Maureen W. Myers

Suppression of plasma viral load below 20 copies/ml is required to achieve a long-term response to therapy

Background:Current guidelines state that the goal of antiretroviral therapy for HIV-infected individuals is to suppress plasma viral load (pVL) to below 400 copies/ml Methods:Predictors of achieving and maintaining pVL suppression were examined in a randomized trial of combinations of zidovudine, nevirapine and didanosine in patients with CD4+ T cell counts of between 200 and 600 × 106 cells/I who were naive to antiretroviral therapy and AIDS-free at enrolment. Results:One hundred and four patients had pVL > 500 copies/ml at baseline and a pVL nadir below 500 copies/ml. Of these, 77 patients experienced an increase in pVL above 500 copies/ml. The median number of days of pVL suppression to below 500 copies/ml was 285 (42) for patients with pVL nadir ≤ (>) 20 copies/ml (P = 00.0001). The relative risk of an increase in pVL above 500 copies/ml associated with a pVL nadir below 20 copies/ml was 0.11 (P = 0.0001). The relative risks of an increase in pVL above 5000 copies/ml associated with a pVL nadir below 20 copies/ml or between 20 and 400 copies/ml were 0.05 [95% confidence interval (CI), 0.02–0.12] and 0.37 (95% CI, 0.23–0.61) respectively, compared with individuals with a pVL nadir > 400 copies/ml. Individuals with a pVL nadir ≤ 20 copies/ml were at a significantly lower risk of virologic failure than individuals with a pVL nadir of between 21 and 400 copies/ml (P = 0.0001). Conclusions:Our results demonstrate that suppression of pVL below 20 copies/ml is necessary to achieve a long-term antiretroviral response. Our data support the need for a revision of current therapeutic guidelines for the management of HIV infection.

Phase I/II evaluation of nevirapine alone and in combination with zidovudine for infection with human immunodeficiency virus

In these Phase I/II open-label clinical trials, 62 persons with human immunodeficiency virus type 1 (HIV-1) infection and CD4+ cell counts < 400/mm3 received nevirapine at doses of 12.5, 50, and 200 mg/day, alone or in combination with zidovudine, 200 mg q8h. Nevirapine was well tolerated in the doses tested. Mean steady-state trough levels were 0.23, 1.1, and 1.9 micrograms/ml for the 12.5, 50, and 200 mg/day doses, respectively. Early suppression of p24 antigen levels and increase in CD4+ cell count were reversed following rapid emergence of virus less susceptible to nevirapine. Resistant strains were isolated from all participants by 8 weeks. Nevertheless, reduction of p24 antigen levels to < 50% of baseline values persisted for 12 weeks or more in four of seven persons who received 200 mg nevirapine/day in combination with zidovudine: these individuals had been antigenemic on long-term zidovudine therapy. This study demonstrates a direct relationship between drug resistance and effects on surrogate markers in HIV-1 infection.

Adeno-associated virus autointerference

We have analyzed an autointerference phenomenon exhibited by adeno-associated virus type 2 (AAV) when grown in KB cells coinfected with adenovirus type 2 as the helper. Infectious AAV particles that banded at 1.41 g/cm3 in CsCl were purified by three cycles of centrifuging in CsCl equilibrium gradients. When cells were infected with an increasing multiplicity of these AAV particles there was a corresponding decrease in production of infectious progeny AAV. There was also an AAV multiplicity-dependent inhibition of production of infectious adenovirus and inhibition of Ad DNA replication. The viral DNA in the Hirt supernatant fraction extracted from cells infected with different multiplicities of AAV was analyzed in neutral sucrose gradients. At low multiplicities of infection with AAV, the main AAV DNA species synthesized was the mature 14.5 S (standard) viral genome. In higher multiplicity infections with AAV increasing amounts of aberrant 10 S AAV DNA molecules accumulated and the proportion of 14.5 S AAV DNA decreased. Restriction endonuclease cleavage showed that the 10 S DNA was enriched for the left- or right-hand terminal regions of the AAV genome. These molecules may be analogous to the previously characterized aberrant DNA molecules found in light-density AAV particles. Thus, the AAV autointerference is correlated with production of the aberrant deleted AAV genomes.

