[Isolation of single chain antibodies against cell surface molecules by pathfinder selection].
OBJECTIVE
To isolate single chain antibody fragments (scFv) against cell surface molecules by pathfinder selection from an anti-KG1a cell scFv phage library.


METHODS
The anti-KG1a scFv library was enriched by KGla cell panning for three rounds, or unenriched, then processed for pathfinder selection respectively using anti-CD34 monoclonal antibody as pathfinder molecule. ScFv phage clones were randomly picked and identified by binding KG1a cells using immunofluorescein and flow cytometry. The KG1a+ clones were further identified by KG1a, HL60, U937, and CEM cell lines and ELISA. Their antigenic molecules on cell surface were digested by chymopapain and analyzed by flow cytometry. DNAs from ten positive clones were sequenced. The scFv clones with different primary structure were used to analyze the molecular weight of their antigens by Western blot.


RESULTS
One hundred and two KG1a+ scFv phage clones were isolated from 144 enriched and 96 unenriched scFv phage library respectively, among which 47 bound KG1a, HL60, U937, and CEM cells, 55 bound KG1a cells exclusively. None of 28 KG1a+, HL60-, U937-, and CEM- scFv clones bound to the CD34 antigen, as confirmed by ELISA, although most of their antigens were sensitive to chymopapain digestion. DNA sequences from ten positive clones showed that they were from four different clones. They bound antigens with different molecular weight.


CONCLUSIONS
One hundred and two scFv phage clones specific for hematopoietic stem and progenitor cells have been isolated from an anti-KG1a cell scFv phage library. The pathfinder selection has showed advantages to improve the screening efficacy of scFv phage clones against antigens, which present at very low densities on the cell surface.
Liu
Jun-xia
JX
National Key Laboratory of Experimental Hematology, Institute of Hematology, CAMS and PUMC, Tianjin 300020, China.
Meng
Lei
L
Xu
Jing
J
Jia
Hai-rong
HR
Song
Zeng-xuan
ZX
D000888:Antibodies, Anti-Idiotypic / Q000276:immunology*; D000911:Antibodies, Monoclonal / Q000235:genetics*; D000918:Antibody Specificity; D001435:Bacteriophages / Q000235:genetics; D003001:Cloning, Molecular; D006412:Hematopoietic Stem Cells / Q000276:immunology*; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D007128:Immunoglobulin Fragments / Q000235:genetics / Q000276:immunology; D007135:Immunoglobulin Variable Region / Q000235:genetics / Q000276:immunology; D019151:Peptide Library; D057127:Single-Chain Antibodies
D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D007141:Immunoglobulin Fc Fragments; D007128:Immunoglobulin Fragments; D007135:Immunoglobulin Variable Region; D019151:Peptide Library; D057127:Single-Chain Antibodies; C114805:scFv fragment SW1