GFRA4 and medullary thyroid gland carcinoma: Measuring GFP expression by flow cytometry, P4-10bbz expressing Jurkat cells showed activation over basal levels when grown in wells coated with recombinant or containing soluble GFRα4 as well as when co-cultured with TT and MZ-CRC1 cells (two human MTC cell lines, which express the target antigen GFRα4).