HIV-1 RNA, CD4 T-lymphocytes, and clinical response to highly active antiretroviral therapy

Objective: To determine if HIV-1 RNA and CD4 lymphocyte thresholds for the initiation of highly active antiretroviral therapy (HAART) are associated with clinical response to therapy.

Design: Observational cohort study.

Setting: Johns Hopkins Hospital HIV Clinic.

Patients: HIV-infected adults.

Intervention: Patients initiating HAART (n = 530) were compared with concurrent patients who did not receive HAART (n = 484).

Main outcome measure: Progression to a new AIDS-defining illness or death.

Cited Here...: The average duration of follow-up for the cohort was 22 months. HAART resulted in decreased disease progression among persons with fewer than, but not more than, 200 × 10⁶ CD4 lymphocytes/l prior to treatment. Among persons receiving HAART, plasma HIV-1 RNA level prior to therapy was not associated with HIV disease progression within CD4 T-lymphoctye count strata. In a Cox multivariate proportional hazards model that adjusted for age, sex, race, prior opportunistic infection, and CD4 T lymphocytes, ≤ 200 × 10⁶ CD4 lymphocytes/l was the strongest predictor of disease progression. HIV-1 RNA level prior to starting HAART of < 5000 copies/ml, 5001-55 000 copies/ml, or > 55 000 copies/ml was not associated with disease progression on therapy, particularly among persons with > 200 × 10⁶ CD4 lymphocytes/l. There was no sex difference in disease progression on treatment.

Conclusions: Our data suggest that current guidelines for initiating HAART should place greater emphasis on CD4 lymphocyte than HIV-1 RNA level for both men and women. Further longitudinal follow-up will be needed to better ascertain whether HAART initiated at > 200 × 10⁶ CD4 lymphocytes/l is effective in slowing disease progression.

Introduction

The optimal time to initiate antiretroviral therapy in asymptomatic HIV-infected persons is unknown. Although highly active antiretroviral therapy [HAART; treatment regimens that include an HIV-1 protease inhibitor (PI) or non-nucleoside reverse transcriptase inhibitor (NNRTI)] can suppress viral replication and prolong disease-free survival, such therapy is associated with substantial toxicity (e.g., lipodystrophy syndrome, glucose intolerance, hyperlipidemia, and lactic acidosis) ^[1-3]. Maintaining long-term viral suppression can be difficult, and drug resistance can develop in patients with incomplete viral suppression. In addition, even prolonged suppression of viral replication is unlikely to eradicate HIV-1 infection ^[4,5].

Current treatment guidelines recommend that antiretroviral therapy be initiated in asymptomatic HIV-infected persons with fewer than 350 × 10⁶ CD4 lymphocytes/l ^[6,7]. For persons with > 350 × 10⁶ CD4 lymphocytes/l, the International AIDS Society recommends initiating therapy if HIV-1 RNA exceeds 5000 copies/ml ^[6]. The US Department of Health and Human Services uses a cutoff of 55 000 copies/ml at this CD4 T-lymphocyte count ^[7]. These HIV-1 RNA and CD4 T-lymphocyte cutoffs are less stringent than previous recommendations, ^[8,9] due in large part to concerns about the toxicity and tolerability of HAART. However, the validity of these thresholds has not been assessed.

We assessed clinical disease progression on HAART according to CD4+ T-lymphocyte and HIV-1 RNA levels prior to initiating therapy among patients in the Johns Hopkins HIV Clinic Cohort. We also assessed disease progression among persons receiving HAART compared to those who did not.

Methods

Study population

The Johns Hopkins HIV Clinic provides care for a large proportion of HIV-infected patients in the Baltimore metropolitan area. Longitudinal primary and subspecialty care are integrated in one hospital-based Clinic. An observational clinical database of persons receiving care through the Clinic has been maintained since 1990. Information from clinical records is reviewed and abstracted by trained medical record technicians onto structured data collection forms, and then entered into an automated database. The clinic medical record, the main hospital medical record, and various institutional automated databases are abstracted. Comprehensive demographic, clinical, laboratory, pharmaceutical, and psychosocial data are collected at enrollment into the HIV Clinic and at 6 month intervals thereafter. Information on death is obtained from a death registry maintained by the Clinic that receives reports from families, funeral homes, other medical institutions, and local coroners. In addition, death records of the Maryland Bureau of Vital Records and the national Social Security death index are regularly searched. Details of database design and method of follow-up have been published previously ^[10].

