Paradoxical prognostic phenomenon of plasma T-cell-derived circulating DNA level in advanced non-small cell lung...

Non-tumor-derived circulating DNA (nt-cirDNA) of advanced non-small cell lung cancer (NSCLC), with unclear origination, is associated with prognosis. We hypothesized that a part of nt-cirDNA release from CD3 or CD8 tumor-infiltrating lymphocytes (TILs) could have clinical implications.

To investigate the feasibility of T-cell-derived circulating DNA (T-cirDNA) detection, real-time PCR with Taqman assay-specific rearranged TCRβ CDR3 region was conducted in plasma of 103 advanced NSCLC. CD3 and CD8-specific immunohistochemistry from biopsy specimen, was reviewed by one blinded pathologist to the T-cirDNA results. Prognostic impact including demographic characteristics was integrated into the model.

Circulating DNA was detectable in 100 patients with median of 4 ng ml^-1, while median of plasma T-cirDNA was 1.71 pg ml^-1. Median %ratio of T-cirDNA/cirDNA was 0.02%. T-cirDNA was categorized by %ratio of T-cirDNA/cirDNA as undetectable, low (≤ 1%) and high (> 1%). Paradoxical prognostic impact of T-cirDNA/cirDNA was observed. Undetectable and high T-cirDNA/cirDNA translated to independent favorable prognostic outcome, HR of 0.54 [95% CI 0.30-0.96] and 0.41 [95% CI 0.21-0.80], respectively. 43 patients were assessed for CD3/CD8 TILs and PD-L1. High intratumoral CD3/CD8 TILs but not stromal CD3 TILs was correlated with high T-cirDNA/cirDNA representing active T-lymphocyte activity to eliminate cancer cells. While the prognosis of undetectable T-cirDNA/cirDNA, represents inactivated naïve T-cell, was determined by the presence of EGFR mutation and had long durable response of EGFR inhibitors.

T-cirDNA could be a novel biomarker representing adaptive immune resistance in NSCLC patients. Further exploration as a predictive biomarker for EGFR inhibitors in setting of EGFR mutation might be warranted.