Antigen specificities and proviral integration sites differ in HIV-infected cells by timing of antiretroviral treatment initiation.

Despite effective antiretroviral therapy (ART), persons living with HIV harbor reservoirs of persistently infected CD4+ cells, which constitute a barrier to cure. Initiation of ART during acute infection reduces the size of the HIV reservoir, and we hypothesized that in addition, it would favor integration of proviruses in HIV-specific CD4+ T cells, while initiation of ART during chronic HIV infection would favor relatively more proviruses in herpesvirus-specific cells. We further hypothesized that proviruses in acute ART initiators would be integrated into antiviral genes, whereas integration sites (ISs) in chronic ART initiators would favor genes associated with cell proliferation and exhaustion. We found that the HIV DNA distribution across HIV-specific versus herpesvirus-specific CD4+ T cells was as hypothesized. HIV ISs in acute ART initiators were significantly enriched in gene sets controlling lipid metabolism and HIF-1α-mediated hypoxia, both metabolic pathways active in early HIV infection. Persistence of these infected cells during prolonged ART suggests a survival advantage. ISs in chronic ART initiators were enriched in a gene set controlling EZH2 histone methylation, and methylation has been associated with diminished long terminal repeat transcription. These differences that we found in antigen specificities and IS distributions within HIV-infected cells might be leveraged in designing cure strategies tailored to the timing of ART initiation.

Optimized SMRT-UMI protocol produces highly accurate sequence datasets from diverse populations-Application to HIV-1 quasispecies.

Pathogen diversity resulting in quasispecies can enable persistence and adaptation to host defenses and therapies. However, accurate quasispecies characterization can be impeded by errors introduced during sample handling and sequencing, which can require extensive optimizations to overcome. We present complete laboratory and bioinformatics workflows to overcome many of these hurdles. The Pacific Biosciences single molecule real-time platform was used to sequence polymerase-chain reaction (PCR) amplicons derived from cDNA templates tagged with unique molecular identifiers (SMRT-UMI). Optimized laboratory protocols were developed through extensive testing of different sample preparation conditions to minimize between-template recombination during PCR. The use of UMI allowed accurate template quantitation as well as removal of point mutations introduced during PCR and sequencing to produce a highly accurate consensus sequence from each template. Production of highly accurate sequences from the large datasets produced from SMRT-UMI sequencing is facilitated by a novel bioinformatic pipeline, Probabilistic Offspring Resolver for Primer IDs (PORPIDpipeline). PORPIDpipeline automatically filters and parses circular consensus reads by sample, identifies and discards reads with UMIs likely created from PCR and sequencing errors, generates consensus sequences, checks for contamination within the dataset, and removes any sequence with evidence of PCR recombination, heteroduplex formation, or early cycle PCR errors. The optimized SMRT-UMI sequencing and PORPIDpipeline methods presented here represent a highly adaptable and established starting point for accurate sequencing of diverse pathogens. These methods are illustrated through characterization of human immunodeficiency virus quasispecies in a virus transmitter-recipient pair of individuals.

Prevention efficacy of the broadly neutralizing antibody VRC01 depends on HIV-1 envelope sequence features.

In the Antibody Mediated Prevention (AMP) trials (HVTN 704/HPTN 085 and HVTN 703/HPTN 081), prevention efficacy (PE) of the monoclonal broadly neutralizing antibody (bnAb) VRC01 (vs. placebo) against HIV-1 acquisition diagnosis varied according to the HIV-1 Envelope (Env) neutralization sensitivity to VRC01, as measured by 80% inhibitory concentration (IC80). Here, we performed a genotypic sieve analysis, a complementary approach to gaining insight into correlates of protection that assesses how PE varies with HIV-1 sequence features. We analyzed HIV-1 Env amino acid (AA) sequences from the earliest available HIV-1 RNA-positive plasma samples from AMP participants diagnosed with HIV-1 and identified Env sequence features that associated with PE. The strongest Env AA sequence correlate in both trials was VRC01 epitope distance that quantifies the divergence of the VRC01 epitope in an acquired HIV-1 isolate from the VRC01 epitope of reference HIV-1 strains that were most sensitive to VRC01-mediated neutralization. In HVTN 704/HPTN 085, the Env sequence-based predicted probability that VRC01 IC80 against the acquired isolate exceeded 1 µg/mL also significantly associated with PE. In HVTN 703/HPTN 081, a physicochemical-weighted Hamming distance across 50 VRC01 binding-associated Env AA positions of the acquired isolate from the most VRC01-sensitive HIV-1 strain significantly associated with PE. These results suggest that incorporating mutation scoring by BLOSUM62 and weighting by the strength of interactions at AA positions in the epitope:VRC01 interface can optimize performance of an Env sequence-based biomarker of VRC01 prevention efficacy. Future work could determine whether these results extend to other bnAbs and bnAb combinations.

