Supplemental Data:

Fig. S1. The binding specificity of consensus sequence CWCWR to MDA-MB-435 and MDA-MB-231 cells. The binding ability of control peptide to MDA-MB-231 (A), consensus sequence to MDA-MB-231 (B), control peptide to MDA-MB-435 (C) and consensus sequence to MDA-MB-435 (D).

Fig. S2. A, The schematic illustration of construction the focused library. B, Ten clones were randomly selected for sequencing to examine the diversity of the focused library.

Fig. S3. Binding properties of peptides displayed on the bacteria surface. A, The binding ability of the clone 1, clone 2, clone 3 and a random library clone to PD-L1 at 2 nM (n=3). The binding ability with different PD-L1 concentrations (B) (n=3), under different washing procedures(C) (n=3). D. Binding specificity of peptides to PD-L1 (n=3). All the experiments were examined by flow cytometry. Data were presented as mean ± SEM, *P<0.05, unpaired t-test.

Fig. S4. The binding properties of TPP-1 and SPP-1 to PD-L1 were determined by the ELISA (n=3).

Fig. S5. A, The PD-L1 expression of CHO-K1/PD-L1, MDA-MB-231 and MDA-MB-435 cell lines were determined by anti-PD-L1 antibody and flow cytometer. B, The binding properties of TPP-1 to MDA-MB-231 and MDA-MB-435 cell lines.

Fig. S6. The bright field (A) and fluorescence microscopic image (B) of TPP-1 to CHO-K1. The bright field (C) and fluorescence microscopic image (D) of TPP-1 to CHO-K1/PD-L1.

Fig. S7. A, The ED50 of PD-L1 to block the activated T cells (n=3). B, The TPP-1 peptide or PD-L1 plus TPP-1 peptide did not activate the T cells without the CD3 antibody. C, TPP-1 could effectively restore T cells proliferation which were inhibited by PD-L1 evaluated by T cell activation assay (n=3). Data were presented as mean ± SEM, *P<0.05, **P<0.01, unpaired t-test.

Fig. S8. A, The PD-L1 expression in matured DCs, the dotted line represented the isotype mAb and filled line represented the anti-PD-L1 mAb. B, The proliferation of T cells in MLR assay (n=3).

Fig. S9. A, The bioluminescence signals of H460-Luc cells were determined by Cytation 3. B, The expression of PD-L1 on H460 was detected with flow cytometry. The dotted line represented the isotype mAb and filled line represented the anti-PD-L1 mAb. Data were presented as mean ± SEM, **P<0.01, unpaired t-test.

Fig. S10. A, In vivo fluorescence images of mice taken at different time points post s.c. injection of FITC labeled TPP-1. B, The statistical result of the relative fluorescence unit.

Fig. S11. A, The location of CWCWR (yellow) in TPP-1 peptide. B, The possible binding location of TPP-1 (blue) peptide to PD-L1 (PDB ID of PD-L1: 3BIS). C, The crystal structures of PD-1 (light sea green) and PD-L1 (dark khaki) complex (PDB ID of the complex: 3BIK).

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