The Arsenal Files 8/The Arsenal Files Collection #8 (Arsenal Computer) (1996).ISO/health/ain149.txt

Text File | 1996-11-11 | 29KB | 514 lines

                   AIDS INFORMATION NEWSLETTER
                   Michael Howe, MSLS, Editor
                     AIDS Information Center
                VA Medical Center, San Francisco
                     [phone] ext 3305
                        November 8, 1996

                Antiretroviral Therapy (Part II)

  Viral Load, Combination Therapy, and the Eradication of HIV:
Demystifying Results from the XI International Conference on AIDS

                  Special Bulletin, August 1996
              American Foundation for AIDS Research

[Tim Horn (Associate Editor, AIDS/HIV Treatment Directory); Ellen
C. Cooper, M.D., M.P.H. (Department of Clinical Research and
Information, American Foundation for AIDS Research)]

     Much exciting new data were presented at the XI International
Conference on AIDS (July 1996) in Vancouver, British Columbia.
However, the complexities involved have made the interpretation of
these data increasingly difficult. The following question-and-
answer report was developed by the staff of AmFAR's Department of
Clinical Research and Information to shed some light on the most
recent developments in HIV/AIDS research. This report should by no
means be considered medical advice; rather, it is a resource guide
for all who are interested in the progress of HIV/AIDS research.

1. There has been a lot of talk about "viral dynamics." What does
this mean?

     Over the past few years, we have learned a great deal about
how HIV causes damage to a person's immune system. HIV was once
thought to enter a period of "clinical latency"--that is, a period
of very little activity in the body for a number of years following
initial infection--while the infected person remains asymptomatic
("outwardly health"). By studying the dynamics of HIV, we now know
that this virus, from the beginning, is constantly reproducing at
an extraordinary rate--over 10 billion viral particles (virions)
a day. The life span of a free-floating virion ("a single viral
particle") in the blood is about six hours. It takes about 2.6 days
for a newly produced virion to infect a cell and begin replicating
itself. Once a lymphocyte, or T-cell, has been infected with HIV,
the cell generally lives about 1.6 days. Because HIV replicates at
such a rapid rate, it makes many "copying" errors. Therefore, a
mere 100 million virions per day are actually infectious and
capable of replicating. (Noninfectious virions are often referred
to as "defective particles.")

2.  Is this what is meant by viral load?

     Yes. If it wasn't for new technologies with the ability to
actually measure the amount of virus per milliliter of blood plasma
and the availability of powerful new drugs like the protease
inhibitors, the important research mentioned above would not have
been possible. At present, there are two methods of analysis, or
assays, commonly used by researchers and physicians in [the United
States] to measure the amount of HIV in blood plasma. The first
technology, PCR (polymerase chain reaction), allows for a precise
measurement of the number of copies (i.e., the amount) of HIV
present in a milliliter of blood plasma. A second technology, bDNA
(branched DNA) amplication, has also been developed into an
automated kit that reproducibly measures the amount of HIV in
plasma. A third quantitative assay, called NASBA, was developed in
Europe. It differs from both of the U.S. technologies, but is more
similar to the PCR-based assays. NASBA is often used to measure the
amount of virus in infants and children because smaller plasma
samples are required. None of these assays distinguishes between
infectious and noninfectious virions.
     The newer versions, or generations, of these assays that are
being developed are even more sensitive (i.e., able to detect
smaller numbers of copies of HIV in a blood sample). The first
generation of the PCR-based assay (Amplicor, made by Roche
Diagnostics) has been approved by the Food and Drug Administration
(FDA) for prognostic uses, and the first and second generation
bDNA-based assay for HIV (Quantiplex, made by Chiron Corporation)
is now under FDA review.
     These technologies differ in how they measure the level of
virus in the blood, but they provide comparable results and
reliability. To maximize consistency, it's best to choose one and
continue to use that same one in following a patient's viral load
over time.

