HI Stephenw,
Please be careful with your statements as most of these are not correct and can damage the understanding of patients.
Especially Nass’s last comment - his understanding is not correct.
Functional cure and cccDNA
It is widely recognized that removal of all cccDNA in the liver will not be possible. The reason for this is the ability of cccDNA to exist in a latent state (as heterochromatin) where it is not active, insoluble, not targeted by any current technologies in development, immunologically silent and very long lived. The futility of the cccDNA targeting approach has been well demonstrated in several clinical studies where removal of NUC therapy with undetectable cccDNA in the liver or with strong crush of HBV DNA with NUCs + CAMs leads to rapid rebound. Latent cccDNA is the basis for reactivation of patients with functional cure for decades when they receive immunosuppressive agents.
Even if you could get to removal of all cccDNA then in theory where would be no more viremia but still the increased prevalence of HCC - this is driven both HBsAg and integrated HBV DNA. Again you need to read the reviews. Only HBsAg loss has ever been shown to have long term benefit to patients with removal of therapy.
Integrated HBV DNA and ALT flares
Removal of integrated HBV DNA and the accompanying ALT flares are a hallmark of functional cure. For more than 20 years studies of these (host immune mediated) flares have shown that they are very well tolerated and essential for functional cure. Even when functional cure is not achieved, these flares are beneficial in increasing the rates of HBV DNA decline and HBeAg seroconversion in the absence of therapy, HBV DNA decline and HBsAg decline with NUC therapy and improved liver disease, even in patients with decompensated cirrhosis. You will have to read the reviews I suggested to understand this better.
Nucleotide polymorphisms and siRNA / ASO effects
Your are not understanding what the J&J conclusions mean in abstract 1213. HBsAg decline with a double stranded RNA designed as a siRNA where siRNA escape mutations are present at the baseline confirms that the HBsAg decline is not coming from degradation of HBV mRNA. Neither siRNA or ASO mediated mRNA degradation can occur with these mismatches present. This a fundamental limitation of the approached we have also known for decades. Again you need to read the reviews. Another fundamental problem with the study presented by J&J (Abstract 1213) is that they limit the scoring of patients with escape mutations to patients with at least 15% of observed HBV DNA sequences bearing escape mutations. This is an incorrect threshold since even patients with trace amounts of escape mutations will see these rapidly become fixed with the selection pressure of siRNA or ASO present (this was already demonstrated in animals for two different siRNA triggers for HBV). Undoubtedly the presence of escape mutations is present to some degree in almost all patients. The persistent HBsAg decline in the presence of escape mutations means that the HBsAg decline is not from an siRNA effect. Therefore, subviral particles (SVP) from integrated HBV DNA are not affected. This is the basis for the plateau of limited effect for all siRNA (1.5-2 log decline of HBsAg from baseline): SVP from integrated HBV DNA will always be present with these agents.
Bepirovirsen and which TLR?
Unfortunately, the preclinical immunological studies GSK conducted with bepirovirsen were conducted in mice, which have very different TLR reactivities than humans (this issue has been well known for some time). As such they have been led to incorrect conclusions regarding the TLR agonistic properties of bepirovirsen which fly in the face of decades of research. The biochemistry of how oligonucleotides stimulate TLRs has been investigated intensely for 30 years. There is no TLR8 reactive element in bepirovirsen (in fact its modifications have been shown to very efficiently suppress TLR8 reactivity) but there is a fully reactive TLR9 DNA motif (class II CpG) present in the unmodified central portion of bepirovirsen which can stimulate TLR9. This was missed in the mice studies because mice have different sequences for TLR9 stimulation than humans. Importantly, we have had other TLR8 agonists evaluated in clinical studies where potent TLR8 stimulation was confirmed but no antiviral effects. These issues were discussed in a recent editorial here.
Does bepirovirsen have ASO effects?
Bepirovirsen is targeted mainly to the immunoreactive cells of the liver (where there is no HBV infection). GSK3389404 is targets bepirovirsen mainly to hepatocytes (where the HBV infection exists).
If there were even a trace of ASO effect in bepirovirsen, the HBsAg declines would be stronger with GSK3389404. In fact they are much weaker and absent in some patients and GSK has abandoned this ASO.
Another ASO with no TLR reactivity (RG6004 aka RO7062931) had almost no HBsAg effect at all.
Remember that single point mutations equivalently destroy the activity of ASO and siRNA. In other diseases of the liver, all ASO and siRNA have IDENTICAL effects on target mRNAs and reduction of proteins. This disconnect between ASO and siRNA tells you that the HBsAg effects siRNA are not mediated by mRNA degradation.
The only reason why bepirovirsen exhibits HBsAg decline (and flares) in patients with low HBsAg while all other ASOs fail (including hepatocyte targeted bepirovirsen) is becuase ALL of the activity is coming from TLR9 stimulation.
Again hopefully you can see that there many complex issues at play (all of which are unfortunately ignored in the presentation of clinical data with oligonucleotide-based compounds).
Best regards,