For this analysis, two groups of HIV-infected patients were identified from the Johns Hopkins HIV Clinic Cohort. Group 1 included all patients enrolled into the Clinic after 1 July 1996 who used HAART for at least 90 days. HAART was defined as two nucleoside reverse transcriptase inhibitors (NRTI) in combination with ≥ 1 PI or with a NNRTI. Regimens containing three NRTI were also considered HAART. Persons who received saquinavir hard-capsule therapy but no other PI or NNRTI were excluded, because of the relatively poor bioavailability of this drug when used alone. Group 2 included all patients enrolled into the Clinic after 1 July 1996 who did not receive a HAART regimen. These patients received non-HAART therapy or no antiretroviral therapy at all. Groups 1 and 2 were concurrent comparison groups in which to assess the effectiveness of HAART.

Disease progression was defined as death or a new AIDS-defining illness based on the 1993 Centers for Disease Control clinical case definition ^[11], excluding CD4 T-lymphocyte counts < 200 × 10⁶/l.

Laboratory analysis

CD4 T lymphocytes were quantified by flow cytometry ^[12]. HIV-1 RNA levels were quantified by reverse transcriptase (RT)-PCR (Roche Molecular Systems; Branchburg, New Jersey, USA).

Statistical analysis

Categorical variables were compared by the Yates-corrected Chi-square test. Continuous variables were compared by the Student's t-test. Kaplan-Meier analyses of time to a new AIDS-defining illness or death (combined endpoint) from the date of first HAART treatment regimen were performed; curves were compared using the log-rank test. Kaplan-Meier analyses were stratified by CD4 lymphocyte count (≤ 200, 201-350, > 350 × 10⁶ cells/l) and HIV-1 RNA level (≤ 5000, 5001-55 000, > 55 000 copies/ml) prior to initiation of therapy. Kaplan-Meier analyses of time to a new AIDS-defining illness or death from the date of first HAART or non-HAART treatment regimen were also performed; curves were compared using the log-rank test. For Groups 1 and 2, the HIV-1 RNA and CD4 T-lymphocyte counts used to stratify Kaplan-Meier estimates were measured within 90 days prior to starting therapy and closest to the start of therapy. Kaplan-Meier analyses of a new AIDS-defining illness or death by sex, HIV-1 RNA level, and CD4 T-lymphocyte counts were also performed.

A Cox multivariate proportional hazards analysis was used to assess the relative hazard of developing a new AIDS-defining illness or death according to CD4 T-lymphocyte and HIV-1 RNA strata among persons treated with HAART, adjusting for age, sex, race, HIV transmission risk group, and history of prior opportunistic illness.

Results

There were 530 patients who received HAART (Group 1) and 484 patients who did not receive HAART (Group 2) after 1 July 1996. The demographic and clinical characteristics of these patients are shown in Table 1. Those who used HAART were significantly more likely to be male, white (non-Hispanic), have male-male sexual contact as their HIV risk factor, have a prior AIDS-defining illness, an initial CD4 lymphocyte count of < 200 × 10⁶/l , and initial HIV-1 RNA > 55 000 copies/ml. Of the 530 persons on HAART, 420 (79%) received PI + NRTI, 54 (10%) received NNRTI + NRTI, 51 (10%) received PI + NNRTI + NRTI, and three (0.5%) received triple NRTI therapy. The average duration of follow-up for the entire cohort was 22 months.

