The Receptor Binding Site of Feline Leukemia Virus Surface Glycoprotein Is Distinct from the Site Involved in Virus Neutralization

ABSTRACT The external surface glycoprotein (SU) of feline leukemia virus (FeLV) contains sites which define the viral subgroup and induce virus-neutralizing antibodies. The subgroup phenotypic determinants have been located to a small variable region, VR1, towards the amino terminus of SU. The sites which function as neutralizing epitopes in vivo are unknown. Recombinant SU proteins were produced by using baculoviruses that contained sequences encoding the SUs of FeLV subgroup A (FeLV-A), FeLV-C, and two chimeric FeLVs (FeLV-215 and FeLV-VC) in which the VR1 domain of FeLV-A had been replaced by the corresponding regions of FeLV-C isolates. The recombinant glycoproteins, designated Bgp70-A, -C, -215, and -VC, respectively, were similar to their wild-type counterparts in several immunoblots and inhibited infection of susceptible cell lines in a subgroup-specific manner. Thus, Bgp70-A interfered with infection by FeLV-A, whereas Bgp70-C, -VC, and -215 did not. Conversely, Bgp70-C, -VC, and -215 blocked infection with FeLV-C, while Bgp70-A had no effect. These results indicate that the site on SU which binds to the FeLV cell surface receptor was preserved in the recombinant glycoproteins. It was also found that the recombinant proteins were able to bind naturally occurring neutralizing antibodies. Bgp70-A, -VC, and -215 interfered with the action of anti-FeLV-A neutralizing antibodies, whereas Bgp70-C did not. Furthermore, Bgp70-C interfered with the action of anti-FeLV-C neutralizing antibodies, while the other proteins did not. These results indicate that the neutralizing epitope(s) of FeLV SU lies outside the subgroup-determining VR1 domain.

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Longitudinal Analysis of Feline Leukemia Virus-Specific Cytotoxic T Lymphocytes: Correlation with Recovery from Infection

Journal of Virology ◽

10.1128/jvi.76.5.2306-2315.2002 ◽

2002 ◽

Vol 76 (5) ◽

pp. 2306-2315 ◽

Cited By ~ 39

Author(s):

J. Norman Flynn ◽

Stephen P. Dunham ◽

Vivien Watson ◽

Oswald Jarrett

Keyword(s):

T Lymphocytes ◽

Cytotoxic T Lymphocytes ◽

Neutralizing Antibodies ◽

Ex Vivo ◽

Leukemia Virus ◽

Feline Leukemia Virus ◽

Immune Effector ◽

Viral Burden ◽

Effector Mechanisms

ABSTRACT Feline leukemia virus (FeLV) is a common naturally occurring gammaretrovirus of domestic cats that is associated with degenerative diseases of the hematopoietic system, immunodeficiency, and neoplasia. Although the majority of cats exposed to FeLV develop a transient infection and recover, a proportion of cats become persistently viremic and many subsequently develop fatal diseases. To define the dominant host immune effector mechanisms responsible for the outcome of infection, we studied the longitudinal changes in FeLV-specific cytotoxic T lymphocytes (CTLs) in a group of na|$$|Ad|five cats following oronasal exposure to FeLV. Using 51Cr release assays to measure ex vivo virus-specific cytotoxicity, the emerging virus-specific CTL response was correlated with modulations in viral burden as assessed by detection of infectious virus, FeLV p27 capsid antigen, and proviral DNA in the blood. High levels of circulating FeLV-specific effector CTLs appeared before virus neutralizing antibodies in cats that recovered from exposure to FeLV. In contrast, persistent viremia was associated with a silencing of virus-specific humoral and cell-mediated host immune effector mechanisms. A single transfer of between 2 × 107 and 1 × 108 autologous, antigen-activated lymphoblasts was associated with a downmodulation in viral burden in vivo. The results suggest an important role for FeLV-specific CTLs in retroviral immunity and demonstrate the potential to modulate disease outcome by the adoptive transfer of antigen-specific T cells in vivo.

