l86 MORTEN SIMONSEN 



they have good reasons to believe was largely isogenic with the 

 host, except for a single locus of a strong transplantation antigen, 

 produced as many foci on the CAM as did similar cell suspensions 

 from entirely unrelated donors. On their own hypothesis, the 

 prediction would surely have been that the former donor, 

 having only one clone of its immunologically competent cell 

 population stimulated, would form fewer foci on the membrane 

 than would the latter, which had many different clones being 

 stimulated. 



The present experiments, of which a preliminary account has 

 been given by Simonsen (1962), were dehberately designed 

 to challenge the hypothesis of clonal selection on a cellular 

 basis. 



The challenge consists in testing if specific immunization of the 

 prospective donor for a subsequent GVH reaction does in fact 

 lead to higher immunological competence per unit number of 

 grafted spleen cells, as compared with normal donors. If this is 

 actually found, it will only support the notion, which clonal 

 selection shares with other theories of immunity, that antigenic 

 stimulation leads to proliferation of antibody-forming cells, or 

 their precursors. It would, however, have no bearing on the 

 fundamental postulate in Burnet's theory, i.e. that the entire 

 population of immunologically competent cells can be sub- 

 divided into clones with different predetermined affinities to 

 different antigens. 



If, on the other hand, it turns out that preimmunization of the 

 grafted donor cell population makes it no more active than the 

 non-preimmunized normal population, it would speak very 

 strongly against the validity of clonal selection on a cellular 

 basis. It would suggest that any immunologically competent 

 member of the grafted normal cell population has in fact affinity to 

 the antigen, provided it gets maximally stimulated, as it 

 supposedly does by being grafted to a host containing the foreign 

 antigen. Any prohferation which might have occurred during 



