Mario H. Skiadopoulos Presentation on "Evaluation of the Antibody Threshold of Protection Conferred by a NextGeneration Anthrax Vaccine Candidate Adjuvanted with the Immunostimulatory

Pre-Exposure Anthrax Prophylaxis Rabbit Studies

refine the TNA Threshold of Protection for the

BioThrax Vaccine

The Biology of Anthrax Conference 15 November – 18 November 2016

Mario H. Skiadopoulos, PhD

Biodefense Division, Emergent BioSolutions

Pre-Exposure Anthrax Prophylaxis Rabbit Studies Refine the TNA Threshold of Protection for BioThrax® (Anthrax Vaccine Adsorbed) (AVA)

BioThrax licensure for post-exposure prophylaxis

against anthrax

Licensure under the FDA Animal Rule pathway

Logistic regression for estimating probability of

survival

Factors that can affect the logistic regression and

TNA threshold estimation

2

Anthrax Vaccine

3

BioThrax vaccine is FDA-approved for the Prevention of Anthrax

Licensure in 1970 based partly on field efficacy

trial (Brachman et al., 1962) and animal studies

Indicated for active immunization for anthrax:

– IM administration

– Primary series: 0, 1, 6 months

– Boosters: 12, 18 months, and annual thereafter

Used by DoD for pre-exposure prophylaxis (PrEP)

Stockpiled for civilian biodefense preparedness for

post-exposure prophylaxis (PEP)

Anthrax Vaccine

BioThrax Licensure

BioThrax vaccine is a sterile product, made from cell-free filtrates of

cultures of a strain of a non-pathogenic strain of B. anthracis. The vaccine

is prepared from the solution that results after the filtration of the culture

of anthrax bacteria and is adjuvanted with Alhydrogel® adjuvant 2%

(Aluminum hydroxide gel)

BioThrax vaccine is the only FDA-licensed vaccine available for protection

against anthrax disease. It is indicated for the active immunization of

individuals between the ages of 18 and 65 who are at high risk of exposure

BioThrax vaccine was licensed in 2015 under the FDA Animal Rule for use

in post-exposure prophylaxis of disease following suspected or confirmed

B. anthracis exposure, when administered in conjunction with

recommended antibacterial drugs

4

Anthrax Vaccine

5

Licensure Strategy for PEP

Licensure under Animal Rule:

– Demonstrated immunogenicity and efficacy in animals

– Identified TNA threshold of protection based on TNA titer associated with

protection

– Demonstrated ability of vaccine to generate protective TNA titers in humans

Non-Clinical Studies:

– Passive transfer studies in rabbits & NHPs demonstrated that TNA can

confer protection

– Post-exposure studies in rabbits demonstrated added value over

antibiotics

– Pre-exposure prophylaxis studies in rabbits and NHPs identified TNA

threshold of protection

Post-Exposure Prophylaxis

Animal Models for Anthrax Vaccines

6

Animal Models

New Zealand White rabbit

Cynomolgus macaque

7

Animal Efficacy Models Used to Address the Requirements of the Animal Rule

PrEP (pre-exposure prophylaxis) PEP (post-exposure prophylaxis) Passive transfer

Role of

Model

Demonstrates added value

of vaccine over antibiotics

alone, in a post-exposure

setting

Establishes correlation

between pre-challenge TNA

titer and probability of

survival

Demonstrates that

neutralizing antibody alone

is capable of protection

Value in

Deriving

Correlate of

Protection

Limited:

Due to dynamic nature of

the model

Complicated because

immune response is due to

both vaccination and

infection

Most appropriate:

Immune response is due

to vaccination only

Protection conferred by

circulating antibody and

memory response

Timing of challenge

simulates residual spore

exposure in humans

Limited:

Protection conferred by

circulating antibody only

Overestimates protective

antibody titer vs. active

immunization scenario

Post-Exposure Prophylaxis

8 8

Rabbit PreP Study: Survival is Dose-Dependent

Group N Vaccine

Immunization

Schedule

(days)

Challenge

(day)

Survivors

/Total

Percent

Survival

1 24 BioThrax 1:4 0, 28 70 24/24 100

2 24 BioThrax 1:16 0, 28 70 23/24 96

3 24 BioThrax 1:64 0, 28 70 15/24 63

4 24 BioThrax 1:256 0, 28 70 3/24 13

5 12 Alhydrogel 0, 28 70 0/24 0

Emergent Study 646-N107247: Pre-Exposure Immunization and Challenge Study in NZW Rabbits

BioThrax Rabbit Studies

9

Immunization of Animals with Various Dilutions of Vaccine Stratifies the Immune Response Prior to Challenge

0.01

0.1

1

10

100

0 14 28 42 56 70

TN

A N

F50

(GM

T +

95

% C

I)

