Vaccine-elicited SIV and HIV envelope-specific IgA and IgG memory B cells in rhesus macaque peripheral blood correlate with functional antibody responses and reduced viremia

Loss of HIV candidate vaccine efficacy in male macaques by mucosal nanoparticle immunization rescued by V2-specific response

Systemic vaccination of macaques with V1-deleted (ΔV1) envelope immunogens reduce the risk of SIVmac251 acquisition by approximately 60%, with protective roles played by V2-specific ADCC and envelope-specific mucosal IL-17+NKp44+ innate lymphoid cells (ILCs). We investigated whether increased mucosal responses to V2 benefit vaccine efficacy by delivering oral nanoparticles (NPs) that release V2-scaffolded on Typhoid Toxin B (TTB) to the large intestine. Strikingly, mucosal immunization of male macaques abrogated vaccine efficacy with control TTB or empty NPs, but vaccine efficacy of up to 47.6% was preserved with V2-TTB NPs. The deleterious effects of NPs were linked to preferential recruitment of mucosal plasmacytoid dendritic cells (pDCs), reduction of protective mucosal NKp44+ ILCs, increased non-protective mucosal PMA/Ionomycin-induced IFN-γ+NKG2A-NKp44-ILCs, and increased levels of mucosal activated Ki67+CD4+ T cells, a potential target for virus infection. V2-TTB NP mucosal boosting rescued vaccine efficacy, likely via high avidity V2-specific antibodies mediating ADCC, and higher frequencies of mucosal NKp44+ ILCs and of ∆V1gp120 binding antibody-secreting B cells in the rectal mucosa. These findings emphasize the central role of systemic immunization and mucosal V2-specific antibodies in the protection afforded by ΔV1 envelope immunogens and encourage careful evaluation of vaccine delivery platforms to avoid inducing immune responses favorable to HIV transmission.

E4orf1 Suppresses E1B-Deleted Adenovirus Vaccine-Induced Immune Responses

As demonstrated by the recent COVID pandemic, vaccines can reduce the burden arising from infectious agents. Adenoviruses (Ads) with deletion of the early region 1B55K (ΔE1B Ad) are currently being explored for use in vaccine delivery. ΔE1B Ads are different from Ads with deletions in early region 1 and early region 3 (ΔE1/E3) used in most Ad vaccine vectors in that they contain the Ad early region 1A (E1A), and therefore the ability to replicate. Common to almost all Ads that are being explored for clinical use is the Ad early region 4 (E4). Among the E4 genes is open reading frame 1 (E4orf1), which mediates signals through the PI3-kinase/Akt pathway that is known to modulate immune responses. This suggests that E4orf1 might also modulate immune responses, although it has remained unexplored in ΔE1B Ad. Here, we show that cells infected with an E1B55K and E4orf1-deleted (ΔE41) Ad exhibited reduced levels of phosphorylated Akt (Ser473 and Thr308)) and expressed different intrinsic innate immune cytokines from those induced in cells infected with an E4orf1-containing, ΔE1B parental Ad that exhibited elevated levels of phosphorylated Akt. Rhesus macaques immunized with a ΔE41 Ad that expressed rhFLSC (HIV-1BaL gp120 linked to rhesus CD4 D1 and D2), exhibited higher levels of rhFLSC-specific interferon γ-producing memory T-cells, higher titers of rhFLSC-specific IgG1 binding antibody in serum, and antibodies able to mediate antibody-dependent cellular cytotoxicity (ADCC) with greater killing capacity than the ΔE1B Ad. Therefore, E4orf1, perhaps by acting through the PI3-kinase/Akt pathway, limits intrinsic innate and system-wide adaptive immune responses that are important for improved ΔE1B Ad-based vaccines.

Novel monkey mAbs induced by a therapeutic vaccine targeting the hepatitis B surface antigen effectively suppress hepatitis B virus in mice

Background

We have previously obtained a mouse anti-hepatitis B surface antigen (HBsAg) antibody E6F6 with long-lasting serum HBsAg clearance effects. The E6F6 epitope-based protein CR-T3-SEQ13 (HBsAg aa 113-135) vaccination therapy in cynomolgus monkeys induced long-term polyclonal antibodies-mediated clearance of HBsAg in the HBV transgenic (HBV-Tg) mice.

Methods

We isolated monoclonal antibodies from CR-T3-SEQ13 vaccinated cynomolgus monkeys, compared their therapeutic effects with E6F6, identified their epitopes on HBsAg, determined the pharmacokinetics and studied their physical property.

Results

A panel of anti-HBsAg mAbs was generated through memory B cell stimulatory culture. Two lead monkey-human chimeric antibodies, C1-23 and C3-23, effectively suppressed HBsAg and HBV DNA in HBV-Tg mice. The humanized antibodies and humanized-mouse reverse chimeric antibodies of two antibodies exhibited comparable HBsAg clearance and viral suppression efficacy as those versions of E6F6 in HBV-Tg mice. Humanized antibody hu1-23 exhibited more efficacy HBsAg-suppressing effects than huE6F6-1 and hu3-23 in HBV-Tg mice at dose levels of 10 and 20 mg/kg. Evaluation of the binding sites indicates that the epitope recognized by hu1-23 is located in HBsAg aa 118-125 and 121-125 for hu3-23. Physical property study revealed that hu1-23 and hu3-23 are stable enough for further development as a drug candidate.

Conclusions

Our data suggest that the CR-T3-SEQ13 protein is a promising HBV therapeutic vaccine candidate, and hu1-23 and hu3-23 are therapeutic candidates for the treatment of chronic hepatitis b. Moreover, the generation of antibodies from the epitope-based vaccinated subjects may be an alternative approach for novel antibody drug discovery.

The high-affinity immunoglobulin receptor FcγRI potentiates HIV-1 neutralization via antibodies against the gp41 N-heptad repeat

Despite decades of research, an effective HIV-1 vaccine remains elusive. One potential vaccine target is the N-heptad repeat (NHR) region of gp41, which is the target of the FDA-approved drug enfuvirtide. However, monoclonal antibodies and antisera targeting this region have only been modestly neutralizing to date. Here, we show that the neutralization potency of the well-characterized anti-NHR antibody D5 is increased >5,000-fold by expression of FcγRI (CD64) on cells. Since FcγRI is expressed on macrophages and dendritic cells, which are implicated in the early establishment of HIV-1 infection following sexual transmission, these results may be important to HIV-1 vaccine development.

The HIV-1 gp41 N-heptad repeat (NHR) region of the prehairpin intermediate, which is transiently exposed during HIV-1 viral membrane fusion, is a validated clinical target in humans and is inhibited by the Food and Drug Administration (FDA)-approved drug enfuvirtide. However, vaccine candidates targeting the NHR have yielded only modest neutralization activities in animals; this inhibition has been largely restricted to tier-1 viruses, which are most sensitive to neutralization by sera from HIV-1–infected individuals. Here, we show that the neutralization activity of the well-characterized NHR-targeting antibody D5 is potentiated >5,000-fold in TZM-bl cells expressing FcγRI compared with those without, resulting in neutralization of many tier-2 viruses (which are less susceptible to neutralization by sera from HIV-1–infected individuals and are the target of current antibody-based vaccine efforts). Further, antisera from guinea pigs immunized with the NHR-based vaccine candidate (ccIZN36)₃ neutralized tier-2 viruses from multiple clades in an FcγRI-dependent manner. As FcγRI is expressed on macrophages and dendritic cells, which are present at mucosal surfaces and are implicated in the early establishment of HIV-1 infection following sexual transmission, these results may be important in the development of a prophylactic HIV-1 vaccine.

