Expression vectors encoding bispecific fusion proteins and methods of producing biologically active bispecific fusion proteins in a mammalian cell

DETAILED DESCRIPTION OF THE INVENTION DEFINITIONS As used in this application, the following words or phrases have the meanings specified.
As used herein, a "bispecific fusion protein" means any immunologically reactive molecule which specifically recognizes and binds at least two different targets at alternate times or at the same time and is expressed as a single chain.
As used herein, a "monospecific fusion protein" means any immunologically reactive molecule which specifically recognizes and binds a target and is a complex comprising two heavy immunoglobulin chains, two light immunoglobulin chains, or a heavy and/or light immunoglobulin chain and/or any portions thereof and is expressed as a single chain.
As used herein, an "expression vector" means a nucleic acid molecule comprising (1) a promoter and other sequences (e.
g.
leader sequences) necessary to direct expression of a desired gene or DNA sequence and (2) the desired gene or DNA sequence.
Optionally, the nucleic acid molecule may comprise a poly A signal sequence to enhance the stability of the gene transcript and/or an enhancer sequence to increase the transcription of the gene thereby affecting the expression of the gene.
As used herein, a "binding domain" means a binding site which recognizes and binds the entire binding area of a target or any portion thereof.
Examples include, but are not limited to, (1) a single variable region of an antibody (V.
sub.
L or V.
sub.
H); (2) two or more variable regions (e.
g.
V.
sub.
L +V.
sub.
H ; V.
sub.
L +V.
sub.
L ; or V.
sub.
H +V.
sub.
H) or the complementary determining region (CDR) thereof, or (3) an antigen (such as a leucocyte antigen) or a portion thereof.
As used herein, a "molecular tag" includes any DNA sequence encoding a molecule which may facilitate detection and purification of the fusion proteins described herein.
As used herein, a "bispecific single chain cassette" includes a DNA sequence encoding a first binding domain capable of binding a target and a DNA sequence encoding a second binding domain capable of binding a target, each domain capable of binding a different target at alternate times or at the same time, both domains encoded by DNA sequences being on the same cassette