Vicissitudes of viral load
From 30 July to 1 August 1999, a diverse, international group of biomedical researchers, statisticians, clinicians, research administrators and community treatment advocates met to discuss and develop plans for research on structured treatment interruptions (STIs) in the context of highly active antiretroviral therapy (HAART). Participants reviewed observations to date, currently available virologic, immunologic and clinical hypotheses, and reviewed studies now underway or in the planning stages. They evaluated STI research in the context of fully-virally suppressed patients with primary or chronic HIV infection, as well as multi-drug resistant (MDR) patients who are failing to achieve full viral suppression. In a series of intradisciplinary and interdisciplinary breakout-groups, participants identified gaps in current STI research and developed several proposals and mechanisms to address these gaps, coordinate and expedite the overall STI research effort. Among the conclusions and follow-up steps to emerge by consensus from the STI Workshop were the following:

1. The need to establish a prospective observational STI cohort study to pool observations regarding patients who elect to undergo an STI and to assess its safety, efficacy, and virologic, immunologic and clinical impact;
2. The need to establish an STI Laboratory Working Group to pool resources and improve the ability of researchers to take advantage of new virologic, immunologic and pathologic assays;
3. The need to develop and promulgate a carefully-worded and thought-out clinical practice guideline outlining the potential risks & benefits, and the knowns and (far more) the unknowns about undertaking an STI at various stages of HIV disease;
4. The need to address pharmacologic and quality-of-life considerations in STI research; and
5. The need to coordinate STI research, particularly vis-à-vis studies of STIs in heavily pre-treated patients with few treatment options and (possibly) low CD4 T cell counts, or those at risk for a CD4 T cell plunge or clinical progression during an STI.

Workshop participants discussed these and other objectives. The following draft report summarizes the workshop proceedings and the discussions that led to the workshop conclusions and follow-up recommendations. The STI Steering Committee will undertake to facilitate their implementation.

The Structured Treatment Interruptions (STI) Workshop was held on July 30-August 1, 1999 at the Boston Marriott Newton Hotel. This workshop was co-sponsored by the Foundation for AIDS & Immune Research (FAIR), Project Inform and Treatment Action Group (TAG).

Preliminary Observations

• Some individuals who discontinue highly active antiretroviral therapy (HAART) continue to maintain viral suppression during an STI.
• In some cases, prolonged suppression of plasma viral load to beneath 500 copies/ml in the absence of drug therapy has been observed-is this related to start/stop therapy?
• There are observational indications that the time to rebound of viral load increases in some people with each subsequent start/stop STI cycle.

Researchers from the Aaron Diamond AIDS Research Center (ADARC) have shown that slower decay rates in the latently infected cell compartment (L cell) occur in people who have intermittent episodes of plasma viremia (gt;50 but lt;500 copies/ml) while on HAART. Those with more than two episodes of intermittent viremia per year had non-decaying L cell slopes.Treatment interruptions have been studied in several settings:

Primary HIV infection

• Lori et al.
• Ortiz et al.

Chronic HIV infection with full suppression

• Comet study (Results reported quick viral rebound, but retreatment was successful, with no evidence of the development of resistance.)
• NoHRT (Rich Davey/NIAID; 22 treated; HAART + IL-2, STIs, different patterns)
• Gatell/Garcia (Barcelona, one or two STIs, all patients. below 20 copies/ml, viral load went up to 200 copies/ml, re-initiation, then 2nd STI. Evidence of immune activity in some patients; some interesting viral load rebound curves -- evidence of containment of viral load by immune system)
• Phillips (AIDS, compared rebound in STIs; patients with low CD4 T cell cells had double rebound kinetics vs. those with high CD4 T cell counts - 5 in each group)
• Several additional reports made since the STI meeting, including a case of 3 patients in Brussels who discontinued therapy with no (or low) rebound of virus.

Late salvage/MDR patients

• Frankfurt HIV Cohort (Miller et al.)
• Royal Free Hospital, London (Youle et al.)

