Predictive value of viral load measurements in asymptomatic untreated HIV-1 infection: a mathematical model

CD25+ FoxP3+ Memory CD4 T Cells Are Frequent Targets of HIV Infection In Vivo

Interleukin 2 (IL-2) signaling through the IL-2 receptor alpha chain (CD25) facilitates HIV replication in vitro and facilitates homeostatic proliferation of CD25(+) FoxP3(+) CD4(+) T cells. CD25(+) FoxP3(+) CD4(+) T cells may therefore constitute a suitable subset for HIV infection and plasma virion production. CD25(+) FoxP3(+) CD4(+) T cell frequencies, absolute numbers, and the expression of CCR5 and cell cycle marker Ki67 were studied in peripheral blood from HIV(+) and HIV(-) study volunteers. Different memory CD4(+) T cell subsets were then sorted for quantification of cell-associated HIV DNA and phylogenetic analyses of the highly variable EnvV1V3 region in comparison to plasma-derived virus sequences. In HIV(+) subjects, 51% (median) of CD25(+) FoxP3(+) CD4(+) T cells expressed the HIV coreceptor CCR5. Very high frequencies of Ki67(+) cells were detected in CD25(+) FoxP3(+) memory CD4(+) T cells (median, 27.6%) in comparison to CD25(-) FoxP3(-) memory CD4(+) T cells (median, 4.1%; P < 0.0001). HIV DNA content was 15-fold higher in CD25(+) FoxP3(+) memory CD4(+) T cells than in CD25(-) FoxP3(-) T cells (P = 0.003). EnvV1V3 sequences derived from CD25(+) FoxP3(+) memory CD4(+) T cells did not preferentially cluster with plasma-derived sequences. Quasi-identical cell-plasma sequence pairs were rare, and their proportion decreased with the estimated HIV infection duration. These data suggest that specific cellular characteristics of CD25(+) FoxP3(+) memory CD4(+) T cells might facilitate efficient HIV infection in vivo and passage of HIV DNA to cell progeny in the absence of active viral replication. The contribution of this cell population to plasma virion production remains unclear.

IMPORTANCE

Despite recent advances in the understanding of AIDS virus pathogenesis, which cell subsets support HIV infection and replication in vivo is incompletely understood. In vitro, the IL-2 signaling pathway and IL-2-dependent cell cycle induction are essential for HIV infection of stimulated T cells. CD25(+) FoxP3(+) memory CD4 T cells, often referred to as regulatory CD4 T cells, depend on IL-2 signaling for homeostatic proliferation in vivo Our results show that CD25(+) FoxP3(+) memory CD4(+) T cells often express the HIV coreceptor CCR5, are significantly more proliferative, and contain more HIV DNA than CD25(-) FoxP3(-) memory CD4 T cell subsets. The specific cellular characteristics of CD25(+) FoxP3(+) memory CD4(+) T cells probably facilitate efficient HIV infection in vivo and passage of HIV DNA to cell progeny in the absence of active viral replication. However, the contribution of this cell subset to plasma viremia remains unclear.

Cost-effectiveness of screening for HIV in the era of highly active antiretroviral therapy

BACKGROUND

The costs, benefits, and cost-effectiveness of screening for human immunodeficiency virus (HIV) in health care settings during the era of highly active antiretroviral therapy (HAART) have not been determined.

METHODS

We developed a Markov model of costs, quality of life, and survival associated with an HIV-screening program as compared with current practice. In both strategies, symptomatic patients were identified through symptom-based case finding. Identified patients started treatment when their CD4 count dropped to 350 cells per cubic millimeter. Disease progression was defined on the basis of CD4 levels and viral load. The likelihood of sexual transmission was based on viral load, knowledge of HIV status, and efficacy of counseling.

RESULTS

Given a 1 percent prevalence of unidentified HIV infection, screening increased life expectancy by 5.48 days, or 4.70 quality-adjusted days, at an estimated cost of 194 dollars per screened patient, for a cost-effectiveness ratio of 15,078 dollars per quality-adjusted life-year. Screening cost less than 50,000 dollars per quality-adjusted life-year if the prevalence of unidentified HIV infection exceeded 0.05 percent. Excluding HIV transmission, the cost-effectiveness of screening was 41,736 dollars per quality-adjusted life-year. Screening every five years, as compared with a one-time screening program, cost 57,138 dollars per quality-adjusted life-year, but was more attractive in settings with a high incidence of infection. Our results were sensitive to the efficacy of behavior modification, the benefit of early identification and therapy, and the prevalence and incidence of HIV infection.

