Nine hundred participants from all around the world attended the opening ceremony where Robert Gallo gave a talk on "AIDS : challenges for the 21st Century ". Gallo first reviewed the history of AIDS research, from the clinical recognition of the syndrome to the latest discoveries. He warned that as human behaviour changes cannot be predicted, microbes will continue to evolve and new infectious diseases to emerge. In fact, a new viral disease can be explained by three mechanisms:

• sometimes, an old virus suddenly becomes pathogenic for humans;
• sometimes, it results from a recent entry into humans from animal reservoirs;
• sometimes the virus is around but restricted in human populations then spreads as a result of human behaviour (like increased plane travel, prostitution, drug addiction).

In fact, all three of these mechanisms appear to be involved in HIV. Obviously, despite major advances, the epidemic is not over . HIV continues to rise exponentially in Asia, although it appears to be stabilizing in Africa (although this plateau still represents one million newly-infected adults each year !).

There is evidence that HIV-1 and HIV-2 diverged about 1000 years ago. Despite the discovery in the 1980's of HTLV-1 and HTLV-2, several scientists thought at that time that microbiology was finished. This was not the case. In parallel, at the current time, due to the important results of HAART in terms of mortality and morbidity decrease, some believe the AIDS problem is over. This is not the case.

A preventive vaccine would be a major development, but AIDS remains a complex problem which continues to hang over us.  Of course, HAART has given cause for hope, but we must keep in mind lessons from leukemia therapy : we still have to kill the last cell. Unfortunately, since the advent of HAART, compliance problems and resistance problems have emerged ; and infected cells appears to live longer than we thought. Currently, there are 2 possibilities besides HAART for achieving HIV remission or eradication : targeting cellular factors and biological interventions. 

Hydroxyurea and other factors under development to target cellular factors will be discussed during this 3-day conference.

Biological interventions can be of a diverse nature:

• currently, there are 4 chemokines (RANTES, MIP-1 alpha, MIP-1 beta, MDC) which represent a sort of innate immunity against HIV ; 
• Other biological products have been isolated that are not chemokines and which act at the transcription level. The Gallo group has studied -Interferon and Tat extensively over the last few years. -Interferon is an immune suppressor factor in HIV-infected patients that is over-produced in this setting. The in vitro use of anti--Interferon antibodies shows that this effect can be partially reversed. Tat is essential for HIV-1 replication and when it interacts with nearby activated uninfected T cells it inhibits their proliferation. Tat also has the independent capacity to increase -Interferon production ; it equally increases the expression of CXCR4 and possibly CCR5 receptors. So, an approach targeting Tat would be of importance in HIV therapy and vaccination.

In the last part of his talk, Gallo emphasized recent advances in his lab on the activity of a human chorionic gonadotropin (beta hCG) as a factor against HIV. His team has recently discovered the chemical nature of this peptide and begun several experiments. In a monkey model, when this molecule is injected prior to viral infection, infection is not prevented but appears at a latent stage. All animals are still alive after 2.5 years (although all control animals died), and there is barely detectable viral replication.

Gallo concluded his presentation by saying that the HIV problem is still far from over, and that we need the help of industry, governments and the world bank to go further.

The first plenary session of the meeting was dedicated to HIV reservoirs and sanctuaries. David HO presented data from his team demonstrating that even despite optimal suppression of plasma viremia with HAART (6 patients on triple therapy and 2 on a quadruple regimen), genetic evolution can be proven, thereby demonstrating ongoing viral replication at very low levels. HO considers that this residual replication can be explained by cellular compartments rather than anatomical compartments. Therefore, it is impossible to measure the decay of the latently infected cells accurately if this pool is permanently replenished by ongoing viral replication. Using an indirect approach (proviral DNA levels), HO found a half life of 6 months in average, although other authors like FINZI have found 44 months. HO studied 33 patients with a coculture technique to analyse this half life, and found 3 different patterns :

-complete viral suppression in some of them ;

-stability of the pool or increase in size if viremia episodes occur ;

-intermediate pattern.

In fact, overall, the slopes varied from 3 months to flat, and were a function of the viremic episodes.

