Monoclonal Antibody Disrupts Biofilm Structure and Restores Antibiotic Susceptibility in an Orthopedic Implant Infection Model

Bacterial biofilms on orthopedic implants are resistant to the host immune response and to traditional systemic antibiotics. Novel therapies are needed to improve patient outcomes. TRL1068 is a human monoclonal antibody (mAb) against a biofilm anchoring protein. For assessment of this agent in an orthopedic implant infection model, efficacy was measured by reduction in bacterial burden of Staphylococcus aureus, the most common pathogen for prosthetic joint infections (PJI). Systemic treatment with the biofilm disrupting mAb TRL1068 in conjunction with vancomycin eradicated S. aureus from steel pins implanted in the spine for 26 of 27 mice, significantly more than for vancomycin alone. The mechanism of action was elucidated by two microscopy studies. First, TRL1068 was localized to biofilm using a fluorescent antibody tag. Second, a qualitative effect on biofilm structure was observed using scanning electron microscopy (SEM) to examine steel pins that had been treated in vivo. SEM images of implants retrieved from control mice showed abundant three-dimensional biofilms, whereas those from mice treated with TRL1068 did not. Clinical Significance: TRL1068 binds at high affinity to S. aureus biofilms, thereby disrupting the three-dimensional structure and significantly reducing implant CFUs in a well-characterized orthopedic model for which prior tested agents have shown only partial efficacy. TRL1068 represents a promising systemic treatment for orthopedic implant infection.

Immune Prophylaxis Targeting the Respiratory Syncytial Virus (RSV) G Protein

The respiratory syncytial virus (RSV) causes significant respiratory disease in young infants and the elderly. Immune prophylaxis in infants is currently limited to palivizumab, an anti-RSV fusion (F) protein monoclonal antibody (mAb). While anti-F protein mAbs neutralize RSV, they are unable to prevent aberrant pathogenic responses provoked by the RSV attachment (G) protein. Recently, the co-crystal structures of two high-affinity anti-G protein mAbs that bind the central conserved domain (CCD) at distinct non-overlapping epitopes were solved. mAbs 3D3 and 2D10 are broadly neutralizing and block G protein CX3C-mediated chemotaxis by binding antigenic sites γ1 and γ2, respectively, which is known to reduce RSV disease. Previous studies have established 3D3 as a potential immunoprophylactic and therapeutic; however, there has been no similar evaluation of 2D10 available. Here, we sought to determine the differences in neutralization and immunity to RSV Line19F infection which recapitulates human RSV infection in mouse models making it useful for therapeutic antibody studies. Prophylactic (24 h prior to infection) or therapeutic (72 h post-infection) treatment of mice with 3D3, 2D10, or palivizumab were compared to isotype control antibody treatment. The results show that 2D10 can neutralize RSV Line19F both prophylactically and therapeutically, and can reduce disease-causing immune responses in a prophylactic but not therapeutic context. In contrast, 3D3 was able to significantly (p < 0.05) reduce lung virus titers and IL-13 in a prophylactic and therapeutic regimen suggesting subtle but important differences in immune responses to RSV infection with mAbs that bind distinct epitopes.

Anti-G protein antibodies targeting the RSV G protein CX3C chemokine region improve the interferon response

Background

Respiratory syncytial virus (RSV) is a poor inducer of antiviral interferon (IFN) responses which result in incomplete immunity and RSV disease. Several RSV proteins alter antiviral responses, including the non-structural proteins (NS1, NS2) and the major viral surface proteins, that is, fusion (F) and attachment (G) proteins. The G protein modifies the host immune response to infection linked in part through a CX3 C chemokine motif. Anti-G protein monoclonal antibodies (mAbs), that is, clones 3D3 and 2D10 that target the G protein CX3C chemokine motif can neutralize RSV and inhibit G protein-CX3CR1 mediated chemotaxis.

Objectives

Determine how monoclonal antibodies against the RSV F and G proteins modify the type I and III IFN responses to RSV infection.

Design

As the G protein CX3 C motif is implicated in IFN antagonism, we evaluated two mAbs that block G protein CX3C-CX3CR1 interaction and compared responses to isotype mAb control using a functional cellular assay and mouse model.

Methods

Mouse lung epithelial cells (MLE-15 cells) and BALB/c mice were infected with RSV Line19 F following prophylactic mAb treatment. Cell supernatant or bronchoalveolar lavage fluid (BALF) were assayed for types I and III IFNs. Cells were interrogated for changes in IFN-related gene expression.

Results

Treatment with an anti-G protein mAb (3D3) resulted in improved IFN responses compared with isotype control following infection with RSV, partially independently of neutralization, and this was linked to upregulated SOCS1 expression.

Conclusions

These findings show that anti-G protein antibodies improve the protective early antiviral response, which has important implications for vaccine and therapeutic design.

Plain Language Summary

RSV is a leading cause of respiratory disease in infants and the elderly. The only Food and Drug Administration-approved prophylactic treatment is limited to an anti-F protein monoclonal antibody (mAb), that is, palivizumab which has modest efficacy against RSV disease. Accumulating evidence suggests that targeting the RSV attachment (G) protein may provide improved protection from RSV disease. It is known that the G protein is an IFN antagonist, and IFN has been shown to be protective against RSV disease. In this study, we compared IFN responses in mouse lung epithelial (MLE-15) cells and in mice infected with RSV Line19 F treated with anti-G protein or anti-F protein mAbs. The levels of type I and III IFNs were determined. Anti-G protein mAbs improved the levels of IFNs compared with isotype-treated controls. These findings support the concept that anti-G protein mAbs mediate improved IFN responses against RSV disease, which may enable improved treatment of RSV infections.

Native Human Antibody to Shr Promotes Mice Survival After Intraperitoneal Challenge With Invasive Group A Streptococcus

BACKGROUND

A vaccine against group A Streptococcus (GAS) has been actively pursued for decades. The surface receptor Shr is vital in GAS heme uptake and provides an effective target for active and passive immunization. Here, we isolated human monoclonal antibodies (mAbs) against Shr and evaluated their efficacy and mechanism.