Table 1

Among persons with ≤ 200 × 10⁶ CD4 lymphocytes/l prior to starting therapy, HAART was associated with a decreased risk of disease progression (AIDS-defining diagnosis or death) compared to persons who did not receive HAART (Fig. 1;P = 0.005). However, among persons with 201-350 × 10⁶ or > 350 × 10⁶ CD4 T lymphocytes/l prior to initiating HAART, HAART did not have a statistically significant effect on disease progression. Group 2 (non-HAART) was analyzed according to whether or not dual NRTI therapy had been received. There was no significant difference in disease progression among patients who did or did not receive dual NRTI antiretroviral therapy (data not shown), so the group was not stratified when compared with Group 1 (HAART).

Fig. 1

Among persons receiving HAART, HIV-1 RNA level prior to initiating therapy was not associated with the risk of developing a new AIDS-defining diagnosis or with death in all CD4 T-lymphocyte count strata (Fig. 2).

Fig. 2

In a Cox multivariate proportional hazards model that adjusted for age, sex, race, injecting drug use, prior opportunistic infection, and HIV-1 RNA level, ≤ 200 × 10⁶ CD4 T lymphocytes/l was the variable most strongly associated with disease progression among persons receiving HAART (Table 2). Patients with ≤ 200 × 10⁶ CD4 T lymphocytes/l were at the highest risk for disease progression, irrespective of HIV-1 RNA level. At CD4 T-lymphocyte counts of 201-350 × 10⁶/l, the risk of disease progression was not significantly greater than among persons with baseline CD4 T lymphocyte counts of > 350 × 10⁶/l. HIV-1 RNA level did not significantly alter the risk of disease progression for patients with > 200 × 10⁶ CD4 T lymphocytes/l. Prior opportunistic infection was also independently associated with disease progression. There were no violations of the proportional hazards assumption for these covariates by log-log plots.

Table 2

To assess for a possible sex difference in disease progression, an analysis of progression at different HIV-1 RNA levels was performed, stratified by CD4 T-lymphocyte count and sex. There were no statistically significant sex differences in disease progression within any of the HIV-1 RNA or CD4 lymphocyte count strata (data not shown).

Among persons starting HAART, the proportion who switched to a second HAART regimen during follow-up was 53% among those with ≤ 200 CD4 T lymphocytes/l, 59% of those with 201-350 × 10⁶ CD4 T lymphocytes/l, and 53% of those with > 350 × 10⁶ CD4 T lymphocytes/l prior to starting therapy. The proportions switching to a third HAART regimen were 9, 7, and 2%, respectively.

Discussion

This study demonstrated that over an average of 22 months of follow-up, CD4 T lymphocyte counts were better than HIV-1 RNA levels in predicting which patients would derive clinical benefit from HAART. At ≤ 200 × 10⁶ CD4 T lymphocytes/l, HAART was associated with a lower rate of disease progression than non-HAART regimens. For CD4 T-lymphocyte counts of 201-350 × 10⁶/l and > 350 × 10⁶/l prior to initiating HAART, there was no significant difference in disease progression associated with HAART. This is consistent with recent studies in which the risk of death was increased only among persons who initiated HAART at < 200 × 10⁶ CD4 lymphocytes/l ^[13], and in which there was no difference in disease progression among persons receiving HAART versus dual nucleoside regimens ^[14].

In persons who received HAART, we did not detect an association between HIV-1 RNA level prior to initiating HAART and subsequent disease progression. This lack of an association was noted for three HIV-1 RNA cutoffs in current treatment guidelines. This contrasts with data from the pre-HAART era, in which baseline HIV-1 RNA level prior to therapy predicted disease progression in patients who received no treatment or nucleoside analogue therapy only ^[15,16]. This finding is consistent with a recent study from British Columbia in which HIV-1 RNA level prior to initiating HAART did not predict subsequent mortality ^[13] and another study conducted prior to widespread use of HAART in which CD4 T-lymphocyte counts were a better predictor of survival than HIV-1 RNA level ^[17]. This study extends those preliminary findings, however, by directly comparing patients who received HAART to those who did not, and by comparing the development of new AIDS-defining diagnoses and death rather than death alone. Interestingly, although clinical disease progression on HAART does not appear to be predicted by HIV-1 RNA level, the likelihood of virologic suppression on HAART is greater at lower HIV-1 RNA levels ^[18,19]. It is therefore possible that patients followed longer than the average duration of 22 months in this study might exhibit differences in disease progression based on HIV-1 RNA level prior to starting HAART.

