Failure of T-cell homeostasis preceding AIDS in HIV-1 infection. The Multicenter AIDS Cohort Study

Late entry to HIV care limits the impact of anti-retroviral therapy in The Netherlands

Objective

To explain differences in survival in the first three years of combination anti-retroviral therapy (cART) between HIV treatment centres in the Netherlands.

Methodology/Principal Findings

We developed a mathematical simulation model, parameterised using data from the ATHENA cohort that describes patients entering care, being monitored and starting cART. Three scenarios were used to represent three treatment centres with widely varying mortality rates on cART that were differentiated by: (i) the distribution of CD4 counts of patients entering care; (ii) the age distribution of patients entering care; (iii) the average rate of monitoring the patients not on cART. At the level of the treatment centre, the fraction of Dutch MSM dying in the first three years of treatment ranged from 0% to 8%. The mathematical model captured the large variation in observed mortality between the three treatment centres. Manipulating the age-distribution of patients or the frequency of monitoring did not affect the model predictions. In contrast, when the same national average distribution of CD4 count at entry was used in all the scenarios, the variation in predicted mortality between all centres was diminished.

Conclusions/Significance

Patients entering care with low CD4 counts appears to be the main source of variation in the mortality rates between Dutch treatment centres. Recruiting HIV-infected individuals to care earlier could lead to substantial improvements in cART outcomes. For example, if patients were to present with at least 400 CD4 cells/mm³, as they do already in some centres, then our model predicts that the mortality in the first three years of cART could be reduced by approximately 20%.

Recreational drug use and T lymphocyte subpopulations in HIV-uninfected and HIV-infected men

The effects of recreational drugs on CD4 and CD8 T cells in humans are not well understood. We conducted a longitudinal analysis of men who have sex with men (MSM) enrolled in the Multicenter AIDS Cohort Study (MACS) to define associations between self-reported use of marijuana, cocaine, poppers and amphetamines, and CD4 and CD8 T cell parameters in both HIV-uninfected and HIV-infected MSM. For the HIV-infected MSM, we used clinical and laboratory data collected semiannually before 1996 to avoid potential effects of antiretroviral treatment. A regression model that allowed random intercepts and slopes as well as autoregressive covariance structure for within subject errors was used. Potential confounders adjusted for included length of follow-up, demographics, tobacco smoking, alcohol use, risky sexual behaviors, history of sexually transmitted infections, and antiviral therapy. We found no clinically meaningful associations between use of marijuana, cocaine, poppers, or amphetamines and CD4 and CD8 T cell counts, percentages, or rates of change in either HIV-uninfected or -infected men. The regression coefficients were of minimum magnitude despite some reaching statistical significance. No threshold effect was detected for frequent (at least weekly) or continuous substance use in the previous year. These results indicate that use of these substances does not adversely affect the numbers and percentages of circulating CD4 or CD8 T cells in either HIV-uninfected or -infected MSM.

The impact of monitoring HIV patients prior to treatment in resource-poor settings: insights from mathematical modelling

BACKGROUND

The roll-out of antiretroviral treatment (ART) in developing countries concentrates on finding patients currently in need, but over time many HIV-infected individuals will be identified who will require treatment in the future. We investigated the potential influence of alternative patient management and ART initiation strategies on the impact of ART programmes in sub-Saharan Africa.

METHODS AND FINDINGS

We developed a stochastic mathematical model representing disease progression, diagnosis, clinical monitoring, and survival in a cohort of 1,000 hypothetical HIV-infected individuals in Africa. If individuals primarily enter ART programmes when symptomatic, the model predicts that only 25% will start treatment and, on average, 6 life-years will be saved per person treated. If individuals are recruited to programmes while still healthy and are frequently monitored, and CD4(+) cell counts are used to help decide when to initiate ART, three times as many are expected to be treated, and average life-years saved among those treated increases to 15. The impact of programmes can be improved further by performing a second CD4(+) cell count when the initial value is close to the threshold for starting treatment, maintaining high patient follow-up rates, and prioritising monitoring the oldest (> or = 35 y) and most immune-suppressed patients (CD4(+) cell count < or = 350). Initiating ART at higher CD4(+) cell counts than WHO recommends leads to more life-years saved, but disproportionately more years spent on ART.

CONCLUSIONS

The overall impact of ART programmes will be limited if rates of diagnosis are low and individuals enter care too late. Frequently monitoring individuals at all stages of HIV infection and using CD4 cell count information to determine when to start treatment can maximise the impact of ART.

The HIV RNA setpoint theory revisited

Background

The evolution of plasma viral load after HIV infection has been described as reaching a setpoint, only to start rising again shortly before AIDS diagnosis. In contrast, CD4 T-cell count is considered to show a stable decrease. However, characteristics of marker evolution over time depend on the scale that is used to visualize trends. In reconsidering the setpoint theory for HIV RNA, we analyzed the evolution of CD4 T-cell count and HIV-1 RNA level from HIV seroconversion to AIDS diagnosis. Follow-up data were used from two cohort studies among homosexual men (N = 400), restricting to the period before highly active antiretroviral therapy became widely available (1984 until 1996). Individual trajectories of both markers were fitted and averaged, both from seroconversion onwards and in the four years preceding AIDS diagnosis, using a bivariate random effects model. Both markers were evaluated on a scale that is directly related to AIDS risk.

Results

Individuals with faster AIDS progression had higher HIV RNA level six months after seroconversion. For CD4 T-cell count, this ordering was less clearly present. However, HIV RNA level and CD4 T-cell count showed qualitatively similar evolution over time after seroconversion, also when stratified by rate of progression to AIDS. In the four years preceding AIDS diagnosis, a non-significant change in HIV RNA increase was seen, whereas a significant biphasic pattern was present for CD4 T-cell decline.

Conclusion

HIV RNA level has more setpoint behaviour than CD4 T-cell count as far as the level shortly after seroconversion is concerned. However, with respect to the, clinically more relevant, marker evolution over time after seroconversion, a setpoint theory holds as much for CD4 T-cell count as for HIV RNA level.

Depletion of CD8+ cells in sooty mangabey monkeys naturally infected with simian immunodeficiency virus reveals limited role for immune control of virus replication in a natural host species

SIV infection of sooty mangabeys (SMs), a natural host species, does not cause AIDS despite high-level virus replication. In contrast, SIV infection of nonnatural hosts such as rhesus macaques (RMs) induces an AIDS-like disease. The depletion of CD8+ T cells during SIV infection of RMs results in marked increases in plasma viremia, suggesting a key role for CD8+ T cells in controlling levels of SIV replication. To assess the role that CD8+ T cells play in determining the virologic and immunologic features of nonpathogenic SIV infection in SMs, we transiently depleted CD8+ T cells in SIV-infected and uninfected SMs using a CD8alpha-specific Ab (OKT8F) previously used in studies of SIV-infected RMs. Treatment of SMs with the OKT8F Ab resulted in the prompt and profound depletion of CD8+ T cells. However, in contrast to CD8+ cell depleted, SIV-infected RMs, only minor changes in the levels of plasma viremia were observed in most SIV-infected SMs during the period of CD8+ cell deficiency. Those SMs demonstrating greater increases in SIV replication following CD8+ cell depletion also displayed higher levels of CD4+ T cell activation and/or evidence of CMV reactivation, suggesting that an expanded target cell pool rather than the absence of CD8+ T cell control may have been primarily responsible for transient increases in viremia. These data indicate that CD8+ T cells exert a limited influence in determining the levels of SIV replication in SMs and provide additional evidence demonstrating that the absence of AIDS in SIV-infected SMs is not due to the effective control of viral replication by cellular immune responses.