METHODS

We used a single B-lymphocyte screen to discover the mAbs TRL186 and TRL96. Interactions of the mAbs with whole cells, proteins, and peptides were investigated. Growth assays and cultured phagocytes were used to study the mAbs' impact on heme uptake and bacterial killing. Efficacy was tested in prophylactic and therapeutic vaccination using intraperitoneal mAb administration and GAS challenge.

RESULTS

Both TRL186 and TRL96 interact with whole GAS cells, recognizing the NTR and NEAT1 domains of Shr, respectively. Both mAbs promoted killing by phagocytes in vitro, but prophylactic administration of only TRL186 increased mice survival. TRL186 improved survival also in a therapeutic mode. TRL186 but not TRL96 also impeded Shr binding to hemoglobin and GAS growth on hemoglobin iron.

CONCLUSIONS

Interference with iron acquisition is central for TRL186 efficacy against GAS. This study supports the concept of antibody-based immunotherapy targeting the heme uptake proteins to combat streptococcal infections.

Advances in the Development of Therapeutics for Cytomegalovirus Infections

The development of therapeutics for cytomegalovirus (CMV) infections, while progressing, has not matched the pace of new treatments of human immunodeficiency virus (HIV) infections; nevertheless, recent developments in the treatment of CMV infections have resulted in improved human health and perhaps will encourage the development of new therapeutic approaches. First, the deployment of ganciclovir and valganciclovir for both the prevention and treatment of CMV infections and disease in transplant recipients has been further improved with the licensure of the efficacious and less toxic letermovir. Regardless, late-onset CMV disease, specifically pneumonia, remains problematic. Second, the treatment of congenital CMV infections with valganciclovir has beneficially improved both hearing and neurologic outcomes, both fundamental advances for these children. In these pediatric studies, viral load was decreased but not eliminated. Thus, an important lesson learned from studies in both populations is the need for new antiviral agents and the necessity for combination therapies as has been shown to be beneficial in the treatment of HIV infections, among others. The development of monoclonal antibodies, sirtuins, and cyclopropovir may provide new treatment options.

Comparative neutralizing potencies of antibodies suggest conservation as well as mechanistic differences in human cytomegalovirus entry into epithelial and endothelial cells

Antibody neutralization of cytomegalovirus (CMV) entry into diverse cell types is a key consideration for development of vaccines and immunotherapeutics. CMV entry into fibroblasts differs significantly from entry into epithelial or endothelial cells: fibroblast entry is mediated by gB and gH/gL/gO, whereas both epithelial and endothelial cell entry require an additional pentameric complex (PC) comprised of gH/gL/UL128/UL130/UL131A. Because PC-specific antibodies in CMV-seropositive human sera do not affect fibroblast entry but potently block entry into epithelial or endothelial cells, substantially higher neutralizing potencies for CMV-positive sera are observed when assayed using epithelial cells as targets than when using fibroblasts. That certain sera exhibit similar discordances between neutralizing potencies measured using epithelial vs. endothelial cells (Gerna G. et al.J Gen Virol, 89:853–865, 2008) suggested that additional mechanistic differences may also exist between epithelial and endothelial cell entry. To further explore this issue, neutralizing potencies using epithelial and endothelial cells were simultaneously determined for eight CMV-positive human sera, CMV-hyperimmune globulin, and a panel of monoclonal or anti-peptide antibodies targeting specific epitopes in gB, gH, gH/gL, or the PC. No significant differences were observed between epithelial and endothelial neutralizing potencies of epitope-specific antibodies, CMV-hyperimmune globulin, or seven of the eight human sera. However, one human serum exhibited a six-fold higher potency for neutralizing entry into epithelial cells vs. endothelial cells. These results suggest that epitopes exist that are important for epithelial entry but are less critical, or perhaps dispensable, for endothelial cell entry. Their existence should be considered when developing monoclonal antibody therapies or subunit vaccines representing limited epitopes.

Human antibody repertoire frequently includes antibodies to a bacterial biofilm associated protein

We have previously described a native human monoclonal antibody, TRL1068, that disrupts bacterial biofilms by extracting from the biofilm matrix key scaffolding proteins in the DNABII family, which are present in both gram positive and gram negative bacterial species. The antibiotic resistant sessile bacteria released from the biofilm then revert to the antibiotic sensitive planktonic state. Qualitative resensitization to antibiotics has been demonstrated in three rodent models of acute infections. We report here the surprising discovery that antibodies against the target family were found in all twenty healthy humans surveyed, albeit at a low level requiring a sensitive single B-cell assay for detection. We have cloned 21 such antibodies. Aside from TRL1068, only one (TRL1330) has all the biochemical properties believed necessary for pharmacological efficacy (broad spectrum epitope specificity and high affinity). We suggest that the other anti-DNABII antibodies, while not necessarily curative, reflect an immune response at some point in the donor's history to these components of biofilms. Such an immune response could reflect exposure to bacterial reservoirs that have been previously described in chronic non-healing wounds, periodontal disease, chronic obstructive pulmonary disease, colorectal cancer, rheumatoid arthritis, and atherosclerotic artery explants. The detection of anti-DNABII antibodies in all twenty surveyed donors with no active infection suggests that bacterial biofilm reservoirs may be present periodically in most healthy individuals. Biofilms routinely shed bacteria, creating a continuous low level inflammatory stimulus. Since chronic subclinical inflammation is thought to contribute to most aging-related diseases, suppression of bacterial biofilm has potential value in delaying age-related pathology.

