Both mucosal and systemic routes of immunization with the live, attenuated NYVAC/simian immunodeficiency virus SIV(gpe) recombinant vaccine result in gag-specific CD8(+) T-cell responses in mucosal tissues of macaques

Generation of protective pneumococcal-specific nasal resident memory CD4+ T cells via parenteral immunization

The generation of tissue-resident memory T cells (T_RM) is an essential aspect of immunity at mucosal surfaces, and it has been suggested that preferential generation of T_RM is one of the principal advantages of mucosally administered vaccines. We have previously shown that antigen-specific, IL-17-producing CD4⁺ T cells can provide capsular antibody-independent protection against nasal carriage of Streptococcus pneumoniae; but whether pneumococcus-responsive T_RM are localized within the nasal mucosa and are sufficient for protection from carriage has not been determined. Here, we show that intranasal administration of live or killed pneumococci to mice generates pneumococcus-responsive IL-17A-producing CD4⁺ mucosal T_RM. Furthermore, we show that these cells are sufficient to mediate long-lived, neutrophil-dependent protection against subsequent pneumococcal nasal challenge. Unexpectedly, and in contrast with the prevailing paradigm, we found that parenteral administration of killed pneumococci also generates protective IL-17A⁺CD4⁺ T_RM in the nasal mucosa. These results demonstrate a critical and sufficient role of T_RM in prevention of pneumococcal colonization, and further that these cells can be generated by parenteral immunization. Our findings therefore have important implications regarding the generation of immune protection at mucosal surfaces by vaccination.

Skin immunisation activates an innate lymphoid cell-monocyte axis regulating CD8+ effector recruitment to mucosal tissues

CD8⁺ T cells provide a critical defence from pathogens at mucosal epithelia including the female reproductive tract (FRT). Mucosal immunisation is considered essential to initiate this response, however this is difficult to reconcile with evidence that antigen delivered to skin can recruit protective CD8⁺ T cells to mucosal tissues. Here we dissect the underlying mechanism. We show that adenovirus serotype 5 (Ad5) bio-distributes at very low level to non-lymphoid tissues after skin immunisation. This drives the expansion and activation of CD3^- NK1.1⁺ group 1 innate lymphoid cells (ILC1) within the FRT, essential for recruitment of CD8⁺ T-cell effectors. Interferon gamma produced by activated ILC1 is critical to licence CD11b⁺Ly6C⁺ monocyte production of CXCL9, a chemokine required to recruit skin primed CXCR3⁺ CD8⁺T-cells to the FRT. Our findings reveal a novel role for ILC1 to recruit effector CD8⁺ T-cells to prevent virus spread and establish immune surveillance at barrier tissues.

Mucosal Vaccine Approaches for Prevention of HIV and SIV Transmission

Optimal protective immunity to HIV will likely require that plasma cells, memory B cells and memory T cells be stationed in mucosal tissues at portals of viral entry. Mucosal vaccine administration is more effective than parenteral vaccine delivery for this purpose. The challenge has been to achieve efficient vaccine uptake at mucosal surfaces, and to identify safe and effective adjuvants, especially for mucosally administered HIV envelope protein immunogens. Here, we discuss strategies used to deliver potential HIV vaccine candidates in the intestine, respiratory tract, and male and female genital tract of humans and nonhuman primates. We also review mucosal adjuvants, including Toll-like receptor agonists, which may adjuvant both mucosal humoral and cellular immune responses to HIV protein immunogens.

Emerging Targets for Developing T Cell-Mediated Vaccines for Human Immunodeficiency Virus (HIV)-1

Human immunodeficiency virus (HIV)-1 has infected >75 million individuals globally, and, according to the UN, is responsible for ~2.1 million new infections and 1.1 million deaths each year. Currently, there are ~37 million individuals with HIV infection and the epidemic has already resulted in 35 million deaths. Despite the advances of anti-retroviral therapy (ART), a cost-effective vaccine remains the best long-term solution to end the HIV-1 epidemic especially given that the vast majority of infected individuals live in poor socio-economic regions of the world such as Sub-Saharan Africa which limits their accessibility to ART. The modest efficacy of the RV144 Thai trial provides hope that a vaccine for HIV-1 is possible, but as markers for sterilizing immunity are unknown, the design of an effective vaccine is empirical, although broadly cross-reactive neutralizing antibodies (bNAb) that can neutralize various quasispecies of HIV-1 are considered crucial. Since HIV-1 transmission often occurs at the genito-rectal mucosa and is cell-associated, there is a need to develop vaccines that can elicit CD8⁺ T cell immunity with the capacity to kill virus infected cells at the genito-rectal mucosa and the gut. Here we discuss the recent progress made in developing T cell-mediated vaccines for HIV-1 and emphasize the need to elicit mucosal tissue-resident memory CD8⁺ T (CD8⁺ Trm) cells. CD8⁺ Trm cells will likely form a robust front-line defense against HIV-1 and eliminate transmitter/founder virus-infected cells which are responsible for propagating HIV-1 infections following transmission in vast majority of cases.

Membrane-anchored CCL20 augments HIV Env-specific mucosal immune responses

Background

Induction of broad immune responses at mucosal site remains a primary goal for most vaccines against mucosal pathogens. Abundance of evidence indicates that the co-delivery of mucosal adjuvants, including cytokines, is necessary to induce effective mucosal immunity. In the present study, we set out to evaluate the role of a chemokine, CCL20, as an effective mucosal adjuvant for HIV vaccine.

Methods

To evaluate the role of CCL20 as a potent adjuvant for HIV vaccine, we examined its effects on antigen-specific antibody responses, level of antibody-secreting cells, cytokine production and intestinal homing of plasma cells in vaccine immunized mice.

Results

CCL20-incorporated VLP administered by mucosal route (intranasal (n = 10, p = 0.0085) or intravaginal (n = 10, p = 0.0091)) showed much higher potency in inducing Env-specific IgA antibody response than those administered by intramuscular route (n = 10). For intranasal administration, the HIV Env-specific IFN-γ(751 pg/ml), IL-4 (566 pg/ml), IL-5 (811 pg/ml) production and IgA-secreting plasma cells (62 IgA-secreting plasma cells/10⁶ cells) in mucosal lamina propria were significantly augmented in CCL20-incorporated VLP immunized mice as compared to those immunized with Env only VLPs (p = 0.0332, 0.0398, 0.033, 0.0302 for IFN-γ, IL-4, IL-5, and IgA-secreting plasma cells, respectively).

Further, anti-CCL20 mAb partially suppressed homing of Env-specific IgA ASCs into small intestine in mice immunized with CCL20-incorporated VLP by intranasal (62 decreased to 16 IgA- secreting plasma cells/10⁶ cells, p = 0.0341) or intravaginal (52 decreased to 13 IgA- secreting plasma cells/10⁶ cells, p = 0.0332) routes.

Conclusion

Our data indicated that the VLP-incorporated CCL20 can enhance HIV Env-specific immune responses in mice, especially those occurring in the mucosal sites. We also found that i.m. prime followed by mucosal boost is critical and required for CCL20 to exert its full function as an effective mucosal adjuvant. Therefore, co-incorporation of CCL20 into Env VLPs when combined with mucosal administration could represent a novel and promising HIV vaccine candidate.