Prospective Accuracy for Longitudinal Markers

In this article we focus on appropriate statistical methods for characterizing the prognostic value of a longitudinal clinical marker. Frequently it is possible to obtain repeated measurements. If the measurement has the ability to signify a pending change in the clinical status of a patient then the marker has the potential to guide key medical decisions. Heagerty, Lumley, and Pepe (2000, Biometrics 56, 337-344) proposed characterizing the diagnostic accuracy of a marker measured at baseline by calculating receiver operating characteristic curves for cumulative disease or death incidence by time t. They considered disease status as a function of time, D(t) = 1(T<or=t), for a clinical event time T. In this article we aim to address the question of how well Y(s), a diagnostic marker measured at time s(s>or= 0, after the baseline time) can discriminate between people who become diseased and those who do not in a subsequent time interval [s, t]. We assume the disease status is derived from an observed event time T and thus interest is in individuals who transition from disease free to diseased. We seek methods that also allow the inclusion of prognostic covariates that permit patient-specific decision guidelines when forecasting a future change in health status. Our proposal is to use flexible semiparametric models to characterize the bivariate distribution of the event time and marker values at an arbitrary time s. We illustrate the new methods by analyzing a well-known data set from HIV research, the Multicenter AIDS Cohort Study data.

Idiopathic CD4+ T lymphocytopenia is associated with increases in immature/transitional B cells and serum levels of IL-7

Idiopathic CD4+ T lymphocytopenia (ICL) is a rare heterogeneous disorder defined by CD4+ T-cell counts below 300 cells/muL in the absence of human immunodeficiency virus (HIV) infection or other known immune deficiency disorders. Here, we report the expansion of immature/transitional B cells in patients with ICL, which is associated with elevated serum levels of IL-7. Both the percentage of immature/transitional B cells and levels of IL-7 were inversely correlated with levels of CD4+ T-cell counts and directly correlated to each other. Further analyses of B cells indicated that, in contrast to the activating effects of HIV disease on mature B cells, the expansion of immature/transitional B cells in patients with ICL occurred at the expense of memory B cells. These findings extend previous reports on primary immunodeficiencies as well as HIV disease by suggesting that CD4+ T-cell lymphopenia has an impact on human B-cell development either directly or indirectly via the associated elevation of IL-7 levels.

Combined analysis of retrospective and prospective occurrences in cohort studies: HIV-1 serostatus and incident pneumonia

BACKGROUND

The authors show how information collected on retrospective occurrence times may be combined with prospective occurrence times in the analysis of recurrent events from cohort studies.

METHODS

We demonstrate how the observed data can be expanded from one to two records per participant and account for the within-individual dependence when estimating variances. We illustrate our methods using data from the Women's Interagency HIV Study, which recorded 384 retrospective and 352 prospective occurrences of pneumonia in 9478 retrospective and 7857 prospective person-years among 2610 adult women.

RESULTS

The hazard of non-Pneumocystis carinii pneumonia among the 2056 HIV-1 infected women was 2.24 times (95% confidence limits: 1.74, 2.89) that of the 554 uninfected women, independent of age. This hazard ratio was homogeneous across retrospective and prospective occurrences (P for interaction = 0.96) and combining occurrence types increased the precision by reducing the standard error by about a fourth.

CONCLUSIONS

As expected, HIV-1 infection increases the hazard of pneumonia, with more precise inference obtained by combining information available on bidirectional occurrences. The proposed method for the analysis of bidirectional occurrence times will improve precision when the estimated associations are homogeneous across occurrence types, or may provide added insight into either the data collection or disease process when the estimated associations are heterogeneous.

Longitudinal assessment of de novo T cell production in relation to HIV-associated T cell homeostasis failure

Loss of circulating CD4+ T cells in HIV-1 disease is balanced by CD8+ lymphocytosis to maintain normal CD3+ T cell counts [blind T cell homeostasis (TCH)]. However, for unknown reasons TCH generally fails 1.5-2.5 years before clinically defined AIDS. We investigated whether TCH failure was associated with changes in thymic production of T cells. Using specimens stored prospectively in the Multicenter AIDS Cohort Study (MACS), we measured expression of signal-joint T cell receptor excision circles (sjTRECs), a marker for thymic T cell production, and the fraction of proliferating naive and memory T cells during a 6-8 year period bracketing TCH failure. Segmented regression modeling assessed (1) rates of change in TREC levels before and after TCH failure, and (2) whether these were affected by cellular proliferation, which may dilute sjTREC levels. TCH failure was associated with a large decline in sjTREC (median 1109-fold, p = 0.028); the rate of this decline was only slightly affected when increased proliferation of naive T cells or other peripheral lymphocytes was taken into account. Preferential loss of naive CD4+ T cells was also noted before TCH failure, as has been seen in other studies. These results suggest that deficits in de novo T cell production, either through the decline of thymic function or the destruction of naive T cells, are likely to play an important role in TCH failure and progression of HIV-1 disease.

Evolutionary dynamics of HIV-1 and the control of AIDS

Human immunodeficiency viruses (HIV) have exhibited an extraordinary capacity for genetic change, exploring new evolutionary space after each transmission to a new host. This presents a great challenge to the prevention and management of HIV-1 infection. At the same time, the relentless diversification of HIV-1, developing as it does under the constraints imposed by the human immune system and other selective forces, contains within it information useful for understanding HIV epidemiology and pathogenesis. Comparing the sheer mutational potential of HIV with actual data representing viral lineages that can survive selection suggests that HIV does not have unlimited capacity for change. Rather, clinical and bioinformatic data suggest that, even in the most diverse gene of the most highly variable organism, natural selection places severe limits on the portion of amino acid sequence space that ensures viability. This suggests some optimism for those attempting to identify sets of antigens that can generate effective humoral and cellular immune responses against HIV.

Naïve and memory cell turnover as drivers of CCR5-to-CXCR4 tropism switch in human immunodeficiency virus type 1: implications for therapy

Early human immunodeficiency virus infection is characterized by the predominance of CCR5-tropic (R5) virus. However, in many individuals CXCR4-tropic (X4) virus appears in late infection. The reasons for this phenotypic switch are unclear. The patterns of chemokine receptor expression suggest that X4 and R5 viruses have a preferential tropism for naïve and memory T cells, respectively. Since memory cells divide approximately 10 times as often as naïve cells in uninfected individuals, a tropism for memory cells in early infection may provide an advantage. However, with disease progression both naïve and memory cell division frequencies increase, and at low CD4 counts, the naïve cell division frequency approaches that of memory cells. This may provide a basis for the phenotypic switch from R5 to X4 virus observed in late infection. We show that a model of infection using observed values for cell turnover supports this mechanism. The phenotypic switch from R5 to X4 virus occurs at low CD4 counts and is accompanied by a rapid rise in viral load and drop in CD4 count. Thus, low CD4 counts are both a cause and an effect of X4 virus dominance. We also investigate the effects of different antiviral strategies. Surprisingly, these results suggest that both conventional antiretroviral regimens and CCR5 receptor-blocking drugs will promote R5 virus over X4 virus.

Characterization of the immunological features of tuberculous pericardial effusions in HIV positive and HIV negative patients in contrast with non-tuberculous effusions

OBJECTIVE

To investigate the immunopathogenesis of pericardial tuberculosis (TB) and the influence of human immunodeficiency virus (HIV) on the anti-tuberculous immune response.

DESIGN

Consecutive patients presenting with large pericardial effusions were subjected to a full clinical examination and pericardiocentesis. Aspirated fluid was sent for biochemistry, differential leukocyte count, flow cytometric analysis and determination of cytokine levels. Pericardial tissue was sent for TB culture and histopathological evaluation. Diagnoses were made according to pre-determined criteria.

