November 30, 1960

Dr. George Klein

Department of Tumor Blology
Karolinska Institutet
Stockholm 60, Sweden

Dear George:

Your report on the virus susceptibility of the polyoma tumor is quite
a startling result. | wonder If It does not reopen a question | think we
have discussed before, namely, that the virus (IIke methylcholanthrene!)
may act not primarily on the somatic cells which engender the tumor but on
the host to allow the expression of spontaneous mutants. [| had the impression
until now that there was good evidence that the virus was concentrated in the
actual tumors and thls | take [t, Is no longer tenable.

Yours sincerely,

Joshua Lederberg
Professor of Genetics