CONCLUSIONS

The cost-effectiveness of routine HIV screening in health care settings, even in relatively low-prevalence populations, is similar to that of commonly accepted interventions, and such programs should be expanded.

AIDS vaccines that allow HIV-1 to infect and escape immunologic control: a mathematic analysis of mass vaccination

Cytotoxic T lymphocyte (CTL)-based HIV vaccine concepts shown to reduce viremia and postpone disease but not to prevent infection in monkeys are currently in human phase 1 trials. To evaluate the potential efficacy of vaccines that cannot prevent HIV-1 to infect and escape immunologic control, we designed a mathematic model that correlates the level of viremia to both infectiousness and disease progression. We speculate that vaccinees will have a virologic set point and disease progression rates comparable to untreated HIV-1-infected individuals with the best prognosis. Our model (illustrated with R0 = 3) shows that a sexually active population can ultimately be reduced to 26% of its initial size as a result of AIDS-related mortality in the absence of treatment or vaccination. Start of vaccination when HIV-1 prevalence is still low might postpone the peak incidence of infection and the dramatic decline in population size by up to 22 years. In conclusion, CTL-based vaccines that do not prevent HIV-1 infection but do postpone the time to onset of AIDS have considerable potential to curb the spread of HIV-1 and to postpone high AIDS-related mortality on a population level. The number of long-term survivors is substantially increased only when vaccination is initiated early in an AIDS epidemic, however.

Long-term methadone treatment: effect on CD4+ lymphocyte counts and HIV-1 plasma RNA level in patients with HIV infection

The objective was to examine the effect of methadone on CD4+ lymphocyte counts and viral load and to expect to document the safety of methadone maintenance in patients with human immune deficiency syndrome. This is a retrospective chart analysis comparing the trends in CD4+ count and viral load in two populations of 21 human immunodeficiency virus (HIV) infected patients, one on methadone maintenance and a methadone non-using group. Each methadone user was matched with a control methadone non-user that had a similar CD4+ at the beginning of the study. For the CD4+ count we compared the slope of regression for each couple of patients. In 15 patients we also collected the viral load, which was measured at 4-6 monthly intervals. The mean length of follow-up was 811 days for the methadone group and 797 days in the control group. There was no statistical difference in the treatment received by the two groups of patients during the study. The slope of regression of CD4+ count showed a significantly steeper decline in the methadone-using patients compared with the methadone non-users (r= 0.487; p< 0.05). The evolution of the HIV-1 RNA levels was the same during the follow-up of mean 186 months in a few of the patients in each of the two groups. Long-term methadone use was associated with a significantly faster decrease of CD4+ count in HIV-1 affected patients compared with methadone non-users. HIV-1 RNA data were found in too few patients to enable any conclusions about the development of viral load in the two groups.

Antibody masking renders HIV-1 resistant to cationic membrane filtration through alteration of its electrostatic characteristics

Previously, it was demonstrated that any human immunodeficiency virus type 1 (HIV-1) strain proliferating in peripheral blood mononuclear cells (PBMCs) in vitro, and resuspended in seronegative plasma, could be captured efficiently (mean > 95%) by a porous polypropylene (PP) membrane modified cationically. We investigated if this cationic membrane could capture HIV-1 obtained from seropositive plasma, and confirmed whether this membrane was effective for the preparation of safe plasma products against HIV-1 transmission. Thirty-six seropositive plasma samples derived from HIV-1 positive cohorts in New York and Lusaka (Republic of Zambia), including 18 cases of acquired immunodeficiency syndrome (AIDS) related complex, AIDS and five terminal cases of AIDS, were filtered through the cationic membrane to determine the reduction of RNA concentration, the gag p24 concentration, and infectious titer. Only a small reduction in RNA concentration (mean < 20%) and almost no decrease in gag concentration (mean < 2%) were obtained, despite the fact that the infectivity was eliminated entirely by the filtration. Due to the possibility that anti-HIV-1 antibodies in patients' plasma combine with HIV-1, laboratory-adapted HIV-1(HTLV-IIIB) was mixed with seropositive plasma to test the effect of antibodies on HIV-1 adsorption, and also to investigate the interfacial electrokinetic potential (zeta-potential) of both intact and plasma-treated HIV-1. The zeta-potential of HIV-1(HTLV-IIIB) in the presence of seropositive plasma was neutral as opposed to negative when stored in seronegative plasma or culture medium. Also the rate of HIV-1 capture by the membrane, as determined by the reduction in RNA concentration, sank from 95% to 20%, the same capture percentage observed when filtering plasma of patients. These findings suggested that in patients' plasma, the antibody-masked HIV-1 comprise most of the viral population, and was not trapped on the cationic membrane because of its electrostatic character. Conversely, the cationic membrane was thought to adsorb antibody-free HIV-1 exclusively. It was suggested that each viral swarm had its own zeta-potential, and this difference in electrostatic character determined the extent of the viral adsorption by the cationic membrane.

