Blood immune cells cooperate to prevent the progression of tumors through cancer immunosurveillance. Since activated peripheral immune cell clones trigger a sensitive transcriptional response upon recognition of tumors, which can be identified by transcriptional profiling, we hypothesised that peripheral blood mononuclear cells (PBMCs) could be used as reporters for cancer detection.
Materials and methods
We used a model system in which groups of immunocompetent BALB-c mice were subcutaneously injected with different numbers of tumorigenic B61 fibrosarcoma cells. The groups of study were: (i) tumoral group with serial injections of 102 to 106 cells; (ii) negative control group represented by sterile nonpyrogenic saline, (iii) inflammation group by Zymozan (Sigma) and (iv) bacterial infection group by injection of 107colony forming units [cfu] pool from mice feces. Mouse peripheral blood was collected three days after injection; blood samples (N=10) were pooled according to experimental conditions. Mononuclear cells were separated by centrifugation on a Ficoll-Hypaque cushion (GE Healthcare) and RNA was extracted using Trizol Reagent (Invitrogen). Samples were hybridizated on miRNA microarrays (Agilent).
We identified four microRNAs, miR-451, miR-144, miR-486 and miR-494, which were differentially expressed when compared to control groups, including inflammation and bacterial infection.
Our results showed that PBMC microRNA expression profiling can serve as a sensitive method for detection of preclinical cancer.