RESULTS

Fifty-six patients were included and divided into HIV positive TB (n = 22), HIV negative TB (n = 21) and non-tuberculous effusions (n = 13). Peripheral blood neutrophil, lymphocyte and monocyte counts were significantly lower in HIV positive TB patients. Lymphocytes were the dominant cell type in tuberculous pericardial effusions. CD4+ cells dominated in HIV negative tuberculous effusions, whereas CD8+ cells dominated in HIV positive TB. The difference in the concentration of IFN-gamma levels in the tuberculous and non-tuberculous pericardial effusions was statistically significant. Despite significant differences in pericardial CD4+ cell counts, IFN-gamma levels were similarly elevated in HIV negative and HIV positive tuberculous effusions. Highest levels of pericardial IL-10 were observed in samples associated with least tissue necrosis, suggesting the possibility of a tissue protective immunoregulatory role for IL-10.

CONCLUSIONS

Tuberculous pericardial effusions result from a T helper1 (Th1)-dominant immune response. IFN-gamma producing CD4+ lymphocytes dominate in HIV negative patients, whereas CD8+ seem to play a more important role in HIV positive patients. Infection with HIV leads to the depletion of immunocompetent cells such as monocytes, NK cells and neutrophils.

Thymic pathogenicity of an HIV-1 envelope is associated with increased CXCR4 binding efficiency and V5-gp41-dependent activity, but not V1/V2-associated CD4 binding efficiency and viral entry

We previously described a thymus-tropic HIV-1 envelope (R3A Env) from a rapid progressor obtained at the time of transmission. An HIV-1 molecular recombinant with the R3A Env supported extensive replication and pathogenesis in the thymus and did not require Nef. Another Env from the same patient did not display the same thymus-tropic pathogenesis (R3B Env). Here, we show that relative to R3B Env, R3A Env enhances viral entry of T cells, increases fusion-induced cytopathicity, and shows elevated binding efficiency for both CD4 and CXCR4, but not CCR5, in vitro. We created chimeric envelopes to determine the region(s) responsible for each in vitro phenotype and for thymic pathogenesis. Surprisingly, while V1/V2 contributed to enhanced viral entry, CD4 binding efficiency, and cytopathicity in vitro, it made no contribution to thymic pathogenesis. Rather, CXCR4 binding efficiency and V5-gp41-associated activity appear to independently contribute to thymic pathogenesis of the R3A Env. These data highlight the contribution of unique HIV pathogenic factors in the thymic microenvironment and suggest that novel mechanisms may be involved in Env pathogenic activity in vivo.

Alterations of self-reactive antibody repertoires in HIV disease: An insight into the role of T cells in the selection of autoreactive B cells

Infection with human immunodeficiency virus (HIV) is characterized by a progressive depletion of CD4(+) T cells that parallels a dysfunction of the B cell compartment and a disturbed recognition of self-antigens. The relationship between T lymphocyte homeostasis and abnormalities in the selection of self-reactive B cells is not clear as yet. We have therefore compared repertoires of natural antibodies of healthy donors and of patients at various stages of HIV infection. The reactivity of IgM and IgG antibodies in plasma of healthy blood donors and of HIV-positive patients with high and low CD4(+) T cell counts was assessed by semi-quantitative immunoblotting using self-antigens extracted from normal human tissues. Repertoires of reactivites were compared between groups of individuals by means of multiparametric statistical analysis. We observed that repertoires of self-reactive IgM and IgG from HIV-seropositive patients exhibited significantly altered patterns of reactivity, as compared to those of healthy controls. Further, self-reactive repertoires of IgM and IgG of patients with high CD4(+) T cell counts differed significantly from those of patients with low CD4(+) T cell counts. A longitudinal analysis of self-reactive antibody repertoires of progressor and non-progressor patients suggested an influence of CD4(+) T cell counts on immunoglobulin reactivity toward self-antigens. These observations support the hypothesis that altered T cell/B cell interactions due to altered CD4(+) T cell help severely impact on the selection of self-reactive antibody repertoires and may contribute to the onset of pathological autoimmunity in HIV disease.

Distinct mechanisms of CD4+ and CD8+ T-cell activation and bystander apoptosis induced by human immunodeficiency virus type 1 virions

Apoptosis of uninfected bystander T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection. HIV-1 envelope/receptor interactions and immune activation have been implicated as contributors to bystander apoptosis. To better understand the relationship between T-cell activation and bystander apoptosis during HIV-1 pathogenesis, we investigated the effects of the highly cytopathic CXCR4-tropic HIV-1 variant ELI6 on primary CD4(+) and CD8(+) T cells. Infection of primary T-cell cultures with ELI6 induced CD4(+) T-cell depletion by direct cell lysis and bystander apoptosis. Exposure of primary CD4(+) and CD8(+) T cells to nonreplicating ELI6 virions induced bystander apoptosis through a Fas-independent mechanism. Bystander apoptosis of CD4(+) T cells required direct contact with virions and Env/CXCR4 binding. In contrast, the apoptosis of CD8(+) T cells was triggered by a soluble factor(s) secreted by CD4(+) T cells. HIV-1 virions activated CD4(+) and CD8(+) T cells to express CD25 and HLA-DR and preferentially induced apoptosis in CD25(+)HLA-DR(+) T cells in a CXCR4-dependent manner. Maximal levels of binding, activation, and apoptosis were induced by virions that incorporated MHC class II and B7-2 into the viral membrane. These results suggest that nonreplicating HIV-1 virions contribute to chronic immune activation and T-cell depletion during HIV-1 pathogenesis by activating CD4(+) and CD8(+) T cells, which then proceed to die via apoptosis. This mechanism may represent a viral immune evasion strategy to increase viral replication by activating target cells while killing immune effector cells that are not productively infected.

Application of case-crossover and case-time-control study designs in analyses of time-varying predictors of T-cell homeostasis failure

PURPOSE

To evaluate the association of sexual behavior and recreational drug exposures with T-cell homeostasis failure (TCHF), which corresponds to the onset of a rapid decline in an individual's T lymphocyte count, which occurs on average approximately 1.75 years prior to an initial diagnosis of acquired immunodeficiency syndrome (AIDS).

METHODS

A case-crossover design and a case-time-control design, both nested within the Multicenter AIDS Cohort Study of 4954 homosexual and bisexual men initiated in 1983.

RESULTS

In the case-crossover analysis, use of both recreational drugs and hashish were found to be protective against TCHF (odds ratios < or = 0.41), based on comparisons with four earlier control periods. However, a significant decreasing trend in the prevalence of these exposures was observed over time, thus motivating the implementation of the case-time-control design. Using the latter approach, the associations of drug use (odds ratio=0.53; 95% confidence interval (CI): 0.22, 1.28) and hashish use (odds ratio=0.46; 95% CI: 0.20, 1.05) with TCHF were no longer statistically significant.

CONCLUSIONS

The difference in inferences between these approaches demonstrates the importance of evaluating temporal trends in exposures when using a case-crossover design.

