Phase 1 Randomized, Double-Blind, Placebo-Controlled Study of RG7667, an Anticytomegalovirus Combination Monoclonal Antibody Therapy, in Healthy Adults

A broadly neutralizing human monoclonal antibody generated from transgenic mice immunized with HCMV particles limits virus infection and proliferation

Human cytomegalovirus (HCMV) is a β-herpesvirus that poses severe disease risk for immunocompromised patients who experience primary infection or reactivation. Development and optimization of safe and effective anti-HCMV therapeutics is of urgent necessity for the prevention and treatment of HCMV-associated diseases in diverse populations. The use of neutralizing monoclonal antibodies (mAbs) to limit HCMV infection poses a promising therapeutic strategy, as anti-HCMV mAbs largely inhibit infection by targeting virion glycoprotein complexes. In contrast, the small-molecule compounds currently approved for patients (e.g., ganciclovir, letermovir, and maribavir) target later stages of the HCMV life cycle. Here, we present a broadly neutralizing human mAb, designated 1C10, elicited from a VelocImmune mouse immunized with infectious HCMV particles. Clone 1C10 neutralizes infection after virion binding to cells by targeting gH/gL envelope complexes and potently reduces infection of diverse HCMV strains in fibroblast, trophoblast, and epithelial cells. Antibody competition assays found that 1C10 recognizes a region of gH associated with broad neutralization and binds to soluble pentamer in the low nanomolar range. Importantly, 1C10 treatment significantly reduced virus proliferation in both fibroblast and epithelial cells. Further, the combination treatment of mAb 1C10 with ganciclovir reduced HCMV infection and proliferation in a synergistic manner. This work characterizes a neutralizing human mAb for potential use as a HCMV treatment, as well as a possible therapeutic strategy utilizing combination-based treatments targeting disparate steps of the viral life cycle. Collectively, the findings support an antibody-based therapy to effectively treat patients at risk for HCMV-associated diseases.

IMPORTANCE

Human cytomegalovirus is a herpesvirus that infects a large proportion of the population and can cause significant disease in diverse patient populations whose immune systems are suppressed or compromised. The development and optimization of safe anti-HCMV therapeutics, especially those that have viral targets and inhibition mechanisms different from current HCMV treatments, are of urgent necessity to better public health. Human monoclonal antibodies (mAbs) that prevent HCMV entry of cells were identified by immunizing transgenic mice and screened for broad and effective neutralization capability. Here, we describe one such mAb, which was found to target gH/gL envelope complexes and effectively limit HCMV infection and dissemination. Further, administration of the antibody in combination with the antiviral drug ganciclovir inhibited HCMV in a synergistic manner, highlighting this approach and the use of anti-HCMV mAbs more broadly, as a potential therapeutic strategy for the treatment of diverse patient populations.

Ligands and receptors in human cytomegalovirus entry: Current therapies and new directions

The demand for human cytomegalovirus (HCMV) vaccines was first raised by a committee convened during the 1990s. A comprehensive investigation into the mechanism of viral infection supports the prioritization of developing drugs or vaccines that specifically target receptors and ligands involved in the infection process. As primary targets for neutralizing antibodies to combat HCMV, viral ligands (trimer, pentamer, and glycoprotein B) have crucial roles and exhibit substantial antiviral potential, which could be exploited for breakthroughs in antiviral research.

Single-cell analysis of memory B cells from top neutralizers reveals multiple sites of vulnerability within HCMV Trimer and Pentamer

Human cytomegalovirus (HCMV) can cause severe diseases in fetuses, newborns, and immunocompromised individuals. Currently, no vaccines are approved, and treatment options are limited. Here, we analyzed the human B cell response of four HCMV top neutralizers from a cohort of 9,000 individuals. By single-cell analyses of memory B cells targeting the pentameric and trimeric HCMV surface complexes, we identified vulnerable sites on the shared gH/gL subunits as well as complex-specific subunits UL128/130/131A and gO. Using high-resolution cryogenic electron microscopy, we revealed the structural basis of the neutralization mechanisms of antibodies targeting various binding sites. Moreover, we identified highly potent antibodies that neutralized a broad spectrum of HCMV strains, including primary clinical isolates, that outperform known antibodies used in clinical trials. Our study provides a deep understanding of the mechanisms of HCMV neutralization and identifies promising antibody candidates to prevent and treat HCMV infection.

Novel monoclonal antibody-based therapies: implications for the treatment and prevention of HCMV disease

Human cytomegalovirus (HCMV) is an important pathogen worldwide. Although HCMV infection is often asymptomatic in immunocompetent individuals, it can cause severe or even life-threatening symptoms in immunocompromised patients. Due to limitations of antiviral treatments, it is necessary to search for new therapeutic alternatives. Recent studies have highlighted the contribution of antibodies in protecting against HCMV disease, including neutralizing and non-neutralizing antibodies. Given the immunocompromised target population, monoclonal antibodies (mAbs) may represent an alternative to the clinical management of HCMV infection. In this context, we provide a synthesis of recent data revising the literature supporting and arguing about the role of the humoral immunity in controlling HCMV infection. Additionally, we review the state of the art in the development of therapies based on mAbs.

