HIV RNA: New Blood Test for Individualized Therapy and Faster Trials

During the last two years, new blood tests for HIV viral load
have increasingly been used in clinical trials and other
scientific research. There is great interest among
researchers, as the early, preliminary results of major
studies are showing that changes in viral load due to change
in therapy can predict clinical benefit in patients.
Meanwhile, the tests are about to come into use (outside of
formal studies) in medical practice for individualizing
patient care; the challenge will be learning when to use them
and how to interpret the results. But it is widely agreed
that a reliable blood test for viral activity in the body --
if it can help predict which drugs will be successful for a
particular patient, as these tests do seem to do -- could
revolutionize HIV medicine by improving treatment with
existing drugs, as well as shortening the time required for
new treatments to be proven.

We believe that this development is more important than most
physicians, treatment activists, or even the scientists
working with the tests may realize, for the following
reasons:

* Existing treatments do seem to work well at certain times
for many people. A scientifically validated way to guide each
patient to the best treatment for him or her could
substantially improve patient care now, without the need to
wait for better drugs to become available.

* A reliable viral test would enable antiviral drugs -- and
even some immune-based and other kinds of therapies to be
tested much more rapidly and less expensively than under the
current system. This should greatly shorten the time required
to make better treatments available.

Now it usually takes years, and hundreds (if not thousands)
of patients to show that an AIDS treatment improves survival,
or reduces the number of opportunistic infections. In
contrast, blood tests often show clear results in weeks, and
relatively few patients may be enough to produce statistical
proof. But first, it must be shown that a decrease in viral
load caused by a change in drug therapy indicates a real
benefit for the patient.

* "Alternative" treatments -- those without a rich, well-
connected institution behind them -- could also be tested
scientifically, perhaps in small, community-based studies.
Those which are worthless can be discarded, and those which
are found to be effective can be targeted to the particular
patients most likely to benefit.

* Similarly, traditional medicines being used around the
world in HIV treatment could be screened with these tests,
potentially making effective treatment available for the
first time for millions of people who cannot obtain high-
priced pharmaceuticals. At the same time, validating
traditional remedies may provide new options to improve
treatment for those who already have access to conventional
medical care.

* We believe that the biggest obstacle to AIDS treatment
development, the major reason it has not been productive, is
that the combination of high regulatory hurdles and lack of
national will has made it impossible for low-priority
treatment ideas, those with only a few champions and little
or no industry or government support, to begin to be tested
so that they can build credibility if they work. Since most
major medical advances start as low-priority ideas, and prove
themselves through a series of surprises, the current system
-- which limits the field to projects which already have
major support -- chokes off the wellspring of innovation,
virtually guaranteeing stagnation. This problem does not
correct itself, due to peoples' natural tendency to focus on
what they already consider important, instead of cultivating
development paths for ideas which are currently outside of
their understanding and therefore may not appear attractive.
Giving the power to determine what works to individual
patients and physicians can allow new ideas to proceed,
breaking the existing monopoly on drug development and the
resulting choke hold on our future.

All these benefits depend, of course, on whether what is
being measured by the new tests is a useful indicator of how
well a treatment is working. It would seem logical that
lowering the amount of HIV in the blood would be an
improvement. But experts are cautious, because prior viral
tests (especially the p24 antigen test) have been too
inaccurate to be very useful in drug development. Much
remains to be learned; but the information now available is
encouraging.

Background: What Is HIV RNA?

The genetic information for almost all living things is
stored in the nucleus of cells, in a chemical called DNA. In
the body, the same information in DNA can be transcribed into
RNA; then the information in the RNA is translated into
proteins, which determine the structure and function of the
cell.

Retroviruses (such as HIV), however, have their genetic
information in RNA. When the virus gets inside a cell, the
information is transcribed in reverse into DNA, which then
becomes part of the cell's genetic inheritance. The cell can
then produce new viruses, or be damaged in various other
ways, sometimes producing abnormal cytokines which can cause
illness.

