Anti-HSA VHH antibodies and compositions thereof

Abstract

The present disclosure provides, among other things, single domain antibodies that bind to human serum albumin. Pharmaceutical compositions comprising the single domain antibodies disclosed herein are provided.

Description

ANTI-HSA ANTIBODIES AND COMPOSITIONS THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. Provisional Application No. 63 / 633,665, filed April 12, 2024, U.S. Provisional Application No. 63 / 702,592, filed October 2, 2024, and U.S. Provisional Application No. 63 / 719,077, filed November 11, 2024, the disclosure of each of which is hereby incorporated by reference in its entirety.BACKGROUND

[0002] Human serum albumin (HSA), produced by the liver, is the most abundant plasma protein with high solubility, high stability, and a long circulatory half-life. HSA has several functions, including acting as a drug transport protein and carrier for many metabolites and fatty acids. HSA can also be used to improve the half-life of therapeutic proteins.SUMMARY OF THE INVENTION

[0003] The present disclosure, among other things, addresses certain unmet needs in making and using biotherapeutics. Compositions of the disclosure provide and leverage albumin binding proteins to extend length of serum-half lives of therapeutic molecules. In particular, the present invention provides improved single domain antibodies (sdAbs) that bind to human serum albumin (HSA) with high affinity. Additionally, inventive anti-HSA antibodies described herein exhibit desirable characteristics that facilitate high yield production, cost-efficient purification, and improved stability.

[0004] In one aspect, the present invention provides, among other things, a single domain antibody (sdAb) that binds to human serum albumin (HSA), wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residuesfrom AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 consisting of an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 consisting of an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0005] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprisingan amino acid sequence of GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of SAGMS (SEQ ID NO: 93), a CDR2 consisting of an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 consisting of an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0006] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of SFGAS (SEQ ID NO: 94), a CDR2 consisting of an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 consisting of an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0007] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acidresidues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 consisting of an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 consisting of an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0008] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTR (SEQ ID NO: 110),and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 consisting of an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 consisting of an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0009] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 consisting of an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 consisting of an amino acid sequence of TIGQSTSR (SEQ ID NO:

[0010] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of GFTFGSFG (SEQ ID NO: 119), a CDR2 consisting of an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 consisting of an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).[OU] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of GFTFGSAG (SEQ ID NO: 122), a CDR2 consisting of an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 consisting of an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0012] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of GFTFGSF(SEQ ID NO: 128), a CDR2 consisting of an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 consisting of an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0013] In one aspect, the present invention provides, among other things, a sdAb that binds to HSA, wherein the sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSA (SEQ ID NO:131), a CDR2 comprising an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101). In some embodiments, the sdAb comprises a CDR1 consisting of an amino acid sequence of GFTFGSA (SEQ ID NO: 131), a CDR2 consisting of an amino acid sequence of DSGGTD (SEQ ID NO:132), and a CDR3 consisting of an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0014] In some embodiments, the sdAb comprises an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence at least 85% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence at least 90% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence at least 95% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence at least 96% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence at least 97% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments,the sdAb comprises an amino acid sequence at least 98% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence at least 99% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb comprises an amino acid sequence identical to any one of SEQ ID NOs: 1 or 9-11.

[0015] In some embodiments, the sdAb comprises an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 1. In some embodiments, the sdAb comprises an amino acid sequence identical to SEQ ID NO: 1.

[0016] In some embodiments, the sdAb comprises an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 9. In some embodiments, the sdAb comprises an amino acid sequence identical to SEQ ID NO: 9.

[0017] In some embodiments, the sdAb comprises an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 95%identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 10. In some embodiments, the sdAb comprises an amino acid sequence identical to SEQ ID NO: 10.

[0018] In some embodiments, the sdAb comprises an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 11. In some embodiments, the sdAb comprises an amino acid sequence identical to SEQ ID NO: 11.

[0019] In some embodiments, the sdAb has an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 85% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 90% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 95% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 96% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 97% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 98% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence at least 99% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb has an amino acid sequence identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the sdAb consists of an amino acid sequence identical to any one of SEQ ID NOs: 1 or 9-11.

[0020] In some embodiments, the sdAb has an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 96% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 98% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 1. In some embodiments, the sdAb has an amino acid sequence identical to SEQ ID NO: 1. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 1.

[0021] In some embodiments, the sdAb has an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 96% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 98% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 9. In some embodiments, the sdAb has an amino acid sequence identical to SEQ ID NO: 9. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 9.

[0022] In some embodiments, the sdAb has an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence at least 96% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence at least 98% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence atleast 99% identical to SEQ ID NO: 10. In some embodiments, the sdAb has an amino acid sequence identical to SEQ ID NO: 10. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 10.

[0023] In some embodiments, the sdAb has an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 96% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 98% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 11. In some embodiments, the sdAb has an amino acid sequence identical to SEQ ID NO: 11. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 11.

