Since B7-H3 has been reported to be expressed on both myeloid and lymphoid leukemia cells, the investigators also tested the CAR against a murine model of leukemia generated by injection of K562, a well-characterized line of myeloid leukemia cells.
“While we found some increase in survival in the mice that received the B7-H3 CAR T cells, compared to mice that received untransduced CAR T cells, this clearly is not as effective as in our solid tumor models,” Dr. Majzner said.
Going back to the cell line, they discovered that expression of B7-H3 was considerably lower in the K562 cells than in either the osteosarcoma or medulloblastoma cell lines used in their other models.
They found that both in vitro and in vivo, high levels of B7-H3 expression were necessary to provoke the immune system into releasing cytokines necessary for an adequate antitumor response.