These patients were later challenged with mega-HAART regimens. Patients who had experienced an STI seemed to have an independently elevated chance of going beneath the limit of quantitation when resuming therapy.

There were important differences in the Frankfurt patients between those whose virus shifted to wild-type and those whose virus did not shift (see September '99 TAGLine). Those who experienced a treatment interruption and had a viral shift back towards wild-type had a five-fold greater chance of having their viral load go beneath the limit of quantitation (500 copies/ml) than those who did not revert to wild-type during the interruption.

However, there is a major unresolved risk/benefit equation in the disconnect between rising viral load and persistently elevated CD4 T cell counts in patients experiencing partial suppression. The immunologic benefit may persist, but at the cost of the further evolution of multi-drug resistance. The disconnect between viral load and CD4 T cells in partial suppression-disconnect vs. further evolution of multi-drug resistant virus. How far will those viruses evolve?

Virologic Issues
Why is viral replication contained in some individuals during an STI? Several observational studies have observed temporary containment of HIV replication during treatment interruptions. The Berlin patient's HIV-specific CD4 T cell response increased despite a lack of significant viral activity.

Why is viral load contained (for variable-to-indefinite periods) in some individuals who interrupt treatment?

• It could be stochastic (due to random variation).
• The individuals could actually be long-term non-progressors.
• It could be due to immunologically mediated suppression, change in virologic type, both or other causes.
• It could reflect direct HIV-specific immune responses or other immune responses.
• There may be other unexplained factors.

Primary HIV infection (PHI)
We know that in most PHI patients there is a quick rebound in virus levels, but in some individuals there is a delayed rebound. Usually the subsequent response to therapy has been good with no evidence of drug resistance.

Chronic HIV infection (CHI), suppressed viral load
In the untreated state, the HIV/CD4 T cell interaction typically leads to advanced stage disease ("AIDS"). When intervening with HAART, suppressing HIV replication reduces the HIV/CD4 interaction and reverses disease. When measurable plasma viremia returns, disease progression eventually resumes (although possibly in different forms). So the question of stopping therapy immediately raises the danger that the patient will experience an immediate recurrence of the HIV/CD4 interaction that could once again lead to progression. It is unclear whether the timing and pace of progression, however, follow the same patterns as seen in natural history data.

Immunologic Issues
What causes the rapid declines in CD4 T cells observed in some people during an STI? Is it T cell destruction or redistribution? How functional are those cells? Why is this drop (perhaps less often) seen in people who never achieved a large gain in CD4 T cells from HAART?

• Will viral replication after STI stimulate an antiviral immune response that can keep viral replication in check?
• How can the immune response be broadened assuming that broader equals better?
• In chronically-infected patients who are suppressed, can re-exposure to the virus after an STI lead to a stronger immune response to HIV?
• In salvage patients who are not suppressed, can an STI convert the drug-resistant virus into a drug-responsive one?

Do individuals, particularly those in late-stage disease, lack the residual capacity to mount an immune response against HIV, possibly due to insufficient CD4 or CD8 T cells, defects in antigen presenting cells (APCs), defective microenvironments? Can anything be done to help?

Proposed STI Studies
Several different trials were proposed and would involve different entry criteria:

• Observational studies-to gather information regarding the incidence, safety, virologic, immunologic and clinical impact of STIs occurring due to decisions of people with HIV and/or their clinicians;
• Safety trials-open to all comers, regardless of the duration of suppression;
• Studies in primary HIV infection and chronic HIV infection, suppressed virologically-enter if viral load was suppressed for at least one year;
• Studies in multi-drug resistant/salvage patients-comparing various strategies to encourage the virus to revert to wild-type before undertaking a mega-HAART or salvage regimen;
• Quality-of-life studies in people experiencing poor quality of life as a result of ART or experiencing disease progression.