[0024] In one aspect, the present invention provides, among other things, a single domain antibody comprising the means for binding to HSA.

[0025] In some embodiments, the sdAb does not comprise a light chain, a constant domain, or an Fc region. In some embodiments, the sdAb does not comprise a light chain. In some embodiments, the sdAb does not comprise a constant domain. In some embodiments, the sdAb does not comprise an Fc region. In some embodiments, the sdAb comprises an Fc region.

[0026] In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively), when produced in a recombinant cell (e.g., CHO cell), results in a yield of at least 400 mg / mL. In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has low self-interaction, for example, a wavelength shift of 1 nm or less using affinity-capture self-interaction nanoparticle spectroscopy (AC-SINS). In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has a DNA score of less than 3, for example, according to a polyreactive ELISA. In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has a Tmof at least 55°C (e.g., at least 56°C, at least 57°C, at least 58°C, at least 59°C, or at least 60°C). In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and101, respectively) has a Tagg266 of at least 65°C (e.g., at least 66°C, at least 68°C, or least 70°C).

[0027] In some embodiments, the present invention provides, among other things, nucleic acids encoding an anti-HSA sdAb described herein. In some embodiments, the present invention provides, among other things, a vector comprising the nucleic acid encoding the anti- HSA sdAbs. In some embodiments, the present invention provides, among other things, a host cell comprising the nucleic acid or the vector.

[0028] In some embodiments, the present invention provides, among other things, a pharmaceutical composition comprising the anti-HSA sdAb described herein, and a pharmaceutically acceptable carrier. In some embodiments, the pharmaceutical composition comprises the nucleic acid described herein, and a pharmaceutically acceptable carrier. In some embodiments, the pharmaceutical composition comprises the vector described herein, and a pharmaceutically acceptable carrier. In some embodiments, the pharmaceutical composition comprises the host cell described herein, and a pharmaceutically acceptable carrier.

[0029] In some embodiments, the present invention provides, among other things, a method of treating a disease or disorder in a subject in need thereof. In some embodiments, the method comprises administering to the subject the anti-HSA sdAb described herein. In some embodiments, the method comprises administering to the subject the pharmaceutical composition described herein.

[0030] In some embodiments, the present invention provides, among other things, a method of preventing a disease or disorder in a subject in need thereof. In some embodiments, the method comprises administering to the subject the anti-HSA sdAb described herein. In some embodiments, the method comprises administering to the subject the pharmaceutical composition described herein.

[0031] In one aspect, the present invention provides, among other things, a sdAb that competes with a reference sdAb for binding to HSA, wherein the reference sdAb comprises a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0032] In one aspect, the present invention provides, among other things, a method of producing a sdAb variant that binds to HSA, comprising introducing one or more amino acid additions, deletions, or substitutions to a reference sdAb, wherein the reference sdAb comprises a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101). In some embodiments, the reference sdAb comprises an amino acid sequence identical to SEQ ID NO: 1. In some embodiments, the reference sdAb consists of an amino acid sequence identical to SEQ ID NO: 1.

[0033] In some embodiments, the method comprises introducing one or more amino acid additions to the reference sdAb. In some embodiments, the method comprises introducing one or more amino acid additions at the C-terminus of the reference sdAb. In some embodiments, the one or more amino acid additions is an addition of one or more alanine residues. In some embodiments, the method comprises introducing one or more additions of alanine residues at the C-terminus of the reference sdAb.

[0034] In some embodiments, the method comprises introducing one or more amino acid deletions to the reference sdAb.

[0035] In some embodiments, the method comprises introducing one or more amino acid substitutions to the reference sdAb. In some embodiments, the method comprises introducing one or more amino acid substitutions in the CDRs and / or framework regions of the reference sdAb. In some embodiments, the method comprises introducing one or more amino acid substitutions in the CDRs of the reference sdAb. In some embodiments, the method comprises introducing one or more amino acid substitutions in the framework regions of the reference sdAb. In some embodiments, the method comprises introducing one or more amino acid substitutions in the CDRs and framework regions of the reference sdAb. In some embodiments, the method comprises introducing one or more amino acid substitutions in the CDRs or framework regions of the reference sdAb.

[0036] In some embodiments, the one or more amino acid substitutions comprises F32A and / or M34A. In some embodiments, the one or more amino acid substitutions comprises F32A. In some embodiments, the one or more amino acid substitutions comprises M34A. In some embodiments, the one or more amino acid substitutions comprises F32A and M34A. In some embodiments, the one or more amino acid substitutions comprises F32A or M34A.

