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Recently physicians have noticed that some patients,
being treated with a protease-inhibitor-containing
regimen which failed to control the virus, still
maintained a better CD4 (T-helper) count, and seemed to
be doing better clinically, than would have been
expected given their viral load. The most extensive
report yet on this observation -- from a cohort of 143
"virologic failure" patients followed for a median of 18
months at San Francisco General Hospital -- was presented
as a poster at the 5th Conference on Retroviruses and
Opportunistic Infections in Chicago.1 AIDS Treatment
News interviewed lead author Steven G. Deeks, M.D. on
the findings of this study, and also on the current
practices of physicians at San Francisco General
Hospital in treating patients whose viral load could not
be reduced to undetectable levels by antiretroviral
therapy.
Summary of the Poster Presented at the Retroviruses
Conference
The study by Deeks and others was a retrospective review
of the medical records of a cohort of patients at San
Francisco General who met a strict definition of
"virologic failure." To be included in this cohort,
patients had to:
- have had more than 24 weeks of
continuous treatment with regimen containing a protease
inhibitor (either indinavir, ritonavir, nelfinavir, or
ritonavir plus saquinavir),
- have had two consecutive
viral load measurements of greater than 500 copies/ml
(using the branched DNA test) at their last two clinic
visits, and
- have received ongoing care at San
Francisco General Hospital. 143 patients met these
criteria and were included in the review. Of the 108 who
had a viral load test available before starting protease
inhibitors, the median baseline viral load was 4.84 logs
(about 70,000 copies), and the median baseline CD4 count
was 82.
In the entire cohort of 143, followed for a median of 18
months, there were seven deaths: four were not AIDS
related, two were from AIDS-related dementia which
preceded the protease inhibitor treatment, and one was
from invasive aspergillus. In the entire cohort, there
were only eight new AIDS-defining events during the
followup period: two cases of non-Hodgkin's lymphoma,
two pneumocystis, one cryptococcal meningitis, one
cutaneous Kaposi's sarcoma, one PML, and one invasive
aspergillus. There were no new cases of CMV or MAC.
More analysis was possible on the 108 patients who had a
baseline viral load. Before the analysis, the patients
were divided into three mutually exclusive groups:
- Non-responders, with no viral load reduction greater
than one log below the baseline (meaning that the
antiretroviral regimen never reduced the amount of virus
in their blood to a tenth or less of its pre-treatment
level);
- Transient responders, who did have at least
one viral load measurement one log below baseline, but
whose viral load had returned to within one log of
baseline at their last visit; and
- Durable responders, who had a greater than one log reduction in
viral load at their last visit (but who, like all the
others, still met the strict "failure" definition of not
being below 500 copies on either of their last two
visits). By these measures of response, there were 22
non-responders, 45 transient responders, and 41 durable
responders (total 108).
At 18 months, even the "non-responders" had a median CD4
count increase of approximately 50. The transient
responders had a median CD4 increase of more than 100,
and the durable responders had over 150. The median CD4
increase for all 108 of these "virologic failure"
patients was approximately 100.
The following conclusions are quoted from the poster:
"Despite a median duration of 18 months since initiating
a potent PI-containing [protease inhibitor containing]
regimen, and greater than 12 months since the emergence
of virologic failure, the median absolute CD4 T-cell
level in this cohort remained approximately 100
cells/mm3 above the pre-PI baseline.
"A significant proportion of patients with an incomplete
response to a PI-containing regimen had a durable 1 log
or greater decrease in viral load. This durable
suppression was associated with a sustained increase in
the absolute C4 T-cell count.
"Patients who had a transient virologic response to a
PI-containing regimen had also significant and
sustained increase in the absolute CD4 T-cell count.
"New AIDS related events were uncommon in this cohort of
143 patients failing a potent PI containing regimen
(n=8). There were no new cases of CMV or MAC.
"These observations suggest that failure of a
PI-containing regimen, defined virologically, may not be
predictive of subsequent CD4 T-cell decline (over the
following 12 months).
"These observations must be considered in light of the
retrospective nature of this study, and the limited
duration of follow-up. Long-term follow-up of this
cohort is needed to further examine the clinical
implications of PI failure."
