scholarly journals Potent Bispecific Neutralizing Antibody Targeting Glycoprotein B and the gH/gL/pUL128/130/131 Complex of Human Cytomegalovirus

2020 ◽  
Vol 65 (3) ◽  
Author(s):  
Hang Su ◽  
Xiaohua Ye ◽  
Daniel C. Freed ◽  
Leike Li ◽  
Zhiqiang Ku ◽  
...  
Keyword(s):  
Human Cytomegalovirus ◽  
Neutralizing Antibodies ◽  
Developmental Disorders ◽  
Bispecific Antibody ◽  
Hcmv Infection ◽  
Rhesus Macaques ◽  
Congenital Infection ◽  
Neutralizing Antibody ◽  
Glycoprotein B ◽  
Single Chain

ABSTRACT Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause developmental disorders following congenital infection and life-threatening complications among transplant patients. Potent neutralizing monoclonal antibodies (MAbs) are promising drug candidates against HCMV infection. HCMV can infect a broad range of cell types. Therefore, single neutralizing antibodies targeting one HCMV glycoprotein often lack either potency or broad cell-type coverage. We previously characterized two human-derived HCMV neutralizing MAbs. One was the broadly neutralizing MAb 3-25, which targets the antigenic domain 2 of glycoprotein B (gB). The other was the highly potent MAb 2-18, which specifically recognizes the gH/gL/pUL128/130/131 complex (pentamer). To combine the strengths of gB- and pentamer-targeting MAbs, we developed an IgG–single-chain variable fragment (scFv) bispecific antibody by fusing the 2-18 scFv to the heavy-chain C terminus of MAb 3-25. The resulting bispecific antibody showed high-affinity binding to both gB and pentamer. Functionally, the bispecific antibody demonstrated a combined neutralization breadth and potency of the parental MAbs in multiple cell lines and inhibited postinfection viral spreading. Furthermore, the bispecific antibody was easily produced in CHO cells at a yield above 1 g/liter and showed a single-dose pharmacokinetic profile comparable to that of parental MAb 3-25 in rhesus macaques. Importantly, the bispecific antibody retained broadly and potent neutralizing activity after 21 days in circulation. Taken together, our research provides a proof-of-concept study for developing bispecific neutralizing antibody therapies against HCMV infection.

scholarly journals Vaccine-Derived Neutralizing Antibodies to the Human Cytomegalovirus gH/gL Pentamer Potently Block Primary Cytotrophoblast Infection

2015 ◽  
Vol 89 (23) ◽  
pp. 11884-11898 ◽  
Author(s):  
Flavia Chiuppesi ◽  
Felix Wussow ◽  
Erica Johnson ◽  
Chao Bian ◽  
Meng Zhuo ◽  
...  
Keyword(s):  
Human Cytomegalovirus ◽  
Neutralizing Antibodies ◽  
Hcmv Infection ◽  
Rhesus Macaques ◽  
High Titer ◽  
Neutralizing Antibody ◽  
Cell Types ◽  
Cell Type ◽  
Vaccine Strategy ◽  
Placental Cells

