efficacy of hepatitis b vaccine against antiviral drug-resistant hepatitis b virus mutants in the...

Efficacy of Hepatitis B Vaccine Against Efficacy of Hepatitis B Vaccine Against

Antiviral Drug-Resistant Hepatitis B Antiviral Drug-Resistant Hepatitis B

Virus Mutants in the Chimpanzee ModelVirus Mutants in the Chimpanzee Model

Saleem Kamili, Vitini Sozzi, Geoff Thompson. et al. HEPATOLOGY, Month 2009

AbstractAbstract

Hepatitis B virus (HBV) mutants resistant to Hepatitis B virus (HBV) mutants resistant to

treatment with nucleoside or nucleotide treatment with nucleoside or nucleotide

analogs and those with the ability to escape analogs and those with the ability to escape

from HBV-neutralizing antibody have the from HBV-neutralizing antibody have the

potential to infect HBV-vaccinated individuals potential to infect HBV-vaccinated individuals


AbstractAbstract

To address this potential serious public health To address this potential serious public health

challenge, we tested the efficacy of immunity challenge, we tested the efficacy of immunity

induced by a commercial hepatitis B vaccine induced by a commercial hepatitis B vaccine

against a tissue culture-derived, clonal HBV against a tissue culture-derived, clonal HBV

polymerase mutant in HBV seronegative chipolymerase mutant in HBV seronegative chi

mpanzeesmpanzees


AbstractAbstract

The polymerase gene mutant contained a The polymerase gene mutant contained a

combination of three mutations (rtV173L, combination of three mutations (rtV173L,

rtL180M, rtM204V), two of which resulted in rtL180M, rtM204V), two of which resulted in

changes to the overlapping viral envelope of changes to the overlapping viral envelope of

the hepatitis B surface antigen (sE164D, the hepatitis B surface antigen (sE164D,

sI195M) sI195M)


AbstractAbstract

Prior to the HBV mutant challenge of vaccinated Prior to the HBV mutant challenge of vaccinated

chimpanzees, we established virologic, serologic, chimpanzees, we established virologic, serologic,

and pathologic characteristics of infections resultiand pathologic characteristics of infections resulti

ng from intravenous inoculation of the HBV polyng from intravenous inoculation of the HBV poly

merase gene mutant and the sG145R vaccine-escamerase gene mutant and the sG145R vaccine-esca

pe surface gene mutantpe surface gene mutant


AbstractAbstract

Cloning and sequencing experiments Cloning and sequencing experiments

determined that the three mutations in the determined that the three mutations in the

polymerase gene mutant remained stable and polymerase gene mutant remained stable and

that the single mutation in the surface gene that the single mutation in the surface gene

mutant reverted to the wild-type sequencemutant reverted to the wild-type sequence


AbstractAbstract

Immunological evidence of HBV replication wImmunological evidence of HBV replication was observed in the vaccinated chimpanzees afteas observed in the vaccinated chimpanzees after challenge with the polymerase gene mutant ar challenge with the polymerase gene mutant as well as after rechallenge with serum-derived s well as after rechallenge with serum-derived wild-type HBV (5,000 chimpanzee infectious wild-type HBV (5,000 chimpanzee infectious doses administered intravenously), despite robdoses administered intravenously), despite robust humoral and cellular anti-HBV immune resust humoral and cellular anti-HBV immune responses after hepatitis B vaccinationponses after hepatitis B vaccination


Abstract ——ConclusionAbstract ——Conclusion

Our data showing successful experimental infeOur data showing successful experimental infection by HBV mutants despite the presence of ction by HBV mutants despite the presence of high anti-HBs levels considered protective in thigh anti-HBs levels considered protective in the vaccinated host are consistent with clinical he vaccinated host are consistent with clinical reports on breakthrough infection in anti-HBs-reports on breakthrough infection in anti-HBs-positive patients infected with HBV mutants. positive patients infected with HBV mutants.


