Transmission of HIV-1
Where Epidemiology Meets Biology
Myron S. Cohen, MD
J. Herbert Bate Professor
Medicine, Microbiology and
Immunology and Epidemiology
The University of North Carolina at
Chapel Hill
Epidemic Spread of HIV
Ro = bDC
When Ro >1 epidemic is sustained
b = Efficiency of transmission (…a
biological event)
D = Duration of infectiousness
C = Number of people (partners)
exposed
Transmission of HIV:
Biological Requirements
Infectious
Susceptibility
Inoculum (concentration) Hereditary resistance
Phenotypic factors
Innate resistance
Acquired (immune)
resistance
…from Cohen and Galvin
Nature Microbiology Reviews 2:33-42, 2004
UNC HIV Transmission Group
• The Swanstrom Lab (and CFAR)
• The Fiscus Lab
• The Eron Clinical Research Group (ACTG)
• The Kashuba Pharmacology Group
• The Hobb’s STD Research Group (CRC)
• The Hoffman Malawi Research Team
…and most recently the Margolis Lab
NSI HIV (M-tropic)
SI HIV (T-tropic)
semen
exposure
at mucosal
epithelium
lamina propria
dendritic cell
CD4+
CCR5+
DC-SIGN+
CD4
DC-SIGN
migration
to lymphoid organs
CCR5
T cell
V3 isn't variable for subtype C.
Routes of Exposure and H.I.V.
INFECTION ROUTE
RISK OF INFECTION
Sexual Transmission
a.
Female-to-male transmission…………1 in 700 to 1 in 3,000
b. Male-to-female transmission……...…..1 in 200 to 1 in 2,000
c.
Male-to-male transmission………...….1 in 10 to 1 in 1,600
d. Fellatio??…………………………….. .0 (CDC) or 6% (SF)
Parenteral transmission
a.
Transfusion of infected blood………….95 in 100
b. Needle sharing………………………….1 in 150
c.
Needle stick…………………………..…1 in 200
d. Needle stick /AZT PEP…………………1 in 10,000
Transmission from mother to infant
a.
Without AZT treatment………...…….1 in 4
b. With AZT treatment………………….Less than 1 in 10
Royce, Sena, Cates and Cohen, NEJM 336:1072-1078, 1997
Coital frequency per Month
Coital Frequency per Month by
Age
11
10
10.02
8.98
9
9.11
8
7.44
7
6
5
4
15-24
25-29
Age
30-34
35-59
55%
HIV Prevalence by Age and Gender among
South African youth age 15-24 years
50%
45%
Males
Females
40%
35%
95% Confidence Interval
31.2%
28.9%
30%
26.3%
25.0%
25%
20%
13.8%
15%
14.4%
12.2%
9.4%
10%
11.0%
7.9%
5%2.3%
4.1%
3.6%
4.0%
6.0%
2.1%
4.1%
2.0%
5.8%
2.6%
0%
Age 15
Age 16
Age 17
Age 18
Pettifor A, et al. AIDS 2005, 19: 1525,
Pettifore et al. AIDS 2007 21:2007 862.
Age 19
Age 20
Age 21
Age 22
Age 23
Age 24
Comparison of age of coital debut among young women aged 18-24 years in South
Africa (SA) in 2003 and the United States (US) in 2002 (Pettifore et al., submitted)
Percentage of young women out of total population
25
SA girls
US girls
20
15
10
5
0
<=14
15
16
17
Age of coital debut
18
19
20+
Hypothesis
1) Estimated
transmission rates from earlier
studies are too low to explain the epidemic
2) HIV transmission is intermittently
AMPLIFIED by increased genital tract
shedding
3) AMPLIFIED transmission is critical to the
spread of HIV
Factors that Amplify HIV Transmission
INFECTIOUSNESS
• Stage of Disease … ACUTE INFECTION?
• Systemic co-infections
-Malaria, Tuberculosis, Helminthic infections (?)
