Flow cytometry developments and perspectives in clinical studies: examples in ICU patients

Prospective flow cytometry analysis of leucocyte subsets in critically ill patients who develop sepsis: a pilot study

PURPOSE

Sepsis in critically ill patients with injury bears a high morbidity and mortality. Extensive phenotypic monitoring of leucocyte subsets in critically ill patients at ICU admission and during sepsis development is still scarce. The main objective of this study was to identify early changes in leukocyte phenotype which would correlate with later development of sepsis.

METHODS

Patients who were admitted in a tertiary ICU for organ support after severe injury (elective cardiac surgery, trauma, necessity of prolonged ventilation or stroke) were sampled on admission (T1) and 48-72 h later (T2) for phenotyping of leukocyte subsets by flow cytometry and cytokines measurements. Those who developed secondary sepsis or septic shock were sampled again on the day of sepsis diagnosis (Tx).

RESULTS

Ninety-nine patients were included in the final analysis. Nineteen (19.2%) patients developed secondary sepsis or septic shock. They presented significantly higher absolute monocyte counts and CRP at T1 compared to non-septic patients (1030/µl versus 550/µl, p = 0.013 and 5.1 mg/ml versus 2.5 mg/ml, p = 0.046, respectively). They also presented elevated levels of monocytes with low expression of L-selectin (CD62Lneg monocytes) (OR[95%CI] 4.5 (1.4-14.5), p = 0.01) and higher SOFA score (p < 0.0001) at T1 and low mHLA-DR at T2 (OR[95%CI] 0.003 (0.00-0.17), p = 0.049). Stepwise logistic regression analysis showed that both monocyte markers and high SOFA score (> 8) were independently associated with nosocomial sepsis occurrence. No other leucocyte count or surface marker nor any cytokine measurement correlated with sepsis occurrence.

CONCLUSION

Monocyte counts and change of phenotype are associated with secondary sepsis occurrence in critically ill patients with injury.

Bicentric evaluation of stabilizing sampling tubes for assessment of monocyte HLA-DR expression in clinical samples

BACKGROUND

Diminished expression of human leukocyte antigen DR on circulating monocytes (mHLA-DR), measured by standardized flow cytometry procedure, is a reliable indicator of immunosuppression in severely injured intensive care unit patients. As such, it is used as stratification criteria in clinical trials evaluating novel immunostimulating therapies. Preanalytical constraints relative to the short delay between blood sampling and flow cytometry staining have nevertheless limited its use in multicentric studies. The objective of the present work was to compare mHLA-DR expression between whole blood samples simultaneously drawn in EDTA or Cyto-Chex BCT tubes.

METHODS

In two university hospitals, mHLA-DR was assessed in fresh whole blood from septic patients (n = 12) and healthy donors (n = 6) simultaneously sampled on EDTA and Cyto-Chex BCT tubes. Staining was performed immediately after sampling and after blood storage at room temperature.

RESULTS

We confirmed that samples collected in Cyto-Chex tube had substantially enhanced stability for mHLA-DR results (48-72 h) over those collected in EDTA. On baseline values, despite good correlation between tubes (r = 0.98, p < 0.001), mHLA-DR expression was systematically lower with Cyto-Chex BCT.

CONCLUSION

The present reports confirms the potential of Cyto-Chex BCT tubes to stabilize mHLA-DR expression before staining and extends the work of Quadrini et al. [Cytometry B 2021;100:103-114]. In centers without rapid access to flow cytometry facilities, it enables to tolerate delays in mHLA-DR staining. However, a 30% gap exists between results obtained with EDTA and Cyto-Chex BCT tubes. As current thresholds for clinical decisions were obtained with EDTA samples, further studies are needed to confirm clinical thresholds with Cyto-Chex BCT tubes.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Early PREdiction of sepsis using leukocyte surface biomarkers: the ExPRES-sepsis cohort study

PURPOSE

Reliable biomarkers for predicting subsequent sepsis among patients with suspected acute infection are lacking. In patients presenting to emergency departments (EDs) with suspected acute infection, we aimed to evaluate the reliability and discriminant ability of 47 leukocyte biomarkers as predictors of sepsis (Sequential Organ Failure Assessment score ≥ 2 at 24 h and/or 72 h following ED presentation).

METHODS

In a multi-centre cohort study in four EDs and intensive care units (ICUs), we standardised flow-cytometric leukocyte biomarker measurement and compared patients with suspected acute infection (cohort-1) with two comparator cohorts: ICU patients with established sepsis (cohort-2), and ED patients without infection or systemic inflammation but requiring hospitalization (cohort-3).

