Seattle/Kenya Collaboration- MTCT Julie Overbaugh Collaborating - - PowerPoint PPT Presentation

Collaborating Institutions:

University of Nairobi

Seattle/Kenya Collaboration- MTCT

Julie Overbaugh

Fred Hutchinson Cancer Research Center University of Washington

Target cell

(e.g. T Cell) Antibody

Designing an effective vaccine:

• > Identifying immune correlates
• A major focus of HIV vaccine efforts is trying to elicit HIV-

specific NAbs.

• Most successful vaccines are thought to work through

antibody-mediated protection.

• Do NAbs protect against HIV?

(Mascola et al.

• Nat. Med. 2000)

NAbs can block HIV (SHIV) infection in macaques

Controls Given HIV NAb (HIVIG/2F5/2G12) Virus levels

• 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

HIV is both genetically and antigenically diverse

Neutralization sensitivity

Easy to neutraliz e Hard to neutraliz e

• 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 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

MTCT

Nairobi breastfeeding clinical trial 1992-1998:

Ruth Nduati

University of Nairobi

• 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.

Joan Kreiss

University of Washington

Dorothy Mbori-Ngacha Grace John-Stewart Barb Richardson

Child age

0% 10% 20% 30% 40%

6 wks 14 wks 6 months 12 months 24 months 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

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

~ Sixty % of infants do not get infected despite exposure in utero, intrapartum and through breastfeeding

100% 80% 60% 40% 20% 0%

Do NAb contribute to protection?

uninfected

Do NAb play a role in protection of infants?

100% 80% 60% 40% 20% 0%

N=32 N=68

Select 100 infants in the breastfeeding arm who were HIV negative at birth

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

Neutralization sensitivity This heterologous panel gives a measure or breadth and potency of the NAb response

Easy to neutraliz e Hard to neutraliz e

• A range of NAb sensitivities

Plasma RNA

• Variants from early in

infection representing circulating viruses

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

Virus 1 IC50 = 620 Virus 2 IC50 <100

Neutralization is quantified by determining IC50 values

IC50s were determined for each virus/plasma combination 1:100 1:200 1:400 1:800 1:1600 1:3200 Plasma dilution

20 55 148 403 1096

IC50

Lynch et al. J. Virol. 2011

100 infant plasma at birth

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

100% 80% 60% 40% 20% 0%

Do NAbs protect against the most neutralization sensitive viruses?

}

Infected

Baby virus

(week 6)

Mom virus

(week 0)

Isolate maternal and infant envelope variants and test neutralization sensitivity (N= 12 pairs, 96 envs)

NAbS NAbR NAbR?

Maternal antibodies (wk 0)

10 100 1000

Neutralization sensitivity

IC50 values versus autologous Ab near the time of infection

Transmitting mothers Infected infants

Infant viruses variants are poorly neutralized by maternal NAbs.

Viruses neutralized by maternal plasma No detectable neutralization p=0.02

Wu, JV, 2006

• X. Wu

10 100 1000

Neutralization sensitivity

IC50 values versus autologous Ab near the time of infection

Transmitting mothers Infected infants

Infant viruses variants are poorly neutralized by maternal NAbs.

Sensitive variants are not transmitted

Wu, JV 2006

Easy to neutraliz e Hard to neutraliz e

Nab elicited by HIV infection may have adequate potency to block the most neutralization sensitive variants

Ab needed to neutralize

10 100 1000

Transmitting mothers Infected infants

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”

Ab needed to neutralize

Mom’s virus

How does this fit with the first study, showing a lack of association between breadth and potency and risk of infant infection?

(Mascola et al.

• Nat. Med. 2000)

NAbs can block HIV (SHIV) infection in macaques

Controls Given HIV NAb (HIVIG/2F5/2G12) Virus levels

• Antibody was matched to the virus (SHIV89.6PD), which was a very

neutralization sensitive virus.

Easy to neutraliz e Hard to neutraliz e 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

Ab needed to neutralize

10 100 1000

Transmitting mothers Infected infants Current SHIVs

Perhaps the protective antibodies are acting locally, e.g. in breast milk to reduce infectiousness?

Courtesy, Grace John-Stewart

Breastmilk NAbs are low

• 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).

Mabuka, J et.al PloS Path 2012

• J. Mabuka

1.11 1.67

Rousseau, JID 2004

Transmitting mothers have higher levels of cell-associated breast milk HIV than non transmitting mothers.

Non transmitting Transmitting Cell-associated BM levels

(Log10 BM cell DNA/106 cells)

Adjusted p =0.002

• C. Rousseau

Cell-free virus RNA form Cell-associated virus DNA form

Infected cell

Fc Receptor

ADCC : Antibody-dependent cell cytotoxicity

Leads to elimination of infected cells

Antibody neutralization

Prevents new rounds of infection

Target cell

(e.g. T Cell)

Effector cell

(e.g. NK cell)

granzymes, perforin

Infected cell

ADCC assay measures killing of HIV coated cells in the presence of Ab.

HIV Envelope protein

(subtype A)

Target cell (CEM.NKr cells)

CFSE PKH-26

Effector cell (PBMCs

Envelope Coated Target cells Uncoated Target cells

CFSE PKH-26

BMS 1:100

*ADCC % Killing= %PKH+ cells, CFSE- cells - 2x background

42.8 57.2 4.0 96

+ +

BM Abs

Breast Milk ADCC is correlated with risk of infant infection

• J. Mabuka

Non transmitting Transmitting

p =0.039

Mabuka, J et.al PloS Path 2012

• 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.

Take home