Synthetic biology approach for the development of conditionally replicating HIV-1 vaccine.

While the combined antiretroviral therapy has resulted in a significant decrease in HIV-1 related morbidity and mortality, the HIV-1 pandemic has not been substantially averted. To curtail the 2.4 million new infections each year, a prophylactic HIV-1 vaccine is urgently needed. This review first summarizes four major completed clinical efficacy trials of prophylactic HIV-1 vaccine and their outcomes. Next, it discusses several other approaches that have not yet advanced to clinical efficacy trials, but provided valuable insights into vaccine design. Among them, live-attenuated vaccines (LAVs) provided excellent protection in a non-human primate model. However, safety concerns have precluded the current version of LAVs from clinical application. As the major component of this review, two synthetic biology approaches for improving the safety of HIV-1 LAVs through controlling HIV-1 replication are discussed. Particular focus is on a novel approach that uses unnatural amino acid-mediated suppression of amber nonsense codon to generate conditionally replicating HIV-1 variants. The objective is to attract more attention towards this promising research field and to provoke creative designs and innovative utilization of the two control strategies.