Download Seattle/Kenya Collaboration- MTCT

Seattle/Kenya Collaboration- MTCT
Julie Overbaugh
Collaborating Institutions:
University of Nairobi
Fred Hutchinson
Cancer Research
Center
University of
Washington
Designing an effective vaccine:
-> Identifying immune correlates
• A major focus of HIV vaccine efforts is trying to elicit HIVspecific NAbs.
• Most successful vaccines are thought to work through
antibody-mediated protection.
• Do NAbs protect against HIV?
Antibody
Target cell
(e.g. T Cell)
NAbs can block HIV (SHIV) infection in macaques
Virus levels
Controls
Given HIV NAb (HIVIG/2F5/2G12)
(Mascola et al.
Nat. Med. 2000)
• High levels of antibodies were used, much higher than in HIV infection.
• Challenge dose was high
• Antibody was matched to the virus (SHIV89.6PD), but would not have
‘matched’ most viruses in the ‘real world’
There is surprisingly little evidence that NAbs contribute
to protection from HIV in humans
Easy to
neutraliz
e
Hard to
neutraliz
e
Neutralization sensitivity
HIV is both genetically and antigenically diverse
•At any given time, most
people harbor a mixture of
neutralization sensitive and
neutralization resistant
viruses due to the dynamic
process of immune escape.
Studies of HIV-exposed cohorts: MTCT
MTCT
MTCT occurs in the presence of a HIV-specific NAb
response in the mother.
HIV-specific NAbs are present in the infant due to
passive transfer, especially near the time of delivery and
during breastfeeding
Nairobi breastfeeding clinical trial 1992-1998:
Ruth
Nduati
Joan
Kreiss
University of
Nairobi
University of
Washington
• Randomized clinical trial comparing infant HIV-1 infection
between breast-fed and formula-fed groups (N=425) to
determine the frequency and timing of breast milk HIV-1
transmission from a mother to her infant.
• In 1992: Risk was unclear and ARVs were not available.
Dorothy Mbori-Ngacha
Grace John-Stewart
Barb Richardson
Nairobi Breastfeeding Clinical Trial (1992-1998)
Breast feeding doubles the risk of infant infection
The majority of breastfeeding transmission occurs in the first 6 weeks postpartum
% infected
40%
6 months
14 wks
12 months
24 months
30% 6 wks
20%
10%
0%
Child age
HIV Infection rate-Breastfeeding
HIV Infection rate-Formula feeding
Nduati, et al. Effect of Breastfeeding and Formula Feeding on Transmission of HIV-1.
JAMA 2000:283:1167-1174
~ Sixty % of infants do not get infected despite
exposure in utero, intrapartum and through
breastfeeding
Do NAb contribute to protection?
100%
80%
uninfected
60%
40%
20%
0%
Do NAb play a role in protection of infants?
100%
Select 100 infants in the
breastfeeding arm who
were HIV negative at birth
80%
N=68
60%
40%
20%
N=32
0%
Examine the breadth of the NAb response
near delivery: mom and baby
Hypothesis: NAb contribute to protection
If a broad and potent NAb response
provides protection, then these infants are
less likely to be infected
To measure breadth and potency of the NAb
response, we use a panel of circulating HIV variants
• Variants from early in
infection representing
circulating viruses
Plasma RNA
Hard to
neutraliz
e
• A range of NAb sensitivities
Neutralization sensitivity
Easy to
neutraliz
e
This heterologous panel gives a measure or breadth and potency of the NAb
response
Neutralization is quantified by determining IC50 values
IC50s were determined for each virus/plasma combination
Virus 1 IC50 = 620
Virus 2 IC50 <100
1:100 1:200 1:400 1:800 1:1600 1:3200
Plasma dilution
IC50s are defined as the reciprocal dilution of plasma or MAb
required to inhibit infection by 50% (based on the dose response curve, log
function).
Higher IC50 means more potent neutralization
100 infant plasma at birth
IC50
Lynch et al. J. Virol. 2011
10
9
6
40
3
14
8
20
55
There was no difference in the breadth or potency of HIV NAb in
infants who became infected versus those who remained
uninfected
Lynch et al., JV 2011
Similar results were obtained when we examined the breadth of the
maternal Nab response in relation to infant infection. Majiwa, submitted.
