The Path Hunter FcγR1a clustering cell line is a stable, engineered cell line designed to increase signal produced from a Checkpoint Cell Line via antibody-mediated crosslinking of the receptors. This product is a companion product used to determine cross-linking based increases in potency of agonist antibodies. The cell line included overexpresses FcγR1a Fcg receptor. When co-cultured with a Checkpoint Cell Line in the presence of agonist antibody, the Fcg receptor binds to the antibody, inducing receptor clustering. The induced receptor clustering leads to increased activation and downstream signaling, leading to increased EFC signal production. This stable modified cell line is provided as two vials of cryopreserved cells.