Each individual HIV virus has two copies of the RNA which
specifies its genetic information. The new tests for viral
load detect this RNA, and the test results are usually given
as number of copies per milliliter of blood plasma. For
example, if someone get a test result of 100,000 (a fairly
high number), it means they have 100,000 copies of the RNA
(or 50,000 virus particles) per milliliter of plasma.

What a Blood Test Needs to Do to Be Useful

First, of course, any test used in research or in clinical
care must be accurate and reliable. Quality assurance is
necessary; it can be done by sending known samples to the
labs that run the test. The samples are coded so that the
labs do not know what is in each; their answers are then
compared against the correct values.

But also, to be useful for drug development or for
individualizing patient care, a test must be validated --
that is, we need to know that what the test measures has
clinical usefulness. Different tests are useful for different
purposes.

For example, the T-helper count (CD4 count) clearly is useful
for prognosis -- predicting how an individual patient is
likely to do. For example, pneumocystis almost always occurs
when the T-helper count is under 200 or 250, and CMV
retinitis when the count is under 50. (These numbers are for
adults; the numbers for young children are entirely
different.) But while the T-helper count clearly provides
predictive information, this does not automatically mean that
a change in T-helper count caused by a drug will indicate a
corresponding change in the prognosis of patients. In fact,
the well-known Concorde study of early use of AZT found that
those taking the drug had higher average T-helper counts than
those who did not, and this difference persisted for the
three years of the study; however, for reasons not well
understood, it did not make much difference in death rates or
other clinical outcomes -- casting doubt on the use of the T-
helper count as an early signal of whether a treatment is
working.

In analyzing a clinical trial where some patients are
randomly assigned to one treatment regimen and some to
another, it is easy to tell if one treatment raises the T-
helper count (or other blood-test result) more than the
other. Also, it is statistically straightforward to determine
if one treatment group does better than the other. But it
takes more complex statistics to tell that the blood test is
actually showing that the drug is working -- to rule out the
possibility that the drug helps the patient, and also just
happens to change the blood test independently. In the latter
case, the test could be worthless for indicating in advance
whether another drug is also going to work.

This means that a trial with clinical endpoints (which may
take several years to generate enough deaths or serious
illnesses to produce statistical proof that one treatment is
better than the other) may be necessary to validate a new
blood test. Fortunately, the tests for HIV RNA can be run
with frozen blood samples, which have already been saved from
past trials, where the outcome for each patient has already
been recorded. This retrospective validation is now well
underway, and preliminary results from three major trials,
presented by different groups at a recent scientific meeting,
have suggested that changes in HIV RNA do indeed predict
changes in clinical outcome cause by drug treatment. These
results are preliminary, and questions remain.

[Note: An alternative strategy would be to not wait for the
validation step, by making the reasonable presumption that,
other things being equal, a low viral load in patients is
better than a high viral load. Then a drug which reduced
viral load could be considered effective for purposes of
approval, unless there was other information which rebutted
the presumption; safety, of course, would have to be proven
separately, but proof of efficacy, not safety, is the
bottleneck in drug development. The benefit of this approach
is that small companies would have a chance to develop and
market AIDS treatments; and large companies would have the
ability and incentive to develop their drugs rapidly. We
believe that this strategy would serve the public better than
current approaches for discovering and developing better AIDS
treatments; but for various reasons it would be difficult to
sell politically.

What we do unquestionably need is better information on how
to use and interpret these tests. There is a danger that
future studies will focus too much on definitive academic
proof that the tests can be useful -- which we are learning
anyway. Instead, they should focus on getting practical
information for physicians who are caring for patients.]

Testing for HIV RNA -- Two Different Technologies

Two completely different methods, quantitative PCR (currently
being developed as a standardized test kit by Roche Molecular
Systems, Somerville, New Jersey) and branched DNA (developed
by Chiron Corporation, Emeryville, California), are now being
widely used in research to test for the amount of HIV RNA in
blood. A short explanation of how they work appeared in
"Better Tests for HIV Activity; Interview with Mark B.
Feinberg, M.D., Ph.D., AIDS Treatment News # 186, November 5,
1993. These two different kinds of tests measure the same
thing, and usually they give comparable results.