[0037] In some embodiments, the present invention provides, among other things, a sdAb variant produced by the method described herein. In some embodiments, the sdAb variant comprises an amino acid sequence identical to any one of SEQ ID NOs: 9-11. In some embodiments, the sdAb variant comprises an amino acid sequence identical to SEQ ID NO: 9. In some embodiments, the sdAb variant comprises an amino acid sequence identical to SEQ IDNO: 10. In some embodiments, the sdAb variant comprises an amino acid sequence identical to SEQ ID NO: 11. In some embodiments, the sdAb variant consists of an amino acid sequence identical to any one of SEQ ID NOs: 9-11. In some embodiments, the sdAb variant consists of an amino acid sequence identical to SEQ ID NO: 9. In some embodiments, the sdAb variant consists of an amino acid sequence identical to SEQ ID NO: 10. In some embodiments, the sdAb variant consists of an amino acid sequence identical to SEQ ID NO: 11.DEFINITIONS

[0038] In order for the present disclosure to be more readily understood, certain terms are first defined below. Additional definitions for the following terms and other terms are set forth throughout the specification.

[0039] Antibody. As used herein, the term “antibody” refers to immunoglobulin molecules and immunologically active portions of immunoglobulin (Ig) molecules, i.e., molecules that contain an antigen binding site that binds (immunoreacts with) an antigen. By “binds” or “immunoreacts with” is meant that the antibody reacts with one or more antigenic determinants of the desired. Antibodies include antibody fragments. Antibodies also include, but are not limited to, polyclonal, monoclonal, chimeric domain antibody, single chain, Fab, Fab’, F(ab’)2 fragments, scFvs, single-domain antibodies (sdAb). An antibody may be a whole antibody, or immunoglobulin, or an antibody fragment. As used herein, an antibody fragment includes a monomeric heavy chain or monomeric light chain, or a fragment thereof.

[0040] Acidic pH. As used herein, the term “acidic pH” refers to a pH that is less than a physiological pH. Acidic pH may also be used to describe the pH in endosomes or lysosomes. In some embodiments, acidic pH refers to a pH range of 4.5-6.8. In some embodiments, acidic pH refers to a pH range of 4.8-6.8. In some embodiments, acidic pH refers to a pH range of 4.8-6.0. In some embodiments, acidic pH refers to a pH range of 6.0-6.8. In some embodiments, acidic pH refers to a pH of 6.0.

[0041] Physiological pH: As used herein, the term “physiological pH’ refers to the pH that is outside the endosome. In some embodiments, physiological pH refers to the normal range of pH levels in the body’s essential fluids and tissues. In some embodiments, physiological pH is slightly alkaline. In some embodiments, physiological pH is between 7.0 and 7.8. In some embodiments, physiological pH is between 7.2 and 7.6. In some embodiments, physiological pH is between 7.3 and 7.5. In some embodiments, physiological pH is between 7.35 and 7.45. In some embodiments, physiological pH is 7.4.

[0042] CDRs'. As used herein, the term “CDR” refers to complementarity determining regions of an antibody or antigen binding fragment thereof. The CDRs are three flexible loops within a variable domain of an antibody that fold into specific structures in order to target and / or bind specific antigens. In some embodiments, the sdAbs described herein comprise 3 CDRs: a CDR1, a CDR2, and a CDR3. In some embodiments, the CDR sequences are determined by Kabat, IMGT, Chothia, or North conventions known in the art.

[0043] KD AS used herein, the term “KD”, as used herein, refers to the dissociation constant of a particular antibody-antigen interaction as is known in the art, and would apply as a parameter of the binding affinity of a targeting moiety to its cognate ligand for the subject compositions.

[0044] sdAb'. As used herein, the term “sdAb,” also referred to as a single domain antibody, domain antibody, VHH, VNAR, nanobody, or other grammatical equivalents, refers to an antibody fragment comprising a single monomeric variable antibody domain comprising a CDR1, CDR2, and CDR3. In some embodiments, the sdAb does not comprise a light chain, a constant domain, or an Fc region. In some embodiments, a sdAb comprises a constant region or an Fc region. In some embodiments, a sdAb is an antigen binding protein of a heavy chain only antibody or single domain antibody. In some embodiments, a sdAb is a binding protein (e.g., antibody, fragment thereof) comprising at least one monomeric domain, such as a VHH domain, devoid of a light chain, and, optionally, an Fc region. However, the sdAbs described herein may be used in any other antibody formats as a variable domain. In some embodiments, an sdAb is a monomer. In some embodiments, an sdAb is a homodimer. In some embodiments, an sdAb is a heterodimer.

[0045] In vitro'. As used herein, the term “in vitro" refers to events that occur in an artificial environment, e.g., in a test tube or reaction vessel, in cell culture, etc., rather than within a multi-cellular organism.

[0046] In vivo'. As used herein, the term “in vivo" refers to events that occur within a multicellular organism, such as a human and a non-human animal. In the context of cell-based systems, the term may be used to refer to events that occur within a living cell (as opposed to, for example, in vitro systems).

