A low dose of RBD and TLR7/8 agonist displayed on influenza virosome particles protects rhesus macaque against SARS-CoV-2 challenge

Influenza virosomes serve as antigen delivery vehicles and pre-existing immunity toward influenza improves the immune responses toward antigens. Here, vaccine efficacy was evaluated in non-human primates with a COVID-19 virosome-based vaccine containing a low dose of RBD protein (15 µg) and the adjuvant 3M-052 (1 µg), displayed together on virosomes. Vaccinated animals (n = 6) received two intramuscular administrations at week 0 and 4 and challenged with SARS-CoV-2 at week 8, together with unvaccinated control animals (n = 4). The vaccine was safe and well tolerated and serum RBD IgG antibodies were induced in all animals and in the nasal washes and bronchoalveolar lavages in the three youngest animals. All control animals became strongly sgRNA positive in BAL, while all vaccinated animals were protected, although the oldest vaccinated animal (V1) was transiently weakly positive. The three youngest animals had also no detectable sgRNA in nasal wash and throat. Cross-strain serum neutralizing antibodies toward Wuhan-like, Alpha, Beta, and Delta viruses were observed in animals with the highest serum titers. Pro-inflammatory cytokines IL-8, CXCL-10 and IL-6 were increased in BALs of infected control animals but not in vaccinated animals. Virosomes-RBD/3M-052 prevented severe SARS-CoV-2, as shown by a lower total lung inflammatory pathology score than control animals.

Primary antibody response after influenza virus infection is first dominated by low-mutated HA-stem antibodies followed by higher-mutated HA-head antibodies

Several studies have shown that the first encounter with influenza virus shapes the immune response to future infections or vaccinations. However, a detailed analysis of the primary antibody response is lacking as this is difficult to study in humans. It is therefore not known what the frequency and dynamics of the strain-specific hemagglutinin (HA) head- and stem-directed antibody responses are directly after primary influenza virus infection. Here, sera of twelve H1N1pdm2009 influenza virus-infected cynomolgus macaques were evaluated for HA-head and HA-stem domain antibody responses. We observed an early induction of HA-stem antibody responses, which was already decreased by day 56. In contrast, responses against the HA-head domain were low early after infection and increased at later timepoint. The HA-specific B cell repertoires in each animal showed diverse VH-gene usage with preferred VH-gene and JH-gene family usage for HA-head or HA-stem B cells but a highly diverse allelic variation within the VH-usage. HA-head B cells had shorter CDRH3s and higher VH-gene somatic hyper mutation levels relative to HA-stem B cells. In conclusion, our data suggest that HA-stem antibodies are the first to react to the infection while HA-head antibodies show a delayed response, but a greater propensity to enter the germinal center and undergo affinity maturation.

A Capsid Virus-Like Particle-Based SARS-CoV-2 Vaccine Induces High Levels of Antibodies and Protects Rhesus Macaques

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a worldwide pandemic. Here, we present non-human primate immunogenicity and protective efficacy data generated with the capsid virus-like particle (cVLP)-based vaccine ABNCoV2 that has previously demonstrated immunogenicity in mice. In rhesus macaques, a single vaccination with either 15 or 100 μg ABNCoV2 induced binding and neutralizing antibodies in a dose-dependent manner, at levels comparable to those measured in human convalescents. A second vaccine administration led to a >50-fold increase in neutralizing antibodies, with 2-log higher mean levels in the 100-μg ABNCoV2 group compared with convalescent samples. Upon SARS-CoV-2 challenge, a significant reduction in viral load was observed for both vaccine groups relative to the challenge control group, with no evidence of enhanced disease. Remarkably, neutralizing antibody titers against an original SARS-CoV-2 isolate and against variants of concern were comparable, indicating a potential for broad protection afforded by ABNCoV2, which is currently in clinical testing.

