Preexisting vs. de novo antibodies against SARS-CoV-2 in individuals without or with virus infection: impact on antibody therapy, vaccine research and serological testing.

The causative agent of the ongoing pandemic in the world is SARS-CoV-2. The research on SARS-CoV-2 has progressed with lightning speed on various fronts, including clinical research and treatment, virology, epidemiology, drug development, and vaccine research. Recent studies reported that sera from healthy individuals, who were confirmed negative for SARS-CoV-2 by RT-PCR method, tested positive for antibodies against spike and nucleocapsid proteins of SARS-CoV-2. Further, such antibodies also exhibited neutralizing activity against the virus. These observations have prompted us to prepare a commentary on this topic. While the preexisting antibodies are likely to protect against SARS-CoV-2 infection, they may also complicate serological testing results. Another unknown is the influence of preexisting antibodies on immune responses in individuals receiving vaccines against  SARS-CoV-2. The commentary identifies the potential limitations with the serological tests based on spike and nucleocapsid proteins as these tests may overestimate the seroprevalence due to cross-reactive antibodies. The inclusion of tests specific to SARS-CoV-2 (such as RBD of spike protein) could overcome these limitations.

Landscape of humoral immune responses against SARS-CoV-2 in patients with COVID-19 disease and the value of antibody testing.

A new pandemic is ongoing in several parts of the world. The agent responsible is the newly emerged severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The symptoms associated with this virus are known as the coronavirus disease-2019 (COVID-19). In this review, we summarize the published data on virus specific antibodies in hospitalized patients with COVID-19 disease, patients recovered from the disease and the individuals who are asymptomatic with SARS-CoV-2 infections. The review highlights the following: i) an adjunct role of antibody tests in the diagnosis of COVID-19 in combination with RT-PCR; ii) status of antibodies from COVID-19 convalescent patients to select donors for plasma therapy; iii) the potential confounding effects of other coronaviruses, measles, mumps and rubella in antibody testing due to homology of certain viral genes; and iv) the role of antibody testing for conducting surveillance in populations, incidence estimation, contact tracing and epidemiologic studies.

DNA prime/protein boost vaccination elicits robust humoral response in rhesus macaques using oligomeric simian immunodeficiency virus envelope and Advax delta inulin adjuvant.

The partial success of the RV144 trial underscores the importance of envelope-specific antibody responses for an effective HIV-1 vaccine. Oligomeric HIV-1 envelope proteins delivered with a potent adjuvant are expected to elicit strong antibody responses with broad neutralization specificity. To test this hypothesis, two SIV envelope proteins were formulated with delta inulin-based adjuvant (Advax) and used to immunize nonhuman primates. Oligomeric gp140-gp145 from SIVmac251 and SIVsmE660 was purified to homogeneity. Oligomers showed high-affinity interaction with CD4 and were highly immunogenic in rabbits, inducing Tier 2 SIV-neutralizing antibodies. The immunogenicity of an oligomeric Env DNA prime and protein boost together with Advax was evaluated in Chinese rhesus macaques. DNA administration elicited antibodies to both envelopes, and titres were markedly enhanced following homologous protein boosts via intranasal and intramuscular routes. Strong antibody responses were detected against the V1 and V2 domains of gp120. During peak immune responses, a low to moderate level of neutralizing activity was detected against Tier 1A/1B SIV isolates, with a moderate level noted against a Tier 2 isolate. Increased serum antibody affinity to SIVmac251 gp140 and generation of Env-specific memory B cells were observed in the immunized macaques. Animals were subjected to low-dose intravaginal challenge with SIVmac251 one week after the last protein boost. One out of three immunized animals was protected from infection. Although performed with a small number of macaques, this study demonstrates the utility of oligomeric envelopes formulated with Advax in eliciting broad antibody responses with the potential to provide protection against SIV transmission.

Adjuvant-dependent innate and adaptive immune signatures of risk of SIVmac251 acquisition.

