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Efficacy Trial of a DNA/rAd5 HIV
The
n e w e ng l a n d j o u r na l
of
m e dic i n e
original article
Efficacy Trial of a DNA/rAd5 HIV-1
Preventive Vaccine
Scott M. Hammer, M.D., Magdalena E. Sobieszczyk, M.D., M.P.H., Holly Janes, Ph.D.,
Shelly T. Karuna, M.D., Mark J. Mulligan, M.D., Doug Grove, M.S.,
Beryl A. Koblin, Ph.D., Susan P. Buchbinder, M.D., Michael C. Keefer, M.D.,
Georgia D. Tomaras, Ph.D., Nicole Frahm, Ph.D., John Hural, Ph.D.,
Chuka Anude, M.D., Ph.D., Barney S. Graham, M.D., Ph.D.,
Mary E. Enama, M.A., P.A.-C., Elizabeth Adams, M.D., Edwin DeJesus, M.D.,
Richard M. Novak, M.D., Ian Frank, M.D., Carter Bentley, Ph.D., Shelly Ramirez, M.A.,
Rong Fu, M.S., Richard A. Koup, M.D., John R. Mascola, M.D.,
Gary J. Nabel, M.D., Ph.D., David C. Montefiori, Ph.D.,
James Kublin, M.D., M.P.H., M. Juliana McElrath, M.D., Ph.D.,
Lawrence Corey, M.D., and Peter B. Gilbert, Ph.D., for the HVTN 505 Study Team*
A BS T R AC T
Background
A safe and effective vaccine for the prevention of human immunodeficiency virus
type 1 (HIV-1) infection is a global priority. We tested the efficacy of a DNA prime–
recombinant adenovirus type 5 boost (DNA/rAd5) vaccine regimen in persons at
increased risk for HIV-1 infection in the United States.
Methods
At 21 sites, we randomly assigned 2504 men or transgender women who have sex
with men to receive the DNA/rAd5 vaccine (1253 participants) or placebo (1251 participants). We assessed HIV-1 acquisition from week 28 through month 24 (termed
week 28+ infection), viral-load set point (mean plasma HIV-1 RNA level 10 to 20 weeks
after diagnosis), and safety. The 6-plasmid DNA vaccine (expressing clade B Gag,
Pol, and Nef and Env proteins from clades A, B, and C) was administered at weeks
0, 4, and 8. The rAd5 vector boost (expressing clade B Gag-Pol fusion protein and
Env glycoproteins from clades A, B, and C) was administered at week 24.
The authors’ affiliations are listed in the
Appendix. Address reprint requests to Dr.
Hammer at the Division of Infectious Diseases, Columbia University Medical Center, 630 W. 168th St., New York, NY 10032,
or at [email protected]
*Additional members of the HIV Vaccine
Trials Network (HVTN) 505 study team
are listed in the Supplementary Appendix, available at NEJM.org.
This article was published on October 7,
2013, at NEJM.org.
N Engl J Med 2013.
DOI: 10.1056/NEJMoa1310566
Copyright © 2013 Massachusetts Medical Society
Results
In April 2013, the data and safety monitoring board recommended halting vaccinations for lack of efficacy. The primary analysis showed that week 28+ infection had
been diagnosed in 27 participants in the vaccine group and 21 in the placebo group
(vaccine efficacy, −25.0%; 95% confidence interval, −121.2 to 29.3; P = 0.44), with
mean viral-load set points of 4.46 and 4.47 HIV-1 RNA log10 copies per milliliter,
respectively. Analysis of all infections during the study period (41 in the vaccine
group and 31 in the placebo group) also showed lack of vaccine efficacy (P = 0.28).
The vaccine regimen had an acceptable side-effect profile.
Conclusions
The DNA/rAd5 vaccine regimen did not reduce either the rate of HIV-1 acquisition
or the viral-load set point in the population studied. (Funded by the National Institute of Allergy and Infectious Diseases; ClinicalTrials.gov number, NCT00865566.)
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1
The
n e w e ng l a n d j o u r na l
T
he epidemic infection caused by the
human immunodeficiency virus type 1
(HIV-1) is now in its fourth decade, with
an estimated 2.5 million new infections occurring annually worldwide.1 The number of newly
infected persons, although diminishing, outpaces the number of patients who initiate antiretroviral therapy. Despite a number of successful prevention interventions that have been reported,
including preexposure prophylaxis and treatment
as prevention,2-9 ultimate control of the HIV epidemic will most likely come only with the development of a safe and effective preventive vaccine.