AbstractAbstract ————ConclusionConclusion

In the absence of a protective humoral immuniIn the absence of a protective humoral immuni

ty, adaptive cellular immune responses elicited ty, adaptive cellular immune responses elicited

by infection may limit HBV replication and peby infection may limit HBV replication and pe

rsistencersistence


BackgroundBackground Hepatitis B is a global health problem that related to chronic Hepatitis B is a global health problem that related to chronic

active hepatitis, liver cirrhosis, and primary liver canceractive hepatitis, liver cirrhosis, and primary liver cancer

Vaccination against HBV prevents new infections and effortVaccination against HBV prevents new infections and effort

s toward the control of chronic disease have involved the ths toward the control of chronic disease have involved the th

erapeutic inhibition of viral replication using analogs of nucerapeutic inhibition of viral replication using analogs of nuc

leotides or nucleosidesleotides or nucleosides

Lamivudine was the first drug in this class to be licensed for Lamivudine was the first drug in this class to be licensed for

the treatment of chronic hepatitis B and remains in widesprethe treatment of chronic hepatitis B and remains in widespre

ad usead use


HBsAg capsid

Partial Double-stranded DNA

Lamivudine Adefovir Entecavir

A(n)

Infective HBV particles

(-)-DNA

Infective HBV particles

mRNAcccDNA

DNA polymerase RT

wrapped Pre-genome

mRNA

Mechanism of Mechanism of analogs of analogs of nucleotides or nnucleotides or nucleosidesucleosides


BackgroundBackground Pol gene (HBV Polymerase gene)

Its reverse transcriptase district contains seven functi

onal sequence (A-G)， The main target area of nucleThe main target area of nucle

oside or nucleotide analogs widely used in clinical is loside or nucleotide analogs widely used in clinical is l

ocated in the reverse transcriptase (RT) domain B and ocated in the reverse transcriptase (RT) domain B and

C, therefore resistant variantion is located in the domC, therefore resistant variantion is located in the dom

ain B and Cain B and C


BackgroundBackground

Antiviral drug-resistant mutations selected duriAntiviral drug-resistant mutations selected duri

ng treatment with lamivudine in the HBV polyng treatment with lamivudine in the HBV poly

merase gene (Pol) clustered within its B domaimerase gene (Pol) clustered within its B domai

n (rtV173L, rtL180M) and in the C domain in tn (rtV173L, rtL180M) and in the C domain in t

he conserved YMDD motif (rtM204V)he conserved YMDD motif (rtM204V)


It has been reported that these mutant It has been reported that these mutant viruses are transmissible and may have the viruses are transmissible and may have the potential to cause breakthrough infections potential to cause breakthrough infections among recipients of hepatitis B vaccineamong recipients of hepatitis B vaccine

The development of neutralizing antibody The development of neutralizing antibody escape in those individuals may result from escape in those individuals may result from the changed amino acid composition of the the changed amino acid composition of the HBV envelope protein, as the envelope and HBV envelope protein, as the envelope and polymerase open reading frames overlap in polymerase open reading frames overlap in the circular HBV genomethe circular HBV genome


Hepatitis B virus genome

ORF

S: coding for

HBV envelope protei

n

[neutralization of the

“a” determinant of the

hepatitis B surface antige

n (HBsAg) protein]

P: coding for

DNA polymerase


alterations in the neutralization of the “a” determinant alterations in the neutralization of the “a” determinant

of the hepatitis B surface antigen (HBsAg) protein haof the hepatitis B surface antigen (HBsAg) protein ha

ve been reported in patients with mutations in the Pove been reported in patients with mutations in the Po

l-gene receiving therapy with lamivudinel-gene receiving therapy with lamivudine

A markedly reduced binding of anti-HBs antibodies tA markedly reduced binding of anti-HBs antibodies t

o HBsAg with mutations corresponding to Pol-proteio HBsAg with mutations corresponding to Pol-protei

n changes (rtV173L, rtL180M, rtM204V) has been den changes (rtV173L, rtL180M, rtM204V) has been de

monstrated in vitromonstrated in vitro


These findings raise the possibility of the selecThese findings raise the possibility of the selec

tion of lamivudine-resistant HBV mutants with tion of lamivudine-resistant HBV mutants with

antigenically modified HBsAg proteins that coantigenically modified HBsAg proteins that co

uld act as vaccine escape mutants and infect vauld act as vaccine escape mutants and infect va

ccinated individuals in whom anti-HBs exerts ccinated individuals in whom anti-HBs exerts

a further positive selection pressurea further positive selection pressure


The most common mutation in the S-gene product is glThe most common mutation in the S-gene product is glycine to arginine at position 145 (sG145R)ycine to arginine at position 145 (sG145R)

It has been suggested that the immunity induced by exiIt has been suggested that the immunity induced by existing vaccines may not be protective against various Hsting vaccines may not be protective against various HBV mutants with altered surface proteins because of the BV mutants with altered surface proteins because of the conformational nature of the “a” determinantconformational nature of the “a” determinant