3.  What do my viral load numbers mean?

     A measurement of viral load is usually reported as a copy
number or a log copy number per milliliter of blood. (A log is a
factor of ten: a one log change is the same as a ten-fold change.)
For example, if a person has a viral load of 5 logs (which is the
same as 10 to the 5th power copies), that person has a level of
100,000 copies per milliliter (ml) of blood. Someone with a viral
load of 3.4 log (10 to the 3.4 power) has a viral level of 2,511
copies/ml (which is between 1000 [10 to the 3rd power] and 10,000
[10 to the 4th power]).
     Success in reducing the level of virus in the blood by using
a specific treatment or treatments is often reported--by
researchers, anyway--in terms of log reductions. Thus, a 2 log
reduction in someone with a pretreatment level of 100,000 HIV-RNA
copies/ml of blood would be a 100-fold decrease that reduces the
viral level to 1,000 HIV-RNA copies.

4.  Will my viral load measurement help me figure out if or when
I will develop AIDS?

     A number of studies reported recently--including some reported
at the XI International Conference on AIDS--have opened up the
meaning of viral load measurements. Generally speaking, a
pretreatment level of 5,000 HIV-RNA copies/ml of blood or lower
indicates a relatively good prognosis, whereas anything above
50,000 HIV-RNA copies/ml of blood indicates an increased risk of
disease progression. The level of virus in patients already on
antiretroviral therapy is more difficult to interpret in absolute
terms, but the principle holds: the lower, the better.
     More specific results from a recently completed retrospective
study indicate that viral-load levels can predict disease
progression as far as ten years into the future. In this study of
almost 2000 initially asymptomatic HIV-infected men who were
followed for over ten years--and most of the time had no
antiretroviral treatment--those patients who began with viral loads
under 5000 copies/ml had an average time of over ten years to
development of AIDS or death. Those with more than 50,000 copies/ml
at baseline had an average time to development of AIDS of 3.5 years
and an average survival time of just over five years. Those with
intermediate viral-load levels had moderate risk of progression.
The "take home" message is that the lower the viral load in
disease, the better one's prognosis. In this study, viral load at
baseline was a more accurate predictor of time to AIDS or death
than was a CD4 count alone, but the use of both indicators was an
even better predictor.
     Of course, there is still a log more to learn about the
importance of these numbers. Will drastically--or moderately--
reducing the level of virus in the blood by using anti-HIV
treatments keep people alive and disease-free longer? Although
preliminary data so far seems to indicate that the answer to this
question is yes, it's still too early to so say so with confidence.

5.  I keep hearing the term undetectable virus. What does this
mean--really?

     The term undetectable virus can be misleading. When used, it
almost always refers to the level of virus in the blood as measured
by one of the new viral load assays. Each viral load test has its
own limitations. The currently approved PCR assay cannot accurately
detect less than 400 HIV-RNA copies/ml in a blood sample. The first
generation bDNA test (now under review at the FDA, but available
from research laboratories) cannot reliably detect copy numbers of
HIV-RNA of less than 10,000 copies/ml in blood. Some research
laboratories are equipped with the second generation bDNA test,
which is more sensitive than the first generation assay, but sill
cannot reliably detect less than 500 copies.ml of HIV-RNA. (Check
with your doctor to find out which generation bDNA assay is being
used). Thus, HIV may still be present in the blood, but cannot be
detected due to the limitations of viral-load tests. Of course, a
reduction in HIV-RNA level from 300,000 copies/ml to 300
(undetectable by the current PCR assay), which is a 3 log
reduction, would be considered a significant decrease by both
researchers and physicians.
     An undetectable viral load generally refers to a low level of
virus in blood plasma. It usually does not refer to levels of virus
in the lymph nodes or the central nervous system (including the
brain), two major reservoirs for HIV that are difficult to access.
Detecting the level of virus in the lymph nodes or brain requires
a biopsy, which is not general practice in the medical management
of patients with HIV. Furthermore, measuring the level of HIV in
the fluid surrounding the brain is difficult and may be unreliable.
     The second- and third-generation assays being developed by the
manufacturers of PCR and bDNA are more sensitive to the level of
virus in the blood and are also being used in research to measure
the level of HIV in the lymph nodes. In plasma, the newer PCR assay
can detect down to ten copies per milliliter of blood; the newer
third-generation bDNA assay, approximately 25 copies per
milliliter. Neither the second-generation PCR assay nor the third-
generation bDNA assay is yet generally available.

