The HIV/AIDS Pandemic:
Advances Made and Challenges Ahead
David D. Ho, M.D.
Aaron Diamond AIDS Research Center,
The Rockefeller University
Los Angeles, 1981: tip of the iceberg –
acquired immunodeficiency syndrome (AIDS)
Common characteristics: gay men with marked depletion of CD4 T cells
CDC: Groups at risk for AIDS
•
•
•
•
•
•
Homosexual men
Sex
Female sex partners
Injection drug users
Blood
Blood transfusion recipients
Hemophiliacs treated with factor VIII
Mother to child
Children born to infected women
1983: detection of the causative agent –
human immunodeficiency virus (HIV)
F. Barre-Sinoussi & L. Montagnier
The Global HIV Pandemic: 25 million dead and 35 million living
The epidemic rages on with 2.5 million new infections per year
Leading causes of death in Africa, 2000
25.0
22.6
20.0
% of
Total
15.0
10.1
9.1
10.0
6.7
5.5
4.3
5.0
3.6
3.1
2.9
2.3
0.0
HIV/AIDS
Malaria
Lower
respiratory
infections
Perinatal
conditions
Diarrheal
disease
Measles
TB
Ischemic
heart
disease
Cerebrovascular
disease
Maternal
conditions
HIV prevalence among pregnant women
in South Africa, 1990 to 2001
HIV prevalence (%)
30
25
20
15
10
5
0
‘90 ‘91 ‘92 ‘93 ‘94 ‘95 ‘96 ‘97 ‘98 ‘99 ‘00 ‘01
Orphans in Sub-Saharan Africa: >12 million
HIV-1: the causative agent of AIDS
HIV-1 genomic organization
HIV-1 life cycle and cellular factors that facilitate or restrict
virus replication
Tetherin
(Vpu)
CD4, CCR5, CXCR4
Tsg101, ALIX, ESCRT
TRIM5α
Why?
APOBEC3G
(Vif)
P-TEFb
LEDGF
HIV-1 life cycle and antiretroviral drugs
entry inhibitors
protease inhibitors
RT inhibitors
Integrase inhibitors
HIV-1 replication dynamics
Duration: 1 d
Cell t1/2: 0.7 d
Virus t1/2: 30 min
Virus production: 1010 to 1012
Darwinian evolution fast forward:
>107 mutants per day:
treat hard
Heightened (4-6-fold) turnover of CD4 T-cells: treat early
Sustained reduction of viral load by combination antiviral therapy
850,000
New AIDS cases
450,000
750,000
Death
People living
With AIDS
350,000
650,000
300,000
550,000
250,000
450,000
200,000
350,000
150,000
250,000
100,000
150,000
50,000
5,000
0
0
1986 1988 1990 1992 1994 1996 1998 2000 2002
Year
No. of persons living with AIDS
No. of cases and no. of deaths
Decline in AIDS mortality in the U.S. with the use
of combination antiretroviral therapy since 1995
Social injustice: U.S. vs. Africa
1. The delivery of drugs and services
to the developing world
2. The importance of prevention:
education and vaccine
Where are we in HIV vaccine development?
• No protective vaccine available
• No protective vaccine in the foreseeable future
Difficulties in developing an HIV vaccine
• During the natural course of HIV infection, the virus is
seldom (<1%) well controlled by the immune system
• Superinfection has been well documented
• HIV is extremely plastic and rapidly escapes from
immune recognition
• HIV is relatively resistant to antibody neutralization
Features of gp120 that preclude the efficient
neutralization of HIV by antibodies
Variable loops
Glycosylation
Entropic forces
Chen et al. Nature, 433: 834, 2005.
Notable HIV-neutralizing monoclonal antibodies
b12: CD4-binding site on gp120
2G12: carbohydrate on gp120
2F5, 4E10: membrane-proximal region of gp41
PG9: conformational epitope on gp120 (Science, 2009)
VRC01: CD4-binding site on gp120 (Science, 2010)
PRO140: anti-CCR5 (anti-co-receptor)
Ibalizumab: anti-CD4 (anti-receptor)
Pre-exposure prophylaxis (PrEP)
with HIV-neutralizing monoclonal antibodies
If we are unable to induce neutralizing antibodies in vivo, why
not produce them ex vivo for passive administration?
And turn a heretofore intractable basic discovery problem into
a more tangible engineering challenge.