Furthermore, the existence of such HBV isolates and thFurthermore, the existence of such HBV isolates and the potential of these mutants to infect hepatitis B-vaccine potential of these mutants to infect hepatitis B-vaccinated individuals may lead to occult HBV infection and, ated individuals may lead to occult HBV infection and, consequently, have serious public health implicationsconsequently, have serious public health implications


Materials and Methods


Tissue Culture-Derived Mutant and Wild-Tissue Culture-Derived Mutant and Wild-TypeType HBV InoculaHBV Inocula

Point mutations were introduced by site-directed Point mutations were introduced by site-directed mutagenesis into a 1.5-times genome-length wt-HBV mutagenesis into a 1.5-times genome-length wt-HBV belonging to genotype A, belonging to genotype A, subtype adw 2subtype adw 2

The sG145R mutation was produced in the S-gene with overThe sG145R mutation was produced in the S-gene with overlapping rtW153Q mutation in the Pol-genelapping rtW153Q mutation in the Pol-gene （（ HBsAg ClassHBsAg Classical immune evasion strain ical immune evasion strain ））

A combination of three HBV Pol-gene mutations, rtV173L, A combination of three HBV Pol-gene mutations, rtV173L, rtL180M, and rtM204V, was produced that correspond to srtL180M, and rtM204V, was produced that correspond to sE164D and sI195M mutations in the S-gene (rtL180M does E164D and sI195M mutations in the S-gene (rtL180M does not result in an amino acid change in the S-gene)not result in an amino acid change in the S-gene)


Chimpanzee Infectivity Chimpanzee Infectivity ExperimentsExperiments

Eleven colony-born chimpanzees (six females and five males, rEleven colony-born chimpanzees (six females and five males, r

anging in age from3 to 11 years and weighing between 11 to 3anging in age from3 to 11 years and weighing between 11 to 3

7 kg), determined to be seronegative for markers of HBV infec7 kg), determined to be seronegative for markers of HBV infec

tion, were used for infectivity, vaccination, and challenge studition, were used for infectivity, vaccination, and challenge studi

eses

All chimpanzees inoculated with the wild-type and mutant HBAll chimpanzees inoculated with the wild-type and mutant HB

V inocula were followed up for 180 to 200 days after inoculatiV inocula were followed up for 180 to 200 days after inoculati

onon


Chimpanzee HBV Immunization Chimpanzee HBV Immunization and and Challenge ExperimentsChallenge Experiments Two chimpanzees (CH10364 and CH10369) were given a pediTwo chimpanzees (CH10364 and CH10369) were given a pedi

atric dose (10 μg/0.5mL) of a licensed recombinant hepatitis B atric dose (10 μg/0.5mL) of a licensed recombinant hepatitis B

vaccine at 0, 28, and 56 daysvaccine at 0, 28, and 56 days

One control chimpanzee(CH10301) was vaccinated with hepatOne control chimpanzee(CH10301) was vaccinated with hepat

itis A vaccineitis A vaccine

All three vaccinated chimpanzees were challenged with the cloAll three vaccinated chimpanzees were challenged with the clo

nal HBV Pol-gene mutant containing 9.8* 10nal HBV Pol-gene mutant containing 9.8* 109 9 copies of HBV copies of HBV

DNA 42 days after the third vaccine doseDNA 42 days after the third vaccine dose


Chimpanzee HBV Immunization Chimpanzee HBV Immunization and and Challenge ExperimentsChallenge Experiments the control chimpanzee was challenged 35 days after the hepatthe control chimpanzee was challenged 35 days after the hepat

itis A vaccinationitis A vaccination

The two hepatitis B-vaccinated chimpanzees were further crosThe two hepatitis B-vaccinated chimpanzees were further cros

s-challenged with 5,000 chimpanzee infectious doses (CID) of s-challenged with 5,000 chimpanzee infectious doses (CID) of

human serum-derived wt-HBV inoculum 216 days after the Pohuman serum-derived wt-HBV inoculum 216 days after the Po

l-gene mutant challengel-gene mutant challenge

A naive chimpanzee, CH10270, served as a control for the wt-A naive chimpanzee, CH10270, served as a control for the wt-