The Interview
We asked Dr. Deeks about this study, and about treatment
of such patients at San Francisco General Hospital,
which is widely recognized as a leader in AIDS care. The
interview took place on February 12, 1998.
AIDS Treatment News: In this study of clinical
consequences of virologic failure of protease inhibitor
therapy, why were the "durable responders" counted as
treatment failures?
Dr. Deeks: They did not meet the strict criterion that
has become the gold standard of therapy, which is to
achieve sustained undetectable viral load. They had a
clear response; the viral load went down and stayed
down, but at least in the last two visits it was
detectable (greater than 500 copies/ml using standard
bDNA assay).
ATN: In this study, were there predictors of who would
do poorly -- predictors that might be helpful for
clinicians in managing patients?
Dr. Deeks: Our presentation was only meant to report,
"This is what we saw." To take this observation and
conclude how clinicians should use viral load and CD4
data would be premature.
Our data simply state that the patients we identified as
having "failed" protease inhibitor treatment still
clearly had a sustained CD4 increase. That is a major
point of this presentation. We are not saying that
patients will not progress eventually. But as far as we
can tell, over the 12 to 18 months after we recorded
failure, for the vast majority of patients, CD4 decrease
or clinical progression did not occur.
We did have a small group who developed opportunistic
infections: only eight in this cohort of 143. What was
constant with most of them is that even though they may
have had a viral load response to their therapy, they
never had a CD4 count response. This was consistent with
what Dr. Judy Currier reported in her analysis of ACTG
320; 2 that analysis showed that for patients who
received AZT and 3TC, or AZT, 3TC and indinavir, just a
small increase in CD4 count above their baseline (after
eight weeks of treatment) was highly associated with a
good clinical outcome. Our data were consistent with
their observations.
One possible take-home message is that if patients do
get even a small T-cell response, that may translate
into prolonged clinical benefit. Patients who do not see
a T-cell response to protease inhibitor therapy might
benefit from more aggressive prophylaxis of
opportunistic infections.
Yet our results cannot prove that if you fail protease
inhibitor therapies virologically then you should stay
on that particular regimen -- or even that you should
necessarily stay on therapy. To answer those questions
would require a prospective clinical trial comparing the
different options that patients have: stopping therapy,
switching therapy, or staying on therapy.
ATN: What are the risks of staying on therapy despite
virologic failure?
Dr. Deeks: By allowing viral replication in the face of
a selective pressure, high level drug resistance may
develop. This process may continue to occur long after
the viral load starts to increase. It may limit future
options with so-called "salvage therapy" down the line.
A second risk is continued side effects, which for some
patients may outweigh any durable benefit from these
therapies. And the cost of these drugs will be a factor
for some.
In our clinic the vast majority of patients, once they
failed the protease inhibitor virologically, either
stayed on that therapy or switched to a second protease
inhibitor containing regimen. And virologically, those
groups basically did about equally well. We have not had
many patients achieve durable viral suppression after
switching to a second protease inhibitor containing
regimen. Whether or not these people would have done as
well had they stopped all their drugs, we do not know.
Of note, clinical investigators at Johns Hopkins
University have reported reasonable success in patients
who switch early to a second protease inhibitor
containing regimen.3 The fact that some of their
patients switched early may be critical. Delaying the
switch for months, which was common in most of the
patients we studied, may allow for the development of
high-level resistance.
ATN: Is there any observation from those who did choose
to stop everything?
Dr. Deeks: We only had about half a dozen patients who
chose to stop antiretrovirals because of virological
treatment failure. Among clinicians at San Francisco
General Hospital, there is a strong sense that stopping
therapy is not a good thing to do. So we do not have
data to make a comparison.
One possible criticism of our data is that only those
patients who did well stayed on therapy. We do not
believe this was a significant issue in our analysis,
since very few patients stopped therapy -- and all
patients, including those who stopped, remained in the
analysis.
So again, we can only offer the observation that
virological failure is not necessarily equal to clinical
failure, over 12 to 18 months. But people should not
take this and say, "I failed my protease inhibitor, but
I should stay on it." We really do not know that, and
certainly there are risks in staying on the drugs.
ATN: Have you seen increased viral resistance in these
patients?
Dr. Deeks: We have not looked for it yet, and do not
have much resistance data on these patients now. We need
to do this analysis.
