LiverIs There a Role for Hepatitis B Immunoglobulin? Is Antiviral Monotherapy Sufficient?. The risk of hepatitis B virus (HBV) recurrence following liver transplantation (LT) has progressively decreased from 75% in the late 1980s, when no prophylaxis was available, to <5% at the present time [1][2][3] (Fig. 1). Combination therapy with a nucleos(t)ide analogue (NUC) plus low-dose intramuscular hepatitis B immunoglobulin (HBIg) has become the standard of care worldwide. Most likely, entecavir (ETV) or tenofovir (TDF) will be increasingly used in combination with HBIg instead of lamivudine (LAM) or adefovir. Although experience is limited, recent studies showed complete absence of HBV recurrence when using low-dose HBIg þ ETV. HBIg requires parenteral administration, has limited availability, and is expensive. However, when used in combination therapy, high doses and indefinite administration are no longer required. Pre-and post-LT monotherapy with LAM resulted in high rates of recurrence (40%), mostly due to the emergence of YMDD mutations. Fung et al. 4 recently showed that among 80 patients who received ETV monoprophylaxis the cumulative rate of hepatitis B surface antigen (HBsAg) loss was 91% with 98.8% of patients achieving undetectable HBV DNA. However, 18 patients (22.5%) were HBsAg-positive at the time of their last follow-up (persistence in eight and reappearance in 10). Are these results ''good enough'' to recommend HBIg-free prophylaxis to all patients transplanted for hepatitis B? The answer to this important question mostly relies on the definition of HBV recurrence. For many years, recurrent infection has been defined as persistence or reappearance of HBsAg in serum after its initial disappearance following LT. Based on this definition, results of the study by Fung et al. are inferior to those obtained with combination therapy in which >95% of patients remain HBsAg-negative after LT. In contrast, if HBV recurrence is defined as detectable serum HBV DNA, then persistence or reappearance of HBsAg after LT in the absence of viral replication should not be regarded as an inferior outcome. In any case, longer follow-up is required to establish whether patients with an inactive post-LT HBV carrier state induced by ETV will eventually clear HBsAg or go on to develop breakthrough and elevated ALT, as described with LAM. Clearance of HBsAg from serum is the most desired endpoint of antiviral therapy in patients with chronic hepatitis B. It is now considered that levels of HBsAg in serum reflect the transcriptional activity of covalently closed circular DNA (ccc DNA) in the liver. Although the HBsAg secretory pathway is partially independent of HBV replication, it can provide an indirect measure of the number of infected hepatocytes. Therefore, HBsAg negativity after LT appears to be a desirable goal in addition to the absence of replication.Although the mechanisms by which HBIg prevents graft reinfection are not completely understood, it is known that it binds circulating virions and may also decrease the hor...