Analysis of IGG and IGG4 in HIV-1 seropositive patients and correlation with biological and genetic markers

We have compared the levels of immunoglobulins G (IgG) and G4 (IgG4) in extreme seropositive patients from the GRIV cohort consisting of 168 patients with slow progression (SP) and 60 with rapid progression (RP) as well as in 173 healthy controls. IgG levels were significantly higher in SP patients than in RP patients (P = 0.008), both higher than in seronegative individuals. IgG4 levels were significantly lower in SP patients than in RP patients (P = 0.001), both lower than in seronegative individuals. We tried to correlate these levels with biological parameters (CD4(+) and CD8(+) cells, total lymphocytes, white blood cell counts, percentage of CD4(+) cells, and viral load) as well as with genetic markers from Th1/Th2 cytokines (IL2, IL4, IL6, IL10, IL13, and IFNgamma). IgG levels were correlated with the percentage of CD4(+) cells in SP while IgG4 levels were correlated with CD8(+) cell count in SP and with percentage of CD4(+) cells in RP patients. Among the parameters measured in SP patients at the time of inclusion in the study, the best predictor of progression towards AIDS was the viral load, the best predictor for stability was CD4(+) cell count, but overall, the best predictor for SP evolution (stability vs. progression) appeared to be the percentage of CD4(+) cells. Interestingly, correlations between the levels of IgG or IgG4 and the cytokine gene polymorphisms were found, notably in the IL10 gene.

Optimal Frequency of Cd4 Cell Count and HIV Rna Monitoring Prior to Initiation of Antiretroviral Therapy in HIV-Infected Patients

Context

Guidelines regarding the frequency of CD4 cell count and HIV RNA monitoring in HIV-infected patients vary, with recommended strategies ranging from every 2 to every 6 months.

Objective

To determine optimal CD4 cell count and HIV RNA monitoring frequency in HIV-infected patients prior to antiretroviral therapy initiation. Design: Cost-effectiveness (CE) analysis using an HIV simulation model incorporating CD4 cell count and HIV RNA as immunological and virological predictors of clinical outcomes.

Setting

Hypothetical clinical setting.

Patients

Simulated cohort based on initial clinical presentation of HIV-infected patients in the US.

Intervention

CD4 cell count and HIV RNA monitoring at frequencies ranging from every 2 to 24 months prior to antiretroviral initiation, as well as accelerated monitoring frequencies as CD4 cell counts approach a specified treatment threshold.

Outcome measures

Life expectancy, quality-adjusted life expectancy and costs.

Results

For patients presenting with median CD4 cell count 546/mm3 and median HIV RNA 4.8 log10 copies/ml, incremental CE ratios ranged from US$37800/quality-adjusted life year (QALY) gained for a constant testing frequency of every 18 months compared with every 24 months, to US$303300/QALY gained for a constant testing frequency of every 2 months compared with every 4 months when starting treatment at a CD4 cell count of 350/mm3. Monitoring every 12 months until a warning CD4 cell count threshold of 450/mm3 followed by every 3 months until 350/mm3 had an incremental CE ratio of US$74700/QALY gained. When starting antiretroviral therapy at CD4 cell count 200/mm3, monitoring every 12 months until 300/mm3 followed by every 2 months until treatment initiation yielded an incremental CE ratio of US$52200/QALY gained compared with the next best strategy. Increasing monitoring frequency as CD4 cell counts approached a treatment threshold yielded greater incremental clinical benefit for less cost than strategies using a constant frequency.

Conclusions

Monitoring HIV-infected patients every 12 months until 100 CD4 cells/mm3 prior to a specified treatment threshold followed by more frequent monitoring every 2 or 3 months until antiretroviral therapy initiation is both more effective and cost-effective than the current standard of care.

Characterization of a thymus-tropic HIV-1 isolate from a rapid progressor: role of the envelope

Loss of T cell homeostasis usually precedes the onset of AIDS. We hypothesized that rapid progressors may be transmitted with HIV-1 that is particularly able to perturb T cell homeostasis. To this end, we have tested two transmitted, syncytium-inducing (SI) viral isolates from a rapid progressor in two thymus models. One of the isolates (R3A) exhibited markedly rapid kinetics of replication and thymocyte depletion. These phenotypes mapped to the envelope, as a recombinant NL4-3 virus encoding the R3A envelope had similar phenotypes, even in the absence of nef. Notably, the viruses with high pathogenic activity in the thymus (R3A and NL4-R3A) did not show enhanced replication or cytopathicity in PHA-stimulated PBMCs. Furthermore, NL4-R3A did not enhance replication of the coinfected NL4-3 virus in the thymus, suggesting an intrinsic advantage of the R3A envelope. The R3A envelope showed higher entry activity in infecting human T cells and in depleting CD4+ thymocytes when expressed in trans. These data suggest that SI viruses with unique envelope functions which can overcome barriers to transmission may hasten disease progression by perturbing T cell homeostasis.

Influence of random genetic drift on human immunodeficiency virus type 1 env evolution during chronic infection

Human immunodeficiency virus type 1 (HIV-1) has high replication and mutation rates that generate large census populations and high levels of genetic variation. We examined the roles of natural selection, population growth, random genetic drift, and recombination in shaping the variation in 1509 C2-V5 env sequences derived from nine men with chronic HIV-1 infection. These sequences were obtained from clinical visits that reflect the first 6-13.7 years of infection. Pairwise comparisons of nonsynonymous and synonymous distances, Tajima's D test, Fu and Li's D* test, and a test of recurrent mutation revealed evidence for episodes of nonneutral evolution in a total of 22 out of 145 blood samples, representing six of the nine individuals. Using three coalescent-based maximum-likelihood estimators, we found viral effective population sizes in all nine individuals to be approximately 10(3). We also show that a previous estimate of the effective population size of approximately 10(5) based on rare haplotype frequencies decreases to approximately 10(3) upon correcting a biased sampling procedure. We conclude that the genetic variation in these data sets can be explained by a predominance of random genetic drift of neutral mutations with brief episodes of natural selection that were frequently masked by recombination.

The impact of highly active antiretroviral therapy by the oral route on the CD8 subset in monkeys infected chronically with SHIV 89.6P

The objective of this study was to assess the impact of highly active antiretroviral therapy (HAART) by an oral route on the peripheral blood CD8 subset in the monkeys infected persistently with a pathogenic strain, SHIV(89.6P). Two rhesus macaques were inoculated intravenously with SHIV(89.6P), then treated with the combination of AZT, 3TC and Lopinavir/Ritonavir (LPV/RTV) as recommended in humans by the oral route with confectionery continued for 28 days. In one of two chronically infected macaques, MM260, the viral load was maintained in the range of 10(4)-10(5) copies/ml before HAART. The plasma viral load and proviral DNA decreased dramatically during the treatment, and cessation of this therapy the viral load rebounded to the pre-treatment level but the proviral DNA rebound was delayed. The other monkey, MM242, had low viral loads (1.2x10(3)-<5x10(2) copies/ml) both before and after HAART. CD4(+) and CD8(+) T cell counts and proviral DNA level were not significantly changed after the treatment. The percentages of CD8(+)CD45RA(-)Ki67(+)cells increased during (MM260) or after (MM242) HAART and the subset was maintained at a high percentage until 18 weeks post HAART in MM242. These findings suggest that this primate model might serve an important role in testing the virological and immunological efficacy of novel therapeutic strategies combined with HAART.

HIV-1 replication and pathogenesis in the human thymus

How HIV replicates and causes destruction of the thymus, and how to restore thymic function, are among the most important questions of HIV-1 pathogenesis and therapy in adult as well as pediatric patients. The thymus appears to function, albeit at reduced levels, throughout the life of adults, to respond to T cell depletion induced by HIV and to be suppressed by HIV. In this review, we summarize recent findings concerning HIV replication and pathogenesis in the human thymus, focusing on mechanistic insights gleaned from studies in the SCID-hu Thy/Liv mouse and human fetal-thymus organ culture (HF-TOC) models. First, we discuss HIV viral determinants and host factors involved in the replication of HIV in the thymus. Second, we consider evidence that both viral factors and host factors contribute to HIV-induced thymocyte depletion. We thus propose that multiple mechanisms, including depletion and suppression of progenitor cells, paracrine and direct lytic depletion of thymocytes, and altered thymocyte selection are involved in HIV-induced pathology in the thymus. With the SCID-hu Thy/Liv mouse and HF-TOC models, it will be important in the coming years to further clarify the virological, cell biological, and immunological mechanisms of HIV replication and pathogenesis in human thymus, and to correlate their significance in HIV disease progression.