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A Putative Cell Surface Receptor for Anemia-Inducing Feline Leukemia Virus Subgroup C Is a Member of a Transporter Superfamily

Journal of Virology ◽

10.1128/jvi.73.8.6500-6505.1999 ◽

1999 ◽

Vol 73 (8) ◽

pp. 6500-6505 ◽

Cited By ~ 89

Author(s):

Chetankumar S. Tailor ◽

Brian J. Willett ◽

David Kabat

Keyword(s):

Cell Surface ◽

Chinese Hamster Ovary Cells ◽

Leukemia Virus ◽

Organic Anion ◽

Chinese Hamster ◽

Major Facilitator Superfamily ◽

Feline Leukemia Virus ◽

Cell Surface Receptor ◽

Surface Receptor

ABSTRACT Domestic cats infected with the horizontally transmitted feline leukemia virus subgroup A (FeLV-A) often produce mutants (termed FeLV-C) that bind to a distinct cell surface receptor and cause severe aplastic anemia in vivo and erythroblast destruction in bone marrow cultures. The major determinant for FeLV-C-induced anemia has been mapped to a small region of the surface envelope glycoprotein that is responsible for its receptor binding specificity. Thus, erythroblast destruction may directly or indirectly result from FeLV-C binding to its receptor. To address these issues, we functionally cloned a putative cell surface receptor for FeLV-C (FLVCR) by using a human T-lymphocyte cDNA library in a retroviral vector. Expression of the 2.0-kbp FLVCR cDNA in naturally resistant Swiss mouse fibroblasts and Chinese hamster ovary cells caused substantial susceptibility to FeLV-C but no change in susceptibilities to FeLV-B and other retroviruses. The predicted FLVCR protein contains 555 amino acids and 12 hydrophobic potential membrane-spanning sequences. Database searches indicated that FLVCR is a member of the major-facilitator superfamily of transporters and implied that it may transport an organic anion. RNA blot analyses showed that FLVCR mRNA is expressed in multiple hematopoietic lineages rather than specifically in erythroblasts. These results suggest that the targeted destruction of erythroblasts by FeLV-C may derive from their greater sensitivity to this virus rather than from a preferential susceptibility to infection.

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Cloning of the cellular receptor for feline leukemia virus subgroup C (FeLV-C), a retrovirus that induces red cell aplasia

Blood ◽

10.1182/blood.v95.3.1093.003k01_1093_1099 ◽

2000 ◽

Vol 95 (3) ◽

pp. 1093-1099 ◽

Cited By ~ 86

Author(s):

John G. Quigley ◽

Cara C. Burns ◽

Maria M. Anderson ◽

Eric D. Lynch ◽

Kathleen M. Sabo ◽

...

Keyword(s):

Leukemia Virus ◽

Major Facilitator Superfamily ◽

Feline Leukemia Virus ◽

Cell Surface Receptor ◽

Chromosome 1 ◽

Functional Screening ◽

Red Cell ◽

Cdna Sequences ◽

Red Cell Aplasia

Feline leukemia virus-C (FeLV-C) causes red cell aplasia in cats, likely through its interaction with its cell surface receptor. We identified this receptor by the functional screening of a library of complementary DNAs (cDNA) from feline T cells. The library, which was cloned into a retroviral vector, was introduced into FeLV-C–resistant murine (NIH 3T3) cells. The gene conferring susceptibility to FeLV-C was isolated and reintroduced into the same cell type, as well as into FeLV-C–resistant rat (NRK 52E) cells, to verify its role in viral infection. The receptor cDNA is predicted to encode a protein of 560 amino acids with 12 membrane-spanning domains, termed FLVCR. FLVCR has significant amino acid sequence homology with members of the major facilitator superfamily and especially D-glucarate transporters described in bacteria and in C. elegans. As FeLV-C impairs the in vivo differentiation of burst-forming unit–erythroid to colony-forming unit–erythroid, we hypothesize that this transporter system could have an essential role in early erythropoiesis. In further studies, a 6-kb fragment of the human FLVCR gene was amplified by polymerase chain reaction from genomic DNA, using homologous cDNA sequences identified in the human Expressed Sequence Tags database. By radiation hybrid mapping, the human gene was localized to a 0.5-centiMorgan region on the long arm of chromosome 1 at q31.3.

