The 4T1 murine mammary carcinoma cell line is a well characterized model known to spontaneously metastasize to the lungs and we previously reported a significantly reduced 4T1 metastasis in endosialin knockout (Cd248KO) mice.14 To investigate the ability of CD8+-heavy C57BL/6 E3K CAR-T cells to impair 4T1 metastasis, a pilot study was performed to determine the optimal timing of CAR-T cell treatment (online supplemental figure 5). Here, CD248 is linked to breast carcinoma.