Poxvirus MVA Expressing SARS-CoV-2 S Protein Induces Robust Immunity and Protects Rhesus Macaques From SARS-CoV-2

Novel safe, immunogenic, and effective vaccines are needed to control the COVID-19 pandemic, caused by SARS-CoV-2. Here, we describe the safety, robust immunogenicity, and potent efficacy elicited in rhesus macaques by a modified vaccinia virus Ankara (MVA) vector expressing a full-length SARS-CoV-2 spike (S) protein (MVA-S). MVA-S vaccination was well tolerated and induced S and receptor-binding domain (RBD)-binding IgG antibodies and neutralizing antibodies against SARS-CoV-2 and several variants of concern. S-specific IFNγ, but not IL-4, -producing cells were also elicited. After SARS-CoV-2 challenge, vaccinated animals showed a significant strong reduction of virus loads in bronchoalveolar lavages (BAL) and decreased levels in throat and nasal mucosa. Remarkably, MVA-S also protected macaques from fever and infection-induced cytokine storm. Computed tomography and histological examination of the lungs showed reduced lung pathology in MVA-S-vaccinated animals. These findings favor the use of MVA-S as a potential vaccine for SARS-CoV-2 in clinical trials.

Aerosolized Exposure to H5N1 Influenza Virus Causes Less Severe Disease Than Infection via Combined Intrabronchial, Oral, and Nasal Inoculation in Cynomolgus Macaques

Infection with highly pathogenic avian H5N1 influenza virus in humans often leads to severe respiratory disease with high mortality. Experimental infection in non-human primates can provide additional insight into disease pathogenesis. However, such a model should recapitulate the disease symptoms observed in humans, such as pneumonia and inflammatory cytokine response. While previous studies in macaques have demonstrated the occurrence of typical lesions in the lungs early after infection and a high level of immune activation, progression to severe disease and lethality were rarely observed. Here, we evaluated a routinely used combined route of infection via intra-bronchial, oral, and intra-nasal virus inoculation with aerosolized H5N1 exposure, with or without the regular collection of bronchoalveolar lavages early after infection. Both combined route and aerosol exposure resulted in similar levels of virus replication in nose and throat and similar levels of immune activation, cytokine, and chemokine release in the blood. However, while animals exposed to H5N1 by combined-route inoculation developed severe disease with high lethality, aerosolized exposure resulted in less lesions, as measured by consecutive computed tomography and less fever and lethal disease. In conclusion, not virus levels or immune activation, but route of infection determines fatal outcome for highly pathogenic avian H5N1 influenza infection.

Aerosolized pH1N1 influenza infection induces less systemic and local immune activation in the lung than combined intrabronchial, nasal and oral exposure in cynomolgus macaques

Non-human primates form an important animal model for the evaluation of immunogenicity and efficacy of novel 'universal' vaccine candidates against influenza virus. However, in most studies a combination of intra-tracheal or intra-bronchial, oral and nasal virus inoculation is used with a standard virus dose of between 1 and 10 million tissue culture infective doses, which differs from typical modes of virus exposure in humans. This paper studies the systemic and local inflammatory and immune effects of aerosolized versus combined-route exposure to pandemic H1N1 influenza virus. In agreement with a previous study, both combined-route and aerosol exposure resulted in similar levels of virus replication in nose, throat and lung lavages. However, the acute release of pro-inflammatory cytokines and chemokines, acute monocyte activation in peripheral blood as well as increased cytokine production and T-cell proliferation in the lungs were only observed after combined-route infection and not after aerosol exposure. Longitudinal evaluation by computed tomography demonstrated persistence of lung lesions after resolution of the infection and a tendency for more lesions in the lower lung lobes after combined-route exposure versus upper and middle lung lobes after aerosol exposure. Computed tomography scores were observed to correlate with fever. In conclusion, influenza virus infection by aerosol exposure is accompanied by less immune-activation and inflammation in comparison with direct virus installation, despite similar levels of virus replication and development of lesions in the lungs.

