CD28 and neoplasm: We next evaluated CD28 and 4-1BB MSLN CAR T cells antitumor potency against K562 tumor cells expressing GFP and MSLN after 3 GC exposures (10 μg/ml Dx and 50 μg/ml MP) over a one-week period using a flow cytometry based killing assay (Fig. 5A and Additional file 1: Figure S5A).