A Prime/Boost Vaccine Regimen Alters the Rectal Microbiome and Impacts Immune Responses and Viremia Control Post-Simian Immunodeficiency Virus Infection in Male and Female Rhesus Macaques

An efficacious human immunodeficiency virus (HIV) vaccine will likely require induction of both mucosal and systemic immune responses. We compared the immunogenicity and protective efficacy of two mucosal/systemic vaccine regimens and investigated their effects on the rectal microbiome. Rhesus macaques were primed twice mucosally with replication-competent adenovirus type 5 host range mutant (Ad5hr)-simian immunodeficiency virus (SIV) recombinants and boosted twice intramuscularly with ALVAC-SIV recombinant plus SIV gp120 protein or with DNA for SIV genes and rhesus interleukin-12 plus SIV gp120 protein. Controls received empty Ad5hr vector and alum adjuvant only. Both regimens elicited strong, comparable mucosal and systemic cellular and humoral immunity. Prevaccination rectal microbiomes of males and females differed and significantly changed over the course of immunization, most strongly in females after Ad5hr immunizations. Following repeated low-dose intrarectal SIV challenges, both vaccine groups exhibited modestly but significantly reduced acute viremia. Male and female controls exhibited similar acute viral loads; however, vaccinated females, but not males, exhibited lower levels of acute viremia, compared to same-sex controls. Few differences in adaptive immune responses were observed between the sexes. Striking differences in correlations of the rectal microbiome of males and females with acute viremia and immune responses associated with protection were seen and point to effects of the microbiome on vaccine-induced immunity and viremia control. Our study clearly demonstrates direct effects of a mucosal SIV vaccine regimen on the rectal microbiome and validates our previously reported SIV vaccine-induced sex bias. Sex and the microbiome are critical factors that should not be overlooked in vaccine design and evaluation.IMPORTANCE Differences in HIV pathogenesis between males and females, including immunity postinfection, have been well documented, as have steroid hormone effects on the microbiome, which is known to influence mucosal immune responses. Few studies have applied this knowledge to vaccine trials. We investigated two SIV vaccine regimens combining mucosal priming immunizations and systemic protein boosting. We again report a vaccine-induced sex bias, with female rhesus macaques but not males displaying significantly reduced acute viremia. The vaccine regimens, especially the mucosal primes, significantly altered the rectal microbiome. The greatest effects were in females. Striking differences between female and male macaques in correlations of prevalent rectal bacteria with viral loads and potentially protective immune responses were observed. Effects of the microbiome on vaccine-induced immunity and viremia control require further study by microbiome transfer. However, the findings presented highlight the critical importance of considering effects of sex and the microbiome in vaccine design and evaluation.

The PRRSV-Specific Memory B Cell Response Is Long-Lived in Blood and Is Boosted During Live Virus Re-exposure

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen of swine health and well-being worldwide largely due to an insufficient understanding of the adaptive immune response to infection leading to ineffective PRRSV control. The memory and anamnestic response to infection are critical gaps in knowledge in PRRSV immunity. The lack of effective tools for the evaluation of the memory response previously hindered the ability to effectively characterize the porcine memory response to infection. However, the creation and validation of a PRRSV nsp7-specific B cell tetramer now facilitates the ability to detect very rare memory B cells and thus define the memory response of the pig. Here, we describe the PRRSV nsp7-specific B cell response following vaccination and challenge in six key secondary lymphoid organs including the identification of PBMCs as the tissue of interest for the memory immune response in pigs. Following live virus challenge of immune animals, an anamnestic response of nsp7-specific memory B cells and neutralizing antibodies was observed. This characterization of the functional humoral immune response to PRRSV answers key questions involved in regional specialization of the immune response following intramuscular inoculation of PRRSV MLV.

Quantifying Anti-HIV Envelope-Specific Antibodies in Plasma from HIV Infected Individuals

Quantifying HIV Envelope (Env)-specific antibodies in HIV⁺ plasma is useful for interpreting antibody dependent cellular cytotoxicity assay results. HIV Env, the only viral protein expressed on the surface of infected cells, has a native trimeric closed conformation on cells infected with wild-type HIV. However, CD4⁺ uninfected bystander cells in HIV⁺ cell cultures bind gp120 shed from HIV⁺ cells exposing CD4-induced epitopes normally hidden in native Env. We used flow-cytometry based assays to quantify antibodies in HIV⁺ plasma specific for native trimeric Env or gp120/CD4 conjugates using CEM.NKr.CCR5 (CEM) cells infected with HIV (iCEM) or coated with recombinant gp120 (cCEM), as a surrogate for gp120⁺ HIV^- bystander cells. Results from both assays were compared to those of a plate-based ELISA to monomeric gp120. The levels of Env-specific antibodies to cCEM and iCEM, measured by flow cytometry, and to gp120 by ELISA were positively correlated. More antibodies in HIV⁺ plasma recognized the gp120 conformation exposed on cCEM than on iCEM. Comparisons of plasma from untreated progressors, treated progressors, and elite controllers revealed that antibodies to Env epitopes were the lowest in treated progressors. Plasma from elite controllers and untreated progressors had similarly high levels of Env-specific antibodies, despite elite controllers having undetectable HIV viral loads, while untreated progressors maintained high viral loads.

Replicating Adenovirus-SIV Immunization of Rhesus Macaques Induces Mucosal Dendritic Cell Activation and Function Leading to Rectal Immune Responses

Inducing strong mucosal immune responses by vaccination is important for providing protection against simian immunodeficiency virus (SIV). A replicating adenovirus type 5 host range mutant vector (Ad5hr) expressing SIV proteins induced mucosal immune responses in rectal tissue associated with delayed SIV acquisition in female rhesus macaques, but the initial mechanisms leading to the induced immunity have not been elucidated. As dendritic cells (DCs) are known to orchestrate both innate and adaptive effector immune cell responses, we investigated their role here. Rhesus macaques were immunized twice mucosally with a replicating Ad5hr expressing SIV Env, Gag, and Nef (Ad-SIV) or empty Ad5hr vector (Ad-Empty). DC subsets and their activation were examined in rectal tissue, blood, and LNs at 3 timepoints after each immunization. Plasmacytoid DCs, myeloid DCs, and Langerhans cells were significantly increased in the rectal mucosa, but only myeloid DCs were significantly increased in blood post-immunizations. All rectal DC subsets showed increased frequencies of cells expressing activation markers and cytokines post-immunization, blood DCs showed mixed results, and LN DCs showed few changes. Rectal DCs responded strongly to the vector rather than expressed SIV antigens, but rectal DC frequencies positively correlated with induced rectal antigen-specific memory T and B cells. These correlations were confirmed by in vitro co-cultures showing that rectal Ad-SIV DCs induced proliferation and antigen-specific cytokine production by autologous naïve T cells. Our results highlight the rapid response of DCs to Ad immunization and their role in mucosal immune activation and identify initial cellular mechanisms of the replicating Ad-SIV vaccine in the rhesus macaque model.

Mind the Gap: How Interspecies Variability in IgG and Its Receptors May Complicate Comparisons of Human and Non-human Primate Effector Function

The field of HIV research relies heavily on non-human primates, particularly the members of the macaque genus, as models for the evaluation of candidate vaccines and monoclonal antibodies. A growing body of research suggests that successful protection of humans will not solely rely on the neutralization activity of an antibody's antigen binding fragment. Rather, immunological effector functions prompted by the interaction of the immunoglobulin G constant region and its cognate Fc receptors help contribute to favorable outcomes. Inherent differences in the sequences, expression, and activities of human and non-human primate antibody receptors and immunoglobulins have the potential to produce disparate results in the observations made in studies conducted in differing species. Having a more complete understanding of these differences, however, should permit the more fluent translation of observations between model organisms and the clinic. Here we present a guide to such translations that encompasses not only what is presently known regarding the affinity of the receptor-ligand interactions but also the influence of expression patterns and allelic variation, with a focus on insights gained from use of this model in HIV vaccines and passive antibody therapy and treatment.

Oral Coadministration of an Intramuscular DNA/Modified Vaccinia Ankara Vaccine for Simian Immunodeficiency Virus Is Associated with Better Control of Infection in Orally Exposed Infant Macaques

The majority of human immunodeficiency virus (HIV) type 1 infections in infants are acquired orally through breastfeeding. Toward development of a pediatric HIV vaccine to prevent breastmilk transmission, we tested the efficacy of a simultaneous oral and intramuscular (IM) vaccination regimen for preventing oral simian immunodeficiency virus (SIV) transmission in infant rhesus macaques. Two groups of neonatal macaques were immunized with DNA encoding SIV virus-like particles (DNA-SIV) on weeks 0 and 3, then boosted with modified vaccinia Ankara (MVA) virus expressing SIV antigens (MVA-SIV) on weeks 6 and 9. One group was prime/boosted by the IM route only. Another group was immunized with DNA by both the IM and topical oral (O) buccal routes, and boosted with MVA-SIV by both the IM and sublingual (SL) routes. A third group of control animals received saline by O + IM routes on weeks 0 and 3, and empty MVA by SL + IM routes on weeks 6 and 9. On week 12, infants were orally challenged once weekly with SIVmac251 until infected. The vaccine regimen that included oral routes resulted in reduced peak viremia. The rate of infection acquisition in vaccinated infants was found to be associated with prechallenge intestinal immunoglobulin G (IgG) responses to SIV gp120 and V1V2. Peak viremia was inversely correlated with postinfection intestinal IgG responses to gp120, gp41, and V1V2. These results suggest that codelivery of a pediatric HIV vaccine by an oral route may be superior to IM-only regimens for generating mucosal antibodies and preventing HIV breastmilk transmission in neonates.

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.

