NEOPLASTIC ABNORMAL GROWTH 2^7 



a graft containing a dominant allele which it itself does not have. The 

 reverse, however, is not true, and dominant alleles in the host are with- 

 out effect upon the acceptability of the graft. It is probable that these 

 dominant genes are concerned with antigen formation. Lacking a gene 

 competent to form an antigen, the foreign cell has no power to evoke 

 an antibody response and so to subject itself to destruction. If the 

 foreign cell or graft contains or can form antigens not shared by the 

 host, antibodies are induced which react with the graft antigens so that 

 the graft is cast off or resorbed. The publication of Medawar should 

 be consulted on this topic (78). 



Ample evidence exists from the extensive work of the Little group 

 (79) that the ability of tumor cells to survive in the host is dependent 

 on both their constitution and that of the host. A tumor cell graft obeys, 

 in part, the rules which apply to a graft of normal tissue. If the tumor 

 carries one or more dominant genes which produce antigens and the 

 host has no, or inactive, alleles of these genes, the tumor graft induces 

 antibody formation against itself. Regression can result under these 

 circumstances. It is known, moreover, that transplantable tumors may 

 mutate so that fewer dominant genes are required in the host for suc- 

 cessful transplantation. This is, of course, the same thing as saying 

 that there are fewer dominant genes in the transplant capable of setting 

 up antibody formation. Some mouse tumors, for example sarcoma 180, 

 are almost without strain specificity, and further immunologic study 

 of this strain is desirable. Other mouse neoplasms are exceedingly sensi- 

 tive to genetic differences, particularly certain strains of mouse leu- 

 kemia (Furth (80)). MacDo well's (81) consideration of the immuno- 

 logic asp€cts of this disease has been particularly detailed. He advances 

 evidence that as soon as a leukemic cell is transplanted it becomes anti- 

 genically altered. Homozygous animals can be rendered immune to 

 leukemia of their own line, but this does not serve to prevent the devel- 

 opment of the spontaneous disease in the same animals. This concept, 

 however, does not take into consideration the possibility that when the 

 spontaneous disorder occurs the host may be altered in some way so 

 as to be no longer capable of immune response. 



It is interesting to consider a correlation between decreasing numbers 

 of dominant genes and increased transplantability. It almost seems as 

 if the cell which has the least number of distinguishing characteristics 

 is the cell which is the most virulent, most capable of surviving under 

 circumstances set up by the body as adverse ones, and, perhaps the most 

 malignant. This is consistent with the thesis that the neoplastic cell is 