HBV challenge and was also inoculated with 5,000 CIDs of thHBV challenge and was also inoculated with 5,000 CIDs of th

e wt-HBVe wt-HBV inoculum inoculum


Chimpanzee HBV Immunization Chimpanzee HBV Immunization and and Challenge ExperimentsChallenge Experiments Serial serum specimens were collected from all the chimpanzeSerial serum specimens were collected from all the chimpanze

es twice weekly and whole blood samples for peripheral blood es twice weekly and whole blood samples for peripheral blood

mononuclear cells (PBMCs) isolation were collected every 2 mononuclear cells (PBMCs) isolation were collected every 2

weeksweeks

Serum alanine aminotransferase (ALT) levels were measured iSerum alanine aminotransferase (ALT) levels were measured i

n fresh serum specimens. Individual cutoff values for ALT levn fresh serum specimens. Individual cutoff values for ALT lev

els were established for each animal using at least 10 preinoculels were established for each animal using at least 10 preinocul

ation measurementsation measurements


Serological Markers of HBV InfectionSerological Markers of HBV Infection

All serum samples were tested for :All serum samples were tested for :

HBsAg HBsAg

antibody to HBsAg (anti-HBs)antibody to HBsAg (anti-HBs)

total antibody to hepatitis B core antigen (anti-HBc)total antibody to hepatitis B core antigen (anti-HBc)

IgM anti-HBcIgM anti-HBc

hepatitis B e antigen (HBeAg)hepatitis B e antigen (HBeAg)

total anti-HBetotal anti-HBe

The levels of anti-HBs in samples collected during vaccination and The levels of anti-HBs in samples collected during vaccination and

challenge periods were also quantitatively measuredchallenge periods were also quantitatively measured


T-Cell ResponsesT-Cell Responses PBMCs from the chimpanzees were enriched and tested in an interferPBMCs from the chimpanzees were enriched and tested in an interfer

on-ΥELISpot assay for reactivity to HBV surface and polymerase antigon-ΥELISpot assay for reactivity to HBV surface and polymerase antigensens

Millipore were precoated with antibodies to human interferon-Υ and 2Millipore were precoated with antibodies to human interferon-Υ and 2*10*1055 chimpanzee PBMCs in medium added to each well chimpanzee PBMCs in medium added to each well

Duplicate wells received pools of overlapping synthetic peptides that Duplicate wells received pools of overlapping synthetic peptides that spanned either amino acids 67-237 of the HBsAg or amino acids 1-344 spanned either amino acids 67-237 of the HBsAg or amino acids 1-344 of the reverse transcriptase domain of the polymerase proteinof the reverse transcriptase domain of the polymerase protein

Plates were incubated and developed for spot formation using a seconPlates were incubated and developed for spot formation using a second antibody to interferon-Υ conjugated to enzyme followed by substratd antibody to interferon-Υ conjugated to enzyme followed by substratee

Spot-forming cells (SFCs) in the microtiter wells were quantified using Spot-forming cells (SFCs) in the microtiter wells were quantified using a CTL analyzer a CTL analyzer

Responses were considered positive when an average of 10 SF Cover bResponses were considered positive when an average of 10 SF Cover background was detected in the duplicate wellsackground was detected in the duplicate wells


ResultsResults


Wild-Type HBVWild-Type HBV


Sequencing studies showed that all clones frSequencing studies showed that all clones fr

om the inoculum and samples collected froom the inoculum and samples collected fro

m the two infected chimpanzees at the beginm the two infected chimpanzees at the begin

ning, during, and at the end of viremia mainning, during, and at the end of viremia main

tained the wild-type sequencetained the wild-type sequence


HBV S-Gene Mutant (sG145R)HBV S-Gene Mutant (sG145R)


Sequencing studies of 24 clones from the firsSequencing studies of 24 clones from the firs

t HBV DNA-positive serum sample postinot HBV DNA-positive serum sample postino

culation (day 98) showed the preservation of culation (day 98) showed the preservation of

the inoculum sequence in only 33% of the clthe inoculum sequence in only 33% of the cl

ones, whereas 67% had the wild-type sequeones, whereas 67% had the wild-type seque

ncence


HBV Pol-Gene Mutant HBV Pol-Gene Mutant (rtV173L, rtL180M,rtM204V)(rtV173L, rtL180M,rtM204V)