Zidovudine in Asymptomatic Human Immunodeficiency Virus Infection

Zidovudine (AZT) is a potent inhibitor of the replication of the human immunodeficiency virus (HIV), and it has been shown to improve survival in advanced HIV disease. We conducted a randomized, double-blind trial in adults with asymptomatic HIV infection who had CD4+ cell counts of fewer than 500 per cubic millimeter on entry into the study. The subjects (92 percent male) were randomly assigned to one of three treatment groups: placebo (428 subjects); zidovudine, 500 mg per day (453); or zidovudine, 1500 mg per day (457). After a mean follow-up of 55 weeks (range, 19 to 107), 33 of the subjects assigned to placebo had the acquired immunodeficiency syndrome (AIDS), as compared with 11 of those assigned to receive 500 mg of zidovudine (P = 0.002; relative risk, 2.8; 95 percent confidence interval, 1.4 to 5.6) and 14 of those assigned to receive 1500 mg of zidovudine (P = 0.05; relative risk, 1.9; 95 percent confidence interval, 1.0 to 3.5). In the three treatment groups, the rates of progression (per 100 person-years) to either AIDS or advanced AIDS-related complex were 7.6, 3.6, and 4.3, respectively. As compared with those assigned to placebo, the subjects in the zidovudine groups had significant increases in the number of CD4+ cells and significant declines in p24 antigen levels. In the 1500-mg zidovudine group, severe hematologic toxicity (anemia or neutropenia) was more frequent than in the other groups (P less than 0.0001). In the 500-mg zidovudine group, nausea was the only toxicity that was significantly more frequent (in 3.3 percent) than in the placebo group (P = 0.001). We conclude that zidovudine is safe and effective in persons with asymptomatic HIV infection and fewer than 500 CD4+ cells per cubic millimeter. Additional study will be required to determine whether such treatment will ultimately improve survival for persons infected with HIV.

Induction–maintenance antiretroviral therapy: proof of concept

Objective:To investigate the concept of aggressive initial combination therapy followed by reduction to a less demanding maintenance regimen with respect to its potential for sustaining viral suppression. Design:Durable viral suppression to < 20 HIV RNA copies/ml plasma was achieved with zidovudine–nevirapine–didanosine (ZDV–NVP–ddI) therapy. Potential for sustained antiviral response was explored for patients who began with ZDV–NVP–ddI and subsequently interrupted ddI. Methods:Antiretroviral-naive patients were treated with ZDV–NVP, ZDV–ddI, or ZDV–NVP–ddI. Viral load was measured with the Amplicor assay (limit of quantification 400 copies/ml) and by the Ultra Direct assay (limit of quantification 20 copies/ml) when the Amplicor result was < 500 copies/ml. Treatment adherence for each drug was recorded, including all dose adjustments. Results:Five patients who had begun treatment with ZDV–NVP–ddI discontinued ddI for at least 6 weeks after achieving viral load levels below detection. All were documented to have sustained their viral load at < 20 copies/ml during the ddI interruption. Two patients permanently discontinued ddI, both with sustained viral load below detection for more than 1 year while treated with ZDV–NVP. In contrast, no patient initially receiving ZDV–NVP was able to maintain viral load below detection for sustained periods; none had viral load below detection after week 12 of treatment. Conclusions:After induction with ZDV–NVP–ddI, patients were able to sustain viral suppression with a regimen (ZDV–NVP) that was only transiently effective as initial therapy. There was no evidence of virologic escape, even with the most sensitive measure of plasma viral load.

