Long-read sequencing identified intronic repeat expansions in SAMD12 from Chinese pedigrees affected with familial cortical myoclonic tremor with epilepsy.

BACKGROUND: The locus for familial cortical myoclonic tremor with epilepsy (FCMTE) has long been mapped to 8q24 in linkage studies, but the causative mutations remain unclear. Recently, expansions of intronic TTTCA and TTTTA repeat motifs within SAMD12 were found to be involved in the pathogenesis of FCMTE in Japanese pedigrees. We aim to identify the causative mutations of FCMTE in Chinese pedigrees. METHODS: We performed genetic linkage analysis by microsatellite markers in a five-generation Chinese pedigree with 55 members. We also used array-comparative genomic hybridisation (CGH) and next-generation sequencing (NGS) technologies (whole-exome sequencing, capture region deep sequencing and whole-genome sequencing) to identify the causative mutations in the disease locus. Recently, we used low-coverage (~10×) long-read genome sequencing (LRS) on the PacBio Sequel and Oxford Nanopore platforms to identify the causative mutations, and used repeat-primed PCR for validation of the repeat expansions. RESULTS: Linkage analysis mapped the disease locus to 8q23.3-24.23. Array-CGH and NGS failed to identify causative mutations in this locus. LRS identified the intronic TTTCA and TTTTA repeat expansions in SAMD12 as the causative mutations, thus corroborating the recently published results in Japanese pedigrees. CONCLUSIONS: We identified the pentanucleotide repeat expansion in SAMD12 as the causative mutation in Chinese FCMTE pedigrees. Our study also suggested that LRS is an effective tool for molecular diagnosis of genetic disorders, especially for neurological diseases that cannot be positively diagnosed by conventional clinical microarray and NGS technologies.

GPCR structure and function relationship: identification of a biased apelin receptor mutant.

Biased ligands of G protein-coupled receptors (GPCRs) may have improved therapeutic benefits and safety profiles. However, the molecular mechanism of GPCR biased signaling remains largely unknown. Using apelin receptor (APJ) as a model, we systematically investigated the potential effects of amino acid residues around the orthosteric binding site on biased signaling. We discovered that a single residue mutation I109A (I1093.32) in the transmembrane domain 3 (TM3) located in the deep ligand-binding pocket was sufficient to convert a balanced APJ into a G protein signaling biased receptor. APJ I109A mutant receptor retained full capabilities in ligand binding and G protein activation, but was defective in GRK recruitment, ß-arrestin recruitment, and downstream receptor-mediated ERK activation. Based on molecular dynamics simulations, we proposed a molecular mechanism for biased signaling of I109A mutant receptor. We postulate that due to the extra space created by I109A mutation, the phenyl group of the last residue (Phe-13) of apelin rotates down and initiates a cascade of conformational changes in TM3. Phe-13 formed a new cluster of hydrophobic interactions with the sidechains of residues in TM3, including F1103.33 and M1133.36, which stabilizes the mutant receptor in a conformation favoring biased signaling. Interruption of these stabilizing interactions by double mutation F110A/I109A or M113A/I109A largely restored the ß-arrestin-mediated signaling. Taken together, we describe herein the discovery of a biased APJ mutant receptor and provide detailed molecular insights into APJ signaling selectivity, facilitating the discovery of novel therapeutics targeting APJ.

Using the Delphi method to establish nursing-sensitive quality indicators for ICU nursing in China.

In this study, the Delphi method was used to develop evidence-based indicators of intensive care unit (ICU) nursing quality of care in China. Nursing quality indicators reflect elements of patient care that are directly affected by nursing practice. A comprehensive literature search identified 2,857 potentially relevant articles. From the 50 articles that were included in this study, researchers identified 38 commonly used nursing quality indicators. A panel of experts reduced these to 20, which were then subjected to two rounds of Delphi discussion by a different panel, and a final consensus was achieved. The 20 indicators were grouped into three dimensions: structure, process, and outcome (including adverse consequences). The agreement among the experts for the 20 indicators was high. These evidence-based nursing quality indicators provide for ease in data collection and a basis for clinical application and improvement in the quality of ICU nursing throughout China.