Role of Type I Interferon (IFN) in the Respiratory Syncytial Virus (RSV) Immune Response and Disease Severity

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract disease in children <2 years of age. Increased morbidity and mortality have been reported in high-risk patients, such as premature infants, patients with cardiac disease, and severely immune compromised patients. Severe disease is associated with the virulence of the virus as well as host factors specifically including the innate immune response. The role of type I interferons (IFNs) in the response to RSV infection is important in regulating the rate of virus clearance and in directing the character of the immune response, which is normally associated with protection and less severe disease. Two RSV non-structural proteins, NS1 and NS2, as well as the envelope G glycoprotein are known to suppress type I IFN production and a robust type I IFN response to RSV does not occur in human infants or neonatal mouse models of RSV infection. Additionally, presence of type I IFNs are associated with mild symptoms in infants and administration of IFN-α prior to infection of neonatal mice with RSV reduces immunopathology. This evidence has driven RSV prophylaxis and therapeutic efforts to consider strategies for enhancing type I IFN production.

Structures of respiratory syncytial virus G antigen bound to broadly neutralizing antibodies

Respiratory syncytial virus (RSV) is a top cause of severe lower respiratory tract disease and mortality in young children and the elderly. The viral envelope G glycoprotein contributes to pathogenesis through its roles in host cell attachment and modulation of host immunity. Although the G glycoprotein is a target of protective RSV-neutralizing antibodies, its development as a vaccine antigen has been hindered by its heterogeneous glycosylation and sequence variability outside a conserved central domain (CCD). We describe the cocrystal structures of two high-affinity broadly neutralizing human monoclonal antibodies bound to the RSV G CCD. The antibodies bind to neighboring conformational epitopes, which we named antigenic sites γ1 and γ2, that span a highly conserved surface, illuminating an important region of vulnerability. We further show that isolated RSV G CCD activates the chemokine receptor CX3CR1 and that antibodies block this activity. These studies provide a template for rational vaccine design targeting this key contributor to RSV disease.

High affinity anti-TIM-3 and anti-KIR monoclonal antibodies cloned from healthy human individuals

We report here the cloning of native high affinity anti-TIM-3 and anti-KIR IgG monoclonal antibodies (mAbs) from peripheral blood mononuclear cells (PBMC) of healthy human donors. The cells that express these mAbs are rare, present at a frequency of less than one per 10⁵ memory B-cells. Using our proprietary multiplexed screening and cloning technology CellSpot™ we assessed the presence of memory B-cells reactive to foreign and endogenous disease-associated antigens within the same individual. When comparing the frequencies of antigen-specific memory B-cells analyzed in over 20 screening campaigns, we found a strong correlation of the presence of anti-TIM-3 memory B-cells with memory B-cells expressing mAbs against three disease-associated antigens: (i) bacterial DNABII proteins that are a marker for Gram negative and Gram positive bacterial infections, (ii) hemagglutinin (HA) of influenza virus and (iii) the extracellular domain of anaplastic lymphoma kinase (ALK). One of the native anti-KIR mAbs has similar characteristics as lirilumab, an anti-KIR mAb derived from immunization of humanized transgenic mice that is in ongoing clinical trials. It is interesting to speculate that these native anti-TIM-3 and anti-KIR antibodies may function as natural regulatory antibodies, analogous to the pharmacological use in cancer treatment of engineered antibodies against the same targets. Further characterization studies are needed to define the mechanisms through which these native antibodies may function in healthy and disease conditions.

Maternal Antibody Responses and Nonprimary Congenital Cytomegalovirus Infection of HIV-1-Exposed Infants

Risk of congenital cytomegalovirus (cCMV) transmission is highly dependent on the presence of preexisting maternal immunity, with the lowest rates observed in CMV-seroimmune populations. Among infants of CMV-seroimmune women, those who are exposed to human immunodeficiency virus (HIV) have an increased risk of acquiring cCMV infection as compared to HIV-unexposed infants. To better understand the risk factors of nonprimary cCMV transmission in HIV-infected women, we performed a case-control study in which CMV-specific plasma antibody responses from 19 CMV-transmitting and 57 CMV-nontransmitting women with chronic CMV/HIV coinfection were evaluated for the ability to predict the risk of cCMV infection. Primary multivariable conditional logistic regression analysis revealed an association between epithelial-tropic CMV neutralizing titers and a reduced risk of cCMV transmission (odds ratio [OR], 0.18; 95% confidence interval [CI], .03-.93; P = .04), although this effect was not significant following correction for multiple comparisons (false-discovery rate, 0.12). Exploratory analysis of the CMV specificity of plasma antibodies revealed that immunoglobulin G (IgG) responses against the glycoprotein B (gB) neutralizing epitope AD-2 had a borderline association with low risk of transmission (OR, 0.72; 95% CI, .51-1.00; P = .05), although this was not confirmed in a post hoc plasma anti-AD-2 IgG blocking assay. Our data suggest that maternal neutralizing antibody responses may play a role in protection against cCMV in HIV/CMV-coinfected populations.

Human cytomegalovirus infection interferes with the maintenance and differentiation of trophoblast progenitor cells of the human placenta

Human cytomegalovirus (HCMV) is a major cause of birth defects that include severe neurological deficits, hearing and vision loss, and intrauterine growth restriction. Viral infection of the placenta leads to development of avascular villi, edema, and hypoxia associated with symptomatic congenital infection. Studies of primary cytotrophoblasts (CTBs) revealed that HCMV infection impedes terminal stages of differentiation and invasion by various molecular mechanisms. We recently discovered that HCMV arrests earlier stages involving development of human trophoblast progenitor cells (TBPCs), which give rise to the mature cell types of chorionic villi-syncytiotrophoblasts on the surfaces of floating villi and invasive CTBs that remodel the uterine vasculature. Here, we show that viral proteins are present in TBPCs of the chorion in cases of symptomatic congenital infection. In vitro studies revealed that HCMV replicates in continuously self-renewing TBPC lines derived from the chorion and alters expression and subcellular localization of proteins required for cell cycle progression, pluripotency, and early differentiation. In addition, treatment with a human monoclonal antibody to HCMV glycoprotein B rescues differentiation capacity, and thus, TBPCs have potential utility for evaluation of the efficacies of novel antiviral antibodies in protecting and restoring placental development. Our results suggest that HCMV replicates in TBPCs in the chorion in vivo, interfering with the earliest steps in the growth of new villi, contributing to virus transmission and impairing compensatory development. In cases of congenital infection, reduced responsiveness of the placenta to hypoxia limits the transport of substances from maternal blood and contributes to fetal growth restriction.

