Method for generating and identifying antibodies directed against a B7

DETAILED DESCRIPTION Accordingly, the present invention identifies the B7 antigen as a ligand recognized by the CD28 receptor.
The B7 antigen, or its fragments or derivatives are reacted with CD28 positive T cells to regulate T cell interactions with other cells.
Alternatively, the CD28 receptor, its fragments or derivatives are reacted with B7 antigen to regulate interactions of B7 positive cells with T cells.
In addition, antibodies or other molecules reactive with the B7 antigen or CD28 receptor may be used to inhibit interaction of cells associated with these molecules, thereby regulating T cell responses.
A preferred embodiment of the invention provides a method for regulating CD28 specific T cell interactions by reacting CD28 positive T cells with B7 antigen, or its fragments or derivatives, so as to block the functional interaction of T cells with other cells.
The method for reacting a ligand for CD28 with T cells may additionally include the use of anti-CD monoclonal antibodies such as anti-CD2 and/or anti-CD3 monoclonal antibody.
In an alternative embodiment, the invention provides a method for regulating immune responses by contacting CD28 positive T cells with fragments containing at least a portion of the DNA sequence encoding the amino acid sequence corresponding to the extracellular domain of B7 antigen.
In addition, derivatives of B7 antigen may be used to regulate immune responses, wherein the derivatives are fusion protein constructs including at least a portion of the extracellular domain of B7 antigen and another protein, such as human immunoglobulin C gamma 1, that alters the solubility, binding affinity and/or valency of B7 antigen.
For example, in a preferred embodiment, DNA encoding amino acid residues from about position 1 to about position 215 of the sequence corresponding to the extracellular domain of B7 antigen is joined to DNA encoding amino acid residues of the sequences corresponding to the hinge, CH2 and CH3 regions of human Ig C.
gamma.
1 to form a DNA fusion product which encodes B7Ig fusion protein