A recombinant vaccine containing Aventis Pasteur's canarypox vector (ALVAC)-HIV and gp120 alum decreased the risk of HIV acquisition in the RV144 vaccine trial. The substitution of alum with the more immunogenic MF59 adjuvant is under consideration for the next efficacy human trial. We found here that an ALVAC-simian immunodeficiency virus (SIV) and gp120 alum (ALVAC-SIV + gp120) equivalent vaccine, but not an ALVAC-SIV + gp120 MF59 vaccine, was efficacious in delaying the onset of SIVmac251 in rhesus macaques, despite the higher immunogenicity of the latter adjuvant. Vaccine efficacy was associated with alum-induced, but not with MF59-induced, envelope (Env)-dependent mucosal innate lymphoid cells (ILCs) that produce interleukin (IL)-17, as well as with mucosal IgG to the gp120 variable region 2 (V2) and the expression of 12 genes, ten of which are part of the RAS pathway. The association between RAS activation and vaccine efficacy was also observed in an independent efficacious SIV-vaccine approach. Whether RAS activation, mucosal ILCs and antibodies to V2 are also important hallmarks of HIV-vaccine efficacy in humans will require further studies.

Characterization of protective immune response elicited by a trimeric envelope protein from an Indian clade C HIV-1 isolate in rhesus macaques.

BACKGROUND: Recent preclinical studies have demonstrated the use of properly folded trimeric HIV-1 envelope proteins as immunogen for eliciting protecting immune response in macaques. METHODS: Trimeric gp145 protein of Indian clade C HIV-1 (93IN101) was characterized for antigenicity by evaluating its binding to sCD4, and several monoclonal antibodies to HIV-1 by bio-layer interferometry. Ten macaques were immunized four times with purified gp145 in adjuplex adjuvant, and serum antibodies were characterized for binding to gp145 and neutralization. Immunized macaques were subjected to weekly low-dose vaginal challenge with SHIV1157-ipEL-p for 8 weeks. RESULTS: Env protein elicited strong antibody response in macaques. Following challenge, seven of ten immunized macaques resisted challenge, while six of eight control animals were infected. CONCLUSIONS: Env proteins from a clade C Indian isolate can elicit protective immune response and therefore may be a candidate for inclusion in a multiclade-based HIV-1 vaccine.

Comparable Antigenicity and Immunogenicity of Oligomeric Forms of a Novel, Acute HIV-1 Subtype C gp145 Envelope for Use in Preclinical and Clinical Vaccine Research.

UNLABELLED: Eliciting broadly reactive functional antibodies remains a challenge in human immunodeficiency virus type 1 (HIV-1) vaccine development that is complicated by variations in envelope (Env) subtype and structure. The majority of new global HIV-1 infections are subtype C, and novel antigenic properties have been described for subtype C Env proteins. Thus, an HIV-1 subtype C Env protein (CO6980v0c22) from an infected person in the acute phase (Fiebig stage I/II) was developed as a research reagent and candidate immunogen. The gp145 envelope is a novel immunogen with a fully intact membrane-proximal external region (MPER), extended by a polylysine tail. Soluble gp145 was enriched for trimers that yielded the expected "fan blade" motifs when visualized by cryoelectron microscopy. CO6980v0c22 gp145 reacts with the 4E10, PG9, PG16, and VRC01 HIV-1 neutralizing monoclonal antibodies (MAbs), as well as the V1/V2-specific PGT121, 697, 2158, and 2297 MAbs. Different gp145 oligomers were tested for immunogenicity in rabbits, and purified dimers, trimers, and larger multimers elicited similar levels of cross-subtype binding and neutralizing antibodies to tier 1 and some tier 2 viruses. Immunized rabbit sera did not neutralize the highly resistant CO6980v0c22 pseudovirus but did inhibit the homologous infectious molecular clone in a peripheral blood mononuclear cell (PBMC) assay. This Env is currently in good manufacturing practice (GMP) production to be made available for use as a clinical research tool and further evaluation as a candidate vaccine. IMPORTANCE: At present, the product pipeline for HIV vaccines is insufficient and is limited by inadequate capacity to produce large quantities of vaccine to standards required for human clinical trials. Such products are required to evaluate critical questions of vaccine formulation, route, dosing, and schedule, as well as to establish vaccine efficacy. The gp145 Env protein presented in this study forms physical trimers, binds to many of the well-characterized broad neutralizing MAbs that target conserved Env epitopes, and induce cross-subtype neutralizing antibodies as measured in both cell line and primary cell assays. This subtype C Env gp145 protein is currently undergoing good manufacturing practice production for use as a reagent for preclinical studies and for human clinical research. This product will serve as a reagent for comparative studies and may represent a next-generation candidate HIV immunogen.

