Now that the HBV world has gathered extensive clinical experience with
interferons and polymerase inhibitors (NUCs) and with the resolve to finally find a
cure for a serious disease afflicting hundreds of millions worldwide, the
hepatitis B surface antigen (HBsAg) has become recognized as the key determinant for treatment
outcome. This is being confirmed by trial after trial investigating combining the actions of both NUCs and interferons,
either one after the other or together at once.
Some of these studies were presented at the International
Liver Congress last week in Vienna (ILC2015). Emerging from them are actionable HBsAg rules which
can predict fairly well whether a patient will eventually seroconvert to (or at least
lose) HBsAg. No matter the excitement around CRISPR technologies, HBsAg seroconversion remains the gold standard outcome in HBV treatment in the foreseeable future.
These rules can be divided into pre- and post-IFN treatment onset.
In the pre-IFN setting, it is
those patients that have below ~500 IU/ml serum
HBsAg as a result of NUC treatment that will most likely respond to interferon
treatment/immune stimulation with s-antigen seroconversion (see earlier blog entry). Since NUCs alone hardly do anything to
promote s-antigen seroconversion despite its dramatic lowering of viral HBV
titers, it appears to be their slow impact on HBsAg levels ( 0.1 log per year HBsAg reduction) that has the synergistic effect with interferon: with HBsAg
lowering you take off the foot on the immune brake, with interferon you step on
the immmune gas pedal.
As such, HBsAg knockdown by RNA(i) Therapeutics would seem
to do the same for interferons as NUCs do, only in a more rapid and potent
manner. Of course, both could be used
concurrently as a run-in to IFN treatment.
However, once on IFNs (post-IFN onset),
it is the relative HBsAg decline that has high
positive predictive value in prognosticating who will seroconvert. Of note, the HBsAg decline comes before any adaptive immunity can be
detected. This supports that HBsAg decline in itself contributes to seroconversion
rather than it being a mere correlation.
In that setting, it is a 1 log decline
in HBsAg the first few weeks after IFN treatment onset that separates the winners
from the losers.
It is uncertain to me, however, whether 1 log is a precondition to s-antigen seroconversion as the non-responders do not
even come close to that (maybe 0.3log).
It is therefore possible that anything that pushes HBsAg below say -0.3-0.5log
could have a dramatic effect on s-antigen seroconversion rates.
An RNAi Therapeutic for HBV used simultaneously with IFNs may
therefore aim at helping IFNs to get to the
0.5-1log reduction threshold, and rapidly at that.
Ergo, there are now a number of obvious strategies that one
can apply regarding the use of RNAi Therapeutics in HBV with various knockdown goals,
both absolute and relative. The exact strategy would depend on how the RNA
agent is combined with polymerase inhibition/NUCs or immune
stimulation.
While a number of other HBV targets were reported at the
conference such as core assembly and entry inhibitors, HBsAg (and HBV mRNA
knockdown in general) lowering remains the most distinguished and the mechanism predicted to be most synergistic to existing treatment approaches. As combination treatment is strongly
predicted to be the future of HBV, HBsAg lowering should become a pillar of
those treatment regimes.
Disclosure: long
ARWR, looking for lower entry in TKMR.
10 comments:
I am a patient with chronic HBV. Have been previously treated with adefovir and now tenofovir. I am about to start interferon combo with TDF in a few months. My viral load is essentially undetectable but HBsAg still pos. Hoping for the best! Very intrigued with the work coming out of ARWR and will be curious to see further data.
I am an avid reader of your Twitter and blog - keep them coming!
I'm only partially hopeful at the prospect of seroconverting s-antigen with this new therapy starting in a few months. But I can hope!
What is your HBsAg titer?
The regimen I'm on right now only gives me a pos/neg result for HBsAg unfortunately. I believe that once I transition to the new study in May they will start measuring that. All I know at this point is it is positive.
For further reference, however I am HBeAg negative and have been bouncing back and forth between having the E antibodies and not having them.
Will hopefully have a measure on surface antigen sometime mid-May.
Very nice post, but a couple of comments must be made to clarify the state of the art:
1) The gold standard for an HBV cure is not HBsAg seroconversion, it is loss of hepatic cccDNA, which does not always occur because people who have resolved infection (HBsAg neg, serum DNA negative) are still at high risk for reactivation when undergoing immunosuppressive therapy. HBsAg is a convenient biomarker for cccDNA in lieu of liver biopsy, but the existence of "inactive carriers" and "occult HepB" indicates that loss of HBsAg is not the same as clearance, i.e. being cured.