This goal has proved to be elusive. Of the efficacy trials of HIV vaccines that have been reported thus far,10-15 only one15 has shown a
modest relative reduction of 31% in HIV infections in a general Thai population. The Dale and
Betty Bumpers Vaccine Research Center (VRC) of
the National Institute of Allergy and Infectious
Diseases was established with a charge to facilitate the development of an HIV vaccine. The lead
candidate was designed to elicit HIV-specific,
multifunctional responses in CD4+ and CD8+
T cells and antibodies to envelopes of the major
circulating strains. The resultant multigene,
multiclade DNA prime–recombinant adenovirus
type 5 vector boost (DNA/rAd5) vaccine underwent extensive preclinical and early-phase clinical testing and was found to be safe and immunogenic.16-24 The HIV Vaccine Trials Network
(HVTN) conducted a phase 2b efficacy trial of
this vaccine regimen in at-risk populations in
the United States.
Me thods
m e dic i n e
alanine aminotransferase level of no more than
2.5 times the upper limit of the normal range.
Participants were enrolled at 21 sites in the United States and provided written informed consent.
The original efficacy objective of the study
was to evaluate the regimen’s effect on viral load
in 1350 participants. During the course of the
study, the protocol was amended to raise the
sample size to 2500 to provide sufficient statistical power to assess efficacy in the prevention of
HIV-1 acquisition and to account for the use of
preexposure prophylaxis.7,15,16
Study End Points
The primary efficacy end points were HIV infections diagnosed after week 28 (day 196) following enrollment through the 24-month study visit
(termed week 28+ infection, which permitted
time for receipt of the full immunization series
and elicitation of an immune response) and the
HIV-1 viral-load set point, which was defined as
the mean plasma HIV-1 RNA level obtained 10 to
20 weeks after the diagnosis of HIV-1 infection
and before the initiation of antiretroviral therapy.
Primary safety end points were local and systemic reactogenicity and adverse events.
Secondary objectives included evaluation of
all infections from enrollment through the
24-month visit in participants who were HIVuninfected at enrollment (the modified intentionto-treat cohort) and evaluation of vaccine-induced
immune responses. Exploratory objectives included the evaluation of risk behaviors and the
use of antiretroviral drugs as prophylaxis before
and after exposure.
Study Oversight
Design and Study Population
This study, called HVTN 505, was a randomized,
double-blind, placebo-controlled trial of the VRC’s
DNA/rAd5 HIV-1 vaccine. To be eligible for the
study, men and transgender women between the
ages of 18 and 50 years were required to be fully
circumcised, to have a history of unprotected
anal intercourse with one or more male or maleto-female transgender partners or anal intercourse with two or more male or male-to-female
transgender partners in the 6 months before randomization, to have negative results on serum
HIV-1 and HIV-2 antibody testing, to have an adenovirus serotype 5 (Ad5) serum neutralizing
antibody titer of less than 1:18, and to have an
2
of
The study was approved by the institutional review board at the Fred Hutchinson Cancer Research Center, which served as a central insti­
tutional review board for 11 sites through
agreements with these institutions. At the remaining 10 sites, the study was approved by the
local institutional review board. All authors attest to the fidelity of the report to the protocol,
which is available with the full text of this article
at NEJM.org.
Vaccine Regimen and Administration
The DNA prime consisted of six closed circular
plasmids (in a 1:1:1:1:1:1 ratio) designed to individually express HIV-1 clade B Gag, Pol, and Nef
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Efficacy of an HIV-1 Preventive Vaccine
and Env proteins from clades A, B, and C.17,18
The DNA vaccine was administered in a 4-mg
dose intramuscularly in the deltoid by means of
Biojector at enrollment (week 0), week 4, and
week 8. The DNA placebo was phosphate-buffered saline. The rAd5 boost consisted of four
rAd5 vectors (in a 3:1:1:1 ratio) expressing an
HIV-1 clade B Gag-Pol fusion protein and Env
glycoproteins from clades A, B, and C.19 The dose
of 1010 particle units was administered intramuscularly in the deltoid by means of needle and
syringe at week 24. The rAd5 placebo was the
vector-free diluent.
