Study design issues in evaluating immune biomarkers

Causal Organic Indirect and Direct Effects: Closer to the Original Approach to Mediation Analysis, with a Product Method for Binary Mediators

Mediation analysis, which started in the mid-1980s, is used extensively by applied researchers. Indirect and direct effects are the part of a treatment effect that is mediated by a covariate and the part that is not. Subsequent work on natural indirect and direct effects provides a formal causal interpretation, based on cross-worlds counterfactuals: outcomes under treatment with the mediator set to its value without treatment. Organic indirect and direct effects avoid cross-worlds counterfactuals, using so-called organic interventions on the mediator while keeping the initial treatment fixed at treatment. Organic indirect and direct effects apply also to settings where the mediator cannot be set. In linear models where the outcome model does not have treatment-mediator interaction, both organic and natural indirect and direct effects lead to the same estimators as in the original formulation of mediation analysis. Here, we generalize organic interventions on the mediator to include interventions combined with the initial treatment fixed at no treatment. We show that the product method holds in linear models for organic indirect and direct effects relative to no treatment even if there is treatment-mediator interaction. Moreover, we find a product method for binary mediators. Furthermore, we argue that the organic indirect effect relative to no treatment is very relevant for drug development. We illustrate the benefits of our approach by estimating the organic indirect effect of curative HIV treatments mediated by two HIV persistence measures, using data on interruption of antiretroviral therapy without curative HIV treatments combined with an estimated or hypothesized effect of the curative HIV treatments on these mediators. See video abstract at http://links.lww.com/EDE/B796.

Immune Correlates of Herpes Zoster in People Living with HIV on Effective Antiretroviral Therapy

Herpes zoster (HZ) has high morbidity in people living with HIV (PLHIV). We investigated immunological factors that correlated with the development of HZ in PLHIV with controlled HIV replication on antiretroviral therapy (ART). PLHIV who developed HZ on ART (cases), with undetectable plasma HIV RNA, and CD4 counts ≥200 cells/μL were matched 1:1 to controls by CD4 count, age, gender, race, and duration of ART. Varicella-zoster virus (VZV)-specific T cells and circulating regulatory T cells (Treg) were measured by flow cytometry before and after HZ. Differences between cases and controls were assessed by paired t-tests and longitudinal changes by Wilcoxon signed rank test. HZ cases (N = 31) had higher CD4⁺FOXP3⁺CD25⁺% Treg before HZ compared with 31 controls. After VZV ex vivo restimulation, cases had lower T cell responses, including CD8⁺perforin⁺% cytotoxic T lymphocytes (CTLs), CD4⁺IL10⁺%, and CD4⁺TGFβ⁺% compared with controls. Overall, Treg negatively correlated with VZV-specific Th1 responses. Moreover, Treg decreased over time on ART in HZ cases, VZV-CTLs were stable and did not increase even after HZ. Increased circulating Treg and decreased VZV-specific T cell immune responses were associated with the risk of HZ in PLHIV. The kinetics of Treg over time, but not of VZV-CTLs, paralleled the natural history of HZ, whose incidence decreases over time on effective ART.

Development and reliability assessment of a new quality appraisal tool for cross-sectional studies using biomarker data (BIOCROSS)

Background

Biomarker-based analyses are commonly reported in observational epidemiological studies; however currently there are no specific study quality assessment tools to assist evaluation of conducted research. Accounting for study design and biomarker measurement would be important for deriving valid conclusions when conducting systematic data evaluation.

Methods

We developed a study quality assessment tool designed specifically to assess biomarker-based cross-sectional studies (BIOCROSS) and evaluated its inter-rater reliability. The tool includes 10-items covering 5 domains: ‘Study rational’, ‘Design/Methods’, ‘Data analysis’, ‘Data interpretation’ and ‘Biomarker measurement’, aiming to assess different quality features of biomarker cross-sectional studies. To evaluate the inter-rater reliability, 30 studies were distributed among 5 raters and intraclass correlation coefficients (ICC-s) were derived from respective ratings.