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Screening of potent neutralizing antibodies against SARS-CoV-2 using convalescent patients-derived phage-display libraries

Cell Discovery ◽

10.1038/s41421-021-00295-w ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Yongbing Pan ◽

Jianhui Du ◽

Jia Liu ◽

Hai Wu ◽

Fang Gui ◽

...

Keyword(s):

Phage Display ◽

Neutralizing Antibodies ◽

Variable Region ◽

Neutralizing Antibody ◽

Chain Gene ◽

Prophylactic Efficacy ◽

Heavy Chains ◽

Effective Interventions ◽

Phage Display Libraries

AbstractAs the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to threaten public health worldwide, the development of effective interventions is urgently needed. Neutralizing antibodies (nAbs) have great potential for the prevention and treatment of SARS-CoV-2 infection. In this study, ten nAbs were isolated from two phage-display immune libraries constructed from the pooled PBMCs of eight COVID-19 convalescent patients. Eight of them, consisting of heavy chains encoded by the immunoglobulin heavy-chain gene-variable region (IGHV)3-66 or IGHV3-53 genes, recognized the same epitope on the receptor-binding domain (RBD), while the remaining two bound to different epitopes. Among the ten antibodies, 2B11 exhibited the highest affinity and neutralization potency against the original wild-type (WT) SARS-CoV-2 virus (KD = 4.76 nM for the S1 protein, IC50 = 6 ng/mL for pseudoviruses, and IC50 = 1 ng/mL for authentic viruses), and potent neutralizing ability against B.1.1.7 pseudoviruses. Furthermore, 1E10, targeting a distinct epitope on RBD, exhibited different neutralization efficiency against WT SARS-CoV-2 and its variants B.1.1.7, B.1.351, and P.1. The crystal structure of the 2B11–RBD complexes revealed that the epitope of 2B11 highly overlaps with the ACE2-binding site. The in vivo experiment of 2B11 using AdV5-hACE2-transduced mice showed encouraging therapeutic and prophylactic efficacy against SARS-CoV-2. Taken together, our results suggest that the highly potent SARS-CoV-2-neutralizing antibody, 2B11, could be used against the WT SARS-CoV-2 and B.1.1.7 variant, or in combination with a different epitope-targeted neutralizing antibody, such as 1E10, against SARS-CoV-2 variants.

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In vivo evolution and selection of recombinant feline leukemia virus species

Virus Research ◽

10.1016/s0168-1702(98)00015-x ◽

1998 ◽

Vol 54 (1) ◽

pp. 71-86 ◽

Cited By ~ 7

Author(s):

Marta K Bechtel ◽

Lawrence E Mathes ◽

Kathleen A Hayes ◽

Andrew J Phipps ◽

Pradip Roy-Burman

Keyword(s):

Leukemia Virus ◽

Feline Leukemia Virus ◽

Virus Species ◽

Selection Of

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Feline Pit2 Functions as a Receptor for Subgroup B Feline Leukemia Viruses

Journal of Virology ◽

10.1128/jvi.75.22.10563-10572.2001 ◽

2001 ◽

Vol 75 (22) ◽

pp. 10563-10572 ◽

Cited By ~ 25

Author(s):

Maria M. Anderson ◽

Adam S. Lauring ◽

Scott Robertson ◽

Clarissa Dirks ◽

Julie Overbaugh

Keyword(s):

