When simulating the cocktail of CD19 Si-CAR T cells and CD20 Si-CAR T cells by coculture of two Si-CAR T cells with tumor cells, it was found that CD19 Si-CAR T cells are preferentially amplified over CD20 Si-CAR T cells in vitro [21], which could lessen the effect of CD20 Si-CAR T cells in eliminating CD19-negative cells. The gene discussed is CD19; the disease is neoplasm.