Screening, Randomization, and Enrollment
During the 56-day screening period, we obtained
a medical history, performed a physical examination (including reporting of circumcision status),
performed HIV and Ad5 serologic analyses, and
measured serum alanine aminotransferase levels.
We provided education concerning HIV vaccines,
HIV testing, and risk reduction and reviewed alternatives to participation in this study. Eligible
participants underwent randomization, with enrollment defined as receipt of the first dose of
vaccine.
Study Evaluations
Study visits were scheduled at months 0, 1, 2,
2.5, 6, 7, and 9 and then every 3 months through
24 months. A medical-history update, symptomdirected physical examination, and risk-reduction counseling (including the provision of free
condoms), a social impact assessment, concomitant medications, HIV testing, and a questionnaire
on behavioral risk and the use of prophylactic
antiretroviral agents were performed at regular
intervals. Screening for sexually transmitted infections occurred every 6 months.
HIV-Infected Participants
Participants with confirmed HIV-1 infection were
asked to come to the study site for counseling,
education, and referral to care. Follow-up within
this study continued, and plasma HIV-1 RNA
levels that were measured at 10, 12, 14, 16, and
20 weeks after diagnosis were averaged to determine the mean viral-load set point.
Immunogenicity Assays
We used validated, described methods to assess
vaccine-induced HIV-1–specific CD4+ and CD8+
T cells,25 serum HIV-1–specific binding antibodies,26-28 and neutralizing antibodies29 4 weeks
after the administration of the rAd5 vaccine in a
randomly selected pilot sample of 40 vaccine
­recipients (with data missing for T-cell studies in
1 recipient) and 10 placebo recipients who remained HIV-uninfected at 24 months. (For details, see Sections 2.1, 2.2, and 2.3 in the Supplementary Appendix, available at NEJM.org.)
Statistical Analysis
Participants underwent block randomization according to site with the use of computer-generated
random numbers provided by the Statistical
Center for HIV/AIDS Research and Prevention
(SCHARP). We measured vaccine efficacy as
1 minus the hazard ratio for a diagnosis of HIV-1
infection after week 28 (day 196) following enrollment through the 24-month study visit and
reported as a percentage. Vaccine efficacy was
estimated with the use of a Cox proportionalhazards model with event time being the number
of days from day 196 until the diagnosis of infection. Data for participants in whom infection
was not diagnosed by the 24-month visit were
censored at the time of the last test showing HIV-1
negativity. We used the log-rank test to assess
whether vaccine efficacy differed from 0% and
Kaplan–Meier plots to display the cumulative incidences of HIV-1 infection over time. The vaccine efficacy for preventing infection in the modified intention-to-treat population was analyzed
similarly on the basis of the time from randomization.
We assessed the vaccine effect on the viralload set point in participants with week 28+ infection by estimating the mean set points in the
two study groups with a robust likelihood-based
method.30 This method accounts for missing
viral-load values by means of linear model-based
imputation (see Section 1.7 in the Supplementary Appendix).
The sample size of 2500 participants provided
a power of 80% to detect a vaccine efficacy of
50% and a power of 84% or more to detect a
mean difference of 1.0 log10 copies per milliliter
in the viral-load set point if the vaccine efficacy
were 50% or less.
We planned two interim analyses for efficacy
futility to occur once the 30th and 48th participant with week 28+ infection had the study visit
20 weeks after diagnosis. The prespecified guide-
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3
The
n e w e ng l a n d j o u r na l
line for efficacy futility was that both the 95%
confidence intervals for vaccine efficacy and the
difference in viral load were below their respective design alternatives of reductions of 50% and
1.0 log10 copies per milliliter, respectively. These
criteria were met at the time of the data freeze
(March 22, 2013) for the April 22, 2013, review
by the data and safety monitoring board (upper
confidence limits, 29% for vaccine efficacy and
0.95 for the difference in viral load). This milestone
triggered the recommendation to halt vaccinations.
Site personnel were immediately notified and
administered no further vaccinations; participants were informed and were made aware of
their study-group assignment. The data presented
are complete through April 22, 2013. All P values
are two-sided, and a P value of less than 0.05
was considered to indicate statistical significance.