Pandemic Swine-Origin H1N1 Influenza Virus Replicates to Higher Levels and Induces More Fever and Acute Inflammatory Cytokines in Cynomolgus versus Rhesus Monkeys and Can Replicate in Common Marmosets

The close immunological and physiological resemblance with humans makes non-human primates a valuable model for studying influenza virus pathogenesis and immunity and vaccine efficacy against infection. Although both cynomolgus and rhesus macaques are frequently used in influenza virus research, a direct comparison of susceptibility to infection and disease has not yet been performed. In the current study a head-to-head comparison was made between these species, by using a recently described swine-origin pandemic H1N1 strain, A/Mexico/InDRE4487/2009. In comparison to rhesus macaques, cynomolgus macaques developed significantly higher levels of virus replication in the upper airways and in the lungs, involving both peak level and duration of virus production, as well as higher increases in body temperature. In contrast, clinical symptoms, including respiratory distress, were more easily observed in rhesus macaques. Expression of sialyl-α-2,6-Gal saccharides, the main receptor for human influenza A viruses, was 50 to 73 times more abundant in trachea and bronchus of cynomolgus macaques relative to rhesus macaques. The study also shows that common marmosets, a New World non-human primate species, are susceptible to infection with pandemic H1N1. The study results favor the cynomolgus macaque as model for pandemic H1N1 influenza virus research because of the more uniform and high levels of virus replication, as well as temperature increases, which may be due to a more abundant expression of the main human influenza virus receptor in the trachea and bronchi.

Synthetic long peptide booster immunization in rhesus macaques primed with replication-competent NYVAC-C-KC induces a balanced CD4/CD8 T-cell and antibody response against the conserved regions of HIV-1

The Thai trial (RV144) indicates that a prime-boost vaccine combination that induces both T-cell and antibody responses may be desirable for an effective HIV vaccine. We have previously shown that immunization with synthetic long peptides (SLP), covering the conserved parts of SIV, induced strong CD4 T-cell and antibody responses, but only modest CD8 T-cell responses. To generate a more balanced CD4/CD8 T-cell and antibody response, this study evaluated a pox-vector prime/SLP boost strategy in rhesus macaques. Priming with a replication-competent NYVAC, encoding HIV-1 clade C gag, pol and nef, induced modest IFNγ T-cell immune responses, predominantly directed against HIV-1 Gag. Booster immunization with SLP, covering the conserved parts of HIV-1 Gag, Pol and Env, resulted in a more than 10-fold increase in IFNγ ELISpot responses in four of six animals, which were predominantly HIV-1 Pol-specific. The animals showed a balanced polyfunctional CD4 and CD8 T-cell response and high Ab titres.

Whole blood stimulation with Toll-like receptor (TLR)-7/8 and TLR-9 agonists induces interleukin-12p40 expression in plasmacytoid dendritic cells in rhesus macaques but not in humans

Macaques provide important animal models in biomedical research into infectious and chronic inflammatory disease. Therefore, a proper understanding of the similarities and differences in immune function between macaques and humans is needed for adequate interpretation of the data and translation to the human situation. Dendritic cells are important as key regulators of innate and adaptive immune responses. Using a new whole blood assay we investigated functional characteristics of blood plasmacytoid dendritic cells (pDC), myeloid dendritic cells (mDC) and monocytes in rhesus macaques by studying induction of activation markers and cytokine expression upon Toll-like receptor (TLR) stimulation. In a head-to-head comparison we observed that rhesus macaque venous blood contained relatively lower numbers of pDC than human venous blood, while mDC and monocytes were present at similar percentages. In contrast to humans, pDC in rhesus macaques expressed the interleukin (IL)-12p40 subunit in response to TLR-7/8 as well as TLR-9 stimulation. Expression of IL-12p40 was confirmed by using different monoclonal antibodies and by reverse transcription-polymerase chain reaction (RT-PCR). Both in humans and rhesus macaques, TLR-4 stimulation induced IL-12p40 expression in mDC and monocytes, but not in pDC. The data show that, in contrast to humans, pDC in macaques are able to express IL-12p40, which could have consequences for evaluation of human vaccine candidates and viral infection.