Study design considerations

1. Randomization-will patients be willing to be randomized to such studies?
2. In patients who stopped treatment, would they be willing to go back on treatment?
3. Care has to be taken to ensure that OI prophylaxis or maintenance therapy is resumed, as needed, prior to study randomization.
4. Individual CD4 T cell nadirs should be considered in the study design
5. Durability-Short term responses will not give us adequate answers; we need long-term follow-up.
6. Access to medications. When a patient has discontinued, to re-get the medications in some states could be a problem... Could you get that PI again if you go to the bottom of the list?
7. It's hard to plan trials today with the development of new, easier drugs and regimens and immune-based therapies.

Studies in People Chronically Infected/Suppressed
There is a need for two studies, one for those with viral load below 50 copies/ml (profoundly suppressed) and those with 50-5,000 copies/ml (somewhat suppressed). One study design would randomize individuals to continual vs. intermittent HAART or HAART with one (or more) STIs. Therapy would be resumed in people in the STI group when the CD4 T cell count dropped below 300/mm3. The endpoints would be:

1. The proportion of people who responded to HAART after re-initiation of therapy, or
2. Both viral load declines and CD4 T cell rebounds post-re-challenge.

The studies should be stratified by pre-treatment and baseline viral load. The studies also need to incorporate an evaluation of the impact of hydroxyurea, which blunts CD4 T cell responses. There needs to be an evaluation of whether the studies are doing patients harm.

Studies for Chronically Infected/Unsuppressed (viral load detectable
There are profound differences between people with unsuppressed viral load and high CD4 counts and those with similar viral load but falling CD4 counts, for whom the drugs might be doing no good at all. While return to wild type virus may increase the chances of future response to therapy, if it fails to result in renewed ability to suppress virus, it may do harm. Wild type is the pathogenic virus which originally led to immune depletion and the decision to initiate therapy. It's quite possible that the drug-resistant, but possibly less fit, virus is less pathogenic and hence more desirable. Some researchers would prefer to understand pathogenesis better in this subgroup before generating new hypotheses.

An important control arm in the heavily pre-treated population with few treatment options might be people who are continued on partially-suppressive regimens. Data suggests that partial viral suppression still has an effects on prolonging health and life. Their results could be compared to those of people who change to a new, more aggressive mega-HAART regimen either with or without an intervening STI:

1. Continue on partially-suppressive regimen;
2. Initiate mega-HAART immediately; or
3. Take an STI, then mega-HAART

Recommendations
It is important to develop and promulgate a statement about what is known and issues to consider for researchers, clinicians and people with HIV when considering a structured treatment interruption.

The issue of STIs for people taking drugs with long half-lives such as efavirenz and nevirapine is complicated by the fact that patients may have to stop their NNRTIs before stopping their nucleoside analogues and/or protease inhibitors. Based on these basic principles Can all nucleosides and protease inhibitors be stopped at the same time (after all, within 24 hours all will be undetectable in plasma or near undetectable)? Or should nevirapine and efavirenz (the only two with significantly longer half-lives) be stopped two to three days earlier than the others? Many of these critical issues are expected to be worked out over the course of the next year. ¤

How Can We Determine the Long-Term Effectiveness of Antiretroviral Therapy?
The First Era of HIV treatment employed a single agent that, in early trials, prolonged the lives of those who received it compared to those who received placebo. Subsequently it was shown that single agent therapy was able to delay the onset of symptoms of AIDS and temporarily arrest the decline of immune surrogate markers but did not extend the survival time of those who started treatment earlier compared to those who started treatment later. Finally, at the end of the First Era, it was shown that combining two agents was more effective than using one agent alone.

The Second Era of HIV treatment extended the strategy of combination therapy by adding a new generation of drugs that inhibited replication of HIV in distinctly different ways. This has produced a dramatic reduction in AIDS-related death and disease wherever it has been applied. However, these treatments are not a cure and life-long therapy currently appears necessary.

As the number of people surviving HIV rises and their time on treatment lengthens, a new syndrome of symptoms and disease has begun to appear. Lipid abnormalities, body shape changes, cardiac disease, myopathy, liver and pancreas disease, insulin resistance and metabolic abnormalities -- as well as treatment fatigue, drug interactions and viral resistance have emerged as intractable problems that may be having increasingly fatal consequences.

