Immune-based therapies Zadaxin: Zadaxin (thymosin alpha 1), a synthetic peptide of 28 amino acids, is a substance found naturally in the circulation and produced in the body’s thymus gland. Zadaxin has been evaluated for its immunomodulatory activities and related therapeutic potential in several conditions and diseases, including cancer (such as HCC, lung cancer, and melanoma) and infectious disease (sepsis, infections after bone marrow transplant, lung infections including chronic obstructive pulmonary disorder (COPD), SARS, hepatitis B or C, and HIV). Investigation of Zadaxin’s mechanism of action at the cellular level has revealed both immune-modulating and direct-acting effects. Interest in using Zadaxin for treating CHB has been based on the drug’s immunomodulating effects, which can trigger lymphocyte maturation, augment T-cell function, and reconstitute immune defects. A study revealed that Zadaxin added to lamivudine was not superior to lamivudine alone and did not prevent resistance to lamivudine despite increased HBeAg seroconversion[82]. The data from a meta-analysis showed that, compared with IFN-α, the benefit of thymosin alpha-1 was not immediately significant at the end of therapy but that the virological, biochemical, and complete response had a tendency to increase or accumulate gradually after the therapy[83]. No persuasive data have yet emerged to suggest a great potential for Zadaxin. NOV-205 (BAM 205): NOV-205 acts as a hepatoprotective agent with immunomodulating and anti-inflammatory properties and, thus, likely requires treatment periods longer than 14 d to affect a clinical response. Its regulatory approval in the Russian Federation under the trade name Molixan® in 2001 was based on clinical studies in 178 Russian hepatitis B and C patients. When used as mono-therapy for 1 mo in hepatitis B and for 2 mo in hepatitis C patients, NOV-205 has been shown to greatly reduce/eliminate viral loads and to significantly improve liver function. NOV-205 was also well-tolerated in those studies. GS 9620: Toll-like receptors (TLRs) are components of the innate immune system and serve as a first line of defense against invading pathogens. TLR activation could represent a powerful and novel therapeutic strategy for the treatment of chronic HBV infection[84]. GS-9620, a potent selective TLR-7 agonist, was designed to have rapid clearance and low systemic levels after oral administration. In chimpanzees chronically infected with HBV, the effects of immune activation have been investigated using GS-9620 administered 3 times each week for 4 wk at 1 mg/kg and a 1-wk rest period, for a second cycle of 4 wk at 2 mg/kg[85]. A detailed evaluation was performed that included an assessment of the pharmacokinetics of GS-9620, viral load, IFN-stimulated gene (ISG) expression, cytokine and chemokine levels, and lymphocyte and NK cell activation, as well as safety and tolerability parameters. Short term administration of GS-9620 provided long-term suppression of serum and liver HBV DNA. Serum levels of HBsAg and HBeAg, as well as numbers of HBV antigen-positive hepatocytes, were reduced as hepatocyte apoptosis increased. In parallel, GS-9620 administration induced the production of IFN-α and other cytokines and chemokines, up-regulated ISGs expression, and activated NK-cell and lymphocyte subsets, confirming the activation of TLR-7 signaling. The safety, tolerability, pharmacokinetics and pharmacodynamics of GS-9620 in 75 healthy volunteers were evaluated with a single ascending-dose up to 12 mg. GS-9620 demonstrated safety and pharmacodynamic activity at doses up to 12 mg and induced an antiviral response before systemic adverse events were observed[86]. The novel approach inhibiting HBV replication and inducing infected cell clearance represents a step toward the development of a true combination therapy for CHB. GI-13020: HBV-specific T cell responses have been shown to have a positive association with infectious status in patients with chronic HBV, with the weakest T cell responses observed in patients with untreated chronic active infection and the strongest T cell responses observed in patients who have achieved seroconversion or cure. GI-13020 is a recombinant yeast-based biological product engineered to express a chimera of HBV X, S, and C antigens. GI-13020 is immunogenic in murine models and has also been used to stimulate human immune cell samples ex vivo to elicit HBV specific T cell responses, which could predict the immune responses in patients dosed with GI-13020. A phase Ia trial assessing the safety, tolerability, and ability to elicit HBV-specific T cell responses of GI-13020 at various doses and with various regimens in healthy adults is ongoing but is not recruiting participants (ClinicalTrials.gov Identifier: NCT01779505). In the future, GI-13020 could be used in combination with HBV antivirals in an attempt to improve HBsAg seroconversion rates in patients with chronic HBV infection. DV-601: Therapeutic vaccines may promote the resolution of chronic HBV infection through the stimulation of specific cytotoxic T-lymphocyte and B-cell antibody responses against dominant HBV-antigens. DV-601, which comprises recombinant HBsAg and HBcAg, is an investigational therapeutic vaccine. A phase Ib dose-escalation study has been completed to determine whether DV-601 would be well-tolerated and induce HBV-specific virological and immunological responses in CHB patients undergoing concurrent treatment with a nucleoside analogue (ClinicalTrials.gov, Identifier: NCT01023230). In this initial dose-escalation study of DV-601, 6 injections of DV-601 were administered over a period of 12 wk. The primary objective was to assess the safety and tolerability of DV-601 by evaluating local and systemic adverse events on Day 99, including changes in laboratory analyses. Secondary objectives were to evaluate the virological response and immunogenicity of DV-601 based on viral load, and humoral and T cell immunological responses. DV-601 appears to be a safe and well-tolerated therapeutic vaccine for the treatment of CHB, and virological response is evident[87].
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