| HIV is a devastating disease without a cure due to a treatment resistant latent reservoir that predominantly exists in resting CD4+T cells. Understanding resting cell infection and latency are necessary for developing the best approaches to treating this reservoir. Previous data showed direct infection of resting cells leads to HIV integration. However, several key questions remained. First, we still did not fully understand the requirements for resting cell infection, particularly the role of HIV co-receptor signaling. Second, as HIV can integrate into both activated and resting cells but only activated cells support productive infection, the difference in the course of infection between these cell types was not fully understood. To address co-receptor signaling, we examined the entry mechanism of HIV particles containing both R5 HIV Env and VSV-G as these particles infected naive and memory cells similarly, despite the two cell types having different levels of CCR5. We found that these particles fused independently of CCR5, suggesting co-receptor signaling was not required for successful infection of resting cells. Next, to address the difference in resting and activated cells, we measured several steps of the HIV life cycle in resting and activated cells including binding, reverse transcription, integration, transcription and translation of viral proteins and the release of infectious particles. Importantly, we found that resting cells were able to produce HIV Gag but did not release detectable infectious virus likely due to low levels of Env. Activated cells, on the other hand, were able to produce significantly more Env and released replication competent virions. These results provide key insight into why resting cells do not produce infectious virus. Furthermore, our results have important implications for resting cell infection and targeting the HIV reservoir. First, our data indicate that therapies blocking co-receptor signaling will not affect resting cell infection. Second, our results suggest that latent cells may not be invisible to the immune system. This has important implications for treating the reservoir as methods that merely induce protein expression will likely not affect cells already producing Gag. Additionally, therapies generating a more robust immune response may also reduce the latent reservoir. |
