Autoantibody spark response predicts treatment outcome in patients receiving chemoradiation followed by durvalumab therapy.

The PACIFIC regimen, comprising chemoradiotherapy (CRT) followed by maintenance with the immune checkpoint inhibitor (ICI) durvalumab, has become the standard of care for patients with unresectable non-small cell lung cancer (NSCLC). Although ICI is used to prevent recurrence by targeting residual microtumors, biomarkers capable of monitoring immune activity during this phase remain lacking. Here, we evaluated whether temporal changes in serum autoantibody levels can predict treatment efficacy. This retrospective study included 20 patients with unresectable stage II or III NSCLC who received the PACIFIC regimen. Serum autoantibodies against 130 antigens were quantified before CRT, after CRT, and two weeks after the first ICI dose. The primary outcome was progression-free survival (PFS), and its association with autoantibody dynamics was examined. We observed an immediate and strong autoantibody response (spark response [SR]) after ICI initiation in patients with favorable treatment outcomes. Patients with SR and programmed death ligand 1 (PD-L1) expression ≥ 50% showed better PFS (two-year PFS; 72.9% vs. 18.2%, p = 0.0021). These findings suggest that serial monitoring of serum autoantibodies can provide a noninvasive approach to assess immune activity and predict treatment outcomes in patients receiving CRT or ICI therapy.