[0047] Identity '. As used herein, the term “identity” refers a relationship between the sequences of two or more polypeptide molecules or two or more nucleic acid molecules as known in the art, comparing the sequences of these molecules. The relationship determined by doing. In the art, “identity” also means the degree of sequence relatedness between nucleic acidmolecules or polypeptides, and in some cases more than one nucleotide sequence or more than one. It may be determined by a match between amino acid sequence strings. “Identity” means between a gap alignment (if any) addressed by a particular mathematical model or computer program (i.e., an “algorithm”) and a smaller sequence of two or more sequences. Measure the percent identity match.

[0048] Treating'. As used herein, the term “treat,” “treatment,” or “treating” refers to any method used to partially or completely alleviate, ameliorate, relieve, inhibit, prevent, delay onset of, reduce severity of and / or reduce incidence of one or more symptoms or features of a particular disease, disorder, and / or condition. Treatment may be administered to a subject who does not exhibit signs of a disease and / or exhibits only early signs of the disease for the purpose of decreasing the risk of developing pathology associated with the disease.DETAILED DESCRIPTION

[0049] The present invention provides, among other things, single domain antibodies (sdAbs) that bind to human serum albumin (HSA) with high affinity.A. Human Serum Albumin (HSA)

[0050] Human serum albumin (HSA) is the most abundant protein in plasma and has several functions. HSA plays a role in maintaining osmotic pressure in blood vessels and plasma pH, but it also serves as a drug transport protein and carrier for many metabolites and fatty acids. Further, HSA has a serum half-life of approximately 3 -weeks, and association with therapeutic proteins has shown to significantly improve their serum half-life.

[0051] Described herein are anti-HSA single domain antibodies (sdAbs) that bind and recruit albumin to prolong the half-life of therapeutic protein. The anti-HSA sdAbs are significantly smaller than albumin, which comprises 585 amino acids, and offer an alternative to direct conjugation of albumin to the therapeutic protein.B. Anti-HSA Antibodies

[0052] In one aspect, the present invention provides, among other things, single domain antibodies that bind to HSA. In some embodiments, the present invention provides albumin binding domains that can be adapted to various antibody formats.

[0053] A traditional antibody, also known as an immunoglobulin, is a Y-shaped structuring consisting of four polypeptides, two heavy chains and two light chains. The light chain consists of one variable region (VL) and one constant region (CL). The heavy chain consists of one variable region (VH) and at least three constant regions (CHI, CH2, CH3). The two light and two heavy chains are joined by disulfide bonds in the Y-shaped structure, with the light chains bracketing the heavy chains at the mouth of the Y-shape and continuing through the variable region. The variable regions determine the binding specificity of the antibody. Each variable region contains three hypervariable regions known as complementarity determining regions (CDRs) flanked by four relatively conserved regions known as framework regions (FRs). The three CDRs, referred to as CDR1, CDR2, and CDR3, contribute to the antibody binding specificity. Naturally occurring antibodies have often been used as starting material for engineered antibodies, such as chimeric antibodies and humanized antibodies. Examples of antibody-based antigen binding fragments include Fab, Fab’, (Fab’)2, Fv, single chain antibodies (e.g., scFv), minibodies, and diabodies. Examples of antibodies that have been modified or engineered include chimeric antibodies, humanized antibodies, and multispecific antibodies (e.g., bispecific antibodies).

[0054] Similarly, an anti-HSA sdAb described herein may be used in engineered antibodies or antibody-based antigen binding fragments. In some embodiments, the present invention provides, among other things, an anti-HSA antibody. In some embodiments, the present invention provides, among other things, an anti-HSA Fab. In some embodiments, the present invention provides, among other things, an anti-HSA Fab’. In some embodiments, the present invention provides, among other things, an anti-HSA (Fab’)2. In some embodiments, the present invention provides, among other things, an anti-HSA Fv. In some embodiments, the present invention provides, among other things, an anti-HSA single chain antibodies (e.g., scFv). In some embodiments, the present invention provides, among other things, anti-HSA minibodies. In some embodiments, the present invention provides, among other things, anti- HSA diabodies.Exemplary anti-HSA Binding Domains

[0055] In some embodiments, the anti-HSA sdAb is derived from a camelid VHH. In some embodiments, the anti-HSA sdAb is derived from a cartilaginous fish VNAR. In some embodiments, the anti-HSA sdAb is derived from a camelid VHH and humanized. In some embodiments, the anti-HSA sdAb is derived from a cartilaginous fish VNAR and humanized.

[0056] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence selected from Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 70% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 80% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 96% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 98% identical to an amino acid sequence in Table Al. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to an amino acid sequence in Table Al.Table Al. Exemplary amino acid sequences of anti-HSA sdAbs.

[0057] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 70% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 80% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85%identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 96% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 98% identical to any one of SEQ ID NOs: 1 or 9-11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to any one of SEQ ID NOs: 1 or 9-11.

