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.

Bibliography Note: Recent preliminary information on the validation of HIV RNA (as an indicator of benefit of drug therapy) is not yet public, so it is not described in the references below.

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