ABSTRACTHuman cytomegalovirus (HCMV) elicits neutralizing antibodies (NAb) of various potencies and cell type specificities to prevent HCMV entry into fibroblasts (FB) and epithelial/endothelial cells (EpC/EnC). NAb targeting the major essential envelope glycoprotein complexes gB and gH/gL inhibit both FB and EpC/EnC entry. In contrast to FB infection, HCMV entry into EpC/EnC is additionally blocked by extremely potent NAb to conformational epitopes of the gH/gL/UL128/130/131A pentamer complex (PC). We recently developed a vaccine concept based on coexpression of all five PC subunits by a single modified vaccinia virus Ankara (MVA) vector, termed MVA-PC. Vaccination of mice and rhesus macaques with MVA-PC resulted in a high titer and sustained NAb that blocked EpC/EnC infection and lower-titer NAb that inhibited FB entry. However, antibody function responsible for the neutralizing activity induced by the MVA-PC vaccine is uncharacterized. Here, we demonstrate that MVA-PC elicits NAb with cell type-specific neutralization potency and antigen recognition pattern similar to human NAb targeting conformational and linear epitopes of the UL128/130/131A subunits or gH. In addition, we show that the vaccine-derived PC-specific NAb are significantly more potent than the anti-gH NAb to prevent HCMV spread in EpC and infection of human placental cytotrophoblasts, cell types thought to be of critical importance for HCMV transmission to the fetus. These findings further validate MVA-PC as a clinical vaccine candidate to elicit NAb that resembles those induced during HCMV infection and provide valuable insights into the potency of PC-specific NAb to interfere with HCMV cell-associated spread and infection of key placental cells.IMPORTANCEAs a consequence of the leading role of human cytomegalovirus (HCMV) in causing permanent birth defects, developing a vaccine against HCMV has been assigned a major public health priority. We have recently introduced a vaccine strategy based on a widely used, safe, and well-characterized poxvirus vector platform to elicit potent and durable neutralizing antibody (NAb) responses targeting the HCMV envelope pentamer complex (PC), which has been suggested as a critical component for a vaccine to prevent congenital HCMV infection. With this work, we confirm that the NAb elicited by the vaccine vector have properties that are similar to those of human NAb isolated from individuals chronically infected with HCMV. In addition, we show that PC-specific NAb have potent ability to prevent infection of key placental cells that HCMV utilizes to cross the fetal-maternal interface, suggesting that NAb targeting the PC may be essential to prevent HCMV vertical transmission.

scholarly journals Maternal Fc-mediated non-neutralizing antibody responses correlate with protection against congenital human cytomegalovirus infection

2021 ◽  
Author(s):  
Eleanor C. Semmes ◽  
Itzayana G. Miller ◽  
Jennifer A. Jenks ◽  
Courtney E. Wimberly ◽  
Stella J. Berendam ◽  
...  
Keyword(s):  
Cord Blood ◽  
Human Cytomegalovirus ◽  
Hcmv Infection ◽  
Passive Immunization ◽  
Congenital Infection ◽  
Neutralizing Antibody ◽  
Antibody Responses ◽  
High Avidity ◽  
Igg Binding ◽  
Congenital Hcmv Infection

AbstractHuman cytomegalovirus (HCMV) is the most common congenital infection and a leading cause of stillbirth, neurodevelopmental impairment, and pediatric hearing loss worldwide. Development of a maternal vaccine or therapeutic to prevent congenital infection has been hindered by limited knowledge of the immune responses that protect against placental HCMV transmission in maternal primary and nonprimary infection. To identify protective antibody responses, we measured anti-HCMV IgG binding and anti-viral functions in maternal and cord blood sera from HCMV transmitting (n=41) and non- transmitting (n=40) mother-infant dyads identified via a large U.S.-based public cord blood bank. In a predefined immune correlate analysis, maternal monocyte-mediated antibody-dependent cellular phagocytosis (ADCP) and high avidity IgG binding to HCMV envelope glycoproteins were associated with decreased risk of congenital HCMV infection. Moreover, HCMV-specific IgG engagement of FcγRI and FcγRIIA, which mediate non-neutralizing antibody responses, was enhanced in non-transmitting mother-infant dyads and strongly correlated with ADCP. These findings suggest that Fc effector functions including ADCP protect against placental HCMV transmission. Taken together, our data indicate that future active and passive immunization strategies to prevent congenital HCMV infection should target Fc-mediated non-neutralizing antibody responses.

scholarly journals Targeting Human-Cytomegalovirus-Infected Cells by Redirecting T Cells Using an Anti-CD3/Anti-Glycoprotein B Bispecific Antibody

2017 ◽  
Vol 62 (1) ◽  
Author(s):  
Weixu Meng ◽  
Aimin Tang ◽  
Xiaohua Ye ◽  
Xun Gui ◽  
Leike Li ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Human Cytomegalovirus ◽  
T Cell Activation ◽  
Cell Activation ◽  
Bispecific Antibody ◽  
Hcmv Infection ◽  
Glycoprotein B ◽  
Transplant Recipients ◽  
Infected Cells

