Isolating Cells Expressing Secreted Proteins

Abstract

A method of detecting and isolating cells that produce a secreted protein of interest (POI) that has a T cell receptor variable domain, comprising: a) constructing a cell line transiently or stably expressing a cell surface capture molecule, which binds the POI, by transfecting the cell line with a nucleic acid that encodes such cell surface capture molecule; b) transfecting said cell simultaneously or subsequently with a second nucleic acid that encodes a POI wherein such POI is secreted; c) detecting the surface-displayed POI by contacting the cells with a detection molecule, which binds the POI; and d) isolating cells based on the detection molecule.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation-in-part of application Ser. No. 11 / 434,403 filed 15 May 2006, now U.S. Pat. No. 0,000,000, which is a continuation of U.S. Ser. No. 11 / 099,158 filed 5 Apr. 2005, now abandoned, which is a divisional of U.S. Ser. No. 10 / 050,279 filed 16 Jan. 2002, now U.S. Pat. No. 6,919,183, which claims the benefit under 35 USC § 119(e) of U.S. Provisional Patent Application Ser. No. 60 / 261,999 filed 16 Jan. 2001, which applications are each herein specifically incorporated by reference in their entirety.BACKGROUNDField of the Invention[0002]The field of this invention is a method for identifying and isolating cells that produce secreted proteins. More specifically, the method allows rapid isolation of high expression recombinant antibody-producing cell lines, or may be applied directly to rapid isolation of specific hybridomas.[0003]Prior art methods for expressing a gene of interest (GOI) in a host cell are known. Bri...

AI Technical Summary

Benefits of technology

[0039]The instant invention describes a novel and previously unknown method of identifying and isolating cells that produce secreted proteins. The invention is based on the production of a cell line that expresses a molecule, localized to the cell surface, which binds the POI. The cell surface-displayed POI can then be detected by labeling with various detection molecules. The amount of POI displayed on the cell surface, under specific conditions, is a direct measure of the total amount of POI secreted. POI producers may then be isolated from non-producers, and levels of production or POI characteristics may be differentiated. The advantage of the invention is that it directly quantifies the secreted POI rather than indirectly measuring the mRNA.

[0040]This invention relates to the construction or use of cells that express cell surface capture molecules which bind various secreted POIs in the same cell that produces the POI. As the cell secretes the POI, these cell surface capture molecules bind it, or complexes of POI and cell surface capture molecules may form intracellularly and then get secreted. Binding may occur in an autocrine manner or while being secreted. The cells that produce the secreted POI may then be identified and isolated. Such identification and isolation may be based on characteristics of the POI, production of the POI or lack thereof, or by specified levels of production. The cell surface capture molecule and / or the POI may be produced by the cell in its native state, or the cell surface capture molecules and / or the POI may be recombinantly produced. Through the construction or use of such a cell, any secreted protein may be captured by the cell surface capture molecule provided there is a corresponding affinity between the two. As explained further, any molecule may be manipulated such that it can be used as a cell surface capture molecule. Therefore, this invention may be utilized to isolate any cell that secretes a protein.

[0041]Most any protein has the capacity to function as a cell surface capture molecule as described by the invention. What is necessary is the ability of the desired protein to be anchored to the cell membrane and exposed to the extracellular space. If the desired cell has a signal sequence then only a membrane anchor, including but not limited to a transmembrane anchor or a GPI linkage signal, need be added to the cell surface capture molecule such that it remains anchored in the cell membrane exposed to the outside of the cell. Furthermore, if the desired protein lacks a signal sequence, a signal sequence may be added to the amino terminus of the desired protein, such that it is transported to the cell surface. A signal sequence and a membrane anchor may be native to the cell, recombinant, or synthetic.

[0042]Cells often secrete a wide variety of proteins, endogenously or following the introduction of recombinant DNA. Any secreted protein may be identified and the cell producing it may be isolated according to the method of this invention. Such secreted proteins include but are not limited to growth factors, growth factor receptors, ligands, soluble receptor components, antibodies, sTCRs, TCR-Fc's, and peptide hormones. Such secreted proteins may or may not be recombinant. That is, the secretion of some proteins of interest from the desired cell may not require the introduction of additional nucleotide sequences. For example, the secretion of antibodies from B-cells or plasma cells is not the result of introduction of recombinant nucleotide sequences into the B-cell or plasma cell. Recombinant secreted proteins may be produced by standard molecular biology techniques well known to the skilled artisan (see e.g., Sambrook, J., E. F. Fritsch And T. Maniatis. Molecular Cloning: A Laboratory Manual, Second Edition, Vols 1, 2, and 3, 1989; Current Protocols in Molecular Biology, Eds. Ausubel et al., Greene Publ. Assoc., Wiley Interscience, NY). These secreted proteins are useful for many commercial and research purposes. This invention encompasses the production of such secreted proteins through the methodologies of the invention. Detection of the cells with the displayed POI may be accomplished through the use of any molecule capable of directly or indirectly binding the displayed POI. Such detection molecules may facilitate the detection and / or isolation of the cells displaying the POI.

[0043]The invention is applicable to the isolation of, inter alia, a) ligand-producing cells by using the ligand-specific receptor as the cell surface capture molecule, b) soluble receptor-producing cells by using a surface bound receptor-specific ligand as the cell surface capture molecule, c) antibody-producing cells by using an antibody-binding protein as the cell surface capture molecule, d) sTCR's by using an s-TCR-binding protein (e.g., and antigen recognized by the TCR) as the cell surface capture molecule, or e) TCR-Fc's, by using an Fc-binding protein as a cell surface capture molecule.

[0044]In accordance with the methodology of this invention, a cell is first transfected with a vector containing a nucleotide sequence that encodes a cell surface capture molecule that is capable of binding the secreted POI, under conditions in which such cell surface capture molecule is expressed. Transfected cells which are appropriate producers of such cell surface capture molecules are then detected and isolated, and such cells are cultured. These cells may either naturally produce the POI, or the POI may be recombinantly produced. If the cells naturally produce the POI, they are ready for detection and isolation. If the POI is to be recombinantly produced, then the isolated and cultured cells expressing the specified cell surface capture molecule are transfected with second nucleotide sequence that encodes the secreted POI, under conditions in which the secreted POI is expressed. Upon expression, the secreted POI binds to the cell surface capture molecules and the cells displaying bound POI are detected and isolated.

Problems solved by technology

These procedures are laborious, inefficient, expensive, and the number of clones that can be analyzed is usually limited to a few hundred.

Moreover, the collection of clone pools, or hand-picked colonies, risks losing high expression cells, which often grow more slowly, to faster growing low expression cells.

Incorporation of flow cytometry into methods used for the isolation of stable expression cell lines has improved the capability of screening large numbers of individual clones, however, currently available methods remain inadequate for diverse reasons.

Diffusion of the POI between cells of different characteristics was also a problem.