In our previous studies, a novel gene therapy approach was developed based on a plasmid vector pSecTag2B in which recombinant HNP1 gene was regulated under a cytomegalovirus promoter to encode a mature HNP1 form. We showed for the first time in various tumor models including human cancer xenografts that overexpression of HNP1 in the tumor milieu by intratumoral pSecTag-HNP1 (pHNP1) administration efficiently attenuated in vivo tumor progression, mediated host immune responses to tumors, and produced a synergistic effect when combined with chemotherapeutics. In current study, a preclinical safety investigation of HNP1 gene therapy was conducted in non-human primates. Eleven cynomolgus monkeys were divided into 3 groups of 3 to 4 animals each and received either repeated s.c. injections of pHNP1/cationic liposome complexes at low (0.625 mg/kg) or high (2.5 mg/kg) dose or glucose as control. Significant HNP1 in vivo accumulation was detected after consecutive administrations. All primates reached the end of the study with good body conditions. Injection site inflammation was the only obvious toxic reaction during observation period. In addition, elevation of monocyte/macrophage and neutrophil as well as decline of lymphocyte were detected in the peripheral blood of pHNP1-treated primates. These alterations were partially alleviated at the end of observation period. Besides, dose-related histopathological changes of the immune organs were observed at necropsy, including a minimal thymic lymphocyte decrease and a minimal-to-mild lymph node erythrocyte increase, but which cannot be excluded from HNP1 induced immune reactions. Together, these data support future clinical studies of pHNP1-based local gene delivery in tumor patients.