HIV, 'an evolving species'. Roles of cellular activation and co-infections

Each small variation of the genome of a species can be preserved if it is useful for the survival of the species in a given environment. Within this framework, the finality of the biological cycle of HIV consists in a search for harmony (biological coherence) with man, which is to say a stable condition. Cellular activation appears to be the strategy developed by HIV in order to achieve this coherence. The price of this strategy is the AIDS. The first contact between HIV and immune system appears to determine the subsequent clinical outcome and the future of HIV. Lymphocytic activation varies during the course of the vital cycle of HIV. For each individual, this lymphocytic activation depends on both the HLA repertoire acquired during thymic ontogenesis and the antigenic experience before and after HIV infection. Thus intercurrent infections alter the immune condition of the organism and influence the outcome of HIV. We described a synthetic analysis of the effects of HIV on the surface protein expression and the cellular activation pathways which should provide insights in the evolutionary relationship between HIV and man and should permit to do a more physiological therapeutic approach.

Virus load correlates inversely with the expression of cytotoxic T lymphocyte activation markers in HIV-1-infected/AIDS patients showing MHC-unrestricted CTL-mediated lysis

Cytotoxic T lymphocytes (CTL) are key players to suppress viral load (VL) but CTL responses become compromised with progression of HIV-infection/AIDS. Some progressors develop MHC-unrestricted CTL with anti-CD4+ cytocidal activity. Immune activation status of these CTL and its significance in disease progression are unknown. To determine the relationship between VL and T cell activation, a cross-sectional study was carried out using blood samples from 13 HIV-1-infected/AIDS patients at various stages of progression and seven age-matched seronegative controls. We examined expression of HLA-DR and CD38 activation markers on purified CTL. MHC-unrestricted killing by these CTL was also evaluated against uninfected, allogeneic CD4+ T cells as well as several human cell lines. The expression of activation markers correlated inversely (rs = - 0.91, P < 0.0001) with VL of the subjects. CTL effectors of these patients killed targets expressing or lacking CD4+, independently of MHC class I recognition. Interestingly, the patients with higher VL showed an increased number of gammadeltaTCR-bearing CTL in blood and their MHC-unrestricted killing activity was blocked significantly (P < 0.01) by gammadeltaTCR-specific monoclonal antibody. CD3+ T counts of these patients were also consistently subnormal. Inverse correlation between VL and CD8+ T cell activation markers seems to be an indicator of CTL-associated immunopathogenesis in HIV patients with elevated gammadeltaCTL in the peripheral blood.

Timeline: AIDS pathogenesis: what have two decades of HIV research taught us?

22 years ago, the first cases of an acquired immunodeficiency syndrome afflicting young, homosexual American men were reported, heralding what we now know to be the beginning of the HIV epidemic. Since then, billions of US dollars have been invested in HIV research in the hope of gaining a better understanding of this infection and how to prevent and treat it. What are the landmarks in HIV research over the past two decades, and what questions still remain to be answered? What has the intense study of HIV infection taught us about other virus infections and how our immune system responds to them?

Low blood CD8+ T-lymphocytes and high circulating monocytes are predictors of HIV-1-associated progressive encephalopathy in children

OBJECTIVE

Human immunodeficiency virus type 1 (HIV-1)-associated progressive encephalopathy (PE) is a common and devastating complication of HIV-1 infection in children, whose risk factors have not yet been clearly defined. Regardless of the age of presentation, PE shortens life expectancy. Paradoxically, as survival of patients has been prolonged as a result of the use of antiretroviral therapy, the prevalence of PE has increased. Therefore, a predictive marker of PE emergence is critical. The objective of this study was to determine in an observational study whether any immunologic (CD4(+) and CD8(+) T-lymphocyte counts, monocyte counts) or virologic (viral load [VL], biological characteristics of viral isolates) marker might be predictive of PE and whether any particular marker may be involved in the timing of clinical onset of PE.

METHODS

A total of 189 children who were vertically infected with HIV-1 were studied retrospectively, 58 of whom fulfilled criteria of the American Academy of Neurology for PE. T-lymphocyte subsets and monocytes in peripheral blood were quantified by flow cytometry. HIV-1 RNA was measured in plasma using a quantitative reverse transcriptase polymerase chain reaction assay. Demographic, clinical, and viro-immunologic characteristics in infants were compared with control groups using logistic regression. Proportions were compared using the chi(2) test or Fisher exact test. For each child, immunologic and virologic markers were analyzed in parallel closely before clinical onset of PE and closely after PE onset and compared by using the Student t test for paired samples.

RESULTS

Overall, mortality of 58 HIV-1-infected children who developed PE was significantly higher than of children who did not develop this complication. Blood CD8(+) T-lymphocytes <25% in the first months of life suggested a relative risk of progressing to PE 4-fold higher than those with CD8(+) >25% (95% confidence interval: 1.2-13.9) and remained statistically significant after adjustment for treatment. When we compared the PE-positive group with the acquired immunodeficiency syndrome (AIDS)/PE-negative group (children who developed clinical category C and without neurologic manifestations) in a cross-sectional study within 12 months before PE or AIDS diagnosis, respectively, the %CD8(+) T-lymphocytes were significantly lower in the PE-positive group. Normalized absolute counts of CD8(+) T-lymphocytes with respect to seroreverting children were significantly lower in the group of children with encephalopathy with respect to the AIDS/PE-negative group (data not shown). It is interesting that a statistically significant increase was observed in circulating monocyte percentages and absolute counts shortly before the first neurologic symptoms compared with values after PE was established and with those from HIV-1-infected controls. With respect to AIDS-related events, PE was strongly associated with anemia and lymphoid interstitial pneumonitis in the PE-positive group with respect to a group of children with AIDS but without PE.

CONCLUSION

HIV-1 infection of the central nervous system (CNS) remains an important clinical concern. The first step toward PE prevention in HIV-1-infected children should be directed at predicting risk of PE and thus the prompt and reliable identification of infants who are at risk for CNS disease progression. Low blood CD8(+) T-lymphocytes is a strong early predictive marker of PE emergence in vertical HIV-1 infection. Indeed, among all of the immunologic and virologic variables assessed in this observational study, the only significant difference during the first months of life are the CD8(+) T-lymphocytes. A peak of significantly higher peripheral monocytes before the onset of PE with respect to established PE has not been previously described, and strengthens the growing evidence that an increased traffic of monocytes to the brain may be a key factor in triggering neurologic symptoms. The suppression of HIV-1 replication is dependent on the presence of a relatively small number of HIV-1-specifof HIV-1-specific CD8(+) T-lymphocytes, and it is possible that the duration of the neurologically asymptomatic phase for any given child may depend mostly on the magnitude of specific CD8(+) T-lymphocyte responses. Thus, a decrease of CD8(+) T-lymphocytes would diminish the host capacity to control viral infection, as reported in animal models, enabling infected macrophages to cross the blood-brain barrier. Our results advocate the use of CD8(+) T-lymphocyte and monocyte counts to follow-up HIV-1-infected children. We suggest that CD8(+) T-lymphocytes may be the nexus for many different aspects of the disease, namely loss of control of HIV-1 replication determining higher VL, increased traffic of activated and/or infected monocytes, spread of infection to immune sanctuaries, and finally clinical neurologic emergence of PE. Moreover, we suggest that CD8(+) T-lymphocytes or/and monocytes may be used as putative biological markers of neuropathogenicity. This might suggest their use in decision making of when to start more effective antiretroviral regimens for HIV-1 infection of the CNS and the need of new therapies either to preserve or to augment an adequate CD8(+) T-lymphocyte immune response. Early detection of children who are at risk for developing PE is particularly important because aggressive highly active antiretroviral therapy improves neurologic symptoms, allows possible use of neuroprotective treatment to prevent further development of encephalopathy, and emphasizes the relevance of developing therapies aimed to enhance CD8(+) T-lymphocyte function. In conclusion, the surrogate markers routinely used in clinical practice for HIV-1 infection (ie, CD4(+) T-lymphocyte counts and VL) seem to be insufficient to evaluate the clinical involvement of the CNS. Other systemic markers, as the recent proposed markers for PE evolution (cerebrospinal fluid VL by lumbar puncture and brain atrophy by cerebral magnetic resonance imaging) are undoubtedly more invasive than measuring CD8(+) T-lymphocyte and monocyte counts, when the neurologic manifestations of PE are still preventable.