IMPORTANCE

Human cytomegalovirus (HCMV) is a leading cause of birth defects in the United States. Congenital infection can result in permanent neurological defects, mental retardation, hearing loss, visual impairment, and pregnancy complications, including intrauterine growth restriction, preterm delivery, and stillbirth. Currently, there is neither a vaccine nor any approved treatment for congenital HCMV infection during gestation. The molecular mechanisms underlying structural deficiencies in the placenta that undermine fetal development are poorly understood. Here we report that HCMV replicates in trophoblast progenitor cells (TBPCs)-precursors of the mature placental cells, syncytiotrophoblasts and cytotrophoblasts, in chorionic villi-in clinical cases of congenital infection. Virus replication in TBPCs in vitro dysregulates key proteins required for self-renewal and differentiation and inhibits normal division and development into mature placental cells. Our findings provide insights into the underlying molecular mechanisms by which HCMV replication interferes with placental maturation and transport functions.

HCMV infection of human trophoblast progenitor cells of the placenta is neutralized by a human monoclonal antibody to glycoprotein B and not by antibodies to the pentamer complex

Human cytomegalovirus (HCMV) is the major viral cause of congenital infection and birth defects. Primary maternal infection often results in virus transmission, and symptomatic babies can have permanent neurological deficiencies and deafness. Congenital infection can also lead to intrauterine growth restriction, a defect in placental transport. HCMV replicates in primary cytotrophoblasts (CTBs), the specialized cells of the placenta, and inhibits differentiation/invasion. Human trophoblast progenitor cells (TBPCs) give rise to the mature cell types of the chorionic villi, CTBs and multi-nucleated syncytiotrophoblasts (STBs). Here we report that TBPCs are fully permissive for pathogenic and attenuated HCMV strains. Studies with a mutant virus lacking a functional pentamer complex (gH/gL/pUL128-131A) showed that virion entry into TBPCs is independent of the pentamer. In addition, infection is blocked by a potent human neutralizing monoclonal antibody (mAb), TRL345, reactive with glycoprotein B (gB), but not mAbs to the pentamer proteins pUL130/pUL131A. Functional studies revealed that neutralization of infection preserved the capacity of TBPCs to differentiate and assemble into trophospheres composed of CTBs and STBs in vitro. Our results indicate that mAbs to gB protect trophoblast progenitors of the placenta and could be included in antibody treatments developed to suppress congenital infection and prevent disease.

Multiplexed screening of natural humoral immunity identifies antibodies at fine specificity for complex and dynamic viral targets

Viral entry targets with therapeutic neutralizing potential are subject to multiple escape mechanisms, including antigenic drift, immune dominance of functionally irrelevant epitopes, and subtle variations in host cell mechanisms. A surprising finding of recent years is that potent neutralizing antibodies to viral epitopes independent of strain exist, but are poorly represented across the diverse human population. Identifying these antibodies and understanding the biology mediating the specific immune response is thus difficult. An effective strategy for meeting this challenge is to incorporate multiplexed antigen screening into a high throughput survey of the memory B cell repertoire from immune individuals. We used this approach to discover suites of cross-clade antibodies directed to conformational epitopes in the stalk region of the influenza A hemagglutinin (HA) protein and to select high-affinity anti-peptide antibodies to the glycoprotein B (gB) of human cytomegalovirus. In each case, our screens revealed a restricted VH and VL germline usage, including published and previously unidentified gene families. The in vivo evolution of paratope specificity with optimal neutralizing activity was understandable after correlating biological activities with kinetic binding and epitope recognition. Iterative feedback between antigen probe design based on structure and function information with high throughput multiplexed screening demonstrated a generally applicable strategy for efficient identification of safe, native, finely tuned antibodies with the potential for high genetic barriers to viral escape.

Intrauterine growth restriction caused by underlying congenital cytomegalovirus infection

BACKGROUND

Human cytomegalovirus (HCMV) is the major viral etiology of congenital infection and birth defects. Fetal transmission is high (30%-40%) in primary maternal infection, and symptomatic babies have permanent neurological, hearing, and vision defects. Recurrent infection is infrequently transmitted (2%) and largely asymptomatic. Congenital infection is also associated with intrauterine growth restriction (IUGR).

METHODS

To investigate possible underlying HCMV infection in cases of idiopathic IUGR, we studied maternal and cord sera and placentas from 19 pregnancies. Anti-HCMV antibodies, hypoxia-related factors, and cmvIL-10 were measured in sera. Placental biopsy specimens were examined for viral DNA, expression of infected cell proteins, and pathology.

RESULTS

Among 7 IUGR cases, we identified 2 primary and 3 recurrent HCMV infections. Virus replicated in glandular epithelium and lymphatic endothelium in the decidua, cytotrophoblasts, and smooth muscle cells in blood vessels of floating villi and the chorion. Large fibrinoids with avascular villi, edema, and inflammation were significantly increased. Detection of viral proteins in the amniotic epithelium indicated transmission in 2 cases of IUGR with primary infection and 3 asymptomatic recurrent infections.

CONCLUSIONS

Congenital HCMV infection impairs placental development and functions and should be considered as an underlying cause of IUGR, regardless of virus transmission to the fetus.

Therapeutic targeting of respiratory syncytial virus G-protein

Respiratory syncytial virus (RSV) is a leading cause of pneumonia and bronchiolitis in infants and young children and an important pathogen of the elderly and immune suppressed. The only intervention currently available is a monoclonal antibody against the RSV fusion protein, which has shown utility as a prophylactic for high-risk premature infants, but which has not shown postinfection therapeutic efficacy in the specific RSV-infected populations studied. Thus, for the major susceptible populations, there remains a great need for effective treatment. Recent results support monoclonal antibody targeting of the RSV G-protein for therapeutic use. This objective encompasses a dual mechanism: reduction in the ability of RSV G-protein to distort the host innate immune response, and direct complement-mediated antiviral activity.

