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IL-2 Taken to HAART

By Dave Gilden

February 1999

The introduction of highly active antiretroviral therapy (HAART) has greatly expanded the potential of IL-2, a natural CD4 cell proliferation stimulant (see Treatment Issues, November 1996). A few reports suggest that HAART plus IL-2 can reach the goal of cleansing the body of HIV. The 6th Retrovirus Conference included several reports on this score. But the function of IL-2 remains unclear, and even its dose is subject to speculation. As in the past, only two obvious verities exist: CD4 counts increase rapidly under IL-2's influence, while, at the same time, the agent has serious side effects and has to be used with care.

Dr. Tae-Wok Chun of the NIH Laboratory of Immunoregulation (headed by Dr. Tony Fauci) gave a further presentation at the 6th Retrovirus Conference (abstract 496) of a retrospective study comparing people successfully responding to HAART plus IL-2 to those responding to HAART combinations alone. The NIH researchers compared retrospectively matched cohorts of 14 patients on HAART plus IL-2 and 12 on HAART alone (abstract 496). Everyone had had viral loads under 50 copies/ml for at least six months. When the researchers checked for latently infected CD4 cells, they found the usual pool of quiescent HIV in the HAART alone group (a median of 0.44 infected cells per million total CD4 cells), but the median amount was only a tenth as much in the 14 IL-2 recipients. Six of these 14 had no detectable HIV at all in these assays, which stimulate 10 to 20 million blood CD4 cells in an effort to induce any competent virus to begin replicating. Of these six, three had no inducible HIV in an ultrasensitive assay that cultured 330 million cells. Lymph node biopsies were conducted in two of the individuals, and the tests failed to find any HIV in this tissue either. These two are now enrolled in an NIH trial that takes volunteers off drugs and then monitors for viral rebound. One of them had been off drugs for three weeks at the time of Dr. Chun's talk and was still free of resurgent HIV. NIH scientists are mum about his progress since then.

A success rate that is at best two or three out of 14 selected examples is not overwhelming. As Dr. Fauci commented, "The latent pools in the IL-2 group were smaller, but less does not mean 'not there.' Also, this was not a randomized trial." Other researchers in Dr. Fauci's lab have detected some HIV activity even in volunteers with successful HIV suppression whether or not they were receiving IL-2 (see V. Natarajan et al., The Lancet, January 9, 1999, pages 119-20). This result was obtained using a different sort of assay, one that checked for HIV gene activity (RNA production) in cells as they were extracted from blood or lymph nodes. This assay could not distinguish between real virus production and the chronic partial genetic activity in a cell containing a defective HIV gene set.

Dr. Fauci commented, "The two studies are not contradictory at all ... But it may yet turn out that there is HIV replication [in the people on IL-2], and our culture technique is not sensitive enough."

Part of the uncertainty stems from ignorance about IL-2's exact function. Trials on the compound originally occurred because of IL-2's ability to increase CD4 cell counts. Stimulating CD4 cell replication in this manner would help the immune system outrun the deleterious effects of HIV. It was noticed at the time that untreated people undergoing a course of IL-2 experienced a rather disturbing HIV upswing. With the advent of HAART, Dr. Fauci suggested that this promotion of HIV might be a good thing under controlled conditions: IL-2 would activate quiescent cells with latent HIV infections, thus forcing the HIV to replicate. Such cells would then die, while the HAART regimen would prevent the infection of new cells. In this way, IL-2 would deplete the small reservoir of latent HIV that the drugs otherwise could not eliminate.

It is still not sure that IL-2 operates in this way. Yet another report from Dr. Fauci's lab suggests that the burst of HIV triggered by IL-2 does not entirely come from the latent cells (6th Retrovirus Conference, poster 358). The researchers looked at six persons on antiviral therapy plus the usual intermittent course of high dose IL-2 (18 million units per day for five days every eight weeks). Their viral loads at the beginning of the five days were all below 10,000 copies/ml, and viral loads increased substantially in four of the six by the end of the IL-2 course. A genetic analysis of the HIV in the plasma indicated that little or none of the increase could be due to "archival" HIV that had latently infected blood cells some time in the past. Rather, the HIV present was closely related to the actively replicating HIV at day one.

Another theory is that administering IL-2 boosts anti-HIV immunity by forcing the entire range of CD4 cells to replicate. Any remaining CD4 cells that target HIV would get caught up in the overall stimulation and reappear as a detectable population. Blips in viral load occurring as a consequence of IL-2 would also tend to stimulate such a response. Evidence for any such response is contradictory at best, with side-by-side posters at the 6th Retrovirus Conference disagreeing about new p24 responding cells consequent to IL-2 (posters 356 and 357). At the World AIDS Conference last summer, one French study comparing persons on AZT/ddI with or without IL-2 found no difference in CD8 CTL responses to HIV envelope protein in the two groups.

If there was some direct benefit to IL-2 in terms of suppressing HIV, the first place to look is at HIV levels, either plasma viral load or number of infected cells. Most recent studies have not found any significant difference between antiviral therapy with or without IL-2 (6th Retrovirus Conference, posters 354, 355 and 356). One exception is the Chiron Corporation's trial CS L2002 (6th Retrovirus Conference, poster 357).