Sequencing studies showed that all clones frSequencing studies showed that all clones fr

om the two inocula and samples collected at om the two inocula and samples collected at

the beginning, during, and at the end of virethe beginning, during, and at the end of vire

mia in the three infected chimpanzees showmia in the three infected chimpanzees show

ed the preservation of the rt173L, rt180M, aed the preservation of the rt173L, rt180M, a

nd rt204V mutationsnd rt204V mutations


Protective Efficacy of HBV Vaccine

The ability of a licensed hepatitis B vaccine to The ability of a licensed hepatitis B vaccine to

provide protection against challenge with the provide protection against challenge with the

HBV Pol-gene mutant was evaluated in two chHBV Pol-gene mutant was evaluated in two ch

impanzees (CH10364 and CH10369) that receiimpanzees (CH10364 and CH10369) that recei

ved the hepatitis B vaccine and a control chimved the hepatitis B vaccine and a control chim

panzee (CH10301) that received the hepatitis panzee (CH10301) that received the hepatitis

A vaccineA vaccine


Both hepatitis B vaccine recipients seroconverteBoth hepatitis B vaccine recipients seroconverted to anti-HBs 1 week after the first dose of the vad to anti-HBs 1 week after the first dose of the vaccine, and anti-HBs levels were boosted to steadccine, and anti-HBs levels were boosted to steady-state levels of >75 mIU/mL after the administry-state levels of >75 mIU/mL after the administration of the second and third vaccine dosesation of the second and third vaccine doses


Neither humoral nor cellular immunity to HBV Neither humoral nor cellular immunity to HBV

antigens was detected in the control chimpanzeantigens was detected in the control chimpanze

e CH10301 vaccinated with HAV vaccinee CH10301 vaccinated with HAV vaccine


All three chimpanzees were challenged with thAll three chimpanzees were challenged with th

e triple mutant to determine if coding changes e triple mutant to determine if coding changes

in the corresponding S-gene (sE164D and sI19in the corresponding S-gene (sE164D and sI19

5M) compromised protective immunity elicite5M) compromised protective immunity elicite

d by hepatitis B vaccinationd by hepatitis B vaccination


Anti-HBc, which is a marker of exposure or inAnti-HBc, which is a marker of exposure or in

fection, was detected on day 7 in CH10364 anfection, was detected on day 7 in CH10364 an

d days 7, 10, and 17 in CH10369 d days 7, 10, and 17 in CH10369


The hepatitis A-immunized control chimpanzee CH1The hepatitis A-immunized control chimpanzee CH10301 was infected because HBV DNA was detected i0301 was infected because HBV DNA was detected in serum from days 42 to 91, not exceeding 1 log IU/n serum from days 42 to 91, not exceeding 1 log IU/mL mL

The chimpanzee seroconverted to total anti-HBc from The chimpanzee seroconverted to total anti-HBc from day 87 and anti-HBs from day 84 post infection.day 87 and anti-HBs from day 84 post infection.

Despite replication of the Pol-gene mutant virus in thiDespite replication of the Pol-gene mutant virus in this chimpanzee, peripheral blood T-cell responses agais chimpanzee, peripheral blood T-cell responses against the surface or polymerase proteins were not detectnst the surface or polymerase proteins were not detecteded

No ALT elevation was observed during the follow-up No ALT elevation was observed during the follow-up period period


The presence of a humoral immune response to the HThe presence of a humoral immune response to the HBV core antigen in both ENGERIX-B-vaccinated chiBV core antigen in both ENGERIX-B-vaccinated chimpanzees and of circulating T-cells against the HBV mpanzees and of circulating T-cells against the HBV polymerase antigen in one chimpanzee (CH10364) inpolymerase antigen in one chimpanzee (CH10364) indicated that dicated that sterilizing immunity against the HBV Posterilizing immunity against the HBV Pol-gene mutant was lackingl-gene mutant was lacking

Therefore, chimpanzees CH10364 and CH10369 werTherefore, chimpanzees CH10364 and CH10369 were challenged with human-derived wt-HBV to determie challenged with human-derived wt-HBV to determine if they were protected against challenge with a virune if they were protected against challenge with a virus encoding intact (that is, unmutated) HBsAgs encoding intact (that is, unmutated) HBsAg


Challenge with the wt-HBV inoculum (HLD1, Challenge with the wt-HBV inoculum (HLD1,

5,000 CIDs) was carried out when anti-HBs le5,000 CIDs) was carried out when anti-HBs le

vels were 63,610 mIU/mL and 18,868 mIU/mvels were 63,610 mIU/mL and 18,868 mIU/m

L in CH10364 and CH10369, respectively, and L in CH10364 and CH10369, respectively, and

after loss of HBV mutant-stimulated T-cell resafter loss of HBV mutant-stimulated T-cell res

ponses in both chimpanzeesponses in both chimpanzees


High frequencies of circulating T-cells against High frequencies of circulating T-cells against

