Overview of STEP and Phambili trial results: two phase IIb test-of-concept studies investigating the efficacy of MRK adenovirus type 5 gag/pol/nef subtype B HIV vaccine. Curr Opin HIV AIDS. 2010;5:357-361. [PMID: 20978374 DOI: 10.1097/coh.0b013e32833d2d2b]

T-cell-inducing vaccines - what's the future

In the twentieth century vaccine development has moved from the use of attenuated or killed micro-organisms to protein sub-unit vaccines, with vaccine immunogenicity assessed by measuring antibodies induced by vaccination. However, for many infectious diseases T cells are an important part of naturally acquired protective immune responses, and inducing these by vaccination has been the aim of much research. The progress that has been made in developing effective T-cell-inducing vaccines against viral and parasitic diseases such as HIV and malaria is discussed, along with recent developments in therapeutic vaccine development for chronic viral infections and cancer. Although many ways of inducing T cells by vaccination have been assessed, the majority result in low level, non-protective responses. Sufficient clinical research has now been conducted to establish that replication-deficient viral vectored vaccines lead the field in inducing strong and broad responses, and efficacy studies of T-cell-inducing vaccines against a number of diseases are finally demonstrating that this is a valid approach to filling the gaps in our defence against not only infectious disease, but some forms of cancer.

Therapeutic vaccination with recombinant adenovirus reduces splenic parasite burden in experimental visceral leishmaniasis

Therapeutic vaccines, when used alone or in combination therapy with antileishmanial drugs, may have an important place in the control of a variety of forms of human leishmaniasis. Here, we describe the development of an adenovirus-based vaccine (Ad5-KH) comprising a synthetic haspb gene linked to a kmp11 gene via a viral 2A sequence. In nonvaccinated Leishmania donovani–infected BALB/c mice, HASPB- and KMP11-specific CD8⁺ T cell responses were undetectable, although IgG1 and IgG2a antibodies were evident. After therapeutic vaccination, antibody responses were boosted, and IFNγ⁺CD8⁺ T cell responses, particularly to HASPB, became apparent. A single vaccination with Ad5-KH inhibited splenic parasite growth by ∼66%, a level of efficacy comparable to that observed in early stage testing of clinically approved antileishmanial drugs in this model. These studies indicate the usefulness of adenoviral vectors to deliver leishmanial antigens in a potent and host protective manner to animals with existing L. donovani infection.

Cognitive factors and willingness to participate in an HIV vaccine trial among HIV-positive injection drug users

There are gaps in our knowledge of the role cognitive factors play in determining people's willingness to participate (WTP) in therapeutic HIV vaccine trials. Using a cross-sectional study of HIV-positive injection drug users (IDU), we determined the role of three cognitive factors: HIV treatment optimism, self-efficacy beliefs, and knowledge of vaccine trial concepts in relation to WTP in a hypothetical phase 3 therapeutic HIV vaccine trial. WTP was 54%. Participants tended to be low in HIV treatment optimism (mean = 3.9/10), high in self-efficacy (mean = 79.8/100), and low in knowledge (mean = 4.1/10). Items pertaining to HIV treatment optimism and knowledge of HIV vaccine trial concepts were generally unrelated to WTP. An increase in self-efficacy had a statistically significant positive association with WTP (OR = 1.61, 95% CI = 1.04-2.46, p < 0.05). Furthermore, most of these HIV-positive participants had high levels of self-efficacy, so we are most confident about this relationship at such levels. These findings indicate that interventions focused on increasing self-efficacy could enhance WTP among HIV-positive IDU.