Vaccine-induced immune responses against both Gag and Env improve control of simian immunodeficiency virus replication in rectally challenged rhesus macaques

The ability to control lentivirus replication may be determined, in part, by the extent to which individual viral proteins are targeted by the immune system. Consequently, defining the antigens that elicit the most protective immune responses may facilitate the design of effective HIV-1 vaccines. Here we vaccinated four groups of rhesus macaques with a heterologous vector prime/boost/boost/boost (PBBB) regimen expressing the following simian immunodeficiency virus (SIV) genes: env, gag, vif, rev, tat, and nef (Group 1); env, vif, rev, tat, and nef (Group 2); gag, vif, rev, tat, and nef (Group 3); or vif, rev, tat, and nef (Group 4). Following repeated intrarectal challenges with a marginal dose of the neutralization-resistant SIVmac239 clone, vaccinees in Groups 1-3 became infected at similar rates compared to control animals. Unexpectedly, vaccinees in Group 4 became infected at a slower pace than the other animals, although this difference was not statistically significant. Group 1 exhibited the best post-acquisition virologic control of SIV infection, with significant reductions in both peak and chronic phase viremia. Indeed, 5/8 Group 1 vaccinees had viral loads of less than 2,000 vRNA copies/mL of plasma in the chronic phase. Vaccine regimens that did not contain gag (Group 2), env (Group 3), or both of these inserts (Group 4) were largely ineffective at decreasing viremia. Thus, vaccine-induced immune responses against both Gag and Env appeared to maximize control of immunodeficiency virus replication. Collectively, these findings are relevant for HIV-1 vaccine design as they provide additional insights into which of the lentiviral proteins might serve as the best vaccine immunogens.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Nasal delivery of PLG microparticle encapsulated defensin peptides adjuvanted gp41 antigen confers strong and long-lasting immunoprotective response against HIV-1

Defensins display immunostimulatory activities including a chemotactic effect for T lymphocytes/immature dendritic cells and secretion of pro-inflammatory cytokines suggest their role in bridging innate and adaptive immunity. We hypothesized whether defensins with separately emulsified HIV-1 immunogen would elicit peptide-specific systemic and mucosal antibody response in mice. The HIV-1 peptide alone in microsphere showed low peptide-specific antibody response in sera and different washes, while the presence of defensins markedly increased the antibody peak titre both in sera (102,400-409,600) (p < 0.05) and in washes (800-25,600) (p < 0.001). Defensins with HIV-1 peptide were showing 43.0-83.2% and 38.7-72.3% in vitro neutralization against laboratory isolates in serum and lavage samples, respectively, higher than HIV-1 peptide alone. Our findings may have implications in the development of new mucosal adjuvant for AIDS vaccination.

The influence of delivery vectors on HIV vaccine efficacy

Development of an effective HIV/AIDS vaccine remains a big challenge, largely due to the enormous HIV diversity which propels immune escape. Thus novel vaccine strategies are targeting multiple variants of conserved antibody and T cell epitopic regions which would incur a huge fitness cost to the virus in the event of mutational escape. Besides immunogen design, the delivery modality is critical for vaccine potency and efficacy, and should be carefully selected in order to not only maximize transgene expression, but to also enhance the immuno-stimulatory potential to activate innate and adaptive immune systems. To date, five HIV vaccine candidates have been evaluated for efficacy and protection from acquisition was only achieved in a small proportion of vaccinees in the RV144 study which used a canarypox vector for delivery. Conversely, in the STEP study (HVTN 502) where human adenovirus serotype 5 (Ad5) was used, strong immune responses were induced but vaccination was more associated with increased risk of HIV acquisition than protection in vaccinees with pre-existing Ad5 immunity. The possibility that pre-existing immunity to a highly promising delivery vector may alter the natural course of HIV to increase acquisition risk is quite worrisome and a huge setback for HIV vaccine development. Thus, HIV vaccine development efforts are now geared toward delivery platforms which attain superior immunogenicity while concurrently limiting potential catastrophic effects likely to arise from pre-existing immunity or vector-related immuno-modulation. However, it still remains unclear whether it is poor immunogenicity of HIV antigens or substandard immunological potency of the safer delivery vectors that has limited the success of HIV vaccines. This article discusses some of the promising delivery vectors to be harnessed for improved HIV vaccine efficacy.

Challenges in mucosal HIV vaccine development: lessons from non-human primate models

An efficacious HIV vaccine is urgently needed to curb the AIDS pandemic. The modest protection elicited in the phase III clinical vaccine trial in Thailand provided hope that this goal might be achieved. However, new approaches are necessary for further advances. As HIV is transmitted primarily across mucosal surfaces, development of immunity at these sites is critical, but few clinical vaccine trials have targeted these sites or assessed vaccine-elicited mucosal immune responses. Pre-clinical studies in non-human primate models have facilitated progress in mucosal vaccine development by evaluating candidate vaccine approaches, developing methodologies for collecting and assessing mucosal samples, and providing clues to immune correlates of protective immunity for further investigation. In this review we have focused on non-human primate studies which have provided important information for future design of vaccine strategies, targeting of mucosal inductive sites, and assessment of mucosal immunity. Knowledge gained in these studies will inform mucosal vaccine design and evaluation in human clinical trials.

Recombinant Mycobacterium bovis bacillus Calmette-Guérin vectors prime for strong cellular responses to simian immunodeficiency virus gag in rhesus macaques

Live attenuated nonpathogenic Mycobacterium bovis bacillus Calmette-Guérin (BCG) mediates long-lasting immune responses, has been safely administered as a tuberculosis vaccine to billions of humans, and is affordable to produce as a vaccine vector. These characteristics make it very attractive as a human immunodeficiency virus (HIV) vaccine vector candidate. Here, we assessed the immunogenicity of recombinant BCG (rBCG) constructs with different simian immunodeficiency virus (SIV)gag expression cassettes as priming agents followed by a recombinant replication-incompetent New York vaccinia virus (NYVAC) boost in rhesus macaques. Unmutated rBCG constructs were used in comparison to mutants with gene deletions identified in an in vitro screen for augmented immunogenicity. We demonstrated that BCG-SIVgag is able to elicit robust transgene-specific priming responses, resulting in strong SIV epitope-specific cellular immune responses. While enhanced immunogenicity was sustained at moderate levels for >1 year following the heterologous boost vaccination, we were unable to demonstrate a protective effect after repeated rectal mucosal challenges with pathogenic SIVmac251. Our findings highlight the potential for rBCG vaccines to stimulate effective cross-priming and enhanced major histocompatibility complex class I presentation, suggesting that combining this approach with other immunogens may contribute to the development of effective vaccine regimens against HIV.

