LAUSR

OBJECTIVE Accumulating evidences suggest that immune checkpoints (ICs) inhibit immune response against cancerous cells and promote tumor cell survival. Up-regulation of ICs in tumor microenvironment is reported in patients with colorectal cancer (CRC). Thus, evaluating the peripheral blood expression of ICs may be used as non-invasive biomarkers for diagnosis and prognosis of CRC. METHODS This study included 60 primary and treatment naïve CRC patients along with 15 age and sex matched healthy volunteers as a control group. Total RNA was extracted from peripheral blood samples and gene expression of cytotoxic T lymphocyte antigen-4 (CTLA-4), B and T lymphocyte attenuator (BTLA), T-cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), and Lymphocyte activation gene-3 (LAG-3) was measured by quantitative real time polymerase chain reaction (qRT-PCR). All patients were followed for 12 months to correlate the measured ICs to patients' survival. RESULTS The gene expression of CTLA-4, BTLA, TIM-3 and LAG-3 was significantly up-regulated in CRC patients compared to the control group (p<0.001). Individually, CTLA-4 and BTLA showed 85% sensitivity in discriminating CRC patients from control group (p<0.001). On the other hand, TIM-3 and LAG-3 expression showed higher sensitivity (93%) for diagnosis of CRC (p<0.001). Conversely, CTLA-4 or BTLA strongly predicted CRC patients' survival (p<0.001) compared to TIM-3 (p=0.018) or LAG-3 (p=0.035). CTLA-4, BTLA, TIM-3 and LAG-3 were independent prognostic factors of survival after adjustment for age and gender. CONCLUSION The current study provided evidence that blood gene expression of ICs was up-regulated in CRC patients and associated with cancer stage and patients' survival, which highlights the diagnostic and prognostic values of ICs expression in CRC. Further investigations and validations in larger cohorts are required.