A fully human neutralizing monoclonal antibody targeting a highly conserved epitope of the human cytomegalovirus glycoprotein B

Human cytomegalovirus causes severe diseases in children (by congenital infection) and immunocompromised patients. Treatment with antiviral agents, such as ganciclovir, is limited by their toxicity. In this study, we investigated the effectiveness of a fully human neutralizing monoclonal antibody to inhibit human cytomegalovirus infection and viral cell-to-cell spread. We isolated a potent neutralizing antibody, EV2038 (IgG1 lambda), targeting human cytomegalovirus glycoprotein B using Epstein-Barr virus transformation. This antibody inhibited human cytomegalovirus infection by all four laboratory strains and 42 Japanese clinical isolates, including ganciclovir-resistant isolates, with a 50% inhibitory concentration (IC50) ranging from 0.013 to 0.105 μg/mL, and 90% inhibitory concentration (IC90) ranging from 0.208 to 1.026 μg/mL, in both human embryonic lung fibroblasts (MRC-5) and human retinal pigment epithelial (ARPE-19) cells. Additionally, EV2038 prevented cell-to-cell spread of eight clinical viral isolates, with IC50 values ranging from 1.0 to 3.1 μg/mL, and IC90 values ranging from 13 to 19 μg/mL, in ARPE-19 cells. EV2038 recognized three discontinuous sequences on antigenic domain 1 of glycoprotein B (amino acids 549-560, 569-576, and 625-632), which were highly conserved among 71 clinical isolates from Japan and the United States. Pharmacokinetics study in cynomolgus monkeys suggested the potential efficacy of EV2038 in vivo, the concentration of which in serum remained higher than the IC90 values of cell-to-cell spread until 28 days after intravenous injection of 10 mg/kg EV2038. Our data strongly support EV2038 as a promising candidate and novel alternative for the treatment of human cytomegalovirus infection.

Characterization of Plasma Immunoglobulin G Responses in Elite Neutralizers of Human Cytomegalovirus

BACKGROUND

Human cytomegalovirus (HCMV) is the most common infectious complication of organ transplantation and cause of birth defects worldwide. There are limited therapeutic options and no licensed vaccine to prevent HCMV infection or disease. To inform development of HCMV antibody-based interventions, a previous study identified individuals with potent and broad plasma HCMV-neutralizing activity, termed elite neutralizers (ENs), from a cohort of HCMV-seropositive (SP) blood donors. However, the specificities and functions of plasma antibodies associated with EN status remained undefined.

METHODS

We sought to determine the plasma antibody specificities, breadth, and Fc-mediated antibody effector functions associated with the most potent HCMV-neutralizing responses in plasma from ENs (n = 25) relative to that from SP donors (n = 19). We measured antibody binding against various HCMV strains and glycoprotein targets and evaluated Fc-mediated effector functions, antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP).

RESULTS

We demonstrate that ENs have elevated immunoglobulin G binding responses against multiple viral glycoproteins, relative to SP donors. Our study also revealed potent HCMV-specific antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis activity of plasma from ENs.

CONCLUSIONS

We conclude that antibody responses against multiple glycoprotein specificities may be needed to achieve potent plasma neutralization and that potently HCMV elite-neutralizing plasma antibodies can also mediate polyfunctional responses.

Recent Progress in the Discovery and Development of Monoclonal Antibodies against Viral Infections

Monoclonal antibodies (mAbs), the new revolutionary class of medications, are fast becoming tools against various diseases thanks to a unique structure and function that allow them to bind highly specific targets or receptors. These specialized proteins can be produced in large quantities via the hybridoma technique introduced in 1975 or by means of modern technologies. Additional methods have been developed to generate mAbs with new biological properties such as humanized, chimeric, or murine. The inclusion of mAbs in therapeutic regimens is a major medical advance and will hopefully lead to significant improvements in infectious disease management. Since the first therapeutic mAb, muromonab-CD3, was approved by the U.S. Food and Drug Administration (FDA) in 1986, the list of approved mAbs and their clinical indications and applications have been proliferating. New technologies have been developed to modify the structure of mAbs, thereby increasing efficacy and improving delivery routes. Gene delivery technologies, such as non-viral synthetic plasmid DNA and messenger RNA vectors (DMabs or mRNA-encoded mAbs), built to express tailored mAb genes, might help overcome some of the challenges of mAb therapy, including production restrictions, cold-chain storage, transportation requirements, and expensive manufacturing and distribution processes. This paper reviews some of the recent developments in mAb discovery against viral infections and illustrates how mAbs can help to combat viral diseases and outbreaks.