Induction of Potent and Long-Lived Antibody and Cellular Immune Responses in the Genitorectal Mucosa Could be the Critical Determinant of HIV Vaccine Efficacy

The field of HIV prevention has indeed progressed in leaps and bounds, but with major limitations of the current prevention and treatment options, the world remains desperate for an HIV vaccine. Sadly, this continues to be elusive, because more than 30 years since its discovery there is no licensed HIV vaccine. Research aiming to define immunological biomarkers to accurately predict vaccine efficacy have focused mainly on systemic immune responses, and as such, studies defining correlates of protection in the genitorectal mucosa, the primary target site for HIV entry and seeding are sparse. Clearly, difficulties in sampling and analysis of mucosal specimens, as well as their limited size have been a major deterrent in characterizing the type (mucosal antibodies, cytokines, chemokines, or CTL), threshold (magnitude, depth, and breadth) and viral inhibitory capacity of HIV-1-specific immune responses in the genitorectal mucosa, where they are needed to immediately block HIV acquisition and arrest subsequent virus dissemination. Nevertheless, a few studies document the existence of HIV-specific immune responses in the genitorectal mucosa of HIV-infected aviremic and viremic controllers, as well as in highly exposed persistently seronegative (HEPS) individuals with natural resistance to HIV-1. Some of these responses strongly correlate with protection from HIV acquisition and/or disease progression, thus providing significant clues of the ideal components of an efficacious HIV vaccine. In this study, we provide an overview of the key features of protective immune responses found in HEPS, elite and viremic controllers, and discuss how these can be achieved through mucosal immunization. Inevitably, HIV vaccine development research will have to consider strategies that elicit potent antibody and cellular immune responses within the genitorectal mucosa or induction of systemic immune cells with an inherent potential to home and persist at mucosal sites of HIV entry.

HIV vaccine research and discovery in the nonhuman primates model: a unified theory in acquisition prevention and control of SIV infection

PURPOSE OF REVIEW

Here we highlight the latest advances in HIV vaccine concepts that will expand our knowledge on how to elicit effective acquisition-prevention and/or control of simian immunodeficiency virus (SIV) replication in the nonhuman primate (NHP) model.

RECENT FINDINGS

In the context of the promising analyses from the RV144 Thai Trial and the effective control of SIV replication exerted by rhCMV-(SIV) elicited EM CD8 T cells, the HIV field has recently shifted toward vaccine concepts that combine protection from acquisition with effective control of SIV replication. Current studies in the NHP model have demonstrated the efficacy of HIV-neutralizing antibodies via passive transfer, the potential importance of the CD4 Tfh subset, the ability to effectively model the RV144 vaccine trial and the capacity of an Ad26 prime and modified vaccinia Ankara virus boost to elicit Env-specific antibody and cellular responses that both limit acquisition and control heterologous SIVmac251 challenge.

SUMMARY

The latest work in the NHP model suggests that the next generation HIV-1 vaccines should aim to provoke a comprehensive adaptive immune response for both prevention of SIV acquisition as well as control of replication in breakthrough infection.

Nonhuman primate models for HIV/AIDS vaccine development

The development of HIV vaccines has been hampered by the lack of an animal model that can accurately predict vaccine efficacy. Chimpanzees can be infected with HIV-1 but are not practical for research. However, several species of macaques are susceptible to the simian immunodeficiency viruses (SIVs) that cause disease in macaques, which also closely mimic HIV in humans. Thus, macaque-SIV models of HIV infection have become a critical foundation for AIDS vaccine development. Here we examine the multiple variables and considerations that must be taken into account in order to use this nonhuman primate (NHP) model effectively. These include the species and subspecies of macaques, virus strain, dose and route of administration, and macaque genetics, including the major histocompatibility complex molecules that affect immune responses, and other virus restriction factors. We illustrate how these NHP models can be used to carry out studies of immune responses in mucosal and other tissues that could not easily be performed on human volunteers. Furthermore, macaques are an ideal model system to optimize adjuvants, test vaccine platforms, and identify correlates of protection that can advance the HIV vaccine field. We also illustrate techniques used to identify different macaque lymphocyte populations and review some poxvirus vaccine candidates that are in various stages of clinical trials. Understanding how to effectively use this valuable model will greatly increase the likelihood of finding a successful vaccine for HIV.

Tissue competence imprinting and tissue residency of CD8 T cells

T cell immunity is characterized by striking tissue specialization. Tissue-specificity imprinting starts during priming by tissue-derived migratory dendritic cells in the non-random, specialized micro-anatomical area of the draining lymph node and is influenced by constitutive and induced cues from local environment. Besides tissue-specific effectors, memory cells also exhibit a tissue-specificity. Long-lived tissue-resident memory T cells likely play a considerable role in preventing pathogen invasion. Understanding of the mechanisms of tissue specialization of T cells is of major importance for the design of optimal vaccination strategies and therapeutic interventions in tissue/organ-specific inflammatory diseases. The present review summarizes our current knowledge and hypothesis about tissue-specificity imprinting and tissue residency of T cells.

The integration of T cell migration, differentiation and function

T cells function locally. Accordingly, T cells' recognition of antigen, their subsequent activation and differentiation, and their role in the processes of infection control, tumour eradication, autoimmunity, allergy and alloreactivity are intrinsically coupled with migration. Recent discoveries revise our understanding of the regulation and patterns of T cell trafficking and reveal limitations in current paradigms. Here, we review classic and emerging concepts, highlight the challenge of integrating new observations with existing T cell classification schemes and summarize the heuristic framework provided by viewing T cell differentiation and function first through the prism of migration.

Systemic vaccination induces clonally diverse SIV-specific CD8+ T-cell populations in systemic and mucosal compartments

An HIV-1 vaccine must elicit a clonally diverse virus-specific CD8+ T-cell response to contain mutant virus forms, and these responses must be present in mucosal tissues, which are the site of early HIV-1 replication. We show that systemic delivery of prototype vaccine vectors in rhesus monkeys induced SIV (simian immunodeficiency virus)-specific CD8+ T-cell responses in systemic and mucosal compartments with comparable clonal compositions. Although clonal sharing was maintained between the peripheral blood and lungs, the clonal constituents of the vaccine-induced CD8+ T-cell populations in the gastrointestinal mucosal tissues evolved away from the peripheral blood population. A phenotypic characterization indicated that the divergence was a consequence of differential trafficking and retention of the vaccine-induced cells in mucosal compartments. These findings highlight the circulation of vaccine-induced CD8+ T-cell populations between systemic and mucosal compartments and the importance of the expression of specific homing molecules for localization in mucosal tissues.

The dynamic lives of T cells: new approaches and themes

Activated T cells have classically been thought to progress unidirectionally through discrete phenotypic states and differentiate into static lineages. It is increasingly evident, however, that T cells exhibit much more complex and flexible dynamic behaviors than initially appreciated, and that these behaviors influence the efficacy of T cell responses to immunological challenges. In this review, we discuss how new technologies for monitoring the dynamics of T cells are enhancing the resolution of the fine phenotypic and functional heterogeneity within populations of T cells and revealing how individual T cells transition among a continuum of states. Such insights into the dynamic properties of T cells should improve immune monitoring and inform strategies for therapeutic interventions.

