[Letter to Jonas Salk from Jon Cohen]

July 20, 1990

4Ui1fto; yP'' C 4.

Dear Dr. Salk,
When we met, and in my note earlier this week,
I forgot to ask a question that riddles me: Do
you plan to add gpl20 to a vaccine for seronegatives? A 1 March 1989 paper you "wrote"
(it recaps an NIH conference) in the Annals
of Internal Medicine implies that you do
not intend to add gpl20 to a seronegative
vaccine. Indeed, the paper concludes, "The
absence of gpl20 from the immunogen makes
it possible under field conditions to monitor
vaccinated persons from time to time for
protection against natural infection."
Assuming that you do not intend to add gpl20,
will a seronegative vaccine be identical to
the seropositive immunogen? If so, I presume
the rationale (and I do this most cautiously)
is that HIV presents cell-associated, requiring
a CMI response. Further, removing the gpl20
may prevent antibody-dependent enhancement.
Is there specific evidence that HIV always
presents cell-associated? And if enhancement
is the concern, why not add a subunit loop?
What's more, is there evidence of in vivo
enhancement from gp-120 antibodies?
If my assumptions are way off base, I apologize
in advance; they are the only way I can ask
these questions in writing.
I look forward to hearing from you.
Sincerely,
'Jon Cohen 3445 17th St. NW, WDC 20010, [phone]