Evaluation of extracellular microRNAs as potential biomarker candidates for assessing chlamydia reinfection risk.

Chlamydia trachomatis infection remains prevalent, with high rates of reinfection. Most infections are asymptomatic, and without treatment, women are at risk for reproductive and perinatal complications that are exacerbated with repeat infections. Currently, no C. trachomatis vaccine is available nor are there clinical biomarkers to predict reinfection risk. Small, non-coding microRNAs (miRNAs) are promising biomarker candidates because of their easy isolation, high stability, and role as molecular messengers. MiRNAs can be intracellular and/or extracellular, with the latter being released from cells and either packaged into extracellular vesicles (EVs) or freely circulating in association with proteins. We identified miRNAs from serum EVs and whole serum collected from 42 women (53 samples) and 35 women (49 samples), respectively. Sera were collected at a baseline treatment visit and a 3-month follow-up visit, where women were determined to be reinfected or not reinfected by nucleic acid amplification test. MiRNA profiles were evaluated using Bruker nCounter microarrays, data were positive ligation normalized, miRNAs were categorized as detected or not detected, nominal significance was calculated using Fisher's exact test, and predicted target mRNAs were assessed with Qiagen's Ingenuity Pathway Analysis (IPA). Detection of EV-derived miR-888-5p at baseline was associated with reinfection at the follow-up visit. For whole serum, detection of miR-1285-5p, -548aa + 548t-3p, and -575 at baseline were associated with absence of reinfection at follow-up. MiRs-888-5p and -548aa aligned with varying degrees to mRNA targets associated with CD8+ and CD4 + T-cell functions, with miR-888-5p demonstrating strong CD8 + T-cell associations while miR-548aa was largely associated with CD4 + T-cell responses. Distinct EV and whole serum miRNAs were identified as potential biomarker candidates that are associated with reinfection risk. Our findings are preliminary, and future work includes validation studies to confirm whether these miRNAs can predict C. trachomatis reinfection risk.