Serum Citrulline As a Biomarker for Blood Stream Infections in Pediatric Hematopoietic Stem Cell Transplant Patients

Background: Invasive microbial infections remain a major cause of morbidity and mortality in hematopoietic stem cell transplant (HSCT) patients. Microbes residing in the GI tract are believed to be the source of mucosal barrier injury-associated blood stream infections (mBSI) in HSCT and cancer patients. Three host factors are critical for preventing microbial translocation from the gut: neutrophils, intact gut barrier function, and gut microbiota homeostasis. Currently there are no reliable biomarkers that can identify patients who will develop mBSIs.

Objectives/Hypothesis: Since all HSCT patients develop severe neutropenia (ANC<100), we hypothesized that HSCT patients who develop mBSI will have more impaired gut barrier function and a greater imbalance in gut microbiota populations (as evidenced by depletion of beneficial obligate anaerobe commensals) compared to counterparts who do not develop mBSI.

Methods: We designed a prospective, non-randomized, case control pilot study for HSCT patients < 20 years of age. Serum citrulline, which has been used as a surrogate to measure overall gut function, was obtained 1-2 times weekly. Bacterial genomic DNA was isolated from stool samples collected every 7 days. Amplicons (16S rRNA V4 variable region) were generated and sequenced using the Illumina MiSeq platform. Microbial taxonomic assignments were determined using QIIME software and further characterized into relative abundances of obligate (beneficial commensal) versus facultative (pathogenic) anaerobes. Clinical characteristics were recorded.

Results: Of the 78 HSCT patients enrolled on the study, 27% (21 patients) developed BSI. Of the patients with confirmed blood stream infections, 16 patients were categorized as mBSI, and ultimately 11 patients were included in our analysis. 48 patients did not develop a BSI and had evaluable citrulline levels and constituted our control group. Patients with mBSI had a more significant decline in citrulline levels during the period from the start of conditioning to the development of mBSIs (linear mixed effect model, p = 0.048, likelihood ratio test) compared to counterparts without mBSI. We found no significant association between levels of facultative (pathogenic) anaerobes and the development of mBSI in this cohort.

Conclusions: Decreased citrulline levels, which suggest impaired gut epithelial function, are associated with the development of severe, invasive bacterial infections. These data suggest that measuring citrulline may have utility as a biomarker for predicting mBSI in HSCT patients.