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monoclonal hbsab HepeX-B and clearance of hbsag
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monoclonal hbsab HepeX-B and clearance of hbsag

link to full study:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3086357/

The present study reveals that the antiviral effect of anti-HBs against HBV involves not only binding of viral particles in the circulation, but it also involves intracellular antiviral activity by blocking viral particles release from the cells. We have previously demonstrated that anti-HBs is endocytosed into hepatocyte-derived cell lines irrespective of the presence or absence of HBsAg (10). This is likely to occur as a receptor-mediated endocytosis of IgG via the major histocompatibility complex class I-like Fc-receptor, FcRn. We have shown that FcRn is expressed on several liver cell lines and Fc elimination abrogated the IgG biding to the cells, as well as its effect on HBsAg secretion (10). FcRn is the transport receptor for IgG and protects IgG from catabolism after entry into cells (32, 33). This process is likely to operate during chronic HBV infection, as anti-envelope antibodies have been detected in the serum of virtually all patients with chronic hepatitis B when using sensitive assays (34). Intracellular binding and blocking the secretion of HBV particles may have a role for containment of HBV when at low level within cells, for example in subjects with spontaneously resolved HBV infection (35) or in liver transplant recipients having effective long-term HBIg prophylaxis without clinical HBV recurrence (9, 36).
The antiviral activity of HBV neutralizing antibodies may have clinical implications for treatment of chronic hepatitis B. Post-treatment rebound of HBV replication occurs frequently after stopping direct antivirals even after prolonged treatment for many years. Application of anti-HBs, in combination with a potent antiviral agent blocking directly HBV replication, will target different sites of HBV replicative cycle within cells and may reduce the relapse rates, analogous to the approach that was applied successfully after HAART withdrawal in patients with HIV infection (37). Furthermore, after prolonged and effective control of HBV replication in patients treated with potent antivirals, an add-on application of anti-HBs may facilitate HBsAg clearance in appropriately selected patients.
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17 Comments Post a Comment
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Avatar_m_tn

oh god again FDA to block cures....i really hope FDA will count nothing in the future as drug makers keep moving to the reach asian markets

http://investors.xoma.com/releasedetail.cfm?ReleaseID=205656
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Avatar_m_tn
This is an amazing paper! Usually we were told that antibodies act outside cells, and now it has been shown that they can also enter cells. Surely, this must have treatment implications?
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Avatar_m_tn

it sure does if combo with antivirals or replicor (combo withinterferon maybe problematic i dont know if we can develop antibodies directed to monoclonal anti-hbs) but as you can see FDA blocked company a long time ago.

replicor did not even consider FDA or US knowing FDA would block them as well, europe and asia are the only places to develop cures

anyway have you see the poster about peginterferon add on to tdf?hbsag around 300iu/ml in less than 24 weeks, that is something!
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Avatar_m_tn
Which one? I read one of the pdf files. It relates to one patient, hard to generalize. We need the big clinical trial. Is it still happening in Italy?
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Avatar_m_tn

it is the same thing you will see in the bigger trials like the one in italy

they already have all data here and it works like in the small trials, no big difference when you apply to bigger trials.

they are actually trying to do this since 2009  but drug makers didn t want to fund the trials and same thing healthcare so in italy most advanced liver specialists are just applying the combos directly, no need of bigger trials
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Avatar_m_tn
This paper is a lale workup - viral dynamics analysis- of the Hepex-B trials that were initiated by XTL, a company based in Israel. Hepex B is a double human monoclonal AB where both antibodies bind to the surface antigen with exceptional high affinity.
Since it is a human monoclonal, no antibodies to the antibody are expected to occur.Thus long term therapy is possible.
The trial used patients with a relatively low HbSAg titer, chronic HBV.
Dramatic, unexpected drops in DNA levels were achieved, also, as expected the surface antigen disappeared temporalily from the patients serum.
The phenomenon of uptake of the antibody into hepatocytes was known from other sources, in this trial it could be shown that this endocytosed AB had an actual effect on virion and likely 22nm particle (HbSAg) secretion.

Dosing was single or multiple, the effect was consistent, but the DNA and surface antigen levels returned to baseline or close to  baseline rapidly.

It  became clear that despite the dramatic virion level lowering effect, this would have to be a long term treatment, where the blocking of production and reinfection was slowly accompanied by the reduction of cccDNA content in the infected hepatocytes, reducing the reservoir from which the HBV machinery would restart within hours after the blocking AB was eliminated by its inherent turnover.
The situation is similar to a treatment with Myrcludex, where the blockage of reinfection will only slowly tilt the balance between daily destruction of cccDNA and refreshing of cccDNA content by reinfection of new hepatocytes.
It is this balance also that hinders the antivirals to be a cure, since even the best antivirals do not block de novo virion production completely. And the fewer virions produced under antivirals all start to count now, since the liver will absorb  und bring all these virions to an infectious event, that leads to a new buildup of a new cccDNA pool in the de novo infected cell.