Combined knockdown of RL13 and UL128 for release of cell-free infectivity from recent HCMV isolates

Due to strictly cell-associated growth, experiments requiring cell-free virus are not applicable to recent clinical HCMV isolates to date. On the other hand, adaptation to cell-free growth is associated with undesirable changes in the viral gene regions RL13 and UL128. We had previously found that siRNA-mediated reduction of UL128 expression allowed transient release of cell-free virus by clinical isolates, and now hypothesized that virus yield could be further increased by additional knockdown of RL13. Despite the extensive polymorphism of RL13, effective RL13-specific siRNAs could be designed for three recent isolates and the Merlin strain. Knockdown efficiency was demonstrated at the protein level with a Merlin variant expressing V5-tagged pRL13. Knockdown of RL13 alone did not result in measurable release of cell-free virus, but combined knockdown of RL13 and UL128 increased infectivity in cell-free supernatants by a factor of 10-2000 compared to knockdown of UL128 alone. These supernatants could be used in dose-response assays to compare the effect of a neutralizing antibody on the various HCMV isolates. In summary, combined knockdown of RL13 and UL128 by specific siRNAs allows reliable release of cell-free infectivity from otherwise strictly cell-associated HCMV isolates without the need to modify the viral genome.

Antibodies to combat viral infections: development strategies and progress

Monoclonal antibodies (mAbs) are appealing as potential therapeutics and prophylactics for viral infections owing to characteristics such as their high specificity and their ability to enhance immune responses. Furthermore, antibody engineering can be used to strengthen effector function and prolong mAb half-life, and advances in structural biology have enabled the selection and optimization of potent neutralizing mAbs through identification of vulnerable regions in viral proteins, which can also be relevant for vaccine design. The COVID-19 pandemic has stimulated extensive efforts to develop neutralizing mAbs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with several mAbs now having received authorization for emergency use, providing not just an important component of strategies to combat COVID-19 but also a boost to efforts to harness mAbs in therapeutic and preventive settings for other infectious diseases. Here, we describe advances in antibody discovery and engineering that have led to the development of mAbs for use against infections caused by viruses including SARS-CoV-2, respiratory syncytial virus (RSV), Ebola virus (EBOV), human cytomegalovirus (HCMV) and influenza. We also discuss the rationale for moving from empirical to structure-guided strategies in vaccine development, based on identifying optimal candidate antigens and vulnerable regions within them that can be targeted by antibodies to result in a strong protective immune response.

Monoclonal antibodies (mAbs) are appealing as potential therapeutics and prophylactics for viral infections. This Review describes advances in antibody discovery and engineering that have led to the development of mAbs that target viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), respiratory syncytial virus and Ebola virus, and also considers the implications for vaccine development.

Development of broadly neutralizing antibodies targeting the cytomegalovirus subdominant antigen gH

Human cytomegalovirus (HCMV) is a β-herpesvirus that increases morbidity and mortality in immunocompromised individuals including transplant recipients and newborns. New anti-HCMV therapies are an urgent medical need for diverse patient populations. HCMV infection of a broad range of host tissues is dependent on the gH/gL/gO trimer and gH/gL/UL28/UL130/UL131A pentamer complexes on the viral envelope. We sought to develop safe and effective therapeutics against HCMV by generating broadly-neutralizing, human monoclonal antibodies (mAbs) from VelocImmune® mice immunized with gH/gL cDNA. Following high-throughput binding and neutralization screening assays, 11 neutralizing antibodies were identified with unique CDR3 regions and a high-affinity (KD 1.4-65 nM) to the pentamer complex. The antibodies bound to distinct regions within Domains 1 and 2 of gH and effectively neutralized diverse clinical strains in physiologically relevant cell types including epithelial cells, trophoblasts, and monocytes. Importantly, combined adminstration of mAbs with ganciclovir, an FDA approved antiviral, greatly limited virus dissemination. Our work identifies several anti-gH/gL mAbs and sheds light on gH neutralizing epitopes that can guide future vaccine strategies.

Recent progress in development of monoclonal antibodies against human cytomegalovirus

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause permanent childhood disabilities following in utero infection and life threatening diseases in immune-compromised individuals such as those post transplantation. Without an effective vaccine, small molecule antiviral drugs are routinely used in high-risk transplant recipients, but the effectiveness of which is limited by side effects and drug resistance. The potentials of antibody-based passive immune therapies alone or in combination with the small molecule antivirals to treat or prevent HCMV infection have been actively studied. In this review, we focus on the recent publications on identification and characterization of monoclonal antibodies that have the potential to be developed as anti-HCMV therapies. We review the progress in clinical evaluation of antibody-based therapies to prevent HCMV-associated diseases.