ATN: What research ought to be done next?
Dr. Deeks: The virologists and immunologists need to
take a close look at this phenomenon, and try to
determine if there is any underlying reason to think
that virologic failure and resistance to a protease
inhibitor confers loss of virologic virulence. This is a
major question clinicians have been asking. There are
some small studies suggesting that it may be true. A
paper published a few months ago suggested that
resistance could result in a switch from a syncytium
inducing phenotype (SI) to a non-syncytium inducing
phenotype (NSI)4; this could explain why resistant
virus would be less destructive to T-cells. Other
observations along those lines would also suggest that
resistance to a protease inhibitor comes at some
significant cost to the virus. These are the kinds of
virologic studies that need to occur. I am told that it
is very difficult, however, to test a virus for
virulence in the laboratory. We are interested in
working on this problem here at the Gladstone Institute
[a privately funded nonprofit research facility
associated with San Francisco General Hospital].
The other issue is what exactly is happening in the
immune system -- which goes back to the fundamental
question of how HIV causes immune destruction. Is it a
direct effect of the virus on the CD4 T-cell, or is it
something much more fundamental earlier, a view many
investigators are coming to support?
ATN: In other words, not the virus killing the CD4
cells, but doing something that prevents the cells from
being produced in the first place?
Dr. Deeks: Yes. And it is possible that the transient
virologic response to a protease inhibitor could lead to
a sustained immunologic benefit. If the problem caused
by the virus occurs early in the development of the
mature immune system, one could envision that even a
brief period of time when the virus was not around could
let the immune system regenerate itself. Therefore
immune function could be more sustained in the face of
the virus coming back up, and that could lead to a
sustained clinical benefit. The implication, however, is
that eventually progression will occur. But when that
may happen is unknown.
If you look closely at the data from the nucleoside
analog trials, the CD4 count response is more sustained
than the virologic response. So what we have reported
may not be associated with protease inhibitor failure
specifically. It may be a phenomenon of antiretroviral
drug failure.
ATN: What would we need to answer the question of
whether people should stay on treatment, or go off?
Would a clinical trial be necessary?
Dr. Deeks: I doubt that people would support such a
trial now -- taking patients who "have no clear options to
switch to" and randomly assigning them to go off all
antiretroviral treatment, or to recycle drugs that had
not worked for them. My sense has been that many
clinicians and patients would not participate in such a
study. So we will always have inconclusive data.
What needs to happen for these patients is not to answer
the question of stop, or change, or recycle -- but to
develop new and better drugs.
Caution on Starting NNRTI Drugs After Protease Inhibitor
Failure
Dr. Deeks: At San Francisco General Hospital, for our
patients who have failed more than one protease
inhibitor -- and they are very common here -- one approach
has generally been to keep them on whatever drug
combination is best tolerated, and avoid adding or
changing to any of the newer drugs, particularly the
non-nucleoside reverse transcriptase inhibitors. The
goal here is to save these drugs for when we know how
best to use them in "salvage" regimens. Until then, the
goal of therapy for patients who have failed their
first-line therapies is to move from seeking viral
suppression, toward seeking sustained clinical benefit.
It can be difficult to distinguish between these two.
But a strong feeling of physicians here is not to play
the non-nucleoside RT inhibitor card for these patients
until you have to -- that is, until patients are
progressing clinically. Perhaps over the next year we
will have clinical evidence on how best to approach
patients no longer responding virologically to protease
inhibitor therapy. Presumably, the non-nucleoside
reverse transcriptase inhibitors will be a critical
component of that strategy.
ATN: Do you mean efavirenz in particular?
Dr. Deeks: Or nevirapine or delavirdine. These are very
potent drugs -- but they rarely do much, unless they can
be given with two other drugs which will be very
effective. And for these patients who have gone through
the first line of antiviral therapies, there probably
are not one or two other drugs that are going to be
effective enough to lead to complete suppression.
Viral Load: How Low Is Low Enough?
ATN: Do you have any thoughts on the issue of whether a
viral load below 400 copies is good enough, or do you
really want to be below 50, 40, or even less?
Dr. Deeks: This is one of the questions that clinicians
are going to struggle with over the next year. The data
that Dale Kempf from Abbott Laboratories presented about
a year ago clearly shows that the lower you get, the
longer you stay down;5 that makes sense. So the goal
of therapy will be to get the viral load as low as
possible; the way to measure that would be with one of
the new ultrasensitive assays.
