Despite notably high response rates to B-cell maturation antigen (BCMA) chimeric antigen receptor (CAR) T cells in multiple myeloma, few patients have a sustained, very good partial or complete response. This article presents a novel strategy to increase the efficacy of BCMA-directed CAR T-cell therapy and shows that γ-secretase inhibitors improve the efficacy of BCMA CAR T cells by increasing BCMA expression and reducing soluble BCMA.
Impressive results have been achieved by adoptively transferring T-cells expressing CD19-specific CARs with binding domains from murine mAbs to treat B-cell malignancies. T-cell mediated immune responses specific for peptides from the murine scFv antigen-binding domain of the CAR can develop in patients and result in premature elimination of CAR-T-cells increasing the risk of tumor relapse. As fully human scFv might reduce immunogenicity, we generated CD19-specific human scFvs with similar binding characteristics as the murine FMC63-derived scFv using human Ab/DNA-libraries. CARs were constructed in various formats from several scFvs and used to transduce primary human T-cells. The resulting CD19-CAR-T-cells were specifically activated by and lysed CD19-positive tumor cell lines and primary CLL cells, and eliminated human lymphoma xenografts in immunodeficient mice. Certain fully human CAR constructs were superior to the FMC63-CAR, which is widely used in clinical trials. Imaging of cell surface distribution of the human CARs revealed no evidence of clustering without target cell engagement, and tonic signaling was not observed. To further reduce potential immunogenicity of the CARs, we also modified the fusion sites between different CAR components. The described fully human CARs for a validated clinical target may reduce immune rejection compared with murine based CARs.
The tactical introduction of Strep-tag II into synthetic antigen
receptors provides engineered T cells with a marker for identification and rapid
purification, and a functional element for selective antibody coated
microbead-driven large-scale expansion. Such receptor designs can be applied to
chimeric antigen receptors of different ligand specificities and costimulatory
domains, and to T cell receptors to facilitate cGMP manufacturing of adoptive T
cell therapies to treat cancer and other diseases.
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