Identification of Human Anti-HIV gp160 Monoclonal Antibodies That Make Effective Immunotoxins.

The envelope (Env) glycoprotein of HIV is the only intact viral protein expressed on the surface of both virions and infected cells. Env is the target of neutralizing antibodies (Abs) and has been the subject of intense study in efforts to produce HIV vaccines. Therapeutic anti-Env Abs can also exert antiviral effects via Fc-mediated effector mechanisms or as cytotoxic immunoconjugates, such as immunotoxins (ITs). In the course of screening monoclonal antibodies (MAbs) for their ability to deliver cytotoxic agents to infected or Env-transfected cells, we noted disparities in their functional activities. Different MAbs showed diverse functions that did not correlate with each other. For example, MAbs against the external loop region of gp41 made the most effective ITs against infected cells but did not neutralize virus and bound only moderately to the same cells that they killed so effectively when they were used in ITs. There were also differences in IT-mediated killing among transfected and infected cell lines that were unrelated to the binding of the MAb to the target cells. Our studies of a well-characterized antigen demonstrate that MAbs against different epitopes have different functional activities and that the binding of one MAb can influence the interaction of other MAbs that bind elsewhere on the antigen. These results have implications for the use of MAbs and ITs to kill HIV-infected cells and eradicate persistent reservoirs of HIV infection. IMPORTANCE: There is increased interest in using antibodies to treat and cure HIV infection. Antibodies can neutralize free virus and kill cells already carrying the virus. The virus envelope (Env) is the only HIV protein expressed on the surfaces of virions and infected cells. In this study, we examined a panel of human anti-Env antibodies for their ability to deliver cell-killing toxins to HIV-infected cells and to perform other antiviral functions. The ability of an antibody to make an effective immunotoxin could not be predicted from its other functional characteristics, such as its neutralizing activity. Anti-HIV immunotoxins could be used to eliminate virus reservoirs that persist despite effective antiretroviral therapy.

Development of evidence-based nursing-sensitive quality indicators for emergency nursing: A Delphi study.

AIMS AND OBJECTIVES: To establish evidence-based nursing-sensitive quality indicators for emergency nursing in China. BACKGROUND: China lacks nursing-sensitive quality indicators necessary for assessing the quality of emergency nursing and essential to nursing management. DESIGN: Prospective. METHODS: A literature search for relevant evidence-based studies was performed using several databases from January 2009-May 2014. Previously reported quality indicators were identified as appropriate for assessment by a panel of 40 experts in emergency medicine and nursing. Two successive rounds of Delphi surveys were conducted using questionnaires designed by the experts. Kendal's W coordination coefficients were calculated for indicator importance, rationality of calculation and feasibility of data collection. RESULTS: Thirty-three quality indicators were initially proposed for expert evaluation. After round 1 of expert discussion, Kendal's W coordination coefficients were .152 for importance, .092 for rationality and .141 for feasibility of data collection (all p < .001). Seven unsuitable items were discarded in round 1 and 11 discarded in round 2, which also added one new item. Finally, the experts reached consensus on 16 items established as appropriate nursing-sensitive quality indicators for emergency nursing care. CONCLUSION: Evidence-based nursing-sensitive quality indicators were established through a consensus of experts in emergency nursing and medicine. RELEVANCE TO CLINICAL PRACTICE: The current findings may provide a theoretical basis for establishing an emergency nursing quality database and improving the quality of emergency nursing care in China.

Using the Delphi method to develop nursing-sensitive quality indicators for the NICU.