Quantitation of bacteria in bone marrow from patients with typhoid fever: relationship between counts and clinical features

Enteric fever is the only bacterial infection of humans for which bone marrow examination is routinely recommended. A prospective study of the concentrations of bacteria in the bone marrow and their relationship to clinical features was conducted with 120 Vietnamese patients with suspected enteric fever, of whom 89 had confirmed typhoid fever. Ninety-three percent of the Salmonella enterica serovar Typhi samples isolated were resistant to ampicillin, chloramphenicol, and co-trimoxazole. For 81 patients with uncomplicated typhoid and satisfactory bone marrow aspirates, the number of serovar Typhi CFU in bone marrow aspirates was a median value of 9 (interquartile range [IQR], 1 to 85; range, 0.1 to 1,580) compared to 0.3 (IQR, 0.1 to 10; range, 0.1 to 399) CFU/ml in simultaneously sampled blood. The ratio of individual blood counts to bone marrow counts was 10 (IQR, 2.3 to 97.5). The number of bacteria in blood but not bone marrow was correlated inversely with the duration of preceding fever. Thus, with increasing duration of illness the ratio of bone marrow-to-blood bacterial concentrations increased; the median ratio was 4.8 (IQR, 1 to 27.5) during the first week compared with 158 (IQR, 60 to 397) during the third week. After lysing the host cells, the median ratio of viable bone marrow to blood increased, reflecting the higher concentration of intracellular serovar Typhi in the bone marrow. Effective antibiotic pretreatment had a significantly greater effect in reducing blood counts compared to bone marrow counts (P < 0.001). Thus, bacteria in the bone marrow of typhoid patients are less affected by antibiotic treatment than bacteria in the blood. The numbers of bacteria in bone marrow correlated negatively with the white blood cell (R = -0.3, P = 0.006) and platelet counts (R = -0.32, P = 0.01) and positively with fever clearance time after treatment (R = 0.4, P < 0.001). The bacterial load in bone marrow therefore may reflect the clinical course of the infection, and high levels may suppress neutrophil proliferation.

Clinical progression of HIV-1 infection according to the viral response during the first year of antiretroviral treatment. Groupe d'Epidémiologie du SIDA en Aquitaine (GECSA)

OBJECTIVE

To compare HIV-disease progression according to changes of plasma HIV RNA observed in the year following initiation of a new antiretroviral treatment.

DESIGN

Prospective cohort treated with two nucleoside analogues or a triple combination including a protease inhibitor.

METHODS

A Cox model was used to estimate the effect of viral response during the first year after initiation of treatment on the subsequent occurrence of new AIDS-defining events or death. Viral response was fitted either as HIV RNA reduction during the initial 4-12 months of treatment or reduction during the first month.

RESULTS

Among 773 patients (47% with triple drug combination) followed for a median period of 27 months, 62 patients experienced a clinical event. Poor viral responders (at least two measurements > 3.7 log10 copies/ml during 4-12 months of treatment) had a higher risk of disease progression than good responders (RNA < 2.7 log10 copies/ml) after adjustment [hazard ratio (HR), 2.24; 95% confidence interval (CI), 1.1 7-4.29]. Intermediate responders (2.7 < or = RNA < or = 3.7 log10 copies/ml) had a risk of progression comparable with that of good responders (HR, 1.43; 95% CI, 0.64-3.22). A large initial viral reduction was also a protective factor for clinical progression (HR, 0.51 for 1 log10 copies/ml increase of the reduction; 95% CI, 0.31-0.85) and was associated with the viral response during the subsequent 4-12 month period. No patient with a reduction < 0.5 log10 copies/ml in the first month was classified as a good responder in the subsequent 4-12 month period (P < 0.01).