Targeting a Neutralizing Epitope of HIV Envelope Gp120 by Immune Complex Vaccine

There are formidable challenges in developing HIV vaccines that elicit potent neutralizing antibodies against a broad array of HIV-1 isolates. The key targets for these neutralizing antibodies are the viral envelope antigens gp120 and gp41. Although broadly reactive neutralizing epitopes on gp120 and gp41 have been mapped and studied extensively, these epitopes are poorly immunogenic. Indeed, various vaccine candidates tested in preclinical and clinical trials do not generate antibodies against these epitopes. Hence, novel immunogen designs to augment the immunogenicity of these neutralizing epitopes are wanted. In this review, a unique immunogen design strategy that exploits immune complexes of gp120 and selected anti-gp120 monoclonal antibodies (mAb) to elicit neutralizing antibodies against cross-reactive V3 epitopes is discussed. The ability of these complexes to stimulate neutralizing antibodies is dictated by fine specificity and affinity of mAbs used to form the complexes, indicating the contribution of Fab-mediated activity, rather than conventional Fc-mediated enhancement. Further improvement of V3 immunogenicity is attainable by forming immune complexes with gp120 mutants lacking site-specific N-linked glycans. The increased V3 immunogenicity on the mutated gp120/mAb complexes correlates with enhancement of in vitro antibody recognition (antigenicity) and proteolytic resistance of V3 epitopes when presented on the complexes. These insights should provide guidelines for the development of more potent immunogens that target not only the prototypic V3 epitopes but also other broadly reactive epitopes on the HIV envelope.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

Willingness to participate in biomedical HIV prevention studies after the HVTN 503/Phambili trial: a survey conducted among adolescents in Soweto, South Africa

OBJECTIVES

Adolescents may be appropriate for inclusion in biomedical HIV prevention trials. Adolescents' overall willingness to participate (WTP) in biomedical HIV prevention trials was examined, including after the prematurely discontinued phase IIb HVTN 503/Phambili HIV vaccine trial, in Soweto, South Africa.

METHODS

An interview-administered cross-sectional survey was conducted among 506 adolescents (16-18 years) between October 2008 and March 2009. The assessment included WTP in HIV prevention trials, sexual and substance use behavior, and related psychosocial constructs. Multivariate logistic regression analyses examined predictors of WTP in biomedical prevention trials.

RESULTS

The sample primarily consisted of female participants (n = 298, 59%), and 50% of all participants were sexually active. WTP in general was high (93%), with 75% WTP in a vaccine trial after being informed about the HVTN 503/Phambili trial. Less exposure to stressors [odds ratio (OR): 2.8, confidence interval (CI): 1.3 to 6.3] was associated with adolescents' WTP in HIV biomedical prevention trials overall. Those with less exposure to stressors (OR: 1.7, CI: 1.1 to 2.8) and not sexually active (OR: 2.1, CI: 1.4 to 3.3) were predictive of WTP after the HVTN 503/Phambili trial. A higher number of sexual partners were associated with unwillingness to participate more generally (P = 0.039) and specifically after the HIV vaccine trial (P = 0.0004).

CONCLUSIONS

The high level of adolescents' WTP in biomedical prevention trials is encouraging, especially after the prematurely discontinued HVTN 503/Phambili HIV vaccine trial. High-risk youth were less likely to be WTP, although those not yet sexually active were more WTP. Future biomedical HIV prevention trials should address challenges to enrollment of high-risk adolescents who may show less WTP.

New paradigms for HIV/AIDS vaccine development

HIV-1 and its simian counterpart SIV have been exquisitely tailored by evolution to evade host immunity. By virtue of specific adaptations that thwart individual innate or adaptive immune mechanisms, and an overall replication strategy that provides for rapid establishment of a large, systemic viral population, capable of dynamic adaptation to almost all immune selection pressures, these viruses, once established, almost invariably stay one step ahead of the host's immune system, and in the vast majority of infected individuals, replicate indefinitely. Although many vaccine approaches tested to date have been able to enhance the magnitude of the immune responses to HIV/SIV infection, most of these responses, whether cellular or humoral, have largely failed to be both effectively antiviral and targeted to prevent the emergence of fully functional escape variants. Recent advances, however, have provided strong evidence that the initial stages of infection following mucosal transmission of these viruses are more vulnerable to immune intervention, and have led to the development of vaccine strategies that elicit responses able to effectively intervene in these early stages of infection, either preventing acquisition of infection or establishing early, stringent, and durable control. Here, we place HIV/AIDS vaccine development in the context of the basic immunobiology of HIV and SIV, review the evidence for their vulnerability to immune responses immediately after mucosal transmission, and discuss how this newly recognized vulnerability might be exploited for the development of an effective HIV/AIDS vaccine.