A simultaneous oral and intramuscular prime/sublingual boost with a DNA/Modified Vaccinia Ankara viral vector-based vaccine induces simian immunodeficiency virus-specific systemic and mucosal immune responses in juvenile rhesus macaques

BACKGROUND

A pediatric vaccine to prevent breast milk transmission of human immunodeficiency virus (HIV) may generate greater immune responses at viral entry sites if given by an oral route.

METHODS

We compared immune responses induced in juvenile macaques by prime/boosting with simian immunodeficiency virus (SIV)-expressing DNA/modified vaccinia Ankara virus (MVA) by the intramuscular route (IM), the oral (O)/tonsillar routes (T), the O/sublingual (SL) routes, and O+IM/SL routes.

RESULTS

O/T or O/SL immunization generated SIV-specific T cells in mucosal tissues but failed to induce SIV-specific IgA in saliva or stool or IgG in plasma. IM/IM or O+IM/SL generated humoral and cellular responses to SIV. IM/IM generated greater frequencies of TFH in spleen, but O+IM/SL animals had higher avidity plasma IgG and more often demonstrated mucosal IgA responses.

CONCLUSION

These results suggest that codelivery of HIV DNA/MVA vaccines by the oral and IM routes might be optimal for generating both systemic and mucosal antibodies.

Neutrophil Vaccination Dynamics and Their Capacity To Mediate B Cell Help in Rhesus Macaques

Neutrophils are the most abundant leukocyte and play a critical role in the initial response to an Ag. Recently, their ability to contribute to adaptive immunity has been highlighted. We evaluated the ability of neutrophils from blood to contribute to the adaptive immune response in a preclinical rhesus macaque SIV vaccine trial. Replication-competent adenovirus-SIV recombinants induced neutrophil activation, B cell help markers, and enhanced ability to generate reactive oxygen species. Boosting with SIV vaccines (adjuvant together with ALVAC or DNA plus envelope protein) elicited significant neutrophil responses. Serum cytokine and chemokine levels induced correlated with the frequency of neutrophil subsets expressing IL-21, myeloperoxidase, and CD64. Post-SIV infection, neutrophils exhibited dysfunction, both phenotypically and functionally. B cells from protected and infected macaques cocultured with autologous polymorphonuclear cells, consisting primarily of neutrophils, were activated, underwent class switching, and produced Abs. This B cell help was not aided by addition of IL-10 and was largely contact dependent. Numerous genes associated with inflammation, Ab production, and chemotaxis were upregulated in the cocultured B cells. We conclude that immune stimulation by vaccination or antigenic exposure imparts a greater ability of neutrophils to contribute to the adaptive immune response. Harnessing this granulocytic response has the potential to improve vaccine efficacy.

Reduced Cell-Associated DNA and Improved Viral Control in Macaques following Passive Transfer of a Single Anti-V2 Monoclonal Antibody and Repeated Simian/Human Immunodeficiency Virus Challenges

A high level of V1V2-specific IgG antibodies (Abs) in vaccinees' sera was the only independent variable that correlated with a reduced risk of human immunodeficiency virus (HIV) acquisition in the RV144 clinical trial. In contrast, IgG avidity, antibody neutralization, and antibody-dependent cellular cytotoxicity each failed as independent correlates of infection. Extended analyses of RV144 samples demonstrated the antiviral activities of V1V2-specific vaccine-induced antibodies. V2-specific antibodies have also been associated with protection from simian immunodeficiency virus (SIV), and the V2i-specific subset of human monoclonal antibodies (MAbs), while poor neutralizers, mediates Fc-dependent antiviral functions in vitro The objective of this study was to determine the protective efficacy of a V2i-specific human MAb, 830A, against mucosal simian/human immunodeficiency virus (SHIV) challenge. V2i MAb binding sites overlap the integrin binding site in the V2 region and are similar to the epitopes bound by antibodies associated with reduced HIV infection rates in RV144. Because the IgG3 subclass was a correlate of reduced infection rates in RV144, we compared passive protection by both IgG1 and IgG3 subclasses of V2i MAb 830A. This experiment represents the first in vivo test of the hypothesis emanating from RV144 and SIV studies that V2i Abs can reduce the risk of infection. The results show that passive transfer with a single V2i MAb, IgG1 830A, reduced plasma and peripheral blood mononuclear cell (PBMC) virus levels and decreased viral DNA in lymphoid tissues compared to controls, but too few animals remained uninfected to achieve significance in reducing the risk of infection. Based on these findings, we conclude that V2i antibodies can impede virus seeding following mucosal challenge, resulting in improved virus control.IMPORTANCE Since the results of the HIV RV144 clinical trial were reported, there has been significant interest in understanding how protection was mediated. Antibodies directed to a subregion of the envelope protein called V1V2 were directly correlated with a reduced risk, and surprisingly low virus neutralization was observed. To determine whether these antibodies alone could mediate protection, we used a human monoclonal antibody directed to V2 with properties similar to those elicited in the vaccine trial for passive infusions in rhesus macaques and challenge with SHIV. The single V2 antibody at the dose given did not significantly reduce the number of infections, but there was a significant reduction in the seeding of virus to the lymph nodes and a decrease in plasma viremia in the HIV antibody-infused macaques compared with the control antibody-infused animals. This finding shows that V2 antibodies mediate antiviral activities in vivo that could contribute to a protective HIV vaccine.

Pre-existing neutralizing antibody mitigates B cell dysregulation and enhances the Env-specific antibody response in SHIV-infected rhesus macaques

Our central hypothesis is that protection against HIV infection will be powerfully influenced by the magnitude and quality of the B cell response. Although sterilizing immunity, mediated by pre-formed abundant and potent antibodies is the ultimate goal for B cell-targeted HIV vaccine strategies, scenarios that fall short of this may still confer beneficial defenses against viremia and disease progression. We evaluated the impact of sub-sterilizing pre-existing neutralizing antibody on the B cell response to SHIV infection. Adult male rhesus macaques received passive transfer of a sub-sterilizing amount of polyclonal neutralizing immunoglobulin (Ig) purified from previously infected animals (SHIVIG) or control Ig prior to intra-rectal challenge with SHIVSF162P4 and extensive longitudinal sampling was performed. SHIVIG treated animals exhibited significantly reduced viral load and increased de novo Env-specific plasma antibody. Dysregulation of the B cell profile was grossly apparent soon after infection in untreated animals; exemplified by a ≈50% decrease in total B cells in the blood evident 2-3 weeks post-infection which was not apparent in SHIVIG treated animals. IgD+CD5+CD21+ B cells phenotypically similar to marginal zone-like B cells were highly sensitive to SHIV infection, becoming significantly decreased as early as 3 days post-infection in control animals, while being maintained in SHIVIG treated animals, and were highly correlated with the induction of Env-specific plasma antibody. These results suggest that B cell dysregulation during the early stages of infection likely contributes to suboptimal Env-specific B cell and antibody responses, and strategies that limit this dysregulation may enhance the host's ability to eliminate HIV.

HIV-specific CD4-induced Antibodies Mediate Broad and Potent Antibody-dependent Cellular Cytotoxicity Activity and Are Commonly Detected in Plasma From HIV-infected humans

HIV-specific antibodies (Abs) can reduce viral burden by blocking new rounds of infection or by destroying infected cells via activation of effector cells through Fc–FcR interaction. This latter process, referred to as antibody-dependent cellular cytotoxicity (ADCC), has been associated with viral control and improved clinical outcome following both HIV and SIV infections. Here we describe an HIV viral-like particle (VLP)-based sorting strategy that led to identification of HIV-specificmemory B cells encoding Abs that mediate ADCC froma subtype A-infected Kenyan woman at 914 days post-infection. Using this strategy, 12 HIV-envelope-specific monoclonal antibodies (mAbs) were isolated and three mediated potent ADCC activitywhen compared to well-characterized ADCC mAbs. The ADCC-mediating Abs also mediated antibody-dependent cell-mediated virus inhibition (ADCVI), which provides a net measure of Fc receptor-triggered effects against replicating virus. Two of the three ADCC-mediating Abs targeted a CD4-induced (CD4i) epitope also bound by the mAb C11; the third antibody targeted the N-terminus of V3. Both CD4i Abs identified here demonstrated strong cross-clade breadth with activity against 10 of 11 envelopes tested, including those from clades A, B, C, A/D and C/D, whereas the V3-specific antibody showed more limited breadth. Variants of these CD4i, C11-like mAbs engineered to interrupt binding to FcγRs inhibited a measurable percentage of the donor's ADCC activity starting as early as 189 days post-infection. C11-like antibodies also accounted for between 18–78% of ADCC activity in 9 chronically infected individuals from the same cohort study. Further, the two CD4i Abs originated from unique B cells, suggesting that antibodies targeting this epitope can be commonly produced. Taken together, these data provide strong evidence that CD4i, C11-like antibodies develop within the first 6 months of infection and they can arise fromunique B-cell lineages in the same individual. Further, thesemAbsmediate potent plasma IgG-specificADCC breadth and potency and contribute to ADCC activity in other HIV-infected individuals.