Menstrual blood as a potential source of endometrial derived CD3+ T cells

Studies of T cell-mediated immunity in the human female genital tract have been problematic due to difficulties associated with the collection of mucosal samples. Consequently, most studies rely on biopsies from the lower female genital tract or remnant tissue from hysterectomies. Availability of samples from healthy women is limited, as most studies are carried out in women with underlying pathologies. Menstruation is the cyclical sloughing off of endometrial tissue, and thus it should be a source of endometrial cells without the need for a biopsy. We isolated and phenotyped T cells from menstrual and peripheral blood and from endometrial biopsy-derived tissue from healthy women to determine the types of T cells present in this compartment. Our data demonstrated that T cells isolated from menstrual blood are a heterogeneous population of cells with markers reminiscent of blood and mucosal cells as well as unique phenotypes not represented in either compartment. T cells isolated from menstrual blood expressed increased levels of HLA-DR, αEβ7 and CXCR4 and reduced levels of CD62L relative to peripheral blood. Menstrual blood CD4+ T cells were enriched for cells expressing both CCR7 and CD45RA, markers identifying naïve T cells and were functional as determined by antigen-specific intracellular cytokine production assays. These data may open new avenues of investigation for cell mediated immune studies involving the female reproductive tract without the need for biopsies.

Durable mucosal simian immunodeficiency virus-specific effector memory T lymphocyte responses elicited by recombinant adenovirus vectors in rhesus monkeys

The induction of potent and durable cellular immune responses in both peripheral and mucosal tissues may be important for the development of effective vaccines against human immunodeficiency virus type 1 and other pathogens. In particular, effector responses at mucosal surfaces may be critical to respond rapidly to incoming mucosal pathogens. Here we report that intramuscular injection of nonreplicating recombinant adenovirus (rAd) vectors into rhesus monkeys induced remarkably durable simian immunodeficiency virus (SIV)-specific T lymphocyte responses that persisted for over 2 years in both peripheral blood and multiple mucosal tissues, including colorectal, duodenal, and vaginal biopsy specimens, as well as bronchoalveolar lavage fluid. In peripheral blood, SIV-specific T lymphocytes underwent the expected phenotypic evolution from effector memory T cells (T(EM)) to central memory T cells (TCM) following vaccination. In contrast, mucosal SIV-specific T lymphocytes exhibited a persistent and durable T(EM) phenotype that did not evolve over time. These data demonstrate that nonreplicating rAd vectors induce durable and widely distributed effector memory mucosal T lymphocyte responses that are phenotypically distinct from peripheral T lymphocyte responses. Vaccine-elicited T(EM) responses at mucosal surfaces may prove critical for affording protection against invading pathogens at the mucosal portals of entry.

Both systemic and mucosal LCMV immunization generate robust viral-specific IgG in mucosal secretions, but elicit poor LCMV-specific IgA

Immunoglobulins in secretions play a critical role in protection at mucosal surfaces. We examined the generation of viral-specific IgG and IgA in plasma and mucosal secretions of mice following systemic or mucosal immunization with lymphocytic choriomeningitis virus (LCMV), a widely used experimental model of viral infection. While there are early differences in humoral responses depending on the route of viral entry, we show that both routes generate comparably robust viral-specific IgG in plasma, vaginal, lung, and nasal secretions of immune mice. In contrast, LCMV elicited poor viral-specific IgA responses. Mice that were infected IN showed elevated viral-specific IgA in nasal and lung washes compared to IP-infected mice; however, LCMV-specific IgG overwhelmingly contributed to the humoral response in all mucosal secretions examined. Thus similarly to HIV-1, and several other mucosally-encountered microbial infections, these data suggest that LCMV infection fails to induce vigorous viral-specific IgA responses.

Update on mucosal HIV vaccine vectors

PURPOSE OF REVIEW

HIV's primary site of infection is at mucosal surfaces. To successfully defend against sexually transmitted diseases (STDs), including HIV, protection may need to be specifically elicited at the mucosal interface, where the organism enters the host. Recent advances in measuring adaptive responses at mucosal sites and optimization of techniques for low-dose repeated mucosal challenge in nonhuman primate animal models allow more in depth studies of mucosal vaccine vectors.

RECENT FINDINGS

Although parenterally administered vaccines can elicit responses at mucosal sites, vaccination of mucosal sites is being explored in an attempt to increase the frequency, strength and distribution of the adaptive mucosal response. Recent studies in nonhuman primates involve vaccination of the gastrointestinal tract and rectum, as well as the nose, oropharynx or respiratory tree in an attempt to elicit responses at the distal mucosal sites where HIV transmission occurs, the rectum and genital tract.

SUMMARY

Recent experiments in nonhuman primates indicate that vaccination at mucosal sites can elicit robust responses in the periphery and at mucosal sites, although the response pattern varies widely by route and regimen used. For most regimens, disease course after challenge did not differ by route of vaccination.

Mucosal immunity and HIV-1 infection: applications for mucosal AIDS vaccine development

Natural transmission of human immunodeficiency virus type 1 (HIV-1) occurs through gastrointestinal and vaginal mucosa. These mucosal tissues are major reservoirs for initial HIV replication and amplification, and the sites of rapid CD4(+) T cell depletion. In both HIV-infected humans and SIV-infected macaques, massive loss of CD4(+) CCR5(+) memory T cells occurs in the gut and vaginal mucosa within the first 10-14 days of infection. Induction of local HIV-specific immune responses by vaccines may facilitate effective control of HIV or SIV replication at these sites. Vaccines that induce mucosal responses, in particular CD8(+) cytotoxic T lymphocytes (CTL), have controlled viral replication at mucosal sites and curtailed systemic dissemination. Thus, there is strong justification for development of next generation vaccines that induce mucosal immune effectors against HIV-1 including CD8(+) CTL, CD4(+) T helper cells and secretory IgA. In addition, further understanding of local innate mechanisms that impact early viral replication will greatly inform future vaccine development. In this review, we examine the current knowledge concerning mucosal AIDS vaccine development. Moreover, we propose immunization strategies that may be able to elicit an effective immune response that can protect against AIDS as well as other mucosal infections.

Mucosal HIV transmission and vaccination strategies through oral compared with vaginal and rectal routes

IMPORTANCE OF THE FIELD

There are currently over thirty million people infected with HIV and there are no vaccines available to prevent HIV infections or disease. The genitourinary, rectal and oral mucosa are the mucosal HIV transmission routes. An effective vaccine that can induce both systemic and local mucosal immunity is generally accepted as a major means of protection against mucosal HIV transmission and AIDS.

WHAT THE READER WILL GAIN

Structure and cells that comprise the oral, vaginal and rectal mucosa pertaining to HIV transmission and vaccination strategies through each mucosal route to prevent mucosal and systemic infection will be discussed.

AREAS COVERED IN THIS REVIEW

Covering publications from 1980s through 2010, mucosal transmission of HIV and current and previous approaches to vaccinations are discussed.

TAKE HOME MESSAGE

Although oral transmission of HIV is far less common than vaginal and rectal transmissions, infections through this route do occur through oral sex as well as vertically from mother to child. Mucosal vaccination strategies against oral and other mucosal HIV transmissions are under intensive research but the lack of consensus on immune correlates of protection and lack of safe and effective mucosal adjuvants and delivery systems hamper progress towards a licensed vaccine.