CONCLUSIONS

A sustained HIV RNA > 3.7 log10 copies/ml should suggest a prompt change of treatment. When the reduction in HIV RNA is < 0.5 log10 after 1 month of treatment, this action should be anticipated. A sustained HIV RNA level between 2.7 and 3.7 log10 copies/ml may permit the deferral of a change of drug regimen according to the patient's history and therapeutic options.

Anti-HIV-1 activity of an ionically modified porous polypropylene membrane determined by filtration of a viral suspension

We describe here a unique anti-HIV-1 membrane, derived from a chemically modified porous polypropylene (PP) membrane, which lowers viral infectivity upon the filtration of HIV-1 suspension. A cationic polymer, polyethyleneimine (PEI) was graft-polymerized onto the PP filter membrane (PP-PEI), and infectious HIV-1(HTLV-IIIB) derived from MOLT-4/HIV-1(HTLV-IIIB) cells (HIV-1(HTLV-IIIB(MOLT-4)) was applied. When a viral suspension of high titer (10(3.93) TCID50 ml(-1) was filtered, efficient reduction (>99%) of gag p24 antigen levels and infectious titer resulted. In a viral suspension of medium titer (10(2.37) TCID50 ml(-1), a significant decrease in the p24 antigen did not occur, although the titer was markedly reduced (>95%). Electron microscopic observation suggested that PEI induced viral aggregations under high titer conditions, and under medium titer conditions, PEI deprived HIV-1(HTLV-IIIB(MOLT-4)) of its infectivity alone to avoid virus adsorption. In contrast, HIV-1 propagated in human peripheral blood mononuclear cells (PBMC) such as HIV-1(HTLV-III(PBMC)) was more efficiently trapped by PP-PEI at lower titers as compared with HIV-1(HTLV-IIIB(MOLT-4)) from MOLT-4/HIV-1(HTLV-IIIB) cells. These data suggest host cell modification in the interactions between PP-PEI and HIV-1 strains. Since HIV-1(HTLV-IIIB(MOLT-4)) and HIV-1(HTLV-IIIB(PBMC)) were almost electrically neutral and negative, respectively, we concluded that the divergent effect of PEI on each HIV-1(HTLV-IIIB) resulted from their different electrical characteristics.

Some state space models of HIV pathogenesis under treatment by anti-viral drugs in HIV-infected individuals

In this paper we have extended the model of HIV pathogenesis under treatment by anti-viral drugs given by Perelson et al. [A.S. Perelson et al., Science 271 (1999) 1582] to a stochastic model. By using this stochastic model as the stochastic system model, we have developed a state space model for the HIV pathogenesis under treatment by anti-viral drugs. In this state space model, the observation model is a statistical model based on the observed numbers of RNA virus copies over different times. For this model we have developed procedures for estimating and predicting the numbers of infectious free HIV and non-infectious free HIV as well as the numbers of different types of T cells through extended Kalman filter method. As an illustration, we have applied the method of this paper to the data of patient Nos. 104, 105 and 107 given by Perelson et al. [A.S. Perelson et al., Science 271 (1999) 1582] under treatment by Ritonavir. For these individuals, it is shown that within two weeks since treatment, most of the free HIV are non-infectious, indicating the usefulness of the treatment. Furthermore, the Kalman filter method revealed a much stronger effect of the treatment within the first 10 to 20 h than that predicted by the deterministic model.

Comparison of viral load and human leukocyte antigen statistical and neural network predictive models for the rate of HIV-1 disease progression across two cohorts of homosexual men

We compared the performance of HIV-1 RNA and models based on human leukocyte antigen (HLA) in predicting the rate of HIV-1 disease progression using both linear regression and neural network models across two different cohorts of homosexual men. In all, 139 seroconverters from the Multicenter AIDS Cohort Study were used as the training set and 97 seroconverters from the District of Columbia Gay (DCG) cohort were used for validation to assess the generalizability of trained predictive models. Both viral load and HLA markers were strongly predictive of disease progression (p < .0001 and p = .001, respectively), with viral load superior to HLA (change in -2 log likelihood [-2LL] 26.7 and 10.2, respectively, in proportional hazards models). Consideration of both HLA markers and viral load offered no significant predictive advantage over viral load alone in most cases; however, HLA-based predictions obtained from neural networks modeling improved the discrimination among patients with high viral load (p = .02). Viral load, HLA scores, and rapid disease progression were moderately correlated (p < .01 for all three pairs of these variables). The median viral load was 10(3.70) copies/ml among DCG patients who had more favorable than unfavorable HLA markers and 10(4.66) copies/ml among patients with more unfavorable than favorable HLA markers. Viral load is a simpler, stronger predictor of disease progression than early developed HLA models, but neural network methods and further refined HLA models may offer additional prognostic information, especially for rapid progressors. The correlation between viral load and HLA markers suggests a possible HLA effect on setting viral load levels.

