9 Recently, in

vitro experiments have shown that HBs-specific immunoglobulin G (IgG) is internalized into hepatocyte-derived cell lines and inhibits U0126 the secretion of HBsAg and virions from these cells.10 The HBsAg and anti-HBs were colocalized within the cells, and the specificity of intracellular HBsAg–anti-HBs interaction was further demonstrated by abrogating the anti-HBs inhibitory effect in cells transfected with HBV genomes expressing antibody-escape mutant HBsAg.10 To investigate further the phenomenon of intracellular blocking of HBV release by antibodies and its potential for therapeutic application, we analyzed both in vivo and in vitro the effect of two human monoclonal antibodies to HBsAg, HBV-Ab17 and HBV-Ab19, which have been shown to have high neutralizing activity against HBV.11, 12 We used mathematical modeling of serum HBV DNA and HBsAg levels to gain information about viral dynamics during a single

or multiple infusions of a combination of the two monoclonal anti-HBs (HepeX-B) in patients with Stem Cell Compound Library chronic hepatitis B. We then replicated this approach in vitro, using cells secreting HBsAg, and compared the prediction of the mathematical modeling obtained from the in vivo kinetics. DMEM, Dulbecco’s modified Eagle medium; ELISA, enzyme-linked immunosorbent assay; Fc, fragment crystallizable; HBV, hepatitis B virus; HBsAg, hepatitis B surface antigen; HCV, hepatitis C virus; IgG, immunoglobulin G. Human monoclonal antibodies to HBsAg (HBV-Ab17 and HBV-Ab19) were generated as described.11 The antibodies bind different epitopes on HBsAg; HBV-Ab17 recognizes a conformational epitope, whereas HBV-Ab19 recognizes a linear epitope between amino acids 140-149. The specific activities of HBV-Ab17 and HBV-Ab19 are 554 IU/mg and 2090 IU/mg, respectively, and their affinity constants (Kd) are 7.6 × 10−10 M and 5 × 10−10 M, respectively.12 HepeX-B is a 3:1 (mg:mg) mixture of HBV-Ab17 and HBV-Ab19.

The serum half-lives of HepeX-B following Phosphoribosylglycinamide formyltransferase a single 10 mg or 40 mg infusion in healthy volunteers were 22.3 ± 5.5 and 24.2 ± 4.4 days, respectively (Rachel Eren and Shlomo Dagan, unpublished data). For the in vitro experiments, a human monoclonal antibody (IgG1) against the envelope protein (E2) of hepatitis C virus (HCV-Ab68) was used as an isotype control. Serum HBV DNA and HBsAg levels were determined in patients with chronic hepatitis B, who participated in Phase 1A and 1B clinical trials for evaluation of HepeX-B.13 Phase 1A was an open-label, single-dose study with a total of 15 patients, each receiving a single dose of HepeX-B (range = 0.26-40 mg) by an intravenous infusion over 2-8 hours. Serum samples were taken at 0, 0.5, 1, 2, 4, 8, 12, 24, 48, and 96 hours after infusion. Phase 1B was an open-label study with ascending multiple doses of HepeX-B.