Major Antiviral Conference Surveys AIDS Research

The First National Conference on Human Retroviruses and
Related Infections was held in Washington, D.C., from
December 12 through 16. The first of an annual series of
meetings, it was a low-key alternative to the huge
International Conference on AIDS, with only 1500 people
attending and 750 papers and posters presented -- compared to
at least 10,000 people and about 5,000 presentations at each
international AIDS conference. The "state of the art"
lectures and roundtable discussions gave an extensive
overview of the latest AIDS research. Other sessions reported
data, much of it preliminary, from scientific studies. The
overviews and discussions were necessary, since much of the
information was conflicting, and the researchers themselves
had a hard time sorting out the implications.

"We don't have the basic paradigm yet, the E=mc(2) of AIDS,"
commented Conference chair Robert Schooley, M.D., of the
University of Colorado.

A New Class of AIDS Drugs

The most interesting drug reports at the Conference concerned
protease inhibitors. After four years of slow progress, data
is finally coming out of the first human trials. About a
dozen companies are now developing this new class of drugs,
which block a viral enzyme (protease) that controls an
essential step in the assembly of new HIV particles within
infected cells. This step does not closely resemble any
normal cell process, so the drugs' disruption of normal cell
operation should be negligible.

Conference reports also indicated that drug resistance is
more difficult to develop and that drug resistant mutations
usually, but not always, impair the efficiency of the HIV
protease (abstracts #265-267 and #418) -- meaning that the
resistant virus is not likely to work as well. In addition,
there does not appear to be any cross-resistance: Each
protease inhibitor requires a different resistance mutation.
According to Martin Bryant of G.D. Searle & Co., it may be
possible to use several protease inhibitors in combination,
thus hitting several sites at once on the protease enzyme.

Bryant said that Hoffmann-La Roche Inc. is "right at the cusp
of the dose response curve." He expects that higher doses
will show major benefits. Unfortunately, though, the Roche
product is not readily absorbed in the digestive track and
has to be infused into a vein.

Merck, G.D. Searle and other companies have created compounds
with high availability when taken by mouth, and Dr. Martin
claims that one of the Searle products is relatively simple
to manufacture -- difficult synthesis has been another
stumbling block for protease inhibitors (abstract #262).
Merck and Searle plan to enter phase II human testing later
this year with their most advanced products.

Merck generated considerable attention at the conference with
a report on the initial human testing of its protease
inhibitor L-735,524 (abstract #L8). Eight volunteers on this
compound showed major drops in their blood HIV levels after
12 days. The decreases observed so far were similar to what
is seen when people first start taking AZT.

Other Promising Anti-HIV Medications

Merck unveiled a new kind of potential drug at the
conference: an integrase inhibitor (abstract 518). This
compound attacks yet another stage of HIV's life cycle, when
HIV genes combine with the cell's normal genetic makeup.

Another potential treatment worth noting was a derivative of
the immune-suppressive drug cyclosporin. The derivative seems
to suppress HIV preferentially, without disturbing helper T-
cells' normal activity (abstract #519). In another test-tube
study (abstract #583), cyclosporin itself "significantly
(>80%) or completely suppressed acute HIV infection with both
AZT-sensitive and resistant isolates of HIV-1." Cyclosporin
worked well with AZT in the laboratory, allowing reduction in
both drugs' effective concentrations.

While waiting for new drugs to become available, there also
was some encouraging reports that should speed development of
two older therapies that have stirred community interest.

One of these reports concerned using AZT in combination with
the anti-herpes drug acyclovir. Two years ago, a British
study found that people with AIDS survived longer when AZT
was combined with acyclovir. That result has been contested,
but the acyclovir-AZT combination remains popular in the
community.

In the present study, 800 HIV-positive men from the
Multicenter AIDS Cohort Study who began AZT prior to
contracting AIDS-related symptoms were followed for up to
five years. Five hundred of the men also took acyclovir at
some point after beginning AZT. Use of acyclovir was
significantly associated with longer survival time but not
AIDS-free time. The effect was not dependent on dosage but
seemed related to length of uninterrupted use of acyclovir.

