[ 68 Ga]Ga-NODAGA-SNA006 PET/CT Reveals CD8 + T-Cell Dynamics in Lung Cancer Progression and Anti–PD-1 Response

Heterogeneous response to anti–programmed cell death protein 1 (PD-1) immunotherapy in lung cancer necessitates reliable biomarkers for monitoring systemic CD8+ T-cell dynamics. This study used [68Ga]Ga-NODAGA-SNA006, a CD8-targeted PET tracer, to evaluate CD8+ T-cell distribution in relation to disease progression and treatment response. Methods: Fourteen patients with stage II–IV lung cancer underwent baseline [68Ga]Ga-NODAGA-SNA006 PET/CT and blood CD8+ T-cell quantification. Eight patients receiving anti–PD-1–based chemoimmunotherapy underwent PET/CT and blood analyses before treatment and after 2 treatment cycles. SUVmax was measured in tumors (along with the tumor-to-background ratio), the spleen, the liver, and axial (sternum, T12, pelvis) and appendicular (femur) bone marrow. Correlations with disease stage, peripheral blood CD8+ T-cell quantification, programmed death ligand 1 (PD-L1) expression, and tumor reduction were assessed. Results: Patients with stage IV disease patients exhibited a lower peripheral blood CD8+ T-cell count and percentage (P < 0.05), whereas the SUVmax in the spleen (P < 0.05) and axial bone marrow (sternum, T12, pelvis; P < 0.01) was higher than that in patients with earlier-stage disease. Peripheral blood CD8+ T-cell percentage was correlated with SUVmax in the spleen (r2 = 0.38, P < 0.05) and axial bone marrow sites (most significant in sternum: r2 = 0.68, P < 0.001). After anti–PD-1 therapy, analysis of combined “axial skeleton SUV” (sternum, T12, pelvis) revealed a significant interaction between time and PD-L1 group (P < 0.001): SUV increased in the low PD-L1 (<10%) group but decreased in the high PD-L1 (≥10%) group. Changes in peripheral blood CD8+ T-cell count and percentage were not significant. Tumor shrinkage was not significantly correlated with peripheral blood CD8+ T-cell percentage or T-cell dynamics. For all target lesions, tumor shrinkage showed moderate positive correlations with baseline lesion SUVmax (r2 = 0.30, P < 0.01) and baseline tumor-to-background ratio (r2 = 0.34, P < 0.001) and a strong positive correlation with the reduction in lesion SUVmax after treatment (r2 = 0.44, P < 0.01). Conclusion: [68Ga]Ga-NODAGA-SNA006 PET/CT revealed systemic CD8+ T-cell depletion and splenic/axial marrow sequestration in advanced lung cancer. During anti–PD-1 therapy, CD8+ T cells redistribute on the basis of PD-L1 status. Baseline intratumoral CD8+ T-cell density and early on-treatment SUVmax reduction are robust imaging biomarkers of response, outperforming peripheral blood monitoring.