Response of serum p24 antigen and antibody to p24 antigen in patients with AIDS and AIDS-related complex treated with zidovudine

Serum HIV-1 p24 antibody, HIV-1 RNA copy number and CD4 lymphocyte percentage are independently associated with risk of mortality in HIV-1-infected children. National Institute of Child Health and Human Development Intravenous Immunoglobulin Clinical Trial Study Group

OBJECTIVE

The role of HIV-1 antibody in modulating disease progression must be assessed in the context of other immune and viral load markers. We evaluated the association between HIV-1 p24 antibody, HIV-1 RNA, immune complex-dissociated (ICD) p24 antigen, CD4 cell percentage, and mortality in a cohort of 218 HIV-infected children enrolled in a trial of intravenous immunoglobulin prophylaxis of bacterial infections.

METHODS

CD4 cell percentage was measured and sera collected and stored at baseline and every 3 months on study (1988-1991). Stored sera were assayed for HIV-1 p24 antibody, HIV-1 RNA, and ICD p24 antigen. Mortality was recorded during the trial and updated through 1996 (mean total follow-up, 6.3 years).

RESULTS

Eighty-one (37%) children died; probability of mortality for children with baseline HIV-1 p24 antibody concentrations of undetectable (< 1), 1-4, 5-124, and > or = 125 reciprocal titer units (RTU) was 61, 50, 24, and 10%, respectively. A 3.5-fold increase in the relative risk (RR) of death [95% confidence interval (CI), 2.2-5.5] was observed among children with baseline HIV-1 p24 antibody concentration < 5 RTU compared with > or = 5 RTU. In multivariate analyses, p24 antibody, HIV-1 RNA, and CD4 cell percentage but not ICD p24 antigen were independently associated with mortality; the RR of death increased by 1.7 (95% CI, 1.3-2.1) for each log10 decrement in baseline HIV-1 p24 antibody.

CONCLUSIONS

HIV-1 p24 antibody, HIV-1 RNA and CD4 cell percentage independently predict mortality amongst infected children. Whereas CD4 cell percentage provides an estimate of the general degree of immune suppression, HIV-1 p24 antibody could provide an easily obtained, inexpensive assessment of CD4 cell function and could augment prognostic information provided by CD4 cell count and viral load for clinical management of infected children.

Relationship between anti-p24 antibody levels and p24 antigenemia in HIV-infected patients

We studied the influence of HIV p24 antigen immune complexing with anti-p24 antibodies on the assessment of their respective levels in HIV-positive sera. ELISAs were used to evaluate anti-p24 antibody levels and p24 antigenemia, with or without acid dissociation. Observations include the following: (1) p24 antigenemia usually coexisted with low anti-p24 levels; (2) the p24 antigen concentration inversely correlated with anti-p24 antibody levels; and (3) acid dissociation increased the percentage of p24 antigen-positive sera, mostly when anti-p24 was low. In contrast, (1) antigenemia and antibodies varied independently in antiretroviral-treated AIDS patients, undetectable p24 antigen coexisting then with low anti-p24; (2) after acid dissociation, antigen was still undetectable in 83% of sera with high antibody levels, and in 20% with low antibody levels; and (3) acid dissociation did not increase low anti-p24 levels. Whereas the first set of observations indicates that p24 antigen and anti-p24 antibodies can be engaged in immune complexes, the second set indicates that p24 antigen and antibodies were not inevitably linked in such complexes: they may actually be indicative of two distinct biological phenomena.

Intermittent Zidovudine Regimen in Patients with Symptomatic HIV Infection and Previous Haematological Toxicity

Thirteen patients with AIDS or ARC on continuous zidovudine therapy (800–1200 mg daily), who developed severe anaemia (median Hb 7.9g dl−1 range 4.9–9.4) after 66 days of treatment (median, range 35–258) were then treated with an intermittent regimen in an open study. The regimen consisted of cycles of 4 weeks on treatment (600–100 mg daily) followed by 2 weeks off. Intermittent treatment was tolerated for a significantly longer period of time (median 257 days range 72–603) and a higher cumulative does ( P < 0.001). Four patients discontinued intermittent therapy in the period of follow-up, three due to bone marrow suppression. Eight of 13 patients needed red cell transfusions on continuous therapy compared to only one on the intermittent regimen. On intermittent therapy median haemoglobin concentration and neutrophil counts remained stable (Hb median 11.9g dl−1 range 9.1–14.8, neut. median 1.7 × 109I−1 range 0.6–4.3). Ten patients had detectable levels of P24 antigen which decreased from a median of 128 pg ml−1 (range 15–242) to 24 pg ml−1 (range 0–53) on continuous therapy. Subsequently, in eight of these patients on the intermittent regimen, levels of P24 Ag remained below 50% of initial pretreatment values (median 28 pg ml−1 range 0–178) or below 50 pg ml−1.

Influence on survival of p24 antigen levels in patients with AIDS or advanced AIDS related complex treated with zidovudine

In a prospective study sixty-eight patients consecutively diagnosed as having AIDS or advanced ARC who were started on zidovudine therapy were followed up for a median period of 725 days. In the 20 patients who had a baseline p24 antigen level above 20 pg/ml, there was a statistically significant trend towards reduction of the p24 antigen levels after the first month of treatment. The median time of survival of the 68 patients was 702 days and the median symptom-free period was 510 days. Treatment with zidovudine significantly reduced the p24 antigen levels. However, the life expectancy and the symptom-free period were not statistically different in the patients with p24 antigen levels always below or with levels always above two arbitrarily chosen cut-off points of 20 pg/ml and 50 pg/ml, respectively.

Zidovudine therapy in combination with intravenous immunoglobulin in HIV infected children

There is little published data on concomitant use of zidovudine and intravenous immunoglobulin (IV IgG). In this paper we review our experience of four HIV-1 infected children treated with zidovudine for periods of 19-33 months (mean 26.5 months) subsequent to starting IV IgG for period of 18-20 months (mean 19 months). In these children the only clear benefit we found was in one child who had developed HIV encephalopathy which resolved after starting zidovudine. The respective roles of zidovudine and intravenous immunoglobulin in HIV-1 infected children need to be clarified in larger comparative trials.

An improved method for monitoring efficacy of anti-retroviral therapy in HIV-infected individuals: a highly sensitive HIV p24 antigen assay

Circulating human immunodeficiency virus (HIV) p24 antigen levels were measured by a highly sensitive HIV p24 antigen-capture enzyme-linked immunosorbent assay (ELISA) in patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex (ARC) otherwise negative for HIV p24 antigen measured by a commercial antigen-capture ELISA. The assays were performed at baseline and at several intervals during treatment with either zidovudine (ZDV) or dideoxyinosine (ddl). To further enhance the rate of antigen detection, serum was pretreated with hydrochloric acid to denature antibody in immune complexes. Utilizing this assay system, we monitored these patients for drug efficacy. HIV p24 antigen levels obtained by using this sensitive assay decreased in 3 of 8 patients receiving ZDV during 8 weeks of ZDV treatment. Similarly, ddl administration was associated with a decrease of HIV p24 antigen levels in 3 of 5 patients. Thus, the use of the highly sensitive HIV p24 antigen assay permitted the monitoring of surrogate HIV p24 antigen as a measure of efficacy of anti-retroviral therapy in all of these patients who were otherwise HIV p24 antigen-negative at the onset of anti-retroviral therapy.