Noncanonical amino acid-aided synthesis of anti-PD-L1 bispecific nanobody for colon cancer immunotherapy

Colorectal cancer (CRC) is the second leading cause of cancer-related mortality, and the incidence of early-onset colon cancer has been increasing globally in recent years. The development of immunotherapies for colon cancer is critical for providing new treatment strategies to combat drug resistance. Here, a bispecific nanobody against PD-L1 (BsNb-PD-L1) constructed using genetically encoded noncanonical amino acids (ncAAs) is reported. A computational protocol was developed to identify appropriate sites in the nanobody for incorporating p-acetylphenylalanine (pAcF). Variants of nanobodies PV2 and PV3 with pAcF incorporated were conjugated with linkers containing an aminooxy functionality to enable oxime ligation. The resulting PV2-S71 + PV3-N77 bispecific nanobody (BsNb-ncAA) exhibited higher thermostability and binding affinity compared to the nanobody monomers and the BsNb constructed by simply fusing two proteins. Moreover, in an in vitro phagocytosis model, the BsNb-ncAA exhibited improved capability to inhibit immune evasion and showed stronger biological activity compared to the fusion protein PV2-PV3. Furthermore, the BsNb-ncAA resulted in a marked increase in the number of CD8⁺ T cells within tumor tissues and demonstrated efficient inhibitory effects against colon tumor growth in vivo. Our study provides a general strategy for constructing BsNbs, which has potential applications in other cancer immunotherapy.