Some long-awaited data also was released concerning the
effect of the new reverse transcriptase inhibitor d4T on HIV
levels in the blood (abstract #432). Monotherapy with d4T
reduced virus levels ten to 100 times, but after a year those
levels seemed to be heading up again.

Single vs. Combination Therapies

The British-French Concorde trial on early use of AZT
provided a somber backdrop for Conference discussions.
Although only a one-page cursory description of the trial has
been published (in the April 17, 1993 issue of Lancet; more
information was presented in talks last summer at the
International Conference on AIDS in Berlin), its conclusion
that beginning AZT early in the course of disease confers no
advantage over starting late was widely accepted at the
Conference. But Michael Saag, M.D., of the University of
Alabama still recommended starting AZT in asymptomatic
patients: "In three to five years we'll have better agents
[to replace AZT] -- it makes sense to start antiretroviral
therapy as early as possible."

Dr. Saag was speaking at a roundtable discussion on "How to
Use Antivirals in Clinical Practice." One the other
participants, San Francisco AIDS specialist Marcus Conant,
M.D., who has long been a proponent of early, energetic
treatment of HIV, acknowledged the changing mood by
discussing how he now evaluates a patient's clinical symptoms
before embarking on therapy with AZT or combinations of
antiretrovirals. Outlining the progression of skin conditions
as immune deficiency encroaches, Dr. Conant said, "The
symptoms alert doctor and patient that the time has come to
be more aggressive."

Elsewhere in the Conference a survey of zidovudine (AZT)
prescription in Ontario, Canada found that AZT use dropped by
45.4 percent in the months following publication of the
Concorde data. A 13 percent decrease was seen even in people
with AIDS, to whom the Concorde findings do not apply
(abstract #435).

Doctors Conant, Saag and others in conclusion pinned their
hopes on combination therapies as a way to avoid the
weaknesses of prescribing AZT alone. In one lecture, Martin
Hirsch, M.D., of Boston's Massachusetts General Hospital,
described a great number of combination regimens. He said,
"The more drugs you use the better it seems, no matter what
those drugs target." None of the new combinations presented
at the conference showed convincing results, however.

In the first data from a "convergent therapy" trial involving
three reverse transcriptase inhibitors (nevirapine given to
volunteers already taking AZT plus ddI or ddC), the addition
of nevirapine to the other two resulted in a sharp drop in
blood levels of HIV's p24 antigen (abstract #270). By day 56,
levels were tending back to baseline, unfortunately.

A combination that added Merck's "L-drug" (L-697,661: like
nevirapine, a reverse transcriptase inhibitor that works by a
different mechanism than AZT) to AZT was so discouraging that
the company decided to abandon the drug (abstract #L9). Use
of the L-drug alone in previous trials had led to great
reductions in viral levels and leaps in T-helper cell counts,
but the compound lost its effectiveness within weeks as HIV
developed resistance to it. Merck hoped that co-administering
its L-drug with AZT would so dampen HIV replication that
drug-resistant HIV mutants would take much longer to appear.

Genetic analysis showed that this was not the case, and the
HIV in all trial participants bore evidence of the feared
mutations within six to 12 weeks. Worse yet, the Merck
presenter noted that one mutation that previously seemed to
confer only mild, low-level resistance to the L-drug now
conferred high-level resistance in a person whose HIV also
contained AZT-resistance mutations.

Drug Resistant Strains of HIV

The significance of drug resistance took up a large amount of
Conference time. Resistance to a particular drug by a
particular strain of HIV is measured in test-tube
experiments, and the implications of such experiments for
human beings remain controversial. Nonetheless, presentations
suggested that drug resistance poses serious obstacles for
combination therapies.

Victoria Johnson, M.D., of the University of Alabama,
reported preliminary data from the nevirapine "convergent
therapy" trial that suggested resistance could develop
against all three drugs at once (session #14; note that
sessions are available on audio tapes; for information on how
to order them, see below), thus defeating the triple
combination's purpose. This may be the cause of the therapy's
apparently short-lived period of benefit.