21
PrEP with tenofovir +/- emtricitabine has gained traction
22
Concerns about daily oral PrEP
-Adherence difficulty of a daily drug regimen in a healthy person
-Potential long-term side effects of the drug(s)
-Tenofovir +/- emtricitabine form the cornerstone of frontline ARV therapy
Ideal PrEP agent
-Infrequently administered
-No side effects
-No overlap with current therapies
23
Ibalizumab: HIV-neutralizing mAb
directed to domain 2 of human CD4
(5A8, TNX-355)
Structure of ibalizumab Fab bound to 2-domain CD4 (2.2Å)
Freeman et al, Structure, in press
Contact sites between ibalizumab and CD4
Superimposition of known structures
of ibalizumab Fab, CD4, and gp120 core
100
10
80
1
60
40
0.1
20
0.01
0
20
40
60
Viruses
80
100
IC5 0 ( g/mL)
M aximum percent inhibition (M PI)
Breadth and potency of ibalizumab (MPI and IC50)
against a panel of 118 HIV clones
Ibalizumab is active and safe in vivo in humans
Gates Foundation support to explore its use for PrEP
Phase
1a
1b
2a
2b
N
30
22
82
113
Dose
10 mg/kg singledose, monotherapy
10 mg/kg weekly,
9 WK monotherapy
10 mg/kg, bi-weekly
+ OBR
800 mg Q2W vs.
2000 mg Q4W,
+OBR
Route
IV
IV
IV
IV
Subjects
HIV-positive adults
on stable therapy
HIV-positive adults
on failing regimens
HIV-positive adults
w/multi-drug
resistant HIV
HIV-positive adults
w/multi-drug
resistant HIV
CD4 D
(cells/uL)
+131
+112
+48
+49
VL D (log)
-1.33
-0.95
-1.00
-1.96
Serious
Events
No drug-related
SAEs
No drug-related
SAEs
No drug-related
SAEs
No drug-related
SAEs to date
Superimposition of known structures
of ibalizumab Fab, CD4, MHC II-TCR,
Ibalizumab as PrEP
Moving toward proof of principle with the current form:
Phase 1 study in healthy volunteers
Passive protection against SIV challenge in macaques
Making a better ibalizumab:
Improve route
Improve stability
Improve affinity
Improve PK
Improve breadth
Ultimate goal:
Decrease dose to <10 mg
Decrease frequency to 2 months
Decrease cost
31
Ibalizumab PK in monkeys: SC versus IV
32
Making a better ibalizumab
“Affinity maturation”
Change IgG4 to IgG1-LALA
Modify Fc to bind FcRn better
Sustained release formulation
Improving the stability of ibalizumab
34
“In vitro affinity maturation” to select higher affinity variants
35
Higher affinity variants of ibalizumab selected
from CDR1H mutants
36
Improving ibalizumab breadth by attacking a second site
m36
PG9, VRC01
A fusion construct attacking CD4 and gp120 simultaneously
iMab-m36
m36
Figure 2. iMabm36 is active against ibalizumab-sensitive
Fusion
with viruses
m36 broadens the breadth of ibalizumab
and resistant
iMab-S viruses
iMab-R viruses
39
iMab-m36 is active against ibalizumab-resistant viruses
iMab
[1.6g/ml]
iMab-m36
Viruses
[1.6g/ml]
G02
G02
m366
iMAb gel con
G07
G07
G08
100
G09
G09
75
G10
50
G08
100
G10
50
G11
G11
25
G12
G12
10 - 4
10 - 3
10 - 2
10 - 1
10 1
-50
10 - 4
10 - 3 G18
10 - 2
G20
10 - 1
-25
-50
10 1
G18
G20
G21
G21
G22
G22
G25
G25
Other fusion constructs attacking both CD4 and gp120
PG9-scFv or VRC01-scFv
PG9-iMab or VRC01-iMab
VRC01 fusion also increases the breadth of ibalizumab
iMab-VRC01
G02
G02
100
G08
100
G08
80
80
G09
G09
60
G11
G11
Neutralization (%)
Neutralization (%)
iMAb
gelIIIcon
iMab
60
40
20
0
-20
-40
0.0001
0.001
0.01
0.1
1
concentration (ug/mL)
10
40
G12
G12
G18
0
G18
G20
-20
G20
-40
G21
G21
20
0.0001
G22
G25
0.001
0.01
0.1
1
concentration (ug/mL)
10
G22
G25
Our ultimate goal
To create improved variants of ibalizumab and other
HIV-neutralizing monoclonal antibodies that are
potent, broad, and could be given in low doses SC
once every 2 months.
It has not escaped us that such improved biologics
could also be used, especially in combination, to
change the paradigm of HIV therapy from daily to
monthly regimens.