AIMS AND OBJECTIVES: To develop nursing-sensitive quality indicators consistent with current medical practices in Chinese neonatal intensive care units. BACKGROUND: The development of nursing-sensitive quality indicators has become a top priority in nursing management. To the best of our knowledge, there has been no objective, scientific and sensitive evaluation of the quality of neonatal intensive care unit nursing in China. DESIGN: A modified Delphi technique was used to seek opinions from experts about what should be used and prioritised as indicators of quality care in neonatal intensive care unit nursing. METHODS: Based on a literature review, we identified 21 indicators of nursing-sensitive quality in the neonatal intensive care unit. Our group of 11 consultants chose 13 indicators to be discussed using the Delphi method. In October and November 2014, 39 neonatal intensive care unit experts in 18 tertiary hospitals spread across six provinces participated in two rounds of Delphi panels. RESULTS: Of the 13 indicators discussed, 11 were identified as indicators of nursing-sensitive quality in the neonatal intensive care unit: rate of nosocomial infections, rate of accidental endotracheal extubation, rate of errors in medication administration, rate of treatment for pain, rate of peripheral venous extravasation, rate of compliance with handwashing techniques, incidence of pressure ulcers, incidence of noise, the bed-to-care ratio, the proportion of nurses with greater than five years neonatal intensive care unit experience and incidence of retinopathy. CONCLUSIONS: The 11 neonatal intensive care unit nursing-sensitive indicators identified by the Delphi method integrated with basic Chinese practices provide a basis for nursing management and the monitoring of nursing quality. RELEVANCE TO CLINICAL PRACTICE: This study identified nursing-sensitive quality indicators for neonatal intensive care unit care that are suitable for current clinical practice in China.

Establishing nursing-sensitive quality indicators for the operating room: A cross-sectional Delphi survey conducted in China.

BACKGROUND: Nursing-sensitive quality indicators comprise principles, procedures, and assessments to quantify the level of nursing quality in hospital departments. Although studies have demonstrated that quality indicators are essential for monitoring nursing practice in the operating room (OR), nursing quality in China is highly subjective and localised OR nursing-sensitive quality indicators are lacking. OBJECTIVE: This study aimed to establish scientific, objective and comprehensive nursing-sensitive quality indicators for the OR to evaluate and monitor OR nursing care quality in China. METHODS: Literature search for relevant evidence-based studies was performed using Cochrane, Medline, PubMed, Embase, and other databases, followed by literature review and group discussion by the expert panel. Two successive rounds of Delphi surveys were conducted using questionnaires completed by the expert panel to reach consensus and define nursing-sensitive quality indicators for the OR. RESULTS: Two rounds of Delphi surveys each had 100% questionnaire retrieval rate, with Kendall W coordination coefficients ranging from 0.096 to 0.263 (P<0.001). In round 1 of expert evaluation of 26 indicators, Kendall's W was 0.263 for importance, 0.126 for rationality, and 0.125 for feasibility of data collection (all P<0.001). After round 2, 23 items were established as OR nursing-sensitive quality indicators, including rates of work time wastage, surgery start-time delay, OR turnover time between surgeries, same-day surgery cancellation, and number of monthly surgeries in each OR; checking surgical patients, surgery site marking, allergy history, and antibiotics use 60min before incision; and also assessing expected surgical time, sterilisation indicator results, availability of surgical instruments and materials, and instrument count. CONCLUSIONS: Scientific, practical, and reliable OR nursing-sensitive quality indicators can be established based on evidence-based studies and expert consensus using the Delphi method. The quality indicators developed in this study may provide an objective and quantitative reference for evaluating nursing quality in Chinese ORs.

Identification of dominant antibody-dependent cell-mediated cytotoxicity epitopes on the hemagglutinin antigen of pandemic H1N1 influenza virus.

Antibody-dependent cell-mediated cytotoxicity (ADCC) bridges innate and adaptive immunity, and it involves both humoral and cellular immune responses. ADCC has been found to be a main route of immune protection against viral infections in vivo. Hemagglutinin (HA) of influenza virus is highly immunogenic and considered the most important target for immune protection. Several potent cross-reactive HA-specific neutralizing monoclonal antibodies (MAbs) have been reported, and their conserved neutralizing epitopes have been revealed, but there has been no report so far about ADCC epitopes on HA. Here we identified two dominant ADCC epitopes, designated E1 (amino acids [aa] 92 to 117) and E2 (aa 124 to 159), on HA of pandemic H1N1 influenza virus by epitope mapping of convalescent-phase plasma IgG antibodies from six H1N1-infected human subjects in China that exhibited different levels of ADCC activity. The E1 and E2 ADCC epitopes overlapped with immunodominant epitopes of HA. Depletion of purified patient plasma IgG antibodies with EBY100 yeast cells expressing E1 or E2 decreased the ADCC activity of the IgG antibodies. E1 and E2 sequences were found to be highly conserved in H1N1 strains but less so in other subtypes of influenza A viruses. Our study may aid in designing immunogens that can elicit antibodies with high ADCC activity. Vaccine immunogens designed to include the structural determinants of potent broadly neutralizing antibodies and ADCC epitopes may confer comprehensive immune protection against influenza virus infection.