Optimized SMRT-UMI protocol produces highly accurate sequence datasets from diverse populations - application to HIV-1 quasispecies.

Pathogen diversity resulting in quasispecies can enable persistence and adaptation to host defenses and therapies. However, accurate quasispecies characterization can be impeded by errors introduced during sample handling and sequencing which can require extensive optimizations to overcome. We present complete laboratory and bioinformatics workflows to overcome many of these hurdles. The Pacific Biosciences single molecule real-time platform was used to sequence PCR amplicons derived from cDNA templates tagged with universal molecular identifiers (SMRT-UMI). Optimized laboratory protocols were developed through extensive testing of different sample preparation conditions to minimize between-template recombination during PCR and the use of UMI allowed accurate template quantitation as well as removal of point mutations introduced during PCR and sequencing to produce a highly accurate consensus sequence from each template. Handling of the large datasets produced from SMRT-UMI sequencing was facilitated by a novel bioinformatic pipeline, Probabilistic Offspring Resolver for Primer IDs (PORPIDpipeline), that automatically filters and parses reads by sample, identifies and discards reads with UMIs likely created from PCR and sequencing errors, generates consensus sequences, checks for contamination within the dataset, and removes any sequence with evidence of PCR recombination or early cycle PCR errors, resulting in highly accurate sequence datasets. The optimized SMRT-UMI sequencing method presented here represents a highly adaptable and established starting point for accurate sequencing of diverse pathogens. These methods are illustrated through characterization of human immunodeficiency virus (HIV) quasispecies.

RV144 vaccine imprinting constrained HIV-1 evolution following breakthrough infection.

The scale of the HIV-1 epidemic underscores the need for a vaccine. The multitude of circulating HIV-1 strains together with HIV-1's high evolvability hints that HIV-1 could adapt to a future vaccine. Here, we wanted to investigate the effect of vaccination on the evolution of the virus post-breakthrough infection. We analyzed 2,635 HIV-1 env sequences sampled up to a year post-diagnosis from 110 vaccine and placebo participants who became infected in the RV144 vaccine efficacy trial. We showed that the Env signature sites that were previously identified to distinguish vaccine and placebo participants were maintained over time. In addition, fewer sites were under diversifying selection in the vaccine group than in the placebo group. These results indicate that HIV-1 would possibly adapt to a vaccine upon its roll-out.

In-depth single-cell analysis of translation-competent HIV-1 reservoirs identifies cellular sources of plasma viremia.

Clonal expansion of HIV-infected cells contributes to the long-term persistence of the HIV reservoir in ART-suppressed individuals. However, the contribution from cell clones that harbor inducible proviruses to plasma viremia is poorly understood. Here, we describe a single-cell approach to simultaneously sequence the TCR, integration sites and proviral genomes from translation-competent reservoir cells, called STIP-Seq. By applying this approach to blood samples from eight participants, we show that the translation-competent reservoir mainly consists of proviruses with short deletions at the 5'-end of the genome, often involving the major splice donor site. TCR and integration site sequencing reveal that cell clones with predicted pathogen-specificity can harbor inducible proviruses integrated into cancer-related genes. Furthermore, we find several matches between proviruses retrieved with STIP-Seq and plasma viruses obtained during ART and upon treatment interruption, suggesting that STIP-Seq can capture clones that are responsible for low-level viremia or viral rebound.

Intra-host changes in Kaposi sarcoma-associated herpesvirus genomes in Ugandan adults with Kaposi sarcoma.