Immune Prophylaxis and Therapy for Human Cytomegalovirus Infection

Human Cytomegalovirus (HCMV) infection is widespread and can result in severe sequelae in susceptible populations. Primary HCMV infection of naïve individuals results in life-long latency characterized by frequent and sporadic reactivations. HCMV infection elicits a robust antibody response, including neutralizing antibodies that can block the infection of susceptible cells in vitro and in vivo. Thus, antibody products and vaccines hold great promise for the prevention and treatment of HCMV, but to date, most attempts to demonstrate their safety and efficacy in clinical trials have been unsuccessful. In this review we summarize publicly available data on these products and highlight new developments and approaches that could assist in successful translation of HCMV immunotherapies.

Targeted mutagenesis on PDGFRα-Fc identifies amino acid modifications that allow efficient inhibition of HCMV infection while abolishing PDGF sequestration

Platelet-derived growth factor receptor alpha (PDGFRα) serves as an entry receptor for the human cytomegalovirus (HCMV), and soluble PDGFRα-Fc can neutralize HCMV at a half-maximal effective concentration (EC50) of about 10 ng/ml. While this indicates a potential for usage as an HCMV entry inhibitor PDGFRα-Fc can also bind the physiological ligands of PDGFRα (PDGFs), which likely interferes with the respective signaling pathways and represents a potential source of side effects. Therefore, we tested the hypothesis that interference with PDGF signaling can be prevented by mutations in PDGFRα-Fc or combinations thereof, without losing the inhibitory potential for HCMV. To this aim, a targeted mutagenesis approach was chosen. The mutations were quantitatively tested in biological assays for interference with PDGF-dependent signaling as well as inhibition of HCMV infection and biochemically for reduced affinity to PDGF-BB, facilitating quantification of PDGFRα-Fc selectivity for HCMV inhibition. Mutation of Ile 139 to Glu and Tyr 206 to Ser strongly reduced the affinity for PDGF-BB and hence interference with PDGF-dependent signaling. Inhibition of HCMV infection was less affected, thus increasing the selectivity by factor 4 and 8, respectively. Surprisingly, the combination of these mutations had an additive effect on binding of PDGF-BB but not on inhibition of HCMV, resulting in a synergistic 260fold increase of selectivity. In addition, a recently reported mutation, Val 242 to Lys, was included in the analysis. PDGFRα-Fc with this mutation was fully effective at blocking HCMV entry and had a drastically reduced affinity for PDGF-BB. Combining Val 242 to Lys with Ile 139 to Glu and/or Tyr 206 to Ser further reduced PDGF ligand binding beyond detection. In conclusion, this targeted mutagenesis approach identified combinations of mutations in PDGFRα-Fc that prevent interference with PDGF-BB but maintain inhibition of HCMV, which qualifies such mutants as candidates for the development of HCMV entry inhibitors.

Monoclonal antibodies targeting nonstructural viral antigens can activate ADCC against human cytomegalovirus

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that causes severe disease following congenital infection and in immunocompromised individuals. No vaccines are licensed, and there are limited treatment options. We now show that the addition of anti-HCMV antibodies (Abs) can activate NK cells prior to the production of new virions, through Ab-dependent cellular cytotoxicity (ADCC), overcoming viral immune evasins. Quantitative proteomics defined the most abundant HCMV proteins on the cell surface, and we screened these targets to identify the viral antigens responsible for activating ADCC. Surprisingly, these were not structural glycoproteins; instead, the immune evasins US28, RL11, UL5, UL141, and UL16 each individually primed ADCC. We isolated human monoclonal Abs (mAbs) specific for UL16 or UL141 from a seropositive donor and optimized them for ADCC. Cloned Abs targeting a single antigen (UL141) were sufficient to mediate ADCC against HCMV-infected cells, even at low concentrations. Collectively, these findings validated an unbiased methodological approach to the identification of immunodominant viral antigens, providing a pathway toward an immunotherapeutic strategy against HCMV and potentially other pathogens.

Pharmacology-Guided Rule-Based Adaptive Dose Escalation in First-in-Human Studies

First-in-human (FIH) studies typically progress through cohorts of fixed, standard size throughout the escalation scheme. This work presents and tests a pharmacology-guided rule-based adaptive dose escalation design that aims at making "best use" of participants in early clinical drug evaluation; it is paper based, not requiring real-time access to computational methods. The design minimizes the number of participants exposed to dose levels with low likelihood of being therapeutically relevant. Using criteria based on dose-limiting adverse event rate and on target exposure or target pharmacodynamics, the design increases the sample size when approaching the dose range of potential clinical relevance. The adaptive escalation design was retrospectively tested on actual data from a sample of 40 recently executed FIH studies with novel small and large molecules, and it was evaluated by simulating trials with three compounds with different therapeutic windows, i.e., representing a promising, unacceptable, and dubious profile. In retrospective evaluation of the adaptive escalation design, none of the cases overshot the actually reported top dose; one case resulted in a top dose that was within 20% under the estimated maximum tolerated dose in the original study. The median reduction of total number of participants per study was 38%. Trial simulations confirmed the retrospective evaluation, showing a similar performance of the adaptive escalation design compared with the conventional 6 + 2 design, at a reduced study size for compounds with a presumed acceptable therapeutic window. The adaptive escalation design was shown to make "best use" of participants in FIH studies without compromising safety.

