Compounds of Formula (I) are provided:and pharmaceutically acceptable salts and stereoisomers thereof； wherein:R1 is a side chain of amino acid Ala, Ser, Thr or Leu；R2 is a side chain of amino acid Asp, Glu, Gln or Asn；[Aaa] is an amino acid residue selected from Ser, ASP, Ala, Ile, Phe, Trp, Lys, Glu or Thr；R3 is hydrogen or alkyl；each of R4 and R4′ independently are hydrogen or alkyl；both Ra and Ra′ are hydrogen； or together are an oxo (═O) group；both Rb and Rb′ are hydrogen； or together are an oxo (═O) group；L isX is CH2, O or S；R5 is hydrogen or alkyl；m is an integer from 1 to 3； andn is an integer from 2 to 20.The compounds are useful for treatment of disorders via immunopotentiation comprising inhibition of immunosuppressive signal induced due to PD-1, PD-L1, or PD-L2 and therapies using them.
