The document details the creation of an anti-idiotypic monoclonal antibody specifically targeting the PGT121 monoclonal antibody (mAb) used in HIV treatment, highlighting its potential in both therapeutic and preventative applications. To ensure the consistent quality and effectiveness of the PGT121 mAb, these anti-idiotypic antibodies are developed for monitoring purposes during clinical applications. The research involved immunizing female BALB/cJ mice with a fragment of the PGT121 antibody, followed by cell fusion, screening for antibody production, and subsequent cloning to establish stable hybridomas. These procedures culminated in the isolation of monoclonal antibodies with desired specificities. The antibodies were then subjected to isotyping, reverse transcription, PCR amplification, and expression in Expi-293 cells, ensuring a consistent supply of high-fidelity reagents for the assessment of PGT121 mAb in various settings.