But each kind of test has different strengths and weaknesses.
At present, the branched DNA test has a cut-off at 10,000
copies of HIV RNA per milliliter; it cannot measure values
lower than that. (Soon the cutoff will be reduced to 5,000
copies per milliliter.) The quantitative PCR testing service
which is now commercially available through reference
laboratories can go down to 200 copies per milliliter. No one
yet knows if keeping the counts under 5,000 is good enough
for maintaining health; if not, some patients will need to
use PCR to track lower counts.

On the other hand, the branched DNA test appears to be more
consistent than quantitative PCR in measuring different
subtypes of HIV (although Roche points out that what matters
is change in time within each patient, so this might not be
an issue). Which test is more accurate is in dispute.
Branched DNA is much easier than PCR to run in the
laboratory, which should help to make it more accepted in
widespread use.

Eventually one of these testing technologies may prove better
overall than the other. But at this time, researchers using
the tests in clinical trials are about equally interested in
both.

Regulatory Issues

Anyone using HIV RNA tests now, before they are part of
standard medical practice, should understand that, because of
how medical tests are regulated, both quantitative PCR and
branched DNA tests are becoming available to physicians and
patients in a test format that does not require FDA approval.
Therefore, the customer must be extra careful about getting a
good-quality test.

In the U.S., medical tests are traditionally regulated in two
different ways. Usually, the test is provided in the form of
a standardized kit, which contains all the materials and
instructions required so that any qualified laboratory can
test samples. The FDA must approve such a kit before it can
be widely used in the U.S. -- and therefore it takes longer
for the standardized test kit to become available for medical
practice.

But a company can also set up its own sophisticated
laboratory, sometimes called a reference laboratory, which
can perform the testing service. To offer this service
without a kit is much more difficult than running a kit
produced by somebody else, since the lab has to buy or make
all of the materials itself, check their purity, etc. In this
case, the company can offer the test commercially as a
service, not a product, and this testing service is not
regulated by the FDA. Because FDA approval can take some
time, the availability of the standardized kit can be a year
or more behind the availability of the same test through a
testing service by a reference laboratory.

During this time before FDA approval, how can one be
confident that the test is accurate? We suggest purchasing
the test through the companies which are experts in this area
-- Roche Biomedical Laboratories for quantitative PCR, and
Chiron Corporation for branched DNA. Other companies can run
these tests through various agreements with the patent
holder, setting up their own reference laboratories; but then
the patent holder does not run these laboratories and cannot
guarantee their quality. Both Roche and Chiron have immense
investments in their technologies (which not only can test
for HIV, but will also have many other uses in medicine); and
both know the technologies at least as well as anyone else.
They have the incentive and also the means to make sure to
have good quality control before offering their tests to
physicians. Also, government and other researchers have done
considerable work with their tests and would quickly notice
any serious problem. These protections are not available if
one selects a "brand X" HIV RNA test.

And later, even after the FDA-approved kits become available,
there will still be concern that the laboratory personnel who
run the tests be properly trained, to avoid significant
variation due to lack of quality control.

The Challenge: Interpreting Test Results

When one has one's blood tested for HIV RNA, the result comes
back as a number of copies of viral RNA per milliliter; this
number can range from a low of 200 to a high of over a
million. Sometimes the result will be that the number of
copies was below the cut-off for the test -- 200 copies for
PCR, 10,000 copies (soon to be 5,000) for branched DNA. A
single number is hard to interpret; it is more important to
watch how the number changes over time.

HIV RNA is a very sensitive measure, and can change
considerably in response to many things. Some persons with
HIV can have as much as a three-fold variation in the number
from day to day, for no known cause; others have less
variability. Immune stimulation -- for example, from a flu
shot -- can cause a large temporary increase. Because of this
variability, a small change -- even a two-fold or three-fold
change -- in a single number might not be meaningful.