Daniel Kuritzkes, M.D., of the University of Colorado gave a
report on the drug resistance issue in the large ACTG
116B/117 trial, which looked at the benefits of ddI in people
with a history of taking AZT. The study found that
participants with AZT-resistant strains did not do as well on
ddI as those who harbored no mutant virus (abstracts #1 and
#460). This data may have relevance for the Merck L-drug plus
AZT trial described above, where most participants had HIV
with mutations known to confer resistance to AZT.

In contrast, a Canadian group observed that changing to ddI
after six months on AZT was universally beneficial (abstract
#2): "Our study demonstrates that an early change to ddI
leads to a sustained increase in [T-helper cell] count,
prevents in vitro resistance and often leads to a decrease
inI AZT resistance [if] present."

The question of whether drug resistance in the test tube has
any consequences for humans was taken up by a group led by
Donald Mayers, M.D., from the Walter Reed Army Institute for
Research. The Army researchers reported that in patients on
AZT monotherapy, the occurrence of AZT-resistant mutant HIV
presages a rapid decline in T-helper cell count in the course
of the next year. But does drug resistance cause this drop,
or does the emergence of more rapidly replicating HIV late in
the course of disease lead to more resistant mutants? The
latter was the view of Dutch researcher Charles Boucher,
M.D., who explained the views of his research team at a
roundtable discussion on the resistance phenomenon (session
#14).

At the same roundtable, Douglas Richman, M.D., of University
of California San Diego, put more emphasis on the effects of
resistance itself. In trials, people with a history of AZT
use don't do as well on the new drug, he observed. The poor
showing is curious because mutant genes by themselves should
make HIV less virulent by rendering the reverse transcriptase
enzyme less efficient in helping HIV infect new cells. In
test-tube cultures, drug-resistant HIV is outgrown by non-
mutant strains.

Finally, Dr. Richman concluded that AZT resistance may be a
marker for some other ability that the virus has gained, such
as greater mutability or greater exploitation of human cells'
natural chemistry. This comment brought Dr. Richman's
position closer to Dr. Boucher's. It also helps explain the
observation of the Canadian group mentioned above (and of the
main results from ACTG 116B/117), that early switching from
AZT to ddI is beneficial. Switching early may give HIV less
opportunity to adapt to conditions in the host.

Immune-based Therapy

One of the reasons why the benefits of anti-HIV drugs are so
transient, and the question of drug-resistant mutations so
critical, is that normally a medication for a disease does
not have to completely kill the infection, just seriously
reduce it and allow the immune response to take care of
surviving microbes. In HIV, the immune response is
insufficient, and medical treatments have to shoulder the
major burden.

One way to overcome this problem is by adjusting the human
immune response so that it has a more positive role to play.
The Conference heard reports on a wide range of "immune-based
therapies." Many of the proposed therapies utilize some of
the most advanced techniques of biotechnology and are in need
of further refinement before they can be used in humans.

The farthest along of the hi-tech immune-based therapies
utilizes periodic infusions of IL-2, a natural immune
activator that stimulates proliferation of immune cells. This
therapy had been tried previously as a steady regimen, but
with that dosage and schedule, the drug was very toxic and
rapidly lost effect. However, intermittent infusions (five
days every two months) produced 75 percent increases in 10
volunteers' T-helper cell counts after a year of therapy
(abstract #301). Improvements in immune responsiveness tests
also occurred. Whether these induced changes have any
clinical importance remains undetermined, however. IL-2 also
has so many side effects that eight of the ten volunteers had
to have their dose reduced. Much less benefit and more
toxicity were observed in a separate trial with people who
had T-helper cell counts of less than 200.

The simplest immune-based therapy is to extract antibodies
against HIV from healthy infected people with high antibody
levels and give them to people with more advanced disease and
lower antibody production. (Antibodies are molecules tailored
by the immune system to adhere to and neutralize a specific
microbe like HIV.) French doctors reported at the Conference
that this kind of passive transfer significantly reduced
clinical symptoms and deaths during a year-long trial in a
group of people with AIDS -- some of the most promising human
trial data that Conference attendees heard (abstract #L12).
The 86 trial participants were infused with antibody-rich
serum or placebo every two weeks. After a year, there were
seven deaths (including one suicide) in the trial's treatment
arm and 11 in the placebo arm. Also, volunteers who received
placebo experienced almost three times the AIDS-defining
events as those in the treatment arm.