In vitro neutralization of low dose inocula at physiological concentrations of a monoclonal antibody which protects macaques against SHIV challenge

BACKGROUND

Passive transfer of antibodies can be protective in the simian human immunodeficiency virus (SHIV)--rhesus macaque challenge model. The human monoclonal antibody IgG1 b12 neutralizes human immunodeficiency type 1 (HIV-1) in vitro and protects against challenge by SHIV. Our hypothesis is that neutralizing antibodies can only completely inactivate a relatively small number of infectious virus.

METHODS AND FINDINGS

We have used GHOST cell assays to quantify individual infectious events with HIV-1SF162 and its SHIV derivatives: the relatively neutralization sensitive SHIV(SF162P4) isolate and the more resistant SHIV(SF162P3). A plot of the number of fluorescent GHOST cells with increasing HIV-1SF162 dose is not linear. It is likely that with high-dose inocula, infection with multiple virus produces additive fluorescence in individual cells. In studies of the neutralization kinetics of IgG1 b12 against these isolates, events during the absorption phase of the assay, as well as the incubation phase, determine the level of neutralization. It is possible that complete inactivation of a virus is limited to the time it is exposed on the cell surface. Assays can be modified so that neutralization of these very low doses of virus can be quantified. A higher concentration of antibody is required to neutralize the same dose of resistant SHIV(SF162P3) than the sensitive SHIV(SF162P4). In the absence of selection during passage, the density of the CCR5 co-receptor on the GHOST cell surface is reduced. Changes in the CD4 : CCR5 density ratio influence neutralization.

CONCLUSIONS

Low concentrations of IgG1 b12 completely inactivate small doses of the neutralization resistant SHIV(SF162P3). Assays need to be modified to quantify this effect. Results from modified assays may predict protection following repeated low-dose shiv challenges in rhesus macaques. It should be possible to induce this level of antibody by vaccination so that modified assays could predict the outcome of human trials.

Protection in macaques immunized with HIV-1 candidate vaccines can be predicted using the kinetics of their neutralizing antibodies

BACKGROUND

A vaccine is needed to control the spread of human immunodeficiency virus type 1 (HIV-1). An in vitro assay that can predict the protection induced by a vaccine would facilitate the development of such a vaccine. A potential candidate would be an assay to quantify neutralization of HIV-1.

METHODS AND FINDINGS

We have used sera from rhesus macaques that have been immunized with HIV candidate vaccines and subsequently challenged with simian human immunodeficiency virus (SHIV). We compared neutralization assays with different formats. In experiments with the standardized and validated TZMbl assay, neutralizing antibody titers against homologous SHIV(SF162P4) pseudovirus gave a variable correlation with reductions in plasma viremia levels. The target cells used in the assays are not just passive indicators of virus infection but are actively involved in the neutralization process. When replicating virus was used with GHOST cell assays, events during the absorption phase, as well as the incubation phase, determine the level of neutralization. Sera that are associated with protection have properties that are closest to the traditional concept of neutralization: the concentration of antibody present during the absorption phase has no effect on the inactivation rate. In GHOST assays, events during the absorption phase may inactivate a fixed number, rather than a proportion, of virus so that while complete neutralization can be obtained, it can only be found at low doses particularly with isolates that are relatively resistant to neutralization.

CONCLUSIONS

Two scenarios have the potential to predict protection by neutralizing antibodies at concentrations that can be induced by vaccination: antibodies that have properties close to the traditional concept of neutralization may protect against a range of challenge doses of neutralization sensitive HIV isolates; a window of opportunity also exists for protection against isolates that are more resistant to neutralization but only at low challenge doses.

