Searchlight Vol. 3, no. 1

Gene Insertion Treatment
Continued from page 8...
peripheral blood CD4s or monocytes, as seems
to be the current fashion, and surely not modified
tumor cell lines, the de facto gold standard of
current experimental research into HIV
therapeutics.
Using Gene Therapy
It is possible to stop HIV at any point in its life
cycle by withholding the gene it uses during that
portion of the cycle. (Not all of the virus genes
are used during various stages of the viral life
cycle. For example, during infection one does
not need a functioning TAT gene, while reverse
transcriptase is not used during the production
of new virus or viral budding.) Consequently,
by removing the TAT gene, which the virus needs
to go into active virus production, the HIV
genome can be manipulated to produce virus
which can infect only one time.
Once this gene-manipulated virus has been created it is necessary to produce it in quantity so as
to promote its use in gene therapy. How would
one produce such a virus construct in any quantity, given the fact that while it can bind, enter,
transform and integrate into a host genome, without the TAT gene it is unable to "turn on" or
amplify itself to produce more virus? One possible answer lies in reintroducing TAT to the cell
culture system, thereby complementing the defective gene product. This new virus construct is
then able to produce more virus particles which
can infect only once.
A rather unique thing about HIV is that a cell can
be infected multiple times by various strains of
HIV. Therefore, it is possible for the HIV construct to infect a cell that is already infected with
a naturally occurring or "wild type" HIV. (A
wild type virus is any virus found in nature which
is causing the disease under study. For example,
there is a wild type polio virus and there is the

attenuated strain of polio which is syntheticone causes the natural disease, the other generally doesn't.) If such a construct were given to a
person with HIV, the wild HIV would complement
the defect in the viral construct (because of the
presence of TAT), allowing it to replicate. That
is, this construct would function like wild type
HIV as long as the patient was already HIV infected; in the absence of an HIV infection, it would
be dormant.
The Role of TK and Acyclovir
Thymidine kinase (TK)-a gene from the herpes
virus-is not normally found in HIV and can act
as a bomb, if you will, when genetically placed in
the construct. When TK is cloned into the HIV
construct, the construct will produce the TK
enzyme any time the cell tries to produce HIV.
Why is this of value? The drug acyclovir
(Zovirax) kills cells which are producing TK; if
HIV can be altered to produce this substance, all
cells which go into active HIV replication will
become susceptible to killing by acyclovir-just
as if they were herpes. Acyclovir is totally inert
until a cell decides to start producing herpes: the
herpes gene product TK activates acyclovir, converting it to acyclovir triphosphate, which kills
the cell trying to produce herpes virus.
If a cell should be molecularly immunized (that
is, have a copy of the defective HIV TAT-minusand-TK-positive construct integrated into it), and
the patient takes acyclovir, nothing will happen
because the construct can't replicate or produce
TK since it is defective in TAT and can't produce
any of its gene products. However, should the
cell have wild HIV actively producing TAT, the
cell will also be producing TK and in the presence of acyclovir it will be killed prior to the
release of any virus. Additionally, as the delivery
system of this gene product is an HIV virus itself,
this gene product will have a limited number of
cells which it can infect, as HIV itself only infects
CD4-bearing tissue. Therefore, this construct will
only infect those tissues and not every cell in the

body. In sum, the construct is essentially a gene
delivery system. It can selectively deliver dormant genes to certain cells and is activated under
very specific conditions, such as when the patient
is taking acyclovir.
Controlling the Experiment
If too many cells start to die as a result of the acyclovir therapy, the acyclovir can be withdrawn
and the killing will stop. The construct will then
infect other cells once. This HIV construct is a
programmed cell killer which destroys prior to
the release of more virion when both HIV and
acyclovir are present-otherwise, it has no
effect. One would expect this to rid the body of
all those cells actively producing virus, and to
ignore cells not producing virus-with the possible exception of cells still infected but in a dormant state. Should these dormant wild type
infected cells ever spring to life, they would be
killed as long as the patient is taking acyclovir.
Another Gene Insertion Option
Finally, if this construct should work, the TKdependent, acyclovir-dependent killer of cells
could be exchanged with another gene which
would kill without the need for acyclovir. This
might be a pseudomonal toxin gene or some
other gene product which will kill the cell in
which it is expressed. The TK gene requires not
only that it be expressed but also that acyclovir be
around for TK to convert to a poison; the pseudomonal toxin gene requires only that it be
expressed, and nothing more. This would reduce
the cost of treatment to a one-time immunization-a molecular immunization.
This gene insertion theory represents one possible solution to the HIV problem. While it is being
worked on by Dr. Zaki Salahuddin and associates, it is not yet available in a usable form.
Thomasj. Magee, M.D. practices HIV medicine
in Los Angeles and is a participating physician
at SEARCHAlliance.

SEARCH Alliance Extends Grateful Thanks to
our Dedicated and Hardworking Volunteers:
Richard Bloch April Klein Joel Pizzo
Denis Chicola Carol Kravetz Claire Putnam
Wanda Clark Nicole Kurland Carole Sharkey
Gilbert Cornilliet Deane Lind Bob Stoltzfus
Duane Doggett Margaret Malone Tim Trueman
Michael Emery Simon Meara Joseph Von Teichert
Sloan Fischer Michael O'Keefe Michael Werner
Aileen Getty Carre Otis Antoine Wilson

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