DESCRIPTION: The primary reservoir of HIV consists of latently infected resting memory CD4 T cells. Emerging information indicates that these cells are intrinsically resistant to apoptosis fr two distinct reasons: (i) chronic HIV infection of T cells induces an apoptosis resistant phenotype by virtue of HIV proteins causing altered expression of a wide variety of apoptosis regulatory proteins, and (ii) resting memory T cells, by virtue of being an historical archive of prior immune responses developing a quiescent and apoptosis resistant state in order to preserve the memory responses. Current approaches to cure HIV broadly involve gene therapy, immune based therapy, and viral reactivation. The latter strategy involves reactivating HIV pharmacologically, with the expectation that CD4 T cells which reactivate virus will die from the cytotoxic effects of viral protein expression. Work to date has established that viral reactivation is possible (e.g., with suberoylanilide hydroxamic acid, SAHA) and safe, but given the intrinsic resistance of these cells to apoptosis, it is not surprising that the cells that reacivate virus neither die after reactivation, nor are they efficiently killed by cytotoxic T lymphocytes. e have characterized the expression of select apoptosis regulatory proteins in resting memory CD4 T cells which contain latent HIV, and found the cells to have low levels of the proapoptotic protein procaspase 8 and high levels of the antiapoptotic protein Bcl2. We propose that this imbalance is the reason why latently HIV infected CD4 T cells do not die after HIV reactivation, despite the fact that they express potent apoptosis-inducing proteins intracellularly - HIV Tat, nef, Vpr and protease after viral reactivation. Therefore, the cells that were latently infected do not die even after they are induced to express proapoptotic HIV proteins such as HIV protease. The overarching goal of the proposed study is to identify ways to alter latently infected HIV T cells such that they die in response to viral reactivation. In this application, we present three independent lines of evidence that this approach is justified and these cells can be altered in such a way that when HIV is reactivated, the cells will die. First using the Lewin model of HIV latency in primary CD4 T cells, we show that pharmacologically up-regulating the host protein procaspase 8, in resting memory CD4 T cells, allows these cells to be killed after viral reactivation, resulting in lower HIV replication (because infected cells are killed) and less integrated HIV copies. Next we summarize our previously published work that treatment of resting memory CD4 T cells from HIV infected patients with TRAIL agonists reduces that amount of replication competent HIV and the amount of HIV provirus, without deleterious effects on uninfected bystander cells. Finally, we present preliminary evidence that the first in class Bcl2 inhibitor, ABT-737, primes latently infected cells to undergo death upon HIV reactivation. These approaches specifically target HIV infected cells to die because, using this tactic, all cell will be primed to become apoptosis susceptible, however, only those cells which contain intracellular HIV proteins (the HIV infected cells) contain the apoptosis inducing stimulus. Having shown proof of concept for our Prime Shock and Kill model of HIV eradication, we now propose to adopt a high throughput screening approach to identify optimum pharmacologic methods of i) inducing apoptosis sensitivity, and then, ii) test these treatments in combination with stimuli that induce viral reactivation. This approach will then be tested for their ability to cause latently HIV infected T cell death using in vitro models of HIV latency and ex vivo testing of primary resting CD4 T cells from HIV-infected patients. Ultimately successful approaches will be fully vetted using the BLT mouse model of HIV infection.
|Effective start/end date||2/15/14 → 1/31/19|
- Immunology and Microbiology(all)