Herpesvirus saimiri infection of rhesus macaques: a model for acute rhadinovirus-induced t-cell transformation and oncogenesis

Herpesvirus saimiri (HVS) causes acute lymphoma and leukemia upon experimental infection of various monkey species. HVS strain C488 is also capable of transforming human T-lymphocytes to stable growth in culture. The most susceptible species for oncogenesis are New World primates, in particular the cottontop tamarin (Saguinus oedipus). However, Old World monkeys such as macaques are the most used animal model for the close-to-human situation. The limited data on HVS infection in Old World monkeys prompted us to investigate susceptibility to infection and disease induction by HVS in macaques. After having established that rhesus macaques can be infected productively, and that rhesus T-cells can be transformed in vivo by HVS, we observed induction of lymphoma in all inoculated animals. Pre-existing humoral immunity in part of the rhesus colony capable of blocking HVS infection could be overcome by preselecting rhesus macaques for lack of this immunity of unknown origin. HVS infection of rhesus macaques as compared to that of New World monkeys has the advantages that disease progression is more prolonged, and larger blood volumes can be collected, which allows more extended analyses. Also, rhesus monkeys are the best immunologically and immunogenetically characterized primate species next to humans. This model could be useful for the evaluation of candidate tumor vaccines and to test novel approaches for cancer immunotherapy. In addition, HVS infection of macaques could eventually be useful as a surrogate model to address certain questions in rhadinovirus-induced human cancer such as effusion lymphoma or Kaposi's sarcoma.

No difference in Gag and Env immune-response profiles between vaccinated and non-vaccinated rhesus macaques that control immunodeficiency virus replication

Recent advances in human immunodeficiency virus (HIV) vaccine design have resulted in induction of strong CD4 T-cell proliferative and polyfunctional cytokine responses, which are also characteristic for long-term non-progressing (LTNP) HIV-infected individuals. However, limited information is available on the persistence of these responses after infection. Results from studies in non-human primates indicate that vaccine-induced immune responses are partially maintained upon viral infection and differ from the responses seen in non-vaccinated animals that typically progress to disease. However, it is unclear how these partially preserved responses compare to immune responses that are acquired naturally by LTNP animals. In this study, immune-response profiles were compared between vaccinated animals that, upon SHIV₈₉.₆ challenge, became infected but were able to control virus replication, and a group of animals having spontaneous control of this viral infection. Both groups were found to develop very similar immune responses with regard to induction of CD4 and CD8 T-cell polyfunctional cytokine responses, proliferative capacity and cytotoxic capacity, as measured by a standard ₅₁Cr release assay and more direct ex vivo and in vivo CTL assays. Hence, vaccinated animals that become infected, but control infection, appear to establish immune responses that are similar to those elicited by long-term non-progressors.

Systemic neutralizing antibodies induced by long interval mucosally primed systemically boosted immunization correlate with protection from mucosal SHIV challenge

Immune correlates of vaccine protection from HIV-1 infection would provide important milestones to guide HIV-1 vaccine development. In a proof of concept study using mucosal priming and systemic boosting, the titer of neutralizing antibodies in sera was found to correlate with protection of mucosally exposed rhesus macaques from SHIV infection. Mucosal priming consisted of two sequential immunizations at 12-week intervals with replicating host range mutants of adenovirus type 5 (Ad5hr) expressing the HIV-1(89.6p) env gene. Following boosting with either heterologous recombinant protein or alphavirus replicons at 12-week intervals animals were intrarectally exposed to infectious doses of the CCR5 tropic SHIV(SF162p4). Heterologous mucosal prime systemic boost immunization elicited neutralizing antibodies (Nabs), antibody-dependent cytotoxicity (ADCC), and specific patterns of antibody binding to envelope peptides. Vaccine induced protection did not correlate with the type of boost nor T-cell responses, but rather with the Nab titer prior to exposure.