J. Lynch
M. Majiwa
Do NAbs protect against the most neutralization
sensitive viruses?
100%
80%
60%
40%
20%
0%
}
Infected
Isolate maternal and infant envelope variants and
test neutralization sensitivity (N= 12 pairs, 96 envs)
Mom virus
(week 0)
Baby virus
(week 6)
NAbS
NAbR?
NAbR
Maternal
antibodies (wk 0)
Infant viruses variants are poorly neutralized
by maternal NAbs.
IC50 values versus autologous Ab
near the time of infection
Neutralization sensitivity
p=0.02
Viruses
neutralized by
maternal
plasma
1000
100
No detectable
neutralization
10
Transmitting
mothers
X. Wu
Infected
infants
Wu, JV, 2006
IC50 values versus autologous Ab
near the time of infection
Neutralization sensitivity
Infant viruses variants are poorly neutralized
by maternal NAbs.
Sensitive
variants are
not
transmitted
1000
Wu, JV 2006
100
10
Transmitting
mothers
Infected
infants
Nab elicited by HIV infection may have adequate potency to
block the most neutralization sensitive variants
Easy to
neutraliz
e
Ab needed to neutralize
1000
100
10
Hard to
neutraliz
e
Transmitting
mothers
Infected
infants
How does this fit with the first study, showing a lack of association
between breadth and potency and risk of infant infection?
Ab needed to neutralize
A broad and potent Nab
response per se does not
correlate with transmission
because the mothers harbor a
mix of neutralization sensitive
and resistant viruses and the
Nab are only able to get the ‘low
hanging fruit”
Mom’s
virus
NAbs can block HIV (SHIV) infection in macaques
Virus levels
Controls
Given HIV NAb (HIVIG/2F5/2G12)
(Mascola et al.
Nat. Med. 2000)
• Antibody was matched to the virus (SHIV89.6PD), which was a very
neutralization sensitive virus.
These data suggest together with animal model studies, suggest that Nab
perhaps can protect against the more neutralization sensitive viruses
> The Nab breadth/potency needed for protection remains unclear
Easy to
neutraliz
Current
e
SHIVs
Ab needed to neutralize
1000
100
10
Hard to
neutraliz
e
Transmitting
mothers
Infected
infants
Perhaps the protective antibodies are acting
locally, e.g. in breast milk to reduce
infectiousness?
Courtesy, Grace John-Stewart
Breastmilk NAbs are low
•
•
Mabuka, J et.al PloS Path 2012
Low level neutralizing activity is detected in BMS,
but much of this is non-specific.
NAbs are only rarely detected in purified antibody
fractions (IgG, IgA).
J. Mabuka
Transmitting mothers have higher levels of cell-associated
breast milk HIV than non transmitting mothers.
(Log10 BM cell DNA/106 cells)
Cell-associated BM levels
Non transmitting
Rousseau, JID 2004
Cell-free virus
RNA form
Transmitting
Adjusted
1.11
p =0.002
1.67
Infected
cell
Cell-associated virus
DNA form
C. Rousseau
Antibody neutralization
ADCC : Antibody-dependent cell cytotoxicity
Prevents new rounds of infection
Leads to elimination of infected cells
Effector cell
Fc Receptor
(e.g. NK cell)
granzymes,
perforin
Target cell
(e.g. T Cell)
Infected
cell
ADCC assay measures killing of HIV coated cells in the presence of Ab.
CFSE
PKH-26
+
HIV Envelope protein
Effector cell
(PBMCs
+
(subtype A)
BM Abs
Target cell
(CEM.NKr cells)
BMS 1:100
96
42.8
57.2
PKH-26
4.0
Uncoated
Target cells
Envelope Coated
Target cells
CFSE
*ADCC % Killing= %PKH+ cells, CFSE- cells - 2x background
Breast Milk ADCC is correlated with
risk of infant infection
p =0.039
Non transmitting
Mabuka, J et.al PloS Path 2012
Transmitting
J. Mabuka
Take home
• NAb can protect against highly sensitive variants in MTCT,
but the amount needed and the breadth to achieve a
protective Nab responses is unclear.
• Suggest the breadth and potency needed to protect against
diverse HIV variants circulating globally is likely higher than
elicited by chronic Hiv infection.
• Antibodies that act through ADCC
may contribute to
protection, especially in settings where cell-associated virus is
contributing to transmission.