Enhancement of anti-programmed cell death protein-1 immunotherapy in non-small cell lung cancer using arginine and citrulline supplementation

Purpose This study aimed to examine the role of citrulline in the lung cancer microenvironment and its potential synergistic effects with other therapies. Methods Murine lung cancer cells (CMT167) were subcutaneously implanted into mice to establish tumor models, followed by treatment with the anti-PD-1 antibody either alone or in combination with arginine or arginine and citrulline. Tumor growth, survival rate, cytokine levels, immune cell populations, and metabolic marker expression were assessed using histological, immunostaining, flow cytometry, and serum analyses. Results Mice in the treatment groups exhibited significantly lower tumor volumes than those in the control group (control, 1161.59 ± 294.73; anti-PD-1, 427.38 ± 355.34; anti-PD-1 plus arginine, 452.10 ± 332.04; anti-PD-1 plus arginine and citrulline, 198.45 ± 236.22 mm ³ ; P  < 0.0001). Furthermore, the anti-PD-1 plus arginine and citrulline group exhibited significantly improved progression-free survival compared with that of the control group ( P  = 0.00039). The anti-PD-1 plus arginine and citrulline group also showed a significantly higher number of tumor-infiltrating CD8 ⁺ lymphocytes per high-power field (hpf) than the control group (control, 24.22 ± 9.13; anti-PD-1, 29.20 ± 9.41; anti-PD-1 plus arginine, 34.33 ± 8.81; anti-PD-1 plus arginine and citrulline, 46.56 ± 10.01 cells/hpf). Conclusion Arginine and citrulline supplementation facilitated CD8 ⁺ lymphocyte infiltration into the tumor microenvironment, thereby augmenting the efficacy of lung cancer immunotherapy.