CD123 is a subunit of the heterodimeric interleukin-3-receptor (IL-3R) which is widely expressed on human hematologic malignancies including acute myeloid leukemia (AML). In addition, CD123 can be found on the surface of B cell acute lymphoblastic leukemia (B-ALL), hairy cell leukemia, blastic plasmacytoid dendritic cell neoplasm (BPDCN), chronic myeloid leukemia (CML) and Hodgkin’s lymphoma.
Of these malignancies, we are currently investigating CD123 as a target for adoptive cellular immunotherapy in AML since high CD123 expression is associated with enhanced AML blast proliferation, increased resistance of blasts to apoptosis, and poor clinical prognosis.
Acute Myeloid Leukemia (AML), is a cancer of the myeloid line of blood cells characterized by rapid growth of abnormal white blood cells that accumulate in the bone marrow. AML is the most common form of acute leukemia. Although AML is a relatively rare disease there are approximately 20,000 new cases per year in the US and 10,000 deaths per year, accounting for approximately 1.8% of cancer deaths in the US (SEER). AML standard of care involves chemotherapy to induce remission followed by additional chemotherapy or hematopoietic stem cell transplant. Allogeneic stem cell transplantation is the preferred treatment route for AML following a second remission. It can lead to a 5-year disease free survival in 26% of patients. Unfortunately however, currently, only about half of relapsed patients are able to achieve a second remission with traditional chemotherapy agents. Patients who do not achieve a second remission are much less likely to benefit from transplantation and face a poor outcome.
The use of CAR T immunotherapy in relapsed AML patients may offer the potential to achieve a complete or longer lasting remission. City of Hope developed CD123 targeted CAR T cells designed to be both activated to proliferate and to kill CD123 expressing tumor cells. The therapy is designed to recognize and eliminate leukemic cells leading to remission in patients with relapsed or refractory AML and could serve as a bridge to potentially curative allogenic stem cell transplant. The manufacturing process genetically modifies T cells isolated from peripheral blood mononuclear cells to express a CD123-specific, hinge–optimized, CD28 co-stimulatory domain expressing CAR as well as an EGFRt selection/safety marker. The last feature acts a safety switch to allow depletion of CAR T cells in the patients if needed.
In collaboration with the COH, we have an on-going phase I clinical study to assess the anti-tumor activity and safety of administering CD123 targeted CAR T cells and are currently treating patients. We will assess the T cell persistence and determine the potential immunogenicity of the cells to determine a recommended phase II dose.