Background: Due to its low tumor immunogenicity and immunosuppressive microenvironment, pancreatic ductal adenocarcinoma (PDAC) remains an immunotherapeutic challenge. LOAd703, an oncolytic adenovirus with transgenes encoding TMZ-CD40L and 4-1BBL, has been shown to lyse tumor cells selectively, induce anti-tumor cytotoxic T-cell responses, reduce myeloid-derived suppressor cell (MDSC) infiltration, and induce tumor regression in preclinical studies. Methods: In this phase I/II trial, patients with unresectable or metastatic PDAC were treated with intratumoral injections of LOAd703 and standard intravenous nab-paclitaxel/gemcitabine (nPG) chemotherapy. Starting on cycle 1 day 15 of nPG, LOAd703 was injected with image guidance into the primary pancreatic tumor or a metastasis every 2 weeks for 6 injections. In the event of sustained tumor control, subjects were eligible to receive up to 6 more injections. Three dose levels of LOAd703 were investigated using a BOIN dose escalation design. Primary endpoints were safety and feasibility. Results: Of the 22 subjects enrolled, 21 received at least 1 LOAd703 injection, and 18 received at least 3 LOAd703 injections (the a priori definitions of evaluability for dose limiting toxicity [DLT] and efficacy, respectively). Of the 21 subjects injected, median age was 61, 81% had stage IV disease, and 57% had already received chemotherapy for advanced disease. Median CA 19-9 was 1494. Of the 18 response evaluable subjects, 3 were treated at dose level 1 (5x10e10 VP), 4 at dose level 2 (1x10e11 VP), and 11 at dose level 3 (5x10e11 VP). The most common adverse events (AEs) attributable to LOAd703 were fever, chills, nausea, and increased liver enzymes. AEs were short-lived and grade 1/2, except for a grade 3 transaminase elevation in one subject receiving dose level 3 (the only DLT). Objective response rate (ORR) among those treated at the highest dose level was 55% (5/11 subjects), thus meeting the predefined criterion for efficacy. Among all response evaluable patients, overall response rate (ORR) was 44%, and disease control rate (DCR) was 94%. CA 19-9 decreased by ≥50% in 61% of evaluable patients. Median overall survival (OS) among the 21 subjects receiving at least 1 LOAd703 injection was 8.7 months. The proportion of T effector memory cells increased after initiation of on-protocol treatment (p = 0.0232) while the proportion of T regulatory cells and myeloid-derived suppressor cells decreased (p = 0.0410, p = 0.0256, respectively). Conclusions: Combining intratumoral injections of LOAd703 with standard nPG chemotherapy was safe and feasible. The target response rate at the highest dose level was met, and treatment-emergent immune responses were observed. A follow-up clinical trial combining LOAd703, nPG, and the anti-PDL-1 inhibitor atezolizumab is underway. Clinical trial information: NCT02705196.