Intra-host tumor virus variants may influence the pathogenesis and treatment responses of some virally-associated cancers. However, the intra-host variability of Kaposi sarcoma-associated herpesvirus (KSHV), the etiologic agent of Kaposi sarcoma (KS), has to date been explored with sequencing technologies that possibly introduce more errors than that which occurs in the viral population, and these studies have only studied variable regions. Here, full-length KSHV genomes in tumors and/or oral swabs from 9 Ugandan adults with HIV-associated KS were characterized. Furthermore, we used deep, short-read sequencing using duplex unique molecular identifiers (dUMI)-random double-stranded oligonucleotides that barcode individual DNA molecules before library amplification. This allowed suppression of PCR and sequencing errors to ~10-9/base as well as afforded accurate determination of KSHV genome numbers sequenced in each sample. KSHV genomes were assembled de novo, and rearrangements observed were confirmed by PCR and Sanger sequencing. 131-kb KSHV genome sequences, excluding major repeat regions, were successfully obtained from 23 clinical specimens, averaging 2.3x104 reads/base. Strikingly, KSHV genomes were virtually identical within individuals at the point mutational level. The intra-host heterogeneity that was observed was confined to tumor-associated KSHV mutations and genome rearrangements, all impacting protein-coding sequences. Although it is unclear whether these changes were important to tumorigenesis or occurred as a result of genomic instability in tumors, similar changes were observed across individuals. These included inactivation of the K8.1 gene in tumors of 3 individuals and retention of a region around the first major internal repeat (IR1) in all instances of genomic deletions and rearrangements. Notably, the same breakpoint junctions were found in distinct tumors within single individuals, suggesting metastatic spread of rearranged KSHV genomes. These findings define KSHV intra-host heterogeneity in vivo with greater precision than has been possible in the past and suggest the possibility that aberrant KSHV genomes may contribute to aspects of KS tumorigenesis. Furthermore, study of KSHV with use of dUMI provides a proof of concept for utilizing this technique for detailed study of other virus populations in vivo.

Sieve analysis of breakthrough HIV-1 sequences in HVTN 505 identifies vaccine pressure targeting the CD4 binding site of Env-gp120.

Although the HVTN 505 DNA/recombinant adenovirus type 5 vector HIV-1 vaccine trial showed no overall efficacy, analysis of breakthrough HIV-1 sequences in participants can help determine whether vaccine-induced immune responses impacted viruses that caused infection. We analyzed 480 HIV-1 genomes sampled from 27 vaccine and 20 placebo recipients and found that intra-host HIV-1 diversity was significantly lower in vaccine recipients (P ≤ 0.04, Q-values ≤ 0.09) in Gag, Pol, Vif and envelope glycoprotein gp120 (Env-gp120). Furthermore, Env-gp120 sequences from vaccine recipients were significantly more distant from the subtype B vaccine insert than sequences from placebo recipients (P = 0.01, Q-value = 0.12). These vaccine effects were associated with signatures mapping to CD4 binding site and CD4-induced monoclonal antibody footprints. These results suggest either (i) no vaccine efficacy to block acquisition of any viral genotype but vaccine-accelerated Env evolution post-acquisition; or (ii) vaccine efficacy against HIV-1s with Env sequences closest to the vaccine insert combined with increased acquisition due to other factors, potentially including the vaccine vector.

Patterns and rates of viral evolution in HIV-1 subtype B infected females and males.

Biological sex differences affect the course of HIV infection, with untreated women having lower viral loads compared to their male counterparts but, for a given viral load, women have a higher rate of progression to AIDS. However, the vast majority of data on viral evolution, a process that is clearly impacted by host immunity and could be impacted by sex differences, has been derived from men. We conducted an intensive analysis of HIV-1 gag and env-gp120 evolution taken over the first 6-11 years of infection from 8 Women's Interagency HIV Study (WIHS) participants who had not received combination antiretroviral therapy (ART). This was compared to similar data previously collected from men, with both groups infected with HIV-1 subtype B. Early virus populations in men and women were generally homogenous with no differences in diversity between sexes. No differences in ensuing nucleotide substitution rates were found between the female and male cohorts studied herein. As previously reported for men, time to peak diversity in env-gp120 in women was positively associated with time to CD4+ cell count below 200 (P = 0.017), and the number of predicted N-linked glycosylation sites generally increased over time, followed by a plateau or decline, with the majority of changes localized to the V1-V2 region. These findings strongly suggest that the sex differences in HIV-1 disease progression attributed to immune system composition and sensitivities are not revealed by, nor do they impact, global patterns of viral evolution, the latter of which proceeds similarly in women and men.