ABSTRACTThe host immune response to human cytomegalovirus (HCMV) is effective against HCMV reactivation from latency, though not sufficient to clear the virus. T cells are primarily responsible for the control of viral reactivation. When the host immune system is compromised, as in transplant recipients with immunosuppression, HCMV reactivation and progressive infection can cause serious morbidity and mortality. Adoptive T cell therapy is effective for the control of HCMV infection in transplant recipients. However, it is a highly personalized therapeutic regimen and is difficult to implement in routine clinical practice. In this study, we explored a bispecific-antibody strategy to direct non-HCMV-specific T cells to recognize and exert effector functions against HCMV-infected cells. Using a knobs-into-holes strategy, we constructed a bispecific antibody in which one arm is specific for CD3 and can trigger T cell activation, while the other arm, specific for HCMV glycoprotein B (gB), recognizes and marks HCMV-infected cells based on the expression of viral gB on their surfaces. We showed that this bispecific antibody was able to redirect T cells with specificity for HCMV-infected cellsin vitro. In the presence of HCMV infection, the engineered antibody was able to activate T cells with no HCMV specificity for cytokine production, proliferation, and the expression of phenotype markers unique to T cell activation. These results suggested the potential of engineered bispecific antibodies, such as the construct described here, as prophylactic or therapeutic agents against HCMV reactivation and infection.

scholarly journals Neutralization of Diverse Human Cytomegalovirus Strains Conferred by Antibodies Targeting Viral gH/gL/pUL128-131 Pentameric Complex

2017 ◽  
Vol 91 (7) ◽  
Author(s):  
Sha Ha ◽  
Fengsheng Li ◽  
Matthew C. Troutman ◽  
Daniel C. Freed ◽  
Aimin Tang ◽  
...  
Keyword(s):  
Public Health ◽  
Human Cytomegalovirus ◽  
Neutralizing Antibodies ◽  
Hcmv Infection ◽  
Rhesus Macaques ◽  
Antibody Responses ◽  
Broadly Neutralizing Antibodies ◽  
Site Specific ◽  
Glycoprotein H

ABSTRACT Human cytomegalovirus (HCMV) is the leading cause of congenital viral infection, and developing a prophylactic vaccine is of high priority to public health. We recently reported a replication-defective human cytomegalovirus with restored pentameric complex glycoprotein H (gH)/gL/pUL128-131 for prevention of congenital HCMV infection. While the quantity of vaccine-induced antibody responses can be measured in a viral neutralization assay, assessing the quality of such responses, including the ability of vaccine-induced antibodies to cross-neutralize the field strains of HCMV, remains a challenge. In this study, with a panel of neutralizing antibodies from three healthy human donors with natural HCMV infection or a vaccinated animal, we mapped eight sites on the dominant virus-neutralizing antigen—the pentameric complex of glycoprotein H (gH), gL, and pUL128, pUL130, and pUL131. By evaluating the site-specific antibodies in vaccine immune sera, we demonstrated that vaccination elicited functional antiviral antibodies to multiple neutralizing sites in rhesus macaques, with quality attributes comparable to those of CMV hyperimmune globulin. Furthermore, these immune sera showed antiviral activities against a panel of genetically distinct HCMV clinical isolates. These results highlighted the importance of understanding the quality of vaccine-induced antibody responses, which includes not only the neutralizing potency in key cell types but also the ability to protect against the genetically diverse field strains. IMPORTANCE HCMV is the leading cause of congenital viral infection, and development of a preventive vaccine is a high public health priority. To understand the strain coverage of vaccine-induced immune responses in comparison with natural immunity, we used a panel of broadly neutralizing antibodies to identify the immunogenic sites of a dominant viral antigen—the pentameric complex. We further demonstrated that following vaccination of a replication-defective virus with the restored pentameric complex, rhesus macaques can develop broadly neutralizing antibodies targeting multiple immunogenic sites of the pentameric complex. Such analyses of site-specific antibody responses are imperative to our assessment of the quality of vaccine-induced immunity in clinical studies.