A serum amyloid P-binding hydrogel speeds healing of partial thickness wounds in pigs

During wound healing, some circulating monocytes enter the wound, differentiate into fibroblast-like cells called fibrocytes, and appear to then further differentiate into myofibroblasts, cells that play a key role in collagen deposition, cytokine release, and wound contraction. The differentiation of monocytes into fibrocytes is inhibited by the serum protein serum amyloid P (SAP). Depleting SAP at a wound site thus might speed wound healing. SAP binds to some types of agarose in the presence of Ca(2+). We found that human SAP binds to an agarose with a K(D) of 7 x 10(-8) M and a B(max) of 2.1 microg SAP/mg wet weight agarose. Mixing this agarose 1 : 5 w/v with 30 microg/mL human SAP (the average SAP concentration in normal serum) in a buffer containing 2 mM Ca(2+) reduced the free SAP concentration to approximately 0.02 microg/mL, well below the concentration that inhibits fibrocyte differentiation. Compared with a hydrogel dressing and a foam dressing, dressings containing this agarose and Ca(2+) significantly increased the speed of wound healing in partial thickness wounds in pigs. This suggests that agarose/Ca(2+) dressings may be beneficial for wound healing in humans.

Potent high-affinity antibodies for treatment and prophylaxis of respiratory syncytial virus derived from B cells of infected patients

Native human Abs represent attractive drug candidates; however, the low frequency of B cells expressing high-quality Abs has posed a barrier to discovery. Using a novel single-cell phenotyping technology, we have overcome this barrier to discover human Abs targeting the conserved but poorly immunogenic central motif of respiratory syncytial virus (RSV) G protein. For the entire cohort of 24 subjects with recent RSV infection, B cells producing Abs meeting these stringent specificity criteria were rare, <10 per million. Several of the newly cloned Abs bind to the RSV G protein central conserved motif with very high affinity (K(d) 1-24 pM). Two of the Abs were characterized in detail and compared with palivizumab, a humanized mAb against the RSV F protein. Relative to palivizumab, the anti-G Abs showed improved viral neutralization potency in vitro and enhanced reduction of infectious virus in a prophylaxis mouse model. Furthermore, in a mouse model for postinfection treatment, both anti-G Abs were significantly more effective than palivizumab at reducing viral load. The combination of activity in mouse models for both prophylaxis and treatment makes these high-affinity human-derived Abs promising candidates for human clinical testing.

Antibody discovery via multiplexed single cell characterization

The secreted immunoglobulin footprint of single hybridoma cells, containing ~10 fg of antibody purified in situ, has been probed for 9 properties concurrently by use of detection labels comprising 280 nm combinatorially colored fluorescent latex beads functionalized with proteins. Specificity of each individual hybridoma cell's product has thereby been assessed in a primary screen. Varying the density of antigen on beads to modulate the avidity of the interaction between bead and secreted antibody footprint allowed rank ordering by affinity in the same primary screen. As more criteria were added to the selection process, the frequency of positive cells went down; in some cases, the favorable cell was present at <1/50,000. Recovery of the cell of interest was accomplished by plating the cells in a viscous medium on top of a membrane. After collecting the antibody footprint on a capture surface beneath the membrane, the immobilized cells were transferred to an incubator while the footprints were analyzed to locate the hybridoma cells of interest. The desired cells were then cloned by picking them from the corresponding locations on the membrane.

Multiplexed Elispot assay

Micron scale latex beads are well established as highly biocompatible reagents. Imbibing two fluorescent dyes into the interior of the beads enables the creation of a family of combinatorially colored labels. Previous use of such beads, in flow cytometry for example, has focused on beads of approximately 5 microm diameter. We show here that 280 nm combinatorially labeled particles can be used to create ELISA-style assays in 200 microm scale virtual wells, using digital microscopy as the readout. The utility of this technique is illustrated by profiling the secreted cytokine footprints of peripheral blood mononuclear cells in a multiparametric version of the popular Elispot assay. Doing so reveals noncanonical classes of T lymphocytes. We further show that the secreting cell type can be concurrently identified by surface staining with a cell type specific antibody conjugated to the same multiplexed beads.

Pharmacological regulation of network kinetics by protein kinase C localization

Protein kinase C (PKC) is a conserved family of 11 serine/threonine kinases. Most cell types express multiple members of the family. Because the catalytic sites are homologous, and able to accommodate a broad range of substrates in vitro, specificity in function is dependent on subcellular localization of each isozyme in each cell type. Physiological stimulation can result in major changes in localization of individual PKC isozymes, mediated through binding to specific anchoring proteins. We describe data demonstrating that disruption of such translocations of PKC isozymes by pharmacological agents, peptides, or antibodies, causes profound effects on T cell functions. The pharmacological opportunity provided by distinct kinetic properties of complex assembly is also discussed.

Direct interaction in T-cells between thetaPKC and the tyrosine kinase p59fyn

The protein kinase C (PKC) family has been clearly implicated in T-cell activation as have several nonreceptor protein-tyrosine kinases associated with the T-cell receptor, including p59fyn. This report demonstrates that thetaPKC and p59fyn specifically interact in vitro, in the yeast two-hybrid system, and in T-cells. Further indications of direct interaction are that p59fyn potentiates thetaPKC catalytic activity and that thetaPKC is a substrate for tyrosine phosphorylation by p59fyn. This interaction may account for the localization of thetaPKC following T-cell activation, pharmacological disruption of which results in specific cell-signaling defects. The demonstration of a physical interaction between a PKC and a protein-tyrosine kinase expands the class of PKC-anchoring proteins (receptors for activated C kinases (RACKs)) and demonstrates a direct connection between these two major T-cell-signaling pathways.

