Le caractère distinctif de l’allogreffe

Pendant longtemps la distinction n’était cependant pas faite entre auto, allo et xénogreffe, et elle ne paraissait même pas essentielle dans l’explication des échecs et des réussites. “For a long time the great variation in the outcomes of organ transplants was explained mainly by factors that did not take into consideration the difference between allogenic and autogenous transplantation”¹⁴⁶. Georg Schöne, en 1912, note éberlué que de nombreux auteurs décrivent dans le même article des auto et allogreffes mais ne tiennent pas compte de la différence entre les deux procédures dans l’analyse de

de la pensée médicale, D. Lecourt ed., Paris, PUF, 2004, pp. 851-3 ; et François Dagognet, La Peau. Découverte, Paris,

Les Empêcheurs de penser en rond, 1993.

144 Thomas Schlich, The Origins of Organ Transplantation, op.cit., p. 189. 145 Ibid., p. 187.

65 leurs résultats147. Christiani, en 1906, infère de ses autogreffes de thyroïde réussies la possibilité de la réussite de toutes les greffes148.

Il devint pourtant essentiel de distinguer, au vu de leurs résultas extrêmement différents, entre les greffes où le greffon provenait du donneur lui-même, d’un donneur autre de la même espèce, ou d’un donneur d’une espèce différente. Ullmann exprime cette distinction essentielle avec la plus grande netteté en 1914 :

Should the removed portion of tissue be replanted into the body from which it was taken, regardless of whether it is replaced on the same site or in a more remote location, it is called autoplastic transplantation. If the tissue is planted into an individual of a like species, it is termed homoplastic transplantation; if into one of another species, heteroplastic transplantation has been performed149.

L’article conclut à la différence radicale entre les procédures d’auto et d’allogreffe :

In homoplasty inherent biochemical characteristics interfere with healing. On this ground only can be explained the unsuccessful results of these types of transplantation as compared to the more favourable and more permanent results in autotransplantation150.

Cependant la différence est plus exprimée comme une différence quantitative (« the more favourable and more permanent results in autotransplantation ») plutôt que de nature. De plus le mécanisme réel du rejet n’est pas encore exactement identifié, puisque les « caractéristiques biochimiques » de chaque individu sont dites seulement « interférer avec la cicatrisation » ; néanmoins la différence entre auto et allogreffe est nettement perçue, au point qu’elle justifie l’établissement d’une typologie et de noms précis dévolus à chaque type d’opération. Il en va de même chez Carrel.

If the transplanted segment is from the same animal, or from another animal of the same kind, or from a different kind of animal, the transplantations are autoplastic, homoplastic or heteroplastic respectively151.

Dans la présentation de ses résultats de greffes expérimentales de rein également il distingue nettement entre les autogreffes et les homogreffes.

147 Ibid., p. 187. 148 Id.

149Emerich Ullmann, “Tissue and Organ Transplantation”, art.cit., p. 195. 150 Ibid., p. 218.

151 Alexis Carrel, “Suture of Blood-Vessels and Transplantation of Organs”, conférence de réception du prix Nobel,

66 Lexer est tout aussi net dans son article de 1914, “Free Transplantation” : “It is common knowledge that the best results are obtained by means of autoplasty, in which method the transplanted tissue is grafted into the body from which it has been obtained”¹⁵². Les résultats de l’homoplastie, par contraste, sont décevants.

In homoplasty, i. e., the transplantation of tissues from one animal to another of a like species, success has been achieved only when the transplanted tissue was homologous to the mother tissues in the following types of tissues, connective tissue, fat, bone, etc.; never with nerves, muscle and organs, in which instance rapid degeneration and cicatrisation occur. […] This is probably due to the irritation of a foreign proteid153.

Mais cette distinction, désormais renommée comme la différence entre auto et homotransplantation, doit encore être rappelée même en 1953 par Simonsen dans le compte-rendu de ses expériences chez l’animal, même si ce sera désormais comme un résultat établi au fil du temps.

The spontaneous course of a homotransplantation was compared at first with the course of an autotransplantation. As in all previous studies it appeared that these two forms of renal transplantation showed great functional and morphological differences within a few days of operation.154

L’homoplastie, c’est-à-dire l’allogreffe, paraît donc à Lexer une procédure qui ne peut être prometteuse à court terme :

I am compelled to say that homoplasty does not yield good results155. […] I regard the usefulness of homoplasty in extreme doubt156. […] Borst and Enderlen have established the fact that only those organs are preserved which have been removed from an animal and replanted into the same animal shortly after. Our knowledge of to-day emphasizes the difficulties of homoplasty in general […] The clinician will be wise not to count upon prematurely awakened hopes for some time to come157.

L’idée de rejet est de plus en plus acceptée, il restera à la défendre contre ses détracteurs qui se maintiennent étonnamment longtemps. Billingham, en 1963, soulignera combien l’idée de rejet mit de temps à être acceptée :

152 Erich Lexer, “Free transplantation”, art. cit., p. 167. 153 Ibid., p. 168.

154 M. Simonsen, J. Buemann, al., “Biological Incompatibility in Kidney Transplantation in Dogs I. Experimental and Morphological Investigations”, Acta Pathologica et Microbiologica Scandinaivia 32, 1, 1953, pp.1-35, ici p.3.

155 Id., p. 172. 156 Id., p. 174. 157 Id., p. 194.

67

Apparently, in these early days of free skin grafting [à la fin du 19ème siècle], even in the case of autografts, no one really knew, or probably cared, whether the grafted tissue grew or not so long as complete epithelialization took place. Some authors, including Reverdin himself, actually believed that the grafts simply promoted a sort of epithelial "transformation" on the part of the granulation tissue. No one resorted to histology to settle the matter on account of a reluctance to compromise the fruits of their labors by removal of biopsy specimens. Although we now know that none of these heterografts could possibly have survived for more than a day or two at most, the possibility cannot be entirely discounted that, in some way or another, they did sometimes facilitate epithelialization. Rather surprisingly, as recently as 1957, the possible benefits of bovine embryonic skin as a temporary form of biologic dressing still attracted the attention of some investigators.

The early pioneers of human skin transplantation made no distinction between the behavior of grafts of a patient's own skin (i.e., autografts) and those derived from the bodies of other individuals (i.e., which we call homografts). George Lawson, of London, undoubtedly voiced the naive opinion of his times when he predicted in 1870 that " the time will come when we shall beg portions of skin from a parent or friend who is willing to give of his abundance for the relief of a suffering child or of a neighbor". Little did he realize that in addition to public spirited generosity, fulfillment of this prediction requires the solution of a formidable biological obstacle which is still the central problem of transplantation research.

Following the popularization of plastic surgery, about 70 years were required before the widespread belief that skin from one individual would form a permanent graft on the body of another received its long overdue burial. This tenacious adherence to a fallacy occurred in the face of compelling evidence and declarations to the contrary by some of the early investigators such as Erich Lexer and Georg Schöne.

In an autobiography of 1930, Sir Winston Churchill narrates how, in 1899, he donated a skin graft to a brother officer, wounded in battle against the Dervishes in Egypt. After describing his sensations as the doctor's razor sawed slowly to and fro, Churchill says, "I managed to hold out until he had cut a beautiful piece of skin with a thin layer of flesh attached to it. This precious fragment was then grafted onto my friend's wound." Always an optimist, the Statesman added, "It remains there to this day and did him lasting good in many ways".158