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B Cells and blood stage malaria. Sean Elias. Malaria Life Cycle. Antigen Constructs. FVO Ectodomain. tPA. 3D7. FVO Terminus. F VO-33 FVO-19. MSP-1. MSP-1: Merozoite surface protein. 19 fragment contains major B cell epitopes (anchored to RBCs during invasion) - PowerPoint PPT Presentation
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B CELLS AND BLOOD STAGE MALARIA
Sean Elias
MALARIA LIFE CYCLE
ANTIGEN CONSTRUCTS
MSP-1: Merozoite surface protein. 19 fragment contains major B cell epitopes (anchored to RBCs during invasion) Preclinical association of 19 antibodies with protection 33 fragment contains Th cell epitopes
AMA-1: Apical membrane antigen. Required for RBC invasion Preclinical association of antibodies with protection
1 3 5 12 3D7-33 3D7-19
F VO-33 FVO-19
Glycine-Proline linker
MSP-1
Glycine-Proline linker
tPA 3D7 FVO Ectodomain
FVO Terminus
AMA-1
CLINICAL TRIAL STRUCTUREVAC36 VAC37
Adeno Prime MVA Boost
8wk
CLINICAL TRIAL STRUCTURE
VAC39
VOLUNTEER BLEEDS
Vac1AdCh63
D0 D2 D14 D28 D56 D90S
Vac1AdCh63
D0 D2 D14 D28 D56 C-1 D63 D58 C+21 / DoDS
Vac 2MVA
Vac1AdCh63
D0 D2 D14 D28 D56 D84 D63 D58 D140S
Vac 2MVA
= Blood test
AdCh63 = AdCh63 AMA-1 (VAC36), MSP-1 (VAC37)
MVA = MVA AMA1 (VAC36), MSP-1 (VAC37)
S = Screening
C+7 C+11 C+35 C+90
2A
0 20 40 60 80 1001
10
100
1000
10000
100000004016
MSP
1 AU
2B
0 50 100 1501
10
100
1000
10000
100000006013019022023
MSP
1 AU
2C
0 50 100 1501
10
100
1000
10000
100000007014017
MSP
1 AU
2C
MEMORY B CELLS AND MALARIA What is the effect of challenge/infection on mBC expansion?
The P. falciparum-specific human memory B cell compartment expands gradually with repeated malaria infections. Weiss 2010
Long-lived antibody and B cell memory to P. falciparum in low transmission areas. Wipasa 2010
P. Yoelii Can Ablate Vaccine-Induced Long Term protection in mice. Wykes 2005
Kenyan children exposed to malaria may develop antibody but not memory to blood stage antigens (AMA-1 more so than MSP-1) Dorfman 2005
Decreases in memory and naive B cell subsets in Kenyan children with acute P. falciparum infection. Asito 2008
Atypical memory B cells (‘exhausted’) are greatly expanded in individuals living in a malaria-endemic area. Weiss 2009
A Positive Correlation between Atypical Memory B Cells and Plasmodium falciparum Transmission Intensity in Cross-Sectional Studies in Peru and Mali Weiss 2011
VAC37 : MSP-1 ANTIBODY DATA
0 20 40 60 80 1001
10
100
1000
10000
100000III
Time (d)
Anti-
MSP
1 19
ELIS
A un
its
1B
0 50 100 1501
10
100
1000
10000
100000IIIIIIIV
Time (d)
Anti-
MSP
1 19
ELIS
A un
its
1A
0 20 40 60 80 1001
10
100
1000
10000
100000III
Time (d)
Anti-
MSP
1 19
ELIS
A u
nits
A B
C D
0 50 100 1501
10
100
1000
10000
100000IIIIIIIVV
Time (d)
Anti-
MSP
1 19
ELIS
A un
itsGroup 1A Group 1B
Group 2A Group 2B+2C
0 50 100 1501
10
100
1000
10000
100000IIIIIIIVVVIVIIVIII
Time (d)
Anti-
MSP
1 19
ELIS
A u
nits
ELISA DATA: S. Draper
VAC37 : MSP-1 MEMORY B CELL ELISPOT
2C Total Ag Specific mBC
0 28 56 84 112 140 1680
50
100
150
200
250
300
350
400
450
500
IIIIII
Day
Ag s
peci
fic m
BC
/Milli
on C
ultu
red
PBM
C
2B Total Ag Specific mBC
0 28 56 84 112 140 1680
50
100
150
200
250
300
350
400
450
500
IVVVIVIIVIII
Day
Ag s
peci
fic m
BC
/Milli
on C
ultu
red
PBM
C
2C % mBC of total
0 28 56 84 112 140 1680.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
IIIIII
Day
Ag S
peci
fic m
BC
's a
s %
of T
otal
IgG
BC
's
2B % mBC of total
0 28 56 84 112 140 1680.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
IVVVIVIIVIII
Day
Ag S
peci
fic m
BC
's a
s %
of T
otal
IgG
BC
's
Challenge
Boost
Prime
Day of Diagnosis
Prime
Boost
VAC37 : MSP-1 MEMORY B CELL ELISPOT
2C Total IgG mBCs
0 28 56 84 112 140 1680
5000
10000
15000
20000
25000
30000
35000
40000
IIIIII
Day
Ag s
peci
fic m
BC
/Milli
on C
ultu
red
PBM
C
2B Total IgG mBCs
0 28 56 84 112 140 1680
5000
10000
15000
20000
25000
30000
35000
40000
IVVVIVIIVIII
Day
Ag s
peci
fic m
BC
/Milli
on C
ultu
red
PBM
C
2C % Dip mBC of total
0 28 56 84 112 140 1680.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
IIIIII
Day
Ag S
peci
fic m
BC
's a
s %
of T
otal
IgG
BC
's
2B % Dip mBC of total
0 28 56 84 112 140 1680.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
IVVVIVIIVIII
Day
Ag S
peci
fic m
BC
's a
s %
of T
otal
IgG
BC
's
VAC37 : MSP-1 MEMORY B CELL ELISPOT
Day 84
0 2000 4000 6000 8000 100000
50
100
150
