Development of surrogate potency assays for cellular immunotherapies

Abstract

Background & Aim Cellular therapy products are required to have meaningful tests determining safety and quality. This is to be achieved by establishing sterility, identity, purity and potency of the final product. As required by FDA per 21 CFR 610, potency of the cell therapy product should be determined by appropriate tests that shows effector function of such products. The methods that are currently being used to test effector function of immune cells include use of tumor cells as target cells and various labelling methods. Target tumor cells add biological variabilities to these tests which already have variabilities introduced by donor sources, tedious set ups, plate conditions, person to person variability in assay set up and readout variabilities from different labelling methods. There is an obvious need of a simpler potency assay with less variability and more reliable results. Methods, Results & Conclusion We are developing potency assays to address the issues of current available assays and to satisfy FDA requirements of potency assay for advanced phase clinical trials of therapeutic effector cells. FDA allows the use of surrogate method to determine potency of the cell therapy product given it correlates with the effector function of such product. Here, we have tested PHA and K562-derived exosomes as easily-standardized surrogate methods to activate NK cells, and have assessed induced cytokine production as correlates of their effector function. Avoiding the use of target cells simplifies set up, and use of these assays removes the variabilities of traditional potency assays. The PHA-based assay can be used to test potency of purified therapeutic effector cells, whereas the exosome-based assay can elicit NK cell potency in pure or complex mixtures and modifications may be developed for specificity to other immune cell products. NK cells expanded with feeder cells expressing membrane-bound IL-21 have shown high IL-2 and IFN-g in correlation with high cytotoxicity against tumor cells. We were able to replicate this effector function using PHA based potency assay. Preliminary experiment for exosome based assay also showed similar trend. This rapidly-advancing industry has need of more rapid and reliable potency assays to test function of therapeutic immune cells. We hope to address this issue with development of these potency assays as a replacement to traditional cytotoxicity tests.