Role of Neutralizing Antibodies in CMV Infection: Implications for New Therapeutic Approaches

Cytomegalovirus (CMV) infection elicits a potent immune response that includes the stimulation of antibodies with neutralizing activity. Recent studies have focused on elucidating the role of neutralizing antibodies in protecting against CMV infection and disease and characterizing viral antigens against which neutralizing antibodies are directed. Here, we provide a synthesis of recent data regarding the role of neutralizing antibodies in protection against CMV infection/disease. We consider the role of humoral immunity in the context of the global CMV-specific immune response, and the implications that recent findings have for vaccine and antibody-based therapy design.

Modeling Human Cytomegalovirus-Induced Microcephaly in Human iPSC-Derived Brain Organoids

Although congenital infection by human cytomegalovirus (HCMV) is well recognized as a leading cause of neurodevelopmental defects, HCMV neuropathogenesis remains poorly understood. A major challenge for investigating HCMV-induced abnormal brain development is the strict CMV species specificity, which prevents the use of animal models to directly study brain defects caused by HCMV. We show that infection of human-induced pluripotent-stem-cell-derived brain organoids by a “clinical-like” HCMV strain results in reduced brain organoid growth, impaired formation of cortical layers, and abnormal calcium signaling and neural network activity. Moreover, we show that the impeded brain organoid development caused by HCMV can be prevented by neutralizing antibodies (NAbs) that recognize the HCMV pentamer complex. These results demonstrate in a three-dimensional cellular biosystem that HCMV can impair the development and function of the human brain and provide insights into the potential capacity of NAbs to mitigate brain defects resulted from HCMV infection.

Human iPSC-derived brain organoids to model HCMV-induced brain malformation

“Clinical-like” HCMV strain impairs human brain organoid growth and structure

HCMV-infected brain organoids exhibit abnormal calcium signaling and neural network

HCMV-induced brain organoid abnormality can be prevented by neutralizing antibodies

The N Terminus of Human Cytomegalovirus Glycoprotein O Is Important for Binding to the Cellular Receptor PDGFRα

The human cytomegalovirus (HCMV) glycoprotein complex gH/gL/gO is required for the infection of cells by cell-free virions. It was recently shown that entry into fibroblasts depends on the interaction of gO with the platelet-derived growth factor receptor alpha (PDGFRα). This interaction can be blocked with soluble PDGFRα-Fc, which binds to HCMV virions and inhibits entry. The aim of this study was to identify parts of gO that contribute to PDGFRα binding. In a systematic mutational approach, we targeted potential interaction sites by exchanging conserved clusters of charged amino acids of gO with alanines. To screen for impaired interaction with PDGFRα, virus mutants were tested for sensitivity to inhibition by soluble PDGFRα-Fc. Two mutants with mutations within the N terminus of gO (amino acids 56 to 61 and 117 to 121) were partially resistant to neutralization. To validate whether these mutations impair interaction with PDGFRα-Fc, we compared binding of PDGFRα-Fc to mutant and wild-type virions via quantitative immunofluorescence analysis. PDGFRα-Fc staining intensities were reduced by 30% to 60% with mutant virus particles compared to wild-type particles. In concordance with the reduced binding to the soluble receptor, virus penetration into fibroblasts, which relies on binding to the cellular PDGFRα, was also reduced. In contrast, PDGFRα-independent penetration into endothelial cells was unaltered, demonstrating that the phenotypes of the gO mutant viruses were specific for the interaction with PDGFRα. In conclusion, the mutational screening of gO revealed that the N terminus of gO contributes to efficient spread in fibroblasts by promoting the interaction of virions with its cellular receptor.IMPORTANCE The human cytomegalovirus is a highly prevalent pathogen that can cause severe disease in immunocompromised hosts. Currently used drugs successfully target the viral replication within the host cell, but their use is restricted due to side effects and the development of resistance. An alternative approach is the inhibition of virus entry, for which understanding the details of the initial virus-cell interaction is desirable. As binding of the viral gH/gL/gO complex to the cellular PDGFRα drives infection of fibroblasts, this is a potential target for inhibition of infection. Our mutational mapping approach suggests the N terminus as the receptor binding portion of the protein. The respective mutants were partially resistant to inhibition by PDGFRα-Fc but also attenuated for infection of fibroblasts, indicating that such mutations have little if any benefit for the virus. These findings highlight the potential of targeting the interaction of gH/gL/gO with PDGFRα for therapeutic inhibition of HCMV.

