The success of the combination therapy suggested that the virus was fully suppressed in patients on HAART. Some initially interpreted this suppression as sign that, with time, the virus might be fully eradicated by the immune system. Others suspected that eradication would be difficult because integrated viruses were found in long-lived resting CD4 cells. The argument could only be resolved by experiments such as those presented in the paper featured this week, which describes the discovery that HIV can persist in a latent form in resting CD4+ T cells even in patients who had suppression of viremia on HAART.
Identification of a reservoir for HIV-1 in patients on highly active antiretroviral therapy.
Science. 1997 Nov 14;278(5341):1295-300.
Finzi D, Hermankova M, Pierson T, Carruth LM, Buck C, Chaisson RE, Quinn TC, Chadwick K, Margolick J, Brookmeyer R, Gallant J, Markowitz M, Ho DD, Richman DD, Siliciano RF.
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1996 < All years > 1998
Commentary by Drs. Diana Finzi and Robert Siliciano
The following account of the discovery was written by Dr. Diana Finzi, who was a graduate student at the time and who played a major role in this discovery.
I remember the day very well. I knew it was probably too soon to run the assay to detect virus in the blood samples, and that a negative result would have been meaningless. Still, a positive would have been unequivocal. I was impatient and ran the samples anyway.
At the time, I was an immunology graduate student in Dr. Robert Siliciano’s lab at the Johns Hopkins University School of Medicine. We had previously found HIV in the resting lymphocytes of HIV-infected patients. Two assays, one PCR-based and one culture-based, showed a stably integrated, and replication-competent form of HIV in resting CD4+ T cells. The culture assay required twenty tubes of patient blood, roughly the same amount of blood from uninfected donors, two labor-intensive days to isolate cells, and then a month of careful culturing and feeding (all under the stress of avoiding any form of contamination). Often, our efforts produced cultured virus in only a few wells.
Shortly after the publication of our findings showing that the virus could be cultured from resting CD4 T cells, “drug cocktails” using the new protease inhibitors and other antiretroviral agents generated optimism about HIV treatment. A dramatic drop observed in the viral loads of patients on HAART led to predictions by prominent HIV physicians that the virus might be eradicated with two to three years of treatment – provided there were no sanctuary sites for HIV to escape the drugs. We knew that resting CD4 T cells could be one such site.
The physicians who predicted possible eradication were eager to know whether the virus persisted in resting cells and were generous in providing us with blood samples from their patients. My labmates and I scampered to New York and Germany to retrieve blood from the first patients treated with the HAART cocktails, and we then raced back to the small, windowless P3 lab, at all hours of the day and night, to begin processing the precious samples.
This particular day was the first time we were testing blood from fully suppressed, HAART-treated patients, but we did not expect results for another ten days. As I stood over the ELISA plate, I watched the control wells with HIV standards turn blue. I became transfixed when I thought I saw a tinge of blue in one of the patient wells. Virus in that well would mean that resting CD4 T cells were not completely free of virus and that HAART therapy did not eliminate all forms of HIV. It would mean that CD4 T cells were in fact a sanctuary site for virus. Obviously, it would be a very bad outcome for HIV-infected patients and a major development for the HIV treatment field.
My bench was the first one outside Bob’s office, but he had a visitor that day, and I was initially too stunned to interrupt his meeting. I stared in disbelief as several wells turned blue, feeling the mixed emotions triggered by something both important and tragic. Could it be a mistake? Could it be contamination? Should I repeat the experiment? And, most importantly, should I tell Bob immediately?
I decided that I couldn’t wait any longer. I interrupted the meeting and asked Bob to look at the results. The positives were clearly positive, and Bob and I stood over the plates repeating three phrases to each other: “Can this be true?” “If it is true, this is very bad news.” “But knowing is better than not knowing.”
The following weeks and months were filled with work and tension as we repeated the experiments. Slowly our data emerged. We found virus in most patients, and the amount of virus, although very small, did not diminish with time on therapy. Our data showed that patients treated with HAART had not been cured of HIV and would have to continue treatment, probably for life. Similar results were obtained by the laboratories of Doug Richman and Tony Fauci.
Over the years, our data have been confirmed, and patients who have stopped therapy invariably have experienced rebounds in plasma viral loads. Although there may be other HIV reservoirs, latent virus in resting CD4s remains the best characterized and one that, without question, must be eliminated to cure HIV-infected patients. Now, 15 years since that day, our search to eliminate latently infected cells continues.
About the authors:
Dr. Robert Siliciano is a Professor of Medicine at the Johns Hopkins University School of Medicine and an Investigator with the Howard Hughes Medical Institute.
Dr. Diana Finzi is the Chief of the Pathogenesis and Basic Research Branch at the Basic Sciences Program of Division of AIDS, NIAID, USA.
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