Comparison of intranasal with targeted lymph node immunization using PR8-Flu ISCOM adjuvanted HIV antigens in macaques

The rapidly spreading HIV epidemic requires a vaccine that elicits potent mucosal immunity to halt or slow transmission. Induction of these responses will depend on the use of appropriate adjuvants and targeting of the mucosal immune system. Previously, immune stimulating complexes (ISCOM) have shown great potency as adjuvant in the induction of mucosal responses in mice and systemic responses in non-human primates. In this study, HIV formulated in PR8-Flu ISCOM adjuvant was applied to immunize rhesus macaques against HIV; targeting the mucosa either via intranasal (IN) application or via targeted lymph node immunization (TLNI). While, strong systemic, HIV specific, cytokine, lymphoproliferative, and antibody responses were induced via the TLNI route, the IN application generated only low responses. Furthermore, all four animals immunized via TLNI developed vaginal IgA antibodies against gp120. In conclusion, in contrast to what has been demonstrated in mice, the IN application of PR8-Flu ISCOM did not induce strong immune responses in rhesus macaques unlike those immunized by the TLNI route.

Experimental norovirus infections in non-human primates

Noroviruses, with Norwalk virus as the prototype strain, are the most common cause of viral gastroenteritis in people of all ages. Limited information on the immunology of Norovirus infections has been obtained by studies both in the natural setting and in experimentally infected volunteers. Interpretation of these studies is difficult due to the lack of information on the history of Norovirus exposure and the cross-reactivity of antibodies. An animal model for Norovirus infections would be important to study the immune response, e.g., for vaccine assessment. In the present study the susceptibility of common marmosets, cotton top tamarins, cynomolgus, and rhesus macaques to Norovirus infection was tested. Following oral inoculation, low level replication may have occurred in common marmosets and cotton top tamarins but not in cynomolgus macaques, based on short-term viral shedding; neither clinical symptoms nor antibody responses were observed in these species. In contrast, rhesus macaques were found susceptible to Norwalk virus infection as one animal shed virus for a longer period of time and developed Norwalk virus specific IgM and IgG responses. Further research on Norovirus susceptibility in rhesus macaques may yield an animal model to study the immune response and pathogenesis after Norovirus infection.

CCR5 targeted SIV vaccination strategy preventing or inhibiting SIV infection

Cell-surface CCR5 is a major coreceptor with CD4 glycoprotein, mediating cellular entry of CCR5 strains of HIV-1 or SIV. We targeted the SIV CCR5 coreceptor in a combined CCR5-SIV antigen immunization strategy. Rhesus macaques were immunized i.m. with the 70 kDa heat shock protein (HSP70) covalently linked to the CCR5 peptides, SIV gpl20 and p27. Intravenous challenge with SIV mac 8980 prevented SIV infection or decreased the viral load with the CCR5-SIV combined vaccine. CC chemokines and antibodies which block and downmodulateCCR5 were induced, as well as immune responses to the subunit SIV antigens. This novel vaccination strategy complements cognate immunity to SIV with innate immunity to the CCR5 coreceptor of SIV.

Qualitative T-helper responses to multiple viral antigens correlate with vaccine-induced immunity to simian/human immunodeficiency virus infection

Evidence is accumulating that CD4(+) T-helper (Th) responses play a critical role in facilitating effector responses which are capable of controlling and even preventing human immunodeficiency virus (HIV) infection. The present work was undertaken to determine whether immunization with multiple antigens influenced individual Th responses and increased protection relative to a single antigen. Rhesus macaques were primed with DNA and boosted (immune-stimulating complex-formulated protein) with a combination of regulatory and structural antigens (Tat-Env-Gag) or with Tat alone. Immunization with combined antigens reduced the magnitude of the responses to Tat compared to the single-antigen immunization. Interestingly, the Th immune responses to the individual antigens were noticeably different. To determine whether the qualitative differences in vaccine-induced Th responses correlated with vaccine efficacy, animals were challenged intravenously with simian/human immunodeficiency virus (strain SHIV(89.6p)) 2 months following the final immunization. Animals that developed combined Th1- and Th2-like responses to Gag and Th2 dominant Env-specific responses were protected from disease progression. Interestingly, one animal that was completely protected from infection had the strongest IFN-gamma and interleukin-2 (IL-2) responses prior to challenge, in addition to very strong IL-4 responses to Gag and Env. In contrast, animals with only a marked vaccine-induced Tat-specific Th2 response (no IFN-gamma) were not protected from infection or disease. These data support the rationale that effective HIV vaccine-induced immunity requires a combination of potent Th1- and Th2-like responses best directed to multiple antigens.

