// Xilin Chen 1, 2, * , Jianfeng Han 3, * , Jianhong Chu 3, 4, * , Lingling Zhang 3, * , Jianying Zhang 5 , Charlie Chen 3 , Luxi Chen 3 , Youwei Wang 3 , Hongwei Wang 3 , Long Yi 3 , J. Bradley Elder 3, 8 , Qi-En Wang 6 , Xiaoming He 7 , Balveen Kaur 3, 8 , E. Antonio Chiocca 9 , Jianhua Yu 1, 3, 10 1 Division of Hematology, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA 2 Lymphoma/Head and Neck Oncology Department, 307 Hospital, Beijing 100071, China 3 The Ohio State University Comprehensive Cancer Center, Columbus, Ohio 43210, USA 4 Institute of Blood and Marrow Transplantation, Soochow University, Suzhou 215000, China 5 Center for Biostatistics, The Ohio State University, Columbus, Ohio 43210, USA 6 Department of Radiology, The Ohio State University, Columbus, Ohio 43210, USA 7 Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio 43210, USA 8 Department of Neurological Surgery, The Ohio State University, Columbus, Ohio 43210, USA 9 Department of Neurosurgery, Brigham and Women’s Hospital and Harvey Cushing Neuro-oncology Laboratories, Harvard Medical School, Boston, Massachusetts 02115, USA 10 The James Cancer Hospital, Columbus, OH 43210, USA * These authors have contributed equally to this work Correspondence to: Jianhua Yu, e-mail: jianhua.yu@osumc.edu Keywords: breast cancer brain metastases, chimeric antigen receptor, natural killer cells, EGFR, oncolytic virus Received: October 13, 2015 Accepted: March 16, 2016 Published: April 01, 2016 ABSTRACT Breast cancer brain metastases (BCBMs) are common in patients with metastatic breast cancer and indicate a poor prognosis. These tumors are especially resistant to currently available treatments due to multiple factors. However, the combination of chimeric antigen receptor (CAR)-modified immune cells and oncolytic herpes simplex virus (oHSV) has not yet been explored in this context. In this study, NK-92 cells and primary NK cells were engineered to express the second generation of EGFR-CAR. The efficacies of anti-BCBMs of EGFR-CAR NK cells, oHSV-1, and their combination were tested in vitro and in a breast cancer intracranial mouse model. In vitro , compared with mock-transduced NK-92 cells or primary NK cells, EGFR-CAR-engineered NK-92 cells and primary NK cells displayed enhanced cytotoxicity and IFN-γ production when co-cultured with breast cancer cell lines MDA-MB-231, MDA-MB-468, and MCF-7. oHSV-1 alone was also capable of lysing and destroying these cells. However, a higher cytolytic effect of EGFR-CAR NK-92 cells was observed when combined with oHSV-1 compared to the monotherapies. In the mice intracranially pre-inoculated with EGFR-expressing MDA-MB-231 cells, intratumoral administration of either EGFR-CAR-transduced NK-92 cells or oHSV-1 mitigated tumor growth. Notably, the combination of EGFR-CAR NK-92 cells with oHSV-1 resulted in more efficient killing of MDA-MB-231 tumor cells and significantly longer survival of tumor-bearing mice when compared to monotherapies. These results demonstrate that regional administration of EGFR-CAR NK-92 cells combined with oHSV-1 therapy is a potentially promising strategy to treat BCBMs.