l1odes. AugmentatlOn ,1 thIS ceil J111~r:ltlOn WilS Jrrempted tn

: l1e ,n:llllll patient iw mtuslUn 01 the ,jlJnor h,lhOO!l none marrow ceils ;lIter ::1C rL'f'ertUSIO!l or rhe lIver .. ,\li the

blood samples collected for this purpose during his postoperative course demon­strated clearly evidence ot cell crumensm by PCR.

A baboon It ver transplanted in a human being contmues to synthesize pro­tein with the donor phenotype_ This con­cept IS the basis for liver allotransplanta­tion in many human congenital metabolic diseases. 67,68 Thus. a baboon-to-human liver xenograft creates in the recipient a baboon-specIfic hepatic metabolism. This fact was already demonstrated in the ham­ster-to-rat combinatlon. two rodents philogenetically far diiferent for 15-40 mil­lion years.69 The study of clotung factors in these two arumals showed sigruficant differences. and when a rat received a hamster liver its coagulation profile became identical to the donor pattern. 70

However, the recipIent rat does not suffer from any coagulative diathesis.

Similar changes happened in the human xenogratts with changes in the metabolIsm of hepatic based clotting fac­tors, albumm, several globulins, uric '!CId, and cholesterop4.S5 The sUlVlval of the two patients was too short to accu­rately state whether or not these events could be the source of a long term meta­bolic baboon/human incompatibility_

The other open question IS related to the complement role in these clinical xenotransplants. It has been shown that total complement was significantly depleted in the first 10 postoperative days while C3, C.+ and C5 were undetectable In the first 1.+ Javs:)~,55 }\lso, dunng the tirst postoperative H davs CirculatIng anti­,.;en-antlbodv complexes were present. .-Vter this lUlUal phase the total comple­ment returned to almost a normal con­centration. The Important role ot com­pkment JctlvatlOn with neutrophIl par­tICipation was emphaSIzed 25 vears ago hv revealing the analogy 01 hvperacute kIdnev relection with the Shwartzman ,md Arthur reactions. ~I. 72

Expenments ,limed to block the path­l'.L:emCltv de[!ved bv the cleavage or C3 ;mc..l CS are bemg currentlv conducted In the laboratorIes Ilt the Pittsburgh fr:msplantauon institute.

CONCLUSION

: t IS OhVIOllS that a prolect ot thIS nature r.l1ses problt:ms that kave the medll:al ,irea and dtrectlv mvolve ethIcal Issues. l'ew ethIcal movements belteve that such ,i prolect IS unethIcal. -.l We do not thmk that thIS IS the n01t place 1m opemng a ,kbate hetween advocates lit mterspeCles L''-!ualHv, J moJern ialrusm .. ~ beilevers 01

InterspeCles lI1equailtv. lInd speClelsrs. '; However. we appreciate and share the

General Surgery 143 SURGICAL TECHNOLOGY INTERNATIONAL n

feelings of Stephen Post 73 who stated that the Pittsburgh prolect "has success­fully reminded us that the human good remains appropnately the highest good, despite the cultural inroads of anthropo­morphism_" • STI

L Sta.rzl TE: Experience In Renal Transplantation WB Saunders Company, Philadelphia. PA. 1964. 2. Stanl TE Iwtth the assIstance CW. Putnaml: Expenence in Hepatic Tr:mspJantatlon WB Saunders Company, Philadelphia, PA, 1969. Ol Terasaki PI and Cecka 1M: Clinical TransllJants 1992. UCLA Tissue Tvpmg Laboratory, The Rellents of the Uruverslty at Califorrua, Los Angeles. California. 1993. 4. Marino lR, Doyle H. Kormos RL. Kang Y, Sta.rzl TE: Multior~ procurement, In: Textbook of Critical Care, Ayres SM, GrenVlk A, Hoo1brook PR, and Shoemaker WC I Eds. I. 3rd Edition, WB Saunders, Philadelphia, 1994. S. Land W, Hammer C. Brvnger H tedsl_ indication for organ transplantatlon. Tr:msplant Proc 18tSuppi l :141: 1102, 1986. M. Memken Kl, Overcast ID: Patient selectlon lor hean transplantatlon: when IS a discnmmatorv chOIce dtscnmmatloni I Health Polit Policy Law 10111:732,1985. 7. Stanl TE, Todo S, Gordon R, Makowka L, T;::ak.is A, Iwatsuki S, Marsh W, Esqwvel C. Van Thiel 0: Liver tr:msplantatlon m older patients. ILetter to the Editor! New Eng! J Med316: 4!l44K5, 1987. H. Auchincloss H: The SCIentific study of xenograttmg: 19641988.ln: Xenotransplantauon The Transplantatlon at Or);ans and Tissues Between Speclcs Cooper DKC Kemp E. Reemtsma K, White DIG ledsl, pp . .1.343. Sp~erYerlag, Ik rlin, I 9'1 1. ,) Homer: Ihad, Book Xl:832, vm Cenrurv B.C. 10. Homer: liiad, Book V1:l7S, VIII Century B.C. 1 I. Caine R Y: Organ transplamatlon between wldelv dIsparate speCies, Transplant Proc 2,-+1:550556. 1'170. I~. lahoulav M: t;re!le de rems au pl! du coude par 'C)udures anenelles et velneuses. Lvon Med 107:575. 1~()6.

1.1. Unger E: !'·l!crentransplant3tlonen. KIin Wschr HS73.1'iIO 1-1. Neuhol H: The Transpiantatlon ot Tissues. Appleton and Co. New York. 1923. p. 160. 1.1 Hitchcock CR. Kiser Ie. T cl:mder RL, Seheskog FL: Baboon renal KJ':ttts. lAMA IS~1121: ;;8161. lYM In Rcemtsma K, McCrJcken BH, Shlegei ru. Pearl .\tA, Pearce CW, DeWitt CW, Smith PE. Hewltt IZL, Flinner Rl. Creech 0: Renal heterotransplan­t.mon In man. Ann Surg lNJ:.384. 1964 . I' Hume OM: DtsCUSSlUn ot paper at Reemt5ma c·t al.: Ann ;,urg loO:.lH4. 1 'JA4. ! ,. Starzl fE . .\t.lfchlOfO rL. Peters GN, Ktrkpatnck CII. Wilson WEe. I\mer KA. Rt.Jlund !, O,den llA. HitchCOCK L:R, Waddell WR: Renal :H:terotf30splantatwn trom h.lhoon to man: [xpencnet: with 0 dsCS. fr.lnsplantatlon l:

I ~ Hardv It). Ch.1yeZ C.\t Kunus I'D, Neeley WA. Lr.15Im". Turner MD. F.Jblan LW. Labeclu rn ! leart transplantJtlon tn man. lAMA I 'H: ll.llll·m I YM

20. Cuoicv D. H.lil"mn GL. llloodwell RD N,'ra II. :.C~dunilll RD. Humilll n~an transplantation: ,'xpenencc WHn 12 CJScs. Am I C.lIdtol .'l;61:W4H1O I"M.

Liver XeuotrlUUplaJItDtioD 144 MARINO, TZAXIS, FUNG, TODO, DOYU, MANEZ, STARZL

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