Background: The introduction of immunotherapy has altered the treatment paradigm for metastatic non-small cell cancer (mNSCLC). Unfortunately, many patients with mNSCLC have limited or no benefit from immune checkpoint inhibitors (ICIs). A variety of approaches have been explored to augment the efficacy of ICIs. Our study’s aim was to determine whether the addition of stereotactic body radiation therapy (SBRT) and intratumoral injection of the oncolytic virus ADV/HSV-tk (adenovirus-mediated expression of herpes simplex virus thymidine kinase) to a monoclonal antibody targeting programmed cell death-1 (PD-1) would improve the ICI’s efficacy in the treatment of mNSCLC. Methods: In this single-arm, open-label phase II study, patients with mNSCLC (squamous or non-squamous) who were ICI-naive or who were previously treated with a maximum of one line of therapy that included an ICI received an intratumoral injection of ADV/HSV-tk (5 x 10¹¹ vp) followed by SBRT (30 Gy in 5 fractions) to the same tumor. An anti-PD-1 agent (pembrolizumab 200 mg IV every 3 weeks or nivolumab 240 mg IV every 2 weeks) was then given for up to 24 months (pembrolizumab) or 12 months (nivolumab), or until disease progression or intolerable toxicity. The primary endpoint was objective response rate (ORR) as defined by the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. A secondary endpoint was clinical benefit rate (CBR). Results: A total of 35 patients were enrolled, with 28 (80%) receiving pembrolizumab and 7 (20%) receiving nivolumab; 14 (40%) had previous ICI therapy while 21 (60%) were ICI-naive. The ORR and CBR were 28.5% and 61.9% in the ICI-naive group, and 14.2% and 64.2% in the group that previously received an ICI, respectively. Grade 3 or higher toxicity was seen in five patients (26.3%) in the ICI-naive group and in one patient (7.1%) in the previously ICI-treated group. No treatment-related deaths were observed. Conclusions: The addition of SBRT and intratumor injection of ADV/HSV-tk to anti-PD-1 therapy in mNSCLC resulted in a CBR of over 60% for both ICI-naive and previously ICI-treated patients without the use of chemotherapy. The combination was able to reinstitute sensitivity to ICIs in patients previously treated with an ICI, and also benefited some patients whose tumors did not express PD-L1. These findings should be further explored in a larger study population. Clinical trial information: NCT03004183

CBR = CR + PR + SD; PD-L1 = Programmed death-ligand 1.