A novel HIV-CCR5 receptor vaccine strategy in the control of mucosal SIV/HIV infection

OBJECTIVE

To develop a novel SIV-CCR5 receptor vaccine strategy that will protect macaques from SHIV infection by the vaginal mucosal route.

DESIGN

The rationale for this strategy is that humans who express the homozygous delta32 CCR5 mutation and the associated upregulation of CC chemokines, the down-modulation of cell-surface expression of CCR5 and antibodies to CCR5 are protected against HIV infection.

METHODS

A vaccine was prepared consisting of three extracellular peptides of CCR5, an N-terminal HIV gp120 fragment generated in transgenic plants and recombinant SIV p27. These were linked to the 70 000 Mr microbial heat shock protein (HSP70) carrier. The vaccine was administered (x3) either by the vaginal mucosal route or by targeting the proximity of the draining iliac lymph nodes.

RESULTS

Serum and vaginal fluid IgG and IgA antibodies, IL-2 and IFN-gamma-producing cells, and macrophage-inflammatory protein (MIP) 1beta and MIP-1alpha (CCL4 and CCL3) were significantly raised in immunized macaques (P = 0.01-0.05). Vaginal challenge with SHIV(89.6P) infected all macaques, but sequential analysis over 24 weeks showed a significant variation in viral loads between the animals (P = 0.05). Whereas SHIV(89.6P) persisted in the four unimmunized macaques, in five of the eight immunized macaques the virus was cleared or became undetectable by reverse transcriptase-polymerase chain reaction. The CD4 cell counts in the immunized macaques were significantly higher than those in unimmunized animals (P < 0.05).

CONCLUSION

An immunization strategy that targets both the virus and its CCR5 receptor has significantly inhibited SHIV(89.6P) infection and may serve as a novel strategy in the prevention of HIV transmission.

Stimulation of both humoral and cellular immune responses to HIV-1 gp120 by interleukin-12 in Rhesus macaques

The adjuvant effect of recombinant Rhesus macaque interleukin-12 (RhIL-12) on the induction of cellular and humoral immune responses elicited by the HIV-1 subunit vaccine protein gp120 in Rhesus macaques was examined. RhIL-12 in conjunction with gp120 was given at day 0, 28 and 84 intramuscularly. Coadministration resulted in an approximate 10-fold increase in plasma anti-gp120 antibody levels as compared to levels generated in control monkeys receiving gp120 alone. Potentiation of the humoral arm of the immune response was evident by both ELISA and an antiviral bioassay. In addition, RhIL-12 was found to produce a significant increase in gp120-specific proliferative responses and in the frequency of antigen-specific IFN-gamma and IL-2 producing T cells after restimulation of PBMC with gp120 in vitro indicating that RhIL-12 potentiates cell-mediated immune responses as well. A critical finding was that during the course of the study, RhIL-12 did not induce a neutralizing antibody response to the administered cytokine. The doses of RhIL-12 were well tolerated and no detectable adverse side-effects on hematopoietic and hepatic parameters were noted. The data revealed that IL-12, when coadministered intramuscularly, acts as a potent adjuvant which is able to enhance not only cellular but also humoral immune responses to gp120 in non-human primates and may have to be considered in future HIV vaccine strategies.