Long-lasting humoral and cellular immune responses and mucosal dissemination after intramuscular DNA immunization

Naïve Indian rhesus macaques were immunized with a mixture of optimized plasmid DNAs expressing several SIV antigens using in vivo electroporation via the intramuscular route. The animals were monitored for the development of SIV-specific systemic (blood) and mucosal (bronchoalveolar lavage) cellular and humoral immune responses. The immune responses were of great magnitude, broad (Gag, Pol, Nef, Tat and Vif), long-lasting (up to 90 weeks post third vaccination) and were boosted with each subsequent immunization, even after an extended 90-week rest period. The SIV-specific cellular immune responses were consistently more abundant in bronchoalveolar lavage (BAL) than in blood, and were characterized as predominantly effector memory CD4(+) and CD8(+) T cells in BAL and as both central and effector memory T cells in blood. SIV-specific T cells containing Granzyme B were readily detected in both blood and BAL, suggesting the presence of effector cells with cytolytic potential. DNA vaccination also elicited long-lasting systemic and mucosal humoral immune responses, including the induction of Gag-specific IgA. The combination of optimized DNA vectors and improved intramuscular delivery by in vivo electroporation has the potential to elicit both cellular and humoral responses and dissemination to the periphery, and thus to improve DNA immunization efficacy.

Route of adenovirus-based HIV-1 vaccine delivery impacts the phenotype and trafficking of vaccine-elicited CD8+ T lymphocytes

Candidate HIV-1 vaccine regimens utilizing intramuscularly (i.m.) administered recombinant adenovirus (rAd)-based vectors can induce potent mucosal cellular immunity. However, the degree to which mucosal rAd vaccine routing might alter the quality and anatomic distribution of vaccine-elicited CD8(+) T lymphocytes remains unclear. We show that the route of vaccination critically impacts not only the magnitude but also the phenotype and trafficking of antigen-specific CD8(+) T lymphocytes in mice. I.m. rAd immunization induced robust local transgene expression and elicited high-frequency, polyfunctional CD8(+) T lymphocytes that trafficked broadly to both systemic and mucosal compartments. In contrast, intranasal (i.n.) rAd immunization led to similarly robust local transgene expression but generated low-frequency, monofunctional CD8(+) T lymphocytes with restricted anatomic trafficking patterns. Respiratory rAd immunization elicited systemic and mucosal CD8(+) T lymphocytes with phenotypes and trafficking properties distinct from those elicited by i.m. or i.n. rAd immunization. Our findings indicate that the anatomic microenvironment of antigen expression critically impacts the phenotype and trafficking of antigen-specific CD8(+) T lymphocytes.

Dynamic T cell migration program provides resident memory within intestinal epithelium

Migration to intestinal mucosa putatively depends on local activation because gastrointestinal lymphoid tissue induces expression of intestinal homing molecules, whereas skin-draining lymph nodes do not. This paradigm is difficult to reconcile with reports of intestinal T cell responses after alternative routes of immunization. We reconcile this discrepancy by demonstrating that activation within spleen results in intermediate induction of homing potential to the intestinal mucosa. We further demonstrate that memory T cells within small intestine epithelium do not routinely recirculate with memory T cells in other tissues, and we provide evidence that homing is similarly dynamic in humans after subcutaneous live yellow fever vaccine immunization. These data explain why systemic immunization routes induce local cell-mediated immunity within the intestine and indicate that this tissue must be seeded with memory T cell precursors shortly after activation.

The development of an AIDS mucosal vaccine

It is well known that mucosal tissues contain the largest surface area of the human body and are the front line of natural host defense against various pathogens. In fact, more than 80% of infectious disease pathogens probably gain entry into the susceptible human hosts through open mucosal surfaces. Human immunodeficiency virus type one (HIV-1), a mainly sexually transmitted virus, also primarily targets the vaginal and gastrointestinal mucosa as entry sites for viral transmission, seeding, replication and amplification. Since HIV-1 establishes its early replication in vaginal or rectal mucosal tissues, the induction of sufficient mucosal immunity at the initial site of HIV-1 transmission becomes essential for a protective vaccine. However, despite the fact that current conventional vaccine strategies have remained unsuccessful in preventing HIV-1 infection, sufficient financial support and resources have yet to be given to develop a vaccine able to elicit protective mucosal immunity against sexual transmissions. Interestingly, Chinese ancestors invented variolation through intranasal administration about one thousand years ago, which led to the discovery of a successful smallpox vaccine and the final eradication of the disease. It is the hope for all mankind that the development of a mucosal AIDS vaccine will ultimately help control the AIDS pandemic. In order to discover an effective mucosal AIDS vaccine, it is necessary to have a deep understanding of mucosal immunology and to test various mucosal vaccination strategies.

Mucosa and vaccine-induced immune protection in nonhuman primates

PURPOSE OF REVIEW

The purpose of this article is to review some of the recent progress in the development of HIV vaccines that induce immune responses in mucosal tissues that may correlate with protection of the mucosal CD4 T cell compartment.

RECENT FINDINGS

Mucosal tissues are the primary sites for viral entry and the resident CD4 T cells serve as readily available target cells for active infection. Viral entry is associated with a massive destruction of these cells. The resident CD4 cells are memory T cells and hence play an important role in the generation of secondary immune responses. Protecting these CD4 T cells is critical for controlling viral infection and for preserving immune competence. Numerous mucosal vaccine regimens currently under development have been shown to induce both B and T cell responses in mucosal tissues. Though induction of neutralizing antibodies still remains an elusive goal, the demonstration that antibodies can have a protective role through alternative mechanisms offers hope that humoral responses can be harnessed to yield a protective response in mucosal tissues.

SUMMARY

The mucosal immune system is highly compartmentalized and hence immunization regimens need to target mucosal tissues to be successful in inducing protective immune responses in mucosal tissues.

Preclinical evaluation of the immunogenicity of C-type HIV-1-based DNA and NYVAC vaccines in the Balb/C mouse model

As part of a European initiative (EuroVacc), we report the design, construction, and immunogenicity of two HIV-1 vaccine candidates based on a clade C virus strain (CN54) representing the current major epidemic in Asia and parts of Africa. Open reading frames encoding an artificial 160-kDa GagPolNef (GPN) polyprotein and the external glycoprotein gp120 were fully RNA and codon optimized. A DNA vaccine (DNA-GPN and DNA-gp120, referred to as DNA-C), and a replication-deficient vaccinia virus encoding both reading frames (NYVAC-C), were assessed regarding immunogenicity in Balb/C mice. The intramuscular administration of both plasmid DNA constructs, followed by two booster DNA immunizations, induced substantial T-cell responses against both antigens as well as Env-specific antibodies. Whereas low doses of NYVAC-C failed to induce specific CTL or antibodies, high doses generated cellular as well as humoral immune responses, but these did not reach the levels seen following DNA vaccination. The most potent immune responses were detectable using prime:boost protocols, regardless of whether DNA-C or NYVAC-C was used as the priming or boosting agent. These preclinical findings revealed the immunogenic response triggered by DNA-C and its enhancement by combining it with NYVAC-C, thus complementing the macaque preclinical and human phase I clinical studies of EuroVacc.