R e sult s
Participant Accrual, Enrollment,
and Disposition
From June 11, 2009, to March 27, 2013, a total of
2504 participants were enrolled (Fig. 1). Of these
participants, 8 were retrospectively determined
to have been HIV-infected at enrollment. Thus, in
the modified intention-to-treat population, 2496
participants underwent randomization to receive
vaccine (1251 participants) or placebo (1245 participants). The yearly rate of loss to follow-up was
4.8% (95% confidence interval [CI], 3.8 to 6.1) in
the vaccine group and 6.6% (95% CI, 5.4 to 8.0)
in the placebo group (P = 0.05) (Fig. S1 in the
Supplementary Appendix).
Baseline Characteristics
In the modified intention-to-treat population,
98% of the participants were men, with a median
age of 29; 70% were white, 16% black, 8% Hispanic, and 1% Asian, with the remaining 5%
listed as “other.” Overall, baseline characteristics
were well balanced in the two study groups (Table S1 in the Supplementary Appendix).
The study population was at substantial risk
for HIV-1 infection, with 29% reporting three to
four male sexual partners and 26% reporting
five or more male partners in the 3 months before enrollment; 18% reported having sexual
activity with a known HIV-positive male partner.
Unprotected insertive anal sex was reported by
55% and unprotected receptive anal sex by 46%.
4
of
m e dic i n e
Primary Efficacy Analyses
The primary analysis cohort consisted of participants who were HIV-negative at 196 days after
enrollment and therefore at risk for week 28+
infection (967 in the vaccine group and 947 in
the placebo group). Of these participants, 95% of
vaccine recipients and 97% of placebo recipients
received all four vaccinations.
Week 28+ infection was diagnosed in 27 participants in the vaccine group and 21 in the
placebo group, yielding annual incidences of
2.8% (95% CI, 1.9 to 4.1) and 2.3% (95% CI, 1.4
to 3.5), respectively; the estimated vaccine efficacy was −25.0% (95% CI, −121.2 to 29.3;
P = 0.44) (Table 1 and Fig. 2A). The estimated
vaccine efficacy in the per-protocol cohort was
−45.3% (95% uncertainty interval, −145.9 to
88.5; P = 0.34) (Section 1.6.4 and Fig. S8 in the
Supplementary Appendix). From enrollment
through 28 weeks, a total of 24 infections occurred (14 in the vaccine group and 10 in the
placebo group), yielding a total of 72 HIV infections from enrollment through the 24-month
visit (41 in the vaccine group and 31 in the placebo group). In the modified intention-to-treat
population, the yearly HIV incidence was 2.7%
(95% CI, 1.9 to 3.6) in the vaccine group and
2.1% (95% CI, 1.4 to 2.9) in the placebo group
(P = 0.28) (Fig. 2B).
Of the 48 participants with week 28+ infection, 47 were included in the analysis of the viralload set point. One placebo recipient in whom
antiretroviral therapy was initiated before infection was diagnosed was excluded from this analysis. The estimated mean HIV-1 RNA viral-load set
points in the vaccine and placebo groups were
4.46 and 4.47 log10 copies per milliliter, respectively, for an overall difference (placebo minus
vaccine) of 0.002 copies per milliliter (95% CI,
−0.55 to 0.68; P = 0.99) (Table 1 and Fig. 3A). In
the modified intention-to-treat population, the
estimated mean viral-load set points in the vaccine and placebo groups were 4.51 and 4.54 log10
copies per milliliter, respectively (Fig. 3B, and
Section 1.8.1 and Table S8 in the Supplementary
Appendix).