Study Day

1:4

1:16

1:64

1:256

Adjuvant

Anthrax Challenge


10

LLOQ

TNA titers of Survivors and Non-Survivors Preceding B. anthracis Exposure


11

Pre-Challenge (day 69) TNA Titer Correlates with Survival in Rabbits

Emergent Study 646-N107247: Pre-Exposure Immunization and Challenge Study in NZW Rabbits

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.01 0.1 1 10

TNA Titer (NF50)

Pro

ba

bil

ity

of

Su

rviv

al

96 animals included in logistic

regression analysis

Dashed lines indicate 95% CI


The BioThrax TNA threshold was set using data from Rabbit Study 646

12

0.56

n = 96


Rabbit pre-exposure prophylaxis study 646 was used to set the TNA threshold of protection of BioThrax for PEP

0.56

TNA Threshold of Protection for AVA Immunized NHPs

13

BioThrax NHP Study

0.29 0.29

14

BioThrax PEP

Rabbit Pre-exposure Prophylaxis Immunogenicity and Efficacy Studies Using BioThrax Vaccine

Since the completion of Study 646 in 2007, a substantial body of additional data has been generated

using different BioThrax (AVA) lots in 5 different studies:

15

Study 2396 (Initial B55 POC study) B12 AVA FAV 373A Group 5 (1:4) n=24 Group 6 (1:16) n=24 Group 7 (1:64) n=24 Group 8 (1:256) n=24

Total: 96

Study 2453 Pilot Efficacy Study 1: B12 AVA lot 373A Group 4 (1:16) n=24 Group 5 (1:32) n=24 Group 6 (1:64) n=16 Total: 64

Study 2454 Pilot Efficacy Study 2: B12 AVA FAV373A Group 1 (1:32) n=48 Group 5 (1:16) n=48 Total: 96

Study 2455 Pilot GLP Efficacy Study 3: B12 AVA lot FAV423 Group 1 (1:16) n=32 Group 2 (1:32) n=32 Total: 64 B12 AVA lot FAV424 Group 3 (1:16) n=32 Group 6 (1:32) n=32 Total: 64

Study 3237 Pivotal, GLP, blinded study B12 AVA FAV423 Group 1 (1:64) n=16 Group 4 (1:4) n=16 Group 6 (1:16) n=60 Group 7 (1:32) n=60 Total: 152

Additional Rabbit PrEP Studies

GLP and blinded rabbit PrEP study 16

TNA Threshold of Protection for AVA Immunized Rabbits

BioThrax TNA Threshold

0.17

n=152

17

TNA Threshold of Protection for AVA from Selected Rabbit Efficacy Studies


0.17 0.18

n = 152 n = 96

Pivotal, blinded GLP study Pilot GLP study

18

o A total of five additional GUP studies were completed between 2012 and 2015 for the B55 program, using AVA manufactured

in B12 o TNA threshold of protection analysis for each of the five GUP studies indicated that 70% probability of survival was

associated with an NF50 between 0.16 and 0.24

o A meta-analysis of all study data from B12 AVA immunized rabbits indicates that the threshold of protection associated with a 70% probability of survival is 0.21 NF50

BioThrax TNA Threshold TNA threshold of protection for AVA

immunized rabbits

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.01 0.1 1 10 100

TNA (NF50)

Pro

ba

bility o

f S

urv

iva

l

646

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.01 0.1 1 10 100

TNA (NF50)

Pro

ba

bility o

f S

urv

iva

l

All AVA(B12) Studies

0.56 0.21 n = 96 n = 632

TNA threshold of protection for AVA immunized rabbits

19

• A TNA titer of 0.56 is associated nearly 100% protection


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.01 0.1 1 10 100

TNA (NF50)

Pro

ba

bility o

f S

urv

iva

l

646

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.01 0.1 1 10 100

TNA (NF50)

Pro

ba

bility o

f S

urv

iva

l

All AVA(B12) Studies

0.56 0.56

20

Several factors may have accounted for the differences observed between the original determination and subsequent

estimations of the TNA threshold of protection

Logistic Regression

R a b b it S tu d y 3 2 3 7

TN

A (

NF

50

)

No

n-S

urv

ivo

rs

Su

rviv

ors

0 .0 1

0 .1

1

1 0

1 0 0

37n 115nL L O Q

21

Comparison of Pre-challenge TNA titers for AVA Immunized Survivors vs Non-Survivors from Two Pivotal GLP Studies

R a b b it S tu d y 6 4 6

TN

A (

NF

50

)

No

n-S

urv

ivo

rs

Su

rviv

ors

0 .0 1

0 .1

1

1 0

1 0 0

31n 65n

L L O Q

In Study 646, 8 animals with titers above ~ 0.3 did not survive Very few to no animals with titers above ~ 0.3 died in any of the subsequent GUP studies

1)


R a b b it S tu d y 3 2 3 7

TN

A (

NF

50

)

No

n-S

urv

ivo

rs

Su

rviv

ors

0 .0 1

0 .1

1

1 0

1 0 0

37n 115nL L O Q

22

R a b b it S tu d y 6 4 6

TN

A (

NF

50

)