2) It is not at all clear whether initial HBsAg loss contributes to HBsAg seroconversion and/or resolution of infection, or whether the HBsAg loss and seroconversion are a RESULT of resolution of infection. Using adaptive immunity as a gauge in IFN treatment may be misleading because it is know that IFN treatment controls infection mostly through innate immune response. Also, in resolution of acute infection without treatment, the adaptive immunity again lags behind serum DNA and HBsAg loss, but in that scenario this means that cccDNA levels start falling before HBsAg levels do, which in turn suggests that clearance of infection starts before HBsAg levels drop.
Most people in the "business" believe that the role of HbsAg antigenemia in immunomodulation is still speculative despite some evidence from the woodchuck model and in vitro studies, but the development of HBsAg lowering therapies will actually help to answer that question, and is supported. Anyway, lowering HBsAg may not be fully curative, but it should not hurt, either.
Thanks for the comment. A few quick comments.
1) of course, cccDNA clearance 'would be nice to have', but once you start talk about removing viral DNA altogether you would also need to address the genomic integrants. E.g. at last year's London meeting, I've seen studies where cccDNA dropped dramatically (2-3 logs) on drug treatment, but HBsAg levels were more or less unchanged. This indicates to me that the source is from genomic integrants. Once you start talk about using CRISPR etc for viral DNA removal, for HBV you probably wouldn't want to do that because it would lead to widespread chromosomal rearrangements.
For most practical purposes and from a public health perspective, HBsAg seroconversion is more than sufficient.
2) Yes, IFN is expected to work also by innate immune mechanisms, e.g. by reducing gene expression such as HBsAg.
I wasn't aware that in the resolution of acute infection cccDNA (or viral titers?) drop before HBsAg. Will have to look more into the dynamics here.
Still no answer by Dirk on those consulting fees from ISIS / Regulus. Should we call those advertising fees. I'm sure if ADXS paid a fee they could get some good tweets
$GILD just a month or so ago, exec said the shorter the better.... $RGLS
Are you suggesting a partnership/collaboration cum licencing deal?
Dirk,
The integrated genomes are of no concern to any anti-cccDNA strategy other the highly specious CRSPR-CAS9 approach, and besides they do not maintain infection because they are non-functional for supporting replication (they cannot make a full length pregenomic RNA transcript). They can indeed potentially make some proteins including HBsAg even after cccDNA is gone, which is actually an argument for not relying on HBsAg as a biomarker for clearance, even though it is the most practical.
Re: The kinetics of HBsAg and serum DNA loss in resolved acute infection, check out Chulanov, Gerlich et al JMV 2003.
thanks for this blog, very informative
RE kinetics during acute HBV infection. The critical question here probably is whether clearance during an acute infection is the same as s-antigen seroconversion following chronic HBV infection.
In fact, from the concluding paragraph of the abstract from the reference provided by you suggests that during acute infection innate immune responses shut off gene expression in the virally infected cells so that no new supply is generated from there:
'The initial decrease of HBV ge and HBsAg in serum appears to be caused by decay or non-specific removal in the absence of replacement.'
That's likely to be different during s-antigen seroconversion where changes in adaptive immunity should be the primary driver, also as indicated by the prognostic importance of the HBsAg response.
RE integrated genomes and whether functional HBV can be made from there. I'm not sure why you think no functional HBV can be generated from there. During genome integration of DNA you typically see multimerizations, so I fail to see why you cannot make full-length/functional HBV from those.
Dirk,
Sorry for not checking on your HBV posts, but this thread is getting kinda old. But frankly, I don't see how you argue that HBsAg loss precedes DNA clearance, when there is no evidence for it in the literature, and when there is actually evidence to the contrary...And you should know that this is coming from someone who is studies HBsAg for a living. Anyway, there is no data either way that I'm aware of in cases of spontaneous clearance/seroconversion, and that is the only paper I know of looking at acute infection clearance. But the question is, how exactly do you envision that HBsAg can be lost before cccDNA clearance? More likely, because seroconversion in chronic patients is always preceded by a "flare" in ALT/AST, the immune system is suddenly (and mysteriously) able to clear the remaining infected cells and their accompanying cccDNA load, and that is why HBsAg goes away. That is not to say that the dropping HBsAg levels do not contribute to the rise in immune function, but the idea that HBsAg magically goes away and only then does cccDNA clearance begin just does not make sense.
Not to pile on here, but the integrated genomes are not functional in supporting pgRNA synthesis and replication. All either harbor deletions that result from the recombination, or are head-to-head dimers (not multimers). If you look at the way the genome is layed out, and the complicated process of HBV replication, those genomes cannot work.
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