6.  Is there really a big difference between levels of HIV in the
blood and levels of HIV in the lymph nodes?

     Research on HIV-RNA levels in lymph nodes is still in its
infancy. However, we do know that only about 2% of the body's HIV
circulates in the blood. The rest of the HIV is often found in the
spleen and the lymphatic tissues of the gut and the brain.
According to two studies, HIV levels are 100- to 1,000-fold higher
in the lymphoid tissue than in the blood. In the handful of
relevant studies presented at the XI International Conference on
AIDS, HIV-positive patients with undetectable or very low levels
of virus in the blood reported higher levels of HIV in lymph nodes
removed by biopsies. More research is required to learn whether the
therapeutic changes in viral load that occur in the blood correlate
with viral load changes in the lymphoid tissue.

7.  Do viral load tests mean that T-cell tests are no longer
needed?

     Not at all. Viral load tests show the number of viral
particles in blood plasma. T-cell counts are still needed to assess
the overall immune status of a patient. Together, both are more
predictive of the patient's future course than is either one alone.
Picture it like this: Viral load and T-cells, considered together,
are like a train moving down the track toward a cliff. The T-cell
measurement tells you how close you are to the cliff; the viral
load measurement tells you how fast you are moving toward it.
     Even though a viral load measurement may demonstrate a low
level of virus in the blood, a low T-cell count (generally under
200/cells/mm3) means that the immune system is depleted. A depleted
immune system means that certain opportunistic infections, included
Pneumocystis carinii pneumonia (PCP), can develop. Prophylaxis and
treatments for opportunistic infections are still necessary for
patients with depleted immune systems, even when the viral load is
low.

8.  My T-cells jumped from 100 cells/mm3 to 250 cells/mm3 while I
was taking anti-HIV drugs! Does this mean I can stop taking my PCP
prophylaxis?

     Not really. While a jump in T-cells is certainly a good sign,
we still do not know how healthy these new T-cells are. Once the
immune system has reached an impaired state, the new T-cells it
produces--which may result from anti-HIV treatment--may not be as
strong as those found in people with healthy immune systems. As
yet, no test i available for physicians to sue in determining
whether or not new T-cells are health enough to ward off
opportunistic infections. Thus, remaining on prophylaxis is still
generally recommended.

9.  Okay! What drugs are available to me?

     The number of drugs available to people with HIV has increased
dramatically over the past year. Nine drugs are now FDA-approved
for the treatment of HIV, with several others in the pipeline. Five
of these nine belong to a class of drugs called nucleoside analogue
reverse transcriptase inhibitors, saquinavir, ritonavir, indinavir;
the most recently approved drug, nevirapine, belongs to a third
class called non-nucleoside reverse transcriptase inhibitors
(NNRTIs).
     Simply put, both nucleoside and non-nucleoside reverse
transcriptase inhibitors prevent healthy cells from becoming
infected by inhibiting a key viral enzyme, reverse transcriptase.
Protease inhibitors, on the other hand, act much later in the viral
life cycle to prevent infected cells from producing new virus by
inhibiting another key viral enzyme, protease.
     When taken alone, any one of these drugs provides anti-HIV
activity that ranges from moderate to strong. However, HIV rapidly
changes its genetic structure (that is, it mutates) and develops
resistance to the inhibitory action of any drug to which it is
exposed. To combat viral resistance, new research has found that
combining two or more drugs, especially from different classes,
strengthens and prolongs anti-HIV drug activity (i.e., delays viral
resistance) in many patients.