High Efficiency ◽

Leukemia Virus ◽

Variable Region ◽

Feline Leukemia Virus ◽

Envelope Gene ◽

Lower Efficiency ◽

Critical Determinant ◽

Recombinant Viruses ◽

Ability To Act ◽

Leukemia Viruses

ABSTRACT Different subgroups of feline leukemia virus (FeLV) use different host cell receptors for entry. Subgroup A FeLV (FeLV-A) is the virus that is transmitted from cat to cat, suggesting that cells expressing the FeLV-A receptor are important targets at the earliest stages of infection. FeLV-B evolves from FeLV-A in the infected cat through acquisition of cellular sequences that are related to the FeLV envelope gene. FeLV-Bs have been shown to infect cells using the Pit1 receptor, and some variants can infect cells at a lower efficiency using Pit2. Because these observations were made using receptor proteins of human or rodent origin, the role that Pit1 and Pit2 may play in FeLV-B replication in the cat is unclear. In this study, the feline Pit receptors were cloned and tested for their ability to act as receptors for different FeLV-Bs. Some FeLV-Bs infected cells expressing feline Pit2 and feline Pit1 with equal high efficiency. Variable region A (VRA) in the putative receptor-binding domain (RBD) was a critical determinant for both feline Pit1 and feline Pit2 binding, although other domains in the RBD appear to influence how efficiently the FeLV-B surface unit can bind to feline Pit2 and promote entry via this receptor. An arginine residue at position 73 in VRA was found to be important for envelope binding to feline Pit2 but not feline Pit1. Interestingly, this arginine is not found in endogenous FeLV sequences or in recombinant viruses recovered from feline cells infected with FeLV-A. Thus, while FeLV-Bs that are able to use feline Pit2 can evolve by recombination with endogenous sequences, a subsequent point mutation during reverse transcription may be needed to generate a virus that can efficiently enter the cells using the feline Pit2 as its receptor. These studies suggest that cells expressing the feline Pit2 protein are likely to be targets for FeLV-B infection in the cat.

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Retrovirus-induced feline pure red blood cell aplasia: pathogenesis and response to suramin

Blood ◽

10.1182/blood.v77.7.1442.bloodjournal7771442 ◽

1991 ◽

Vol 77 (7) ◽

pp. 1442-1451

Author(s):

JL Abkowitz

Keyword(s):

Blood Cell ◽

Red Blood Cell ◽

Mononuclear Cells ◽

Leukemia Virus ◽

Transcriptase Inhibitor ◽

Feline Leukemia Virus ◽

Erythroid Progenitors ◽

Marrow Cultures

Feline leukemia virus, subgroup C/Sarma (FeLV-C/Sarma) induces pure red blood cell aplasia in cats. Although erythroid (BFU-E and CFU-E) and granulocyte/macrophage (CFU-GM) progenitors are infected with this virus, only erythropoiesis is impaired. Two to 3 weeks before the onset of anemia, CFU-E become undetectable in marrow cultures while earlier erythroid progenitors (BFU-E) persist, suggesting that FeLV-C/Sarma (presumably via its envelope glycoprotein gp70) inhibits the differentiation of BFU-E to CFU-E in vivo. To correlate in vitro observations with the progression of disease, prospective studies were performed in six cats. These studies showed that at the time that the frequencies of CFU-E decreased in marrow cultures, BFU-E no longer responded to hematopoietic growth factor(s), although the responses of CFU-GM were unchanged. In further studies, anemic cats received suramin, a reverse-transcriptase inhibitor with other diverse effects. Within 4 to 14 days, erythropoiesis improved and up to 1,616 CFU-E were detected per 10(5) marrow mononuclear cells. However, progenitor cells remained infected, suggesting that suramin modulated erythroid differentiation without inhibiting progenitor infection. These observations led to the hypothesis that the gp70 of FeLV-C/Sarma impairs BFU-E differentiation by interference with ligand/receptor interactions or signal transduction pathways unique to erythroid cells. Understanding this mechanism should provide insights into the interactions controlling early erythropoiesis.

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Subtle Mutational Changes in the SU Protein of a Natural Feline Leukemia Virus Subgroup A Isolate Alter Disease Spectrum

Journal of Virology ◽

10.1128/jvi.79.3.1351-1360.2005 ◽

2005 ◽

Vol 79 (3) ◽

pp. 1351-1360 ◽

Cited By ~ 25

Author(s):

Chandtip Chandhasin ◽

Patricia N. Coan ◽

Laura S. Levy

Keyword(s):

