High-affinity FRβ-specific CAR T cells eradicate AML and normal myeloid lineage without HSC toxicity

Area of Science:

• Immunology
• Oncology
• Cell Therapy

Background:

• Acute myeloid leukemia (AML) is an aggressive cancer requiring novel treatments.
• Chimeric antigen receptor (CAR) T-cell therapy shows promise for AML but faces challenges with on-target, off-tumor effects.
• Folate receptor beta (FRβ) is a potential target for AML therapy.

Purpose of the Study:

• To optimize FRβ-targeted CAR T-cell therapy for AML by developing a high-affinity FRβ-specific CAR.
• To evaluate the efficacy and safety of high-affinity FRβ CAR T-cells, including transient expression strategies.

Main Methods:

• Isolated a high-affinity (2.48 nm KD) FRβ-specific single-chain variable fragment for CAR development.
• Generated and tested high-affinity (HA) FRβ CAR T-cells against FRβ(+) AML in vitro and in vivo.
• Assessed FRβ expression on hematopoietic stem cells (HSCs) and mature myeloid cells.
• Evaluated transient CAR expression using mRNA electroporation.

Main Results:

• HA-FRβ CAR T-cells demonstrated superior anti-AML activity compared to low-affinity CAR T-cells.
• FRβ was expressed on mature myeloid cells but nearly undetectable on CD34(+) HSCs.
• HA-FRβ CAR T-cells lysed mature monocytes but did not impair HSC colony formation.
• mRNA-electroporated HA-FRβ CAR T-cells maintained potent anti-leukemia efficacy with reduced toxicity.

Conclusions:

• Antibody affinity is crucial for effective CAR T-cell therapy development.
• Transient delivery of HA-FRβ CAR T-cells offers a promising strategy for AML treatment.
• This approach enhances anti-leukemia efficacy while mitigating the risk of long-term myeloid toxicity.