A
assay for screening or determining the activity of a
lymphocyte-activation
gene 3 (
LAG-3)
agonist is described. According to the
assay, a plurality of
effector T cells is provided, each
effector T cell expressing
LAG-3 and a
T cell receptor (TCR) on its surface and comprising a
reporter gene encoding a reporter
protein, wherein expression of the reporter
protein is regulated by
LAG-3-mediated inhibition of TCR signaling within the
effector T cell. The activity of the
agonist is determined according to the extent to which expression of the reporter
protein is altered in the presence of the
agonist as compared to expression of the reporter protein in the absence of the agonist. The
assay can be used to determine the
potency of a preparation of the agonist, as a
quality control step in the production of the agonist, or for stability testing of a preparation of the agonist. A kit for performing the assay is also described.