About Non-Antigen Specific Functional Assays
Modulating immune checkpoint pathways with agonist or antagonistic therapeutic antibodies has been a recent major breakthrough for cancer therapy. Targeting cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) or its ligand (PD-L1) have demonstrated striking clinical responses with durable disease control resulting in improved survival in some patients across a broad spectrum of cancer types. Agonist antibodies targeting T cell activation pathways such as OX40, CD40, or CD27 are also in active clinical development. Given the power of these new therapies, it is important to evaluate the complex and dynamic immune responses using appropriate in-vitro functional assays as well as understanding the particular nuances associated with target of interest.
Recent assessment reports from the Food and Drug Administration (FDA) or European Medicines Agency (EMA) of approved checkpoint therapies to PD-1 have demonstrated that non-antigen specific functional assays, including Staphylococcal enterotoxin B (SEB) or anti-CD3/-CD28 activation bead stimulation, have an integral part in non-clinical characterization of these immune checkpoint therapies. These assays were used primarily for in-vitro pharmacodynamic assessment of: 1) potentiation of T cell responses in the presence of the biologic, and 2) PK/PD relationship between ex-vivo stimulated patient samples with treatment and correlating receptor occupancy levels on T cells.
With drug development companies understanding the critical role of these non-antigen specific functional assays, many are starting to use them earlier in the drug discovery process by employing them as a primary screening approach with their candidate therapeutics. Other trends include using these assays for translational research where patient’s samples from active clinical trials are stimulated ex-vivo in the presence of other checkpoint inhibitors to explore potential additive responses. Data derived from these clinical research efforts can provide a powerful assessment real-time or post-hoc when evaluating non-responding or responding patients by combining the data with expression data derived from cell profiling panels or sequencing data of T-cell and B-cell receptors.