Before Hepex B there was Ostavir, a humanized monoclonal AB against the surface antigen, that was used in human trials finally in Europe in a combo with Lamuvidine. The trial had to be halted in midstream, because the immune complexes that formed by the association between the Ab and the still substantial amounts of HbSAg accumulated in the patients kkidneys glomerular membranes, causing acute kidney damage. This terminated the Ostavir development.

In the XTL Hepex B trials, this was not seen, possibly because the AB was different and such the nature of the ICs, or the dosing was not long enough or the patients had been better selected for low starting HbSAg or of special interest, the higher intracellular uptake has reduced the serum levels of HbSAg still secreted to such a low level that the ICs became tolerable.
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Avatar_m_tn
After XTL realized a low feasability of market success with HepexB for chronic HBV, they decided to approach the HBV transplant reinfection market. Another US company by trhe name of Cubists, that produced an antibiotic among other things bought the rights to the US market and started development of Hepex B in the transplant setting with the FDA.

Cubist did not manufacture Hepex B themselves, nor did XTL anymore, but instead a US company -XOMA-  spezializing in human hybridoma monoclonal Ab production on the large scale was hired to perform the actual production of the monoclonals to the high standards of the FDA.

A phase II trial with HBV transplant patients was initiated and successfully completed with full protection from reinfection, but, as is the standard now, in combo with an antiviral.

Now cubist wanted to proceed with the phase III registration trial for the transplant setting and XOMA got ready to produce the large quantities of Hepex B needed for this trial for them.

Sadly, the FDA requested such a large number of transplant patients for the phase III that the unavailability and huge cost of this made Cubist to give up on the project and XOMA did not get to produce the Ab for this trial.




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Avatar_m_tn

question a little off topic in this thread but i dont think they will be able to use epex B soon

what do you think about peginterferon add on to stable longterm tenofovir or entecavir or even both antivirals.is there a test on immune system to show when the add-on of peginterferon can lead to svr?

my guess is intrahepatic hbvdna suppression may allow rescue of some immune response since response happened even on relatively high hbsag 2000-8000iu/ml
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Avatar_m_tn
In the pegasys registration trial the combo with LAM did not show a substantial improvement over PEG alone except for an addditonal viral load reduction by about o.7 logs over LAM alone  at the end of the trial year.
It was quite disappointing.

The situation is likely to be much better with a stronger antiviral and a longer pretreatment period with that antiviral,before the start of the add on INF therapy. It might also be that the capacity of the virus to find partial resistance adaption mutations to the complex effects of interferon is now limited due to the small reservoir remaining, allowing IFN to be more effective and yield a higher SVR rate

The longer the add on Interferon treatment duration, the better the chances for SVR, but the side effects of IFN are often quite severe and autoimmunity problems can occur when a patient already is inherently prone to such autoimmune problems.

To my knowledge the currrent presentations of SVR rates using this approach are promising but still limited.

After stopping IFN and antiviral treatment there has to be a strong intrahepatic antigen specific Tcell response with a permanent memory component so as to block the respreading of the remaining virion producing cells by limiting new virion production  and/or a strong anti surface antibody response to prevent such spreading by blocking reinfection by virion coating and therefore entry inhibition..
Please note that such spreading might occur slowly in the beginning, therefore results from these trials are only to be considered true SVRs if a follow up period of up to one year is considered to prove its stability.

In other words the spreading must be blocked by a permanent continuing mechanism, supressing expression of antigens, replication capacity AND entry blocking in concert to achieve a new ultra low equilibrium of still remaing cccDNA that you can consider a "cure" since no external medication is needed to maintain its stability.

In the absence of a strong antibody response a maintenance treatment with Myrcludex might be needed to prevent the spreading. You might ask why then not simply to continue on tenofovir, but in the long long run the long term potential mitochondrial toxicity  (all antivirals block the gamma Polymerase than synthesizes new mitochondrial DNA to a certain degree)of the antiviral might be a bigger problem than the Myrcludex blocking therapy, which will likely have no relevant long term toxicity.
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Avatar_m_tn

i was also thinking about something like etv+tdf+intf+alinia, too bad romark never checked potential of alinia+interferon on hbv, do you know of any in vitro study about potential of this combo?i guess hcv studies cannot help much on this
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Avatar_m_tn
If Alinia can improve on potential SVR rates is quite unknown. You know the in vitro studies of Alinia on HBV replication by Brent Korba, there the effect of Alinia was similar to LAM, quite impressive, an IC50 in the low micromolar concentration range..
In vivo the theoretical synergistic effect of Alinia ( because it has a different mode of action, not effecting the Polymerase) with antivirals does not seem to materialize thus far, maybe a reason is phamakokinetics, with the effective concentration in the liver cells falling too low in between drug administrations. In vitro you have a steady supply from the medium.
Thus far also no convincing effect on quant surface antigen could be demonstrated, as you know from personal experience.
It is possible that Korba is testing such an IFN Alinia combo in vitro, this is his specialty.
Overall a weak synergism is likely, but it is a lot of extra effort.
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Avatar_m_tn
Many thanks for your explanations regarding HepexB and HBsAb - they are most informative.