scholarly journals Enveloped Virus-Like Particle Expression of Human Cytomegalovirus Glycoprotein B Antigen Induces Antibodies with Potent and Broad Neutralizing Activity

2013 ◽  
Vol 21 (2) ◽  
pp. 174-180 ◽  
Author(s):  
Marc Kirchmeier ◽  
Anne-Catherine Fluckiger ◽  
Catalina Soare ◽  
Jasminka Bozic ◽  
Barthelemy Ontsouka ◽  
...  
Keyword(s):  
Epithelial Cell ◽  
Human Cytomegalovirus ◽  
Neutralizing Antibodies ◽  
Matrix Protein ◽  
High Titer ◽  
Neutralizing Antibody ◽  
Glycoprotein B ◽  
Solid Organ ◽  
Neutralizing Activity ◽  
Enveloped Virus

ABSTRACTA prophylactic vaccine to prevent the congenital transmission of human cytomegalovirus (HCMV) in newborns and to reduce life-threatening disease in immunosuppressed recipients of HCMV-infected solid organ transplants is highly desirable. Neutralizing antibodies against HCMV confer significant protection against infection, and glycoprotein B (gB) is a major target of such neutralizing antibodies. However, one shortcoming of past HCMV vaccines may have been their failure to induce high-titer persistent neutralizing antibody responses that prevent the infection of epithelial cells. We used enveloped virus-like particles (eVLPs), in which particles were produced in cells after the expression of murine leukemia virus (MLV) viral matrix protein Gag, to express either full-length CMV gB (gB eVLPs) or the full extracellular domain of CMV gB fused with the transmembrane and cytoplasmic domains from vesicular stomatitis virus (VSV)-G protein (gB-G eVLPs). gB-G-expressing eVLPs induced potent neutralizing antibodies in mice with a much greater propensity toward epithelial cell-neutralizing activity than that induced with soluble recombinant gB protein. An analysis of gB antibody binding titers and T-helper cell responses demonstrated that high neutralizing antibody titers were not simply due to enhanced immunogenicity of the gB-G eVLPs. The cells transiently transfected with gB-G but not gB plasmid formed syncytia, consistent with a prefusion gB conformation like those of infected cells and viral particles. Two of the five gB-G eVLP-induced monoclonal antibodies we examined in detail had neutralizing activities, one of which possessed particularly potent epithelial cell-neutralizing activity. These data differentiate gB-G eVLPs from gB antigens used in the past and support their use in a CMV vaccine candidate with improved neutralizing activity against epithelial cell infection.

scholarly journals A divalent antibody format is required for neutralization of human cytomegalovirus via antigenic domain 2 on glycoprotein B

2002 ◽  
Vol 83 (8) ◽  
pp. 2001-2005 ◽  
Author(s):  
Johan Lantto ◽  
Jean M. Fletcher ◽  
Mats Ohlin
Keyword(s):  
Human Cytomegalovirus ◽  
Neutralizing Antibodies ◽  
Glycoprotein B ◽  
Human Antibody ◽  
Single Chain ◽  
Immunogenic Epitope ◽  
Neutralizing Capacity ◽  
Slow Dissociation ◽  
Kinetics Of ◽  
Antigenic Domain

Glycoprotein B (gB) of human cytomegalovirus (HCMV) is the dominating protein in the envelope of this virus and gives rise to virus-neutralizing antibodies in most infected individuals. We have previously isolated a neutralizing human antibody specific for antigenic domain 2 (AD-2) on gB, a poorly immunogenic epitope, which nevertheless is capable of eliciting potent neutralizing antibodies. In order to define parameters important for the neutralization of HCMV via gB, we have investigated the virus-neutralizing capacity and the kinetics of the interaction with AD-2 of the monomeric and dimeric forms of a single chain variable fragment (scFv) corresponding to this antibody. We demonstrate here that neutralization of HCMV via AD-2 on gB can be mediated by dimeric scFv, while monomeric fragments cannot mediate neutralization of the virus, despite a slow dissociation from the intact glycoprotein. This finding is discussed in the context of possible mechanisms for antibody-mediated virus neutralization.

