ICH5099 is a recombinant, unconjugated non-therapeutic analog of veltuzumab, a humanized anti-CD20 IgG1 kappa monoclonal antibody, supplied for research use only. It reproduces the antigen-binding specificity of the originator biologic, which recognizes a conformational epitope on the large extracellular loop of human CD20 (MS4A1, UniProt P11836), and is offered in an unlabeled format free of clinical formulation excipients. As a bench reagent rather than a drug product, it is well suited to controlled experiments: flow-cytometric detection and quantitation of CD20 on B cells, epitope- and affinity-mapping studies, competitive binding versus other anti-CD20 antibodies, and use as a reference or benchmark antibody in ADCC, CDC, and apoptosis assays. It also serves as a positive control and a starting scaffold for ADC and bispecific development work, and for characterizing Fc-effector engineering. The antibody is available at research grade with low endotoxin (typically <1 EU/mg, with ultra-low <0.5 EU/mg options) and in bulk milligram-to-gram quantities to support in-vitro assay development and preclinical studies. It is not the clinical drug and is not intended for human or veterinary use.
CD20 (MS4A1, UniProt P11836) is a non-glycosylated, four-transmembrane-domain phosphoprotein of the MS4A family, expressed on B lymphocytes from the pre-B through mature and activated stages but absent on hematopoietic stem cells, pro-B cells, and terminally differentiated plasma cells. Its two extracellular loops present a conformational epitope on the larger loop that most therapeutic anti-CD20 antibodies engage. CD20 is not internalized appreciably upon antibody binding and lacks a known natural ligand; it is thought to function as a store-operated calcium channel component and to regulate B-cell activation, proliferation, and cell-cycle progression. Because it is lineage-restricted and stably surface-expressed, CD20 is a validated immunotherapy target, and antibodies against it drive B-cell depletion through complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity/phagocytosis, and direct pro-apoptotic signaling.