Franco LORI gave interesting data on the use of Hydroxyurea (HU) to target HIV-1 reservoirs. In asymptomatic patients, HU associated with ddI or ddI + d4T is well tolerated, with grade 3 toxicity <1%. In a study comparing ddI therapy with or without HU, genotypic resistance mutations were more frequent in the HU arm although this arm worked better in terms of viral load reduction. LORI suggests that HU is able to reduce the IC₅₀ to ddI, thus increasing the phenotypic sensitivity despite genotypic resistance. In the PANDA cohort, 12 patients were treated with ddI + HU for 124 weeks. The mean plasma viral load was 50000 copies/ml at baseline, dropped to 2000 after 40 weeks and additionally by 1 log at 124 weeks. The CD4 increase was blunted (+30 cells in average at week 124). However, there was an increase in the CD4/CD8 ratio, and a complete restoration of naive CD4 and CD8 repertoires. Furthermore, 6 out of 12 patients showed an unusual specific T helper response to HIV antigens. LORI detailed once again the case now known as the "Berlin patient", who is able to control HIV replication despite therapeutic interruption and the proven presence of some cells bearing replication competent HIV. The follow up of this patient is now 900 days ; he still has a strong CTL response and LORI suggests 3 parameters are important in this case :

-early therapy ;

-HU containing regimen ;

-intermittent therapy.

Jan OREINSTEIN reminded us that lymphocytes are not the only possible reservoirs of HIV, but that infection of macrophages is frequent and not necessarily lytic. In late HIV disease, ORENSTEIN has demonstrated that concurrent opportunistic infections can up-regulate HIV replication in these cells. However, the size of the macrophage infected pool in unknown at present.

Giuseppe PANTALEO closed this first session by reviewing the mechanisms of HIV pathogenesis and the possibilities of immune interventions. He discussed the recent findings of FAUCI group showing that in some patients receiving HAART + IL-2, replication competent HIV is undetectable even in lymphoid tissues (in 2 cases). However, although this is not mentioned in the Nature Medicine paper of last June, FAUCI stopped therapy in these 2 patients and viremia rebounded, showing that eradication was not obtained and that even the threshold at which the immune system alone might be able to control a small residual viral pool was not reached.

The second plenary session tackled the issue of immune recovery and immune interventions in HIV disease. The first presentation was from the well-known French leader in this field, Brigitte AUTRAN. In the Pitié-Salpétrière cohort of 320 chronically infected patients receiving HAART for more than 2 years in a "real life" situation, AUTRAN demonstrated a recovery of memory and naive T cells. In a sub-group of 50 patients with prior episodes of CMV retinitis, secondary prophylaxis and a low CD4 cell count of 75 cells/mm³, only 2 CMV relapses were observed after 1 year of stopping preventive therapy. Recently, AUTRAN tackled the issue of specific anti HIV CD4 T cell activity. In a small group of patients treated during primary infection, some persistence of CD4 T cell reactivity against p24 was observed after 2 years of HAART. In 20 patients receiving HAART at an intermediate stage of the chronic disease (250-400 CD4 cells), 5 had such detectable activity. However, no patient treated at an advanced stage (CD4 <250) showed HIV specific CD4 activity. Comparing the nature of the HAART regimen in a subgroup of the Atlantic study, AUTRAN demonstrated that this was not linked with the use, or not, of a protease inhibitor. In a group of 22 long term non-progressors without antiretroviral therapy, anti HIV specific CD4 activity was found at baseline in 11 patients and these cases had a 1 log difference in plasma viremia compared to others. However, after 1 year, only 9 patients were still responders and this dropped to 4 after 2 years, with no viral load differences compared with those who had ceased activity, at least within this small population. AUTRAN concluded that anti HIV CD4 specific activity is an important part of the definitive control of HIV but not the only key.

Paul RACZ showed histological data demonstrating that defects can persist in the lymph node architecture despite HAART.

Mark CONNORS reviewed available studies on the effect of IL-2 therapy during HIV infection. IL-2 is able to induce T cell proliferation and NK cell numbers. Continuous administration produces a progressive decline in this IL-2 activity, so the molecule is best effective when administered intermittently. IL-2 administration can induce a burst of plasma viremia due to the stimulation of pro-inflammatory cytokines like TNF-, IL-6 and GM-CSF. Transient spikes in plasma viremia are still observed with concurrent use of HAART in about 25% of subjects. However, this effect does not produce an increase in plasma viremia in the long term. CD4 expansion concerns both memory and naive cells and is polyclonal as attested by studies of the V repertoire. In a meta-analysis of 3 studies concerning 157 patients, clinical progression tended to decrease after 36 weeks in the group of patients receiving IL-2, although this decrease was not statistically significant. Two large scale phase III studies will begin within a few months : one will include 4000 patients with >300 CD4 cells and the other will include 1400 patients with CD4 cells between 50 and 300. Enrolment will take 2 years and follow-up is planned for an additional 4 years.