• Genital Tract Changes
-Bacterial vaginosis, STDs!!!
• Circumcision
• Hormonal contraception
• Genetic factors (HLA B and C)
SUSCEPTIBILITY
• STDs!!!
• Bacterial vaginosis
• Inate immunity
• Circumcision
• Hormonal contraception
• Genetic factors (CCR5)
A. Fauci, 2006
Why is Acute HIV Important?
Pilcher and Cohen, J Clin Invest, 2005
• Vaccine Development (CHAVI)
• Prevention Opportunities (HPTN)
• Treatment
-for secondary prevention (HPTN)
-for viral load reduction (ACTG)
- to attack “persistance” (ACTG)
The acute retroviral syndrome
• 49-89% of patients “symptomatic” within 3 mos.
Fever
Fatigue
Pharyngitis
Weight loss
Myalgias
Headache
Schacker
93%
93
70
70
60
55
Kinloch-de Loes
87%
26
48
13
42
39
….BUT LESS THAN 1,000 subjects with acute/early
HIV have been reported out of 60,000,000 infected!!
Fiebig Classification of HIV-1 Infection
Eclipse
Phase
I
II III IV
V
VI
(Fiebig, AIDS 2003)
v RNA+
*
*
Western blot +/Western blot + (p31-)
Env SGA sequence analysis of plasma virus population
Transmitted virus
Western + (p31+)
Pooling Serum Specimens
to Detect HIV RNA
(Pilcher et al JAMA 288:216-221, 2002)
A
Individual
testing on 10
specimens
10 pools of 10
screened
20 Screening
Pools Tested
N=2000
HIV Testing in North Carolina (n=109,250)
(Pilcher, Cohen et al NEJM 352: 1873, 2005
+
EIA/WB
-
Long Term HIV Positive
-
LS-EIA
at UNC
Likely recent
“Detuned”
106
+
Unknown
duration
477
NAAT
-
+
F/U Testing
(Ab+NAAT)
HIV Negative
+
Acute HIV
23
Log HIV RNA cp/ml
Viral Loads at Initial Detection
10
9
8
7
6
5
4
3
2
1
0
median
209,183
29,347
Established HIV+
(n=66)
Acutely HIV +
(n=21)
ADDED BENEFIT OF ROUTINE AHI SCREEING
LOCATION
TESTING
POPULATION
N
ANTIBODY + HIV
PREVALENCE, %
INCREASED YIELD
WITH AHI, %
NORTH CAROLINA1
ALL PUBLIC
TESTING
109,250
0.5
3.6
SAN FRANCISCO2
STD CLINIC
3075
3.4
10.5
LOS ANGELES3
STD CLINIC
1712
0.8
7.1
SEATTLE4
MSM ONLY
6395
2.4
13.5
ATLANTA5
VCT AND
STD CLINIC
2202
3
6.1
JOHANNESBERG,
SOUTH AFRICA6
VCT AND
STD CLINIC
1906
35.2
1.8
LILONGWE,
MALAWI7
STD CLILIC
MALE
929
46.8
5
LILONGWE,
MALAWI8
STD CLINIC
ALL
1450
40.5
3.6
PORTO ALEGRE,
BRAZIL9
VCT CLINIC
933
19.1
2.8
1PILCHER, 2KLAUSNER, 3PATEL, 4STEKLER, 5PRIDDY, 6STEVENTS, 7PILCHER, 8FISCUS, 9
deSOUZA
Infection by testing site: NC
(Pilcher et al. NEJM, 2006)
250
16/23 Acute
Infections from
STD Clinics
200
150
Acute
Recent
Unknown
Duration
100
50
0
STD
N= 44656
HIV
Testing
11688
“Other” Prison,
Jail
7575
3053
Not shown:
Prenatal/OB
FP Drug
Treatment
General
Medical TB
Field visits
STDs Amplify HIV-1 Transmission
• Reducing physical/mechanical barriers
• Increasing HIV in genital lesions, semen
or both
• Evoking a more infectious HIV variant
• Increasing the number of receptor cells or the density
of receptors per cell
…and co-transmission of HIV and STDs leading to
clusters of subjects with acute HIV infection
Malawi Overview
• Population 10 million
• 90% rural
• Per Capita income $190
AIDS impact
• 900,000 people living with HIV
• 15% adult prevalence
• STD Clinic: 47% prevalence
The Tidziwe Center
Lilongwe Central Hospital
Lilongwe, Malawi
Dean Roper Visits Malawi
Acute HIV Infection and STDs
Pilcher et al. AIDS 18:1-8, 2004
• 1,361 men screened in STD and Dermatology
Clinics in Lilongwe Malawi
• 47% antibody + (chronic HIV Infection)
• 2.1% (28) with acute HIV (antibody -, RNA +)
Inguinal nodes: 11.4% acute HIV
Genital ulcer (HSV): 7.8% acute HIV
CSW exposure: 9.1% acute HIV
Acute HIV was detected ONLY in symptomatic STD
patients (!!) implying co-transmission or “staged”
transmission of an STI followed by HIV, or vice-versa.
