Viral vectors are provided for use as genetic immunotherapeutic agents, including preventive and therapeutic vaccines as well as compositions to enhance cellular immune responses and innate immune responses. The vectors are particularly useful for treating or preventing cancer and infectious diseases. The vectors include lentiviral vectors that encode one or more antigens, a combination of adjuvants, and optionally may encode one or more soluble and secreted checkpoint inhibitor molecules. The adjuvants include latent membrane protein 1 (LMP1) from Epstein Barr virus and a fusion protein including LMP1 with in which the intracytoplasmic domain has been replaced by human IPS1 or a variant thereof capable of activating the STING pathway. The vector-encoded sequences are codon optimized for human expression.