1,2,4-oxadiazole derivatives as immunomodulators

A method of modulating an immune response mediated by a PD-1 signaling pathway in a subject, comprising administering to the subject a compound of formula (I) or a pharmaceutically acceptable salt or a pharmaceutically acceptable composition thereof:

• wherein,
• Q is S or O;
• R1 represents a side chain of an amino acid residue Ser or Thr, optionally substituted with alkyl or acyl;
• R2 is hydrogen or —CO-Aaa;
• Aaa is an amino acid residue selected from Thr and Ser;
• wherein a C-terminus thereof is a free terminus, is amidated, or is esterified;
• R3 represents a side chain of an amino acid residue selected from Asn, Asp, Gln, and Glu;
• ----- is an optional bond;
• R4 and R5 independently are hydrogen or absent;
• and
• R6 is hydrogen, alkyl, or acyl.