This trial followed 77 persons for a year. Half the group had IL-2 added on to "standard of care" antiviral therapy. While in the study, 85% of those on IL-2 received protease inhibitors, compared to 77% of those taking antivirals without IL-2. Baseline CD4 counts ranged from 200 to 500 cells/mm3 (average of 348), and viral loads were under 10,000 copies/ml (average of 1,300). At the start of the trial, 40% of those assigned to the IL-2 group had viral loads below 50 copies/ml. After a year of IL-2, 67% were below 50, representing a mean viral load decrease of 0.3 log (50%). Those in the control group were basically stable: The percentage with viral loads below 50 copies/ml only increased from 31% to 36%. Note, though, that the trend to better viral suppression with IL-2 did not reach statistical significance.

The difference in CD4 count gain was much more dramatic and highly significant -- CD4 cell counts more than doubled in the IL-2 group, to 739 cells/mm3. The extent of this increase depended on how high a dose of IL-2 individuals could tolerate. The CD4 increase among those not on IL-2 averaged only 18%.

IL-2 Trials

For now, it is obvious that IL-2 makes CD4 counts look very healthy. Its effect on clearing HIV is still very much open to question. Several ongoing trials will help answer this question. The first is ACTG 328, which has been slowly recruiting 150 protease inhibitor-naïve volunteers since 1997. This trial places persons with CD4 counts between 50 and 300 on indinavir plus two nucleoside analogs for 12 weeks. Those with viral loads below 5,000 copies/ml are then randomized to either receive IL-2 or not for 72 weeks. Three substudies will examine how the virus and the immune system evolve under the effect of IL-2, including the fate of reservoirs of latent HIV. Results are not expected for another two years, unfortunately.

New trials include the 460-person CPCRA 059, which is checking the CD4 count and viral load effects of HAART regimens with or without IL-2. This one-year study may lead to a larger international clinical endpoint trial to study IL-2's effect on disease progression. That trial is still in the planning stages. The NIH Laboratory of Immunoregulation group also has a HAART plus IL-2 protocol, NIAID 99 I-032. Protocol 032 includes 200 persons from the CPCRA trial as well as 30 newly HIV-infected volunteers and another 100 volunteers with chronic infection. The trial is specifically designed to measure how well IL-2 clears out latent HIV when used in conjunction with HAART. Analyses will include quantification of competent virus, characterization of lymphocyte subsets, and assays for protective immune responses.

Persons already on IL-2 plus HAART may enter the Laboratory's treatment termination trial, NIAID 99 I-0015. To be eligible for this trial, applicants must be on HAART and have viral loads less than 500 copies/ml for at least a year and less than 50 copies for at least the past 30 days. CD4 counts must be above 350 cells/mm3. This 50-person trial has already recruited the two patients featured in Dr. Chun's Retrovirus Conference report.

The trial will follow study participants for a year, and therapy will recommence when viral loads exceed 5,000 or CD4 counts drop by 25%. A variety of immune and viral parameters will be monitored. Lymph node biopsies and lumbar punctures will check for latent HIV in lymph and central nervous system tissues. This trial is sort of a shot in the dark. Rick Davey, the lead investigator, says, "The subset with an innate ability to fight off the virus may be only 5%. People with low reservoirs, such as those on IL-2, may be less likely to relapse. The point is to find what distinguishes the non-relapsers."

A treatment termination trial specifically geared around IL-2 is now recruiting at New York Hospital-Cornell Medical Center. The study is looking for ten volunteers on HAART and viral loads below 400 for at least three months. Trial participants will receive at least three months of IL-2. After these three months, they will stop all antivirals, but not the IL-2, once their CD4 count is greater than 600 cells/mm3, i.e., within the normal range. CD8 cells and NK cells (another type of virus-fighting white blood cell) are supposed to be present at elevated levels.

This study uses a different IL-2 regimen than the NIH protocols. At the NIH, patients receive up to 9 million international units twice daily for five consecutive days every eight weeks. The exact dose depends on the patients' tolerance, since IL-2 produces severe flu-like symptoms and swelling. At Cornell, the trial participants commence at a lesser dose, about 2 million international units/day, but they receive that dose every day without interruption. At Treatment Issues' press time, the first patient had gone four weeks without HIV rebound after stopping all therapy except the IL-2.

Commented Kendall Smith, M.D., the originator of the low-dose IL-2 protocol, "Low dose IL-2 seems to restore CD8 and NK activity, which maintain latency in other infections, in addition to CD4 cells. It also has low toxicity. Our approach is to hope the immune system can contain virus rather than trying to eliminate the virus with drugs."

Nonetheless Michael Giordano, M.D., who heads Cornell's AIDS clinical trials unit, warned, "People should not go on IL-2 if they are not part of clinical research or seeing one of the few experts. The pitfalls are toxicity and stimulating HIV with possible acceleration of disease progression. There is danger of massive edema, hypothyroidism and high fever."

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