It is this background of unavoidable long-term treatment, with its unknown consequences, that has led many to consider using existing drugs in novel strategies designed to reduce toxicity and improve quality of life while continuing to inhibit disease progression. At the same time, many are beginning to ask what would constitute a truly effective long-term therapy.

What is effectiveness, anyway?
Effectiveness sounds a lot like efficacy, and, in common usage, the efficacy of HIV drugs is measured by their ability to lower plasma viral load and raise CD4+ cell counts, the two most important surrogate markers of disease progression. Surrogate markers can be influenced quickly and directly, enabling trials of new drugs to find results within twenty-four weeks. Even long-term trials out to two years continue to place emphasis upon sustaining viral load below levels of quantification.

Other, more subjective measures of treatment effectiveness should be discussed, such as the incidence of new AIDS defining illness, quality-of-life (QOL) measures, the incidence of drug-related adverse events, and economic costs among them. But the significance of these measures are difficult to agree upon, and their collection is difficult to obtain.

Unfortunately, death is the significant endpoint. Death is why most people care about AIDS. It is a singular event and an objective fact that is simple to ascertain. A few of the first drugs of the Second Era were proved in trials that measured the number of deaths in both arms. When the ability of these drugs to suppress viral load was seen, it was accepted that suppressed virus correlated with survival, and "death trials" were seen as unethical and unnecessary. But a "death trial" is a survival study, and after the first flush of success with HIV, long-term survival is still unknown.

This probably sounds confusing. Longer-term survival is clearly accomplished with treatment. The death rate has plummeted in countries with access to new drugs. No one would want to go back to the days before effective combination therapy. But as the survival horizon has extended, serious questions must be asked about sustaining survival benefit for as long as possible. It is possible that new drugs with greater potency and less toxicity will come along to inaugurate a Third Era in HIV treatment, but nothing is guaranteed. Until then, the prudent course is to presume that people will still be taking AZT and the others well into the new century and to continue learning how best to maximize their effectiveness.

We are possibly in the early stages of an epidemic of treatment-related disease. It is important that we respond to this threat before the survival gains made in the nineties are erased by a new wave of mortality due to avoidable toxicity. Whether this can be done with a trial of 'when-to-begin-therapy' should be investigated.

When to begin treatment?
One controversial treatment decision concerns the best time to begin taking combination drug therapy: Should one begin treating as soon as possible to prevent the risk of progression to AIDS? Or can one improve his or her ultimate survival chances by delaying treatment until immune deterioration is imminent, thus minimizing extended exposure to the harmful effects of drug therapy?

In the First Era of HIV treatment, several large randomized clinical trials investigated the question of when to begin treatment. In these trials of AZT given immediately or deferred, despite a reduction of the number and severity of opportunistic infections in those who started treatment early, no survival benefit was seen.

Recently, treatment activists have proposed organizing a study to investigate the long-term effectiveness of Second Era therapy, whether started immediately or later. The call for this research addresses concerns people have about the feasibility of taking HIV drugs for perhaps decades, and a fear that, in the long run, the drugs may be as deadly as the disease.

Designing a trial: "The Effect of Immediate versus Deferred Antiretroviral Therapy on Long-Term Survival in HIV Infection"
Sometimes the question of when to start treatment has been posed as: "Early versus Late." But when exactly is "early?" Is it time after infection? Few know precisely when they were infected and people progress at different rates. So, although there are trials of treatment during primary infection which have their own rationale, it might be better to wait until later in the progression of the infection to establish a practical time for early treatment.

Is "early" some time after testing positive? This is easier to determine and it might be a very common real-world point to start therapy, but it doesn't respect the correlation between CD4+ count and the risk of AIDS.

Is "early" some stage of disease as stratified by surrogate markers? To be truly early in the disease, perhaps only people should be admitted with CD4+ over 500 cells. But as early AZT trials found, if everyone in the trial is early in disease (> 500 cells) at the outset, then the trial will take a long time to produce endpoints.

