IFN␣, a cytokine with multiple functions in innate and adaptive immunity and a potent inhibitor of HIV, exerts antiviral activity, in part, by enhancing apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3 (APOBEC3) family members. Although IFN␣ therapy is associated with reduced viral burden, this cytokine also mediates immune dysfunction and toxicities. Through detailed mapping of IFN␣ receptor binding sites, we generated IFN␣ hybrids and mutants and determined that structural changes in the C-helix alter the ability of IFN to limit retroviral activity. Selective IFN␣ constructs differentially block HIV replication and their directional magnitude of inhibition correlates with APOBEC3 levels. Importantly, certain mutants exhibited reduced toxicity as reflected by induced indoleamine 2,3-dioxygenase (IDO), suggesting discreet and shared intracellular signaling pathways. Defining IFN structure and function relative to APOBEC and other antiviral genes may enable design of novel IFN-related molecules preserving beneficial antiviral roles while minimizing negative effects. (Blood. 2011;118(9): 2567-2577)
IntroductionHighly active antiretroviral therapy (HAART) may not eradicate all long-lived and productive reservoirs of HIV, including macrophages, 1-3 and additional approaches to viral suppression continue to center on host cell-derived molecules that antagonize the virus life cycle. Although hundreds of host cell factors are required by HIV for successful infection 4 and may serve as potential intervention targets, considerable effort has focused on those endogenous factors that contribute to cellular resistance to HIV. Among the innate intracellular HIV antagonists are the apolipoprotein-B mRNA-editing enzyme-catalytic polypeptide-like 3 (APOBEC3) family of cytidine deaminases, 5,6 and members of the tripartite motif family (TRIM), 7 but HIV has the potential to effectively eliminate or neutralize these resistance factors.In vitro studies demonstrated that IFN␣ enhances innate antiviral molecules including APOBEC family members as a counter-maneuver to HIV viral infectivity factor (VIF). 8,9 Importantly, treatment of HIV and HCV coinfected patients with pegylated-IFN␣-2a (peg-IFN␣) and Ribavirin or HIV monoinfected patients with peg-IFN␣ only 10 resulted in enhanced APOBEC expression in PBMCs along with other IFN stimulated genes (ISGs). 10 These studies illustrate the potential to alter the virus-host imbalance and suppression of de novo synthesis of HIV. Despite these promising findings, the use of IFN␣ therapeutically is fraught with potential side effects, including cytotoxicity, immune dysregulation, neuropathicity and apoptosis. [11][12][13][14] Although the use of peg-IFN␣ with its longer half-life has enabled reductions in levels of administered cytokine on a less frequent regimen, toxicity remains a deterrent.Based on the potential utility of IFN␣ in the arsenal of anti-HIV therapies, we have attempted to determine whether its antiviral capacities can be dissociated from its toxic functions....