A new therapeutic vaccine which, since January, has been the focus of a landmark Phase IIb/III clinical trial, could revolutionise the treatment of chronic hepatitis B (CHB), a disease that currently affects 350 million people worldwide and results in one million deaths every year. Not only has it already been shown to have significantly fewer side effects than current immunotherapeutic approaches, and is easier to administer; researchers hope to prove through this study that it can control viral load (the amount of the virus in a patient’s blood) for a much longer period of time than other available drugs.
The drug, called ABX203, is being developed by France-based clinical stage biotech company ABIVAX, after being licensed from the Center for Genetic Engineering and Biotechnology (CIGB) in Havana, Cuba, in 2013. It is a therapeutic vaccine designed to produce immune responses in patients with CHB similar to those that occur in patients with a self-resolving acute hepatitis B virus (HBV) infection.
HBV infections can lead to several different liver diseases including subclinical infection, acute self-limited hepatitis, and, following persistent infection, CHB. The one million deaths that result from CHB mainly occur as a result of the disease evolving into two potentially fatal complications, liver cirrhosis and liver cancer.
ABX203 has already shown promising results in trials carried out by CIGB in Cuba and Bangladesh, performing significantly better than the immunotherapy currently on the market, pegylated interferon, in a number of ways.
"Pegylated interferon is the standard immunotherapy that has been used up until now, but it has a number of substantial shortcomings," explains physician and ABIVAX CEO Professor Hartmut Ehrlich, MD. "First, you need to treat the patient with weekly injections for one year, secondly it has many side effects, and finally once you stop the therapy, the virus comes back very rapidly."
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This has all been overcome with ABX203, according to Ehrlich. "Not only does the treatment only need to be administered over 24 weeks, half the length of the standard interferon regime, it can be delivered through a combination of intranasal administration and injections, while interferon can only be given via injections. Moreover, in a study carried out by CIGB in Bangladesh on 160 patients, the vaccine was shown to be much better tolerated and the time for the virus to come back after treatment was stopped increased by at least a factor of three compared to pegylated interferon."
The current trial
So what do Ehrlich and his team hope to prove in the current study?
It differs from the previous trial in two important ways, the ABIVAX CEO explains. "Firstly, the current trial will test the drug on pre-treated patients, which means, in this scenario, patients that have been on nucleotide or nucleoside analogues (NUCs) for at least two years. The previous trial only recruited patients that had never been treated before," he notes.
NUCs are the other standard treatment option for patients with CHB and can be very effective at reducing viral load, although when the treatment is stopped, the virus tends to come back in a matter of days or weeks.
"And secondly, ABX203 will not be tested against interferon. We have already established that ABX203 is clinically differentiated with critical therapeutic advantages over interferon; we don’t need to repeat this," Ehrlich says.
Instead, in the current trial, half of the 234 patients the researchers aim to recruit will receive ABX203 for 24 weeks on top of NUCs and the other half, the control group, will receive only NUCs.
"After half a year we will withdraw all therapy, and see how rapidly the virus comes back in both groups," Ehrlich notes. "We know in the NUCs group it will be a matter of days or maximum weeks, whereas in the other group, which will have had NUCs and ABX203, we believe we will be able to not only reproduce the data that we had from the initial study done by the Cubans on 160 subjects, but see an even more protracted effect on viral load."
Then, after six months without any treatment, during which time the researchers predict viral load will remain low, they plan to also give half the patients a booster dose of ABX203. "This could potentially eliminate the virus in these patients," Ehrlich says.
So far, recruitment for the trial, which is expected to take place at 50 different clinics in eight countries in the Asia Pacific region, is going well, according to Ehrlich – largely because of careful and realistic planning. "We’re working with one of the best CROs in the Asia Pacific region and we have been very aggressive about the number of sites we will recruit from," he explains. "Because CHB is a very frequent disease, we believe we will be able to recruit all 234 subjects by the end of Q3 of this year, and so far we are essentially on track."
Then, if the trial is successful, which should be confirmed by late 2016, ABIVAX will look to get market authorisation in selected countries in Asia, and subsequently bring the drug to Europe. "We would initiate a European confirmatory study, for potential licensing in Europe, but, when it comes to the European study design, we want to wait and see how big the effect of the drug is in the current trial," Ehrlich remarks.
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Ultimately, he hopes that ABX203 won’t be just another weapon in the fight against CHB, but "a new treatment paradigm" for the disease. "We believe that with the prolonged effect on viral load we have already seen, we will be able to keep patients off drugs for an extended period of time without the virus returning," he explains, adding that if the booster dose that will be tested in the current study works, too, we could even be looking at eliminating the virus in a significant population. "It would then be a functional cure for the disease and that would dramatically change the way people look at the treatment of CHB.
"We hope it will be similar to the situation that occurred with chronic hepatitis C. The introduction of new effective therapies has changed the way patients and physicians look at the disease and we are going in the same direction with our therapeutic vaccine."