Purified ICOS polypeptides are described, as well as nucleic acids encoding the polypeptides, vectors including the nucleic acids, host cells containing the vectors, and methods for using the polypeptides, nucleic acids, and host cells.
1. A purified polypeptide consisting of:
(a) a variant of
a wild-type ICOS amino acid sequence consisting of an extracellular domain of wild-type ICOS, the wild-type ICOS extracellular domain being SEQ ID NO:10 or SEQ ID NO:9,
the variant:
consisting of an amino acid sequence that differs by one or more amino acid substitutions from, but is at least 85% homologous to, its corresponding wild-type ICOS amino acid sequence; and
having altered affinity for human B7-H2 (SEQ ID NO:43) compared to its corresponding wild-type ICOS amino acid sequence, wherein said affinity for human B7-H2 is increased by at least 10% relative to the affinity of the corresponding wild-type ICOS amino acid sequence for human B7-H2; or
(b) the variant of (a) and: (I) a peptide sequence unrelated to ICOS attached to the N-terminus of the variant of (a); (II) a peptide sequence unrelated to ICOS attached to the C-terminus of the variant of (a); or (III) a peptide sequence unrelated to ICOS attached to the N-terminus of the variant of (a) and a second peptide sequence unrelated to ICOS attached to the C-terminus of the variant of (a).
2. The purified polypeptide of claim 1 , wherein the variant differs from its corresponding wild-type amino acid sequence at a position corresponding to amino acid 76 of SEQ ID NO:12.
3. The purified polypeptide of claim 2 , wherein, in the variant, the amino acid at the position corresponding to said amino acid 76 of SEQ ID NO:12 is glutamine.
4. The purified polypeptide of claim 1 , wherein the variant differs from its corresponding wild-type amino acid sequence at a position corresponding to amino acid 52 of SEQ ID NO:12.
5. The purified polypeptide of claim 4 , wherein, in the variant, the amino acid at the position corresponding to said amino acid 52 of SEQ ID NO:12 is serine.
6. The purified polypeptide of claim 1 , wherein said variant is capable of inhibiting T cell activation in a T cell proliferation assay.
7. The purified polypeptide of claim 1 , wherein the peptide sequence unrelated to the ICOS or the second peptide sequence unrelated to ICOS is a blocking agent that facilitates survival of the polypeptide in vivo.
8. The purified polypeptide of claim 1 , wherein the peptide sequence unrelated to the ICOS or the second peptide sequence unrelated to ICOS is a tag amino acid sequence.
9. The purified polypeptide of claim 1 , wherein the peptide sequence unrelated to the ICOS or the second peptide sequence unrelated to ICOS is a human IgG1 CH2-CH3 sequence.