BACKGROUND: (blind field). METHODS: Patients with recurrent high grade gliomas were enrolled in one of two arms. Group A patients (clinical assessment group) received a single intratumoral injection of DNX-2401 into biopsy-proven recurrent glioma. Group B patients (biological endpoint group) received an initial intratumoral injection through a permanently implanted catheter (to identify the injection site) followed 14 days later by en bloc tumor resection (to obtain post-treatment specimens) and subsequent injection of DNX-2401 into the post-resection tumor bed. Dose was escalated from 1x10^7 to 3x10^10 viral particles (vp) in 8 cohorts. Patients were followed with clinical exams, MRIs, and laboratory studies. RESULTS: Histological analysis of post-treatment en bloc surgical specimens cut perpendicular to the implanted catheter proved for the first time that DNX-2401 was capable of infecting, replicating in, and killing human glioma tumor cells (Group B; N = 12). The maximum dose achieved was 3 × 10^10 vp as planned (Group A; N = 25). DNX-2401 resulted in no toxicity in each cohort. Ongoing outcome analyses show an overall median survival of 11 months. Remarkably, complete responses were seen in 3 patients (12%) (#12, #33, #37), all of whom are currently alive with no evidence of disease (3.2, 2 and 1.75 years after treatment). Serial MRIs revealed a period of increased enhancement prior to tumor regression, consistent with an inflammatory response. Histological analysis of a resected tumor from a symptomatic patient (#20) in Arm A during this period of increased MRI-enhancement identified primarily inflammatory cells (macrophages/CD8 T-cells) and only rare glioma cells. Analyses of inflammatory cytokines in serum revealed that, compared with all other patients, the 3 responders had 10-fold to 10,000-fold increases in Interleukin-12p70 (which polarizes T(h)0-cells to T(h)1-cells and promotes cell-mediated immunity). CONCLUSIONS: DNX-2401 is a new oncolytic virus with a favorable toxicity profile that is capable of replicating in and killing human glioma cells. Efficacy in this early stage trial was impressive with a 12% complete response-rate that has proven to be durable. Molecular studies suggest that viral-induced, anti-tumor cytotoxic immunity (in situ vaccine) may play a role in the anti-glioma effect of DNX-2401. SECONDARY CATEGORY: Immunobiology & Immunotherapy.