Similar to CD19, CD22-directed immunotherapies for acute leukemias are also susceptible to low antigen density as a mechanism of therapy resistance, as observed under the selective pressures of both the CD22-targeting ADC inotuzumab ozogamicin (Paul et al. 2019, Shah et al. 2015) and CD22-directed CAR T cells (Fry et al. 2018). The gene discussed is CD19; the disease is acute leukemia.