Translational Mini-Review Series on Vaccines for HIV: T lymphocyte trafficking and vaccine-elicited mucosal immunity

Many pathogens use mucosal surfaces to enter and propagate within the host, making particularly desirable vaccines that target immune responses specifically to mucosal compartments. The majority of mucosal vaccine design strategies to date have been empirical in nature. However, an emerging body of basic immunological knowledge is providing new insights into the regulation of tissue-specific lymphocyte trafficking and differentiation. These insights afford the opportunity for the rational design of vaccines that focus immune responses at mucosal surfaces. Mucosal cellular immunity may prove critical for protection in the context of HIV infection, and thus there has been considerable interest in developing vaccines that target HIV-specific cellular immune responses to the gastrointestinal and vaginal mucosa. However, the optimal strategies for eliciting mucosal cellular immune responses through vaccination remain to be determined. Here, we review both recent vaccine studies and emerging paradigms from the basic immunological literature that are relevant to the elicitation of potent and protective mucosal cellular immune memory. Increasing the synergy between these avenues of research may afford new opportunities for mucosal vaccine design.

Migration, maintenance and recall of memory T cells in peripheral tissues

After the resolution of an immune response, antigen-specific memory T cells persist at many sites in the body. The antigen-specific memory T-cell pool includes memory T cells that preferentially reside in peripheral tissues, such as the skin, gut and lungs, where they provide a first line of defence against secondary pathogen infection. Determining how peripheral memory T cells are regulated is essential for our understanding of host-pathogen interactions and for vaccine development. In this Review, we discuss recent insights into the generation, control and recall of peripheral T-cell memory responses.

Broad, high-magnitude and multifunctional CD4+ and CD8+ T-cell responses elicited by a DNA and modified vaccinia Ankara vaccine containing human immunodeficiency virus type 1 subtype C genes in baboons

Candidate human immunodeficiency virus (HIV) vaccine regimens based on DNA boosted with recombinant modified vaccinia Ankara (MVA) have been in development for some time, and there is evidence for improved immunogenicity of newly developed constructs. This study describes immune responses to candidate DNA and MVA vaccines expressing multiple genes (gag, RT, tat, nef and env) from HIV-1 subtype C in chacma baboons (Papio ursinus). The vaccine regimen induced (i) strong T-cell responses, with a median of 4103 spot forming units per 10(6) peripheral blood mononuclear cells by gamma interferon (IFN-gamma) ELISPOT, (ii) broad T-cell responses targeting all five vaccine-expressed genes, with a median of 12 peptides targeted per animal and without any single protein dominating the response, (iii) balanced CD4(+) and CD8(+) responses, which produced both IFN-gamma and interleukin (IL)-2, including IL-2-only responses not detected by the ELISPOT assay, (iv) vaccine memory, which persisted 1 year after immunization and could be boosted further, despite strong anti-vector responses, and (v) mucosal T-cell responses in iliac and mesenteric lymph nodes in two animals tested. The majority of peptide responses mapped contained epitopes previously identified in human HIV infection, and two high-avidity HIV epitope responses were confirmed, indicating the utility of the baboon model for immunogenicity testing. Together, our data show that a combination of DNA and MVA immunization induced robust, durable, multifunctional CD4(+) and CD8(+) responses in baboons targeting multiple HIV epitopes that may home to mucosal sites. These candidate vaccines, which are immunogenic in this pre-clinical model, represent an alternative to adenoviral-based vaccines and have been approved for clinical trials.

CD4+ T-cell loss and delayed expression of modulators of immune responses at mucosal sites of vaccinated macaques following SIV(mac251) infection

Systemic immunization of macaques with a combination of DNA-poxvirus-based vaccines confers protection from high level of both systemic and mucosal viral replication following rectal exposure to the pathogenic SIV(mac251). Here we investigated early post-infection events in rectal and vaginal tissues, and found that the loss of CCR5+CD4+ T cells was equivalent in vaccinated and control macaques, despite a three logs reduction at mucosal sites of simian immunodeficiency virus (SIV) RNA in the vaccinated group. Even though a normal CD4+ T cell number is not reconstituted at mucosal sites in either group, vaccination appeared to confer a better preservation of the CD4+ CCR5+ T cells that replenish these sites. Analysis of rectal tissues RNA following challenge exposure demonstrated a decreased expression in vaccinated macaques of transforming growth factor-beta, cytotoxic T lymphocyte antigen-4, FoxP3, and indoleamine 2,3-dioxygenase, an immune suppressive enzyme expressed by dendritic cells that converts tryptophan to kynurenine and limits T-cell responses. Accordingly, the ratio of kynurenine and tryptophan in the plasma was significantly reduced in the vaccinated animals respect to the controls. Thus, preexisting adaptive immune responses induced by these vaccine modalities, although they do not protect from CD4+ T-cell depletion, nevertheless, they contain SIV(mac251) replication and delay expression of markers of T-cell activation and/or suppression at mucosal sites.

Immunity to HIV-1 is influenced by continued natural exposure to exogenous virus

Unprotected sexual intercourse between individuals who are both infected with HIV-1 can lead to exposure to their partner's virus, and potentially to super-infection. However, the immunological consequences of continued exposure to HIV-1 by individuals already infected, has to our knowledge never been reported. We measured T cell responses in 49 HIV-1 infected individuals who were on antiretroviral therapy with suppressed viral loads. All the individuals were in a long-term sexual partnership with another HIV-1 infected individual, who was either also on HAART and suppressing their viral loads, or viremic (>9000 copies/ml). T cell responses to HIV-1 epitopes were measured directly ex-vivo by the IFN-γ enzyme linked immuno-spot assay and by cytokine flow cytometry. Sexual exposure data was generated from questionnaires given to both individuals within each partnership. Individuals who continued to have regular sexual contact with a HIV-1 infected viremic partner had significantly higher frequencies of HIV-1-specific T cell responses, compared to individuals with aviremic partners. Strikingly, the magnitude of the HIV-1-specific T cell response correlated strongly with the level and route of exposure. Responses consisted of both CD4⁺ and CD8⁺ T cell subsets. Longitudinally, decreases in exposure were mirrored by a lower T cell response. However, no evidence for systemic super-infection was found in any of the individuals. Continued sexual exposure to exogenous HIV-1 was associated with increased HIV-1-specific T cell responses, in the absence of systemic super-infection, and correlated with the level and type of exposure.

Serosorting, the practice of seeking to engage in unprotected sexual activities only with partners who are of the same HIV-1 status, is a growing trend. Unprotected sexual intercourse between two HIV-1 infected individuals can lead to consequences such as HIV-1 super-infection. However, continued exposure to HIV-1 may also have an important influence on the immune response. Here, we explored this influence in a cohort of HIV-1 infected individuals who were in long-term partnerships with other HIV-1 infected individuals. We found that individuals, who regularly engaged in unprotected receptive sexual intercourse with an HIV-1 infected viremic partner, displayed higher T cell responses to HIV proteins compared to those who were not regularly exposed to a viremic partner. None of the individuals within this study showed evidence of systemic super-infection. Exposure had limited impact on general activation or poly-functionality. These results are clearly of importance for HIV-1 infected individuals who chose to engage in unprotected sexual activity with other HIV-1 infected individuals. These data also reveal a more general mechanism that occurs in infectious diseases: immune responses to chronic viruses are influenced not only by the virus within the host, but also by exposure to the virus from without.

