A recombinant humanized immunoglobulin G1 (IgG1) monoclonal antibody directed against the tumor-associated antigen (TAA) Claudin18.2 (CLDN18.2; A2 isoform of claudin-18), with potential immunostimulating and antineoplastic activities. Upon administration, osemitamab specifically targets, binds to and inhibits CLDN18.2 expressed on tumor cells. This may kill CLDN18.2-expressing tumor cells by antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), and inhibit cell proliferation. CLDN18.2, a tight junction protein and stomach-specific isoform of claudin-18, is overexpressed on a variety of tumor cells, but its expression in healthy tissues is strictly confined to short-lived differentiated epithelial cells of the gastric mucosa. Osemitamab is produced with reduced fucosylation.