A Tat subunit vaccine confers protective immunity against the immune-modulating activity of the human immunodeficiency virus type-1 Tat protein in mice

The rational design of new therapies against HIV-1 necessitates an improved understanding of the mechanisms underlying the production of ineffective immune responses to HIV-1 in most infected individuals. This report shows that the CD8(+) T cell responses to gp120 were greatly diminished in mice vaccinated with a bicistronic gp120-Tat DNA vaccine, compared with those induced by a DNA vaccine encoding gp120 alone. The CD8(+) T cell responses induced by the latter included strong gp120-specific IFN-gamma secretion and protective antiviral immunity against challenge by a vaccinia-env pseudotype. The degree to which Tat influenced CD8(+) T cell responses depended on the bioactivity of Tat. Thus, a bicistronic DNA vaccine that expresses gp120 and a truncated Tat defective for LTR activation elicited strong IFN-gamma -secreting CD8(+) T cell responses to gp120 but conferred only marginal protection against the vaccinia-env challenge. The effect of Tat was completely blocked, however, by immunization with inactivated Tat protein before vaccination with the bicistronic gp120-Tat DNA vaccine.

T-cell dynamics after high-dose chemotherapy in adults: elucidation of the elusive CD8+ subset reveals multiple homeostatic T-cell compartments with distinct implications for immune competence

Recovery of total T cell numbers after in vivo T-cell depletion in humans is accompanied by complex perturbation within the CD8+ subset. We aimed to elucidate the reconstitution of CD8+ T cells by separate analysis of putative naïve CD95- CD28+, memory CD95+ CD28+ and CD28- T cell compartments after acute maximal depletion by high-dose chemotherapy (HD-ChT) in women with high-risk breast cancer. We found that recovery of putative naïve CD8+ CD95- CD28+ and CD4+ CD95- CD28+ T cells, was compatible with a thymus-dependent regenerative pathway since their recovery was slow and time-dependent, their values were tightly related to each other, and their reconstitution patterns were inversely related to age. By analysing non-naïve T cells, a striking diversion between putative memory T cells and CD28- T cells was found. These latter increased early well beyond normal values, thus playing a pivotal role in total T-cell homeostasis, and contributed to reduce the CD4 : CD8 ratio. In contrast, putative memory T cells returned to values not significantly different from those seen in patients at diagnosis, indicating that this compartment may recover after HD-ChT. At 3-5 years after treatment, naïve T cells persisted at low levels, with expansion of CD28- T cells, suggesting that such alterations may extend further. These findings indicate that CD28- T cells were responsible for 'blind' T-cell homeostasis, but support the notion that memory and naïve T cells are regulated separately. Given their distinct dynamics, quantitative evaluation of T-cell pools in patients undergoing chemotherapy should take into account separate analysis of naïve, memory and CD28- T cells.

TCRBV CDR3 diversity of CD4+ and CD8+ T-lymphocytes in HIV-infected individuals

TCRBV CDR3 repertoire diversity was analyzed in a cross-sectional study of HIV-infected individuals by CDR3 fingerprinting/spectratyping and single strand conformation polymorphism (SSCP). Most TCRBV families were detected in CD4+ cells of HIV-infected patients with CD4 counts ranging from 35 to 1103. In patients with CD4 counts >500, CD4+ TCRBV CDR3 fingerprinting profiles contained subtle variations with generally gaussian-distributed sizes. Lower CD4 counts coincided with more fragmented TCRBV CDR3 repertoires, containing dominant bands and bands missing from the CDR3 profiles. The CD8+ population of the same patients exhibited skewed CDR3 profiles of the majority of TCR BV families at CD4 counts >500. Irregularity of CD8+ CDR3 size distribution was most profound at low CD4 counts and suggested domination of the CD8+ TCRBV repertoire by a limited number of clones. Skewed patterns of CDR3 diversity probably reflect (oligo)clonal expansion of particular CD4+ and CD8+ cell populations during chronic infection with HIV. In addition, irregular CDR3 profiles of CD4+ and CD8+ at low CD4 counts suggest diminished TCR repertoire diversity, which may contribute to immunodeficiency.

Surrogate markers for disease progression in treated HIV infection

OBJECTIVE

To characterize the relationships among highly active antiretroviral therapy (HAART), HIV-1 RNA levels, immune system markers, and clinical outcome in a cohort of HIV-1-infected homosexual men.

PATIENTS

A total of 123 men enrolled in the Amsterdam cohort study of HIV-1 infection and AIDS with a documented seroconversion for HIV-1 antibodies and known date of seroconversion were included in this study.

METHODS

CD4 + /CD8 + T-cell counts and HIV-1 RNA levels in plasma were measured approximately every 6 months. Dates of starting and stopping antiretroviral therapy were also recorded. The relationship between HIV-1 RNA in plasma, CD4 + /CD8 + T-cell counts and HAART and their influence on clinical outcome were examined using a graphical chain modeling approach. Generalized estimating equations were used to examine correlations among the three disease markers. Hazards models with time-dependent covariates were used to examine the influence of HAART and the disease markers on progression to AIDS.

RESULTS

HAART was significantly associated with reduced disease progression (relative hazard [RH] of AIDS, 0.20;, 95% confidence interval [CI], 0.05-0.85). The most recent HIV-1 RNA measurement and CD4 + T-cell count are independently associated with disease progression (adjusted RH for HIV-1 RNA 1.8 per log 10 increase; 95% CI, 1.2-2.6, p =.002; adjusted RH for CD4 + 0.48 per 100 x 10(6)/L increase; 95% CI, 0.40-0.58; p <.001). Depending on these measurements, HAART was no longer significantly associated with AIDS (adjusted RH, 0.81; 95% CI, 0.18-3.6; p =.78).

CONCLUSIONS

HIV-1 RNA levels in plasma and CD4 + T-cell counts are currently considered as effective surrogate markers for the effect of HAART on disease progression in this cohort.

The role of antigenic stimulation and cytotoxic T cell activity in regulating the long-term immunopathogenesis of HIV: mechanisms and clinical implications

This paper develops a predictive mathematical model of cell infection, host immune response and viral replication that reproduces observed long-term trends in human immunodeficiency virus (HIV) pathogenesis. Cell activation induced by repeated exposure to many different antigens is proposed as the principal mechanism of providing target cells for HIV infection and, hence, of CD4+ T cell depletion, with regulation of the overall T cell pool size causing concomitant CD8 pool increases. The model correctly predicts the cross-patient variability in disease progression, the rate of which is found to depend on the efficacy of anti-HIV cytotoxic T lymphocyte responses, overall viral pathogenicity and random effects. The model also predicts a variety of responses to anti-viral therapy, including episodic residual viral replication and discordant responses and we find that such effects can be suppressed by increasing the potency of treatment.

