CD19 and infection: Even if the retrovirus vector was diluted 4 times, the percentage of CD19 CAR-T cells transduced with BaEV-CD19 CAR-RV was maintained at the same level as that of the stock medium, indicating that BaEV-CD19 CAR-RV still had good transduction efficiency for T cells at very low titers and low MOI(multiplicity of infection, the ratio of the virus to the cells at the time of transduction).