**Abstract**

DNA vaccines (nucleic acid vaccines) have been gaining importance as promising therapeutics against infectious diseases, cancer, autoimmune disorders and allergy for the past two decades. However, the immune responses elicited by the DNA vaccines are not at the desired level to stimulate a protective immune response. Thus, studies are focused on the enhancement of DNA vaccine-induced immune response by different approaches. The most common approach is to use biomaterial-based adjuvants for enhanced antigen delivery and uptake by antigenpresenting cells. Some of these adjuvants are alum, saponins, microspheres, nanoparticles, liposomes, polymers, etc. used in vaccine formulations. In addition, molecular adjuvants like cytokines, chemokines and heat shock proteins have been shown to be promising in designing DNA vaccines. In this chapter, molecular adjuvants to improve DNA vaccination-induced immune responses will be summarized with a special focus on Bcl-xL anti-apoptotic protein.

**Keywords:** DNA vaccine, molecular adjuvant, delivery systems, antigen-presenting cells, Bcl-xL anti-apoptotic protein