Antiretroviral Prophylaxis
We assessed the use of antiretroviral agents for
prevention by means of case-report forms obtained during the study and by an audio computerassisted self-administered interview (ACASI)
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Efficacy of an HIV-1 Preventive Vaccine
8147 Patients were assessed for eligibility
5617 Were excluded
4543 Were ineligible
3026 Had Ad5-positive status
594 Did not meet HIV risk criteria
531 Had physical exam findings
250 Had HIV-positive test result
1074 Were eligible but declined to participate
2530 Underwent randomization
1264 Were assigned to receive vaccine
1266 Were assigned to receive placebo
26 Were not enrolled
8 Withdrew consent
9 Had venipuncture issue
8 Were newly ineligible
1 Had other reasons
1251 Were HIV-negative at enrollment
2 Were HIV-positive
967 Were HIV-negative at 28 wk
49 Dropped out before 28 wk
14 Were HIV-infected before 28 wk
221 Had not yet reached 28 wk at study
unblinding
Modified
Intention-toTreat Cohort
At-Risk for
Wk 28+ Infection
(Contributed
Data to Primary
Acquisition
Analysis)
1245 Were HIV-negative at enrollment
6 Were HIV-positive
947 Were HIV-negative at 28 wk
69 Dropped out before 28 wk
10 Were HIV-infected before 28 wk
219 Had not yet reached 28 wk at study
unblinding
905 Received all 4 vaccinations according
to protocol
52 Missed vaccinations
5 Received vaccine too early or late
5 Received incorrect product or dose
Per-Protocol
Cohort
904 Received all 4 vaccinations according
to protocol
32 Missed vaccinations
7 Received vaccine too early or late
4 Received incorrect product or dose
27 Were HIV-infected by 28 wk
Week 28+
Infection Cohort
21 Were HIV-infected by 28 wk
Contributed Data to
Primary Analysis of
Set-Point Viral Load
20 Were included in primary analysis of viralload set point
1 Initiated ART before HIV diagnosis
27 Were included in primary analysis
of viral-load set point
Figure 1. Enrollment and Outcomes.
Participants could have more than one reason for ineligibility; only the four most common reasons are listed. Participants who were not included in the per-protocol cohort for multiple reasons are listed in the category in which the
first protocol violation was reported.
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5
The
n e w e ng l a n d j o u r na l
of
m e dic i n e
Table 1. Rate of Week 28+ HIV-1 Infection, Vaccine Efficacy, Mean Viral-Load Set Point, and Difference in Viral Load
(Modified Intention-to-Treat Population).*
Variable
Vaccine (N = 1251)
No.
Evaluated
All participants
No. with
Infection
Rate
Mean
HIV-1 RNA
Viral-Load Set
Point
no./
person-yr
log10 copies/
ml
1539.3
0.018
4.46
No. of
PersonYears
1251
27
Nonwhite or Hispanic
389
12
480.3
0.025
4.06
Non-Hispanic white
862
15
1059.1
0.014
4.90
Low
454
5
566.8
0.009
4.96
Low to medium
337
5
397.6
0.013
4.58
Medium to high
208
4
267.9
0.015
2.87
High
252
13
307.1
0.042
4.41
≤25.34
619
15
750.1
0.02
4.59
>25.34
631
12
787.2
0.015
4.20
Race or ethnic group§
Risk score¶
Body-mass index‖
*Results are based on all data entered into the database before the date of unblinding (April 23, 2013), with the exception of viral-load data, which are included if they were received by July 22, 2013.
†Vaccine efficacy was measured as 1 minus the hazard ratio for a diagnosis of HIV-1 infection after week 28 (day 196)
following enrollment through the 24-month study visit; this value is reported as a percentage. Vaccine efficacy was estimated with the use of a Cox proportional-hazards model.
‡The difference in viral load, which was measured as the mean viral-load set point in the placebo group minus that in
the vaccine group, was estimated with the use of the method of Little and An.30
§Race or ethnic group was self-reported.
¶The risk score is a function of two risk-behavior variables collected at enrollment by means of a questionnaire: an indicator that the number of male sexual partners was greater than three and an indicator of unprotected receptive anal
sexual activity during the past 3 months.
‖The body-mass index is the weight in kilograms divided by the square of the height in meters.
questionnaire, which was implemented after the
release of the results of the Preexposure Prophylaxis Initiative (iPrEx) study.7 Preexposure prophylaxis was reported by 13 participants (1.0%)
in each study group, and postexposure prophylaxis was reported by 41 participants (3.3%) in
each group.
Behavioral Risk
An analysis of baseline data with respect to behavioral risk obtained from ACASI questionnaires identified two variables that predicted the
risk of HIV-1 infection: a history of more than
three male sexual partners or unprotected receptive anal sex in the 3 months before enrollment.
The behavioral risk score, a weighted average of
these two variables (Section 1.3 in the Supplementary Appendix), was highly predictive of the
6
risk of HIV-1 infection, with a hazard ratio of
6.01 (95% CI, 3.15 to 11.48) for participants with
both risk factors, as compared with those with
neither risk factor (P<0.001).
The frequency of these two risk behaviors
remained at or below baseline levels throughout
the study, with no significant between-group differences (Fig. S2 through S5 in the Supplementary Appendix).