Targeted Isolation of Antibodies Directed against Major Sites of SIV Env Vulnerability

The simian immunodeficiency virus (SIV) challenge model of lentiviral infection is often used as a model to human immunodeficiency virus type 1 (HIV-1) for studying vaccine mediated and immune correlates of protection. However, knowledge of the structure of the SIV envelope (Env) glycoprotein is limited, as is knowledge of binding specificity, function and potential efficacy of SIV antibody responses. In this study we describe the use of a competitive probe binding sort strategy as well as scaffolded probes for targeted isolation of SIV Env-specific monoclonal antibodies (mAbs). We isolated nearly 70 SIV-specific mAbs directed against major sites of SIV Env vulnerability analogous to broadly neutralizing antibody (bnAb) targets of HIV-1, namely, the CD4 binding site (CD4bs), CD4-induced (CD4i)-site, peptide epitopes in variable loops 1, 2 and 3 (V1, V2, V3) and potentially glycan targets of SIV Env. The range of SIV mAbs isolated includes those exhibiting varying degrees of neutralization breadth and potency as well as others that demonstrated binding but not neutralization. Several SIV mAbs displayed broad and potent neutralization of a diverse panel of 20 SIV viral isolates with some also neutralizing HIV-2_7312A. This extensive panel of SIV mAbs will facilitate more effective use of the SIV non-human primate (NHP) model for understanding the variables in development of a HIV vaccine or immunotherapy.

An antibody-based approach targeting human immunodeficiency virus (HIV) envelope (Env) protein may eventually prove to be effective in treating or preventing HIV infection. However, before any candidate HIV treatment or vaccine can be tested in humans, it must first be evaluated in nonhuman primates (NHPs)–the closest living relatives to humans. Simian immunodeficiency virus (SIV) is the closest available non-chimeric virus—NHP model for studying and testing HIV vaccines or therapies. The SIV model complements the simian-human immunodeficiency virus (SHIV) model in distinctive ways, although less is known about SIV Env-specific antibody responses in NHPs. There are several sites on HIV Env that are vulnerable to antibody-mediated protection, and here we isolated and analyzed monoclonal antibodies (mAbs) from NHPs targeting analogous sites on SIV Env. In particular, we studied mAbs for their ability to bind the viral Env protein and to block infection of cells by widely divergent strains of SIV. These well-characterized SIV Env-specific antibodies will allow for more thorough NHP pre-clinical testing of various antibody-based SIV/HIV vaccine and immunotherapeutic strategies before proceeding to human clinical trials and may yield unanticipated findings relating to molecular mechanisms underlying the unusual breadth of neutralization observed in HIV-2 infection.

Macaque Monoclonal Antibodies Targeting Novel Conserved Epitopes within Filovirus Glycoprotein

Filoviruses cause highly lethal viral hemorrhagic fever in humans and nonhuman primates. Current immunotherapeutic options for filoviruses are mostly specific to Ebola virus (EBOV), although other members of Filoviridae such as Sudan virus (SUDV), Bundibugyo virus (BDBV), and Marburg virus (MARV) have also caused sizeable human outbreaks. Here we report a set of pan-ebolavirus and pan-filovirus monoclonal antibodies (MAbs) derived from cynomolgus macaques immunized repeatedly with a mixture of engineered glycoproteins (GPs) and virus-like particles (VLPs) for three different filovirus species. The antibodies recognize novel neutralizing and nonneutralizing epitopes on the filovirus glycoprotein, including conserved conformational epitopes within the core regions of the GP1 subunit and a novel linear epitope within the glycan cap. We further report the first filovirus antibody binding to a highly conserved epitope within the fusion loop of ebolavirus and marburgvirus species. One of the antibodies binding to the core GP1 region of all ebolavirus species and with lower affinity to MARV GP cross neutralized both SUDV and EBOV, the most divergent ebolavirus species. In a mouse model of EBOV infection, this antibody provided 100% protection when administered in two doses and partial, but significant, protection when given once at the peak of viremia 3 days postinfection. Furthermore, we describe novel cocktails of antibodies with enhanced protective efficacy compared to individual MAbs. In summary, the present work describes multiple novel, cross-reactive filovirus epitopes and innovative combination concepts that challenge the current therapeutic models.

IMPORTANCE

Filoviruses are among the most deadly human pathogens. The 2014-2015 outbreak of Ebola virus disease (EVD) led to more than 27,000 cases and 11,000 fatalities. While there are five species of Ebolavirus and several strains of marburgvirus, the current immunotherapeutics primarily target Ebola virus. Since the nature of future outbreaks cannot be predicted, there is an urgent need for therapeutics with broad protective efficacy against multiple filoviruses. Here we describe a set of monoclonal antibodies cross-reactive with multiple filovirus species. These antibodies target novel conserved epitopes within the envelope glycoprotein and exhibit protective efficacy in mice. We further present novel concepts for combination of cross-reactive antibodies against multiple epitopes that show enhanced efficacy compared to monotherapy and provide complete protection in mice. These findings set the stage for further evaluation of these antibodies in nonhuman primates and development of effective pan-filovirus immunotherapeutics for use in future outbreaks.

Mucosal B Cells Are Associated with Delayed SIV Acquisition in Vaccinated Female but Not Male Rhesus Macaques Following SIVmac251 Rectal Challenge

Many viral infections, including HIV, exhibit sex-based pathogenic differences. However, few studies have examined vaccine-related sex differences. We compared immunogenicity and protective efficacy of monomeric SIV gp120 with oligomeric SIV gp140 in a pre-clinical rhesus macaque study and explored a subsequent sex bias in vaccine outcome. Each immunization group (16 females, 8 males) was primed twice mucosally with replication-competent Ad-recombinants encoding SIV_smH4env/rev, SIV₂₃₉gag and SIV₂₃₉nefΔ_1–13 and boosted twice intramuscularly with SIV_mac239 monomeric gp120 or oligomeric gp140 in MF59 adjuvant. Controls (7 females, 5 males) received empty Ad and MF59. Up to 9 weekly intrarectal challenges with low-dose SIV_mac251 were administered until macaques became infected. We assessed vaccine-induced binding, neutralizing, and non-neutralizing antibodies, Env-specific memory B cells and plasmablasts/plasma cells (PB/PC) in bone marrow and rectal tissue, mucosal Env-specific antibodies, and Env-specific T-cells. Post-challenge, only one macaque (gp140-immunized) remained uninfected. However, SIV acquisition was significantly delayed in vaccinated females but not males, correlated with Env-specific IgA in rectal secretions, rectal Env-specific memory B cells, and PC in rectal tissue. These results extend previous correlations of mucosal antibodies and memory B cells with protective efficacy. The gp140 regimen was more immunogenic, stimulating elevated gp140 and cyclic V2 binding antibodies, ADCC and ADCP activities, bone marrow Env-specific PB/PC, and rectal gp140-specific IgG. However, immunization with gp120, the form of envelope immunogen used in RV144, the only vaccine trial to show some efficacy, provided more significant acquisition delay. Further over 40 weeks of follow-up, no gp120 immunized macaques met euthanasia criteria in contrast to 7 gp140-immunized and 2 control animals. Although males had higher binding antibodies than females, ADCC and ADCP activities were similar. The complex challenge outcomes may reflect differences in IgG subtypes, Fc glycosylation, Fc-R polymorphisms, and/or the microbiome, key areas for future studies. This first demonstration of a sex-difference in SIV vaccine-induced protection emphasizes the need for sex-balancing in vaccine trials. Our results highlight the importance of mucosal immunity and memory B cells at the SIV exposure site for protection.

Viral infections can have different disease courses in men and women. Following HIV infection, women generally exhibit lower viral loads and higher CD4 counts than men, but paradoxically progress faster to AIDS. Sex differences result from effects of X-linked genes and hormonal influences, and are believed to be largely based on immune response differences. Nevertheless, little is known about potential sex differences following vaccination. Here we report for the first time a sex bias in response to a SIV vaccine in rhesus macaques, showing that female animals were better protected against acquisition of SIV compared to males. The vaccine-induced immune responses that contributed to this better protection were viral-specific antibodies and immune antibody-secreting B cells, both at the local rectal site of SIV exposure. These results suggest that HIV/SIV vaccines should be better designed to target mucosal exposure sites. Additionally, they indicate that more vaccine studies should include animals of both sexes to address potential differences. Our study also illustrates that inclusion of both sexes can lead to greater complexity in vaccine trial outcomes, necessitating more in depth analyses. However, we believe sex balancing to be particularly important, as approximately 50% of HIV infections worldwide occur in women.