Interleukin-7: master regulator of peripheral T-cell homeostasis?

Recent evidence has implicated interleukin-7 (IL-7) as a master regulator of T-cell homeostasis, based upon its essential role in the homeostatic expansion of naive T-cell populations in response to low-affinity antigens (Ags) and its capacity to enhance dramatically the expansion of peripheral T-cell populations in response to high-affinity Ags. Furthermore, T-cell-depleted humans have a unique inverse relationship between the peripheral CD4(+) T-cell count and the level of circulating IL-7. Together, these data suggest that increased amounts of IL-7 become available following T-cell depletion, thus, enhancing the high- and low-affinity Ag-driven expansion of the population of residual, mature T cells and boosting thymic regenerative capacity, as a means to restore T-cell homeostasis.

Markers of cell death-activation in lymphocytes of vertically HIV-infected children naive to highly active antiretroviral therapy: the role of age

BACKGROUND

Apoptosis plays a major role in depleting CD4(+) lymphocytes during infection with HIV-1. Few data exist on its role during HIV infection of children. Sensitivity of peripheral blood lymphocytes (PBLs) to apoptotic stimuli and the importance of the patient's age remain unclear.

OBJECTIVES

We sought to analyze the following: (1) markers of cell death-activation (CD95, CD45 isoforms, and CD28) in PBLs from vertically HIV-infected children of different ages before highly active antiretroviral therapy; (2) changes in other PBL populations; (3) PBL sensitivity to cell death and mitochondrial damages; and (4) role of age during progression of infection.

METHODS

Cell culture techniques and flow cytometry were used to analyze surface antigens, PBL susceptibility to apoptosis, or PBL susceptibility to change of mitochondrial membrane potential.

RESULTS

Donor age had a strong negative correlation with numbers of CD4(+) and CD8(+) T cells. Virgin T lymphocyte (CD45RA(+), CD95(-)) levels and those of CD95(+) cells showed no correlation with the children's clinical status but did show a correlation with patient age. CD28(-) T lymphocytes were markedly augmented in HIV-infected children but were unrelated to stage of infection or age. A relevant decrease in B lymphocytes and an increase in natural killer cells were also found. Finally, PBLs from HIV-positive children had a marked tendency to undergo apoptosis and mitochondrial damage.

CONCLUSION

Changes in PBL phenotype, increased expression of CD95, and high sensitivity to apoptosis suggest that a precocious aging of the immune system occurs in HIV-infected children.

Immune activation correlates better than HIV plasma viral load with CD4 T-cell decline during HIV infection

This study addressed the role of T-cell immune activation in determining HIV-1 plasma viral load and CD4+ T-cell blood levels during HIV-1 infection. A decrease of blood CD4 levels and CD4/CD8 ratios and an increase of CD8 levels in both treated (n = 35) and untreated (n = 19) HIV-positive individuals were more strongly correlated to immune activation (log percentage of HLA-DR+CD3+ cells; R = -0.78, R = -0.77, and R = 0.58, respectively; p <.0001) than to CD4 T-cell proliferation (log percentage of Ki-67+CD4+ cells; R = -0.57 [p <.0001], R = -0.48 [p <.001], and R = 0.37 [p <.01], respectively) or to viral load (R = -0.36 [p <.01], R = -0.23 [p =.09], R = 0.13 [p =.35], respectively). Because almost half of the Ki-67+CD4+ cells were also positive for CTLA-4 (a marker for activated nonproliferating cells), the correlation of CD4 levels to Ki-67 expression is only partially related to cell proliferation and more likely represents mainly immune activation of the cells without proliferation. Taken together, these results suggest that immune activation is the major determinant of CD4 decline and should therefore be considered central for the monitoring of HIV infection and its outcome after antiviral treatment.

[Opportunistic episodes in patients infected with the human immunodeficiency virus during the first 6 months of HAART]

BACKGROUND

We aimed at analysing the incidence and characteristics of opportunistic events (OE) within a few months after starting highly active antiretroviral therapy (HAART) in HIV infected patients.

PATIENTS AND METHOD

Retrospective study of HIV infected outclinic patients attended in a HIV/AIDS reference hospital in Madrid, who initiated HAART during the second semester of 1998, with a baseline CD4 cell count 250 x 10(6) cells/l. We recorded the incidence of OE within 6 months after beginning HAART and analysed virological and immunological parameters, sociodemographic variables and types of antiretroviral treatment.

RESULTS

The study included 269 patients. Twenty-one (7.8%) OE were recorded. At the onset of HAART, the mean CD4 cell count in these 21 patients was 137 (92) x 10(6)/land the median viral load was 24,043 cop/ml. At the time of OE diagnosis, these parameters were 218 (114) x 10(6)/l (p = 0.012) and < 500 cop/ml, respectively. OE were distributed as follows: herpes zoster, 9 cases (43%), Pneumocystis carinii pneumonia, 5 cases (24%), Kaposi sarcoma,3 cases (14%) and tuberculosis, cerebral toxoplasmosis, cytomegalovirus retinitis, and non-Hodgkin lymphoma, 1 case each. Overall, 78% of OE occurred within first 4 months after beginning HAART. In addition, an OE was developed by 8% patients treated with NRTI and PI, 2% treated with NRTI and NNRTI, and 10% treated with NRTI,NNRTI and PI (p = 0.44).

CONCLUSIONS

HIV-infected subjects with low CD4 counts are prone to develop OE within the first few moths after beginning HAART. An inflammatory response to latent antigens due to the immune recovery might explain this fact.

Increase and plateau of CD4 T-cell counts in the 3(1/2) years after initiation of potent antiretroviral therapy

We evaluated CD4 cell counts over a 3(1/2) year period following the initiation of potent antiretroviral therapy (ART) in the Multicenter AIDS Cohort Study. The study population included 314 HIV-infected gay men who provided CD4 cell counts for at least 2 years after the initiation of potent ART. Trends in CD4 cell counts and plasma HIV-RNA were analyzed by regression methods that incorporated the statistical dependencies of outcomes measured over time within individuals. Regardless of CD4 cell count at initiation of potent ART, CD4 cell counts increased significantly (p <.05) in the first 2 years after initiation. However, between 2 and 3(1/2) years after initiation, these counts neither increased nor decreased. The pattern of the proportion with plasma HIV-RNA <400 copies/ml was similar to CD4 cell count (i.e., increased significantly after initiation and plateau in the subsequent 1(1/2) years). The single most important predictor of the steady state CD4 cell count that was maintained between 2 and 3(1/2) years after initiation was the change in plasma HIV-RNA in the first year after initiation of potent ART.

Molecular correlates in AIDS patients following antiretroviral therapy: diversified T-cell receptor repertoires and in vivo control of cytomegalovirus replication

OBJECTIVES

To evaluate whether successful, long-term immune reconstitution in vivo can be achieved in end-stage AIDS patients following antiretroviral therapy (ART).

METHODS

A 1-year prospective study of changes of CD4+ and CD8+ T-cell surface phenotypes, T-cell receptor (TCR) repertoires and capacity to control in vivo replication of cytomegalovirus (CMV) was performed in five treatment-naive end-stage AIDS patients (median CD4+ T-cell counts of 19 cells/microL) following therapy. Proportions of CD45RA+, CD45RO+ and CD28+ cells within the CD4+ and CD8+ subsets, were determined by flow cytometry. Changes in TCR Vbeta repertoires within the CD4+ and CD8+ T-cell compartments were evaluated using CDR3 spectratyping. CMV replication was determined by a sensitive polymerase chain reaction (PCR) assay using whole blood.

