By tracking the dynamics of immune cells in the tumor microenvironment over time, for example, with anti‐CD45 labeling of the tumor‐infiltrating lymphocytes, factors can be identified that contribute to the development of CAR‐T cell exhaustion, modest anti‐tumor activity, and restricted trafficking, and thus may help to limit tumor infiltration and the incidence of severe life‐threatening toxicities.2 Here, PTPRC is linked to neoplasm.