If you want to compare the difference between treating at high or low CD4+ counts, you need to have subjects in a range of CD4+ cells where there is some controversy about whether treatment is a good idea or not, yet be in a range where epidemiology suggests disease progression can be expected. This begins to restrict the entry criteria. Ethically you can only admit people with more than 200 CD4+ cells because there is good evidence that people with fewer than 200 CD4+ should be treated right away before they enter a zone of risk for opportunistic infections. Many questions can complicate the issue: Should the lower limit for entry actually be 300 cells to allow a cushion for avoiding the 200 region? Do you need to consider the rate of change of CD4+ or average the last two or three T-cell counts to establish a baseline? How about percentage? Does viral load have a role?

But "Early versus Late" probably describes a scientific question: "When in the disease (as measured by CD4+ count) is it best to start treatment in order to suppress the virus?" This concept concerns an idealized virus and an idealized disease and may be an artifact of a strategy that considered eradication possible. It doesn't reflect the real-world problem individuals face when they ask "When should I start treatment?"

Immediate vs. Deferred (Now vs. Later)
Immediate means starting treatment right away. In a trial, this means as soon as randomized. This is a simple concept and reflects a real-world practice and recommendation that probably won't change soon. Many accept this as the standard of care in the U.S. for those who are treated. It allows inclusive criteria that could be appropriate for someone at any stage of disease. It is also open as to the kind or quality of treatment, Hard or Soft, etc.

Deferred means not starting right away. This is also a simple concept and reflects a widely practiced approach that is attractive because the transition from person to patient is postponed. But, again, it introduces restrictions on who can enter the trial. People with CD4+ below 200 cells can't ethically enter because they shouldn't wait to start treatment. People around 300 are likely to be in mid-trend towards 200 and thinking about starting. The lowest number many people feel may comfortable with is 350 because it leaves a safety margin.

What about people over 500 CD4+ cells? They can go for years without progression. What is standard practice now? If it is to start people over when 500 cells, then they may be appropriate for inclusion in the trial. But this may make the trial slow to give answers because there will be less disease and fewer endpoints from healthy people. The practical and ethical entry criteria is probably: CD4+ count between 300-350 to 500-600. Other questions must be answered to design this trial, its sample size and its duration:

• What is the rate of T-cell drop within this strata, on and off treatment?
• What is the rate of death in this strata?
• How many potential subjects are in or expected to be in this strata.
• How acceptable is uncertainty in this strata?
• Does viral load play a predictive role?
• Is this is a trial for the treatment naïve?

Since the question is when to start and starting can only happen once, no one in the study should have used antiretroviral treatment in the past. This is because starting treatment incurs the possibility of resistance, the possibility of immune activation, the possibility of a drug sensitivity or hidden toxicity. But mostly, starting treatment before entering the trial introduces the possibility of the unknown. And it is the unknown that we are trying to tease out. This is done by proposing a hypothesis for what is happening in people who stay on long-term therapy then testing the hypothesis.

Some hypotheses:

1. Individuals with CD4+ between 300 and 500 who begin treatment immediately have a lower probability of survival than those who delay treatment.
2. Individuals with CD4+ between 300 and 500 who begin treatment immediately have a higher probability of survival than those who delay treatment.
3. Individuals with CD4+ between 300 and 500 who delay treatment live just as long as those who begin treatment immediately.

From the literature we can probably establish that:

Early Starters:
Have more deaths due to toxicity.
Have more hospitalizations due to toxicity.
Have more symptoms and pain due to drug toxicity.
Incur more costs from drugs and toxicity management.
Have a greater variety of drug-resistant virus.
Have a lower QOL (quality of life).
But Early Starters may also:
Have fewer AIDS events.
Preserve immune competency and repertoire.
Have less HIV damage.
Have slower progression.
Get more medical attention.
We can also probably expect that Late Starters:
Have more deaths due to opportunistic infections.
Progress to AIDS faster.
Have more HIV symptoms.
May (or may not) have incomplete immune recovery.
Have more serious toxicity when they do start.
Don't develop adherence habits.
But they also
Have better early QOL.
Save the healthcare system money.
Retain susceptible virus.
Have less cumulative toxicity.