Protein affinity map of chemical space

Affinity fingerprinting is a quantitative method for mapping chemical space based on binding preferences of compounds for a reference panel of proteins. An effective reference panel of <20 proteins can be empirically selected which shows differential interaction with nearly all compounds. By using this map to iteratively sample the chemical space, identification of active ligands from a library of 30,000 candidate compounds has been accomplished for a wide spectrum of specific protein targets. In each case, <200 compounds were directly assayed against the target. Further, analysis of the fingerprint database suggests a strategy for effective selection of affinity chromatography ligands and scaffolds for combinatorial chemistry. With such a system, the large numbers of potential therapeutic targets emerging from genome research can be categorized according to ligand binding properties, complementing sequence based classification.

Deciphering cryptic similarities in protein binding sites

Rapid expansion in the number of plausible drug targets arising from genomics research has created new pressures for increased efficiency in discovery of high specificity candidate drug compounds. Improved understanding of conserved features among protein structures provides a promising route to achieving this goal. Indirect evidence implies that important similarities are now ripe for elucidation by emerging experimental approaches.

Tumor efficacy and bone marrow-sparing properties of TER286, a cytotoxin activated by glutathione S-transferase

TER286 is a latent drug activated by human glutathione S-transferase (GST) isoforms P1-1 and A1-1 to produce a nitrogen mustard alkylating agent. M7609 human colon carcinoma, selected for resistance to doxorubicin, and MCF-7 human breast carcinoma, selected for resistance to cyclophosphamide, both showed increased sensitivity to TER286 over their parental lines in parallel with increased expression of GST P1-1. In primary human tumor clonogenic assays, the spectrum of cytotoxic activity observed for TER286 was both broad and unusual when compared to a variety of current drugs. In murine xenografts of M7609 engineered to have high, medium, or low GST P1-1, responses to TER286 were positively correlated with the level of P1-1. Cytotoxicity was also observed in several other cell culture and xenograft models. In xenografts of the MX-1 human breast carcinoma, tumor growth inhibition or regression was observed in nearly all of the animals treated with an aggressive regimen of five daily doses. This schedule resulted in a 24-h posttreatment decline in bone marrow progenitors to 60% of control and was no worse than for a single dose of TER286. These studies have motivated election of TER286 as a clinical candidate.

Glutathione based approaches to improving cancer treatment

The use of cytotoxic chemotherapy for cancer therapy has been very successful in the treatment and often cure of patients with particular neoplasms, such as testicular carcinomas and some lymphomas. In addition, the use of adjuvant chemotherapy in patients whose primary tumor has been surgically removed contributes significantly to cure rates in some of the more common malignancies such as breast carcinoma and colon cancer. Nonetheless, for most patients with metastatic malignancies, current antineoplastic drugs provide only brief remissions with few or no long term cures. In addition, the side effects of therapy lead to substantial morbidity in nearly all patients. Insights derived from model system studies on two glutathione based lead compounds, TER286 and TER199, suggest new clinical strategies and raise interesting basic research questions regarding the cell biology foundations of cancer chemotherapy.

Glubodies: randomized libraries of glutathione transferase enzymes

BACKGROUND

The immunoglobulin framework has been mutagenized to engineer recombinant libraries of proteins as potential diagnostics and novel catalysts, although the often shallow binding cleft may limit the utility of this framework for binding diverse small organic molecules. By contrast, the glutathione S-transferase (GST) family of enzymes contains a deep binding cleft, which has evolved to accommodate a broad range of hydrophobic xenobiotics. We set out to determine whether GST molecules with novel ligand-binding characteristics could be produced by random mutagenesis of segments of the binding cleft.

RESULTS

We have identified two ligand-recognition segments (LRSs) in human GST P1, which are near the active site in the folded protein, but have characteristics indicating that the integrity of their sequence is not essential for the overall structure or activity of the protein. Libraries of GST P1-derived proteins were produced by substituting randomized sequences for an LRS or inserting random sequences into an LRS. The recombinant proteins in the libraries, collectively designated as 'glubodies,' generally retain enzymatic activity but differ markedly both from each other and from the parent enzyme in sensitivity to inhibition by diverse small organic compounds. In some instances, a glubody is inhibited by completely novel structures.

CONCLUSIONS

We have shown that a non-antibody framework can be used to create large libraries of proteins with a wide range of binding specificities for small organic molecules. The glubodies provide a rich source of data for correlating the structural and functional features of proteins relevant to ligand binding. The criteria applied for identifying an LRS in GST P1 are generally applicable to other protein frameworks.

Isozyme-specific glutathione S-transferase inhibitors potentiate drug sensitivity in cultured human tumor cell lines

Novel glutathione (GSH) analogs, previously shown to inhibit glutathione S-transferase (GST) activity at about 1 microM in vitro, were tested for their ability to potentiate the killing of cultured tumor cells by chemotherapeutic drugs. When tested at doses up to 200 microM, the analogs were neither toxic nor capable of potentiating drug toxicity unless the diethyl ester (DEE) form was used for treatment of the cells. HPLC analysis revealed rapid internalization of the DEE and intracellular conversion to a monoethyl ester form that accumulated in the cell, followed by a more gradual loss of the second ester to generate the active parent form. For the four GSH analogs tested, the ability of the DEE forms to potentiate chlorambucil (CMB) toxicity in HT-29 human colon adenocarcinoma cells strongly correlated with the in vitro ability of the parent form to inhibit recombinant human P1-1. This isozyme is the dominant form of GST present in HT-29 cells. Of the four analog DEEs tested, gamma-glutamyl-S-(benzyl)cysteinyl-R(-)-phenyl glycine (TER 117) DEE was the most effective in potentiating CMB toxicity in several cell lines: HT-29, HT4-1 (HT-29 subclone), SKOV-3 ovarian carcinoma, and SK VLB (vinblastine-resistant variant of SKOV-3) cells. gamma-Glutamyl-S-(octyl)cysteinyl-glycine (TER 143) DEE potentiated mitomycin C (MTC) toxicity in HT4-1 and SK VLB cells while TER 117 DEE did not. TER 117 DEE enhanced melphalan effects on xenografts of HT4-1 in mice to a similar extent as that achieved with the previously described nonspecific GST inhibitor, ethacrynic acid. Taken together, our results indicate that cell-permeable analogs of GSH can potentiate cytotoxicity of common chemotherapeutic drugs and this effect has a strong positive correlation with the ability of the analogs to inhibit specific GST isozymes.