No

n-S

urv

ivo

rs

Su

rviv

ors

0 .0 1

0 .1

1

1 0

1 0 0

31n 65n

L L O Q

A ‘gap’ in TNA values between the LLOQ (0.086) and ~ NF50 = ~0.3 (survivors or non-survivors) may also have contributed to an overestimation of the threshold of protection in Study 646

2)

Comparison of Pre-challenge TNA titers for AVA Immunized Survivors vs Non-Survivors from Two Pivotal GLP Studies


23

The Slope of the Curve is Affected by the TNA Values in the Analysis


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.01 0.1 1 10 100

TNA (NF50)

Pro

ba

bility o

f S

urv

iva

l

646

In the original Study 646, the combined effect of multiple deaths at relatively high TNA titers, as well as the relatively few TNA values between ~LLOQ and ~0.3 had a net effect of decreasing the slope and increasing the TNA NF50 value associated with 70 % survival

0.56

24

BioThrax TNA Threshold The Slope of the Curve is Affected by the

TNA Values in the Analysis

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.01 0.1 1 10 100

TNA (NF50)

Pro

ba

bility o

f S

urv

iva

l

3237

In the original Study 646, the combined effect of multiple deaths at relatively high TNA titers, as well as the relatively few TNA values between ~LLOQ and ~0.3 had a net effect of decreasing the slope and increasing the TNA NF50 value associated with 70 % survival

0.17

PA-based anthrax vaccines have a unique TNA threshold of protection depending on the antigen-

adjuvant components

25

Anthrax Vaccine TNA

Threshold

AVA B55 pivotal rabbit study

26

AV7909 pilot GP study 2 rPA 7909 pilot GP study 1

TNA Titers of Survivors and Non-Survivors Preceding B. anthracis Exposure

Anthrax Vaccine TNA Threshold

Addition of CpG to BioThrax Vaccine Significantly Reduces the TNA Threshold Required for Protection

27

n=138 0.063


This threshold has been confirmed in 2 guinea pig and 2 NHP studies, including a total of 307 animals

0.08

Reference Standard BMI526 was used; RS AVR801 converted TNA value is 0.08 NF50

28

A Recombinant-PA Based Anthrax Vaccine Candidate Alhydrogel Adjuvant and CpG Has a Significantly Higher TNA Threshold of Protection

n=111

Reference Standard BMI526 was used; AVR801 converted TNA value is 0.74 NF50

0.94


Antigen-Adjuvant Combinations Affect the TNA Threshold Associated with Protection

29


AVA AV7909 rPA7909

0.08 0.74 0.21 NF50 associated with a 70% probability of survival:

AVA B55 pivotal rabbit study AV7909 pilot GP study 2 rPA 7909 pilot GP study 1

30


o The antigens and adjuvants used to elicit the immune response can have a direct impact on the quality of the immune response and affect:

the circulating TNA level present after immunization antibody avidity B-cell repertoire

o Study design is critical:

A pilot and confirmatory study should be conducted

The immune response must be stratified from very low to high titers:

appropriate vaccine dilutions must be used A pilot study can inform which dilutions to use

An appropriate number of animals must be used in order for the threshold

estimation to be robust

Conclusions

Acknowledgments

31

Non-Clinical Development Jeffry Shearer

Vladimir Savransky Tanya Nelson

Former members:

Boris Ionin Nina Malkevich

Regulatory Brenda Wolling

Former members:

Brett Pleune Danielle Craig

CDC Jarad Schiffer for SAS logistic regression program

Clinical Development Robert Hopkins

Victor Montalvo-Lugo

Battelle Biomedical Research Center Gloria Sivko Dan Sanford Lisa Henning Greg Stark

Statistics Na Li

Grace Lin Yukon Wu

These programs have been funded in part with federal funds from the Biomedical Advanced Research and Development Authority (BARDA), Department of Health and Human Services, under contracts no. HHSO100200700037C; HHSO100201000034C; HHSO100201000035C; HHSO100201000059C; National Institute of Allergy and Infectious Diseases (NIAID) Grant No. 1U01AI082224; U01 AI078169-02; BARDA/NIAID Contract No. HHSN272200800051C; HHSO100201500004C;Defense Advanced Research Projects Administration (DARPA; Contract No. DAAD1903C0002)

BioThrax® and any and all Emergent BioSolutions Inc. brand, product, service and feature names, logos and slogans are trademarks or registered trademarks of Emergent BioSolutions Inc. or its subsidiaries in the United States or other countries. All rights Reserved.

Alhydrogel® is a trademark of Brenntag Nordic A/S Public Limited Company. All other brand, product, service and feature names of trademarks are the property of their respective owners.

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Mario H. Skiadopoulos Presentation on "Evaluation of the Antibody Threshold of Protection Conferred by a NextGeneration Anthrax Vaccine Candidate Adjuvanted with the Immunostimulatory