BACKGROUND:
Whereas the mode of action of lamivudine (LAM) against hepatitis B virus (HBV) is well established, the inhibition mechanism(s) of interferon-α are less completely defined. To advance our understanding, we mathematically modelled HBV kinetics during pegylated interferon-α-2a (pegIFN), LAM and pegIFN+LAM treatment of chronically HBV-infected humanized uPA/SCID chimeric mice.
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METHODS:
Thirty-nine uPA/SCID mice with humanized livers whose pre-treatment steady-state serum HBV reached 9.2±0.4 logIU/mL were treated with pegIFN, LAM or pegIFN+LAM for 14 days. Serum HBV DNA and intracellular HBV DNA were measured frequently. We developed a nonlinear mixed effect viral kinetic model and simultaneously fit it to the serum and intracellular HBV DNA data.

RESULTS:
Unexpectedly, even in the absence of an adaptive-immune response, a biphasic decline in serum HBV DNA and intracellular HBV DNA was observed in response to all treatments. Modeling predicts that the first phase represents pegIFN inhibiting intracellular HBV DNA synthesis with efficacy of 86%, which was similar under LAM and pegIFN+LAM. In contrast, there were distinct differences in HBV decline during the 2nd phase which was accounted for in the model by a time-dependent inhibition of intracellular HBV DNA synthesis with the steepest decline observed during pegIFN+LAM (0.46/d) and the slowest (0.052/d) during pegIFN mono-treatment.



CONCLUSIONS:
Reminiscent of observations in patients treated with pegIFN and/or LAM, a biphasic HBV decline was observed in treated humanized mice in the absence of adaptive immune response. Interestingly, combination treatment does not increase the initial inhibition of HBV production; however, enhancement of second phase decline is observed providing insight into the dynamics of HBV treatment response and the mode of action of interferon-α against HBV.