10.  Which protease inhibitor is the best?

     This question is difficult to answer. We know that saquinavir
(Invirase, made by Hoffmann-La Roche), the first protease inhibitor
to be approved by the FDA, is absorbed poorly by the body when
taken by mouth and, as a result, is somewhat weaker than the other
two approved drugs of this class. A new formulation of saquinavir
is now being tested to counter this problem, but it is not yet
available for widespread use. Ritonavir (Norvir, made by Abbott
Laboratories and indinavir (Crixivan, made by Merck & Company) are
both powerful protease inhibitors. When taken alone, however,
resistance to these compounds develops relatively quickly.
     No head-to-head comparisons in clinical trials of any of the
approved protease inhibitors--or of those in development--are
underway or completed. The decision as to which protease inhibitor
to take depends on a broad range of factors. For example, Abbott's
ritonavir, one of the most potent ("active") anti-HIV treatments
approved to date, often causes significant nausea and/or diarrhea
in a substantial number of patients, as well as headache, liver
problems, and tingling around the mouth. Because it is broken down
by the liver in a manner different from that of other protease
inhibitors, ritonavir cannot be taken with the fairly large number
of other drugs that are metabolized by the same liver enzymes,
including some important antibiotics and antidepressants often used
by patients with AIDS. Ritonavir also must be refrigerated at all
times.
     Merck's indinavir, on the other hand, also may cause nausea
and diarrhea and has been known to cause kidney stones,
particularly in patients who do not drink a lot of fluids.
Indinavir must be taken three times a day on an empty stomach
(i.e., at least one hour before or two hours after eating). In
contrast, Roche's saquinavir must be taken three times a day on a
full stomach. Thus, the decision as to which protease inhibitor to
use is a highly individualized process during which a patient's
medical profile and lifestyle factors must be carefully considered.

11.  What's all this talk about combination therapy?

     The idea behind combining therapies is to hit the virus as
hard as possible and make it more difficult for resistance to
develop. Results from several clinical trials in which one protease
inhibitor or one NNRTI has been combined with two nucleoside
analogues show significant activity in suppressing the viral load
to undetectable levels in a large proportion of antiretroviral
naive (no prior use of antiretroviral drugs) individuals. So far,
the most promising of these combinations consists of a protease
inhibitor (indinavir) and two nucleoside analogues (AZT and 3TC).
Many patients who started taking this combination reported dramatic
decreases in viral load--sometimes going below the level of
detection--within a few weeks. Many of these patients continue,
after a year on the combination therapy, to have low levels of
virus in the blood and increased T-cell counts.
     While a large number of drug combinations are possible, very
few have been studied in clinical trials. For example, we still do
not know whether it is safe and more effective to take two protease
inhibitors at once or if more than three anti-HIV drugs taken at
once is safe.

12.  Which drug or combination of drugs will help me live the
longest?

     Again, we don't know. Relatively few trials of particular
drugs or combinations of drugs have been conducted to determine
possible survival benefits. However, we do know that anti-HIV
therapy keeps people alive longer than taking nothing. Moreover,
we know that taking certain nucleoside analogue combinations (e.g.,
AZT and ddI or AZT and ddC) rather than AZT alone allows some
people to live longer, healthier lives.

13.  If I keep my viral load low (or undetectable) for as long as
possible, could it extend my life and keep me healthy?

     According to a number of researchers, yes. In a newly infected
person, the level of HIV in the blood is remarkably high--ranging
from one million to one hundred million viral particles/ml of
blood-during the first 6-12 weeks of infection. Once the immune
system begins to recognize and fight HIV, the viral load falls. In
some patients, the immune response causes a drastic reduction in
the level of HIV; in others, the reduction in HIV is only moderate.
The reduction in virus usually researchers a set point, i.e., a
level at which HIV production and destruction (or clearance)
reaches an equilibrium for a prolonged period of time (the
asymptomatic period). Patients with an HIV set point of under 5,000
copies/ml have a relatively good prognosis. Patients with an HIV
set point of greater than 50,000 copies/ml are much more likely to
develop AIDS-defining illnesses and progress to death more quickly.
     Based on a handful of short-term studies, many researchers
recommend keeping the level of virus in the blood as low as
possible for as long as possible. The goal is complete viral
suppression, as best we can achieve and measure it with currently
available drugs and assays. However, it is still not known whether
keeping the level of virus at very low (<5000copies/ml) levels will
keep patients alive and healthy indefinitely, although there is
considerable optimism that this may be the case. Only long-term
clinical trials will tell us for sure.