Structural definition of a conserved neutralization epitope on HIV-1 gp120.

The remarkable diversity, glycosylation and conformational flexibility of the human immunodeficiency virus type 1 (HIV-1) envelope (Env), including substantial rearrangement of the gp120 glycoprotein upon binding the CD4 receptor, allow it to evade antibody-mediated neutralization. Despite this complexity, the HIV-1 Env must retain conserved determinants that mediate CD4 binding. To evaluate how these determinants might provide opportunities for antibody recognition, we created variants of gp120 stabilized in the CD4-bound state, assessed binding of CD4 and of receptor-binding-site antibodies, and determined the structure at 2.3 A resolution of the broadly neutralizing antibody b12 in complex with gp120. b12 binds to a conformationally invariant surface that overlaps a distinct subset of the CD4-binding site. This surface is involved in the metastable attachment of CD4, before the gp120 rearrangement required for stable engagement. A site of vulnerability, related to a functional requirement for efficient association with CD4, can therefore be targeted by antibody to neutralize HIV-1.

Pain Prevalence and Management in a General Hospital Through Repeated Cross-Sectional Surveys in 2011 and 2021.

Background: There is great scope for improving the quality of pain management. Although pain prevalence has been investigated in several countries, few studies have comparatively assessed changes in pain prevalence and management over a span of multiple years. Aim: This work was aimed at determining the pain prevalence and evaluating the condition of pain management in a Chinese general hospital in 2021 and comparing them with corresponding data from 10 years ago. Methods: Repeated single-center cross-sectional studies were initiated on June 14th, 2011, and September 2nd, 2021, in the same tertiary grade A Chinese general hospital. The same structured questionnaire was used to collect inpatient data on pain intensity and classification and pain management outcomes. We performed statistical analyses to compare categorical variables to assess changes over time. Results: The sample sizes for the investigations in 2011 and 2021 were 2323 and 4454, respectively. In 2021, 24.34% of patients experienced pain; this percentage was significantly lower than that in 2011. Meanwhile, the prevalence of moderate and severe pain decreased from 14.73% in 2011 to 4.98% in 2021. The other six indicators of pain management outcomes also improved significantly. The percentages of patients using painkillers, opioid analgesics, and multiple analgesics increased from 44.61 to 51.38%, 24.01% to 44.61%, and 6.82% to 14.11%, respectively. Furthermore, the percentages of patients who received pain information and who actively reported pain increased from 27.56% to 96.5% and from 85.54% to 98.71%, respectively. The percentage of patients qualified to accurately use the Numerical Rating Scale increased from 10.5% to 79.98%. Conclusion: The quality and outcomes of pain management improved greatly after the establishment and implementation of the pain management system. Nonetheless, pain of different intensities is common after major surgeries, and it is recommended that hospitals popularize and implement perioperative multimodal analgesia strategies to reduce the incidence of postoperative pain.

[Expression of Bcl-2, PD-L1 and its clinical significance in colorectal cancer].

OBJECTIVE: To study the expression of Bcl-2 and PD-L1 in colon cancer and its relationship with metastasis. METHODS: Tumor samples were collected from 57 cases of colon cancer, and tumor adjacent normal mucous tissue were obtained as normal control. The expressions of Bcl-2 and PD-L1 were assayed by immunohistochemical staining, and its correlations with patients' clinical pathological indexes were analyzed. RESULTS: The positive rate of Bcl-2 protein was 75.43% and 52.63% in colon cancer tissues and tumor adjacent colon mucous tissue respectively, with statistically significant difference (P<0.05). While the positive rate of PD-L1 was 45.61% and 15.79% in colon cancer tissues and tumor adjacent colon mucous tissue respectively, also with signficant difference (P<0.01). The positive rate of Bcl-2 was correlated with cellular differentiation, and the positive rate of PD-L1 protein was correlated with lymph node metastasis (P<0.05). CONCLUSION: The expression of Bcl-2 may be associated with colon cancer pathologic differentiation, and the expression of PD-L1 may be associated with colon cancer metastasis.