RESULTS

Following ART, proportionate increases in 'naive' (CD45RA+) and 'memory' (CD45RO+) T cells were observed within both CD4+ and CD8+ T-cell subsets, while increased numbers of CD28+ T cells were mainly observed within the CD4+ subset. Diversification of CD4+ and CD8+ TCR repertoires was established concomitantly with renewed in vivo control of CMV replication.

CONCLUSIONS

An important degree of molecular and functional immune recovery is possible in end-stage AIDS patients introduced to therapy. Diversification of TCR repertoires and the in vivo restoration of immunocompetence to control opportunistic infections clearly show that an important degree of molecular immune reconstitution is established following the initiation of ART even in late-stage AIDS.

A new entry route for HIV

Identification of HIV-1 variants capable of entering T cells via the CD8 receptor suggests a new mode of viral pathogenesis. But are these variants rare, aberrant viruses or a real problem?

Immunological benefits of antiretroviral therapy in very early stages of asymptomatic chronic HIV-1 infection

OBJECTIVES

To assess whether an almost complete restoration of immune system can be achieved when antiretroviral therapy is initiated at very early stages of asymptomatic chronic HIV-1 infection.

DESIGN

T cell subsets and cell-mediated responses were analysed at baseline and after 12 months of either a double or a triple antiretroviral therapy in 26 asymptomatic HIV-1-infected patients with CD4 T cell counts > 500 x 10(6) cells/l and a baseline plasma viral load > 10000 copies/ml.

RESULTS

Triple therapy was significantly more effective in reducing plasma HIV RNA to undetectable levels, in returning CD4:CD8 ratio to nearly normal levels, in reducing activated cells (CD38) and in increasing naive (CD45RA+CD45RO-) and memory (CD45RA-CD45RO+) CD4 cells. Both double and triple therapies caused a clear decrease in memory (CD45RA-CD45RO+) CD8 cells as well as a significant increase in the CD28 subset of CD8 cells. At baseline, there was an important increase in cells producing interferon-gamma (IFNgamma) with no significant abnormalities in T lymphocytes producing interleukin 2 (IL-2), tumour necrosis factor alpha and interleukin 4. Both types of therapy reduced IFNgamma- and IL2-producing CD4 T lymphocytes while IFNgamma-producing CD8 cells remained increased. Even before therapy, these HIV-1-positive patients lacked significant abnormalities in the T cell responsiveness to polyclonal stimuli as well as in the secretion of CCR5 chemokines by peripheral blood mononuclear cells.

CONCLUSIONS

Initiating highly active antiretroviral therapy at very early stages of chronic HIV-1 infection allows rapid and almost complete normalization of T cell subsets and preservation of T cell functions. These early-treated patients could be excellent candidates for receiving additional HIV-specific immune-based therapies, which might be essential for the control of HIV infection.

Human immunodeficiency virus type 1 induces apoptosis in CD4(+) but not in CD8(+) T cells in ex vivo-infected human lymphoid tissue

Progression of human immunodeficiency virus (HIV) disease is associated with massive death of CD4(+) T cells along with death and/or dysfunction of CD8(+) T cells. In vivo, both HIV infection per se and host factors may contribute to the death and/or dysfunction of CD4(+) and CD8(+) T cells. Progression of HIV disease is often characterized by a switch from R5 to X4 HIV type 1 (HIV-1) variants. In human lymphoid tissues ex vivo, it was shown that HIV infection is sufficient for CD4(+) T-cell depletion. Here we address the question of whether infection of human lymphoid tissue ex vivo with prototypic R5 or X4 HIV variants also depletes or impairs CD8(+) T cells. We report that whereas productive infection of lymphoid tissue ex vivo with R5 and X4 HIV-1 isolates induced apoptosis in CD4(+) T cells, neither viral isolate induced apoptosis in CD8(+) T cells. Moreover, in both infected and control tissues we found similar numbers of CD8(+) T cells and similar production of cytokines by these cells in response to phorbol myristate acetate or anti-CD3-anti-CD28 stimulation. Thus, whereas HIV-1 infection per se in human lymphoid tissue is sufficient to trigger apoptosis in CD4(+) T cells, the death of CD8(+) T cells apparently requires additional factors.

Expansion of rare CD8+ CD28- CD11b- T cells with impaired effector functions in HIV-1-infected patients

The decline in the number of CD4+ T cells in HIV-1-infected patients is known to be related to the increased number of CD8+CD28- T cells. In this paper, we show that CD8+CD28- T cells from HIV-positive patients have an impaired capability to interact with human endothelial cells. This is due to the dramatic expansion, within this subset, of rare CD11b- cells lacking cell-cell adhesion functions. In 50 HIV-positive patients, 19.5% +/- 6.5% of all T cells were CD8+CD28-CD11b-, whereas only 0.8% +/- 0.4% of all T cells from healthy donors showed this uncommon phenotype. The percentage of circulating CD8+CD28-CD11b- T cells was strongly related to the percentage of CD4+ T cells (r = -0.82). This population is peculiar in terms of HIV infection and was found to possess some characteristics associated with effector functions but its cytotoxic properties were impaired. The percentage of target cells lysed by CD8+CD28-CD11b- was significantly lower than that of cells lysed by its CD11b- counterpart (p <.05) both at low (5:1) or at relatively high (20:1) effector/target ratios. CD8+CD28-CD11b- T cells, which lack the ability to interact with endothelial cells, are likely to accumulate and persist in circulation. The biologic properties of CD8+CD28-CD11b- T cells suggest that these cells might be endstage or aberrant differentiated effector cells. Lack of cell-cell adhesion and impaired cytolytic functions favor the hypothesis of a role for CD8+CD28-CD11b- T cells in the development of immunodeficiency.

Immune reconstitution syndromes in human immuno-deficiency virus infection following effective antiretroviral therapy

Effective antiretroviral therapy leads to rapid decrease in plasma HIV-1 RNA, frequently followed by an increase in CD4 T-helper cell counts. The improvement of immune function during highly active antiretroviral therapy has important impact on natural history of AIDS-related opportunistic disorders. Here we describe cases of unusual clinical inflammatory syndromes in CMV retinitis, hepatitis C, and atypical mycobacteriosis in HIV-1 infected patients associated with the initiation of antiretroviral therapy. Pathogenetic implications and therapeutic management of these new immunopathologic syndromes are discussed.

Strong association between failure of T cell homeostasis and the syncytium-inducing phenotype among HIV-1-infected men in the Amsterdam Cohort Study

OBJECTIVE

To assess the association between T cell homeostasis and its failure and 1.) the occurrence of AIDS and 2.) the switch from the non-syncytium-inducing (NSI) to the syncytium-inducing (SI) HIV virus phenotype.

METHODS

For each of 325 homosexual men in the Amsterdam Cohort Study, the slope of the CD3 T cell count versus time was determined. The timing (T cell inflection point (IP)) and magnitude of the change in slope were correlated with the time of the NSI/SI switch.

RESULTS

Median T cell slopes before the IP (pre-IP) were nearly zero regardless of whether AIDS occurred; the slopes after the IP (post-IP) were associated with clinical outcomes, with a median annual decline of 17.6% among those who developed AIDS and increase of 4.6% in those remaining AIDS free. Among subjects considered to have a true IP (decline > 8.2%/year post-IP), the times of the SI switch and the IP slope were highly correlated (r = 0.65); among those with AIDS, the SI switch preceded the IP by a median of 0.63 years.

CONCLUSION

These results support the concept of blind T cell homeostasis and also suggest that HIV-1 SI variants play an important role in the failure of T cell homeostasis.