[0058] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 70% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 80% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence identical to SEQ ID NO: 1.

[0059] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 70% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 80% identical to SEQ ID NO: 9. In someembodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence identical to SEQ ID NO:9.

[0060] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 70% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 80% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence identical to SEQ ID NO:10.

[0061] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 60% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 70% identical to SEQ ID NO: 11. In some embodiments, the anti-HSAsdAb comprises an amino acid sequence at least 80% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 96% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 98% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 11. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence identical to SEQ ID NO: 11.

[0062] In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3. The CDR1, CDR2, and CDR3 can be defined by any numbering convention commonly known in the art (e.g., Chothia, North, IM GT, Kabat). In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 as defined in any one of SEQ ID NOs: 1 or 9-11.

[0063] In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 as defined in SEQ ID NO: 1. In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 as defined in SEQ ID NO: 9. In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 as defined in SEQ ID NO: 10. In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 as defined in SEQ ID NO: 11.

[0064] In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 as defined in Table A2.Table A2. Exemplary amino acid sequences of anti-HSA sdAbs. The CDRs, as defined by different numbering conventions, are in bold.

[0065] It is contemplated that a sdAb provided by the present invention may consist of an VHH described herein. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 1. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 9. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 10. In some embodiments, the sdAb consists of an amino acid sequence identical to SEQ ID NO: 11.

[0066] In some embodiments, the anti-HSA sdAb comprises a CDR1, CDR2, and CDR3 comprising sequences selected from Table Bl, Table B2, Table B3, and / or Table B4.Table Bl. Kabat CDR Sequences of Exemplary anti-HSA sdAbs.Table B2. North CDR Sequences of Exemplary anti-HSA sdAbs.Table B3. IMGT CDR Sequences of Exemplary anti-HSA sdAbs.| sdAb 11 | 122| GFTFGSAG | 123 | IDSGGTDT | 115|Table B4. Chothia CDR Sequences of Exemplary anti-HSA sdAbs.

[0067] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0068] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In someembodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0069] In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 1 with no more than 5 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 1 with no more than 4 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 1 with no more than 3 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 1 with no more than 2 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 1 with no more than 1 amino acid change as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0070] In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ IDNO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0071] In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 1 with no more than 5 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 1 with no more than 4 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 1 with no more than 3 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 1 with no more than 2 amino acid changes as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 1 with no more than 1 amino acid change as compared to SEQ ID NO: 1, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 91, the CDR2 hasthe amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0072] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence of SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0073] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 9, provided that the CDR1 has the aminoacid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0074] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0075] In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 9 with no more than 5 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 9 with no more than 4 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 9 with nomore than 3 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 9 with no more than 2 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 9 with no more than 1 amino acid change as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0076] In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 11 with no more than 5 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 11 with no more than 4 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 11 with no more than 3 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 11 with no more than 2 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 11 with no more than 1 amino acid change as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0077] In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ IDNO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0078] In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0079] In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 9 with no more than 5 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 9 with no more than 4 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 9 with no more than 3 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 9 with no more than 2 amino acid changes as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 9 with no more than 1 amino acid change as compared to SEQ ID NO: 9, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0080] In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 11 with no more than 5 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 11 with no more than 4 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 11 with no more than 3 amino acid changes as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 11 with no more than 2 amino acid changes ascompared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 11 with no more than 1 amino acid change as compared to SEQ ID NO: 11, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 93, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0081] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti- HSA sdAb comprises a CDR1 comprising an amino acid sequence of SFGAS (SEQ ID NO:94), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO:95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0082] In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 85% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 90% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In someembodiments, the anti-HSA sdAb comprises an amino acid sequence at least 95% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 97% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises an amino acid sequence at least 99% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0083] In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 10 with no more than 5 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 10 with no more than 4 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 10 with no more than 3 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 10 with no more than 2 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb comprises a variant sequence of SEQ ID NO: 10 with no more than 1 amino acid change as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0084] In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 85% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ IDNO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 90% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 95% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 97% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has an amino acid sequence at least 99% identical to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0085] In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 10 with no more than 5 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 10 with no more than 4 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 10 with no more than 3 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 10 with no more than 2 amino acid changes as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, the CDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-HSA sdAb has a variant sequence of SEQ ID NO: 10 with no more than 1 amino acid change as compared to SEQ ID NO: 10, provided that the CDR1 has the amino acid sequence of SEQ ID NO: 94, theCDR2 has the amino acid sequence of SEQ ID NO: 95, and the CDR3 has the amino acid sequence of SEQ ID NO: 101.

[0086] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0087] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In someembodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0088] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0089] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), anda CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0090] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from TIGQSTSR (SEQ ID NO: 115). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSAG (SEQ ID NO: 122), aCDR2 comprising an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115).