Safety
The vaccine regimen had an acceptable side-­
effect profile. Vaccine recipients had a significantly higher rate of reactogenicity than did placebo recipients, but most reactions were mild or
moderate (Section 1.4 and Table S2 in the Supplementary Appendix). Nonfatal adverse events were
balanced in the two study groups, with only one
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Efficacy of an HIV-1 Preventive Vaccine
Placebo (N = 1245)
No.
No. with
Evaluated Infection
1245
21
No. of
PersonYears
1508.5
Vaccine Efficacy†
Difference in Viral Load‡
Rate
Mean
HIV-1 RNA
Viral-Load Set
Point
no./
person-yr
log10 copies/
ml
% (95% CI)
value (95% CI)
0.014
4.47
−25.0 (−121.2 to 29.3)
0.00 (−0.55 to 0.68)
369
7
472.6
0.015
4.52
−70.9 (−334.1 to 32.7)
0.45 (−0.21 to 1.42)
876
14
1035.9
0.014
4.43
−3.0 (−113.4 to 50.3)
−0.47 (−1.10 to 0.62)
465
3
574.3
0.005
4.46
−69.2 (−607.9 to 59.6)
−0.50 (−1.31 to 0.14)
313
6
371.2
0.016
4.29
23.0 (−152.4 to 76.5)
−0.29 (−1.30 to 0.92)
209
6
254.4
0.024
4.68
37.7 (−120.6 to 82.4)
1.80 (−0.67 to 3.04)
258
6
308.6
0.019
4.59
−114.4 (−464.0 to 18.5)
0.18 (−1.18 to 1.39)
629
16
741.0
0.022
4.37
615
5
765.6
0.007
5.62
event (a severe viral syndrome) judged to be related to a study product. Six participants (all in
the placebo group) died during the study (Section
1.4.2 in the Supplementary Appendix).
Immunogenicity
Vaccine-induced, HIV-specific response rates in
CD4+ T cells (61.5%) and CD8+ T cells (64.1%)
were detected ex vivo by intracellular cytokine
staining (Fig. S14 in the Supplementary Appendix). The median frequency of expression of
interferon-γ, interleukin-2, or both by CD4+ T cells
was 0.1%; these cells predominantly targeted
Gag (48.7%) and Env (38.5%) antigens. By contrast, the median frequency of total cytokineexpressing CD8+ T cells was 0.2%, with predominant recognition of Env (56.4%).
The vaccine induced a rate of IgG response of
100% to the vaccine strain envelopes (VRC
clades A, B, and C), to the group M consensus
envelope (ConS glycoprotein [gp]140), and to
gp41 but a rate of only 48% to the gp120 antigen
(Fig. S15 and S16 in the Supplementary Appendix). IgG response rates to V1-V2 Env were low
as measured either to the gp70 V1-V2 (case A2)
antigen from the correlates analysis in the
RV144 trial27 (18%) or to the matched VRC clade
8.7 (−84.7 to 54.9)
−133.2 (−561.9 to 17.9)
−0.22 (−0.98 to 0.58)
1.42 (0.46 to 2.58)
A gp70 V1-V2 (VRC clade A) antigen (20%). Serum
Env IgA response rates and magnitudes were
lower than those for IgG. Serum IgA responses
to A1.Con gp140 (a clade A envelope protein), a
positive correlate of infection risk in the RV144
trial,27,31 were 43% (Fig. S15 in the Supplementary Appendix). Response rates for neutralizing
antibodies were low (2.5 to 27.5%) and when
present were only against tier 1 isolates, which
can be more easily neutralized in vitro32 (Fig. S17
in the Supplementary Appendix).
Discussion
Thirty years after the discovery of HIV, a safe and
effective vaccine is still not in sight. Of the six
efficacy trials that have been conducted to date
(including this study), only one, the RV144 Thai
trial of ALVAC/gp120, showed protective efficacy.15 Two trials of recombinant bivalent gp120
showed no benefit, and the Step study (HVTN
502) of another Ad5 vector vaccine expressing the
internal proteins Gag, Pol, and Nef showed not
only futility but an increased early risk of HIV
acquisition in men who were uncircumcised or
Ad5-seropositive at baseline.33 In the Phambili
study of the same vaccine, investigators in South
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7
The
n e w e ng l a n d j o u r na l
A Week 28+ Analysis
Placebo (N=1245) yearly rate, 0.023 (95% CI, 0.014–0.035)
Vaccine (N=1251) yearly rate, 0.028 (95% CI, 0.019–0.041)
Probability of Week 28+ Infection
1.0
0.06
0.8
0.6
0.04
0.4
0.02
0.2
0.00
0.0
0
P=0.44 by log-rank test
0
3
3
6
6
9
9
12
12
15
15
18
18
21
24
21
24
Months since Enrollment
No. at Risk
Placebo
Vaccine
972
990
824
848
718
741
619
640
538
553
438
437
132
159
0
0
6
5
12
8
15
12
18
17
19
22
21
27
Cumulative No.