Stressful events, pessimism, natural killer cell cytotoxicity, and cytotoxic/suppressor T cells in HIV+ black women at risk for cervical cancer

OBJECTIVE

This study examines whether stressful negative life events and pessimism were associated with lower natural killer cell cytotoxicity (NKCC) and T cytotoxic/suppressor cell (CD8+CD3+) percentage in black women co-infected with human immunodeficiency virus Type 1 (HIV-1) and human papillomavirus (HPV), a viral initiator of cervical cancer.

METHOD

Psychosocial interviews, immunological evaluations, and cervical swabs for HPV detection and subtyping were conducted on 36 HIV+ African-American, Haitian, and Caribbean women.

RESULTS

Greater pessimism was related to lower NKCC and cytotoxic/suppressor cells after controlling for presence/absence of HPV Types 16 or 18, behavioral/lifestyle factors, and subjective impact of negative life events.

CONCLUSIONS

A pessimistic attitude may be associated with immune decrements, and possibly poorer control over HPV infection and increased risk for future promotion of cervical dysplasia to invasive cervical cancer in HIV+ minority women co-infected with HPV.

Predictive factors influencing peak viral load drop in response to nucleoside reverse transcriptase inhibitors in antiretroviral-naive HIV-1-infected patients

Therapy with two nucleoside reverse transcriptase inhibitors (NRTI), the backbone of triple combinations, is still widely used in early stages of HIV-1 disease. However, factors influencing virologic response need to be further analyzed, to test the hypothesis that the reduction of plasma RNA viremia with NRTI may be greater in patients with higher baseline viral load (BVL) and to analyze the predictive factors of viral load drop below detection (200 HIV RNA copies/ml of plasma). Selected for the study were 169 HIV-1-infected antiretroviral therapy-naive patients with CD4+ T-lymphocyte counts ranging from 6 to 1040/microl coming from three randomized studies comparing the efficacy of monotherapy (zidovudine [ZDV], 250 mg every 12 hours; N=40) versus two-drug therapy consisting of ZDV (250 mg every 12 hours) with dideoxycytidine (ddC, 0.75 mg every 8 hours) or didanosine (ddI, 200 mg every 12 hours; N=129). Viral load was measured at 1, 3, and 6 months by polymerase chain reaction (PCR). A linear regression model was used to analyze the relation between BVL and the peak reduction of plasma RNA viremia. The variables included in a logistic regression model to determine the likelihood of VLs dropping below detection levels were age, gender, risk group for HIV-1 infection, baseline CD4+ lymphocyte count, BVL, clinical status (AIDS versus non-AIDS), HIV-1 phenotype (syncytium-inducing [SI] versus non-syncytium-inducing [NSI]) and type of treatment (monotherapy versus double therapy). The peak reduction of VL was related to baseline level following a linear model in both monotherapy and double-therapy regimens. In the subgroup of patients treated with two NRTIs, the regression line that fitted best with the data was log10 (peak reduction)=1.8-0.36 log10 (BVL) (F=23.5; p < .0001). This indicates that for every increase of 1 log10 of BVL, the peak reduction would be of 0.64 log10 greater. Forty-nine (29%) of the 169 patients dropped to <200 copies/ml. The likelihood of dropping below detection level was significantly greater in those receiving double therapy versus monotherapy (odds ratio [OR]=16.1; 95% confidence interval [CI], 2-128), in those with baseline CD4+ lymphocyte count >350/microl (OR=2.28; 95% CI, 1.1-4.9) and in those with BVL <10,000 HIV-1 RNA copies/ml (OR= 2.25; 95% CI, 1.1-6.1). None of the 13 patients with an SI phenotype at baseline dropped below detection levels. The reduction of VL in response to two NRTIs was greater in those patients with a higher level of BVL. In conclusion, peak reduction below detection in response to NRTI can be predicted and is associated with double therapy, with a baseline CD4+ cell count >350/microl and with a BVL <10,000 RNA copies/ml.