RESULTS

Between January 2014 and February 2016, we recruited 272, 59 and 75 patients to cohorts 1, 2, and 3, respectively. Of 47 leukocyte biomarkers, 14 were non-reliable, and 17 did not discriminate between the three cohorts. Discriminant analyses for predicting sepsis within cohort-1 were undertaken for eight neutrophil (cluster of differentiation antigens (CD) CD15; CD24; CD35; CD64; CD312; CD11b; CD274; CD279), seven monocyte (CD35; CD64; CD312; CD11b; HLA-DR; CD274; CD279) and a CD8 T-lymphocyte biomarker (CD279). Individually, only higher neutrophil CD279 [OR 1.78 (95% CI 1.23-2.57); P = 0.002], higher monocyte CD279 [1.32 (1.03-1.70); P = 0.03], and lower monocyte HLA-DR [0.73 (0.55-0.97); P = 0.03] expression were associated with subsequent sepsis. With logistic regression the optimum biomarker combination was increased neutrophil CD24 and neutrophil CD279, and reduced monocyte HLA-DR expression, but no combination had clinically relevant predictive validity.

CONCLUSIONS

From a large panel of leukocyte biomarkers, immunosuppression biomarkers were associated with subsequent sepsis in ED patients with suspected acute infection.

CLINICAL TRIAL REGISTRATION

NCT02188992.

Intracellular Flow Cytometry Improvements in Clinical Studies

Flow cytometry has become a basic of biological research and clinical diagnostics, and its application has been crucial to numerous advances in immunology and cell biology. However, several issues remain when considering intracellular stainings, especially in the context of a daily routine use and in multicenter clinical research protocols including large cohorts of patients. The requirements for multiple protocol steps are not only time-consuming but also frequently associated with high cell loss and nonspecific binding or reduced fluorescence. These drawbacks make standardized intracellular flow cytometry use in multicenter studies struggling. As a consequence, intracellular flow cytometry has mostly remained a tool for experimental and clinical research. In the current chapter, we will complete flow cytometry protocols described in the previous edition by presenting novel intracellular protocols usable in clinic. These present with many advantages including shorter time-to-results, one-step whole blood procedures, lyse-no-wash-no-centrifuge protocols, improved staining quality, and lyophilized coated reagents in ready-to-use tubes. This opens novel perspectives for standardization and feasibility in clinical studies, for drug efficacy monitoring and for patients' stratification within a context of personalized medicine. Here, we present illustrative examples taken from septic patients' immunomonitoring. We consider the evaluation of myeloperoxidase and lactoferrin expressions in neutrophils, FOXP3 lymphocyte expression, and STAT5 phosphorylation in lymphocyte subsets.

Quantification of regulatory T cells in septic patients by real-time PCR-based methylation assay and flow cytometry

During sepsis, a relative increase of regulatory T (Treg) cells has been reported. Its persistence is associated with lymphocyte anergy, immunoparalysis and a poor prognosis. Currently, an exact quantification of human Treg cells based on protein expression of marker molecules is ambiguous, as these molecules are expressed also by activated non-regulatory T cells. Furthermore, no firm criteria for flow cytometer gate settings exist so far. Recently, a specific DNA methylation pattern within FOXP3-TSDR has been reported that allows distinguishing Treg and non-regulatory T cells, independent of their activation status. Using this epigenetic marker, we established a single-tube real-time PCR based methylation assay (QAMA) for relative quantification of Treg cells. Validation was performed on defined ratios of methylated and unmethylated target sequence and on mixtures of Treg and non-regulatory T cells. DNA-methylation was measured in CD4⁺ T cells isolated from blood samples of 30 septic patients and 30 healthy subjects and compared with results of Treg cell quantification by flow cytometry based on CD4⁺ CD25^hiCD127^low measurement. In septic patients both methods showed an increased ratio of Treg cells to all CD4⁺ T cells. In healthy individuals, the results obtained by both methods were clearly positively correlated. However, the correlation between both methods in septic patients was only weak. We showed that quantification of Treg cells by QAMA detects CD4⁺ T cells with unmethylated FOXP3-TSDR, hidden in the CD25^med/low fraction of flow cytometry. Given that unmethylated FOXP3-TSDR is the most specific feature of Treg cells to date, our assay precisely quantifies Treg cells, as it additionally detects those committed Treg cells, hidden in the CD25^med/low fraction of CD4⁺ cells. Furthermore, QAMA is a reliable method, which is easier to standardize among laboratories and can thus improve reproducibility of Treg cell quantification.