Natural killer cell education does not affect the magnitude of granzyme B delivery to target cells by antibody-dependent cellular cytotoxicity

OBJECTIVE

Interest in the role of antibody-dependent cellular cytotoxicity (ADCC) in protection from HIV infection has grown since analyses of the RV144 HIV vaccine trial results found ADCC correlated with protection. Natural killer (NK) cells are among the effector cells that mediate ADCC. The level of antibody-induced NK cell activation depends on NK cell education through inhibitory NK cell receptor human leukocyte antigen (HLA) ligand interactions. Here, we investigated the impact of NK cell education on the delivery of Granzyme B (GzB) to target cells.

DESIGN

Lymphocytes from 50 HIV-uninfected [30 Bw4 (Bw4) and 20 Bw4 (Bw6)] KIR3DL1 homozygote persons were used as effectors and cocultured with gp120-coated target cells in the presence of a single source of anti-HIV gp120 antibody to ascertain whether NK cell education status influenced the level of GzB delivered to target cells.

METHODS

The GTL assay assessed the frequency of GzB-positive (%GzB) CEM.NKr.CCR5 target cells generated by effectors from each individual. The frequency of CD107a, interferon (IFN)-γ and CCL4 NK cells was assessed as a measure of antibody-induced NK cell activation.

RESULTS

KIR3DL1 NK cells from the Bw4 group were more functional than KIR3DL1 NK cells. Despite this, the %GzB target cells generated in the GTL assay did not differ according to the KIR3DL1-HLA-B genotype of the effector cells. The %GzB cells positively correlated with the frequency of CD16KIR3DL1 NK cells in the effector population.

CONCLUSION

ADCC potency does not depend on NK cell education.

The role of HIV-specific antibody-dependent cellular cytotoxicity in HIV prevention and the influence of the HIV-1 Vpu protein

There is growing interest in the role of anti-HIV antibody-dependent cellular cytotoxicity (ADCC) antibodies in the prevention and control of HIV infection. Passive transfer studies in macaques support a role for the Fc region of antibodies in assisting in the prevention of simian-human immunodeficiency virus (SHIV) infection. The Thai RV144 HIV-1 vaccine trial induced anti-HIV ADCC antibodies that may have played a role in the partial protection observed. Several observational studies support a role for ADCC antibodies in slowing HIV disease progression. However, HIV evolves to escape ADCC antibodies and chronic HIV infections causes dysfunction of effector cells such as natural killer (NK) cells that mediate the ADCC functions. Further, four recent studies show that the HIV-1 Vpu protein, by promoting release of virions, reduces the capacity of ADCC antibodies to recognize HIV-infected cells. The review dissects some of the recent research on HIV-specific ADCC antibodies and discusses mechanisms to further harness ADCC antibodies in the prevention and control of HIV infection.

HIV-1 CD4-induced (CD4i) gp120 epitope vaccines promote B and T-cell responses that contribute to reduced viral loads in rhesus macaques

To target the HIV CD4i envelope epitope, we primed rhesus macaques with replicating Ad-rhFLSC (HIV-1BaLgp120 linked to macaque CD4 D1 and D2), with or without Ad-SIVgag and Ad-SIVnef. Macaques were boosted with rhFLSC protein. Memory T-cells in PBMC, bronchoalveolar lavage and rectal tissue, antibodies with neutralizing and ADCC activity, and Env-specific secretory IgA in rectal secretions were elicited. Although protective neutralizing antibody levels were induced, SHIVSF162P4 acquisition following rectal challenge was not prevented. Rapid declines in serum ADCC activity, Env-specific memory B cells in PBMC and bone marrow, and systemic and mucosal memory T cells were observed immediately post-challenge together with delayed anamnestic responses. Innate immune signaling resulting from persisting Ad replication and the TLR-4 booster adjuvant may have been in conflict and reoriented adaptive immunity. A different adjuvant paired with replicating Ad, or a longer post-prime interval allowing vector clearance before boosting might foster persistent T- and B-cell memory.

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.

Improved flow-based method for HIV/SIV envelope-specific memory B-cell evaluation in rhesus macaques

The ability to elicit potent and long-lasting broadly neutralizing HIV envelope (Env)-specific antibodies has become a key goal for HIV vaccine development. Consequently, the ability to rapidly and efficiently monitor development of memory B cells in pre-clinical and clinical vaccine trails is critical for continued progress in vaccine design. We have developed an improved flow cytometry-based method for the rapid and efficient identification of gp120-specific memory B cells in peripheral blood, bone marrow, and mucosal tissues which allows their direct staining without the need for prior cell sorting or enrichment. We demonstrate staining of both HIV and SIV Env-specific memory B cells in PBMC, bone marrow, and rectal tissue of vaccinated and infected rhesus macaques. Validation of the method is illustrated by statistically significant correlations with memory B cell levels quantified by ELISPOT assay and with serum binding antibody titers determined by ELISA. In addition to quantification, this method will bring the power of flow cytometry to the study of homing and trafficking of Env-specific memory B cells.

Humoral immunity induced by mucosal and/or systemic SIV-specific vaccine platforms suggests novel combinatorial approaches for enhancing responses

Combinatorial HIV/SIV vaccine approaches targeting multiple arms of the immune system might improve protective efficacy. We compared SIV-specific humoral immunity induced in rhesus macaques by five vaccine regimens. Systemic regimens included ALVAC-SIVenv priming and Env boosting (ALVAC/Env); DNA immunization; and DNA plus Env co-immunization (DNA&Env). RepAd/Env combined mucosal replication-competent Ad-env priming with systemic Env boosting. A Peptide/Env regimen, given solely intrarectally, included HIV/SIV peptides followed by MVA-env and Env boosts. Serum antibodies mediating neutralizing, phagocytic and ADCC activities were induced by ALVAC/Env, RepAd/Env and DNA&Env vaccines. Memory B cells and plasma cells were maintained in the bone marrow. RepAd/Env vaccination induced early SIV-specific IgA in rectal secretions before Env boosting, although mucosal IgA and IgG responses were readily detected at necropsy in ALVAC/Env, RepAd/Env, DNA&Env and DNA vaccinated animals. Our results suggest that combined RepAd priming with ALVAC/Env or DNA&Env regimen boosting might induce potent, functional, long-lasting systemic and mucosal SIV-specific antibodies.

Phenotypes and distribution of mucosal memory B-cell populations in the SIV/SHIV rhesus macaque model

As vaccine-elicited antibodies have now been associated with HIV protective efficacy, a thorough understanding of mucosal and systemic B-cell development and maturation is needed. We phenotyped mucosal memory B-cells, investigated isotype expression and homing patterns, and defined plasmablasts and plasma cells at three mucosal sites (duodenum, jejunum and rectum) in rhesus macaques, the commonly used animal model for pre-clinical vaccine studies. Unlike humans, macaque mucosal memory B-cells lacked CD27 expression; only two sub-populations were present: naïve (CD21(+)CD27(-)) and tissue-like (CD21(-)CD27(-)) memory. Similar to humans, IgA was the dominant isotype expressed. The homing markers CXCR4, CCR6, CCR9 and α4β7 were differentially expressed between naïve and tissue-like memory B-cells. Mucosal plasmablasts were identified as CD19(+)CD20(+/-)HLA-DR(+)Ki-67(+)IRF4(+)CD138(+/-) and mucosal plasma cells as CD19(+)CD20(-)HLA-DR(-)Ki-67(-)IRF4(+)CD138(+). Both populations were CD39(+/-)CD27(-). Plasma cell phenotype was confirmed by spontaneous IgA secretion by ELISpot of positively-selected cells and J-chain expression by real-time PCR. Duodenal, jejunal and rectal samples were similar in B-cell memory phenotype, isotype expression, homing receptors and plasmablast/plasma cell distribution among the three tissues. Thus rectal biopsies adequately monitor B-cell dynamics in the gut mucosa, and provide a critical view of mucosal B-cell events associated with development of vaccine-elicited protective immune responses and SIV/SHIV pathogenesis and disease control.