Advances and future challenges in adenoviral vector pharmacology and targeting

Adenovirus is a robust vector for therapeutic applications, but its use is limited by our understanding of its complex in vivo pharmacology. In this review we describe the necessity of identifying its natural, widespread, and multifaceted interactions with the host since this information will be crucial for efficiently redirecting virus into target cells. In the rational design of vectors, the notion of overcoming a sequence of viral "sinks" must be combined with re-targeting to target populations with capsid as well as shielding the vectors from pre-existing or toxic immune responses. It must also be noted that most known adenoviral pharmacology is deduced from the most commonly used serotypes, Ad5 and Ad2. However, these serotypes may not represent all adenoviruses, and may not even represent the most useful vectors for all purposes. Chimeras between Ad serotypes may become useful in engineering vectors that can selectively evade substantial viral traps, such as Kupffer cells, while retaining the robust qualities of Ad5. Similarly, vectorizing other Ad serotypes may become useful in avoiding immunity against Ad5 altogether. Taken together, this research on basic adenovirus biology will be necessary in developing vectors that interact more strategically with the host for the most optimal therapeutic effect.

HIV vaccines: progress to date

The quest for an effective and safe HIV-1 vaccine has been and still is the aspiration of many scientists and clinicians worldwide. Until recently, the hopes for an effective vaccine were thwarted by the disappointing results and early termination in September 2007 of the STEP study, which saw a subgroup of male vaccine recipients at an increased risk of HIV-1 infection, and the failure of earlier trials of vaccines based on recombinant envelope proteins to provide any level of protection. The results of the STEP study raised important questions in the field of HIV vaccines, including the use of recombinant adenovirus vectors as immunogens, the rationale for the development of T-cell-based vaccines and the development pathway for these vaccines, in terms of assessment of immunogenicity and the challenge models used. The study of neutralizing antibodies has demonstrated that the induction of high-titre, broadly neutralizing antibodies in the majority of recipients is likely to be highly problematic. However, the results of the RV144 Thai trial released in September 2009 have brought new optimism to the field. This study employed envelope-based immunogens delivered as a priming vaccination with a recombinant poxvirus vector and boosting with recombinant proteins. This regimen provided modest protection to HIV-1 infection in a low-risk population. Although the correlates of protection are currently unknown, extensive studies are underway to try to determine these. Neutralizing antibodies were not induced in the RV144 study; however, considerable titres of binding antibodies to HIV-1 viral envelope (Env) were. It is speculated that these antibodies may have provided a means of protection by a mechanism such as antibody-dependent cell-mediated cytotoxicity. In addition, no CD8+ T-cell responses were induced, but robust CD4+ T-cell responses were, and correlates of protection are being sought by analysing the quality of this aspect of the vaccine-induced immune response. The current paradigm for an optimal HIV-1 vaccine is to design immunogens and vaccination protocols that allow the induction of both broadly neutralizing humoral and broadly reactive and effective cell-mediated immunity, to act at sites of possible infection and post-infection, respectively. However, this is challenged by the results of the RV144 trial as neither of these responses were induced but modest protection was observed. Understanding the biology and immunopathology of HIV-1 early following infection, its modes of transmission and the human immune system's response to the virus should aid in the rational design of vaccines of increased efficacy.

Human immunodeficiency virus (HIV) immunopathogenesis and vaccine development: a review

The development of a safe, effective and globally affordable HIV vaccine offers the best hope for the future control of the HIV-1 pandemic. Since 1987, scores of candidate HIV-1 vaccines have been developed which elicited varying degrees of protective responses in nonhuman primate models, including DNA vaccines, subunit vaccines, live vectored recombinant vaccines and various prime-boost combinations. Four of these candidate vaccines have been tested for efficacy in human volunteers, but, to the exception of the recent RV144 Phase III trial in Thailand, which elicited a modest but statistically significant level of protection against infection, none has shown efficacy in preventing HIV-1 infection or in controlling virus replication and delaying progression of disease in humans. Protection against infection was observed in the RV144 trial, but intensive research is needed to try to understand the protective immune mechanisms at stake. Building-up on the results of the RV144 trial and deciphering what possibly are the immune correlates of protection are the top research priorities of the moment, which will certainly accelerate the development of an highly effective vaccine that could be used in conjunction with other HIV prevention and treatment strategies. This article reviews the state of the art of HIV vaccine development and discusses the formidable scientific challenges met in this endeavor, in the context of a better understanding of the immunopathogenesis of the disease.