The efficacy of T cell-mediated immune responses is reduced by the envelope protein of the chimeric HIV-1/SIV-KB9 virus in vivo

Gp120 is a critical component of the envelope of HIV-1. Its role in viral entry is well described. In view of its position on the viral envelope, gp120 is a part of the retrovirus that immune cells encounter first and has the potential to influence antiretroviral immune responses. We propose that high levels of gp120 are present in tissues and may contribute to the failure of the immune system to fully control and ultimately clear the virus. Herein, we show for the first time that lymphoid tissues from acutely HIV-1/SIV (SHIV)-KB9-infected macaques contain deposits of gp120 at concentrations that are high enough to induce suppressive effects on T cells, thus negatively regulating the antiviral CTL response and contributing to virus survival and persistence. We also demonstrate that SHIV-KB9 gp120 influences functional T cell responses during SHIV infection in a manner that suppresses degranulation and cytokine secretion by CTLs. Finally, we show that regulatory T cells accumulate in lymphoid tissues during acute infection and that they respond to gp120 by producing TGFbeta, a known suppressant of cytotoxic T cell activity. These findings have significant implications for our understanding of the contribution of non-entry-related functions of HIV-1 gp120 to the pathogenesis of HIV/AIDS.

Systemic and mucosal infection program protective memory CD8 T cells in the vaginal mucosa

Whether mucosal immunization is required for optimal protective CD8 T cell memory at mucosal surfaces is controversial. In this study, using an adoptive transfer system, we compare the efficacy of two routes of acute lymphocytic choriomeningitis viral infection on the generation, maintenance, and localization of Ag-specific CD8 T cells in tissues, including the vaginal mucosa. Surprisingly, at day 8, i.p. infection results in higher numbers of Ag-specific CD8 T cells in the vaginal mucosa and iliac lymph node, as well as 2-3x more Ag-specific CD8 T cells that coexpress both IFN-gamma and TNF-alpha in comparison to the intranasal route of infection. Expression of the integrin/activation marker CD103 (alphaEbeta7) is low on vaginal mucosal Ag-specific CD8 T cells in comparison to gut mucosal intraepithelial lymphocytes. At memory, no differences are evident in the number, cytokine production, or protective function of Ag-specific CD8 T cells in the vaginal mucosa comparing the two routes of infection. However, differences persist in the cytokine profile of genital tract vs peripheral Ag-specific CD8 T cells. So although the initial route of infection, as well as tissue microenvironment, appear to influence both the magnitude and quality of the effector CD8 T cell response, both systemic and mucosal infection are equally effective in the differentiation of protective memory CD8 T cell responses against vaginal pathogenic challenge.

DNA-MVA vaccine protection after X4 SHIV challenge in macaques correlates with day-of-challenge antiviral CD4+ cell-mediated immunity levels and postchallenge preservation of CD4+ T cell memory

The ability of vaccines to induce immunity both in mucosal and systemic compartments may be required for prevention of HIV infection and AIDS. We compared DNA-MVA vaccination regimens adjuvanted by IL-12 DNA, administered intramuscularly and nasally or only nasally. Most of the vaccinated Rhesus macaques developed mucosal and systemic humoral and cell-mediated SHIV-specific immune responses. Stimulation of mucosal anti-Env IgA responses was limited. After rectal challenge with SHIV 89.6P, all vaccinated and naive animals became infected. However, most of the vaccinated animals showed significant control of viremia and protection from CD4(+) T cell loss and AIDS progression compared to the control animals. The levels of CD4(+) and CD8(+) T cell virus-specific responses measured on the day of challenge correlated with the level of viremia control observed later during the chronic infection. Postchallenge viremia levels inversely correlated with the preservation of SHIV-specific CD4(+)/IL-2(+) and CD8(+)/TNF-alpha(+) T cells but not with CD4(+)/IFN-gamma(+) T cells measured over time after challenge. We also found that during the early chronic infection SHIV vaccination permitted a more significant preservation of both naive and memory CD4(+) T cells compared to controls. In addition, we observed a more significant and prolonged preservation of memory CD4(+) T cells after SHIV vaccination and challenge than that observed after SIV vaccination and challenge. As the antiviral immunity stimulated by vaccination is present in the memory CD4(+) T cell subpopulations, its more limited targeting by SHIV compared to SIV may explain the better control of X4 tropic SHIV than R5 tropic SIVs by vaccination.

Aerosol immunization with NYVAC and MVA vectored vaccines is safe, simple, and immunogenic

Each year, approximately five million people die worldwide from putatively vaccine-preventable mucosally transmitted diseases. With respect to mass vaccination campaigns, one strategy to cope with this formidable challenge is aerosol vaccine delivery, which offers potential safety, logistical, and cost-saving advantages over traditional vaccination routes. Additionally, aerosol vaccination may elicit pivotal mucosal immune responses that could contain or eliminate mucosally transmitted pathogens in a preventative or therapeutic vaccine context. In this current preclinical non-human primate investigation, we demonstrate the feasibility of aerosol vaccination with the recombinant poxvirus-based vaccine vectors NYVAC and MVA. Real-time in vivo scintigraphy experiments with radiolabeled, aerosol-administered NYVAC-C (Clade C, HIV-1 vaccine) and MVA-HPV vaccines revealed consistent mucosal delivery to the respiratory tract. Furthermore, aerosol delivery of the vaccines was safe, inducing no vaccine-associated pathology, in particular in the brain and lungs, and was immunogenic. Administration of a DNA-C/NYVAC-C prime/boost regime resulted in both systemic and anal-genital HIV-specific immune responses that were still detectable 5 months after immunization. Thus, aerosol vaccination with NYVAC and MVA vectored vaccines constitutes a tool for large-scale vaccine efforts against mucosally transmitted pathogens.

HIV infection and the gastrointestinal immune system

There has recently been a resurgence of interest in the gastrointestinal pathology observed in patients infected with HIV. The gastrointestinal tract is a major site of HIV replication, which results in massive depletion of lamina propria CD4 T cells during acute infection. Highly active antiretroviral therapy leads to incomplete suppression of viral replication and substantially delayed and only partial restoration of gastrointestinal CD4 T cells. The gastrointestinal pathology associated with HIV infection comprises significant enteropathy with increased levels of inflammation and decreased levels of mucosal repair and regeneration. Assessment of gut mucosal immune system has provided novel directions for therapeutic interventions that modify the consequences of acute HIV infection.

Mucosal HIV-binding antibody and neutralizing activity in high-risk HIV-uninfected female participants in a trial of HIV-vaccine efficacy

BACKGROUND

This study investigated gp120-binding antibody and neutralizing activity, at the gingival- and cervical-mucosal levels, in response to a bivalent gp120 candidate vaccine.