Are there clinical and laboratory predictors of 5-year mortality in HIV-infected children and adolescents with hemophilia?

To determine factors associated with survival in a cohort of HIV-infected children and adolescents with hemophilia, an analysis of the 5-year mortality data for 207 HIV-infected young men was performed to examine the effect of selected clinical covariates on survival. The subjects were enrolled into the Hemophilia Growth and Development Study cohort from 1989 to 1990. Estimated mean time since infection at baseline was 6.7 years and mean estimated age at infection was 6.5 years. The baseline characteristics examined for their association with the hazard of death over the 5-year follow-up period were the following: absolute CD4+ cell count, hemoglobin status, skin test anergy, results of brain magnetic resonance imaging, non-hemophilia-related muscle atrophy (NHRMA), height for age, and impaired neuropsychological functioning as measured by the Vineland Adaptive Behavior and the Pediatric Behavior Scales. In all, 66 deaths occurred over the 5-year follow-up, 62 of whom met the 1987 (n = 56) or 1993 (n = 6) U.S. Centers for Disease Control and Prevention (CDC) definition of AIDS. Although each of the characteristics listed previously significantly increased the hazard of death by Cox proportional hazard regression models, only NHRMA remained a significant predictor of AIDS-related death when added to models that included each of the other cited baseline covariates.

Maternal cell-free viremia in the natural history of perinatal HIV-1 transmission: a meta-analysis

We performed a meta-analysis of the predictive value of maternal cell-free viral load in vertical HIV-1 transmission, including 9 cohorts with 1115 mother-infant pairs (696 untreated and 419 treated women). The pooled rate of transmission in untreated women was 21.3% (95% confidence interval [CI], 18.3%-24.5%). The rates of transmission for untreated women in the <1000 copies/ml, 1000 to 9999 copies/ml, and > or = 10,000 copies/ml categories were 5% (95% CI, 2%-11%), 15% (95% CI, 11%-20%) and 37% (95% CI, 29%-46% by random effects), respectively. The area under the receiver operating characteristic (ROC) curve in individual studies ranged from 0.67 to 1.00. The predictive performance of RNA differed between cohorts in which different percentages of transmitters had RNA values >10,000 copies/ml. When 95% of transmitters have RNA values >1000 copies/ml, 77% of nontransmitters would also have values above this cutoff. Transmission rates for treated women in the 1000 to 9999 copies/ml category (7%; 95% CI, 4%-11%,) and > or = 10,000 copies/ml category (18%; 95% CI, 12%-27%) were probably lower than those for untreated women, whereas the transmission rate for treated women with <1000 copies/ml was 5% (95% CI, 2%-11 %). Thus, the risk gradient between RNA categories seems attenuated in treated women. Several aspects of the design, analysis, and reporting of research in this area may be improved in the future with attention to selection and observer biases, multivariate adjustment, and technical consistency. Maternal HIV-1 RNA is a modest predictor of transmission for individual mothers, but a strong predictor of the average risk in groups of untreated mothers. Its discriminatory power is better in untreated than in treated populations and is better in cohorts with a high prevalence of elevated viral load values than in cohorts with generally low levels of viremia.

The decline in CD4+ T lymphocytes as a function of the duration of HIV infection, age at seroconversion, and viral load

BACKGROUND

The rate of CD4+ T-lymphocyte decline seen in HIV-infected patients is very variable. Although older patients, a longer duration of HIV infection, and a high level of plasma viraemia, have been associated with a faster fall in CD4+ T-cells, the relationship between these variables is still not well known.

PATIENTS AND METHODS

In a cross-sectional study that included a total of 107 patients of known age and date at HIV seroconversion, the current CD4+ T-cell count and plasma viraemia were examined. Patients were not taking antiretroviral drugs, nor had received immunizations nor were suffering any intercurrent infections at the time of the study.

RESULTS

The mean duration of HIV infection was 8.6+/-2.9 years. The mean CD4+ T-lymphocyte count was 367+/-264 x 10(6)/l. Mean plasma viraemia was 4.3+/-0.9 logs. In a linear regression model, the current CD4+ T-cell count was explained in 21.7% by the duration of HIV infection, while the level of plasma viraemia justified separately up to 37.0%. When both parameters were combined, they explained 58.8%. of the CD4+ lymphocyte values. In this model, a variation of one logarithm in the plasma viraemia had six times greater effect on the number of CD4+ lymphocytes than each year of HIV infection. When the age at seroconversion was added to the model, the CD4+ cell count allowed the explanation of up to 62.2% of cases.

