Low Interleukin-7 Receptor Messenger RNA Expression Is Independently Associated With Day 28 Mortality in Septic Shock Patients

Abstract

Objectives: Septic shock is the primary cause of death in ICUs. A better comprehension of its pathophysiology, in particular, the immune alteration mechanisms, opened new therapeutic perspectives such as the recombinant interleukin-7. The use of biomarkers could improve the identification of eligible patients for this therapy. The soluble form of the interleukin-7 appears as a promising candidate in this regard since an association between its high plasmatic level and mortality in critically ill patients has been demonstrated. Because there are no data available on the transcriptional regulation of the interleukin-7 receptor in such patients, this study aimed to explore the expression level of different interleukin-7 receptor transcripts after septic shock and evaluate their association with mortality.

Design: Retrospective discovery cohort (30 patients) and validation cohort (177 patients).

Setting: Two French ICUs (discovery study) and six French ICUs (validation study).

Patients: Adult septic shock patients.

Interventions: None.

Measurements and main results: The quantification of several interleukin-7 receptor transcripts using specific reverse transcription quantitative polymerase chain reaction designs allowed for global evaluation of interleukin-7 receptor gene expression in whole blood. In the discovery cohort, all interleukin-7 receptor transcripts studied were expressed at lower levels in septic shock patients than in healthy volunteers. Interleukin-7 receptor gene expression at day 3 after septic shock diagnosis was associated with day 28 mortality. Patients at a lower risk of death showed higher expression levels. These results were confirmed in the independent validation cohort. Interestingly, using a threshold obtained on the discovery cohort, we observed in the validation cohort a high negative predictive value for day 28 mortality for the transcript encoding the membrane form of interleukin-7 receptor (0.86; 95% CI, 0.79-0.93).

Conclusions: Interleukin-7 receptor transcripts appear as biomarkers of impaired adaptive immune response in septic shock patients and as a promising tool for patient stratification in clinical trials evaluating immunoadjuvant therapies.

Figure 1.

Interleukin-7 receptor (IL7R) transcripts expression levels in the discovery cohort. A, Comparison of messenger RNA (mRNA) expression between healthy volunteers (HV, n = 19) and septic shock patients at day 1 (D1) and day 3 (D3) after septic shock diagnosis (n = 30). mRNA levels are expressed as absolute concentration in copies/µL. B, Comparison of mRNA expression between day 28 nonsurvivor (NS, n = 9) and survivor (S, n = 21) patients, at D1 and D3 after septic shock diagnosis, and for the D3/D1 expression ratio. mRNA levels are expressed as calibrated normalized relative quantity (CNRQ) using hypoxanthine phosphoribosyltransferase 1 as reference gene. *p < 0.05, **p < 0.01, and ***p < 0.001 Mann-Whitney U test, ##p < 0.01 and ###p < 0.001 paired Wilcoxon test.

Figure 2.

Interleukin-7 receptor (IL7R) membrane transcript (IL7R-001) expression levels in the validation cohort. A, Comparison of IL7R expression levels between day 28 nonsurvivor (NS, n = 42) and survivor (S, n = 135) patients. IL7R expression levels were measured at day 3 (D3) after septic shock diagnosis. Messenger RNA (mRNA) levels are expressed as calibrated normalized relative quantity (CNRQ) using hypoxanthine phosphoribosyltransferase 1 (HPRT1) as reference gene. ***p < 0.001 Mann-Whitney U test. B, Survival curves and 95% CIs in patient groups of the validation cohort defined according to IL7R membrane transcript (IL7R-001) expression levels at D3, using the threshold obtained on the discovery cohort. This threshold of 0.20 is expressed as a CNRQ using HPRT1 as reference gene. The log-rank test was used to compare survival between groups.