[0091] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

[0092] In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence that differs by no more than 1 aminoacid residue from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that differs by no more than 1 amino acid residue from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that differs by no more than 1 amino acid residue from GQSTSR (SEQ ID NO: 101). In some embodiments, the anti-HSA sdAb comprises a CDR1 comprising an amino acid sequence of GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).Properties of anti-HSA Antibodies

[0093] The anti-HSA sdAbs described herein specifically bind to HSA. The term “specifically binds” refers to a measurable and reproducible interaction between the target, HSA, and the anti-HSA sdAb. For example, the anti-HSA sdAb specifically binds to HSA with a higher affinity or avidity, more quickly, and / or for much longer than it binds to another target.

[0094] The binding, affinity, or KD of the sdAbs described herein to HSA can be measured by any method commonly known in the art. For example, and without limitation, the sdAb binding to HSA can be assessed using enzyme-linked immunosorbent assays (ELISAs), flow cytometry, competitive binding assays, surface plasmon resonance (SPR), ligand binding assays, and / or cell-based binding assays.

[0095] In some embodiments, the assay measures the binding affinity (e.g., KD) of the anti- HSA sdAb. In some embodiments, the assay maps the epitope of the anti-HSA sdAb. In some embodiments, the assay compares the binding of the anti-HSA sdAb described herein to a reference antibody that binds to HSA.

[0096] In some embodiments, the anti-HSA sdAb increases the half-life of a linked therapeutic protein, as compared to the therapeutic protein alone. In some embodiments, the anti-HSA sdAb improves the therapeutic effect of the therapeutic protein, as compared to the therapeutic protein alone. In some embodiments, the therapeutic effect is improved by increasing the magnitude of the therapeutic effect (i.e., a higher response to the therapeutic protein). In some embodiments, the therapeutic effect is improved by increasing the duration of the therapeutic effect (i.e., a longer response to the therapeutic protein).

[0097] In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively), when produced in a recombinant cell (e.g., CHO cell), results in a yield of at least 400 mg / mL. In some embodiments, an anti-HSAsdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has low self-interaction, for example, a wavelength shift of 1 nm or less using affinity-capture self-interaction nanoparticle spectroscopy (AC-SINS). In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has a DNA score of less than 3, for example, according to a polyreactive ELISA. In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has a Tmof at least 55°C (e.g., at least 56°C, at least 57°C, at least 58°C, at least 59°C, or at least 60°C). In some embodiments, an anti-HSA sdAb described herein (e.g., a sdAb comprising CDRs of SEQ ID NOs: 91, 95, and 101, respectively) has a Tagg266 of at least 65°C (e.g., at least 66°C, at least 68°C, or least 70°C).C. Pharmaceutical Compositions

[0098] The present invention provides, among other things, pharmaceutical compositions comprising an anti-HSA sdAb described herein. The pharmaceutical composition can be formulated for use in a variety of drug delivery systems.

[0099] In some embodiments, the pharmaceutical composition comprises the anti-HSA sdAb and a pharmaceutically acceptable carrier.

[0100] In some embodiments, an anti-HSA sdAb described herein are formulated for delivery by a liquid nanoparticle (LNP). In some embodiments, the anti-HSA sdAbs are formulated for delivery by an engineered exosome. In some embodiments, the anti-HSA sdAbs are formulated for delivery by a viral like particle (VLP).

[0101] In some embodiments, the present invention provides, among other things, nucleic acids encoding an anti-HSA sdAb described herein. In some embodiments, present inventions provides, among other things, vectors comprising the nucleic acids encoding the anti-HSA sdAbs.

[0102] In some embodiments, the vector is viral vector. In some embodiments, the vector is a lentiviral vector. In some embodiments, the vector is an adeno-associated viral vector. In some embodiments, the vector is a retroviral vector. In some embodiments, the vector is an adenoviral vector.EXAMPLES

[0103] Various aspects of the invention are described in further detail in the following Examples. The following examples describe some of the exemplary modes of making and practicing the present invention. However, it should be understood that these examples are for illustrative purposes only and are not meant to limit the scope of the invention.Example 1. Generation and Humanization of Exemplary anti-HSA sdAbs.

[0104] In this example, exemplary anti-HSA sdAbs were discovered through a llama immunization campaign and humanized.

[0105] Llamas were immunized with human albumin to generate anti-HSA heavy chain only antibodies, comprising a single variable domain and two constant domains. Phage display screening was conducted using the immune repertoire of immunized llamas cloned into an immune phage library which was selected using human and cynomolgus serum albumin proteins. The amino acid sequences of the resulting variable domains were determined using standard sequencing approaches. The variable domains were then expressed and purified according to commonly known methods in the art.

