Immunoglobulin variable domains
VH domain, in which: (i) the amino acid residue at position 112 is one of K or Q; and/or (ii) the amino acid residue at position 89 is T; and/or (iii) the amino acid residue at position 89 is L and the amino acid residue at position 110 is one of K or Q; and (iv) in each of cases (i) to (iii), the amino acid at position 11 is preferably V; and in which said VH domain contains a C-terminal extension (X)n, in which n is 1 to 10, preferably 1 to 5, such as 1, 2, 3, 4 or 5 (and preferably 1 or 2, such as 1); and each X is an (preferably naturally occurring) amino acid residue that is independently chosen, and preferably independently chosen from the group consisting of alanine (A), glycine (G), valine (V), leucine (L) or isoleucine (I).
1. A polypeptide comprising a first immunoglobulin single variable domain (ISVD) that specifically binds to human serum albumin and a second ISVD that specifically binds to a therapeutic target, wherein the second ISVD is at the C-terminal end of the polypeptide, wherein in the second ISVD the amino acid residue at Kabat position 11 is V and the amino acid residue at Kabat position 89 is L.
2. The polypeptide of claim 1 , wherein the first ISVD comprises a CDR1, CDR2, and CDR3, in which CDR1 comprises the amino acid sequence SFGMS (SEQ ID NO:41); CDR2 comprises the amino acid sequence SISGSGSDTLYADSVKG (SEQ ID NO:42); and CDR3 comprises the amino acid sequence GGSLSR (SEQ ID NO:43).
3. The polypeptide of claim 1 , wherein the first ISVD is Alb-8 (SEQ ID NO:46) or Alb-23 (SEQ ID NO:61).
4. The polypeptide of claim 1 , wherein in the first ISVD the amino acid residue at Kabat position 11 is V and the amino acid residue at Kabat position 89 is L.
5. The polypeptide of claim 4 , wherein in the first ISVD:
the amino acid residue at Kabat position 14 is selected from the group consisting of A and P;
the amino acid residue at Kabat position 41 is selected from the group consisting of A and P;
the amino acid residue at Kabat position 108 is selected from the group consisting of Q and L; and
the amino acid residue at Kabat position 110 is selected from the group consisting of T and Q.
6. The polypeptide of claim 5 , wherein in the first ISVD:
the amino acid residue at Kabat position 110 is T and the amino acid residue at Kabat position 112 is S; or
the amino acid residue at Kabat position 110 is Q and the amino acid residue at Kabat position 112 is S.
7. The polypeptide of claim 6 , wherein the first ISVD has at least 90% sequence identity with Alb-8 (SEQ ID NO:46) or Alb-23 (SEQ ID NO:61).
8. The polypeptide of claim 6 , wherein the first ISVD comprises a CDR1, CDR2, and CDR3, in which CDR1 comprises the amino acid sequence SFGMS (SEQ ID NO:41); CDR2 comprises the amino acid sequence SISGSGSDTLYADSVKG (SEQ ID NO:42); and CDR3 comprises the amino acid sequence GGSLSR (SEQ ID NO:43).
9. The polypeptide of claim 1 , wherein the first ISVD is a VHH domain or a humanized VHH domain.
10. The polypeptide of claim 1 , wherein in the second ISVD:
the amino acid residue at Kabat position 14 is selected from the group consisting of A and P;
the amino acid residue at Kabat position 41 is selected from the group consisting of A and P;
the amino acid residue at Kabat position 108 is selected from the group consisting of Q and L; and
the amino acid residue at Kabat position 110 is selected from the group consisting of T and Q.
11. The polypeptide of claim 10 , wherein in the second ISVD:
the amino acid residue at Kabat position 110 is T and the amino acid residue at Kabat position 112 is S; or
the amino acid residue at Kabat position 110 is Q and the amino acid residue at Kabat position 112 is S.
12. The polypeptide of claim 1 , wherein the second ISVD is a VHH domain or a humanized VHH domain.
13. The polypeptide of claim 1 , wherein the first and second ISVDs are connected directly or indirectly via a suitable linker.
14. A composition comprising a polypeptide according to claim 1 and at least one pharmaceutically acceptable carrier, diluent or excipient.
15. The polypeptide of claim 1 , wherein the first ISVD is a camelized VH domain.
16. The polypeptide of claim 1 , wherein the second ISVD is a camelized VH domain.