14.  If my viral load is undetectable, can I practice unsafe sex
with my partner?

     No. Remember, an undetectable viral load level in the blood
plasma does not necessarily mean that no virus is present. While
a few small studies indicate that the level of HIV in sperm may be
drastically reduced after a man begins anti-HIV therapy, some HIV
probably goes undetected by viral load technology. Moreover, some
studies have shown that HIV-RNA levels in sperm do not necessarily
correlate with plasma HIV-RNA levels; they can be either lower or
higher.
     We also do not know whether or not an HIV-infected person can
be reinfected with the virus. We do know, however, that it is
entirely possible for an HIV-uninfected person to become infected
with a drug-resistant strain of the virus. Given that many patients
now are taking anti-HIV drugs and quite possibly developing
resistance to them, the transmission of drug-resistant strains is
potentially a major problem. Studies have shown that some patients
infected with HIV, either by sexual transmission or at birth, are
infected with AZT-resistant forms of the virus. From these data,
it is easy to extrapolate that multiple drug-resistant forms of HIV
can be transmitted.

15.  I've been hearing a lot about eradicating HIV. Is the cure in
sight?

     This is the "million dollar" question everyone seems to be
asking. Some media reports, extrapolating from data presented at
the Vancouver conference and elsewhere, claimed that the initiation
of anti-HIV combination therapy may result in the eradication of
HIV from patient's bodies. This is not really the case. There have
been some patients on triple therapy regimens who have experienced
prolonged undetectable viral loads in their blood and, in a few
patients, in their lymph nodes. Remember, however, that the term
"undetectable" is defined by the limits of technology: virus may
be present, but cannot be detected reliably by current PCR or bDNA
assays. Thus, the conclusion that HIV has been eradicated cannot
be justified until patients are taken off all antiretroviral
therapy, have their viral loads followed for months or years and
it is determined that viral replication has not recurred.
     Some researchers speculate that completely suppressive
antiviral regimens could eventually kill all HIV in the body.
However, most of the currently available drugs, even in
combination, do not readily enter all organs, such as the brain and
the lymph nodes, where HIV may be heavily concentrated. HIV also
infects immune cells called monocytes and macrophages, which are
reservoirs for HIV that many drugs currently in use do not affect.
Moreover, we do not have any experience to speak of with the long-
term side effects of taking multiple drug regimens (about 15 pills
a day) for long periods of time.
     To test the concept of a possible cure through viral
eradication, a small number of acutely infected individuals in a
clinical trial at the Aaron Diamond AIDS Research Center (New York
City) have been put on a powerful combination of drugs. The viral
loads of all became undetectable. Those whose viral loads remain
so for at least a year (the exact time has not yet been determined)
will be taken off their drugs. Their lymph nodes also will be
checked for stalwart HIV. However, even if some of these patients
are technically "cured," i.e. no virus is detected in the absence
of treatment, this does not mean that all patients with HIV can
expect the same benefit. The next step would be to explore the
possibility of viral eradication in other patients at various
stages of disease, including those with AIDS.

