In the first funding cycle, we applied single-cell methods to HBV/HIV co-infected liver tissues and demonstrated that cccDNA is transcriptionally suppressed during NUCs. We now propose to understand the mechanism underlying this finding since permanently exploiting this mechanism therapeutically can lead to a functional cure. We propose an intensive study of NUC-associated cccDNA transcriptional suppression comparing people with HBV/HIV co- and HBV mono-infection. Our proposal fills knowledge gaps in understanding how to transform reversible cccDNA transcriptional suppression to a functional cure.