Fitness-Balanced Escape Determines Resolution of Dynamic Founder Virus Escape Processes in HIV-1 Infection.

UNLABELLED: To understand the interplay between host cytotoxic T-lymphocyte (CTL) responses and the mechanisms by which HIV-1 evades them, we studied viral evolutionary patterns associated with host CTL responses in six linked transmission pairs. HIV-1 sequences corresponding to full-length p17 and p24 gag were generated by 454 pyrosequencing for all pairs near the time of transmission, and seroconverting partners were followed for a median of 847 days postinfection. T-cell responses were screened by gamma interferon/interleukin-2 (IFN-γ/IL-2) FluoroSpot using autologous peptide sets reflecting any Gag variant present in at least 5% of sequence reads in the individual's viral population. While we found little evidence for the occurrence of CTL reversions, CTL escape processes were found to be highly dynamic, with multiple epitope variants emerging simultaneously. We found a correlation between epitope entropy and the number of epitope variants per response (r = 0.43; P = 0.05). In cases in which multiple escape mutations developed within a targeted epitope, a variant with no fitness cost became fixed in the viral population. When multiple mutations within an epitope achieved fitness-balanced escape, these escape mutants were each maintained in the viral population. Additional mutations found to confer escape but undetected in viral populations incurred high fitness costs, suggesting that functional constraints limit the available sites tolerable to escape mutations. These results further our understanding of the impact of CTL escape and reversion from the founder virus in HIV infection and contribute to the identification of immunogenic Gag regions most vulnerable to a targeted T-cell attack. IMPORTANCE: Rapid diversification of the viral population is a hallmark of HIV-1 infection, and understanding the selective forces driving the emergence of viral variants can provide critical insight into the interplay between host immune responses and viral evolution. We used deep sequencing to comprehensively follow viral evolution over time in six linked HIV transmission pairs. We then mapped T-cell responses to explore if mutations arose due to adaption to the host and found that escape processes were often highly dynamic, with multiple mutations arising within targeted epitopes. When we explored the impact of these mutations on replicative capacity, we found that dynamic escape processes only resolve with the selection of mutations that conferred escape with no fitness cost to the virus. These results provide further understanding of the complicated viral-host interactions that occur during early HIV-1 infection and may help inform the design of future vaccine immunogens.

p21(WAF1/CIP1) RNA expression in highly HIV-1 exposed, uninfected individuals.

Some individuals remain HIV-1 antibody and PCR negative after repeated exposures to the virus, and are referred to as HIV-exposed seronegatives (HESN). However, the causes of resistance to HIV-1 infection in cases other than those with a homozygous CCR5Δ32 deletion are unclear. We hypothesized that human p21WAF1/CIP1 (a cyclin-dependent kinase inhibitor) could play a role in resistance to HIV-1 infection in HESN, as p21 expression has been associated with suppression of HIV-1 in elite controllers and reported to block HIV-1 integration in cell culture. We measured p21 RNA expression in PBMC from 40 HESN and 40 low exposure HIV-1 seroconverters (LESC) prior to their infection using a real-time PCR assay. Comparing the 20 HESN with the highest exposure risk (median = 111 partners/2.5 years prior to the 20 LESC with the lowest exposure risk (median = 1 partner/2.5 years prior), p21 expression trended higher in HESN in only one of two experiments (P = 0.11 vs. P = 0.80). Additionally, comparison of p21 expression in the top 40 HESN (median = 73 partners/year) and lowest 40 LESC (median = 2 partners/year) showed no difference between the groups (P = 0.84). There was a weak linear trend between risk of infection after exposure and increasing p21 gene expression (R2 = 0.02, P = 0.12), but again only in one experiment. Hence, if p21 expression contributes to the resistance to viral infection in HESN, it likely plays a minor role evident only in those with extremely high levels of exposure to HIV-1.

Analysis of HLA A*02 association with vaccine efficacy in the RV144 HIV-1 vaccine trial.