Mutagenesis using trinucleotide beta-cyanoethyl phosphoramidites

There is no easy way to selectively introduce mixtures of codon triplets into mutagenesis libraries. Solid-phase-supported DNA synthesis using successive coupling of mixtures of mononucleotides can be made to supply 32 codons, which gives redundancies in coding for 20 natural amino acids, as well as an often unwanted stop codon. Resin-splitting methods have been described, but the representation of all permutations is limited by mechanical factors for a large library, and the method is experimentally cumbersome. To demonstrate a third, improved method, the 3'-cyanoethyl phosphoramidite codon triplets dATA, dCTT, dATC, dATG and dAGC were made by solution-phase methods, with protecting groups fully compatible with modern automated phosphoramidite DNA synthesis chemistry. The reagents were then used to synthesize a 54-mer DNA fragment, wherein 15 internal base pairs were randomized by coupling a mixture of the five codons five times. The fragment was amplified as a cDNA pool, which was subcloned into a phagemid vector, and 16 randomly selected recombinants from this mini-library were sequenced. These clones showed random incorporation of the proper transcribed codon sequences at the correct location. Other functional tests involving the trinucleotide phosphoramidites showed modest (ca. 70%) coupling efficiencies and structural integrity of the DNA produced.

Predicting ligand binding to proteins by affinity fingerprinting

BACKGROUND

There are many ways to represent a molecule's properties, including atomic-connectivity drawings, NMR spectra, and molecular orbital models. Prior methods for predicting the biological activity of compounds have largely depended on these physical representations. Measuring a compound's binding potency against a small reference panel of diverse proteins defines a very different representation of the molecule, which we call an affinity fingerprint. Statistical analysis of such fingerprints provides new insights into aspects of binding interactions that are shared among a wide variety of proteins. These analyses facilitate prediction of the binding properties of these compounds assayed against new proteins.

RESULTS

Affinity fingerprints are reported for 122 structurally-diverse compounds using a reference panel of eight proteins that collectively are able to generate unique fingerprints for about 75% of the small organic compounds tested. Application of multivariate regression techniques to this database enables the creation of computational surrogates to represent new proteins that are surprisingly effective at predicting binding potencies. We illustrate this for two enzymes with no previously recognizable similarity to each other or to any of the reference proteins. Fitting of analogous computational surrogates to four other proteins confirms the generality of the method; when applied to a fingerprinted library of 5000 compounds, several sub-micromolar hits were correctly predicted.

CONCLUSIONS

An affinity fingerprint database, which provides a rich source of data defining operational similarities among proteins, can be used to test theories of cryptic homology unexpected from current understanding of protein structure. Practical applications to drug design include efficient pre-screening of large numbers of compounds against target proteins using fingerprint similarities, supplemented by a small number of empirical measurements, to select promising compounds for further study.

Variability of glutathione S-transferase isoenzyme patterns in matched normal and cancer human breast tissue

The determination of GST levels in blood has been proposed to a marker of tumour burden in general, whereas level of the P1 isoenzyme has been identified as a prognostic factor for breast-cancer patients receiving no adjuvant chemotherapy. Particular glutathione S-transferase (GST) isoenzymes differ in their substrate specificity, however, and their presence or absence might therefore account for the resistance of tumours to particular chemotherapeutic drugs, as already established for cultured cell lines. Determination of the GST isoenzyme profile of a cancer tissue could have prognostic value in the selection of treatment if the levels of expression/activity show a degree of variation comparable with that exhibited by actual patient responses. Using reversed-phase h.p.l.c. to quantify affinity-isolated GSTs, we have analysed full isoenzyme profiles in the first large sample of matched normal and cancer human tissues (18 breast-cancer patients). In no patients did the tumour tissues express any isoenzymes that were not found in normal breast tissue. In addition to the GSTs, another enzyme, identified as enoyl-CoA isomerase, was regularly found in breast tissue cytosol following elution from a hexyl-glutathione affinity column. In most cases, the average level of GST was substantially elevated in the cancer tissues above the levels in normal breast tissue from the same patient. Furthermore, the relative levels of the isoenzymes were substantially more variable in the cancer samples than in the normal breast tissue, providing a plausible mechanism for the well established variable response to treatment.

Amino acid preferences at protein binding sites

An analysis of the amino acid distribution at protein binding sites was carried out using 50 diverse macromolecules for which crystallographic data with a bound ligand are available. The purpose of this study is to determine whether differential trends in amino acid distributions exist at binding sites compared to other regions in the proteins. The results indicate that some residues, particularly Arg, His, Trp and Tyr are substantially more frequent at the binding sites, compared to the number of times these residues are present in proteins generally. These effects go beyond the differences seen comparing surface exposed residues to bulk protein. The resemblance in the residue utilization at the binding sites of unrelated proteins restricts the possible types of interactions with ligands, possibly accounting for the repetition of substructural motifs in chemicals with diverse pharmacological action. Further, the use of these diagnostic features may permit identification of ligand binding pockets in a protein structure deduced from sequence information or from data in the absence of a ligand. Some of these findings complement and extend previously described trends for antibody binding sites.