of Infections
Placebo
Vaccine
B Modified Intention-to-Treat Analysis
Placebo (N=1245) yearly rate, 0.021 (95% CI, 0.014–0.029)
Vaccine (N=1251) yearly rate, 0.027 (95% CI, 0.019–0.036)
Probability of HIV-1 Infection
1.0
0.06
0.8
0.6
0.04
0.4
0.02
0.2
0.00
0.0
0
3
P=0.28 by log-rank test
0
3
6
6
9
9
12
12
15
15
18
18
21
24
21
24
Months since Enrollment
No. at Risk
Placebo
Vaccine
1245
1251
1054
1065
972
990
824
848
718
741
619
640
538
553
438
437
132
159
0
0
6
5
10
12
16
19
22
22
25
26
28
31
29
36
31
41
Cumulative No.
of Infections
Placebo
Vaccine
Figure 2. Cumulative Incidence of HIV-1 Infection in Two Population Subgroups.
Shown are the cumulative incidences of HIV-1 infection diagnosed from
week 28 through month 24 (week 28+ infection) (Panel A) and HIV-1 infection in the modified intention-to-treat population (Panel B). Insets show
the same data on an expanded y axis.
8
of
m e dic i n e
Africa discontinued the trial before full enrollment on the basis of the results of the Step study
but recently reported a possible increase in HIV
infections among vaccine recipients. However,
because of early unblinding, this assessment is
potentially confounded.34
In our study, we enrolled 2504 participants at
21 sites in the United States. On April 22, 2013,
the data and safety monitoring board recommended stopping vaccinations. At that time,
approximately two thirds of the total predicted
person-years of follow-up between enrollment
and the 24-month study visit had been completed. The study definitively showed that the DNA/
rAd5 vaccine regimen did not reduce either HIV-1
acquisition or the viral-load set point, as compared with placebo. Although the greater loss to
follow-up in the placebo group had borderline
significance, the result with respect to vaccine
efficacy was not sensitive to this differential
(Section 1.6.5 in the Supplementary Appendix).
The use of antiretroviral prophylaxis was infrequent and did not appear to affect the results.
The between-group differences in the number
of HIV-1 infections in the week 28+ primary
analysis (27 in the vaccine group and 21 in the
placebo group) and the total number of infections in the modified intention-to-treat analysis
(41 in the vaccine group and 31 in the placebo
group) were not significant. There were no significant between-group differences in behavioral
risk. The rAd5 vector that we used in this study
differed substantially from that used in the Step
study, since it had deletions in more of the adenovirus genome and included HIV-1 gene inserts
coding for Env. Follow-up of the study participants, with the accompanying caveats of potential bias, continues to further assess HIV-1 acquisition in the study cohort after unblinding. In
the first planned updated analysis on September
3, 2013, the numbers of week 28+ infections were
29 in the vaccine group and 26 in the placebo
group (estimated hazard ratio, 1.09; 95% CI,
0.64 to 1.84; P = 0.76). These data show that the
late separation of the estimated cumulative HIV-1
incidence curves after month 21 (Fig. 2, and Fig.
S18 and S19 in the Supplementary Appendix)
was not sustained and emphasize the importance of participant retention in longer-term
follow-up. They also strongly support the conclusion that there is no evidence of an increase
in the risk of HIV-1 acquisition in the vaccine
group in this study.
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Efficacy of an HIV-1 Preventive Vaccine
A Week 28+ Analysis
B Modified Intention-to-Treat Analysis
7
Viral-Load Set Point (log10 copies/ml)
Viral-Load Set Point (log10 copies/ml)
7
6
5
4
3
2
1
LLOQ
Estimated mean
Placebo
Vaccine
6
5
4
3
2
1
LLOQ
Estimated mean
Placebo
Vaccine
Figure 3. Viral-Load Set Points.