Defective-interfering particles of the human parvovirus adeno-associated virus

Abstract We have previously shown that adeno-associated virus (AAV) grown in KB cells with a helper adenovirus, produced several classes of particles defined by their buoyant density in CsCl. The predominant density classes were referred to as AAV(1.450, AAV(1.41), AAV(1.35), and AAV(1.32), respectively, where the density of the particles was written in the parentheses. The AAV(1.45) and AAV(1.41) particles which contained standard genomes were the only infectious AAV particles. These infectious AAV particles exhibited autointerference. The light-density AAV(1.35) and (1.32) particles contained aberrant (deleted and/or snap-back) genomes. We report here experiments which show that the light-density AAV particles were noninfectious but interfered with the replication of AAV(1.41). The interference was intracellular and resulted in inhibition of synthesis of standard (14.5 S) AAV genomes. In some cases there was also a concomitant increase in synthesis of aberrant, shorter AAV DNA. The inhibitory activity of the light-density particles was abolished by uv irradiation. These results show that the population of light AAV particles contained DI particles. The observed autointerference of AAV(1.45) or AAV(1.41) virus is postulated to be due to AAV DI particles. Replication of AAV DI genomes appeared to require the presence of replicating, standard AAV genomes. This is interpreted to mean that progeny strand replication of AAV requires an AAV-specified product, presumably the AAV capsid protein. In contrast to standard, infectious AAV, the AAV DI particles alone do not inhibit replication of the helper adenovirus.

The inhibitory effect of interferon on a temperature-sensitive mutant of Moloney murine leukemia virus.

Abstract Murine leukemia virus (MuLV) ts3 is a temperature-sensitive mutant of Moloney MuLV which harbors a defect in a late stage of virus assembly. Cells chronically infected with ts3 accumulate budding virus particles on the plasma membrane when incubated at the nonpermissive temperature. Interferon has been shown to inhibit the production of oncornaviruses and a similar late stage of virus assembly has been suggested as the site of interferon action. In this study, the temporal relationship between the two inhibitions was examined. It was found that the process of virus assembly affected by the inhibitory action of interferon preceded that affected by the temperature-sensitive defect. Analysis of virus yields by multiple parameters indicated that interferon treatment at the nonpermissive temperature resulted in the release of noninfectious viral particles.

Estimates of the virological benefit of antiretroviral therapy are both assay- and analysis-dependent

Objective:To assess the potential discrepancies in reported changes in plasma viral load (PVL) depending on how values below the detection limit of the assay are handled in the data analysis phase of a randomized controlled clinical trial. Design:Data from a recently completed clinical trial comparing combinations of zidovudine, didanosine and nevirapine were analysed. In this trial, PVL was measured using an assay with a lower quantification limit of 400 HIV-1 RNA copies/ml initially. All PVL values less than 500 copies/ml were retested with a more sensitive assay with a lower quantification limit of 20 copies/ml. Methods:Several summary measures for assessing change in PVL were calculated using three different methods to adjust for PVL values less than the quantification limit of the assay. The differences between these measures were evaluated. Results:We found that the magnitude of the discrepancy between summary measures used to report changes in PVL depended on the proportion of subjects with PVL less than the quantification limit of the assay, how those observations were handled in the data analysis, and the relative difference between the quantification limits of the conventional and more sensitive assay. Conclusion:The lack of consensus in reporting of PVL data in the literature makes the interpretation of published trial results difficult. In the absence of agreement on the most appropriate summary measure of PVL data, we recommend that all summaries include information on the quantification limit of the assay used, the proportion of observations at or below the quantification limit and how these observations were handled in the data analysis.

CURRENT STATUS OF HIV THERAPY. I, ANTIRETROVIRAL AGENTS

Zidovudine has proved to be an important palliative agent in all stages of HIV infection. It delays progression of disease in patients with asymptomatic or mildly symptomatic infection and decreases the frequency and severity of opportunistic disease in those with AIDS. The search for other, more effective antiretroviral agents goes on, with some promising possibilities.

Current Status of HIV Therapy

The clinicians armamentarium is no longer limited to zidovudine as the only antiretroviral agent that enhances both quality and length of life. ddI has shown clinical benefit in patients previously treated with zidovudine. Recently, the combination of zidovudine and ddC has been approved on the basis of surrogate marker activity; its clinical role awaits results of ongoing trials.