The plenary session on antiretroviral strategies began with a lecture by Christine KATLAMA on first line therapy. Katlama underlined that this solution is our only chance of reaching undetectable plasma viremia. She warned that as antiretroviral therapy is a long process, it must always be initiated with caution. She said that it is never urgent to start antiretroviral drugs and that the first prescription can only be made when the illness is progressing and the patient ready to take the drugs. Triple therapy using a protease inhibitor is the current care standard, but attitudes are moving. Working in favor of protease inhibitors are their potency, proven clinical benefit and the availability of data on their use dating back more than 3 years. However, the high pill burden, existence of cross-resistance and possible observation of long term adverse effects like lypodystrophies may limit their use as a first line therapy solution in the future. The alternative regimen uses nNRTI. These molecules are easy to take (often once a day), are thought to give a durable efficacy (linked to a durable decrease in plasma RNA levels) and allow the prescription of "sparing" regimens, saving protease inhibitors for the future. However, they do have an immediate immune toxicity (hypersensitivity) and common cross-resistance. The last option is the triple combination of NRTI. It is a sparing regimen for 2 classes of drugs and a combination without major drug interactions. However, biological and clinical data on this strategy are still rare. Katlama said that primary HIV infection is a particular as, she considers, antiretroviral therapy is systematically indicated and must be studied in combination with immunotherapies and/or Hydroxyurea. In the context of chronic disease, patients must be aware that therapy is a moving concept. Standards of care are evolving and possibilities for simplifying treatments are to be studied. In particular, several trials are under way to establish the possibility of switching patients from 2NRTI + 1PI to 2NRTI + 1nNRTI. However, the concept of maintenance therapy has proven inefficient. In a study done in Switzerland, 40 patients were switched from 2NRTI + 1 PI to Combivir + Ziagen if they did not have a 215 codon mutation, with good results.

At the end of her talk, Katlama underlined the importance of immune mechanisms, in conjunction with antiretroviral drugs, to control HIV replication. Specific immune responses against HIV can be enhanced by using vaccination therapy (similarly to the recombinant canarypox virus in an ongoing trial in France), or regular monitored interruptions of all antiretrovirals to allow a short minor increase in viremia without risk of resistance selection. The results of these original approaches must be awaited before these theories can be put to the clinic.

Joep LANGE then reviewed the most frequent reasons for therapeutic failure. Insufficient potency of currently available combination therapies is the main explanation, followed by the need for high levels of adhesion to maintain efficacy. In terms of salvage therapy, the "future is not so bright" Lange said, because we do not have enough drugs with different action mechanisms and the potency of the salvage regimens studied so far is modest and of short duration. We also have to consider all the possible drug interactions in a given patient, which are sometimes antagonistic. In Lange's experience, plasma dosage of antiretroviral drugs should be performed on a routine basis at each clinical visit before the occurrence of failure.

Julio MONTANER talked about the challenges for dealing with future therapeutic trials. He regretted that the industry is more interested in doing drug studies than strategy studies. The first challenge should be to determine why everything fails in some patients. The second should be to find means to overcome cross-resistance. Montaner underlined that these trials should imitate the "real world situation" to give practical approaches that could be used in practice.

The last plenary session concerned antiretroviral drug resistance. First, Jon CONDRA revieved the genetic basis of resistance. Because HIV replication is a dynamic process and mutations occur daily during this process (10⁴ – 10⁵ variants/day), every mutation can exist prior to antiretroviral therapy. This phenomenon taken as a whole has nothing to do with therapy but reflects Darwinian evolution. Antiretroviral therapy acts simply as a "filter", allowing some mutants to become predominant. As we know that even the most potent antiretroviral combination is not enough to shut down viral replication completely, resistance is a problem common to all current combinations. Condra has studied resistance to P.I. extensively. In particular, resistance to Indinavir has been linked to 11 amino acid substitutions. In this example, resistance is a cumulative effect of mutations and at least 3 mutations are needed in combination to observe an increase of at least 4 fold in the IC₅₀ of the drug. Studies performed over the last few years have shown that cross-resistance is a common phenomenon in P.I. The same is true for nNRTI. However, in a given combination, not all drugs fail at the same time. For example, it is frequent to find a 184 codon mutation conferring resistance to Lamivudine before any P.I. resistance mutation.