UNLABELLED: The RV144 HIV-1 vaccine trial demonstrated partial efficacy of 31% against HIV-1 infection. Studies into possible correlates of protection found that antibodies specific to the V1 and V2 (V1/V2) region of envelope correlated inversely with infection risk and that viruses isolated from trial participants contained genetic signatures of vaccine-induced pressure in the V1/V2 region. We explored the hypothesis that the genetic signatures in V1 and V2 could be partly attributed to selection by vaccine-primed T cells. We performed a T-cell-based sieve analysis of breakthrough viruses in the RV144 trial and found evidence of predicted HLA binding escape that was greater in vaccine versus placebo recipients. The predicted escape depended on class I HLA A*02- and A*11-restricted epitopes in the MN strain rgp120 vaccine immunogen. Though we hypothesized that this was indicative of postacquisition selection pressure, we also found that vaccine efficacy (VE) was greater in A*02-positive (A*02(+)) participants than in A*02(-) participants (VE = 54% versus 3%, P = 0.05). Vaccine efficacy against viruses with a lysine residue at site 169, important to antibody binding and implicated in vaccine-induced immune pressure, was also greater in A*02(+) participants (VE = 74% versus 15%, P = 0.02). Additionally, a reanalysis of vaccine-induced immune responses that focused on those that were shown to correlate with infection risk suggested that the humoral responses may have differed in A*02(+) participants. These exploratory and hypothesis-generating analyses indicate there may be an association between a class I HLA allele and vaccine efficacy, highlighting the importance of considering HLA alleles and host immune genetics in HIV vaccine trials. IMPORTANCE: The RV144 trial was the first to show efficacy against HIV-1 infection. Subsequently, much effort has been directed toward understanding the mechanisms of protection. Here, we conducted a T-cell-based sieve analysis, which compared the genetic sequences of viruses isolated from infected vaccine and placebo recipients. Though we hypothesized that the observed sieve effect indicated postacquisition T-cell selection, we also found that vaccine efficacy was greater for participants who expressed HLA A*02, an allele implicated in the sieve analysis. Though HLA alleles have been associated with disease progression and viral load in HIV-1 infection, these data are the first to suggest the association of a class I HLA allele and vaccine efficacy. While these statistical analyses do not provide mechanistic evidence of protection in RV144, they generate testable hypotheses for the HIV vaccine community and they highlight the importance of assessing the impact of host immune genetics in vaccine-induced immunity and protection. (This study has been registered at ClinicalTrials.gov under registration no. NCT00223080.).

Impact of mutations in highly conserved amino acids of the HIV-1 Gag-p24 and Env-gp120 proteins on viral replication in different genetic backgrounds.

It has been hypothesized that a single mutation at a highly conserved amino acid site (HCS) can be severely deleterious to HIV in most if not all isolate-specific genetic backgrounds. Consequently, potentially universal HIV-1 vaccines exclusively targeting highly conserved regions of the viral proteome have been proposed. To test this hypothesis, we examined the impact of 10 Gag-p24 and 9 Env-gp120 HCS single mutations on viral fitness. In the original founder sequence of the subject in whom these mutations were identified, all Gag-p24 HCS mutations significantly reduced viral replication fitness, including 7 that were lethal. Similar results were obtained at 9/10 sites when the same mutations were introduced into the founder sequences of two epidemiologically unlinked subjects. In contrast, none of the 9 Env-gp120 HCS mutations were lethal in the original founder sequence, and four had no fitness cost. Hence, HCS mutations in Gag-p24 are likely to be severely deleterious in different HIV-1 subtype B backgrounds; however, some HCS mutations in both Gag-p24 and Env-gp120 fragments can be well tolerated. Therefore, when designing HIV-1 immunogens that are intended to force the virus to nonviable escape pathways, the fitness constraints on the HIV segments included should be considered beyond their conservation level.

Improved detection of rare HIV-1 variants using 454 pyrosequencing.

454 pyrosequencing, a massively parallel sequencing (MPS) technology, is often used to study HIV genetic variation. However, the substantial mismatch error rate of the PCR required to prepare HIV-containing samples for pyrosequencing has limited the detection of rare variants within viral populations to those present above ~1%. To improve detection of rare variants, we varied PCR enzymes and conditions to identify those that combined high sensitivity with a low error rate. Substitution errors were found to vary up to 3-fold between the different enzymes tested. The sensitivity of each enzyme, which impacts the number of templates amplified for pyrosequencing, was shown to vary, although not consistently across genes and different samples. We also describe an amplicon-based method to improve the consistency of read coverage over stretches of the HIV-1 genome. Twenty-two primers were designed to amplify 11 overlapping amplicons in the HIV-1 clade B gag-pol and env gp120 coding regions to encompass 4.7 kb of the viral genome per sample at sensitivities as low as 0.01-0.2%.