Rhesus macaque rectal and duodenal tissues exhibit B-cell sub-populations distinct from peripheral blood that continuously secrete antigen-specific IgA in short-term explant cultures

It is becoming increasingly obvious that evaluation of a vaccine aimed at preventing HIV infection should include assessment of induced immunity at mucosal sites of viral entry. Among the most salient immune responses are viral-specific antibodies. A recent report on IgA-secreting plasma cells in human duodenal explants prompted us to examine similar duodenal and rectal biopsies of rhesus macaques, a key animal model for pre-clinical HIV/SIV vaccine studies, and characterize the local resident B-cells. Here we report that non-human primate rectal explants possess similar levels of B-cells as duodenal explants. We characterize the antibody isotype expression on mucosal memory B-cells and show for the first time that the B-cell memory subsets of the duodenum and rectum are distinct from those of PBMC, not only by essentially lacking CD27(+) cells, as previously reported for uninfected macaques (Titanji et al., 2010), but also in being mostly IgD(-). SIV- and SHIV-infected macaques had fewer total IgA-secreting cells in rectal tissue compared to naïve macaques. As expected, the fractions of B-cells with surface expression of IgA were dominant in the rectal and duodenal explants whereas in PBMC IgG surface expression was dominant among IgD(-) B-cells. Mucosal antibody secreting cells were found to be predominantly plasma cells/plasma blasts based on their lack of response to stimulation. Importantly, short-term culture of rectal explants of SIV- and SHIV-positive animals led to secretion of Env-specific IgA into the culture supernatant which could be easily measured by ELISA. Collection of such culture supernatant over several days allows for accumulation of mucosal antibody in amounts that should enable antibody purification, characterization, and use in functional assays. Rectal explants can be readily obtained and unequivocally identify the mucosal tissue as the source of antibody. Overall they facilitate evaluation of mucosal vaccines.

Live attenuated rubella vectors expressing SIV and HIV vaccine antigens replicate and elicit durable immune responses in rhesus macaques

Background

Live attenuated viruses are among our most potent and effective vaccines. For human immunodeficiency virus, however, a live attenuated strain could present substantial safety concerns. We have used the live attenuated rubella vaccine strain RA27/3 as a vector to express SIV and HIV vaccine antigens because its safety and immunogenicity have been demonstrated in millions of children. One dose protects for life against rubella infection. In previous studies, rubella vectors replicated to high titers in cell culture while stably expressing SIV and HIV antigens. Their viability in vivo, however, as well as immunogenicity and antibody persistence, were unknown.

Results

This paper reports the first successful trial of rubella vectors in rhesus macaques, in combination with DNA vaccines in a prime and boost strategy. The vectors grew robustly in vivo, and the protein inserts were highly immunogenic. Antibody titers elicited by the SIV Gag vector were greater than or equal to those elicited by natural SIV infection. The antibodies were long lasting, and they were boosted by a second dose of replication-competent rubella vectors given six months later, indicating the induction of memory B cells.

Conclusions

Rubella vectors can serve as a vaccine platform for safe delivery and expression of SIV and HIV antigens. By presenting these antigens in the context of an acute infection, at a high level and for a prolonged duration, these vectors can stimulate a strong and persistent immune response, including maturation of memory B cells. Rhesus macaques will provide an ideal animal model for demonstrating immunogenicity of novel vectors and protection against SIV or SHIV challenge.

Characterization of humoral responses to soluble trimeric HIV gp140 from a clade A Ugandan field isolate

Trimeric soluble forms of HIV gp140 envelope glycoproteins represent one of the closest molecular structures compared to native spikes present on intact virus particles. Trimeric soluble gp140 have been generated by several groups and such molecules have been shown to induce antibodies with neutralizing activity against homologous and heterologous viruses. In the present study, we generated a recombinant trimeric soluble gp140, derived from a previously identified Ugandan A-clade HIV field isolate (gp140_94UG018). Antibodies elicited in immunized rabbits show a broad binding pattern to HIV envelopes of different clades. An epitope mapping analysis reveals that, on average, the binding is mostly focused on the C1, C2, V3, V5 and C5 regions. Immune sera show neutralization activity to Tier 1 isolates of different clades, demonstrating cross clade neutralizing activity which needs to be further broadened by possible structural modifications of the clade A gp140_94UG018. Our results provide a rationale for the design and evaluation of immunogens and the clade A gp140_94UG018 shows promising characteristics for potential involvement in an effective HIV vaccine with broad activity.

Fc receptor-mediated immune responses: new tools but increased complexity in HIV prevention

The modest success of the RV144 HIV vaccine trial in Thailand and the ensuing suggestion that a Fc-receptormediated antibody activity might have played a role in the protection observed have intensified investigations on Fcrelated immune responses. HIV neutralizing antibodies have been and continue to be the focal point of research into humoral immune protection. However, recent knowledge that their protective efficacy can be augmented by Fc-FcR interactions has increased the complexity of identifying immune correlates of protection. If anything, continued studies of both humoral and cellular immune mechanisms point to the lack of a single protective anti-HIV immune response. Here we focus on humoral immunity, analyzing the role played by Fc receptor-related responses and discussing how new knowledge of their interactions requires further investigation, but may also spur novel vaccination approaches. We initially address classical Fc-receptor mediated anti-viral mechanisms including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cell mediated viral inhibition (ADCVI), and antibody-dependent cellular phagocytosis (ADCP), as well as the effector cells that mediate these functions. Next, we summarize key aspects of FcR-Fc interactions that are important for potential control of HIV/SIV such as FcR polymorphisms and post-transcriptional modifications. Finally we discuss less commonly studied non-mechanistic anti-HIV immune functions: antibody avidity and envelopespecific B cell memory. Overall, a spectrum of immune responses, reflecting the immune system's redundancy, will likely be needed to prevent HIV infection and/or disease progression. Aside from elicitation of critical immune mechanisms, a successful vaccine will need to induce mature B cell responses and long-lasting immune memory.

Unravelling the mechanisms of durable control of HIV-1

Untreated HIV-1 infection typically progresses to AIDS within 10 years, but less than 1% of infected individuals remain healthy and have normal CD4(+) T cell counts and undetectable viral loads; some individuals have remained this way for 35 years and counting. Through a combination of large population studies of cohorts of these 'HIV-1 controllers' and detailed studies of individual patients, a heterogeneous picture has emerged regarding the basis for this remarkable resistance to AIDS progression. In this Review, we highlight the host genetic factors, the viral genetic factors and the immunological factors that are associated with the controller phenotype, we discuss emerging methodological approaches that could facilitate a better understanding of spontaneous HIV-1 immune control in the future, and we delineate implications for a 'functional cure' of HIV-1 infection.

Impact of antibody quality and anamnestic response on viremia control post-challenge in a combined Tat/Env vaccine regimen in rhesus macaques

Previously, priming rhesus macaques with Adenovirus type 5 host range mutant-recombinants encoding Tat and Env and boosting with Tat and Env protein in MPL-SE controlled chronic viremia by 4 logs following homologous intravenous SHIV89.6P challenge. Here we evaluated Tat, Env, and Tat/Env regimens for immunogenicity and protective efficacy using clade C Env, alum adjuvant, and a heterologous intrarectal SHIV1157ipd3N4 challenge. Despite induction of strong cellular and humoral immunity, Tat/Env group T and B-cell memory responses were not significantly enhanced over Tat- or Env-only groups. Lack of viremia control post-challenge was attributed to lower avidity Env antibodies and no anamnestic ADCC response or SHIV1157ipd3N4 neutralizing antibody development post-challenge. Poor biologic activity of the Tat immunogen may have impaired Tat immunity. In the absence of sterilizing immunity, strong anamnestic responses to heterologous virus can help control viremia. Both antibody breadth and optimal adjuvanticity are needed to elicit high-quality antibody for protective efficacy.

Immunogenicity of a vaccine regimen composed of simian immunodeficiency virus DNA, rMVA, and viral particles administered to female rhesus macaques via four different mucosal routes

A comparative evaluation of the immunity stimulated with a vaccine regimen that includes simian immunodeficiency virus (SIV), interleukin 2 (IL-2), and IL-15 DNAs, recombinant modified vaccinia virus Ankara (rMVA), and inactivated SIVmac239 particles administered into the oral and nasal cavities, small intestine, and vagina was carried out in female rhesus macaques to determine the best route to induce diverse anti-SIV immunity that may be critical to protection from SIV infection and disease. All four immunizations generated mucosal SIV-specific IgA. Oral immunization was as effective as vaginal immunization in inducing SIV-specific IgA in vaginal secretions and generated greater IgA responses in rectal secretions and saliva samples compared to the other immunization routes. All four immunizations stimulated systemic T-cell responses against Gag and Env, albeit to a different extent, with oral immunization providing greater magnitude and nasal immunization providing wider functional heterogeneity. SIV-specific T cells producing gamma interferon (IFN-γ) dominated these responses. Limited levels of SIV-specific IgG antibodies were detected in plasma samples, and no SIV-specific IgG antibodies were detected in secretions. Vaccination also induced CD4(+) and CD8(+) T-cell responses in the rectal and vaginal mucosa with greater functional heterogeneity than in blood samples. Rectal T-cell responses were significantly greater in the orally vaccinated animals than in the other animals. The most balanced, diverse, and higher-magnitude vaginal T-cell responses were observed after intestinal vaccination. Significantly higher CD8(+) granzyme B-positive T-cell responses were observed systemically after intestinal vaccination and in rectal cells after oral immunization. The majority of SIV-specific T cells that produced granzyme B did not produce cytokines. Of the immunization routes tested, oral vaccination provided the most diverse and significant response to the vaccine.