AZT and other approved AIDS treatments often cause a drop of
about one log (ten fold) in HIV RNA level; however, this drop
is usually not sustained, probably because the virus develop
resistance to the drugs. Saquinavir, the experimental
Hoffmann-La Roche proteinase (protease) inhibitor, did about
the same -- close to a one-log drop, but not sustained.

Many researchers believe that, to be a major advance in AIDS
treatment, a new drug, combination, or other treatment
regimen should produce at least a two-log (100 fold) drop in
HIV RNA levels, and that this drop must be sustained -- for
many months, hopefully for years. The experimental protease
inhibitor now being tested by Merck & Co. has produced a two-
log or greater drop in a few patients, but again the decrease
was not sustained; within a few months, the HIV RNA levels
went back up. (For a look at indications of clinical benefit
from even the temporary drop, see "Antivirals and Immune
Recovery: Interview with Michael S. Saag, M.D., AIDS
Treatment News #200, June 3, 1994.)

Since an ideal treatment will be hard to find, we will have
to settle for less at first. Perhaps several treatments which
each alone have a smaller effect could be combined to give
better results. As HIV RNA tests come into wider use,
physicians and patients will be trying all kinds of treatment
regimens while watching the viral load. This could lead to
important advances in the search for better treatments or
cures.

Still there are questions. The HIV RNA test only tells how
much virus is in the blood; it does not tell how pathogenic
that virus is. Also, the blood level of the virus might or
might not be a good indicator of what is going on elsewhere
in the body. Much remains to be learned; but meanwhile, it
does seem reasonable to use the level of HIV RNA in the blood
to help guide treatment decisions, with the goal of lowering
the viral load and keeping it low.

The Future

The quantitative PCR test for HIV RNA is now available to
physicians; in fact, it has been available since late 1993,
although this has not been widely known. Chiron has announced
that its branched DNA test will be available to physicians
starting August 15.

A major scientific meeting on these issues -- Surrogate
Markers of HIV: Strategies and Issues for Selection and Use
-- will be held October 12-14 near Washington D.C.; it is
being organized by Cambridge Healthtech Institute, Waltham,
Massachusetts. It's conclusions may soon become obsolete,
however, as important new data from ongoing trials will
become available in the months after the meeting. These new
trials, prospectively designed to include testing for HIV RNA
(as compared to previously-run trials which fortunately
happened to have some frozen blood in storage) are important
for various reasons. For example, the old trials did not
process the blood properly for the new HIV RNA tests; the
tests can still be run, but some of their sensitivity is
lost. HIV RNA testing may work even better in ongoing trials,
where this is not a problem.

A major future regulatory issue is whether HIV RNA will have
to be re-validated for each new class of drugs -- requiring a
large, long-lasting trial with "clinical endpoints" (death or
major opportunistic infections) before the viral load tests
would be accepted as proving efficacy of the new drug class.
[For example, if the viral load as measured by HIV RNA is
shown to predict patient benefit from nucleoside analog
treatments (AZT, ddI, etc.), can it then be used similarly
for protease inhibitors, or will another major trial be
required to validate it for protease inhibitors first?] If
the FDA decides that the answer is yes -- and it may be
leaning that way at this time -- then the result could be to
add years to the development time of every new class of
drugs, and create a multimillion dollar disincentive to the
development of new kinds of AIDS treatment.

How to Order HIV RNA Tests

* Quantitative PCR for HIV RNA: Physicians can order this
test through Roche Biomedical Laboratories, Research Triangle
Park, North Carolina; the customer service number is 800/533-
0567, 8 a.m. - 6 p.m. Monday through Friday, 8 a.m. - noon
Saturday, Eastern time.

* Branched DNA for HIV RNA: Chiron Corporation will offer
this test to the HIV clinician starting August 15, 1994.
Sample collection, shipping, and other client services will
be handled by Nichols Institute, a commercial laboratory
which can serve clients throughout the U.S. Information about
this test can be obtained by calling 800/553-5445.

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Note: Recent preliminary information on the validation of HIV
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