Resolution of unexpected pregnancy-related findings in a rat embryofetal development and toxicokinetic study of monoclonal antibodies specific for hCMV

BACKGROUND

Developmental and reproductive toxicity testing is not uniformly warranted for biopharmaceuticals that lack relevant targets in test species. However, RG7667, consisting of two monoclonal antibodies specific for human cytomegalovirus (hCMV), was intended for administration to pregnant women to prevent transmission of CMV to the developing fetus.

METHODS

Considering the target indication, a Pilot Embryo Fetal Development/Toxicokinetic study was conducted to assess toxicokinetics in the dam and fetuses and general tolerability.

RESULTS

RG7667 administered intravenously to presumed pregnant Sprague-Dawley rats was well tolerated with no clinical signs in any dam and comparable litter sizes and viability across groups. However, at cesarean section, hepatic necrosis and pancreatic edema were identified in two dams administered RG7667, with no clear dose relationship. Investigation of total protein, albumin, and transaminase activity in residual serum from TK samples demonstrated striking hypoproteinemia and elevated transaminases limited to these two dams. Overall, these pathology findings in dams were considered of uncertain relationship to RG7667; therefore, a subsequent Pivotal EFD study was conducted, which did not repeat the liver or pancreatic findings.

CONCLUSIONS

The results of the Pivotal study confirmed the lack of overt toxicity, teratogenicity, or effects on litter size and viability when human or humanized monoclonal antibodies that lack an endogenous target are administered IV to rats during pregnancy. With these additional data, we concluded that the unexpected pathology findings in the Pilot study were not specific to RG7667, but rather highlight some clinical pathology and macroscopic/microscopic findings that can occur during pregnancy in rats.

Large-Scale Screening of HCMV-Seropositive Blood Donors Indicates that HCMV Effectively Escapes from Antibodies by Cell-Associated Spread

Immunoglobulins are only moderately effective for the treatment of human cytomegalovirus (HCMV) infections, possibly due to ineffectiveness against cell-associated virus spread. To overcome this limitation, we aimed to identify individuals with exceptional antibodies in their plasma that can efficiently block the cell-associated spread of HCMV. A Gaussia luciferase-secreting mutant of the cell-associated HCMV strain Merlin was generated, and luciferase activity evaluated as a readout for the extent of cell-associated focal spread. This reporter virus-based assay was then applied to screen plasma samples from 8400 HCMV-seropositive individuals for their inhibitory effect, including direct-acting antiviral drugs as positive controls. None of the plasmas reduced virus spread to the level of these controls. Even the top-scoring samples that partially reduced luciferase activity in the screening assay failed to inhibit focal growth when reevaluated with a more accurate, immunofluorescence-based assay. Selected sera with high neutralizing capacity against free viruses were analyzed separately, and none of them prevented the focal spread of three recent clinical HCMV isolates nor reduced the number of particles transmitted, as demonstrated with a fluorescent Merlin mutant. We concluded that donors with cell-to-cell-spread-inhibiting plasma are nonexistent or extremely rare, emphasizing cell-associated spread as a highly efficient immune escape mechanism of HCMV.

Pharmacokinetics and Exposure-Response Analysis of RG7667, a Combination of Two Anticytomegalovirus Monoclonal Antibodies, in a Phase 2a Randomized Trial To Prevent Cytomegalovirus Infection in High-Risk Kidney Transplant Recipients

RG7667, a novel combination of two anticytomegalovirus (anti-CMV) monoclonal IgG1 antibodies (MCMV5322A and MCMV3068A), was designed to block CMV entry into host cells. It was developed as a potential therapy for preventing CMV infection and disease in transplant recipients. RG7667 was assessed for preventing CMV infection in a phase 2a trial with CMV-seronegative recipients of kidney transplants from CMV-seropositive donors. The patients received 4 intravenous doses of RG7667 (10 mg/kg of body weight of each antibody, n = 60) or placebo (n = 60) at the time of the transplant and at 1, 4, and 8 weeks after the transplant. Serum samples were collected for pharmacokinetic (PK) analysis and antidrug antibody (ADA) evaluation. To guide future dose selection, the relationships between RG7667 exposure and pharmacological activity were evaluated. MCMV5322A and MCMV3068A exposures were confirmed in all RG7667-treated patients. Mean clearances for MCMV5322A and MCMV3068A were 2.97 and 2.65 ml/day/kg, respectively, and the terminal half-lives of MCMV5322A and MCMV3068A were 26.9 and 27.4 days, respectively. The ADA incidence was low and was not associated with lower drug exposure. Patients with RG7667 or component antibody exposures greater than the respective median values had a lower incidence of viremia at 12 weeks and 24 weeks after transplantation and a longer delayed time to detectable CMV viremia than patients with exposures less than the median values. MCMV5322A and MCMV3068A exhibited expected IgG1 PK profiles in high-risk kidney transplant recipients, consistent with the earlier PK behavior of RG7667 in healthy subjects. Higher drug exposure was associated with better anti-CMV pharmacological activity. (This study has been registered at ClinicalTrials.gov under identifier NCT01753167.).