scholarly journals HCMV glycoprotein B subunit vaccine efficacy was mediated by non-neutralizing antibody effector functions

2018 ◽  
Author(s):  
Cody S. Nelson ◽  
Tori Huffman ◽  
Eduardo Cisneros de la Rosa ◽  
Guanhua Xie ◽  
Nathan Vandergrift ◽  
...  
Keyword(s):  
Human Cytomegalovirus ◽  
Vaccine Efficacy ◽  
Subunit Vaccine ◽  
Hcmv Infection ◽  
Neutralizing Antibody ◽  
The United States ◽  
Glycoprotein B ◽  
Vaccine Platform ◽  
Effector Functions ◽  
Epitope Specificity

AbstractHuman cytomegalovirus (HCMV) is the most common congenital infection worldwide, frequently causing hearing loss and brain damage in afflicted infants. A vaccine to prevent maternal acquisition of HCMV during pregnancy is necessary to reduce the incidence of infant disease. The glycoprotein B (gB) + MF59 adjuvant subunit vaccine platform is the most successful HCMV vaccine tested to-date, demonstrating approximately 50% efficacy in preventing HCMV acquisition in phase II trials. However, the mechanism of vaccine protection remains unknown. Plasma from 33 gB/MF59 vaccinees at peak immunogenicity was tested for gB epitope specificity as well as neutralizing and non-neutralizing anti-HCMV effector functions, and compared to an HCMV-seropositive cohort. gB/MF59 vaccination elicited IgG responses with gB-binding magnitude and avidity comparable to natural infection. Additionally, IgG subclass distribution was similar with predominant IgG1 and IgG3 responses induced by gB vaccination and HCMV infection. However, vaccine-elicited antibodies exhibited limited neutralization of the autologous virus, negligible neutralization of multiple heterologous strains, and limited binding responses against gB structural motifs targeted by neutralizing antibodies including AD-1, AD-2, and Domain I. Interestingly, vaccinees had high-magnitude IgG responses against AD-3 linear epitopes, demonstrating immunodominance against this non-neutralizing, cytosolic region. Finally, vaccine-elicited IgG robustly bound trimeric, membrane-associated gB on the surface of transfected or HCMV-infected cells and mediated virion phagocytosis, though were poor mediators of NK cell activation. Altogether, these data suggest that non-neutralizing antibody functions, including virion phagocytosis, likely played a role in the observed 50% vaccine-mediated protection against HCMV acquisition.SignificanceThe CDC estimates that every hour, a child is born in the United States with permanent neurologic disability resulting from human cytomegalovirus (HCMV) infection – more than is caused by Down syndrome, fetal alcohol syndrome, and neural tube defects combined. A maternal vaccine to block transmission of HCMV to the developing fetus is a necessary intervention to prevent these adverse outcomes. The gB/MF59 vaccine is the most successful tested clinically to-date, achieving 50% reduction in HCMV acquisition. This manuscript establishes the function and epitope specificity of the humoral response stimulated by this vaccine that may explain the partial vaccine efficacy. Understanding the mechanism of gB/MF59-elicited protective immune responses will guide rational design and evaluation of the next generation of HCMV vaccines.

scholarly journals Cell Fusion Induced by a Fusion-Active Form of Human Cytomegalovirus Glycoprotein B (gB) Is Inhibited by Antibodies Directed at Antigenic Domain 5 in the Ectodomain of gB

