AAV-mediated gene transfer of a checkpoint inhibitor in combination with HER2-targeted CAR-NK cells as experimental therapy for glioblastoma

Glioblastoma (GB) is the most common primary brain tumor, which is characterized by low immunogenicity of tumor cells and prevalent immunosuppression in the tumor microenvironment (TME). Targeted local combination immunotherapy is a promising strategy to overcome these obstacles. Here, we evaluated tumor-cell specific delivery of an anti-PD-1 immunoadhesin (aPD-1) via a targeted adeno-associated viral vector (AAV) as well as HER2-specific NK-92/5.28.z (anti-HER2.CAR/NK-92) cells as components for a combination immunotherapy. In co-culture experiments, target-activated anti-HER2.CAR/NK-92 cells modified surrounding tumor cells and bystander immune cells by triggering the release of inflammatory cytokines and upregulation of PD-L1. Tumor cell-specific delivery of aPD-1 was achieved by displaying a HER2-specific designed ankyrin repeat protein (DARPin) on the AAV surface. HER2-AAV mediated gene transfer into GB cells correlated with HER2 expression levels, without inducing anti-viral responses in transduced cells. Furthermore, AAV-transduction did not interfere with anti-HER2.CAR/NK-92 cell-mediated tumor cell lysis. After selective transduction of HER2⁺ cells, aPD-1 expression was detected at the mRNA and protein level. The aPD-1 immunoadhesin was secreted in a time-dependent manner, bound its target on PD-1-expressing cells and was able to re-activate T cells by efficiently disrupting the PD-1/PD-L1 axis. Moreover, high intratumoral and low systemic aPD-1 concentrations were achieved following local injection of HER2-AAV into orthotopic tumor grafts in vivo. aPD-1 was selectively produced in tumor tissue and could be detected up to 10 days after a single HER2-AAV injection. In subcutaneous GL261-HER2 and Tu2449-HER2 immunocompetent mouse models, administration of the combination therapy significantly prolonged survival, including complete tumor control in several animals in the GL261-HER2 model. In summary, local therapy with aPD-1 encoding HER2-AAVs in combination with anti-HER2.CAR/NK-92 cells may be a promising novel strategy for GB immunotherapy with the potential to enhance efficacy and reduce systemic side effects of immune-checkpoint inhibitors.

OS12.6.A Combination therapy of CAR-NK-cells and anti-PD-1 results in high efficacy against advanced-stage glioblastoma in a syngeneic mouse model and induces protective anti-tumor immunity in vivo

INTRODUCTION

Checkpoint inhibitors as well as adoptive cell therapy hold promise for cancer therapy and encouraging treatment responses have already been demonstrated in different cancer indications. Glioblastoma (GB) is the most common and aggressive primary brain tumor. Standard therapy has very limited efficacy in the majority of patients. Analysis of the GB microenvironment (TME) has shown prominent immunosuppressive features, including expression of PD-L1 on tumor cells and increased frequency of FOXP3-positive regulatory T cells. While the surrounding brain is HER2-negative, GB are frequently HER2-positive, suggesting HER2 as a promising target for adoptive immunotherapy. Previous results from mouse glioma models showed efficacy of CAR-NK cells (NK-92/5.28.z) targeted against HER2 as monotherapy with early stage but not with advanced-stage tumors.

MATERIALS AND METHODS

The murine glioma cell line GL261 was transfected with human HER2. Tumor cells were implanted either subcutaneously or orthotopically into C57BL/6 mice and treated either with HER2-specific NK-92/5.28.z cells alone or in combination with an anti-PD-1 antibody. Effects on tumor growth and survival were determined. Lymphocyte infiltration and immunosuppressive TME were characterized via highplex multi-color flow cytometry (FACS Symphony) and IHC (Phenoptics). Furthermore, gene expression profiles of tumor-infiltrating cells were determined via bulk RNAseq (NanoString).

RESULTS

Combined treatment with NK-92/5.28.z cells and anti-PD-1 checkpoint blockade resulted in synergistic effects, with tumor regression and long-term survival observed even in advanced-stage tumor bearing mice. Analysis of the TME showed changes in lymphocyte infiltration and increased expression of exhaustion markers in tumor and immune upon combined treatment with NK-92/5.28.z cells and anti-PD-1 antibody resulting in an altered TME. Both, PD-1 and Lag-3 expression are highly upregulated on tumor infiltrating T cells. Total infiltrating lymphocytes show a rather cytotoxic phenotype up combination treatment with NK-92/5.28.z cells and anti-PD-1 antibody

CONCLUSION

Our data demonstrate that efficacy of NK-92/5.28.z cells can be enhanced by combination with checkpoint blockade, resulting in successful treatment of advanced tumors refractory to NK-92/5.28.z monotherapy. Furthermore, the combination therapy induced a cytotoxic rather than immunosuppressive TME, leading to a primed immune system. To translate the concept of CAR-NK-cell therapy plus checkpoint inhibition to a clinical setting, we are adding a combination therapy cohort to our ongoing phase I clinical study (CAR2BRAIN; NCT03383978).

Reduced tumour cell proliferation and delayed development of high-grade mammary carcinomas in cathepsin B-deficient mice

Expression levels of the papain-like cysteine protease cathepsin B (Ctsb) have been positively correlated with mammary tumour progression and metastasis; however, its roles in the hallmark processes of malignant growth remain poorly defined. Using Ctsb-deficient mice we investigated tumour cell differentiation, proliferation and apoptosis in the Tg(MMTV-PyMT) mouse mammary cancer model. Absence of Ctsb significantly impaired development of high-grade invasive ductal carcinomas and reduced the metastatic burden in the lungs. Mice lacking Ctsb exhibited reduced cell proliferation in mammary carcinomas and their lung metastases. Notably, intravenous injection of primarily isolated, Ctsb-expressing tumour cells into congenic Ctsb-deficient mice revealed impaired cell proliferation in the resulting experimental lung metastases, providing evidence for the involvement of Ctsb in paracrine regulation of cancer cell proliferation. No Ctsb genotype-dependent difference in tumour cell death was observed in vivo or by treatment of isolated PyMT cancer cells with tumour necrosis factor-alpha. However, cancer cells lacking Ctsb exhibited significantly higher resistance to apoptosis induction by the lysosomotropic agent Leu-Leu-OMe. Thus, our results indicate an in vivo role for Ctsb in promoting cellular anaplasia in mammary cancers and proliferation in lung metastases.