PDCD1 and neoplasm: This add-on treatment effect upon combination of anti-PD-1 with chitin was anti-PD-1 dose-dependent, as a low (25 μg) anti-PD-1 dose in combination with chitin did not provide a significant additional tumor growth reduction compared to chitin monotherapy in the 4T1-based model based on primary tumor volume (Additional file 5: Fig. S3A) and in vivo imaging (Additional file 5: Fig. S3B,C).