CONCLUSIONS

The age at seroconversion, the duration of HIV infection, and the level of plasma viraemia independently and substantially influence the current CD4+ lymphocyte count in HIV-infected subjects. However, other variables should exist (e.g. virus syncytium-inducing phenotype, host immunogenetic repertoire, etc.), contributing to explaining the different rate of CD4+ T-cell decline seen in HIV-infected subjects.

Stochastic modeling of the dynamics of CD4+ T-cell infection by HIV and some Monte Carlo studies

In this paper, we develop a stochastic model for the interaction between CD4+ T cells and the human immunodeficiency virus (HIV) virus by taking into account the basic biological mechanism as described in [1-4]. We studied this stochastic model through extensive Monte Carlo simulations. Our results show that, in some cases, there is a positive probability that the virus will be eliminated by the process. We have also shown that, at the earlier stage of the infection, the probability distributions of the CD4+ T cells and free HIV are skewed; however, these distributions will eventually converge to the Gaussian distributions after several years. A real-data example is given to illustrate the application of our model.

Quantification of human immunodeficiency virus type 1 RNA from dried plasma spots collected on filter paper

To assess dried plasma spots (DPSs) as a source of material for virus quantification, human immunodeficiency virus type 1 (HIV-1) RNA levels were quantified in matched DPS and liquid plasma samples from 73 infected patients, including 5 neonates and 4 adult patients with acute HIV-1 infection. Quantifications were performed by commercially available assays (NASBA [nucleic acid sequence-based amplification] or Amplicor, or both). There was a strong correlation between HIV-1 RNA levels in plasma and DPSs. More importantly, there was no decline in HIV-1 RNA levels in DPSs stored for as long as 2 weeks at 20 degrees C. Similarly, storage of DPSs for 3 days at 37 degrees C resulted in no decrease in viral RNA levels. For patients with primary infection, the DPS method allowed for the measurement of RNA levels in plasma during the initial spike in the level of viremia and in the subsequent period of suppressed viral replication. DPS quantification was equally informative in the neonatal setting, with all five newborns showing HIV-1 RNA loads of greater than 4.991 log10 copies/ml. We conclude that the viral RNA levels in DPSs are equivalent to those measured in fresh-frozen plasma. The ease and economy of DPS sampling, the minute volumes required, and the unexpected stability of dried RNA suggest that the use of DPSs will be particularly valuable for small-volume neonatal samples and large, population-based studies in which cold storage and transportation present special problems, as is often the case in developing countries. The ability to measure viral changes during primary infection suggests that the method will be useful for assessing vaccine efficacy in large field trials.

The impact of high-risk patients on the results of clinical trials

The results of clinical trials may not reflect equally the experiences of all their individual participants. By modeling populations where patients have very diverse baseline risks of suffering an event of interest, it can be seen that very sick patients of high risk become the major determinants of how many events occur in the whole population, even though they may represent only a small minority. Human immunodeficiency virus-related trials and trials of magnesium in acute myocardial infarction are analyzed. When the benefit or toxicity from a treatment varies with the baseline risk of each patient, the treatment effect may be markedly different in populations with a different representation of high- and low-risk patients. The results of small clinical trials studying heterogeneous populations with binary outcomes depend on the sampling and outcomes of very few high risk participants. Conversely, mega-trials studying homogeneous populations would miss subgroups or individuals with diverse treatment responses. In both cases, aggregate trial results may be misleading for the care of many individuals.

Prospective longitudinal analysis of viral load and surrogate markers in relation to clinical progression in HIV type 1-infected persons

The temporal relationship between viral and surrogate markers and clinical status was analyzed prospectively every 8 weeks in 34 asymptomatic HIV-1-infected persons. After 3 years, 25 persons remained clinically healthy whereas 9 persons showed clinical progression. In accordance with other reports we found that at study entry HIV-RNA load was predictive of clinical progression. All markers tested evolved significantly in time in both progressors and nonprogressors. The HIV RNA load in plasma and HIV DNA load in T cells were linearly related only in nonprogressors. In addition, the RNA/DNA ratio during follow-up was significantly higher in progressors, indicating a higher replication rate in progressors. The HIV DNA load correlated inversely with CD4+ T cell counts and positively with p24 antigenemia in both nonprogressors and progressors. A significant correlation of HIV DNA load with SI phenotype occurred in progressors only. HIV RNA levels correlated with beta 2-microglobulin level and with p24 antigenemia but not with SI phenotype. These three markers can all routinely be measured in plasma; however, only the HIV RNA levels appear to be informative for clinical progression. Six to 8 months before clinical progression, an SI phenotype switch, increased HIV RNA in plasma, and decreased CD4+ T cell counts were all indicative of an impending clinical event.