Viral Loads in Malawi:
Chronic and Acute HIV Infection
10
8
6
4
2
0
HIV Ab+
HIV Ab(acute)
log10 HIV-1 RNA copies per mL
HIV-1 viremia (grey) and Semen (black)
Pilcher et al. AIDS August 2007
Grey=Blood and Black=semen (95% CI)
9
7
5
3
1
0
4
8
12 16 20 24 28
Weeks Since HIV infection
HIV-1 Viremia and Shedding
Pilcher et al. AIDS August 2007
log10 HIV-1 RNA copies per mL
9
7
5
3
1
wk4
wk8
wk16
Acute HIV Infection
CD4>350
CD4<350
Established HIV Infection
Sexual Transmission of HIV
HIV RNA in Semen
(Log10 copies/ml)
(Cohen and Pilcher, JID May 2005)
7
1/301/200
Risk of Transmission
Reflects Genital Viral Burden
5
3
0
1/1000 1/10,000
1/500 1/2000
1/1001/1000
Acute HIV and STD episodes
HIV RNA in Semen
(Log10 copies/ml)
(Cohen and Pilcher, JID, 2005
7
5
3
0
Prevention of HIV
1.
2.
3.
4.
5.
6.
7.
8.
9.
STD control, behavior change, condoms
Vaccines (Trials Ongoing)
Treatment of Bacterial Vaginosis (Planning)
Topical microbicides (Trials Ongoing)
The diaphragm (Trial Completed)
Male circumcision (Trials Ongoing)
HSV-2 treatment/prevention (Trials Ongoing)
Antiretroviral therapy (Trials Ongoing)
Societal (structural) interventions: needle
exchange, poverty reversal, etc…ALL WORK
Impact of MC on HIV : Evidence
from observational studies and RCTs
Reduction of risk
(95% CI)
15
Overall
58 ( 66, 48)
Weiss et al.
AIDS 2000, 14:2361-70
7
South Africa (RCT)
1
60 ( 76, 33)
Auvert et al.
PLoS Med 2005(11): e298.2006
Kenya (RCT)
1
59 ( 76, 30)
Bailey et al.
Lancet 2007; 369: 643–56
51 ( 82, 14)
Gray et al.
Lancet, 2007, 657–66
1
Uganda (RCT)
85
80
70
60
.50
1
Reduction of risk (0%)
Antiviral Therapy
Cohen et al. Annals Internal Med. 2007
Effect on Sexual Transmission of
HIV
?
ART to Prevent Sexual
Transmission of HIV
• Treatment of the infected person?
• Post-exposure prophylaxis (PEP)?
• Pre-Exposure Prophylaxis (PREP)?