Monoclonal antibody m18 paratope leading to dual receptor antagonism of HIV-1 gp120.

We sought to identify sequences in the monoclonal antibody m18 complementarity determining regions (CDRs) that are responsible for its interaction with HIV-1 gp120 and inhibition of the envelope receptor binding sites. In the accompanying paper (DOI 10.1021/bi101160r), we reported that m18 inhibits CD4 binding through a nonactivating mechanism that, at the same time, induces conformational effects leading to inhibition of the coreceptor site. Here, we sought to define the structural elements in m18 responsible for these actions. Direct binding and competition analyses using surface plasmon resonance showed that YU-2 gp120 binding is stabilized by a broad paratope of residues in the m18 CDRs. Additionally, several m18 residues were identified for which mutants retained high affinity for gp120 but had suppressed CD4 and 17b inhibition activities. A subset of these mutants did, however, neutralize HXBc2 viral infection. The results obtained in this work demonstrate that the combined m18 paratope contains subsets of residues that are differentially important for the binding and inhibition functions of the m18 neutralizing antibody. The data also add to prior observations that high-affinity antibodies that do not inhibit monomeric gp120 receptor site interactions may still exhibit significant antiviral activity.

Conformational and structural features of HIV-1 gp120 underlying the dual receptor antagonism by cross-reactive neutralizing antibody m18.

We investigated the interaction between cross-reactive HIV-1 neutralizing human monoclonal antibody m18 and HIV-1YU-2 gp120 in an effort to understand how this antibody inhibits the entry of virus into cells. m18 binds to gp120 with high affinity (KD≈5 nM) as measured by surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). SPR analysis further showed that m18 inhibits interactions of gp120 with both soluble CD4 and CD4-induced antibodies that have epitopes overlapping the coreceptor binding site. This dual receptor site antagonism, which occurs with equal potency for both inhibition effects, argues that m18 is not functioning as a mimic of CD4, in spite of the presence of a putative CD4-like loop formed by HCDR3 in the antibody. Consistent with this view, m18 was found to interact with gp120 in the presence of saturating concentrations of a CD4-mimicking small molecule gp120 inhibitor, suggesting that m18 does not require unoccupied CD4 Phe43 binding cavity residues of gp120. Thermodynamic analysis of the m18-gp120 interaction suggests that m18 stabilizes a conformation of gp120 that is unique from and less structured than the CD4-stabilized conformation. Conformational mutants of gp120 were studied for their impact on m18 interaction. Mutations known to disrupt the coreceptor binding region and to lead to complete suppression of 17b binding had minimal effects on m18 binding. This argues that energetically important epitopes for m18 binding lie outside the disrupted bridging sheet region used for 17b and coreceptor binding. In contrast, mutations in the CD4 region strongly affected m18 binding. Overall, the results obtained in this work argue that m18, rather than mimicking CD4 directly, suppresses both receptor binding site functions of HIV-1 gp120 by stabilizing a nonproductive conformation of the envelope protein. These results can be related to prior findings about the importance of conformational entrapment as a common mode of action for neutralizing CD4bs antibodies, with differences mainly in epitope utilization and the extent of gp120 structuring.

Function-based high-throughput screening for antibody antagonists and agonists against G protein-coupled receptors.

Hybridoma and phage display are two powerful technologies for isolating target-specific monoclonal antibodies based on the binding. However, for complex membrane proteins, such as G protein-coupled receptors (GPCRs), binding-based screening rarely results in functional antibodies. Here we describe a function-based high-throughput screening method for quickly identifying antibody antagonists and agonists against GPCRs by combining glycosylphosphatidylinositol-anchored antibody cell display with ß-arrestin recruitment-based cell sorting and screening. This method links antibody genotype with phenotype and is applicable to all GPCR targets. We validated this method by identifying a panel of antibody antagonists and an antibody agonist to the human apelin receptor from an immune antibody repertoire. In contrast, we obtained only neutral binders and antibody antagonists from the same repertoire by phage display, suggesting that the new approach described here is more efficient than traditional methods in isolating functional antibodies. This new method may create a new paradigm in antibody drug discovery.