HBsAg suggested anHBsAg suggested an anamnestic response prianamnestic response pri

med by vaccination and perhaps the prior infecmed by vaccination and perhaps the prior infec

tion with the HBV Pol-gene mutant. Responsetion with the HBV Pol-gene mutant. Response

s to the polymerase protein were delayed by cos to the polymerase protein were delayed by co

mparisonmparison


Polymerase-specific T-cell lines expanded from the blPolymerase-specific T-cell lines expanded from the blood of both chimpanzees expressed CD4+ and not Cood of both chimpanzees expressed CD4+ and not CD8+ (data not shown).D8+ (data not shown).

Anti-HBs titers increased 6-fold in chimpanzee CH10Anti-HBs titers increased 6-fold in chimpanzee CH10369 and 10-fold in chimpanzee CH10364369 and 10-fold in chimpanzee CH10364

However, HBV DNA, HBsAg, IgM anti-core, and HHowever, HBV DNA, HBsAg, IgM anti-core, and HBeAg were not detected in any of the chimpanzees duBeAg were not detected in any of the chimpanzees during the follow-up period after the challengering the follow-up period after the challenge


A markedly different profile of wt-HBV infection waA markedly different profile of wt-HBV infection wa

s observed in a naive unvaccinated chimpanzee CH10s observed in a naive unvaccinated chimpanzee CH10

270270

The infection was characterized by the presence of HThe infection was characterized by the presence of H

BV DNA, which reached the peak levels of 4.1 log IBV DNA, which reached the peak levels of 4.1 log I

U/mL on day 66, and of HBsAg, HBeAg, and IgM anU/mL on day 66, and of HBsAg, HBeAg, and IgM an

ti-HBc. The chimpanzee subsequently developed acutti-HBc. The chimpanzee subsequently developed acut

e hepatitis with elevated serum ALT levels from days e hepatitis with elevated serum ALT levels from days

66 to 129, with the peak of 2,500 IU/L (cutoff 73 IU/66 to 129, with the peak of 2,500 IU/L (cutoff 73 IU/

L) observed on day 91.L) observed on day 91.


This chimpanzee subsequently seroconverted tThis chimpanzee subsequently seroconverted t

o total anti-HBc, anti-HBe, and anti-HBs o total anti-HBc, anti-HBe, and anti-HBs

Circulating T-cells specific for the surface and Circulating T-cells specific for the surface and

polymerase antigens were not detected in chimpolymerase antigens were not detected in chim

panzee CH10270 by the ELISpot assay panzee CH10270 by the ELISpot assay


DiscussionDiscussion

Breakthrough infections etiologically linked to Breakthrough infections etiologically linked to

S-gene HBV mutants have been reported to ocS-gene HBV mutants have been reported to oc

cur among HBV-immunized populations, despcur among HBV-immunized populations, desp

ite the presence of seroprotective levels of antite the presence of seroprotective levels of ant

i-HBs in the infected individualsi-HBs in the infected individuals


DiscussionDiscussion

In this experimental study, they evaluated the pIn this experimental study, they evaluated the p

rotective efficacy of a commercial hepatitis B rotective efficacy of a commercial hepatitis B

vaccine against the Polg-ene HBV mutant (rtVvaccine against the Polg-ene HBV mutant (rtV

173L, rtL180M, rtM204V) encoding the surfac173L, rtL180M, rtM204V) encoding the surfac

e protein mutations (sE164D, sI195M) that wae protein mutations (sE164D, sI195M) that wa

s previously shown to have significantly reducs previously shown to have significantly reduc

ed anti-HBs binding propertiesed anti-HBs binding properties


The inoculation of naive chimpanzees with cloThe inoculation of naive chimpanzees with clonal HBV mutants allowed studying the virologic,nal HBV mutants allowed studying the virologic, immunologic, and pathologic findings exclusiv immunologic, and pathologic findings exclusively related to the mutant infectionely related to the mutant infection

The subsequent challenge experiment provided The subsequent challenge experiment provided an opportunity to determine whether HBV mutan opportunity to determine whether HBV mutants are infectious to vaccinated chimpanzees ants are infectious to vaccinated chimpanzees

