Wednesday, April 24, 2024
4/24/2024
ABSTRACT HIV infection has been reported in various cells in the CNS, especially microglia. The CNS is also likely to contribute to the reservoir of HIV infection that persists despite ART, although the contribution of the CNS to viral rebound when ART is discontinued has not been clearly established. While a precise understanding of all the body's reservoir(s) is lacking, contributing factors are expected to include gross anatomic features that impact drug penetration and immune surveillance, as well as the transcriptional environment of specific cell types that can lead to post-integration latency. In the case of the brain microglial population, they are not only highly susceptible to HIV infection, but they reside in a compartment that is immune privileged and poorly accessible to many drugs. There is also increasing evidence that between 30 and 50% of well-suppressed HIV patients have neurocognitive dysfunction (HAND), suggesting that even a low level of persistent HIV in the brain can cause neurological damage. Thus, it is crucial to develop strategies that can remove, disable or suppress HIV in the CNS, ideally using methods that do not require viral reactivation because of the risk of exacerbating neuronal damage. One such approach being considered is based on disabling or suppressing HIV replication using sequence-specific genetic tools. By targeting HIV at the genetic level, a powerful suite of emerging technologies could be leveraged for this goal, including RNAi to prevent HIV translation, and engineered nucleases to disrupt, suppress, or epigenetically silence integrated HIV genomes. However, two major problems exist for the development and evaluation of such tools for HIV-CNS reservoir applications. First, efficient methods to specifically deliver the reagents to the CNS need to be developed. Targeting HIV reservoir cells is challenging because of the relative rarity of such cells and because a truly latent cell will not express any phenotypic indicators of its viral passenger. The second major issue is that successful delivery requires properties beyond simple target molecule recognition, including in vivo stability, de-targeting away from vascular sinks, and the ability to enter the CNS. Unfortunately, such complex parameters can only be evaluated in an animal model. To contribute to the broad effort towards an HIV cure, and its many significant technical challenges, we have developed a semi-quantitative model of latent HIV infection in the CNS, based on human microglial cell engraftment in immune-deficient mice reconstituted with human hematopoietic stem cells. The animals contain up to 10% human CD11b+ microglia and perivascular macrophages and can be infected with HIV-1. After suppression of viral replication by ART, infected cells can be recovered from their brains. The current iteration of the model, and anticipated refinements to increase microglial cell populations in these animals, will be used to systematically evaluate the CNS delivery of gene-editing tools designed to disrupt the HIV genome without reactivation.
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