16.  When should I start taking these drugs? Should I start with
a triple-drug combination?

     There is still no clear-cut answer as to when anti-HIV therapy
should be started, although there has been an ongoing debate among
researchers and physicians for quite some time. Most studies
attempting to determine whether to start anti-HIV therapy early or
later have used T-cells as the marker of disease stage. Moreover,
most of these clinical trials studied only one or two nucleoside
analogues, which do not completely suppress viral load. Given the
more potent drugs and drug combinations now available (usually two
nucleoside analogues with either a protease inhibitor or an NNRTI),
many researchers and caregivers recommend that anti-HIV therapy be
initiated in all patients to keep viral levels as low as possible,
regardless of T-cell counts.
     The general exception is asymptomatic patients with high T-
cell counts (over 500 cells) and low viral loads (<5000 copies/ml)
who have never taken antiretroviral drugs. It may be advisable to
continue to observe those patients in whom the viral set point is
low, indicating an effective immune response. Careful monitoring
of viral load and T-cells is in order, however, so that treatment
can be initiated as soon as viral load increases or immunologic
deterioration occurs.
     If one thing is sure it is that anti-HIV therapy should
consist of more than one drug. For asymptomatic patients, with
reasonable intact immune systems, who are starting antiretroviral
therapy for the first time, the current controversy is whether or
not partially suppressive regimens (e.g. two nucleoside-analogue
RTIs, which still allow HIV in the body to develop drug-resistant
strains) should be used before trying a completely suppressive
regimen, consisting of three or even four drugs, with the goal of
driving the viral load down to undetectable levels.
     Many researchers familiar with the new data believe that
complete suppression should be the goal in all patients treated.
Antiretroviral-naive individuals have the best response to
antiretroviral therapy (presumably because the virus has not yet
developed drug resistance), so there is a good rationale for early,
aggressive treatment, using triple combinations with the potential
to drive the viral load to undetectable levels. Partial
suppression, on the other hand, may allow the virus to develop
resistance to the drugs being taken, which may limit the
effectiveness of future regimens.
     There are still many questions regarding the development of
cross resistance to protease inhibitors, meaning that patients who
develop resistance to one protease inhibitor concurrently may also
become resistant to one or several other protease inhibitors. The
possibility that using one protease inhibitor may render others
much less useful is the reason why a decision to use these drugs
early in the course of HIV is a source of concern. Clinical trials
are underway to determine how significant a problem cross
resistance is in people switching from one protease inhibitor to
another.
     An alternative approach to early aggressive treatment of
antiretroviral-naive patients is to begin triple regimen without
a non-protease inhibitor. The one combination in this category that
has promising data now is the combination of AZT, ddI, and a
recently approved NNRTI, nevirapine. In a small, controlled trial
of asymptomatic antiretroviral-naive patients with CD4 >350, this
combination caused the viral load to fall to undetectable levels
in a majority of patients. In some of these patients, an initial
two log fall in viral load dropped further to undetectable levels
after several months of treatment. In patients who took their drugs
as prescribed every day, the viral load has remained undetectable
for up to a year or longer.
     The advantages of this regimen are that it is generally well
tolerated (e.g., the rash that commonly occurs with nevirapine
abates with time) and that nevirapine crosses into the brain well,
a characteristic that is absent in the currently available protease
inhibitors. Thus, a reasonable strategy may be to initiate
combination antiretroviral therapy without a protease inhibitor,
reserving the protease inhibitors for later when significant viral
escape (increased replication) occurs.

17.  What about compliance with therapy? I've heard that it's very
important not to skip doses of the protease inhibitors. How great
a danger is this?

     Careful compliance (i.e., taking drugs as they are prescribed)
is important for all medications, but critical for completely
suppressive antiretroviral regimens. If drug doses are skipped,
particularly doses of the most potent drugs, such as the protease
inhibitors, viral suppression is reduced and HIV can replicate and
develop drug resistance. Restarting drugs at full doses cannot
always overcome this resistance; therefore, it is very important
that resistance not be allowed to develop in the first place. If
side effects or other problems prevent a person from taking full
doses of all their antiretroviral drugs, it is better to stop
temporarily than to take lower doses: the latter "encourages" the
development of resistant strains of HIV.

18.  Should my viral load help me make a decision about when and
how to start treatment? What about when to switch from one
treatment to another?

     Much discussion at the Vancouver conference and at other
recent meetings has attempted to answer this question. The
International AIDS Society (IAS) has drafted preliminary guidelines
on how to use viral load measurements in making treatment
decisions. On a cautionary note, however, large-scale clinical
trials are still needed to determine whether or not starting or
switching anti-HIV therapy, based on viral load, is the optimal
strategy.