Luc PERRIN reviewed the technical aspects of resistance testing. Genotyping can be done on HIV-1 RNA, analysing the viral population actively replicating, or on HIV-1 DNA, reflecting proviral archives and the evolution of the viral population over time. Phenotyping is time-consuming and a 4 fold increase in the IC₅₀ of the drug is required in order to suspect resistance. Tables correlating genotype to phenotype will be available soon.

Ian WELLER spoke about the use of resistance testing in routine practice. Previous studies done retrospectively on stored plasma from mono or dual therapies have shown that the presence of some mutations is an independant outcome parameter. Furthermore, 2 prospective studies have reinforced the clinical interest of using genotyping as a tool to guide the antiretroviral choice:

-The GART study randomized patients with a 3-fold increase in plasma RNA levels with more than 16 weeks of triple therapy to genotype testing (78 patients) or no testing (74 patients). After 8 weeks of changing therapy, 50% in the first group vs 23% in the second reached plasma RNA levels below 500 copies/ml.

-The VIRADAPT study randomized 108 patients to genotyping or not. After 3 months, the drop in plasma RNA was 1.3 log in the genotyping group vs 0.5 in the group without genotyping to adapt the combination.

Several problems remain with the use of these tests:

-the amount of RNA required is not always sufficient;
-minority species are not always detected;
-there are some cases of amplification failure;
-efficient interpretation of the mutations found in terms of phenotypic resistance remains incomplete, but is evolving.

However, despite these caveats, genotyping can currently be prescribed in several situations:

-post-exposure prophylaxis: as the test can be done within 3 days, adaptation of the prophylaxy can be conducted
-primary HIV infection: as the incidence of resistance in this setting is thought to increase;
-naive patients before therapy initiation;
-vertical transmission;
-salvage therapy

TDM- Finally, Jean Pierre SOMMADOSSI presented other parameters of antiretroviral failure like pharmacokinetic parameters. In fact, TDM (Therapeutic Drug Monitoring) could be used to prevent antiretroviral failure due to resistance selection, and there is some evidence that drug concentrations are linked to virological outcome. Even if P.I. are more easily measured because plasma concentrations reflect activity, it is also interesting to measure RTI, although intracellular levels of their triphosphate metabolites must be considered.

Studies using Zidovudine as monotherapy have shown that even a small difference in the intracellular concentration of the drug, e.g. a 1.5 fold, can explain differences in virological response. Similar results have been found with d4T and 3TC. Consequently, a 2-3 fold difference in terms of tri-phosphorylation of these drugs can have a major impact in terms of antiviral activity. Protease Inhibitor dosage is easier to perform and reflects the final contributions of absorption and metabolism. As Cytochrome P450 activity can vary 10-20 fold from one individual to another, plasma concentrations of P.I. can be vary largely even though the same dose is taken by different patients. The metabolic interactions between antiretroviral drugs are not always obvious. As patients differ from one to another when given the same drug dose administration, different results can be found in terms of pharmacokinetics. Possible metabolic disorders in can be found in some people, lending TDM great importance.

In conclusion, TDM appears as an interesting tool for minimizing drug failure and drug intolerance and maximizing drug activity. Such a test has an important role to play in the concept of individualizing therapy.

The X Symposium on HIV infection also included 5 satellite symposia organized by the pharmaceutical industry, and 80 scientific posters. It was closed on Saturday 19 June afternoon with a talk by Professor Jean Louis VILDE from Paris. Professor Vildé emphasized the fact that this symposium is attracting an ever-larger audience and can be seen as a "fortress". Professor Vildé was probably referring to the political tendencies that have been emerging in this southern part of France over the last few years. Extremist orientations based on racism, xenophobia and exclusion have gained enough power to form a political majority. The TOULON Symposium on HIV Infection can therefore be seen as a fortress, emphasizing the fact that the "war is not over" at any level.

The next symposium will be held in this same fortress, from June 14 to June 16, 2001, on the major theme: "AIDS2001: Third decade of an Odyssey".