METHODS

Women who met the study's inclusion criteria for documented high-risk behaviors participated in a nested substudy of the multicenter phase 3 trial of human immunodeficiency virus (HIV)-vaccine efficacy, VAX004. Gingival, cervicovaginal lavage, and plasma specimens were collected at 6-month intervals for 3 years. Binding-antibody and neutralizing-activity assays quantified the presence of anti-HIV activity in mucosal specimens.

RESULTS

Vaccine recipients were more likely than placebo recipients to have IgG binding antibodies in all 3 compartments tested and to have only IgA binding antibody in plasma (P<.0001). The relationship between vaccine and cervicovaginal IgG achieved significance (odds ratio [OR], 6.6 [P=.01]) but was weakened by the presence of cervicovaginal leukocytes. There was no relationship between immunization and the presence of neutralizing activity, in either bivariate or multivariate modeling (OR, 6.0 [P=.29]).

CONCLUSIONS

Vaccination is associated with the presence of both gp120-binding IgG in all compartments and plasma IgA but not with neutralizing activity. There is a role for the measurement of mucosal immunity in response to candidate vaccines and, in particular, for a determination of HIV-specific neutralizing antibodies.

Multiprotein genetic vaccine in the SIV-Macaca animal model: a promising approach to generate sterilizing immunity to HIV infection

BACKGROUND

Vaccine combining structural and regulatory proteins is an emerging approach to develop an HIV/AIDS vaccine and therefore, the immunogenicity and efficacy of two regimens of immunization combining structural (Gag/Pol, Env) and regulatory (Rev, Tat, Nef) Simian immunodeficiency virus (SIV) proteins were compared in cynomolgus monkeys.

METHODS

Monkeys were immunized with Modified Vaccine Ankara vector (MVA-J5) (protocol 1) or with DNA, Semliki forest virus and MVA vectors (DNA/SFV/MVA) (protocol 2). At week 32, all monkeys were challenge intravenously (protocol 1) or intrarectally (protocol 2) with 50 MID(50) of SIVmac251. Humoral, proliferative responses and in particular in protocol 2, the frequency of IFN-gamma producing cells, were measured in all monkeys before and after the challenge.

RESULTS

Both vaccine regimens elicited humoral and proliferative responses but failed to induce neutralizing antibodies. Upon intravenous challenge, two out of three MVA-J5 vaccinated monkeys exhibited a long-term control of the viral replication whereas DNA/SFV/MVA vaccine abrogated the virus replication up to undetectable level in three out of four vaccinated monkeys. A major contribution to this vaccine effect appeared to be the IFN-gamma/ELISPOT responses to vaccine antigens (Gag, Rev Tat and Nef).

CONCLUSIONS

These results, indicate that multiprotein heterologous prime-boost vaccination can induce a robust vaccine-induced immunity able to abrogate virus replication.

A novel functional CTL avidity/activity compartmentalization to the site of mucosal immunization contributes to protection of macaques against simian/human immunodeficiency viral depletion of mucosal CD4+ T cells

The presence of high-avidity CTLs in the right compartment can greatly affect clearance of a virus infection (for example, AIDS viral infection of and dissemination from mucosa). Comparing mucosal vs systemic immunization, we observed a novel compartmentalization of CTL avidity and proportion of functionally active Ag-specific CD8(+) T cells to tissues proximal to sites of immunization. Whereas both s.c. and intrarectal routes of immunization induced tetramer(+) cells in the spleen and gut, the mucosal vaccine induced a higher percentage of functioning IFN-gamma(+) Ag-specific CD8(+) T cells in the gut mucosa in mice. Translating to the CD8(+) CTL avidity distribution in rhesus macaques, intrarectal vaccination induced more high-avidity mucosal CTL than s.c. vaccination and protection of mucosal CD4(+) T cells from AIDS viral depletion, whereas systemic immunization induced higher avidity IFN-gamma-secreting cells in the draining lymph nodes but no protection of mucosal CD4(+) T cells, after mucosal challenge with pathogenic simian/human immunodeficiency virus. Mucosal CD4(+) T cell loss is an early critical step in AIDS pathogenesis. The preservation of CD4(+) T cells in colonic lamina propria and the reduction of virus in the intestine correlated better with high-avidity mucosal CTL induced by the mucosal AIDS vaccine. This preferential localization of high-avidity CTL may explain previous differences in vaccination results and may guide future vaccination strategy.

Ability of herpes simplex virus vectors to boost immune responses to DNA vectors and to protect against challenge by simian immunodeficiency virus

The immunogenicity and protective capacity of replication-defective herpes simplex virus (HSV) vector-based vaccines were examined in rhesus macaques. Three macaques were inoculated with recombinant HSV vectors expressing Gag, Env, and a Tat-Rev-Nef fusion protein of simian immunodeficiency virus (SIV). Three other macaques were primed with recombinant DNA vectors expressing Gag, Env, and a Pol-Tat-Nef-Vif fusion protein prior to boosting with the HSV vectors. Robust anti-Gag and anti-Env cellular responses were detected in all six macaques. Following intravenous challenge with wild-type, cloned SIV239, peak and 12-week plasma viremia levels were significantly lower in vaccinated compared to control macaques. Plasma SIV RNA in vaccinated macaques was inversely correlated with anti-Rev ELISPOT responses on the day of challenge (P value<0.05), anti-Tat ELISPOT responses at 2 weeks post challenge (P value <0.05) and peak neutralizing antibody titers pre-challenge (P value 0.06). These findings support continued study of recombinant herpesviruses as a vaccine approach for AIDS.

Systemic vaccination prevents the total destruction of mucosal CD4 T cells during acute SIV challenge

BACKGROUND

Acute human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infections are accompanied by a systemic loss of memory CD4 T cells, with mucosal sites serving as a major site for viral replication, dissemination and CD4 T cell depletion. Protecting the mucosal CD4 T cell compartment thus is critical to contain HIV, and preserve the integrity of the mucosal immune system. The primary objective of this study was to determine if systemic vaccination with DNA/rAd-5 encoding SIV-mac239-env, gag and pol could prevent the destruction of CD4 T cells in mucosal tissues.

METHODS

Rhesus macaques were immunized with DNA/r-Ad-5 encoding SIV genes and compared with those immunized with sham vectors following high dose intravenous challenge with SIVmac251. SIV specific CD4 and CD8 T cell responses, cell associated viral loads and mucosal CD4 T cell dynamics were evaluated.

RESULTS

Strong SIV specific immune responses were induced in mucosal tissues of vaccinated animals as compared with sham controls. These responses expanded rapidly following challenge suggesting a strong anamnestic response. Immune responses were associated with a decrease in cell associated viral loads, and a loss of fewer mucosal CD4 T cells. Approximately 25% of mucosal CD4 T cells were preserved in vaccinated animals as compared with <5% in sham controls. These results demonstrate that systemic immunization strategies can induce immune responses in mucosal tissues that can protect mucosal CD4 T cells from complete destruction following challenge.

CONCLUSIONS

Preservation of mucosal CD4 T cells can contribute to maintaining immune competence in mucosal tissues and provide a substantial immune benefit to the vaccinees.