Male Genital Tract Exposure
percent of blood plasma
Kashuba et al. and CROI 13 Abstract 569 (Vourvahis), 13th CROI
Abstracts 396 (Stekler), Abstract 618 (Katzenstein)
0
50%
100%
APV (20%) NVP (70%)
ENF (ND)
150%
ABC (150%)
200%
500%
ZDV (200%)
TDF (500%)
600%
3TC (600%)
IDV (100%)
d4T (2%)
EFV (3%)
SQV (3%)
RTV (3%)
LPV (5%)
NFV (5%)
NRTI
PI
NNRTI
FI
Female Genital Tract Exposure
(percent of blood plasma)
Dumond et al. Abstract 129, 13th CROI
0
ddI (100%)
SQV(ND)
EFV (0.6%)
200%
400%
600%
IDV (200%)
3TC (400%)
FTC (600%)
ZDV (200%)
TDF (400%)
ABC (150%)
d4T (4%)
RTV (20%)
DLV (20%)
ATV (30%)
LPV (30%)
ABC (40%)
APV (50%)
NVP (80%)
NRTI
PI
NNRTI
Patients (%) with
detectable HIV in semen
ART Suppresses HIV in Semen:
Biological Plausability
Controls (drug naive) n=55
Potent ART
n=114
100
p<0.0001
80
p=0.025
60
40
20
0
HIV-RNA
HIV-DNA
Vernazza, Cohen et al., AIDS, 2000
Injectable FTC/Tenofovir (n = 6)
% Uninfected animals
100
75
Oral truvada (n = 6); p = 0.0004 [HR = 7.8]
50
Injectable FTC (n = 6); p = 0.005 [HR = 3.9]
Oral TDF (n = 4); p = 0.095
25
Controls (n = 18)
0
0
2
4
6
8 10 12 14
Number of rectal exposures
Potential end-points of HIV-vaccine efficacy trials
no protection
“normal” infection
with variable levels
of viral load
UNAIDS–97100 1 August 1998
protection against HIV protection against disease (modification of
sterilizing immunity
the course of HIV infection in vaccine recipients)
no infection
initial infection
“controlled”
establishment of
chronic infection
with low viral load
This CHAVI web site is at http://www.chavi.org
Interdisciplinary CHAVI 001 Studies
B Cell Discovery
Antibody Studies
Mucosal Immunity
Innate Immunity
Cytokines
T Cell Discovery
Good vs. Bad T cells
Apoptosis
CHAVI 001
Acute HIV-1 Infection
Genetic Data
Computational Biology
Ro Analyses
Sexual Behavioral
Sexual Networks
Sexual Dynamics
Transmitted Sequences
Viral Biology
Structural Biology
The Consequences of Acute Infection
HIV-
Acute HIV
• Massive reduction in mucosal CD4+ T cells
even in acute infection
Douek and Schacker 2004
J Exp Med
Onset of Innate Immune
Responses During Acute HIV-1
Infection
Summary of changes in plasma cytokine levels in AHI
Plasma viraemia
Viral load or cytokine level
IL-18 TNFa
IFNa
IFNg
IL-15
IL-10
SAA elevated
-10
-5
0
5
10
Time relative to T100
15
20
(Kessler/Borrow/Norris)
Apoptosis of CCR5+, CD4+ T
Cells is a Hallmark of
Pathogenic Retrovirus
Infections
Tumor Necrosis Factor Related Apoptosis
Inducing Ligand (TRAIL) And Apoptosis In
Acute HIV-1 Infection
108
107
106
Viral
Load
TRAIL
105
104
Plasma Markers
Virus Concentration in Extracellular Fluid
or
Plasma (Copies/ml)
Window of Opportunity
103
102
101
Plasma
Apoptotic
Microparticles
0
10-1
10-2
10-3
10-4
10-5
0
Transmission
5
10
15
20
25
30
35
40
Time Post Exposure (days)
Smith, Crossman, Haynes, 2007
45
50
55
60
65
70
Onset of Antibody Responses
in Acute HIV-1 Infection
Viral Load Or Antibody Responses
Summary Of Antibody Responses
Immediately Following Acute HIV-1
Infection
10
8
Viral Load
gp41
gp140 Env
Non-Neutralizing
MPER
Cluster II
V3 CD4BS
6
Autologous
NAb
4
2
Transmission
2F5, 4E10,
2G12
0
-20
-10
0
10
20
30
40
50
Days Of Observation
60
70
80
CD8 T Cell Responses In Acute HIV-1
Infection: Too Little Too Late
108
107
Viral
Load
106
105
104
CTL Activity
Virus Concentration in Extracellular Fluid
or
Plasma (Copies/ml)
Window of Opportunity
103
102
101
0
10-1
Limit of detection of
assay for plasma
virus
Anti-HIV-1
10-2
10-3
CTL Activity
10-4
10-5
0
Transmission
5
10
15
20
25
30
35
40
Time Post Exposure (days)