Binding and neutralizing anti-cytomegalovirus activities in immune globulin products

Congenital infection as well as infection of immunocompromised individuals by cytomegalovirus (CMV) can be associated with significant morbidity, mortality, and long-term adverse health outcomes. Assessment of anti-viral activity using appropriate assays is essential for ensuring safe and efficacious use of therapeutic CMV immune globulin (IG) products. In this study, we used commercial ELISA kits to compare anti-CMV antibody binding activity and avidity for lots of CMV-specific and normal IG products available in the US market. Additionally, neutralizing activity of IG products was measured against CMV strains (AD169^wt131 or TB40E-GFP) in MRC-5 human fibroblasts and ARPE-19 human epithelial cells. Our data revealed that, regardless of the method, anti-CMV activity was higher in CMV IG lots we tested compared with normal IG lots; CMV binding activity was at least 4-fold higher, and neutralizing activity at least 2- and 3-fold higher for epithelial and fibroblast cells, respectively, in CMV IG lots compared with normal IG lots. Furthermore, anti-CMV activity values from all three methods (ELISA, neutralization in MRC-5 cells, and neutralization in ARPE-19 cells) were highly correlated, whereas avidity, although higher in CMV IG lots, did not correlate well with either binding or neutralizing activities.

A Phase 1, Randomized, Double-Blind, Placebo-Controlled, Single-Ascending-Dose Study To Investigate the Safety, Tolerability, and Pharmacokinetics of an Anti-Influenza B Virus Monoclonal Antibody, MHAB5553A, in Healthy Volunteers

Influenza B can cause significant morbidity and mortality. MHAB5553A, a human monoclonal immunoglobulin G1 (IgG1) antibody that binds to a highly conserved region of the hemagglutinin protein of influenza B virus, is being examined as a novel therapeutic for the treatment of influenza B patients with severe disease. This phase 1, randomized, double-blind, placebo-controlled, single-ascending-dose study was conducted to assess the safety, tolerability, and pharmacokinetics (PK) of MHAB5553A. Twenty-six healthy male and female volunteers of >18 years of age were randomized into five cohorts receiving a single intravenous (i.v.) dose of 120, 1,200, 3,600, 8,400, or 10,800 mg MHAB5553A or placebo (four active:one placebo, except for the 120-mg cohort [4:2]). Subjects were followed for 120 days after dosing. No subject discontinued the study, no dose-limiting adverse events or serious adverse events were reported, and a maximum tolerated dose (MTD) was not defined. The most commonly reported adverse events were cold symptoms and headache; most were mild and occurred at a similar rate across all cohorts. MHAB5553A showed no relevant time- or dose-related changes in laboratory values or vital signs compared to the placebo. The observed serum PK was linear and generally dose proportional, and the observed nasal PK was nonlinear and generally non-dose proportional. MHAB5553A is generally well tolerated in healthy volunteers up to at least a single i.v. dose of 10,800 mg and demonstrated linear serum PK consistent with those of a human IgG1 antibody lacking known endogenous targets in humans. (This study has been registered at ClinicalTrials.gov under registration no. NCT02528903.).

Antibody therapies for the prevention and treatment of viral infections

Antibodies are an important component in host immune responses to viral pathogens. Because of their unique maturation process, antibodies can evolve to be highly specific to viral antigens. Physicians and researchers have been relying on such high specificity in their quest to understand host–viral interaction and viral pathogenesis mechanisms and to find potential cures for viral infection and disease. With more than 60 recombinant monoclonal antibodies developed for human use in the last 20 years, monoclonal antibodies are now considered a viable therapeutic modality for infectious disease targets, including newly emerging viral pathogens such as Ebola representing heightened public health concerns, as well as pathogens that have long been known, such as human cytomegalovirus. Here, we summarize some recent advances in identification and characterization of monoclonal antibodies suitable as drug candidates for clinical evaluation, and review some promising candidates in the development pipeline.