Because the cellular immunity data indicated tBecause the cellular immunity data indicated that the commercial vaccine did not induce sterihat the commercial vaccine did not induce sterilizing immunity against the Pol-gene HBV mutlizing immunity against the Pol-gene HBV mutant, they further challenged two immunized chant, they further challenged two immunized chimpanzees with the serum-derived wt-HBVimpanzees with the serum-derived wt-HBV


In naive nonimmunized chimpanzeesIn naive nonimmunized chimpanzees ：：

they observed variations in the infectivity profile follothey observed variations in the infectivity profile follo

wing injection with inocula carrying various viral titewing injection with inocula carrying various viral tite

rs of HBV mutantsrs of HBV mutants

The length of the incubation period, measured by first The length of the incubation period, measured by first

appearance of HBV DNA in serum, ranged from 1 weappearance of HBV DNA in serum, ranged from 1 we

ek (clonal Pol-gene HBV mutant and wt-HBV) to 14 ek (clonal Pol-gene HBV mutant and wt-HBV) to 14

weeks (sG145R mutant) and did not correlate with thweeks (sG145R mutant) and did not correlate with th

e number of HBV DNA copies in the inoculae number of HBV DNA copies in the inocula


Also of interest were differences in the stability of mutatioAlso of interest were differences in the stability of mutatio

ns between Pol-gene and S-gene mutants during the experns between Pol-gene and S-gene mutants during the exper

imental infection of chimpanzeesimental infection of chimpanzees

mutations in the Pol-gene remained stable throughout the mutations in the Pol-gene remained stable throughout the

period of viremia in all four chimpanzeesperiod of viremia in all four chimpanzees

the sG145R mutant in one infected chimpanzee readily rethe sG145R mutant in one infected chimpanzee readily re

verted to wild-type, which are at variance with data from verted to wild-type, which are at variance with data from

previous experimental infectivity studies, previous experimental infectivity studies, may be may be

attributed to the mutation site, replication fitness of the attributed to the mutation site, replication fitness of the

mutants, the size of the inocula, or a combination of thesemutants, the size of the inocula, or a combination of these


Vaccinated chimpanzees in this study developed a roVaccinated chimpanzees in this study developed a ro

bust T-cell immunity and had pronounced anti-HBs sbust T-cell immunity and had pronounced anti-HBs s

erum antibody titers (75 mIU/mL) that significantly eerum antibody titers (75 mIU/mL) that significantly e

xceeded those considered protective (10mIU/mL)xceeded those considered protective (10mIU/mL)

Detection of anti-HBc antibodies after challenge with Detection of anti-HBc antibodies after challenge with

the Pol-gene HBV mutant in one serum sample from the Pol-gene HBV mutant in one serum sample from

CH10364 and three consecutive samples from CH103CH10364 and three consecutive samples from CH103

69 provided immunological evidence of the HBV repl69 provided immunological evidence of the HBV repl

ication despite high anti-HBs levelsication despite high anti-HBs levels


Further evidence of the breakthrough infection in the Further evidence of the breakthrough infection in the challenge experiment using the clonal Pol-gene HBV challenge experiment using the clonal Pol-gene HBV mutant was provided by priming of T-cell responses amutant was provided by priming of T-cell responses against the polymerase protein in at least one vaccinategainst the polymerase protein in at least one vaccinated chimpanzeed chimpanzee

This protein is not a component of the vaccine and it iThis protein is not a component of the vaccine and it is unlikely that sufficient quantities are physically assos unlikely that sufficient quantities are physically associated with the Pol-gene mutant virus particles in the ciated with the Pol-gene mutant virus particles in the original inoculum to prime T-cell immunity in the absoriginal inoculum to prime T-cell immunity in the absence of virus replicationence of virus replication

this latter possibility seems remote, as they did not obthis latter possibility seems remote, as they did not observe polymerase specific responses in unvaccinated cserve polymerase specific responses in unvaccinated chimpanzees that received high doses of Pol-gene muthimpanzees that received high doses of Pol-gene mutant or wild-type particles that resulted in infectionant or wild-type particles that resulted in infection


High serum titers of anti-HBs antibodies are a reliable High serum titers of anti-HBs antibodies are a reliable marker of vaccine-induced protective immunity againmarker of vaccine-induced protective immunity against HBV infectionst HBV infection

It is conceivable that virus-specific T cells provide prIt is conceivable that virus-specific T cells provide protection when mutant or wild-type viruses breakthrouotection when mutant or wild-type viruses breakthrough sterilizing humoral immunity gh sterilizing humoral immunity

Their observation that Pol-specific T-cell responses arTheir observation that Pol-specific T-cell responses are elicited in hepatitis B-vaccinated animals challengee elicited in hepatitis B-vaccinated animals challenged with mutant and wild-type viruses is clearly consistd with mutant and wild-type viruses is clearly consistent with this possibility.ent with this possibility.