A novel candidate HIV vaccine vector based on the replication deficient Capripoxvirus, Lumpy skin disease virus (LSDV)

BACKGROUND

The Capripoxvirus, Lumpy skin disease virus (LSDV) has a restricted host-range and is being investigated as a novel HIV-1 vaccine vector. LSDV does not complete its replication cycle in non-ruminant hosts.

METHODS

The safety of LSDV was tested at doses of 104 and 106 plaque forming units in two strains of immunocompromised mice, namely RAG mice and CD4 T cell knockout mice. LSDV expressing HIV-1 subtype C Gag, reverse transcriptase (RT), Tat and Nef as a polyprotein (Grttn), (rLSDV-grttn), was constructed. The immunogenicity of rLSDV-grttn was tested in homologous prime-boost regimens as well as heterologous prime-boost regimes in combination with a DNA vaccine (pVRC-grttn) or modified vaccinia Ankara vaccine (rMVA-grttn) both expressing Grttn.

RESULTS

Safety was demonstrated in two strains of immunocompromised mice.In the immunogenicity experiments mice developed high magnitudes of HIV-specific cells producing IFN-gamma and IL-2. A comparison of rLSDV-grttn and rMVA-grttn to boost a DNA vaccine (pVRC-grttn) indicated a DNA prime and rLSDV-grttn boost induced a 2 fold (p < 0.01) lower cumulative frequency of Gag- and RT-specific IFN-γ CD8 and CD4 cells than a boost with rMVA-grttn. However, the HIV-specific cells induced by the DNA vaccine prime rLSDV-grttn boost produced greater than 3 fold (p < 0.01) more IFN- gamma than the HIV-specific cells induced by the DNA vaccine prime rMVA-grttn boost. A boost of HIV-specific CD4 cells producing IL-2 was only achieved with the DNA vaccine prime and rLSDV-grttn boost. Heterologous prime-boost combinations of rLSDV-grttn and rMVA-grttn induced similar cumulative frequencies of IFN- gamma producing Gag- and RT-specific CD8 and CD4 cells. A significant difference (p < 0.01) between the regimens was the higher capacity (2.1 fold) of Gag-and RT-specific CD4 cells to produce IFN-γ with a rMVA-grttn prime - rLSDV-grttn boost. This regimen also induced a 1.5 fold higher (p < 0.05) frequency of Gag- and RT-specific CD4 cells producing IL-2.

CONCLUSIONS

LSDV was demonstrated to be non-pathogenic in immunocompromised mice. The rLSDV-grttn vaccine was immunogenic in mice particularly in prime-boost regimens. The data suggests that this novel vaccine may be useful for enhancing, in particular, HIV-specific CD4 IFN- gamma and IL-2 responses induced by a priming vaccine.

Dendritic cells exposed to MVA-based HIV-1 vaccine induce highly functional HIV-1-specific CD8(+) T cell responses in HIV-1-infected individuals

