Broadly neutralizing antibodies against HIV-1 pseudoviruses elicited by envelope trimer DNA with chimeric design delivered via silica-calcium phosphate nanoparticles.

DNA vaccines play a significant role in the prevention of infectious diseases, such as influenza and HIV. To enhance the sustained release capability of plasmids and improve the immunogenicity, non-viral silica-calcium phosphate (SCP) nanoparticles were utilized for the delivery of DNA in this study. Optimizing antigen design is also one of the effective strategies for improving DNA vaccines. The proportion of HIV envelope glycoprotein (Env) trimers can be increased using the uncleaved prefusion-optimized (U) strategy, thereby enhancing immunogenicity and effectively inducing broadly neutralizing antibodies (bNAbs). Three nanoparticles were successfully prepared and characterized by dynamic light scattering and transmission electron microscopy, namely pU-B SCP (from BG505), pU-X SCP (from CRF01_AE BJOX18), and pU-BX SCP (a chimera of gp41 from BG505 and gp120 from CRF01_AE BJOX18). The proportion of Env trimers relative to total Env proteins expressed from pU-BX SCP was significantly increased compared to that from pU-X SCP in vitro. After the third immunization in guinea pigs, significant differences in the broad-spectrum and intensity of neutralizing antibody reactions were observed between the pU-B SCP group and the pU-B group. Furthermore, high binding titer induced by SCP nanoparticles in guinea pigs could be maintained for over 15 weeks. A significant difference in serum antibody titer could be observed between the pU-BX SCP and the pU-X SCP groups. Compared to the pU-X SCP group, more extensive neutralizing activities against tier 2 pseudoviruses could be elicited in the guinea pig serum from the pU-BX SCP group. In summary, SCP could effectively deliver DNA expressing chimeric antigens designed using the U strategy, enhance immunogenicity, and induce long-term efficacy, providing new perspectives for the efficient expression of multimer antigens.