200
Ab Titre 3D7
mB
C's
/mill
ion
cultu
red
PBM
C
Day 84 (Outlier Excluded)
0 2000 4000 6000 8000 100000
50
100
150
200
Ab Titre 3D7
mB
C's
/mill
ion
cultu
red
PBM
C
P= 0.076 P= 0.0004
D84/D90
1A 1B 2A 2B0
50
100
150
200
Group
mB
C's
/mill
ion
cultu
red
PBM
C
Boost required for significant B cell response
mBC’s correlate with Ab’s
VAC36 : AMA-1 MEMORY B CELL ELISPOT
D84
I II III IV V VI VII VIII0
50
100
150
200
250
Volunteer
mB
C's
/mill
ion
cultu
red
PBM
C
mBC vs AB
0 1000 2000 3000 40000
50
100
150
200
250
III
III
IV
V
VI
VII
VIII
Ab Titre 3D7
mB
C's
/mill
ion
cultu
red
PBM
C
1B
0 20 40 60 80 100 120 1401
10
100
1000
10000IIIIIIIV
Time (d)
Anti-
AMA1
(3D
7) E
LISA
uni
ts
0 20 40 60 80 100 120 1401
10
100
1000
10000VVIVIIVIII
2B
Time (d)
Anti-
AMA1
(3D
7) E
LISA
uni
ts
P= 0.0962
ELISA DATA: S. Draper, S. Biswas
VAC39 CONTROLS 3/5 controls had mBC response to
MSP-1 at 35 days after challenge No response to AMA-1
Appears to be rough correlation with Ab titre for MSP-1. Needs more power to confirm relationship.
Only 2/5 volunteers showed low Ab titre to AMA-1 at C+35
Kenyan children exposed to malaria may develop antibody but not memory to blood stage antigens (AMA-1 more so than MSP-1) Dorfman 2005
Controls C+35
MSP-1 AMA-10
10
20
30
40
50
mB
C's
/mill
ion
cultu
red
PBM
C
MSP-1 mBC vs Ab
0 200 400 600 800 10000
10
20
30
40
50
Ab Titre 3D7
mB
C's
/mill
ion
cultu
red
PBM
C
MEMORY B CELL ELISPOTS Conclusions:
Ad/MVA prime boost regime induces mBC formation to both MSP-1 & AMA-1
Following this regime with parasite exposure further boosts mBCs to levels much higher than seen through natural exposure (up to x10?)
mBC derived B cells appear to correlate with Ab titre Activation of mBC by malaria antigens does not appear to activate other
mBC’s (Diphtheria) by bystander effect Blood stage parasitemia appears to deplete circulating mBC’s but this
doesn’t effect boosting when patients drug cured at cut-off peak parasitemia.
Will be interesting to see boost effect of challenge on vaccinees on AMA-1 given lack of seroconversion and mBC’s in controls.
VAC39 aims: Replicate data for challenged volunteers (Group 1) Look for effect of challenge on mBC’s for AMA-1 (Group 2) Study effect of dual antigen vaccination on mBC formation (Group 3)
VAC39 : ASC ELISPOT
Ahmed 2008: Showed that for flu vaccination there was a rapid and robust influenza specific IgG+ antibody secreting plasma cell (ASC) response that peaked at approximately day 7 after boosting.
Questions:- What time after boosting can we see a peak? Limited to D63 with
current protocol.- What % of cells detected are antigen specific. - When during challenge can such cells be seen?- Is there a correlation with Antibody production?
VAC39 : ASC ELISPOT
5 7 8 9 150
50
100
150
200
250
300
Days since boost
ASC
's m
illion
PB
MC
13 14 15 16 17 230
10
20
30
40
50
60
Days since boost
ASC
's m
illion
PB
MC
Group Effect D63 (Day 7 only)
1 3 40
50
100
150
200
250
300
Group
ASC
/Mill
ion
PBM
C
Group Effect C-1 (all)
1 3 40
10
20
30
40
50
60
Group
ASC
's m
illion
PB
MC
VAC39 : ASC ELISPOT Answers?:
- Peak likely to be somewhere between day 5 and 8. - Harder to calculate total IgG secreting cells compared to mBC assay.- No ASC’s detected during challenge (C+7, C+11)- No ASC’s detected in protected volunteer at C+21- No significant correlation with Antibody production Day 63.
Ab vs ASC (Day 7 only)
0 2000 4000 60000
100
200
300
Ab Units
AS
C's
milli
on P
BM
C
VAC44 : UPCOMING TRIAL
VAC44 : EXPERIMENTAL PLAN ASC ELIspots:
Additional timepoints for detection (1, 4 & 7 days post boost) More regulation on visit windows so these time points more accurate
Can test whether successive boosts shorten time for peak response Can compare effect of boost regimes. Vectors/Protein/Adjuvant.
mBC ELIspots: Can compare effect of boost regimes. Vectors/Protein. Effect of CPG adjuvant (mBC stimulator)
FUTURE WORK B cell phenotyping
Atypical memory B cells (‘exhausted’): Are they induced in our vaccination regimes or during controlled challenge?
B cell clonality Clonal dissection of mBC repertoire (Pinna 2009).
Clonal burst size Antibody production on clonal level
B cell receptor (BCR) variable region genes will be cloned and sequenced to assess the antibody / BCR repertoire induced by different priming and boosting vaccinations
Does successive vaccinations/challenge give a more directed, higher affinity response?