Detection of low HIV-1 RNA levels in plasma

HIV-1 viremia is a marker of choice for staging, prognosis, and monitoring treatment efficiency in HIV infection. Among the commercial assays, the Amplicor HIV Monitor (Roche, Basel, Switzerland) test has the highest sensitivity for HIV-1 RNA quantitation in plasma with a detection limit of 200 copies per milliliter. To measure HIV-1 viremia below this threshold, boosted versions of the Amplicor assay were developed by adding a centrifugation step prior to RNA extraction and by decreasing dilution factors. In the boosted version, the increase in analytical sensitivity for HIV-1 RNA detection directly correlates with the input of plasma. For 1,500 microl of plasma, the sensitivity of the assay increases by a factor of 30. For routine clinical analysis, we use a boosted assay format with an input plasma volume of 500 microl and a lower detection limit of 20 copies/milliliter. Coefficients of intra- and interassay variation are similar to those reported for the standard assay (approximately 30%). Thirteen (45%) of 29 plasma samples of HIV-infected individuals with undetectable viremia in the standard assay had detectable viremia between 20 and 200 copies/milliliter.

Viral load in asymptomatic patients with CD4+ lymphocyte counts above 500 x 10(6)/l

BACKGROUND

HIV-1-infected patients with a CD4+ lymphocyte count > or = 500 x 10(6)/l may be selected for antiretroviral treatment when viral load is above a given cut-off point.

OBJECTIVES

To assess the stability of viral load measurement at CD4+ T-cell counts above 500 x 10(6)/l, and the proportion of patients selected for treatment if a cut-off point of 10,000 or 30,000 RNA copies/ml is used.

DESIGN AND METHODS

Seventy-eight consecutive asymptomatic antiretroviral-naive HIV-1-infected patients with CD4+ lymphocyte counts > or = 500 x 10(6)/l, presenting for previously scheduled medical visits as outpatients, were enrolled. None of the patients had suffered from symptomatic primary infection or seroconverted within 6 months before enrollment. Two blood samples separated by a 1-month interval [day -30 (screening) and day 0 (enrollment)] were collected in an EDTA tube. Plasma was separated and frozen at -70 degrees C within 4 h of collection. HIV-1 RNA was quantified by polymerase chain reaction. CD4+ T cells were measured by flow cytometry.

RESULTS

Viral load was fairly stable, and only four (13%) out of 30 pairs had a variation > or = 0.5 log10. At day -30 and day 0, log10 HIV RNA levels (mean +/- SD) were 4.24 +/- 0.7 and 4.35 +/- 0.87 log10 copies/ml plasma (P = 0.23). The difference of the mean was -0.11 (95% confidence interval, -0.28 to 0.07). At day 0 (n = 78) mean +/- SD value was 35730 +/- 73700 RNA copies/ml (range, < 200-438480; median, 9331; 25th and 75th percentiles, 1518 and 37193, respectively). In 13 patients (16%) the viral load was < 2000 copies RNA/ml. Seven out of 10 patients, who fulfilled the criteria of long-term non-progressors (LTNP), had viral load > 10,000 RNA copies/ml, and two patients had > 30,000 RNA copies/ml. Only two of the 13 patients with CD4+ T-cell counts > 750 x 10(6)/l had viral load > 10,000 copies/ml.

CONCLUSIONS

A single-point viral load assessment is enough in asymptomatic patients with CD4+ lymphocytes counts > or = 500 x 10(6)/l since plasma HIV RNA measurements obtained 1 month apart are fairly stable. Approximately 25% of these patients (including some patients with LTNP criteria) will be selected for treatment if 30,000 RNA copies/ml is used as cut-off point, and approximately 50% if the cut-off point is 10,000 RNA copies/ml. Viral load > or = 10,000 is very unusual in patients with CD4+ T-cell counts > 750 x 10(6)/l.