Indel and Carryforward Correction (ICC): a new analysis approach for processing 454 pyrosequencing data.

MOTIVATION: Pyrosequencing technology provides an important new approach to more extensively characterize diverse sequence populations and detect low frequency variants. However, the promise of this technology has been difficult to realize, as careful correction of sequencing errors is crucial to distinguish rare variants (∼1%) in an infected host with high sensitivity and specificity. RESULTS: We developed a new approach, referred to as Indel and Carryforward Correction (ICC), to cluster sequences without substitutions and locally correct only indel and carryforward sequencing errors within clusters to ensure that no rare variants are lost. ICC performs sequence clustering in the order of (i) homopolymer indel patterns only, (ii) indel patterns only and (iii) carryforward errors only, without the requirement of a distance cutoff value. Overall, ICC removed 93-95% of sequencing errors found in control datasets. On pyrosequencing data from a PCR fragment derived from 15 HIV-1 plasmid clones mixed at various frequencies as low as 0.1%, ICC achieved the highest sensitivity and similar specificity compared with other commonly used error correction and variant calling algorithms. AVAILABILITY AND IMPLEMENTATION: Source code is freely available for download at http://indra.mullins.microbiol.washington.edu/ICC. It is implemented in Perl and supported on Linux, Mac OS X and MS Windows.

A sensitive real-time PCR based assay to estimate the impact of amino acid substitutions on the competitive replication fitness of human immunodeficiency virus type 1 in cell culture.

Fixation of mutations in human immunodeficiency virus type 1 (HIV-1), such as those conferring drug resistance and immune escape, can result in a change in replication fitness. To assess these changes, a real-time TaqMan PCR detection assay and statistical methods for data analysis were developed to estimate sensitively relative viral fitness in competitive viral replication experiments in cell culture. Chimeric viruses with the gene of interest in an HIV-1NL4-3 backbone were constructed in two forms, vifA (native vif gene in NL4-3) and vifB (vif gene with six synonymous nucleotide differences from vifA). Subsequently, mutations of interest were introduced into the chimeric viruses in NL4-3VifA backbones, and the mutants were competed against the chimera with the isogenic viral sequence in the NL4-3VifB backbone in cell culture. In order to assess subtle fitness differences, culture supernatants were sampled longitudinally, and the viruses differentially quantified using vifA- and vifB-specific primers in real-time PCR assays. Based on an exponential net growth model, the growth rate of each virus was determined and the fitness cost of the mutation(s) distinguishing the two viruses represented as the net growth rate difference between the mutant and the native variants. Using this assay, the fitness impact of eight amino acid substitutions was quantitated at highly conserved sites in HIV-1 Gag and Env.

Increased HIV-1 vaccine efficacy against viruses with genetic signatures in Env V2.

The RV144 trial demonstrated 31% vaccine efficacy at preventing human immunodeficiency virus (HIV)-1 infection. Antibodies against the HIV-1 envelope variable loops 1 and 2 (Env V1 and V2) correlated inversely with infection risk. We proposed that vaccine-induced immune responses against V1/V2 would have a selective effect against, or sieve, HIV-1 breakthrough viruses. A total of 936 HIV-1 genome sequences from 44 vaccine and 66 placebo recipients were examined. We show that vaccine-induced immune responses were associated with two signatures in V2 at amino acid positions 169 and 181. Vaccine efficacy against viruses matching the vaccine at position 169 was 48% (confidence interval 18% to 66%; P = 0.0036), whereas vaccine efficacy against viruses mismatching the vaccine at position 181 was 78% (confidence interval 35% to 93%; P = 0.0028). Residue 169 is in a cationic glycosylated region recognized by broadly neutralizing and RV144-derived antibodies. The predicted distance between the two signature sites (21 ± 7 Å) and their match/mismatch dichotomy indicate that multiple factors may be involved in the protection observed in RV144. Genetic signatures of RV144 vaccination in V2 complement the finding of an association between high V1/V2-binding antibodies and reduced risk of HIV-1 acquisition, and provide evidence that vaccine-induced V2 responses plausibly had a role in the partial protection conferred by the RV144 regimen.