Efficacy of anti-HBV immunity induced by the commEfficacy of anti-HBV immunity induced by the comm

ercial vaccine was further tested by rechallenging the ercial vaccine was further tested by rechallenging the

two chimpanzees, previously vaccinated and challengtwo chimpanzees, previously vaccinated and challeng

ed with the Pol-gene mutant with serum-derived wt-ed with the Pol-gene mutant with serum-derived wt-

HBVHBV

This experiment showed a subsequent boost of anti-HThis experiment showed a subsequent boost of anti-H

Bs levels (6-fold to 10-fold increase) in both chimpanBs levels (6-fold to 10-fold increase) in both chimpan

zees and a surge of T-cell responses against both surfzees and a surge of T-cell responses against both surf

ace-derived and polymerase-derived peptidesace-derived and polymerase-derived peptides


This pattern of cellular and humoral immune rThis pattern of cellular and humoral immune r

esponses against HBV antigens strongly impliesponses against HBV antigens strongly impli

cated viral replication despite very high levels cated viral replication despite very high levels

of anti-HBs suggesting breakthrough HBV infof anti-HBs suggesting breakthrough HBV inf

ection after wt-HBV challengeection after wt-HBV challenge

It is possible, however, that a dose of 5,000 CIIt is possible, however, that a dose of 5,000 CI

Ds used in the challenge experiment may have Ds used in the challenge experiment may have

been large enough to overcome the seroprotectbeen large enough to overcome the seroprotect

ive barrierive barrier


A further challenge inoculum titration study wA further challenge inoculum titration study w

ould be needed to evaluate the relationship betould be needed to evaluate the relationship bet

ween the size of inoculum and protective level ween the size of inoculum and protective level

of anti-HBV immunity induced by a vaccine aof anti-HBV immunity induced by a vaccine a

nd measured by the dynamics of cellular immund measured by the dynamics of cellular immu

nity to HBV polymerase protein and the level nity to HBV polymerase protein and the level

of anti-HBs antibody of anti-HBs antibody


conclusionconclusion They demonstrated that in vitro-generated HBV clonaThey demonstrated that in vitro-generated HBV clona

l Pol-gene mutant, bearing the lamivudine-resistance-l Pol-gene mutant, bearing the lamivudine-resistance-

associated mutations (rtV173L, rtL180M, rtM204V) associated mutations (rtV173L, rtL180M, rtM204V)

and the prototype vaccine-escape S-gene mutant (sG1and the prototype vaccine-escape S-gene mutant (sG1

45R), are infectious in naive chimpanzees 45R), are infectious in naive chimpanzees

The S-gene mutant readily reverted to the wild-type sThe S-gene mutant readily reverted to the wild-type s

equence but the Pol-gene mutant was stable during thequence but the Pol-gene mutant was stable during th

e course of infectione course of infection


conclusionconclusion Vaccination of naive chimpanzees with a commercial hepatitis Vaccination of naive chimpanzees with a commercial hepatitis

B vaccine that resulted in the induction of both humoral and ceB vaccine that resulted in the induction of both humoral and cellular immune responses did not seem to confer sterilizing imllular immune responses did not seem to confer sterilizing immunity against challenge with the Pol-gene mutant and subseqmunity against challenge with the Pol-gene mutant and subsequent challenge with a serum-derived wt-HBVuent challenge with a serum-derived wt-HBV

The data showing successful experimental infection by HBV The data showing successful experimental infection by HBV mutants despite the presence of high anti-HBs levels consideremutants despite the presence of high anti-HBs levels considered protective in the vaccinated host are consistent with clinical rd protective in the vaccinated host are consistent with clinical reports on breakthrough infection in anti-HBs positive patients eports on breakthrough infection in anti-HBs positive patients infected with HBV mutants and warrant further studies of efficinfected with HBV mutants and warrant further studies of efficacy of HBV vaccineacy of HBV vaccine


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efficacy of hepatitis b vaccine against antiviral drug-resistant hepatitis b virus mutants in the...

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