Antigen availability as a determinant of GPC3-directed CAR-T therapy in hepatocellular carcinoma

Glypican-3 (GPC3) is a target for chimeric antigen receptor T-cell (CAR-T) therapy in hepatocellular carcinoma (HCC), yet tissue positivity alone incompletely describes its suitability. Recognition requires sufficient exposed CAR-binding epitopes on viable tumor-cell membranes and contact with functional T cells. This review distinguishes antigen expression, antigen availability, and spatial accessibility through pathology, receptor engineering, soluble-antigen studies, and clinical observations. Heterogeneity and surface-density distributions affect recognition, while proteolytic processing, membrane retention, extracellular vesicles, and soluble GPC3 can separate tissue staining from exposed binding sites. Soluble GPC3 inhibits selected CAR constructs in preclinical models; its clinical effect remains uncertain. Clinical findings implicate antigen loss in resistance, but the contributions of pre-existing selection, genetic alteration, and reversible downregulation are unresolved. Sensitivity tuning, functionally verified OR recognition, and delivery or trafficking interventions address low density, heterogeneous coverage, and spatial exclusion, respectively. Armoring can sustain antigen-driven function but does not restore recognition of antigen-null cells. We propose a multidimensional, explicitly unvalidated GPC3 Antigen Availability Score framework and trial endpoints linking serial antigen measurements to lesion-level response. Prospective studies are needed to relate evolving antigen states and tissue organization to durable CAR-T control.