174 MICHAEL FELDMAN AND DAVID YAFFE 



(2) Loss of histocompatibility genes, and subsequently of anti- 

 gens. Tumours of this property will not elicit an immune res- 

 ponse, and will not be susceptible to an immune response pro- 

 duced by other tissue homografts of the same isoantigenic origin 

 (Hauschka et ah, 1956; Amos, 1956). 



(3) Suppressed production of the strain-specific isoantigens. 

 Tumours of this property will not elicit an immune response, but 

 will remain susceptible to a homograft reaction produced by other 

 tissue homografts of the same isoantigenic origin. 



Experiments were therefore designed to test the homotrans- 

 plantabihty of the SBLx sublines in relation to each of the three 

 postulated mechanisms. In one representative experiment, the 

 following groups were set up: 



(i) C3H mice were challenged with two simultaneous intra- 

 muscular grafts of SBLx, one in each leg. 



(2) C3H mice were challenged with two simultaneous grafts, 

 one leg receiving the strain-specific SBLi, the other the SBLx. 



(3) C3H mice were challenged with two simultaneous grafts, 

 one leg receiving normal C57BL spleen cells, the other the SBLx. 



Table IV 



Susceptibility of SBLx to the homograft reaction produced by a simul- 

 taneous TRANSPLANT OF SBLl OR C57BL SPLEEN CELLS, IN C3H MICE 



Expt. Inoculated Tumour 



group leg Graft growth 



^ /Right SBLx 5/5 



^ I Left SBLx 5/5 



r Right SBLi 0/5 



^ iLeft SBLx 0/5 



Right C57BL 



spleen — 



Left SBLx 0/5 



The results (Table IV) show that the SBLx is susceptible to a 

 homograft reaction produced by tissue grafts of its strain of 

 origin (C57BL). Regression of the SBLx took place when the 

 tumour was grafted simultaneously, either with the strain-specific 