Antigenicity and immunogenicity of a trimeric envelope protein from an Indian clade C HIV-1 isolate.

Human immunodeficiency virus type 1 (HIV-1) isolates from India mainly belong to clade C and are quite distinct from clade C isolates from Africa in terms of their phylogenetic makeup, serotype, and sensitivity to known human broadly neutralizing monoclonal antibodies. Because many of these properties are associated with the envelope proteins of HIV-1, it is of interest to study the envelope proteins of Indian clade C isolates as part of the ongoing efforts to develop a vaccine against HIV-1. To this end, we purified trimeric uncleaved gp145 of a CCR5 tropic Indian clade C HIV-1 (93IN101) from the conditioned medium of 293 cells. The purified protein was shown to be properly folded with stable structure by circular dichroism. Conformational integrity was further demonstrated by its high affinity binding to soluble CD4, CD4 binding site antibodies such as b12 and VRC01, quaternary epitope-specific antibody PG9, and CD4-induced epitope-specific antibody 17b. Sera from rabbits immunized with gp145 elicited high titer antibodies to various domains of gp120 and neutralized a broad spectrum of clade B and clade C HIV-1 isolates. Similar to other clade B and clade C envelope immunogens, most of the Tier 1 neutralizing activity could be absorbed with the V3-specific peptide. Subsequent boosting of these rabbits with a clade B HIV-1 Bal gp145 resulted in an expanded breadth of neutralization of HIV-1 isolates. The present study strongly supports the inclusion of envelopes from Indian isolates in a future mixture of HIV-1 vaccines.

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.

Construction and immunogenicity of replication-competent adenovirus 5 host range mutant recombinants expressing HIV-1 gp160 of SF162 and TV1 strains.

An HIV Env immunogen capable of eliciting broad immunity is critical for a successful vaccine. We constructed and characterized adenovirus 5 host range mutant (Ad5hr) recombinants encoding HIV(SF162) gp160 (subtype B) and HIV(TV1) gp160 (subtype C). Immunization of mice with one or both induced cellular immunity to subtype B and C peptides by ELISpot, and antibody responses with high binding titers to HIV Env of subtypes A, B, C, and E. Notably, Ad5hr-HIV(TV1) gp160 induced better cellular immunity than Ad5hr-HIV(SF162) gp160, either alone or following co-administration. Thus, the TV1 Env recombinant alone may be sufficient for eliciting immune responses against both subtype B and C envelopes. Further studies of Ad5hr-HIV(TV1) gp160 in rhesus macaques will evaluate the suitability of this insert for a future phase I clinical trial using a replication-competent Ad4 vector.

Correlation of vaccine-elicited systemic and mucosal nonneutralizing antibody activities with reduced acute viremia following intrarectal simian immunodeficiency virus SIVmac251 challenge of rhesus macaques.

Cell-mediated immunity and neutralizing antibodies contribute to control of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) infection, but the role of nonneutralizing antibodies is not defined. Previously, we reported that sequential oral/oral or intranasal/oral (I/O) priming with replication-competent adenovirus type 5 host range mutant (Ad5hr)-SIV recombinants, followed by intramuscular envelope protein boosting, elicited systemic and mucosal cellular immunity and exhibited equivalent, significant reductions of chronic viremia after rectal SIV(mac251) challenge. However, I/O priming gave significantly better control of acute viremia. Here, systemic and mucosal humoral immunity were investigated for potential correlates with the acute challenge outcome. Strong serum binding but nonneutralizing antibody responses against SIV(mac251) were induced in both groups. Antibody responses appeared earlier and overall were higher in the I/O group. Reduced acute viremia was significantly correlated with higher serum binding titer, stronger antibody-dependent cellular cytotoxicity activity, and peak prechallenge and 2-week-postchallenge antibody-dependent cell-mediated viral inhibition (ADCVI). The I/O group consistently displayed greater anti-envelope immunoglobulin A (IgA) antibody responses in bronchoalveolar lavage and a stronger rectal anti-envelope IgA anamnestic response 2 weeks postchallenge. Pre- and postchallenge rectal secretions inhibited SIV transcytosis across epithelial cells. The inhibition was significantly higher in the I/O group, although a significant correlation with reduced acute viremia was not reached. Overall, the replicating Ad5hr-SIV priming/envelope boosting approach elicited strong systemic and mucosal antibodies with multiple functional activities. The pattern of elevated immune responses in the I/O group is consistent with its better control of acute viremia mediated, at least in part, by ADCVI activity and transcytosis inhibition.