Structure-guided discovery of a single-domain antibody agonist against human apelin receptor.

Developing antibody agonists targeting the human apelin receptor (APJ) is a promising therapeutic approach for the treatment of chronic heart failure. Here, we report the structure-guided discovery of a single-domain antibody (sdAb) agonist JN241-9, based on the cocrystal structure of APJ with an sdAb antagonist JN241, the first cocrystal structure of a class A G protein-coupled receptor (GPCR) with a functional antibody. As revealed by the structure, JN241 binds to the extracellular side of APJ, makes critical contacts with the second extracellular loop, and inserts the CDR3 into the ligand-binding pocket. We converted JN241 into a full agonist JN241-9 by inserting a tyrosine into the CDR3. Modeling and molecular dynamics simulation shed light on JN241-9-stimulated receptor activation, providing structural insights for finding agonistic antibodies against class A GPCRs.

Germline-like predecessors of broadly neutralizing antibodies lack measurable binding to HIV-1 envelope glycoproteins: implications for evasion of immune responses and design of vaccine immunogens.

Several human monoclonal antibodies (hmAbs) including b12, 2G12, and 2F5 exhibit relatively potent and broad HIV-1-neutralizing activity. However, their elicitation in vivo by vaccine immunogens based on the HIV-1 envelope glycoprotein (Env) has not been successful. We have hypothesized that HIV-1 has evolved a strategy to reduce or eliminate the immunogenicity of the highly conserved epitopes of such antibodies by using "holes" (absence or very weak binding to these epitopes of germline antibodies that is not sufficient to initiate and/or maintain an efficient immune response) in the human germline B cell receptor (BCR) repertoire. To begin to test this hypothesis we have designed germline-like antibodies corresponding most closely to b12, 2G12, and 2F5 as well as to X5, m44, and m46 which are cross-reactive but with relatively modest neutralizing activity as natively occurring antibodies due to size and/or other effects. The germline-like X5, m44, and m46 bound with relatively high affinity to all tested Envs. In contrast, germline-like b12, 2G12, and 2F5 lacked measurable binding to Envs in an ELISA assay although the corresponding mature antibodies did. These results provide initial evidence that Env structures containing conserved vulnerable epitopes may not initiate humoral responses by binding to germline antibodies. Even if such responses are initiated by very weak binding undetectable in our assay it is likely that they will be outcompeted by responses to structures containing the epitopes of X5, m44, m46, and other antibodies that bind germline BCRs with much higher affinity/avidity. This hypothesis, if further supported by data, could contribute to our understanding of how HIV-1 evades immune responses and offer new concepts for design of effective vaccine immunogens.

Cross-reactive human immunodeficiency virus type 1-neutralizing human monoclonal antibody that recognizes a novel conformational epitope on gp41 and lacks reactivity against self-antigens.

Broadly cross-reactive human immunodeficiency virus (HIV)-neutralizing antibodies are infrequently elicited in infected humans. The two best-characterized gp41-specific cross-reactive neutralizing human monoclonal antibodies, 4E10 and 2F5, target linear epitopes in the membrane-proximal external region (MPER) and bind to cardiolipin and several other autoantigens. It has been hypothesized that, because of such reactivity to self-antigens, elicitation of 2F5 and 4E10 and similar antibodies by vaccine immunogens based on the MPER could be affected by tolerance mechanisms. Here, we report the identification and characterization of a novel anti-gp41 monoclonal antibody, designated m44, which neutralized most of the 22 HIV type 1 (HIV-1) primary isolates from different clades tested in assays based on infection of peripheral blood mononuclear cells by replication-competent virus but did not bind to cardiolipin and phosphatidylserine in an enzyme-linked immunosorbent assay and a Biacore assay nor to any protein or DNA autoantigens tested in Luminex assays. m44 bound to membrane-associated HIV-1 envelope glycoproteins (Envs), to recombinant Envs lacking the transmembrane domain and cytoplasmic tail (gp140s), and to gp41 structures containing five-helix bundles and six-helix bundles, but not to N-heptad repeat trimers, suggesting that the C-heptad repeat is involved in m44 binding. In contrast to 2F5, 4E10, and Z13, m44 did not bind to any significant degree to denatured gp140 and linear peptides derived from gp41, suggesting a conformational nature of the epitope. This is the first report of a gp41-specific cross-reactive HIV-1-neutralizing human antibody that does not have detectable reactivity to autoantigens. Its novel conserved conformational epitope on gp41 could be helpful in the design of vaccine immunogens and as a target for therapeutics.

