Calibrator 20 is a lyophilized blend of CD20, CD27, CD28, CD276/B7-H3, CTLA-4, GITRL/TNFSF18, OX40/TNFRSF4, PD1, TIGIT, and TLR1. It is intended for use as an assay calibrator for MSD U-PLEX human assays that measure any of the included proteins. The utility of this product has not been evaluated in other applications. Individual analyte concentrations are provided in the lot-specific certificates of analysis. CD20, CD27, CTLA-4, OX40/TNFRSF4, and PD1 were expressed in a human cell line, CD276/B7-H3, CD28, and TLR1 were expressed in a mouse cell line, TIGIT was expressed in a hamster cell line, and GITRL/TNFSF18 was expressed in E. coli. Instructions on using Calibrator 20 are provided in U-PLEX Immuno-Oncology Group 1 Human Product Inserts.