CD19 and cancer: Although the therapeutic effects of CAR-T cells on hematological malignancies, especially CAR-T cells targeting CD-19, have been elucidated, the development of CARs for the treatment of solid tumors has been hindered by the paucity of optimal antigens, the inability of T cells to migrate to and infiltrate primary lesions, transgene immunogenicity and toxicity, ongoing evolution of cancer cells, possible existence of CSC populations, and the immunosuppressive tumor microenvironment.