Cutting edge: novel vaccination modality provides significant protection against mucosal infection by highly pathogenic simian immunodeficiency virus

Vaccine-induced protection against infection by HIV or highly pathogenic and virulent SIV strains has been limited. In a proof-of-concept study, we show that a novel vaccine approach significantly protects rhesus macaques from mucosal infection by the highly pathogenic strain SIVmac251. We vaccinated three cohorts of 12 macaques each with live, irradiated vaccine cells secreting the modified endoplasmic reticulum chaperone gp96-Ig. Cohort 1 was vaccinated with cells secreting gp96(SIV)Ig carrying SIV peptides. In addition, Cohort 2 received recombinant envelope protein SIV-gp120. Cohort 3 was injected with cells secreting gp96-Ig (no SIV Ags) vaccines. Cohort 2 was protected from infection. After seven rectal challenges with highly pathogenic SIVmac251, the hazard ratio was 0.27, corresponding to a highly significant, 73% reduced risk for viral acquisition. The apparent success of the novel vaccine modality recommends further study.

Dynamics of memory B-cell populations in blood, lymph nodes, and bone marrow during antiretroviral therapy and envelope boosting in simian immunodeficiency virus SIVmac251-infected rhesus macaques

Human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infection causes B-cell dysregulation and the loss of memory B cells in peripheral blood mononuclear cells (PBMC). These effects are not completely reversed by antiretroviral treatment (ART). To further elucidate B-cell changes during chronic SIV infection and treatment, we investigated memory B-cell subpopulations and plasma cells/plasmablasts (PC/PB) in blood, bone marrow, and lymph nodes of rhesus macaques during ART and upon release from ART. Macaques previously immunized with SIV recombinants and the gp120 protein were included to assess the effects of prior vaccination. ART was administered for 11 weeks, with or without gp120 boosting at week 9. Naïve and resting, activated, and tissue-like memory B cells and PC/PB were evaluated by flow cytometry. Antibody-secreting cells (ASC) and serum antibody titers were assessed. No lasting changes in B-cell memory subpopulations occurred in bone marrow and lymph nodes, but significant decreases in numbers of activated memory B cells and increases in numbers of tissue-like memory B cells persisted in PBMC. Macaque PC/PB were found to be either CD27(+) or CD27(-) and therefore were defined as CD19(+) CD38(hi) CD138(+). The numbers of these PC/PB were transiently increased in both PBMC and bone marrow following gp120 boosting of the unvaccinated and vaccinated macaque groups. Similarly, ASC numbers in PBMC and bone marrow of the two macaque groups also transiently increased following envelope boosting. Nevertheless, serum binding titers against SIVgp120 remained unchanged. Thus, even during chronic SIV infection, B cells respond to antigen, but long-term memory does not develop, perhaps due to germinal center destruction. Earlier and/or prolonged treatment to allow the generation of virus-specific long-term memory B cells should benefit ART/therapeutic vaccination regimens.

Accurate measurement of peripheral blood mononuclear cell concentration using image cytometry to eliminate RBC-induced counting error

Peripheral blood mononuclear cells (PBMCs) have been widely researched in the fields of immunology, infectious disease, oncology, transplantation, hematological malignancy, and vaccine development. Specifically, in immunology research, PBMCs have been utilized to monitor concentration, viability, proliferation, and cytokine production from immune cells, which are critical for both clinical trials and biomedical research. The viability and concentration of isolated PBMCs are traditionally measured by manual counting with trypan blue (TB) using a hemacytometer. One of the common issues of PBMC isolation is red blood cell (RBC) contamination. The RBC contamination can be dependent on the donor sample and/or technical skill level of the operator. RBC contamination in a PBMC sample can introduce error to the measured concentration, which can pass down to future experimental assays performed on these cells. To resolve this issue, RBC lysing protocol can be used to eliminate potential error caused by RBC contamination. In the recent years, a rapid fluorescence-based image cytometry system has been utilized for bright-field and fluorescence imaging analysis of cellular characteristics (Nexcelom Bioscience LLC, Lawrence, MA). The Cellometer image cytometry system has demonstrated the capability of automated concentration and viability detection in disposable counting chambers of unpurified mouse splenocytes and PBMCs stained with acridine orange (AO) and propidium iodide (PI) under fluorescence detection. In this work, we demonstrate the ability of Cellometer image cytometry system to accurately measure PBMC concentration, despite RBC contamination, by comparison of five different total PBMC counting methods: (1) manual counting of trypan blue-stained PBMCs in hemacytometer, (2) manual counting of PBMCs in bright-field images, (3) manual counting of acetic acid lysing of RBCs with TB-stained PBMCs, (4) automated counting of acetic acid lysing of RBCs with PI-stained PBMCs, and (5) AO/PI dual staining method. The results show comparable total PBMC counting among all five methods, which validate the AO/PI staining method for PBMC measurement in the image cytometry method.

Antibodies with high avidity to the gp120 envelope protein in protection from simian immunodeficiency virus SIV(mac251) acquisition in an immunization regimen that mimics the RV-144 Thai trial

The recombinant canarypox vector, ALVAC-HIV, together with human immunodeficiency virus (HIV) gp120 envelope glycoprotein, has protected 31.2% of Thai individuals from HIV acquisition in the RV144 HIV vaccine trial. This outcome was unexpected, given the limited ability of the vaccine components to induce CD8(+) T-cell responses or broadly neutralizing antibodies. We vaccinated macaques with an immunization regimen intended to mimic the RV144 trial and exposed them intrarectally to a dose of the simian immunodeficiency virus SIV(mac251) that transmits few virus variants, similar to HIV transmission to humans. Vaccination induced anti-envelope antibodies in all vaccinees and CD4(+) and CD8(+) T-cell responses. Three of the 11 macaques vaccinated with ALVAC-SIV/gp120 were protected from SIV(mac251) acquisition, but the result was not significant. The remaining vaccinees were infected and progressed to disease. The magnitudes of vaccine-induced SIV(mac251)-specific T-cell responses and binding antibodies were not significantly different between protected and infected animals. However, sera from protected animals had higher avidity antibodies to gp120, recognized the variable envelope regions V1/V2, and reduced SIV(mac251) infectivity in cells that express high levels of α(4)β(7) integrins, suggesting a functional role of antibodies to V2. The current results emphasize the utility of determining the titer of repeated mucosal challenge in the preclinical evaluation of HIV vaccines.

Understanding factors that modulate HIV infection at the female genital tract mucosae for the rationale design of microbicides

Women are now becoming the pivot of the epidemiological spread of HIV infection worldwide, especially in developing countries. Therefore, research to develop an efficient microbicide is now a priority for the prevention of HIV-1 acquisition in exposed women. However, recent disappointing failures in microbicide clinical trials revealed major gaps in basic and applied knowledge that hinder the development of effective microbicide formulations. Indeed, the inhibitory power of microbicide molecules may be affected by several physiological and immunological factors present in male and female genital tracts. Furthermore, mucosal crossing of HIV-1 to increase the ability to reach the submucosal target cells (macrophages, lymphocytes, and dendritic cells) may be modulated by supraepithelial factors such as seminal complement components (opsonized HIV-1), by epithelial factors released in the submucosal microenvironment such as antimicrobial soluble factors, cytokines, and chemokines, and by potent intraepithelial and submucosal innate immunity. The design of vaginal microbicide formulations should take into account an understanding of the intimate mechanisms involved in the crossing of HIV through the female genital mucosae, in the context of a mixture of both male and female genital fluids.

Antibody-dependent cellular cytotoxicity-mediating antibodies from an HIV-1 vaccine efficacy trial target multiple epitopes and preferentially use the VH1 gene family

The ALVAC-HIV/AIDSVAX-B/E RV144 vaccine trial showed an estimated efficacy of 31%. RV144 secondary immune correlate analysis demonstrated that the combination of low plasma anti-HIV-1 Env IgA antibodies and high levels of antibody-dependent cellular cytotoxicity (ADCC) inversely correlate with infection risk. One hypothesis is that the observed protection in RV144 is partially due to ADCC-mediating antibodies. We found that the majority (73 to 90%) of a representative group of vaccinees displayed plasma ADCC activity, usually (96.2%) blocked by competition with the C1 region-specific A32 Fab fragment. Using memory B-cell cultures and antigen-specific B-cell sorting, we isolated 23 ADCC-mediating nonclonally related antibodies from 6 vaccine recipients. These antibodies targeted A32-blockable conformational epitopes (n = 19), a non-A32-blockable conformational epitope (n = 1), and the gp120 Env variable loops (n = 3). Fourteen antibodies mediated cross-clade target cell killing. ADCC-mediating antibodies displayed modest levels of V-heavy (VH) chain somatic mutation (0.5 to 1.5%) and also displayed a disproportionate usage of VH1 family genes (74%), a phenomenon recently described for CD4-binding site broadly neutralizing antibodies (bNAbs). Maximal ADCC activity of VH1 antibodies correlated with mutation frequency. The polyclonality and low mutation frequency of these VH1 antibodies reveal fundamental differences in the regulation and maturation of these ADCC-mediating responses compared to VH1 bNAbs.