The problem is, what do you do when the viral load does
not go so low? This is a fundamentally different
question. If you get down to very low levels, less than
400 copies, but the virus is still detectable, and it
stays at this low level, what do you do then? Do you add
drugs? Do you change the entire regimen? Do you continue
to follow patients and watch what happens? The problem
is that these new tests provide you with powerful
information, but we do not know how to use it. So I
myself do not see a dramatic need right now for access
to the ultrasensitive assays. They will cause more
confusion when they become more widely available.
The data from Keith Henry, from his clinic at the
University of Minnesota, would suggest that a large
proportion of patients who are "undetectable" with the
standard assays will be detectable with the
ultrasensitive assays.6 So it will be a real concern.
Some other posters at the Retroviruses meeting are
relevant here. One looked at five vs. four vs. three
drugs7; this was a relatively small study done in
Europe. Researchers looked at viral decay rates over the
first two weeks [how fast the virus decreases when
combination antiretroviral treatment is first started],
and observed that as you increase the number of drugs
the patients begin with, the decay increased
substantially. To me this suggested that the three-drug
combinations now used, for example the classic AZT plus
3TC plus indinavir, might not be enough to fully
suppress viral replication -- since if you go to four or
five drugs, you get more rapid decline. This would
suggest that current three-drug regimens may be
suboptimal for some patients, which may be why we see
drug failures even in patients who are completely
adherent to these regimens.
How important is it to get the viral load to extremely
low levels? Obviously the gold standard test for
answering this question would be lack of clinical
progression. But in people who get to these very low
levels, we see very little clinical progression; it
would take years to distinguish between those under 400,
for example, vs. those under 40. In practice we will
never know the answer for sure.
So it comes back to the theory. Theory drives much of
what we do, and probably it should. Here theory would
suggest that the less viral replication you have, the
less resistance you will develop, and the longer these
drugs will work. So getting the viral load as low as
possible should be a central goal of therapy.
References
Deeks SG, Beatty G, Cohen PT, Grant R, and
Volberding P. Viral load and CD4 + T Cell Changes in
Patients Failing Potent Protease Inhibitor Therapy. 5th
Conference on Retroviruses and Opportunistic Infections,
Chicago, February 1-5, 1998 [abstract #419].
Currier JS, Williams PL, Grimes JM, Squires KS,
Fischl MA, and Hammer SM, for the ACTG 320 Study Team.
Incidence rates and risk factors for opportunistic
infections in a phase III trial comparing indinavir +
ZVD + 3TC to ZVD + 3TC. 5th Conference on Retroviruses
and Opportunistic Infections, Chicago, February 1-5,
1998 [abstract #257].
Gallant JE, Hall C, Barnett S, Raines C.
Ritonavir/Saquinavir (RTV/SQV) as Salvage Therapy after
Failure of Initial Protease Inhibitor (PI) Regimen. 5th
Conference on Retroviruses and Opportunistic Infections,
Chicago, February 1-5, 1998 [abstract 427].
Ercoli L and others. HIV phenotype switching during
antiretroviral therapy: emergence of
saquinavir-resistant strains with less
cytopathogenicity. AIDS. August 1997; volume 11, number
10, pages 1211-1217.
Kempf D, Molla A, Sun E, Danner S, Boucher C, and
Leonard J. The duration of viral suppression is
predicted by viral load during protease inhibitor
therapy. 4th Conference on Retroviruses and
Opportunistic Infections, Washington, January 22-26,
1997 [abstract #603].
Henry K and others. Levels of plasma HIV RNA
measured by the Roche Ultrasensitive assay in HIV
infected individuals with RNA levels below the bDNA
detection limit. 5th Conference on Retroviruses and
Opportunistic Infections, Chicago, February 1-5, 1998
[abstract #529].
De Wolf F, Lukashov VV, Danner SA, Goudsmit J, and
Lange JMA. Clearance of HIV-1 following treatment with
three, four, and five anti-HIV drugs. 5th Conference on
Retroviruses and Opportunistic Infections, Chicago,
February 1-5, 1998 [abstract #384].
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