2020 ◽  
Vol 94 (18) ◽  
Author(s):  
Nina Reuter ◽  
Barbara Kropff ◽  
Julia Karin Schneiderbanger ◽  
Mira Alt ◽  
Adalbert Krawczyk ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Human Cytomegalovirus ◽  
Neutralizing Antibodies ◽  
Hcmv Infection ◽  
Active Form ◽  
Health Concern ◽  
Glycoprotein B ◽  
Viral Fusion ◽  
Viral Fusion Protein ◽  
Antigenic Domain

ABSTRACT Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause severe clinical disease in allograft recipients and infants infected in utero. Virus-neutralizing antibodies defined in vitro have been proposed to confer protection against HCMV infection, and the virion envelope glycoprotein B (gB) serves as a major target of neutralizing antibodies. The viral fusion protein gB is nonfusogenic on its own and requires glycoproteins H (gH) and L (gL) for membrane fusion, which is in contrast to requirements of related class III fusion proteins, including vesicular stomatitis virus glycoprotein G (VSV-G) or baculovirus gp64. To explore requirements for gB’s fusion activity, we generated a set of chimeras composed of gB and VSV-G or gp64, respectively. These gB chimeras were intrinsically fusion active and led to the formation of multinucleated cell syncytia when expressed in the absence of other viral proteins. Utilizing a panel of virus-neutralizing gB-specific monoclonal antibodies (MAbs), we could demonstrate that syncytium formation of the fusogenic gB/VSV-G chimera can be significantly inhibited by only a subset of neutralizing MAbs which target antigenic domain 5 (AD-5) of gB. This observation argues for differential modes of action of neutralizing anti-gB MAbs and suggests that blocking the membrane fusion function of gB could be one mechanism of antibody-mediated virus neutralization. In addition, our data have important implications for the further understanding of the conformation of gB that promotes membrane fusion as well as the identification of structures in AD-5 that could be targeted by antibodies to block this early step in HCMV infection. IMPORTANCE HCMV is a major global health concern, and antiviral chemotherapy remains problematic due to toxicity of available compounds and the emergence of drug-resistant viruses. Thus, an HCMV vaccine represents a priority for both governmental and pharmaceutical research programs. A major obstacle for the development of a vaccine is a lack of knowledge of the nature and specificities of protective immune responses that should be induced by such a vaccine. Glycoprotein B of HCMV is an important target for neutralizing antibodies and, hence, is often included as a component of intervention strategies. By generation of fusion-active gB chimeras, we were able to identify target structures of neutralizing antibodies that potently block gB-induced membrane fusion. This experimental system provides an approach to screen for antibodies that interfere with gB’s fusogenic activity. In summary, our data will likely contribute to both rational vaccine design and the development of antibody-based therapies against HCMV.

scholarly journals SARS-CoV-2 RBD trimer protein adjuvanted with Alum-3M-052 protects from SARS-CoV-2 infection and immune pathology in the lung

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nanda Kishore Routhu ◽  
Narayanaiah Cheedarla ◽  
Venkata Satish Bollimpelli ◽  
Sailaja Gangadhara ◽  
Venkata Viswanadh Edara ◽  
...  
Keyword(s):  
Antibody Response ◽  
Antibody Titer ◽  
Neutralizing Antibodies ◽  
Rhesus Macaques ◽  
Neutralizing Antibody ◽  
Significant Loss ◽  
Lung Pathology ◽  
Live Virus ◽  
Suitable Candidate ◽  
Immune Pathology

AbstractThere is a great need for the development of vaccines that induce potent and long-lasting protective immunity against SARS-CoV-2. Multimeric display of the antigen combined with potent adjuvant can enhance the potency and longevity of the antibody response. The receptor binding domain (RBD) of the spike protein is a primary target of neutralizing antibodies. Here, we developed a trimeric form of the RBD and show that it induces a potent neutralizing antibody response against live virus with diverse effector functions and provides protection against SARS-CoV-2 challenge in mice and rhesus macaques. The trimeric form induces higher neutralizing antibody titer compared to monomer with as low as 1μg antigen dose. In mice, adjuvanting the protein with a TLR7/8 agonist formulation alum-3M-052 induces 100-fold higher neutralizing antibody titer and superior protection from infection compared to alum. SARS-CoV-2 infection causes significant loss of innate cells and pathology in the lung, and vaccination protects from changes in innate cells and lung pathology. These results demonstrate RBD trimer protein as a suitable candidate for vaccine against SARS-CoV-2.