Influence of cytokines on HIV-specific antibody-dependent cellular cytotoxicity activation profile of natural killer cells

There is growing interest in HIV-specific antibody-dependent cellular cytotoxicity (ADCC) as an effective immune response to prevent or control HIV infection. ADCC relies on innate immune effector cells, particularly NK cells, to mediate control of virus-infected cells. The activation of NK cells (i.e., expression of cytokines and/or degranulation) by ADCC antibodies in serum is likely subject to the influence of other factors that are also present. We observed that the HIV-specific ADCC antibodies, within serum samples from a panel of HIV-infected individuals induced divergent activation profiles of NK cells from the same donor. Some serum samples primarily induced NK cell cytokine expression (i.e., IFNγ), some primarily initiated NK cell expression of a degranulation marker (CD107a) and others initiated a similar magnitude of responses across both effector functions. We therefore evaluated a number of HIV-relevant soluble factors for their influence on the activation of NK cells by HIV-specific ADCC antibodies. Key findings were that the cytokines IL-15 and IL-10 consistently enhanced the ability of NK cells to respond to HIV-specific ADCC antibodies. Furthermore, IL-15 was demonstrated to potently activate “educated” KIR3DL1⁺ NK cells from individuals carrying its HLA-Bw4 ligand. The cytokine was also demonstrated to activate “uneducated” KIR3DL1⁺ NK cells from HLA-Bw6 homozygotes, but to a lesser extent. Our results show that cytokines influence the ability of NK cells to respond to ADCC antibodies in vitro. Manipulating the immunological environment to enhance the potency of NK cell-mediated HIV-specific ADCC effector functions could be a promising immunotherapy or vaccine strategy.

Replicating adenovirus-simian immunodeficiency virus (SIV) vectors efficiently prime SIV-specific systemic and mucosal immune responses by targeting myeloid dendritic cells and persisting in rectal macrophages, regardless of immunization route

Although priming with replicating adenovirus type 5 host range mutant (Ad5hr)-human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) recombinants, followed by HIV/SIV envelope boosting, has proven highly immunogenic, resulting in protection from SIV/simian-human immunodeficiency virus (SHIV) challenges, Ad5hr recombinant distribution, replication, and persistence have not been examined comprehensively in nonhuman primates. We utilized Ad5hr-green fluorescent protein and Ad5hr-SIV recombinants to track biodistribution and immunogenicity following mucosal priming of rhesus macaques by the intranasal/intratracheal, sublingual, vaginal, or rectal route. Ad recombinants administered by all routes initially targeted macrophages in bronchoalveolar lavage (BAL) fluid and rectal tissue, later extending to myeloid dendritic cells in BAL fluid with persistent expression in rectal mucosa 25 weeks after the last Ad immunization. Comparable SIV-specific immunity, including cellular responses, serum binding antibody, and mucosal secretory IgA, was elicited among all groups. The ability of the vector to replicate in multiple mucosal sites irrespective of delivery route, together with the targeting of macrophages and professional antigen-presenting cells, which provide potent immunogenicity at localized sites of virus entry, warrants continued use of replicating Ad vectors.

Replicating adenovirus-simian immunodeficiency virus (SIV) recombinant priming and envelope protein boosting elicits localized, mucosal IgA immunity in rhesus macaques correlated with delayed acquisition following a repeated low-dose rectal SIV(mac251) challenge

We have shown that sequential replicating adenovirus type 5 host range mutant human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) recombinant priming delivered first intranasally (i.n.) plus orally and then intratracheally (i.t.), followed by envelope protein boosting, elicits broad cellular immunity and functional, envelope-specific serum and mucosal antibodies that correlate with protection from high-dose SIV and simian/human immunodeficiency virus (SHIV) challenges in rhesus macaques. Here we extended these studies to compare the standard i.n./i.t. regimen with additional mucosal administration routes, including sublingual, rectal, and vaginal routes. Similar systemic cellular and humoral immunity was elicited by all immunization routes. Central and effector memory T cell responses were also elicited by the four immunization routes in bronchoalveolar lavage fluid and jejunal, rectal, and vaginal tissue samples. Cellular responses in vaginal tissue were more compartmentalized, being induced primarily by intravaginal administration. In contrast, all immunization routes elicited secretory IgA (sIgA) responses at multiple mucosal sites. Following a repeated low-dose intrarectal (i.r.) challenge with SIV(mac251) at a dose transmitting one or two variants, protection against acquisition was not achieved except in one macaque in the i.r. immunized group. All immunized macaques exhibited reduced peak viremia compared to that of controls, correlated inversely with prechallenge serum antienvelope avidity, antibody-dependent cellular cytotoxicity (ADCC) titers, and percent antibody-dependent cell-mediated viral inhibition. Both antibody avidity and ADCC titers were correlated with the number of exposures required for infection. Notably, we show for the first time a significant correlation of vaccine-induced sIgA titers in rectal secretions with delayed acquisition. Further investigation of the characteristics and properties of the sIgA should elucidate the mechanism leading to this protective effect.

HIV infection abrogates the functional advantage of natural killer cells educated through KIR3DL1/HLA-Bw4 interactions to mediate anti-HIV antibody-dependent cellular cytotoxicity

Combinations of KIR3DL1 and HLA-Bw4 alleles protect against HIV infection and/or disease progression. These combinations enhance NK cell responsiveness through the ontological process of education. However, educated KIR3DL1(+) NK cells do not have enhanced degranulation upon direct recognition of autologous HIV-infected cells. Since antibody-dependent cellular cytotoxicity (ADCC) is associated with improved HIV infection outcomes and NK cells overcome inhibition through killer cell immunoglobulin-like receptors (KIR) to mediate ADCC, we hypothesized that KIR3DL1-educated NK cells mediate anti-HIV ADCC against autologous cells. A whole-blood flow cytometry assay was used to evaluate ADCC-induced activation of NK cells. This assay assessed activation (gamma interferon [IFN-γ] production and/or CD107a expression) of KIR3DL1(+) and KIR3DL1(-) NK cells, from HLA-Bw4(+) and HLA-Bw4(-) HIV-positive and HIV-negative individuals, in response to autologous HIV-specific ADCC targets. KIR3DL1(+) NK cells were more functional than KIR3DL1(-) NK cells from HLA-Bw4(+), but not HLA-Bw4(-), healthy controls. In HIV-infected individuals, no differences in NK cell functionality were observed between KIR3DL1(+) and KIR3DL1(-) NK cells in HLA-Bw4(+) individuals, consistent with dysfunction of NK cells in the setting of HIV infection. Reflecting the partial normalization of NK cell responsiveness following initiation of antiretroviral therapy, a significant correlation was observed between the peripheral CD4(+) T-lymphocyte counts in antiretroviral therapy-treated subjects and the functionality of NK cells. However, peripheral CD4(+) T-lymphocyte counts were not correlated with an anti-HIV ADCC functional advantage in educated KIR3DL1(+) NK cells. The abrogation of the functional advantage of educated NK cells may enhance HIV disease progression. Strategies to enhance the potency of NK cell-mediated ADCC may improve HIV therapies and vaccines.

Role of IL-21 and IL-21 receptor on B cells in HIV infection

Interleukin (IL)-21 is a member of a family of cytokines that includes IL-2, IL-4, IL-7, IL-9, and IL-15, all of which utilize a common γ chain in their individual receptor complexes for delivering intracellular signals in their target cells. IL-21 is produced by CD4+ T-cells, in particular follicular T-helper cells, and is critically important in the regulation and maintenance of T cells and B cells in innate and adaptive immunity. The effects of IL-21 are pleiotropic because of the broad cellular distribution of the IL-21 receptor, and it plays a critical role in T cell-dependent and -independent human B cell differentiation for generating humoral immune responses. This article reviews the current knowledge about the importance of IL-21 and IL-21 receptor interaction in human B cell responses, immune defects of B cells and IL-21 in HIV infection, and the potential applicability of IL-21 in vaccines/immunotherapeutic approaches to augment relevant immune responses.

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.