R. Koup, D. Watkins, A. McMichael et al.
45
50
55
60
65
70
Acute HIV and the Virus
• A unique signature sequence using single
gene amplification?
• Glycosylation sites?
• Antibody neutralization resistance?
• Envelope length?
• Transmitted drug resistance?
The Transmitted Virus
HIV Env Characterization by SGA
cDNA
synthesis
1:2
1:4
1:8
1:16
1:32
1:64
1:128
1:256
serial
dilutions
1:64
phenotype
genotype
clone/
pseudotype
sequence
100%
100%
100%
92%
67%
33%
17%
0%
The Transmitted/Early VirusThe First 15 Days of Infection
• In 77 subjects (80%), one monophyletic env
lineage, suggesting productive infection by a
single viral infectious unit.
• In 19 subjects (20%), more than one
monophyletic env lineage was identified,
indicating productive infection by multiple viral
infectious units.
• In 13 (14%) multiply infected subjects,
recombinants were identified.
The Transmitted/Early VirusThe First 15 Days of Infection
• Sensitive to MPER antibodies 2F5, 4E10
• Sensitive to HIV-1 entry drugs, Fuzeon (T20) and
T1249
• Variably sensitive to sCD4, HIV Ig, Mab 1b12
• Insensitive to V3 antibodies
• R5 co-receptor usage
Phylogenetic analysis of SGA-derived env
from donor blood/semen vs. recipient plasma
X4tropic
Results:
1. 36 amplicons from donor blood—4.7% nucleotide diversity
11-X4 tropic, 25 R-tropic
2. 15 amplicons from donor semen (S)—1.5% nucleotide diversity
all X4-tropic
3. 29 amplicons from recipient blood—0.2% nucleotide diversity
all X4-tropic
R5tropic
Conclusions:
1.
2.
3.
4.
Single X4-tropic variant transmitted
Recipient env populations were extremely homogenous
Donor env populations are heterogenoeous
Semen compartment has significantly less diversity and
localized enrichment of variants vs. blood plasma
5. Transmission of X4-tropic variant that was detected in
donor blood and not semen, suggests cell-associated vs.
transmission of minor variant
Treatment of Acute HIV??
Walker et al., 2004, Kinloch-de Loes, JID 2006
• Many examples of lack of benefit measured by
REBOUND VIREMIA (Streck et al. JID, 2006)
• AIDRP and CASCADE: Some modest benefit?
• SPARTAC ongoing (Fidler, Weber et al.)
…But remember limited by
i) small n
ii) subject heterogeneity
iii) rebound as the definition of success/failure
Effects of ART on “The Latent Pool”
Margolis: AHI (CROI 2007, Triangles)
Chun: Early HIV (JID 2007, Squares)
UNC HIV Transmission Group
•
•
•
•
•
•
The Swanstrom Lab (and CFAR)
The Fiscus Lab
The Eron Clinical Research Group (ACTG)
The Kashuba Pharmacology Group
The Hobb’s STD Research Group (CRC)
The Hoffman Malawi Research Team