The La-protein as an inducible target for CAR T cell therapy

The La-protein is a multifunctional abundantly expressed protein in the nucleus of all human cells, where it for example functions as a chaperone for newly synthesized RNA-polymerase III transcripts. Recently, it has been shown that La is overexpressed in malignant cells and can be translocated to the cell surface under certain conditions, e. g. radio- or chemotherapy-induced necrosis, where it becomes a promising, inducible target for so-called “Death Targeting” approaches.
The aim of this study was to investigate whether the La-protein could also be used as an inducible target for CAR T cell therapy. Therefore, three different CAR T cells directed against the La-protein (La-CARs) were developed and tested regarding their potential for “Death Targeting” of tumor cells. For construction of the La-CARs, we selected three different anti-La mAbs (5B9, 7B6 and 312B), which recognize distinct epitopes within the La-protein in a redox-dependent manner. This allowed us to determine, if the redox-state influences the ability of the La-CARs to target cell surface-bound La-protein.
We first examined if La-CARs could eliminate tumor cells that were artificially labeled with wildtype La-protein or its oxidation-resistant triple-cysteine-mutant (TCM). By performing luciferase-based killing assays, we showed, that all La-CARs were specifically activated for lysis of La- or TCM-decorated tumor cells, which also resulted in significant secretion of pro-inflammatory cytokines. Redox-dependent differences of the La-CARs could be observed, whereby the non-redox-dependent 5B9-CAR was activated by La-wt- and TCM-labeled cells, the 7B6-CAR preferably by La-wt-labeled and the 312B-CAR preferably by TCM-labeled tumor cells.
We could further prove that La-release from tumor cells could be induced by treatment with the cytotoxic drug cisplatin and La-CARs could be redirected against remaining tumor-cells after cisplatin treatment. Thereby, the 5B9-CAR, which recognizes La-protein independent of its redox-state, induced highest tumor cell killing after cisplatin treatment.
In summary, we could show that the La-protein is a promising target for CAR T cell therapy. Release of La-protein can be induced by the cytotoxic drug cisplatin, making a combinatorial strategy of chemotherapy and CAR T cell therapy a promising approach for tumor immuno-therapy.