I can remember several years ago, monoclonal HBsAg antbodies were the great hope of the HepB community. Dr Misra on the Hepatitis B information and Support List even heralded the first successful response to the monoclonal antibody. But since then we have heard nothing. Even the whole monoclonal antibody area seems to have gone quiet amid talk of difficulties in the manufacturing process. Now, we have a better understanding.

As you stated, the fact that HBsAb can be endocytosed was known back in 2003 (I looked up the reference).

All these bring me to ask you the questions: Since the monoclonal AB were able to cause the serum HBsAg to disappear (temporarily), why then did not the immune system come to the party and exert immune control?
Isn't this the rationale behind REP 9AC - to reduce amount of extracelluar HBsAg in order to remove the immune suppression caused by excess HBsAg? Ignoring the problem of immunocomplex, would a high dosage of monoclonal AB enables some AB to enter the infected liver cells and inhibit the release of virions and HBsAg partcles, thereby acting like REP9Ac and antiviral?

A big thank you in advance.
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Avatar_m_tn
Since the monoclonal AB were able to cause the serum HBsAg to disappear (temporarily), why then did not the immune system come to the party and exert immune control?

The disappearance of HbSAg was only very temporary, the exhausted and tolerized surface antigen specific Tcell pool (Cd8 and cd4) needs much more time to regenerate, presumable even by the recruitment of de novo clones from the thymus.
Furthermore, since the "loss' of surface antigen was mainly by immuncomplexing, less by blocking release, it was not really removed from the circulation, on the contrary, those complexes were everywhere, taken up and presenting the digested epitopes to the class I and class II pathway, driving the remaining Tcell still to exhaustion far from the liver.

Replicor on the other hand  blocks the production of the surface antigen particles inside the cell, nothing is released, thus the Tcell system can truly recuperate.


"Ignoring the problem of immunocomplex, would a high dosage of monoclonal AB enables some AB to enter the infected liver cells and inhibit the release of virions and HBsAg particles, thereby acting like REP9Ac and antiviral"

yes that is ecactly what this study shows, that intracellular inhibition was part of the mechanism for both. However the blockage might not be as perfect as with Replicor and while Replicor has a half life of several weeks, thus it keeps blocking the surface particle release, the antibody does not seem to enjoy a decent half life inside the cell and outside also it is quickly overwhelmed by the outpouring of more surface antigen, rendering the effect very short lived. New injections are needed frequently and they are quite costly. the highest dose in the XTLtrial was 80mg, a very high dose indeed.
Also since only low antigen levels were considered condidates for this treatment, patient selection and criteria probably have severely hampered the market outlook for XTL  in the chronic HBV market. The treatment might have to be done for a year or more to achieve the effects of Replicor and Myrcludex, possibly too expensive for them to try for the US market. They were only interested in the US market, Schlomo Dagan told me at the AASLD meeting in Texas where the data were presented in poster format, i think it was in 2002.

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Avatar_m_tn
Many thanks for the lesson!

"it was not really removed from the circulation, on the contrary, those complexes were everywhere, taken up and presenting the digested epitopes to the class I and class II pathway, driving the remaining Tcell still to exhaustion far from the liver. "

This reminds of the explanation by Professor Wen why her YIC (yeast derived HBsAg-HbsAb Immunocomplex) therapeutic vaccine failed its Phase 3 clinical trial (no better than the placebo of alum). She said too many injections of the vaccine most probably exhausted the immune system rather then just stimulated it.

Thanks, again.
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Avatar_m_tn
first of all thank you for your intervention and explanations regarding diferent discussion.

reading I notice that lately the accent is on HbSAg titer and in different publication they use "low HbSAg titer", "high HbSAg titer", ... and i was looking for a quantification of this low / high  HbSAg titer (e.g. below 10.000 UI/ml is low upper is high or medium or ...)

when is considered low HbSAg titer ?
are this threshold depending on the genotype ?
are this threshold depending on the +/- HBeAg status?
are this threshold depending on the HVb phase or this threshold are use to determin the HVb phase?
are different techniques for determine HbSAg titer ?

i remember that I was look on some publication and they present the HbSAg titer (range /medium ...) in HBeAg negative in different location (Germany / Italy ...) and I was notice that a ~10 fold exits between different city even is they were in the same report.

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Avatar_m_tn
Stefanos recent post  "very good explanation of HbSAg iU" gives all the ranges for the surface antigen quantitation as it is found in the various patient groups. Just go though the slides, it is a very useful compilation that answers the question if there is a "threshold".
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Avatar_m_tn
I've read the post from Stefano regarding qHBsAg.

Thanks for clarification !
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