scholarly journals Characterization and Implementation of a Diverse Simian Immunodeficiency Virus SIVsm Envelope Panel in the Assessment of Neutralizing Antibody Breadth Elicited in Rhesus Macaques by Multimodal Vaccines Expressing the SIVmac239 Envelope

2015 ◽  
Vol 89 (16) ◽  
pp. 8130-8151 ◽  
Author(s):  
Katie M. Kilgore ◽  
Megan K. Murphy ◽  
Samantha L. Burton ◽  
Katherine S. Wetzel ◽  
S. Abigail Smith ◽  
...  
Keyword(s):  
Simian Immunodeficiency Virus ◽  
Nonhuman Primate ◽  
Neutralizing Antibodies ◽  
Rhesus Macaques ◽  
Neutralizing Antibody ◽  
Cd40 Ligand ◽  
Antibody Activity ◽  
Immunodeficiency Virus ◽  
Antibody Profile ◽  
Hiv 1

ABSTRACTAntibodies that can neutralize diverse viral strains are likely to be an important component of a protective human immunodeficiency virus type 1 (HIV-1) vaccine. To this end, preclinical simian immunodeficiency virus (SIV)-based nonhuman primate immunization regimens have been designed to evaluate and enhance antibody-mediated protection. However, these trials often rely on a limited selection of SIV strains with extreme neutralization phenotypes to assess vaccine-elicited antibody activity. To mirror the viral panels used to assess HIV-1 antibody breadth, we created and characterized a novel panel of 14 genetically and phenotypically diverse SIVsm envelope (Env) glycoproteins. To assess the utility of this panel, we characterized the neutralizing activity elicited by four SIVmac239 envelope-expressing DNA/modified vaccinia virus Ankara vector- and protein-based vaccination regimens that included the immunomodulatory adjuvants granulocyte-macrophage colony-stimulating factor, Toll-like receptor (TLR) ligands, and CD40 ligand. The SIVsm Env panel exhibited a spectrum of neutralization sensitivity to SIV-infected plasma pools and monoclonal antibodies, allowing categorization into three tiers. Pooled sera from 91 rhesus macaques immunized in the four trials consistently neutralized only the highly sensitive tier 1a SIVsm Envs, regardless of the immunization regimen. The inability of vaccine-mediated antibodies to neutralize the moderately resistant tier 1b and tier 2 SIVsm Envs defined here suggests that those antibodies were directed toward epitopes that are not accessible on most SIVsm Envs. To achieve a broader and more effective neutralization profile in preclinical vaccine studies that is relevant to known features of HIV-1 neutralization, more emphasis should be placed on optimizing the Env immunogen, as the neutralization profile achieved by the addition of adjuvants does not appear to supersede the neutralizing antibody profile determined by the immunogen.IMPORTANCEMany in the HIV/AIDS vaccine field believe that the ability to elicit broadly neutralizing antibodies capable of blocking genetically diverse HIV-1 variants is a critical component of a protective vaccine. Various SIV-based nonhuman primate vaccine studies have investigated ways to improve antibody-mediated protection against a heterologous SIV challenge, including administering adjuvants that might stimulate a greater neutralization breadth. Using a novel SIV neutralization panel and samples from four rhesus macaque vaccine trials designed for cross comparison, we show that different regimens expressing the same SIV envelope immunogen consistently elicit antibodies that neutralize only the very sensitive tier 1a SIV variants. The results argue that the neutralizing antibody profile elicited by a vaccine is primarily determined by the envelope immunogen and is not substantially broadened by including adjuvants, resulting in the conclusion that the envelope immunogen itself should be the primary consideration in efforts to elicit antibodies with greater neutralization breadth.

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