Sequential antigen panning for selection of broadly cross-reactive HIV-1-neutralizing human monoclonal antibodies.

Many phage display techniques drive selection toward the isolation of highly specific antibodies. However, the identification of monoclonal antibodies that are cross-reactive has implications for the development of diagnostics, therapeutics, and vaccines against pathogens or cancer cells that are able to rapidly generate variants and escape mutants. To identify human monoclonal antibodies with high activity against HIV and broad-spectrum activity, we developed a technique termed sequential antigen panning. This methodology could be used to isolated recombinant antibodies against any antigen that shares epitopes with other antigens.

Competitive antigen panning for selection of HIV-1 neutralizing human monoclonal antibodies specific for gp41.

HIV envelope glycoprotein (Env) is composed of two non-covalently associated subunits: gp120 and gp41. Panning of phage-displayed antibody libraries against gp140 (covalently linked gp120 and the extracellular portion of gp41) has resulted mostly in selection of anti-gp120 antibodies. Native gp41 in the absence of gp120 is unstable. The use of gp41 fragments as antigens has resulted in selection of antibodies with only relatively modest neutralizing activity. To enhance selection of antibodies specific for gp41 in the context of the whole Env we developed a methodology termed competitive antigen panning (CAP). Using CAP, we identified a panel of gp41-specific human monoclonal antibodies from an HIV-1 immune library derived from long-term nonprogressors. These antibodies recognize conformational epitopes in gp41 and exhibited, to various extents, neutralization activity in assays based on spreading infection in peripheral blood mononuclear cells. The CAP methodology is generally applicable for selection of antibodies specific for any epitope that is not a dominant epitope in the antigen. It is superior to a traditional pre-depletion method in avoiding potential loss of target-specific antibodies.

Structural mimicry of CD4 by a cross-reactive HIV-1 neutralizing antibody with CDR-H2 and H3 containing unique motifs.

Human immunodeficiency virus (HIV) entry into cells is initiated by the binding of its envelope glycoprotein (Env) gp120 to receptor CD4. Antibodies that bind to epitopes overlapping the CD4-binding site (CD4bs) on gp120 can prevent HIV entry by competing with cell-associated CD4; their ability to outcompete CD4 is a major determinant of their neutralizing potency and is proportional to their avidity. The breadth of neutralization and the likelihood of the emergence of antibody-resistant virus are critically dependent on the structure of their epitopes. Because CD4bs is highly conserved, it is reasonable to hypothesize that antibodies closely mimicking CD4 could exhibit relatively broad cross-reactivity and a high probability of preventing the emergence of resistant viruses. Previously, in a search for antibodies that mimic CD4 or the co-receptor, we identified and characterized a broadly cross-reactive HIV-neutralizing CD4bs human monoclonal antibody (hmAb), m18. Here, we describe the crystal structure of Fab m18 at 2.03 A resolution, which reveals unique conformations of heavy chain complementarity-determining regions (CDRs) 2 and 3 (H2 and H3). H2 is highly bulged and lacks cross-linking interstrand hydrogen bonds observed in all four canonical structures. H3 is 17.5 A long and rigid, forming an extended beta-sheet decorated with an alpha-turn motif bearing a phenylalanine-isoleucine fork at the apex. It shows striking similarity to the Ig CDR2-like C'C'' region of the CD4 first domain D1 that dominates the binding of CD4 to gp120. Docking simulations suggest significant similarity between the m18 epitope and the CD4bs on gp120. Fab m18 does not enhance binding of CD4-induced (CD4i) antibodies, nor does it induce CD4-independent fusion mediated by the HIV Env. Thus, vaccine immunogens based on the m18 epitope structure are unlikely to elicit antibodies that could enhance infection. The structure can also serve as a basis for the design of novel, highly efficient inhibitors of HIV entry.