Impact of Antibodies and Strain Polymorphisms on Cytomegalovirus Entry and Spread in Fibroblasts and Epithelial Cells

Cytomegalovirus (CMV) entry into fibroblasts differs from entry into epithelial cells. CMV also spreads cell to cell and can induce syncytia. To gain insights into these processes, 27 antibodies targeting epitopes in CMV virion glycoprotein complexes, including glycoprotein B (gB), gH/gL, and the pentamer, were evaluated for their effects on viral entry and spread. No antibodies inhibited CMV spread in fibroblasts, including those with potent neutralizing activity against fibroblast entry, while all antibodies that neutralized epithelial cell entry also inhibited spread in epithelial cells and a correlation existed between the potencies of these two activities. This suggests that exposure of virions to the cell culture medium is obligatory during spread in epithelial cells but not in fibroblasts. In fibroblasts, the formation of syncytiumlike structures was impaired not only by antibodies to gB or gH/gL but also by antibodies to the pentamer, suggesting a potential role for the pentamer in promoting fibroblast fusion. Four antibodies reacted with linear epitopes near the N terminus of gH, exhibited strain specificity, and neutralized both epithelial cell and fibroblast entry. Five other antibodies recognized conformational epitopes in gH/gL and neutralized both fibroblast and epithelial cell entry. That these antibodies were strain specific for neutralizing fibroblast but not epithelial cell entry suggests that polymorphisms external to certain gH/gL epitopes may influence antibody neutralization during fibroblast but not epithelial cell entry. These findings may have implications for elucidating the mechanisms of CMV entry, spread, and antibody evasion and may assist in determining which antibodies may be most efficacious following active immunization or passive administration.IMPORTANCE Cytomegalovirus (CMV) is a significant cause of birth defects among newborns infected in utero and morbidity and mortality in transplant and AIDS patients. Monoclonal antibodies and vaccines targeting humoral responses are under development for prophylactic or therapeutic use. The findings reported here (i) confirm that cell-to-cell spread of CMV is sensitive to antibody inhibition in epithelial cells but not fibroblasts, (ii) demonstrate that antibodies can restrict the formation in vitro of syncytiumlike structures that resemble syncytial cytomegalic cells that are associated with CMV disease in vivo, and (iii) reveal that neutralization of CMV by antibodies to certain epitopes in gH or gH/gL is both strain and cell type dependent and can be governed by polymorphisms in sequences external to the epitopes. These findings serve to elucidate the mechanisms of CMV entry, spread, and antibody evasion and may have important implications for the development of CMV vaccines and immunotherapeutics.

Phase 2 Randomized, Double-Blind, Placebo-Controlled Trial of RG7667, a Combination Monoclonal Antibody, for Prevention of Cytomegalovirus Infection in High-Risk Kidney Transplant Recipients

Cytomegalovirus (CMV) infection is a significant complication after kidney transplantation. We examined the ability of RG7667, a combination of two monoclonal antibodies, to prevent CMV infection in high-risk kidney transplant recipients in a randomized, double-blind, placebo-controlled trial. CMV-seronegative recipients of a kidney transplant from a CMV-seropositive donor (D+R-) were randomized to receive RG7667 (n = 60) or placebo (n = 60) at the time of transplant and 1, 4, and 8 weeks posttransplant. Patients were monitored for CMV viremia every 1 to 2 weeks posttransplant for 24 weeks. Patients who had seroconverted (D+R+) or withdrawn before dosing were excluded from the analysis (n = 4). CMV viremia occurred in 27 of 59 (45.8%) patients receiving RG7667 and 35 of 57 (61.4%) patients receiving placebo (stratum-adjusted difference, 15.3%; P = 0.100) within 12 weeks posttransplant and in 30 of 59 (50.8%) patients receiving RG7667 and 40 of 57 (70.2%) patients receiving placebo (stratum-adjusted difference, 19.3%; P = 0.040) within 24 weeks posttransplant. Median time to CMV viremia was 139 days in patients receiving RG7667 compared to 46 days in patients receiving placebo (hazard ratio, 0.53; P = 0.009). CMV disease was less common in the RG7667 than placebo group (3.4% versus 15.8%; P = 0.030). Adverse events were generally balanced between treatment groups. In high-risk kidney transplant recipients, RG7667 was well tolerated, numerically reduced the incidence of CMV infection within 12 and 24 weeks posttransplant, delayed time to CMV viremia, and was associated with less CMV disease than the placebo. (This study has been registered at ClinicalTrials.gov under registration no. NCT01753167.).

The Cell Biology of Cytomegalovirus: Implications for Transplantation

Interpretation of clinical data regarding the impact of cytomegalovirus (CMV) infection on allograft function is complicated by the diversity of viral strains and substantial variability of cellular receptors and viral gene expression in different tissues. Variation also exists in nonspecific (monocytes and dendritic cells) and specific (NK cells, antibodies) responses that augment T cell antiviral activities. Innate immune signaling pathways and expanded pools of memory NK cells and γδ T cells also serve to amplify host responses to infection. The clinical impact of specific memory T cell anti-CMV responses that cross-react with graft antigens and alloantigens is uncertain but appears to contribute to graft injury and to the abrogation of allograft tolerance. These responses are modified by diverse immunosuppressive regimens and by underlying host immune deficits. The impact of CMV infection on the transplant recipient reflects cellular changes and corresponding host responses, the convergence of which has been termed the "indirect effects" of CMV infection. Future studies will clarify interactions between CMV infection and allograft injury and will guide interventions that may enhance clinical outcomes in transplantation.