[0106] The exemplary llama anti-HSA sdAbs were prepared with the variable domain linked to the N-terminus of a wild-type human IgGl Fc domain (SEQ ID NO: 12) for the sole purpose of facilitating measurement of binding affinity of the anti-HSA sdAb. The llama anti- HSA sdAbs were then screened by surface plasmon resonance (SPR) for binding affinity to human, cynomolgus monkey, mouse, and rat serum albumin (SA), and assessed for developability, as shown in Table 1. As shown, sdAbs A, B and C have desirable characteristics that facilitate manufacturing with high-yield production, high stability and purity. After the developability assessment, the anti-HSA sdAbs were humanized by VH CDR grafting.Table 1. Developability assessment of exemplary anti-HSA sdAbs.

[0107] AlphaFold2 was utilized to predict the VH model. Features taken into account for humanization include homology and developability. That is, homology (of human germline to parental sequence) is evaluated, and germline usage rate in existing humanized or human therapeutic monoclonal antibodies, and distribution of V region gene segments in the natural human antibody repertoire are considered. Here, IGHV3-23*04 was selected as the germline for VH CDR grafting humanization of exemplary anti-HSA sdAbs.

[0108] The humanized anti-HSA sdAbs were prepared with the variable domain linked to the N-terminus (VH-Fc) or C-terminus (Fc-VH) of a wild-type human IgGl Fc domain (SEQ ID NO: 12). A control anti-HSA sdAb (Alb23; SEQ ID NO: 91) that binds to human, cynomolgus, and mouse albumin was similarly prepared as a control.Table 2. Amino acid sequences of an exemplary anti-HSA sdAb control and an exemplary human IgGl Fc region.Example 2. Binding Affinity of Exemplary anti-HSA sdAbs.

[0109] Exemplary anti-HSA sdAbs were evaluated by SPR for binding kinetics at pH 6.0 and pH 7.4.

[0110] The binding affinity of parental llama anti-HSA sdAbs, prepared as described in Example 1, was assessed using surface plasmon resonance (SPR). Results are shown in Table 3.Table 3. Binding kinetics of exemplary parental llama anti-HSA sdAbs (VH-Fc).[OHl] In a second experiment, the binding affinity of humanized anti-HSA sdAbs was similarly assessed by SPR. Results are shown in Table 4.Table 4. Binding kinetics of exemplary humanized anti-HSA sdAbs (Fc-VHH).Example 3. Screening for Additional Variants of anti-HSA sdAbs.

[0112] This example describes the modification of exemplary anti-HSA sdAbs (i.e., sdAb 1). Exemplary anti-HSA sdAbs are further modified for a variety of purposes. For example, and without limitation, the anti-HSA sdAbs are modified to tailor binding affinity (i.e., increase or reduce binding affinity, increase pH-dependent binding), improve selectivity, reduce immunogenicity, increase stability, increase solubility, and / or improve manufacturability. The anti-HSA sdAbs are modified in the CDRs and / or in the framework regions.

[0113] The anti-HSA sdAbs are modified using various methods commonly known in the art. For example, and without limitation, the anti-HSA sdAbs are modified using antibody display technology to tailor specificity (i.e., binding to HSA without binding to other antigens) and / or binding affinity. Antibody display technology includes methods such as phage display, ribosome and mRNA display, bacterial surface display, yeast surface display, and mammalian surface display.

[0114] The anti-HSA sdAbs are also modified using rational design approaches, including for example and without limitation, sequence-based or structure-based prediction tools to modify properties such as aggregation, solubility, stability, and / or binding affinity.

[0115] The anti-HSA sdAbs are modified by conservative amino acid modifications (i.e., exchanging an amino acid residue for another with similar properties). Such modifications can maintain function (i.e., binding to HSA) while improving one or more other properties such as, for example and without limitation, immunogenicity, stability, and / or manufacturability.

[0116] Other methods of modification for the anti-HSA sdAbs include random mutagenesis, alanine scanning mutagenesis, histidine scanning mutagenesis, or other commonly known methods of generating mutant libraries. Such methods of mutagenesis are also paired with a screening methodology, such as, for example and without limitation, the antibody display technology described previously.EQUIVALENTS AND SCOPE

[0117] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

Claims

CLAIMSWhat is claimed is:

