Monoclonal antibody (mAb) based immune checkpoint inhibitors (ICIs) have emerged as an effective and promising therapeutic agent for cancer immunotherapy. In the setting of tumor immune-suppression, an effective delivery of mAbs ICI might be essential to overcome tumor resistance, immune tolerance, and immune-related adverse effects (irAEs). Herein we report engineered MRI visible anti-programmed cell death ligand-1 mAb (aPD-L1) nanoconjugates using nano-bio interface Z-domain (Z) protein adaptors for the local ICI immunotherapy. Z protein adaptors, which are binding with Fc region of IgG mAb, were modified to be attached on the surface of MRI visible ferumoxytol (Fer). Z-protein adaptors on the surface of Fer allowed an oriented conjugation of aPD-L1 exposing active Fab binding sites outward for effective blockage of immune checkpoints. Enhanced affinity and avidity of engineered Z mediated aPD-L1 nanoconjugates (aPD-L1-Z-Fer) to block the PD-1/PD-L1 axis were demonstrated in vitro and in vivo. Transcatheter-directed hepatic intra-arterial (IA) infusion of aPD-L1-Z-Fer showed superior in vivo hepatocellular carcinoma (HCC) tumor suppression, immune conversion, and minimized irAEs compared to the experimental groups treated with systemic aPD-L1, local aPD-L1, or chemically conjugated aPD-L1@Fer. Nano-bio interface Z protein adaptors mediated conjugation of functional nanoparticles and mAbs ICI will provide a new avenue to expand local ICI immunotherapy.