Results

The estimated overall ICC between the 5 raters was 0.57 (95% Confidence Interval (CI): 0.38–0.74) indicating a good inter-rater reliability. The ICC-s ranged from 0.11 (95% CI: 0.01–0.27) for the domain ‘Study rational’ to 0.56 (95% CI: 0.40–0.72) for the domain ‘Data interpretation’.

Conclusion

BIOCROSS is a new study quality assessment tool suitable for evaluation of reporting quality from cross-sectional epidemiological studies employing biomarker data. The tool proved to be reliable for use by biomedical scientists with diverse backgrounds and could facilitate comprehensive review of biomarker studies in human research.

Electronic supplementary material

The online version of this article (10.1186/s12874-018-0583-x) contains supplementary material, which is available to authorized users.

Evaluation of inflammatory biomarkers, carotid intima-media thickness and cardiovascular risk in HIV-1 treatment-naive patients

INTRODUCTION

Mortality among HIV patients is 3-15 times higher than that among the general population. Currently, most deaths are due to non-infectious diseases. Chronic inflammation and adverse events due to antiretroviral therapy play crucial roles in increasing cardiovascular risk (CVR).

METHODS

This cross-sectional study aimed to evaluate carotid intima-media thickness (CIMT) and inflammatory biomarkers (D-dimer, ADAMTS13, GDF-15, sICAM-1, MPO, myoglobin, NGAL, SAA, sVCAM-1, and p-selectin) among naïve patients.

RESULTS

Sixty-seven participants were included: median age, 32 years; males, 82.1%; non-white, 61.1%; higher education level, 62.7%; and exposed to HIV through sexual relationship (men who have sex with men), 68.7%. The median viral load and LTCD4+ value were 42,033 copies/mL and 426 cells/mm³. The prevalence of arterial hypertension was 16.4%; those of diabetes mellitus and dyslipidemia were 3% and 70.1%, respectively. The CIMT was 494.08 (± 96.84mm). The mean vascular age was 33.2 ± 18.9 years, one year longer than the chronological age, without statistical significance.

CONCLUSIONS

The majority of participants had a low CVR (94%). After reclassification, considering the CIMT percentiles, 13 (19.4%) patients had medium/ high CVR, while 54 (80.6%) patients had low CVR. The difference between the proportions of CVR when considering the CIMT and its corresponding percentile was statistically relevant. Body mass index was the only predictor of higher CVR (p = 0.03). No biomarker was found to predict CVR. People living with HIV have a high prevalence of dyslipidemia before ARV therapy.

The effect of HAART-induced HIV suppression on circulating markers of inflammation and immune activation

OBJECTIVES

To investigate the impact of HAART-induced HIV suppression on levels of 24 serological biomarkers of inflammation and immune activation.

DESIGN

A prospective cohort study.

METHODS

Biomarkers were measured with multiplex assays in centralized laboratories using stored serum samples contributed by 1697 men during 8903 person-visits in the Multicenter AIDS Cohort Study (MACS) from 1984 to 2009. Using generalized gamma models, we compared biomarker values across three groups, adjusting for possible confounders: HIV-uninfected (NEG); HIV-positive, HAART-naive (NAI); and HAART-exposed with HIV RNA suppressed to less than 50 copies/ml plasma (SUP). We also estimated changes in biomarker levels associated with duration of HIV suppression, using splined generalized gamma regression with a knot at 1 year.

RESULTS

Most biomarkers were relatively normalized in the SUP group relative to the NAI group; however, 12 biomarkers in the SUP group were distinct (P < 0.002) from NEG values: CXCL10, C-reactive protein (CRP), sCD14, sTNFR2, tumour necrosis factor-alpha (TNF-α), sCD27, sGP130, interleukin (IL)-8, CCL13, BAFF, GM-CSF and IL-12p70. Thirteen biomarkers exhibited significant changes in the first year after viral suppression, but none changed significantly after that time.

CONCLUSION

Biomarkers of inflammation and immune activation moved towards HIV-negative levels within the first year after HAART-induced HIV suppression. Although several markers of T-cell activation returned to levels present in HIV-negative men, residual immune activation, particularly monocyte/macrophage activation, was present. This residual immune activation may represent a therapeutic target to improve the prognosis of HIV-infected individuals receiving HAART.