1. A single domain antibody (sdAb) that binds to human serum albumin (HS A), wherein the sdAb comprises: a. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101); b. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101); c. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101); d. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115); e. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), anda CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115); f. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115); g. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115); h. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from TIGQSTSR (SEQ ID NO: 115); i. a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101); or j . a CDR1 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence that is identical to or differs by no more than 2 amino acid residues from GQSTSR (SEQ ID NO: 101).sdAb of claim 1, wherein the sdAb comprises a. a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101); b. a CDR1 comprising an amino acid sequence of SAGMS (SEQ ID NO: 93), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101); c. a CDR1 comprising an amino acid sequence of SFGAS (SEQ ID NO: 94), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101); d. a CDR1 comprising an amino acid sequence of AASGFTFGSFGMS (SEQ ID NO: 105), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115); e. a CDR1 comprising an amino acid sequence of AASGFTFGSAGMS (SEQ ID NO: 108), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115); f. a CDR1 comprising an amino acid sequence of AASGFTFGSFGAS (SEQ ID NO: 109), a CDR2 comprising an amino acid sequence of AIDSGGTDTR (SEQ ID NO: 110), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115); g. a CDR1 comprising an amino acid sequence of GFTFGSFG (SEQ ID NO: 119), a CDR2 comprising an amino acid sequence of IDSGGTDT (SEQ ID NO: 123), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115); h. a CDR1 comprising an amino acid sequence of GFTFGSAG (SEQ ID NO: 122), a CDR2 comprising an amino acid sequence of IDSGGTDT (SEQ ID NO:123), and a CDR3 comprising an amino acid sequence of TIGQSTSR (SEQ ID NO: 115); i. a CDR1 comprising an amino acid sequence of GFTFGSF (SEQ ID NO: 128), a CDR2 comprising an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101); or j. a CDR1 comprising an amino acid sequence of GFTFGSA (SEQ ID NO: 131), a CDR2 comprising an amino acid sequence of DSGGTD (SEQ ID NO: 132), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

3. The sdAb of claim 1 or claim 2, wherein the sdAb comprises an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one of SEQ ID NOs: 1 or 9-11.

4. The sdAb of any one of the preceding claims, wherein the sdAb comprises an amino acid sequence identical to any one of SEQ ID NOs: 1 or 9-11.

5. The sdAb of claim 1 or claim 2, wherein the sdAb has an amino acid sequence at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one of SEQ ID NOs: 1 or 9- 11.

6. The sdAb of claim 5, wherein the sdAb consists of an amino acid sequence identical to any one of SEQ ID NOs: 1 or 9-11.

7. A single domain antibody (sdAb) comprising means for binding to human serum albumin (HSA).

8. The sdAb of any one of the preceding claims, wherein the sdAb does not comprise a light chain, a constant domain, or an Fc region.

9. The sdAb of any one of the preceding claims, wherein the sdAb, when produced in a recombinant cell, has a yield of at least 400 mg / mL.

10. The sdAb of any one of the preceding claims, wherein the sdAb has a wavelength shift of 1 nm or less according to affinity-capture self-interaction nanoparticle spectroscopy (AC-SINS).

11. The sdAb of any one of the preceding claims, wherein the sdAb has a DNA score of less than 3 according to a polyreactive ELISA.

12. The sdAb of any one of the preceding claims, wherein the sdAb has a Tmof at least 55°C.

13. The sdAb of any one of the preceding claims, wherein the sdAb has a Tagg266 of at least 65°C.

14. A nucleic acid encoding the sdAb of any one of claims 1-13.

15. A vector comprising the nucleic acid of claim 14.

16. A host cell comprising the nucleic acid of claim 14 or the vector of claim 15.

17. A pharmaceutical composition comprising the sdAb of any one of claims 1-13, the nucleic acid of claim 14, the vector of claim 15, or the host cell of claim 16, and a pharmaceutically acceptable carrier.

18. A method of treating a disease or disorder in a subject in need thereof, the method comprising administering to the subject an effective amount of the sdAb of any one of claims 1-13, or the pharmaceutical composition of claim 17.

19. A single domain antibody (sdAb) that competes with a reference sdAb for binding to human serum albumin (HSA), wherein the reference sdAb comprises a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

20. A method of producing a single domain antibody (sdAb) variant that binds to human serum albumin (HSA), comprising introducing one or more amino acid additions,deletions, or substitutions to a reference sdAb, wherein the reference sdAb comprises a CDR1 comprising an amino acid sequence of SFGMS (SEQ ID NO: 91), a CDR2 comprising an amino acid sequence of AIDSGGTDTRYAESIKG (SEQ ID NO: 95), and a CDR3 comprising an amino acid sequence of GQSTSR (SEQ ID NO: 101).

21. The method of claim 20, wherein the reference sdAb comprises an amino acid sequence identical to SEQ ID NO: 1.

22. The method of claim 20 or claim 21, wherein the method comprises introducing one or more amino acid additions at the C-terminus of the reference sdAb.

23. The method of claim 22, wherein the one or more amino acid additions is an addition of one or more alanine residues.

24. The method of any one of claims 20-23, wherein the method comprises introducing one or more amino acid substitutions in the CDRs and / or framework regions of the reference sdAb.

25. The method of claim 24, wherein the one or more amino acid substitutions comprises F32A and / or M34A.

26. A sdAb variant produced by the method of any one of claims 20-25.

27. The sdAb variant of claim 26, wherein the sdAb variant comprises an amino acid sequence identical to any one of SEQ ID NOs: 9-11.

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