Currently, MVA virus vectors carrying HIV-1 genes are being developed as HIV-1/AIDS prophylactic/therapeutic vaccines. Nevertheless, little is known about the impact of these vectors on human dendritic cells (DC) and their capacity to present HIV-1 antigens to human HIV-specific T cells. This study aimed to characterize the interaction of MVA and MVA expressing the HIV-1 genes Env-Gag-Pol-Nef of clade B (referred to as MVA-B) in human monocyte-derived dendritic cells (MDDC) and the subsequent processes of HIV-1 antigen presentation and activation of memory HIV-1-specific T lymphocytes. For these purposes, we performed ex vivo assays with MDDC and autologous lymphocytes from asymptomatic HIV-infected patients. Infection of MDDC with MVA-B or MVA, at the optimal dose of 0.3 PFU/MDDC, induced by itself a moderate degree of maturation of MDDC, involving secretion of cytokines and chemokines (IL1-ra, IL-7, TNF-α, IL-6, IL-12, IL-15, IL-8, MCP-1, MIP-1α, MIP-1β, RANTES, IP-10, MIG, and IFN-α). MDDC infected with MVA or MVA-B and following a period of 48 h or 72 h of maturation were able to migrate toward CCL19 or CCL21 chemokine gradients. MVA-B infection induced apoptosis of the infected cells and the resulting apoptotic bodies were engulfed by the uninfected MDDC, which cross-presented HIV-1 antigens to autologous CD8⁺ T lymphocytes. MVA-B-infected MDDC co-cultured with autologous T lymphocytes induced a highly functional HIV-specific CD8⁺ T cell response including proliferation, secretion of IFN-γ, IL-2, TNF-α, MIP-1β, MIP-1α, RANTES and IL-6, and strong cytotoxic activity against autologous HIV-1-infected CD4⁺ T lymphocytes. These results evidence the adjuvant role of the vector itself (MVA) and support the clinical development of prophylactic and therapeutic anti-HIV vaccines based on MVA-B.

Safety and efficacy of the HVTN 503/Phambili study of a clade-B-based HIV-1 vaccine in South Africa: a double-blind, randomised, placebo-controlled test-of-concept phase 2b study

BACKGROUND

The MRKAd5 HIV-1 gag/pol/nef subtype B vaccine was designed to elicit T-cell-mediated immune responses capable of providing complete or partial protection from HIV-1 infection or a decrease in viral load after acquisition. We aim to assess the safety and efficacy of the vaccine in South Africa, where the major circulating clade is subtype C.

METHODS

We did a phase 2b double-blind, randomised test-of-concept study in sexually active HIV-1 seronegative participants at five sites in South Africa. Randomisation was by a computer-generated random number sequence. The vaccine and placebo were given by intramuscular injection on a 0, 1, 6 month schedule. Our coprimary endpoints were a vaccine-induced reduction in HIV-1 acquisition and viral-load setpoint. These endpoints were assessed independently in the modified intention-to-treat (MITT) cohort with two-tailed significance tests stratified by sex. We assessed immunogenicity by interferon-γ ELISPOT in peripheral-blood mononuclear cells. After the lack of efficacy of the MRKAd5 HIV-1 vaccine in the Step study, enrolment and vaccination in our study was halted, treatment allocations were unmasked, and follow-up continued. This study is registered with the South Africa National Health Research Database, number DOH-27-0207-1539, and ClinicalTrials.gov, number NCT00413725.

FINDINGS

801 of a scheduled 3000 participants, of whom 360 (45%) were women, were randomly assigned to receive either vaccine or placebo. 445 participants (56%) had adenovirus serotype 5 (Ad5) titres greater than 200, and 129 men (29%) were circumcised. 34 MITT participants in the vaccine group were diagnosed with HIV-1 (incidence rate 4·54 per 100 person-years) and 28 in the placebo group (3·70 per 100 person-years). There was no evidence of vaccine efficacy; the hazard ratio adjusted for sex was 1·25 (95% CI 0·76-2·05). Vaccine efficacy did not differ by Ad5 titre, sex, age, herpes simplex virus type 2 status, or circumcision. The geometric mean viral-load setpoint was 20,483 copies per mL (n=33) in the vaccine group and 34,032 copies per mL (n=28) in the placebo group (p=0·39). The vaccine elicited interferon-γ-secreting T cells that recognised both clade B (89%) and C (77%) antigens.

INTERPRETATION

The MRKAd5 HIV-1 vaccine did not prevent HIV-1 infection or lower viral-load setpoint; however, stopping our trial early probably compromised our ability to draw conclusions. The high incidence rates noted in South Africa highlight the crucial need for intensified efforts to develop an efficacious vaccine.