In a roundtable symposium on immune-based therapies, (session
#47), Judy Lieberman, M.D., of the New England Medical Center
in Boston described a nine-person trial that involved
removing white blood cells from volunteers' blood and
selectively culturing the killer cells (cytotoxic CD8+
lymphocytes) that are tailored by the body to seek out and
kill HIV-infected cells. After infusion of the new cells, all
patients had an immediate increase in T-helper cell counts,
and the drop-off after the six-month therapy period was not
dramatic; improvements in killer cell numbers fell after the
end of therapy but seemed to rebound later on.

HIV-specific killer cell expansions were also discussed by a
Johns Hopkins University group (abstract #112). This focused
approach represents an improvement over proliferating all the
CD8+ cells present in somebody's serum, because it gives a
higher concentration of the desired cells. It also avoids the
"promiscuous cytotoxic lymphocyte" phenomenon -- the finding
that some killer cells in people with HIV attack uninfected
helper T-cells (abstracts #322 and #326).

Introducing Protective Genes

Expansion and reintroduction of T-helper cells was also
discussed (abstract #111), but a concern here is that you may
just be feeding the HIV present in patients' bodies. A
proposed way around this would use gene therapy. Genes could
be introduced into the helper T-cells to protect the cells
from HIV infection. Flossie Wong-Staal, M.D., of University
of California San Diego gave a talk (session #68) describing
how to insert a gene for a ribozyme (which has been called a
"molecular scissors" in press reports) in cells before
culturing them and returning them to the patient. These
ribozymes would have the ability to link up with and cut out
a section of HIV genetic material should HIV be present in
the cell nucleus. Gary Nabel, M.D., of the University of
Michigan described a similar process involving a gene for a
molecule that blocks HIV's "rev" protein (session #98). Rev
regulates the construction of HIV's structural components in
infected cells.

Each of these gene therapies have approval to start human
testing. Dr. Nabel indicated that they might be combined into
a single therapeutic approach.

There are a number of unanswered questions with both genetic
repair methods -- the first being how to culture a sufficient
number of protected T-helper cells to have an impact. One
possibility would be to use bone marrow stem cells instead of
helper T-cells. These would divide and mature into helper T-
cells after re-infusion into the body.

But even if one could generate enough protected T-helper
cells, there is still the question of whether these cells
could survive. Anthony Fauci, M.D., in two talks (session #69
and #81), claimed that direct HIV-induced cell killing is a
rare event. Most cells that die during HIV infection do not
themselves harbor the virus and are killed in the lymph nodes
due to immune dysregulation. At the same time, the structure
of the lymph nodes and also the thymus gland is destroyed.

Dr. Fauci warned, "We must consider, in addition to
developing safe and effective anti-HIV drugs, how to
reconstitute an immune system that may have lost part or all
of its ability to regenerate itself."

Despite Dr. Fauci's comments, few of the new treatment
approaches took into account the structural damage to the
organs of the immune system that HIV causes. Tissues like the
lymph nodes and thymus gland are essential to immune
activation and replacement of lost immune cells. To some
extent, at least, the tissues can regenerate themselves if
HIV is eliminated. After all, the partial treatments we have
now usually result in immediate though transient improvements
in immune cell counts and function. Especially in advanced
disease, though, the body may need outside help at bringing
the immune system back to normal.

The next issue of AIDS TREATMENT NEWS will further describe
the Conference debate over the immune disruptions that lead
to AIDS.

Note that abstract numbers refer to the Conference program
and abstract book published by the event's sponsor, the
American Society of Microbiology in Washington, D.C.. Copies
are available for $25 plus shipping from the Society; call
Books International, 703/787-3305. Tapes of individual
sessions are available from AVW, Inc., 2233 Irving Blvd.,
Dallas TX 75207., phone 214/638-0024.