A comprehensive analysis of the naturally occurring polymorphisms in HIV-1 Vpr: potential impact on CTL epitopes.

The enormous genetic variability reported in HIV-1 has posed problems in the treatment of infected individuals. This is evident in the form of HIV-1 resistant to antiviral agents, neutralizing antibodies and cytotoxic T lymphocytes (CTLs) involving multiple viral gene products. Based on this, it has been suggested that a comprehensive analysis of the polymorphisms in HIV proteins is of value for understanding the virus transmission and pathogenesis as well as for the efforts towards developing anti-viral therapeutics and vaccines. This study, for the first time, describes an in-depth analysis of genetic variation in Vpr using information from global HIV-1 isolates involving a total of 976 Vpr sequences. The polymorphisms at the individual amino acid level were analyzed. The residues 9, 33, 39, and 47 showed a single variant amino acid compared to other residues. There are several amino acids which are highly polymorphic. The residues that show ten or more variant amino acids are 15, 16, 28, 36, 37, 48, 55, 58, 59, 77, 84, 86, 89, and 93. Further, the variant amino acids noted at residues 60, 61, 34, 71 and 72 are identical. Interestingly, the frequency of the variant amino acids was found to be low for most residues. Vpr is known to contain multiple CTL epitopes like protease, reverse transcriptase, Env, and Gag proteins of HIV-1. Based on this, we have also extended our analysis of the amino acid polymorphisms to the experimentally defined and predicted CTL epitopes. The results suggest that amino acid polymorphisms may contribute to the immune escape of the virus. The available data on naturally occurring polymorphisms will be useful to assess their potential effect on the structural and functional constraints of Vpr and also on the fitness of HIV-1 for replication.

HIV-1 prophylactic vaccine comprised of topical DermaVir prime and protein boost elicits cellular immune responses and controls pathogenic R5 SHIV162P3.

Topical DNA vaccination (DermaVir) facilitates antigen presentation to naive T cells. DermaVir immunization in mice, using HIV-1 Env and Gag, elicited cellular immune responses. Boosting with HIV-1 gp120 Env and p41 Gag augmented Th1 cytokine levels. Intramuscular DNA administration was less efficient in priming antigen-specific cytokine production and memory T cells. In rhesus macaques, DermaVir immunization induced Gag- and Env-specific Th1 and Th2 cytokines and generation of memory T cells. Boosting of DermaVir-primed serum antibody levels was noted following gp140(SHIV89.6P)/p27(SIV) immunization. Rectal challenge with pathogenic R5-tropic SHIV162P3 resulted in control of plasma viremia (4/5 animals) that was reflected in jejunum, colon and mesenteric lymph nodes. An inverse correlation was found between Gag- and Env-specific central memory T cell responses on the day of challenge and plasma viremia at set point. Overall, the topical DermaVir/protein vaccination yields central memory T cell responses and facilitates control of pathogenic SHIV infection.

Evaluation of passively transferred, nonneutralizing antibody-dependent cellular cytotoxicity-mediating IgG in protection of neonatal rhesus macaques against oral SIVmac251 challenge.