There are at least two possible explanations for the lack of demonstrated benefit of HAART on disease progression among persons with > 200 × 10⁶ CD4 T lymphocytes/l prior to initiating HAART. First, there were relatively few events among persons in this category. Thus, the analysis may not have detected small differences between HAART and non-HAART users. Similar results with a larger sample size would give greater confidence that HAART indeed does not significantly affect disease progression at these CD4 T-lymphocyte counts. In the absence of larger sample size, however, it is striking that our results are so similar to those found in other cohorts ^[13,20]. Second, although the mean duration of follow-up of both HAART and non-HAART users was almost 2 years, longer follow-up may be necessary to adequately assess for differences in disease progression. The duration of follow-up was shorter and loss to follow-up greater among non-HAART than HAART users. It is unclear, however, whether these differences were large enough to result in differences in ascertaining clinical endpoints. We previously noted that persons with > 200 × 10⁶ CD4 T lymphocytes/l tended to be more likely to achieve durable viral suppression on HAART than persons with ≤ 200 × 10⁶ CD4 T lymphocytes/l ^[19]. This suggests that a difference in disease progression among patients with > 200 × 10⁶ CD4 T lymphocytes/l may eventually be seen with longer follow-up.

Among persons with ≤ 200 × 10⁶ CD4 T lymphocytes/l, patients in all three HIV-1 RNA strata assessed had an increased risk of clinical disease progression compared to those with > 350 × 10⁶ CD4 T lymphocytes/l and < 5000 HIV-1 RNA copies/ml. As CD4 T lymphocyte count ≤ 200 × 10⁶/l was such a strong predictor of disease progression in this study, HIV-1 RNA level among persons with low CD4 T lymphocyte counts probably does not provide substantially more prognostic information.

Data from the Multicenter AIDS Cohort Study demonstrated that HIV-1 RNA level is significantly associated with HIV disease progression independently of CD4 T-lymphocyte count ^[21,22]. These studies assessed the natural history of HIV disease progression in patients who had no or minimal antiretroviral therapy. Higher HIV-1 RNA level was associated with a more rapid decline in CD4 T-lymphocyte counts ^[22]. Even if CD4 T-lymphocyte counts alone are used to determine when to initiate HAART, HIV-1 RNA level should not be ignored. Patients with a high HIV-1 RNA will need to have their CD4 T-lymphocyte count measured frequently to determine when the CD4 count has reached the treatment threshold.

Of note, most of the patients on HAART changed to a second HAART regimen during the mean 22 months of follow-up. It has been shown that a second HAART regimen is not as effective in suppressing HIV-1 RNA as the initial regimen ^[23]. If patients fail their initial HAART regimen when they are at relatively low risk of symptomatic disease, only alternative, less effective regimens will be available at more advanced stages of immunosuppression, when patients are at higher risk of symptomatic clinical disease.

Finally, this study demonstrates that men and women in the same HIV-1 RNA and CD4 lymphocyte count strata have the same risk of disease progression on therapy. This is consistent with previous studies demonstrating no sex difference in disease progression, particularly when access to care is equal ^[24-27].

In this study, patients with ≤ 200 × 10⁶ CD4 T lymphocytes/l clearly derived clinical benefit from HAART, but the impact of HAART on disease progression was less clear among patients with > 200 × 10⁶ CD4 T lymphocytes/l prior to initiating HAART. Our data suggest that current guidelines for initiating HAART should place greater emphasis on CD4 lymphocyte count than on HIV-1 RNA level for both men and women. Further longitudinal follow-up will be needed to better ascertain whether HAART initiated at a > 200 × 10⁶ CD4 T lymphocytes/l is effective in slowing HIV disease progression.

Acknowledgements

The authors thank J. Keruly for assistance with management of the Johns Hopkins HIV Clinic database.