FUNDING

The US National Institute of Allergy and Infectious Disease and Merck and Co Inc.

miRNA-mediated silencing in hepatocytes can increase adaptive immune responses to adenovirus vector-delivered transgenic antigens

Adenovirus vectors based on human serotype 5 can induce potent CD8 T cell responses to vector-encoded transgenic antigens. However, the individual contribution of different cell types expressing antigen upon adenovirus vector injection to the generation of antigen-directed adaptive immune responses is poorly understood so far. We investigated the role of hepatocytes, skeletal muscle, and hematopoietic cells for the induction of cellular and humoral immune responses by miRNA-mediated tissue-specific silencing of antigen expression. Using hepatitis B small surface antigen (HBsAg) as the vector-encoded transgene we show that adenovirus vector dissemination from an intramuscular (i.m.) injection site into the liver followed by HBsAg expression in hepatocytes can limit early priming of CD8 T cells and the generation of anti-HBsAg antibody responses. However, hepatocyte-specific miRNA122a-mediated silencing of HBsAg expression overcame these limitations. Early clonal expansion of K(b)/S(190-197)-specific CD8 T cells was significantly enhanced and improved polyfunctionality of CD8 T cells was found. Furthermore, miRNA122a-mediated antigen silencing induced significantly higher anti-HBsAg antibody titers allowing an up to 100-fold vector dose reduction. These results indicate that miRNA-mediated regulation of antigen expression in the context of adenovirus vectors can significantly improve transgene product-directed immune responses. This finding could be of interest for future adenovirus vaccine vector development.

State-of-the-art gene-based therapies: the road ahead

Improvements in the gene transfer vectors used in therapeutic trials have led to substantial clinical successes in patients with serious genetic conditions, such as immunodeficiency syndromes, blindness and some cancer types. Several barriers need to be overcome before this type of therapy becomes a widely accepted treatment for a broad group of medical diseases. However, recent progress in the field is finally realizing some of the promises made more than 20 years ago, providing optimism for additional successes in the near future.

Searching for an effective, safe and universal anti-HIV vaccine: Finding the answer in just one short peptide

We explore the pentapeptide overlapping between human immunodeficiency virus (HIV) proteins and the human proteome. Our intent was to define viral peptides to be used in vaccines effective against different HIV strains, vaccines that are able to overcome the difficulties posed by the tendency of HIV to mutate, and that are also exempt from harmful collateral cross-reactions, as well as being repeatedly administrable to the global population. Analysis of HIV-1 envelope glycoprotein 160 (Env gp160) sequences revealed a set of 15 pentapeptides highly conserved among a number of retroviral sequences, and absent in the human proteome, thus representing unique molecular retroviral signatures. Use of these short viral peptide modules may represent the first concrete step toward the goal of a universal, safe and effective anti-HIV vaccine.

Lessons drawn from recent HIV vaccine efficacy trials

A safe and effective HIV vaccine is needed to curtail the US and global epidemics. However, the search for one has been elusive despite more than 25 years of focused research. Results from the RV144 Thai efficacy trial have renewed hope that a vaccine may protect against HIV acquisition. We can draw several scientific and operational lessons from RV144 and other recent tests-of-concept efficacy trials. Here we describe how trial results, some unexpected, highlight the fundamental role these clinical studies play in HIV vaccine discovery. These trials also teach us that transparency in data analysis and results dissemination can yield substantial rewards and that efforts to engage communities, particularly those most heavily affected by the epidemic, are needed to augment research literacy and trial recruitment. Future efficacy trial designs may incorporate novel, partially effective prevention strategies. Although greater in size and complexity, these trials may offer unique opportunities to explore synergies with vaccines under study.

Induction of immunity to human immunodeficiency virus type-1 by vaccination

Recent findings have brought optimism that development of a successful human immunodeficiency virus type-1 (HIV-1) vaccine lies within reach. Studies of early events in HIV-1 infection have revealed when and where HIV-1 is potentially vulnerable to vaccine-targeted immune responses. With technical advances in human antibody production, clues about how antibodies recognize HIV-1 envelope proteins have uncovered new targets for immunogen design. A recent vaccine regimen has shown modest efficacy against HIV-1 acquisition. However, inducing long-term T and B cell memory and coping with HIV-1 diversity remain high priorities. Mediators of innate immunity may play pivotal roles in blocking infection and shaping immunity; vaccine strategies to capture these activities are under investigation. Challenges remain in integrating basic, preclinical and clinical research to improve predictions of types of immunity associated with vaccine efficacy, to apply these insights to immunogen design, and to accelerate evaluation of vaccine efficacy in persons at-risk for infection.