Clinical Significance of Elevated Levels of Soluble-Form Immune Checkpoint Molecules in Patients With Aggressive...

Immune checkpoint (IC) pathways, including programmed death protein 1 (PD-1), its ligand PD-L1, and CTLA-4, mediate negative regulatory signals in immune responses. Recent studies in autoimmune diseases and malignancies reported that the presence of the soluble form of these ICs would reflect the overall immune status. We assessed the clinical significance of these soluble-form ICs in HTLV-1 carriers and adult T-cell leukemia-lymphoma (ATL) patients.

After obtaining informed consent, plasma from HTLV-1 carriers and ATL patients was prospectively collected in participating centers. Plasma concentrations of soluble-form PD-1, PD-L1, and CTLA-4 (sPD-1, sPD-L1, and sCTLA-4) were measured.

Ninety-six cases were included (HTLV-1 carriers, n = 4; indolent ATL, n = 14; aggressive ATL, n = 78). The median age at sampling was 65.5 (range, 23-85) years. Soluble factors levels were significantly higher in aggressive ATL than in indolent ATL (sPD-1, p = 0.003; sPD-L1, p = 0.017; sCTLA-4, p < 0.001). These markers were strongly correlated with soluble IL-2R (sPD-1, r = 0.80; sPD-L1, r = 0.61; sCTLA-4, r = 0.82). Elevated soluble IC levels were significant adverse prognostic factors.

Soluble IC levels were significantly higher in aggressive ATL than in indolent ATL, and predicted an adverse prognosis. Their clinical significance should be investigated in larger studies.