Shown are viral-load set points (the mean plasma HIV-1 RNA level 10 to 20 weeks after diagnosis) among participants with HIV-1 infection diagnosed from week 28 through month 24 (week 28+ infection) (Panel A) and HIV-1 infection in the modified intention-to-treat population (Panel B). The size of each data point reflects the number of
measurements used to compute the mean viral-load set point, which is indicated by the horizontal blue line, with a
median of 4 measurements (range, 1 to 5). The dashed line indicates the lower limit of quantification (LLOQ) of the
viral-load assay (40 copies per milliliter). The I bars indicate 95% confidence intervals.
The DNA/rAd5 vaccine regimen induced both
cellular and humoral responses, but these results were not associated with protection in this
trial. The CD4+ and CD8+ T-cell response profiles in the random sample of HIV-uninfected
participants who were evaluated in this study
were similar to those seen among U.S. participants in the HVTN 204 study (a phase 2a study
of the same vaccine regimen), who were Ad5seronegative, thus confirming the immunogenicity profile of this regimen.24 IgG-binding–antibody responses to gp140 were strong, but
responses to the V1-V2 loop of gp120 were substantially lower than those seen in the RV144
trial,27 in which V1-V2 IgG was a correlate of a
reduced risk of HIV acquisition. IgA-binding
antibodies to gp140 were higher than those seen
in the RV144 trial, in which this measurement
was shown to be a correlate of an increased risk
of HIV acquisition.27 Detailed analyses of the
quality and breadth of vaccine-induced immune
responses in this study and other efficacy trials
will be required to further define these and
other correlates of risk. Our study gave a definitive, albeit disappointing, result but should provide useful information as newer vaccine regimens and approaches are developed.35
The views expressed in this article are those of the authors
and do not necessarily represent the official views of the National Institutes of Health (NIH).
Supported by grants from the National Institute of Allergy and
Infectious Diseases of the NIH (UM1AI68614, UM1AI068618,
UM1AI68635, UM1AI069496, UM1AI69452, UM1AI069412,
UM1AI069470, UM1AI069481, UM1AI069439, UM1AI069534,
UM1AI069511, UM1AI069554, UM1AI069418, UM1Al069532,
UM1AI069424, UM1AI069501, and UM1AI036219 and contract
HHSN272200800014C), Columbia University’s Clinical and Translational Science Award from the National Center for Advancing
Translational Sciences, NIH (UL1TR000040), the NIH Intramural
Research Program, Emory Center for AIDS Research (P30AI50409),
the Harvard Center for AIDS Research (P30AI06354), the Baylor–
University of Texas Houston Center for AIDS Research
(UM1AI036211), the Colorado Clinical Translational Science Institute (TR000154), and the National Center for Advancing Translational Science, NIH (UL1TR000451).
Disclosure forms provided by the authors are available with
the full text of this article at NEJM.org.
Appendix
The authors’ affiliations are as follows: the Department of Medicine, Columbia University (S.M.H., M.E.S.), and the New York Blood
Center (B.A.K.) — both in New York; Statistical Center for HIV/AIDS Research and Prevention (H.J., D.G., S.R., P.B.G.), Vaccine and
Infectious Disease Division (S.T.K., N.F., J.H., C.B., J.K., M.J. McElrath, L.C.), and Program in Biostatistics and Biomathematics (R.F.),
Fred Hutchinson Cancer Research Center, Seattle; the Department of Medicine, Emory University, Atlanta (M.J. Mulligan); San Francisco Department of Public Health, San Francisco (S.P.B.); University of Rochester School of Medicine, Rochester, NY (M.C.K.); Duke
University, Durham, NC (G.D.T., D.C.M.); the Division of AIDS (DAIDS) (E.A.), Henry M. Jackson Foundation (HJF-DAIDS) (C.A.), and
Vaccine Research Center (B.S.G., M.E.E., R.A.K., J.R.M.), National Institute of Allergy and Infectious Diseases, Bethesda, MD; Orlando
Immunology Center, Orlando, FL (E.D.); University of Illinois at Chicago, Chicago (R.M.N.); the Department of Medicine, University of
Pennsylvania, Philadelphia (I.F.); and Sanofi, Cambridge, MA (G.J.N.).
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9
Efficacy of an HIV-1 Preventive Vaccine
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