CD8+ T cells also play a critical role in HBV clearance, especially intrahepatic HBV-specific CD8+ T cells.3, 6 Although HBV-specific
CD8+ T-cell numbers remain low during infection, their cytokines, including IFN-γ and tumor necrosis factor alpha (TNF-α), are essential for suppressing HBV gene expression and replication.3 Unfortunately, in chronic HBV (CHB)-infected patients, CD8+ T cells lose their ability to proliferate and mediate Seliciclib antiviral function; this dysfunctional state is characterized by coinhibitory molecule overexpression (e.g., PD-1, Tim-3, CTLA-4), low cytokine production, and T-cell exhaustion.7 In addition to exhibiting impaired HBcAg-specific CD8+ T-cell selleck chemicals llc responses, studies on HBV-carrier mice revealed that anti-HBs antibody (Ab) production is also suppressed.8 Lower HBV-specific Abs are also reflected in CHB patients, indicating that HBV persistence impairs both CD8+ T-cell and humoral arms of adaptive immunity. To achieve effective HBV therapy, there is a pressing need to develop strategies to break cell-intrinsic tolerance and reconstitute adaptive immunity against HBV. One promising strategy
to treat CHB infection is simultaneous use of immune stimulation and HBV gene-expression silencing to reduce antigen load; recently, bifunctional 5′-triphosphate-small interfering RNAs (siRNAs) (3p-siRNAs) silenced HBV expression and simultaneously activated the host retinoic acid inducible gene I (RIG-I) signaling pathway to successfully reverse hepatocyte-intrinsic immunotolerance.9, 10 However, whether reversing cell-intrinsic tolerance promotes
recovery of adaptive immunity in vivo is unknown. APC, antigen-presenting cell; CHB, chronically HBV infected patients; HBeAg, hepatitis B e antigen; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; HBx, hepatitis B virus X gene; IFN, interferon; ISG, interferon-stimulated gene; MxA, myxovirus resistance protein A; NF-κB, nuclear factor-κB; PRRs, pathogen recognition receptors; TGF, transforming growth factor; TLR, toll-like IMP dehydrogenase receptor; TNF, tumor necrosis factor; PD-1, Programmed Death-1. The nucleotide-sensing pattern recognition receptors (PRRs), TLR7 and TLR8, are located on endosomes and recognize specific viral single-stranded RNA (ssRNA) sequences, such as GUGUU,11 U-rich sequences, and a GU-rich 4-mer.11, 12 Receptor activation stimulates IFN-regulatory factor 7 (IRF7), nuclear factor-κB (NF-κB), and other downstream signal pathways to induce type I IFN and inflammatory cytokine production.11 TLR7/8 also recognize synthetic imidazoquinoline derivatives and siRNAs with U-rich RNA sequences,12 and these agonists show potential to enhance innate and adaptive immunity in immunotherapy against cancer and infection.