INST, FOR CELLFORSKNING OCH GENETIK
MEDICINSKA NOBELINSTITUTET
KAROLINSKA INSTITUTET .

STOCKHOLM 60 Lu
Telefon 23 54 80
INST. FOR CELL RESEARCH AND GENETICS

KAROLINSKA INSTITUTET
STOCKHOLM 60 Mars 7, 1957

Professor Joshua Lederberg
Devartment of Genetics
University of Wisconsin
Madison 5, Wisconsin
U.S.A.

Dear Josh:

It has been a long time since I wrote you
last. This does not meen however that I have forgotten the
most atimulating and useful discugsions I had with you
two years azo. In fact we have carried along the lines
we discussed quite a great deal. This type of work is al-
ways very slow since you have to produce the necessary
genotyoes and tumors. We have performed the roiel exveri-
ments we have been talking about and they turned out very

hoveful indeed, more so than we should have thousht. I
enclose a photocopy of a recent vaper in Nature. Since
this paver was written we have obtained what seems to
be matations in an y-2°y-25 tumor to the genotype H-28
H-2%, This is sugvested by transplantation tests (the chan-
ged tumor would take in H-25y-2° put not in 4-2H-2?
or any other senotype) and also by a great deal of se-
rological evidence (the unchanged tumor provokes anti-
H-2% antibodies in foreing genotypes while the changed
tumor does not). The amazing thing is that we have ob-
tained this type of change five times but so far failed
to obtain any change to the other homozygous type H-29
H-2°, We have optained the change to H-2°H-2° in one
particular tumor only but not in three other similer
tumors that were studied in a similar way. I am now try-
ing to write this uv for publicetion.

Phere is another cuestion that I am eager
to write you about. The International Congress of Micro-
biology will be hela in Stockholm in 1958, as you pro-
bably know. I have been asked by the local orgzanizinz
Yrofessor «,lLederberg -2- Mars 7, 1957

Madison 4, Wisconsin

committee to heln them to arrange the sessions on trans-
formation, transduction and recombination. I have accen-
ted this under the condition that I may ask an expert

in this field to give us recomrendations as to how these
session should be organized best and whet veopvle should
be invited. Would you be willing to help us in this mat-
ter? Of course we should be most enxious to make it sure
that you would come yourself, The congress will protably
have funds at its disposal to invite a few outstanding
people and cover their expenses, They will not be able
to do this for everybody, of course, and the majority

of the participants in any one session will have to be
chosen necessarily from the spontaneous applications for
membership which are expected to arrive here in about
two months. We should be very anxious, nowever, to in-
vite you in particular and perhaps also a few other people
whose participation would be of great irportance and who
can be expected to have difficulties to obtain travel
funds at home. Please let me know how you would feel about
this, and'whether you would bé willing to advise us in.
this matter. At the vresent stage this 1s all very ex-
ploratory.

Eva and I were over in the United States
last Fall but we had unfortunately no change to come to
Wisconsin. I shall be at a meeting in Rhode Island in
dune but again I am not sure whether I can go towards West,
At any rate we hope very much to see you here in 1958
if we do not meet before,

With warmest regards,

Sincerely yours,

George Klein