no DISCUSSION 



Strain, as superficially as possible into the mesenchymal tissue of these 

 grafts. In some of the subjects this did result in prompt graft rejection, 

 but not in all of them. However, if instead of injecting the marrow 

 cell suspensions into the cheek pouch homografts they were injected 

 intradermally on the opposite side of the body, the pouch skin grafts 

 were promptly and consistently rejected. This suggests that the mar- 

 row cells do not invariably escape from their prison in the connective 

 tissue of the heterotopic pouch skin grafts. 



Medawar: It is possible that the buffy-coat leucocytes are slightly 

 damaged somehow or other in the course of preparation, and this may 

 make them sensitive through the intravenous route. Did you try whole 

 blood? 



Billingham: Yes. Fresh heparinized whole blood is highly effective. 

 However, this finding left us with the question — wxre the red cells 

 responsible for the graft rejections? That is why we used the purified 

 buffy-coat leucocyte suspensions. 



Brent: If you remove the epithelium of the cheek pouch by tryp- 

 sinization and graft it to the chest of the hamster, what happens? 



Billmgham : We have tried repeatedly to separate the epithelium from 

 the cheek pouch skin by the standard trypsin method, but it is not a 

 favourable tissue for this procedure, and we have been unable to obtain 

 suitable sheets ot pouch epidermis for grafting experiments. 



Brent: You said that you destroyed long-established skin grafts by in- 

 jecting antigenic matter by other routes. But have you destroyed them 

 by injecting presensitized cells, i.e. cells sensitized against the graft? 



Billingham: No, we haven't tried that. 



Brent: It seems to me that this would be well worth trying. Quite 

 apart from the interest that the result would carry in its own right, this 

 would provide a fascinating opportunity to study Batchelor's and 

 Gorer's phenomenon of the synergistic action of circulating serum 

 antibody and cell-bound antibody attached to sensitized leucocytes. 

 One could do beautiful quantitative experiments in this system, in 

 which you have unresponsiveness without getting the host all cluttered 

 up with donor cells. 



Billingham: This is a very good suggestion. So far we have con- 

 centrated on documenting this phenomenon because we were doubtful 

 whether anyone would believe it unless we could repeat it with three 