Glutathione-S-transferase activates novel alkylating agents

Alkylating agents which are activated by glutathion-S-transferases (GSTs) have been designed and synthesized. The model compound gamma-glutamyl-alpha-amino-beta-[(2-ethyl N,N,N',N'-tetraethylphosphorodiamidate) sulfonyl]propionylglycine (1) and the nitrogen mustards gamma-glutamyl-alpha- amino-beta-[[2-ethyl N,N,N',N'-tetrakis (2-chloroethyl)phosphorodiamidate] sulfonyl]propionylglycine (2) and gamma-glutamyl-alpha-amino-beta-[[2-ethyl-N,N,N',N'-tetrakis(2- chloroethyl)phosphorodiamidate]sulfonyl]-propionyl-(R)-(-)-phenylg lycine (3) were prepared via multistep chemical synthesis. The compounds were tested with recombinant human A1-1, M1a-1a and P1-1 GSTs. HPLC studies showed that the compounds were differentially and catalytically cleaved by biologically relevant concentrations of the GSTs. Mass spectral studies of the cleavage mixture of 2 showed that M1a-1a GST liberated the cytotoxic phosphate moiety needed for efficacy as an alkylating agent. Cell culture studies with MCF-7 breast cancer cells showed that 1 was not toxic at 200 microM, while 2 and 3 showed IC50S of 40.6 and 37.5 microM, respectively, for the same cell line. MCF-7 cells transfected to overexpress P1-1 GST showed enhanced sensitivity with 2 and 3, with IC50S of 20.9 and 9.5 microM, respectively. This result correlates well with the rates of cleavage of 2 and 3 by P1-1 GST observed in vitro and demonstrates that higher levels of cellular P1-1 GST will give increased sensitivity to these drugs.

Glutathione analogue sorbents selectively bind glutathione S-transferase isoenzymes

Novel affinity sorbents for glutathione S-transferases (GSTs) were created by binding glutathione (GSH) analogues to Sepharose 6B. The GSH molecule was modified at the glycine moiety and at the group attached to the sulphur of cysteine. When tested by affinity chromatography in a flow-through microplate format, several of these sorbents selectively bound GST isoenzymes. gamma E-C(Hx)-phi G (glutathione with a hexyl moiety bound to cysteine and phenylglycine substituted for glycine) specifically bound rat GST 7-7, the Pi-class isoenzyme, from liver, kidney and small intestine. gamma E-C(Bz)-beta A (benzyl bound to cysteine and beta-alanine substituted for glycine) was highly selective for rat subunits 3 and 4, which are Mu-class isoenzymes. By allowing purification of the isoenzymes under mild conditions that preserve activity, the novel sorbents should be useful in characterizing the biological roles of GSTs in both normal animal and cancer tissues.

Isozyme specificity of novel glutathione-S-transferase inhibitors

A systematically diversified set of peptide analogs of the reaction product of glutathione with an electrophilic substrate have been tested as isozyme-specific inhibitors of human glutathione-S-transferase (GST). The potency of the best of the inhibitors is in the 0.5 to 20 micromolar range, with kinetics indicative of competitive inhibition with glutathione at the active site. The specificity observed among three recombinant-derived GST isozymes at both low and high potency ranged from negligible to high (at least 20-fold over the next most sensitive isozyme). These results define a novel strategy for the design of drugs targeting cells with elevated levels of particular GST isozymes, such as tumor cells for which elevated levels of GST are believed to be an important cause of chemotherapeutic drug resistance.

"Paralogs", sorbent families for protein separations

Novel peptide-based (paralog) sorbents are evaluated with respect to performance, reproducibility and reusability in a 96-well test plate screening format, and to utility in protein separations. The results demonstrate that this approach to constructing sorbents provides a new and generally applicable set of tools for separating proteins.

Paralog chromatography

As a mixed mode ligand, a small peptide can mimic an antibody's paratope (antigen recognition site). This report describes the construction of a representative set of paratope analogs, or "paralogs," which can be conjugated to a chromatographic sorbent to combine desirable characteristics of traditional high-performance liquid chromatography columns with the specificity of a moderate affinity antibody. The broad utility of this novel set of protein separatory reagents is illustrated on the complex mixture of proteins in a yeast lysate.

The engrailed locus of Drosophila: structural analysis of an embryonic transcript

cDNA clones originating from the engrailed gene of Drosophila have been isolated from recombinant phage libraries that were made using poly(A)+ RNA extracted from early embryos. The DNA sequence of one of these clones includes a homeo box, a 180 bp sequence present in several other Drosophila genes important in formation of body pattern during development. The homeo boxes found in the other Drosophila genes, as well as in cognate sequences from a wide range of segmented animals, including higher vertebrates, are highly conserved. By contrast, the homeo box within the engrailed gene diverges substantially and, unlike the other homeo boxes, is interrupted by an intervening sequence. The engrailed homeo box is located near the 3' end of a 1700 bp open reading frame. If translated, this sequence would produce a protein of unusual composition. We also show that a neighboring gene has a large region with strong homology to engrailed, and that it also contains a homeo box.

Defective cyclic adenosine 3':5'-monophosphate phosphodiesterase in the Drosophila memory mutant dunce

A detailed characterization of the cyclic nucleotide phosphodiesterase (PDEs) from normal Drosophila melanogaster was made, including purification of the two major enzymes to near homogeneity. A third more labile phosphodiesterase also was identified in crude homogenates. The total activity per fly of one of these three enzymes, PDE-II, is strongly influenced by the dunce locus. Two independently derived dunce mutants produce variations of PDE-II with modified intrinsic properties: a marked decrease of thermal stability in dunce and a 10-fold increase in the Michaelis kinetic constant in dunce. These defects, which persisted in purified preparations of PDE-II, were mapped genetically to dunce. The results support the identification of dunce as the structural locus for PDE-II. The tight connection between the dunce gene and the PDE-II enzyme indicates that defective cyclic adenosine 3':5'-monophosphate metabolism is the primary lesion which leads to failure of dunce flies to learn in the olfactory associative conditioning paradigm of Quinn et al. (Quinn, W. G., W. A. Harris, and S. Benzer (1974) Proct. Natl. Acad. Sci. U. S. A. 71: 708-712).

Reduced [3H]-tetrodotoxin binding in the napts paralytic mutant of Drosophila

The temperature-sensitive paralytic mutant of Drosophila, napts, has been shown to have defects in axonal physiology which suggest that it codes for a component of the voltage-sensitive sodium channel. Ligand binding studies using tritiated tetrodotoxin, a sodium channel antagonist, show a decrease in the apparent number of sodium channels in napts, providing additional support for this hypothesis.