Norman Letvin (Harvard Medical School) gets the party pooper prize at this year's Paris summit: "No one has yet presented compelling evidence that the immune system will be successful by itself in the absence of therapy. It is a seductive idea, but just because it is intuitively comfortable does not necessarily mean it will be borne out in fact."

Frances Gotch (Chelsea and Westminster Hospital, London) presented preliminary results from her 60-patient HAART +/- Remune +/- IL-2 study. Although she reported anti-HIV T helper responses "as strong as or stronger than those in long-term nonprogressors," these Remune induced responses have not yet been shown to result in improved immune control of HIV.

Merck has apparently begun immunizing volunteers in its first HIV vaccine trial. Merck officials say that if their vaccine is shown capable of generating potent cellular immune responses in HIV-negative volunteers, they will move quickly to study it in HIV-positive individuals.

Glaxo Wellcome is reportedly planning a Phase I study of a "therapeutic" HIV vaccine. The company is working with a U.K. based company which develops preventive and therapeutic vaccines using a gene gun delivery system.

Alessandro Gringeri (Maggiore Hospital, Italy) has conducted a Phase II trial of tat toxoid in HIV-infected individuals.The study, according to Daniel Zagury (Universite Pierre et Marie Curie, Paris), showed that tat toxoid is safe, well-tolerated and capable of raising antibodies to tat (Gringeri A et al. Safety and immunogenicity of HIV-1 Tat toxoid in immunocompromised HIV-1-infected patients. Hum Virol 1998 May-Jun;1(4):293-8, see also, Zagury JF et al. Antibodies to the HIV-1 Tat protein correlated with nonprogression to AIDS: a rationale for the use of Tat toxoid as an HIV-1 vaccine. Hum Virol 1998 May-Jun;1(4):282-92).

Results of a monkey study with Zagury's tat toxoid vaccine, according to David Pouza (University of Wisconsin), showed little difference between the treated animals and the controls - although Pouza speculated that such a tat vaccine could attenuate disease in monkeys.

Barbara Ensoli (Instituto Superiore di Sanita, Rome) presented data on two different tat based approaches: an SIV tat protein and an SIV tat DNA. Since her tat protein study was published in a recent issue of Nature Medicine (Cafaro A et al. Control of SHIV-89.6P-infection of cynomolgus monkeys by HIV-1 Tat protein vaccine. Nat Med 1999 Jun;5(6):643-50), Ensoli focused on her tat DNA vaccine data at the Cent Gardes meeting. After SHIV challenge, four monkeys immunized intramuscularly had no detectable viremia and normal CD4 levels - compared to high levels of virus in the control animals. Criticism of Ensoli's work centered around the relatively non-pathogenic nature of the SHIV challenge virus.

In an attempt to create exposed but unifected monkeys, Ron Desrosiers (New England Primate Research Center, Boston) administered a highly attenuated SIV strain via low-dose, escalating rectal immunizations. These monkeys (unlike those immunized intramuscularly) did not develop measurable SIV antibodies, although they did have SIV-specific lymphoproliferative responses. When a more sensitive test was employed, some evidence of SIV antibodies was detected. Desroisers plans to challenge these animals soon. He also plans to use this new ultra-sensitive antibody test in exposed but seronegative humans.

Michael Klein (Pasteur Merieux Connaught, the sponsor of the meeting) concluded his review of PMC's vaccine program with the sobering remarks, "There is reason for optimism, but even if we had an AIDS vaccine, it would take ten years to get in on the market and to the world." PMC will also initiate a therapeutic vaccine trial shortly: poxvirus vectors associated with either gp160 subunits or lipopeptides -- with or without IL-2. ¤