Inhibition of MEK pathway enhances the antitumor efficacy of chimeric antigen receptor T cells against neuroblastoma.

Disialoganglioside (GD2)-specific chimeric antigen receptor (CAR)-T cells (GD2-CAR-T cells) have been developed and tested in early clinical trials in patients with relapsed/refractory neuroblastoma. However, the effectiveness of immunotherapy using these cells is limited, and requires improvement. Combined therapy with CAR-T cells and molecular targeted drugs could be a promising strategy to enhance the antitumor efficacy of CAR T cell immunotherapy. Here, we generated GD2-CAR-T cells through piggyBac transposon (PB)-based gene transfer (PB-GD2-CAR-T cells), and analyzed the combined effect of these cells and a MEK inhibitor in vitro and in vivo on neuroblastoma. Trametinib, a MEK inhibitor, ameliorated the killing efficacy of PB-GD2-CAR-T cells in vitro, whereas a combined treatment of the two showed superior antitumor efficacy in a murine xenograft model compared to that of PB-GD2-CAR-T cell monotherapy, regardless of the mutation status of the MAPK pathway in tumor cells. The results presented here provide new insights into the feasibility of combined treatment with CAR-T cells and MEK inhibitors in patients with neuroblastoma.

A lymphodepleted non-human primate model for the assessment of acute on-target and off-tumor toxicity of human chimeric antigen receptor-T cells.

OBJECTIVES: Chimeric antigen receptor (CAR)-T cell therapy possesses the potential to cause unexpected on-target toxicities that may be life-threatening. Non-human primates (NHPs) share considerable structural homology and expression profiles of most proteins with humans and are therefore utilised as an animal model for non-clinical safety studies. We have developed a lymphodepleted NHP model by conditioning the animals with immunosuppressive chemotherapy designed to simulate clinical practice conditions, to induce transient mixed chimerism before the administration of human CAR-T cells redirected to target Ephrin type-B receptor 4 (EPHB4-CAR-T cells) to evaluate the toxicity of these cells. METHODS: We administered 60 mg m-2 day-1 of fludarabine for 4 days and 30 mg kg-1 day-1 of cyclophosphamide for 2 days intravenously to cynomolgus macaques for lymphodepletion; then, 3.3 × 106 kg-1 of non-transduced or EPHB4-CAR-T cells was infused into the macaques, respectively. All macaques were closely monitored and evaluated for potential toxicity for 7 days. RESULTS: Lymphodepletion was successfully achieved on day -1 before T-cell infusion and persisted over 7 days without severe organ toxicities. A single administration of human EPHB4-CAR-T cells did not induce overt organ toxicities, although EPHB4-CAR-T cells were activated in vivo as evidenced by the elevation in copy numbers of the CAR transgene 24 h after infusion. CONCLUSION: Although this NHP model is limited for the full evaluation of toxicity of human CAR-T cells and the conditioning protocol should be further optimised, this lymphodepleted NHP model could be used to assess acute on-target/off-tumor toxicities of CAR-T cells.

Development of non-viral, ligand-dependent, EPHB4-specific chimeric antigen receptor T cells for treatment of rhabdomyosarcoma.

Ephrin type-B receptor 4 (EPHB4), expressed in tumors including rhabdomyosarcoma, is a suitable target for chimeric antigen receptor (CAR)-T cells. Ligand-independent activation of EPHB4 causes cell proliferation and malignant transformation in rhabdomyosarcoma, whereas ligand-dependent stimulation of EPHB4 induces apoptosis in rhabdomyosarcoma. Therefore, we hypothesized that ligand-based, EPHB4-specific CAR-T cells may kill rhabdomyosarcoma cells without stimulating downstream cell proliferation mechanisms. We developed novel CAR-T cells by targeting EPHB4 via EPHRIN B2, a natural ligand of EPHB4. The generation of EPHB4-CAR-T cells via piggyBac (PB) transposon-based gene transfer resulted in sufficient T cell expansion and CAR positivity (78.5% ± 5.9%). PB-EPHB4-CAR-T cells displayed a dominant stem cell memory fraction (59.4% ± 7.2%) as well as low PD-1 expression (0.60% ± 0.21%) after 14 days of expansion. The PB-EPHB4-CAR-T cells inhibited EPHB4-positive tumor cells without activating cell proliferation downstream of EPHB4, even after multiple tumor re-challenges and suppressed tumor growth in xenograft-bearing mice. Therefore, PB-EPHB4-CAR-T cells possess a memory-rich fraction without early T cell exhaustion and show potential as promising therapeutic agents for treating rhabdomyosarcoma and other EPHB4-positive tumors.