Previously, Ab-dependent cellular cytotoxicity (ADCC) was significantly correlated with reduced acute viremia upon intrarectal SIVmac251 challenge of immunized rhesus macaques. To directly assess ADCC protective efficacy, six neonatal macaques were infused s.c. with immune IgG (220 mg/kg) purified from the immunized animals and positive for ADCC and Ab-dependent cell-mediated viral inhibition (ADCVI) activities. Six neonates received control IgG. The neonates were challenged twice orally with 10(5) 50% inhibiting tissue culture-infective dose of SIVmac251 2 days post-IgG infusion. At challenge, plasma of neonates that received immune IgG did not neutralize SIVmac251 but had geometric mean ADCC titers of 48,130 and 232,850 against SIVmac251 -infected and gp120-coated targets, respectively. Peak ADCVI activity varied from 62 to 81%. ADCC activity declined with the 2-wk IgG half-life but was boosted at wk 4, together with de novo ADCC-mediating Abs in controls, by postchallenge viremia. ADCVI activity was similarly induced. No protection, assessed by viral burdens, CD4 counts, and time to euthanasia was observed. Possible factors contributing to the discrepancy between the previous correlation and lack of protection here include: the high oral challenge dose compared with the 400-fold lower intrarectal dose; the challenge route with regard to viral dissemination and distribution of infused IgG; insufficient NK effector activity and/or poor functionality in newborns; insufficient immune IgG; and the possibility that the previous correlation of ADCC with protection was augmented by cellular immune responses also present at challenge. Future studies should explore additional challenge routes in juvenile macaques using higher amounts of potent IgG preparations.

Subunit recombinant vaccine protects against monkeypox.

The smallpox vaccine Dryvax, a live vaccinia virus (VACV), protects against smallpox and monkeypox, but is contraindicated in immunocompromised individuals. Because Abs to VACV mediate protection, a live virus vaccine could be substituted by a safe subunit protein-based vaccine able to induce a protective Ab response. We immunized rhesus macaques with plasmid DNA encoding the monkeypox orthologs of the VACV L1R, A27L, A33R, and B5R proteins by the intradermal and i.m. routes, either alone or in combination with the equivalent recombinant proteins produced in Escherichia coli. Animals that received only DNA failed to produce high titer Abs, developed innumerable skin lesions after challenge, and died in a manner similar to placebo controls. By contrast, the animals vaccinated with proteins developed moderate to severe disease (20-155 skin lesions) but survived. Importantly, those immunized with DNA and boosted with proteins had mild disease with 15 or fewer lesions that resolved within days. DNA/protein immunization elicited Th responses and binding Ab titers to all four proteins that correlated negatively with the total lesion number. The sera of the immunized macaques recognized a limited number of linear B cell epitopes that are highly conserved among orthopoxviruses. Their identification may guide future efforts to develop simpler, safer, and more effective vaccines for monkeypox and smallpox.

An adenovirus-based HIV subtype B prime/boost vaccine regimen elicits antibodies mediating broad antibody-dependent cellular cytotoxicity against non-subtype B HIV strains.

Although HIV subtype B predominates in North America and Western Europe, most HIV infections worldwide are non-subtype B. Globally effective AIDS vaccines need to elicit broad immunity against multiple HIV strains. In this study, 10 chimpanzees were intranasally primed sequentially with adenovirus type 5 (Ad5)- and Ad7-HIVMNenv/rev recombinants and boosted twice intramuscularly with heterologous oligomeric HIVSF162 gp140DeltaV2 protein in MF59 adjuvant. Sera were evaluated for binding, neutralizing, and antibody-dependent cellular cytotoxicity (ADCC) against HIV clades A, B, C, and CRF01_AE. The vaccine regimen elicited high-titered HIV subtype A, B, C and CRF01_AE gp120-binding antibodies. Sera from 7 of 10 vaccinated chimpanzees cross-neutralized the heterologous South African subtype C primary HIVTV-1 isolate. Significant cross-clade neutralization against other subtype A, C and E isolates was not observed. Sera from all animals mediated ADCC of cells coated with gp120 from HIV subtypes A and B. Nine of 10 animals also exhibited ADCC activity against HIV subtype C and CRF01_AE gp120-coated targets. This subtype B Ad-HIV recombinant prime/envelope protein boost regimen is a promising approach for eliciting broad ADCC activity against diverse HIV clades. Incorporating additional non-subtype B envelope genes and protein boosts in a multivalent strategy may be required to elicit broader neutralizing antibodies against non-subtype B HIV strains.