T Cell ◽

Host Range ◽

Leukemia Virus ◽

Point Mutations ◽

Feline Leukemia Virus ◽

Surface Glycoprotein ◽

Envelope Gene ◽

Disease Spectrum ◽

Functional Differences ◽

Multicentric Lymphoma

ABSTRACT FeLV-945 is a representative isolate of the natural feline leukemia virus (FeLV) variant predominant in non-T-cell malignant, proliferative, and degenerative diseases in a geographic cohort. The FeLV-945 surface glycoprotein (SU) is closely related to natural horizontally transmissible FeLV subgroup A (FeLV-A) but was found to differ from a prototype to a larger extent than the members of FeLV-A differ among themselves. The sequence differences included point mutations restricted largely to the functional domains of SU, i.e., VRA, VRB, and PRR. Despite the sequence differences in these critical domains, measurements of receptor utilization, including host range and superinfection interference, confirmed the assignment of FeLV-945 to subgroup A. Other proviruses isolated from the cohort contained similar sequence hallmarks and were assigned to FeLV subgroup A. A provirus from cat 1046 contained a histidine-to-proline change at SU residue 6 within an SPHQ motif that was previously identified as a critical mediator of fusion events during virus entry. The 1046 pseudotype virus entered cells only in the presence of the soluble cofactor FeLIX provided in trans, but it retained an ecotropic host range even in the presence of FeLIX. The mutational changes in FeLV-945 were shown to confer significant functional differences compared to prototype FeLV-A viruses. The substitution of FeLV-945 envelope gene sequences for FeLV-A/61E sequences conferred a small but statistically significant replicative advantage in some feline cells. Moreover, substitution of the unique FeLV-945 long terminal repeat and envelope gene for those of FeLV-A/61E altered the disease spectrum entirely, from a thymic lymphoma of a T-cell origin to an as yet uncharacterized multicentric lymphoma that did not contain T cells.

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Feline leukemia virus subgroup C phenotype evolves through distinct alterations near the N terminus of the envelope surface glycoprotein.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.89.18.8457 ◽

1992 ◽

Vol 89 (18) ◽

pp. 8457-8461 ◽

Cited By ~ 25

Author(s):

J. Brojatsch ◽

B. S. Kristal ◽

G. A. Viglianti ◽

R. Khiroya ◽

E. A. Hoover ◽

...

Keyword(s):

Leukemia Virus ◽

Feline Leukemia Virus ◽

Surface Glycoprotein ◽

Envelope Surface ◽

N Terminus

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The splenic microenvironment is a source of proangiogenesis/inflammatory mediators accelerating the expansion of murine erythroleukemic cells

Blood ◽

10.1182/blood-2004-08-3210 ◽

2005 ◽

Vol 105 (11) ◽

pp. 4500-4507 ◽

Cited By ~ 24

Author(s):

Yuval Shaked ◽

Dave Cervi ◽

Manuela Neuman ◽

Limor Chen ◽

Giannoula Klement ◽

...

Keyword(s):

Tumor Necrosis Factor ◽

Neutralizing Antibodies ◽

Tumor Necrosis ◽

Leukemia Virus ◽

Survival Times ◽

Extended Survival ◽

Necrosis Factor ◽

Erythroleukemic Cells

Abstract The stromal compartments of hematopoietic organs (eg, spleen) are known to influence the viability and growth of diseased hematopoietic progenitors. Here we have used Friend murine leukemia virus (F-MuLV)–induced erythroleukemia to investigate factors of the splenic microenvironment that may make it fertile for the expansion and survival of malignant erythroblasts. We found that splenectomized, erythroleukemic mice exhibited extended survival compared with age-matched sham controls. In vitro, the proliferation of primary erythroleukemic cells cocultured with leukemic-derived splenic adherent cells or their conditioned media was found to be significantly higher than that observed in cocultures with healthy-derived adherent splenic cells. Cytokine protein arrays revealed that F-MuLV–infected splenocytes secreted elevated levels of interleukin-6 (IL-6), vascular endothelial growth factor-A (VEGF-A), macrophage chemoattractant protein-5 (MCP-5), soluble tumor necrosis factor receptor-1 (sTNFR1), IL-12p70, tumor necrosis factor-α (TNF-α), and IL-2 over normal splenocytes. Medium supplemented with both VEGF-A and MCP-5 could sustain proliferation of primary erythroleukemic cells in vitro, and significant proliferative suppression was observed upon addition of neutralizing antibodies to either of these factors. Furthermore, in vivo administration of a neutralizing antibody to VEGF-A extended survival times of erythroleukemic mice in comparison with controls. These findings suggest that VEGF-A and MCP-5 are potentially pivotal paracrine mediators occurring within the diseased splenic microenvironment capable of promoting disease acceleration and expansion of erythroleukemic blasts.

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