Truvada works best for immune-tolerant hepatitis B patients, but do they need treatment?

A combination of tenofovir and emtricitabine (the drugs in the combination pill Truvada) suppressed hepatitis B virus (HBV) replication more than tenofovir alone over four years for people with inactive or immune-tolerant disease, researchers reported at the 48th International Liver Congress (EASL 2013) last month in Amsterdam. The benefits of treatment at this early stage, however, remain uncertain.

Compared with the rapid developments in the hepatitis C field, treatment for chronic hepatitis has been stable in recent years.

Nucleoside/nucleotide analogues including tenofovir (Viread) and entecavir (Baraclude) can maintain long-term viral suppression, but they seldom produce sustained virological response after stopping treatment, and rarely lead to hepatitis B surface antigen loss or antibody seroconversion.

But the hepatitis B field may be "evolving toward a cure", Fabien Zoulim from Hospital Hôtel Dieu in Paris said at an EASL press briefing during the conference.

Unlike HIV, HBV does not require viral integration into the host cell genome in order to replicate, but integration can trigger liver cancer.

W Ray Kim and colleagues reported that long-term HBV suppression using tenofovir significantly reduced the risk of developing hepatocellular carcinoma (HCC) over six years. Using data from the REVEAL-HBV trial, Jessica Liu and colleagues found that serum HBV DNA clearance significantly lowered the risk of HCC, even if hepatitis B 'e' and 's' antigen (HBeAg and HBsAg) clearance did not occur. Conversely, HCC risk remained elevated in people who achieved 'e' antigen clearance if viral load remained high.

Several researchers at EASL presented preliminary data on potential approaches - some of them similar to ongoing HIV cure research - for silencing, destroying or eradicating free-floating bits of viral genetic material known as cccDNA. Some evidence indicates residual cccDNA increases HCC risk even when blood viral load is undetectable using standard assays.

One study found that small molecules targeting histone acetylation or methylation can suppress HBV transcription and replication. In another, antibodies that target the lymphotoxin beta receptor resulted in degradation of cccDNA in HBV-infected cells. Finally, inducing proliferation of human liver cells in a mouse model led to rapid reduction, though not elimination, of HBV cccDNA. More research is needed to determine if reducing or eliminating cccDNA can lower liver cancer risk.

Researchers are also looking at earlier treatment of chronic hepatitis B. Current guidelines recommend treatment for people with active liver disease progression, indicated by elevated alanine or aspartate transaminase (ALT or AST) levels. Much HBV-related liver damage is not caused by the virus itself, but rather by the body's immune response

Elevated transaminases reflect liver inflammation, which over time promotes fibrosis as the liver attempts to repair itself.

Typically people with normal ALT levels – known as immune-tolerant hepatitis B – are not considered candidates for treatment. But now that highly effective and well-tolerated therapies are available, some experts propose that treatment during this early stage could lower the risk of HCC and reduce HBV transmission, as people with immune-tolerant infection may have high viral loads.

Edward Gane from Auckland General Hospital presented findings from a study comparing tenofovir monotherapy – the current standard of care for active chronic hepatitis B – versus combination therapy using tenofovir plus emtricitabine (marketed as the Truvada coformulation for HIV treatment).

The study enrolled 126 people with chronic hepatitis B who had high HBV viral load but ALT below the upper limit of normal. They were evenly divided between men and women, about 90% were Asian and the average age was 33 years. Though pre-treatment biopsies were not done, they were not known to have cirrhosis. At baseline the mean HBV DNA level was 9.2 log IU/mL.

About half had HBV genotype B and about 40% had genotype C.

Participants were randomly assigned to receive 300mg tenofovir once-daily, either with or without 200mg once-daily emtricitabine, for 192 weeks.

Viral load declined dramatically in both groups soon after starting treatment. By week 192, significantly more people achieved undetectable HBV DNA (< 69 IU/mL) in the combination arm compared with the tenofovir monotherapy arm (76 vs 55%, respectively). About half the patients stopped treatment after 192 weeks, however, and their viral load returned to baseline levels.

Serological response rates were very low in both arms. Six people in the tenofovir monotherapy arm and two people in the combination arm experienced HBeAg loss, and five and zero, respectively, had HBeAg seroconversion, but the differences did not reach statistical significance. No patients in either arm experienced HBsAg loss or seroconversion.

In a univariate analysis female sex, lower baseline HBsAg and HBV DNA, and use of combination therapy were associated with a greater likelihood of viral suppression. In a multivariate analysis, female sex (odds ratio 6.0) and combination therapy (odds ratio 3.9) remained the only significant predictors.

Treatment was generally safe and well tolerated. Six people receiving tenofovir alone and three taking the combination regimen experienced adverse events, which generally were not considered related to study drugs. No participants saw elevated creatinine levels or reduced creatinine clearance suggestive of kidney function impairment (a known side-effect of tenofovir). No tenofovir resistance mutations were detected through 192 weeks.

"Prolonged antiviral therapy maintains potent viral suppression and is safe in immunotolerant patients," the researchers concluded. "The underlying impaired immune responses to HBV in this population may explain the poor serological response rates to antiviral therapy."

The treatment advantage for women in this study was stronger than the effect usually seen in trials of active chronic hepatitis, leading the investigators to suggest that, "Gender may be an effect modifier in treating chronic HBV patients with high viral loads and normal ALT values."

Session chair Mark Thursz asked whether these findings suggest that treatment guidelines should be revised to recommend treatment for immune-tolerant patients.

Gane replied that while the study shows we certainly can treat such individuals, the question is who will benefit? "We need to show that long-term viral suppression in patients with normal ALT will prevent progression and HCC," he said.

He noted that many people in this situation are young women of childbearing potential, who are advised to avoid tenofovir during early pregnancy due to its association with birth defects. An audience member further noted that young people with hepatitis B have a very low risk of liver cancer even without treatment.

"We'd like to know if there's a subset of patients with high risk of progression – such as family history of liver cancer – who may benefit from early treatment," Gane concluded.