Coadsorption of HIV-1 p24 and gp120 proteins to surfactant-free anionic PLA nanoparticles preserves antigenicity and immunogenicity.

Biodegradable micro- or nanoparticles with surface adsorbed antigens represent a promising method for in vivo delivery of vaccines. Most vaccines, licensed or under development, are based on combined delivery of multiple antigens. Thus, we investigated the feasibility of combining two vaccine antigens, HIV-1 p24 and gp120 proteins, on the surface of surfactant-free anionic PLA nanoparticles obtained by an improved solvent diffusion method. The analysis of adsorption isotherms has shown that both proteins had similar and high affinities for the nanoparticles. Coadsorption of p24 and gp120 onto the same PLA particle was evidenced by sandwich ELISA, using antibodies directed against one protein for particle capture and the other one for detection. To assess structural integrity, the antigenicity of free and PLA-adsorbed antigens was compared by competition ELISA, using a set of 6 anti-p24 and 7 anti-gp120 antibodies, as well as soluble CD4. The antigenicity of proteins on the nanoparticle surface was well preserved, adsorbed either individually or in combination. Furthermore, both antigens maintained their immunogenicity, since high antibody titres (10(6) for p24 and 10(5) for gp120) were elicited in mice with monovalent and divalent PLA formulations. Taken together our results show that development of multivalent vaccines based on anionic PLA nanoparticles is possible. Moreover, coadsorption of a ligand for cell-specific targeting or of an immunostimulatory molecule will further extend the field of application of delivery systems based on charged micro- and nanoparticles.

Systemic immunization with an ALVAC-HIV-1/protein boost vaccine strategy protects rhesus macaques from CD4+ T-cell loss and reduces both systemic and mucosal simian-human immunodeficiency virus SHIVKU2 RNA levels.

Transmission of human immunodeficiency virus type 1 (HIV-1) occurs primarily via the mucosal route, suggesting that HIV-1 vaccines may need to elicit mucosal immune responses. Here, we investigated the immunogenicity and relative efficacy of systemic immunization with two human ALVAC-HIV-1 recombinant vaccines expressing Gag, Pol, and gp120 (vCP250) or Gag, Pol, and gp160 (vCP1420) in a prime-boost protocol with their homologous vaccine native Env proteins. The relative efficacy was measured against a high-dose mucosal exposure to the pathogenic neutralization-resistant variant SHIV(KU2) (simian-human immunodeficiency virus). Systemic immunization with both vaccine regimens decreased viral load levels not only in blood but unexpectedly also in mucosal sites and protected macaques from peripheral CD4+ T-cell loss. This protective effect was stronger when the gp120 antigen was included in the vaccine. Inclusion of recombinant Tat protein in the boosting phase along with the Env protein did not contribute further to the preservation of CD4+ T cells. Thus, systemic immunization with ALVAC-HIV-1 vaccine candidates elicits anti-HIV-1 immune responses able to contain virus replication also at mucosal sites in macaques.

Preclinical evaluation of cellular immune responses elicited by a polyvalent DNA prime/protein boost HIV-1 vaccine.

While DNA vaccines have been shown to prime cellular immune responses, levels are often low in nonhuman primates or humans. Hence, efforts have been directed toward boosting responses by combining DNA with different vaccination modalities. To this end, a polyvalent DNA prime/protein boost vaccine, consisting of codon optimized HIV-1 env (A, B, C, E) and gag (C) and homologous gp120 proteins in QS-21, was evaluated in rhesus macaques and BALB/c mice. Humoral and cellular responses, detected following DNA immunization, were increased following protein boost in macaques and mice. In dissecting cellular immune responses in mice, protein-enhanced responses were found to be mediated by CD4+ and CD8+ T cells with a Th1 cytokine bias. Our study reveals that, in addition to augmenting humoral responses, protein boosting of DNA-primed animals augments cellular immune responses mediated by CD8+ CTL, CD4+ T-helper cells and Th1 cytokines; thus, offering much promise in controlling HIV-1 in vaccinees.