CD99 and Ewing sarcoma: To explore whether immunocompetence is the specific characteristic of T-ALL cells and whether the phenomenon of CAR tumor cell fratricide exists only on T-ALL cells or on all hematopoietic and non-hematopoietic tumor cells, we selected varieties of tumor cells to construct CD99 CAR tumor cells and tested their proliferation efficiencies, such as THP-1, MOLM-13 cell lines from (human acute myelocytic leukemia, AML), Raji cell line from lymphoma, SKOV-3 cell line from ovarian carcinoma and the RDES cell line from Ewing’s sarcoma.