Stabilized chimeric Fabs

1. A chimeric heterodimer comprising:

a) a first immunoglobulin heavy chain polypeptide construct (H1) comprising a human heavy chain constant domain 1 (CH1) sequence and a human or mouse heavy chain variable domain (VH) sequence, and

b) a first chimeric immunoglobulin light chain polypeptide construct (L1) comprising a human kappa light chain constant domain (Ckappa) IGKC*01 sequence having the amino acid sequence set forth in SEQ ID NO: 31 and a human or mouse lambda light chain variable domain (Vlambda) sequence,

the Vlambda sequence comprising one or more stabilizing amino acid modifications that increase the melting temperature of the chimeric heterodimer compared to a corresponding wild-type chimeric heterodimer without the stabilizing amino acid modifications, as measured by differential scanning calorimetry (DSC) or differential scanning fluorimetry (DSF),

wherein H1 and L1 form a first Fab region that binds to a first epitope,

wherein the melting temperature of the first Fab region without the stabilizing amino acid modifications is decreased compared to the Fab region of a corresponding parental wild-type antibody,

wherein the one or more stabilizing amino acid modifications comprise a substitution at residue 83, residue 85, or at both residues, wherein residue 83 is substituted with F, V, I, or A, and residue 85 is substituted with T or V; and

wherein the numbering of amino acid residues is according to Kabat.

2. The chimeric heterodimer according to claim 1 , wherein the Vlambda sequence further comprises stabilizing amino acid modifications at one or more amino acid residues at the interface between the Ckappa sequence and the Vlambda sequence, wherein the one or more amino acid residues are selected from the group consisting of residues 80, 105, and 106, wherein residue 80 is substituted with A or P, residue 105 is substituted with E, and residue 106 is substituted with I.

3. The chimeric heterodimer according to claim 1 , wherein the Vlambda sequence of the chimeric heterodimer comprises

a) 83F and 85T;

b) 83V and 85T;

c) 83I and 85T;

d) 83A and 85T;

e) 85T;

f) 85V;

g) 83F;

h) 83V;

i) 83I; or

j) 83A.

4. The chimeric heterodimer according to claim 2 , wherein the Vlambda sequence of the chimeric heterodimer comprises:

a) 83F and 105E;

b) 83F and 106I;

c) 83F, 85T and 105E;

d) 83F, 85V and 105E;

e) 83F, 85T, 105E and 106I;

f) 83F, 85V, 105E and 106I;

g) 83V and 105E;

h) 83V and 106I;

i) 83V, 85T and 105E;

j) 83V, 85V and 105E;

k) 83V, 85T, 105E and 106I;

l) 83I and 105E;

m) 83I, 85T and 105E;

n) 83I, 85T, 105E and 106I;

o) 83A and 105E;

p) 83A, 85T and 105E, or

q) 83A, 85T, 105E and 106I.

5. An antibody construct comprising:

a) a first heterodimer, wherein the first heterodimer is the chimeric heterodimer according to claim 1 , and

b) a scaffold

wherein at least one of H1 and L1 of said first heterodimer is linked with or without a linker to the scaffold.

6. The antibody construct according to claim 5 , further comprising a second heterodimer, said second heterodimer comprising:

i) a second immunoglobulin heavy chain polypeptide construct (H2) comprising a heavy chain constant domain 1 (CH1) sequence, and a heavy chain variable domain (VH) sequence, and

ii) a second immunoglobulin light chain polypeptide construct (L2) comprising a light chain constant domain (CL) sequence and a light chain variable domain (VL) sequence,

wherein H2 and L2 form a second Fab region that binds to a second epitope, and at least one of H2 and L2 is linked with or without linkers to the scaffold.

7. The antibody construct according to claim 6 , wherein the first epitope and the second epitope are the same.

8. The antibody construct according to claim 6 , wherein the first epitope and the second epitope are different from each other.

9. The antibody construct according to claim 6 , wherein the first heterodimer, the second heterodimer, or both heterodimers, further comprise one or more amino acid substitutions that promote light chain pairing.

10. The antibody construct according to claim 5 , wherein the scaffold is an Fc region comprising a first heavy chain constant domain 3 (CH3) sequence and a second CH3 sequence.

11. The antibody construct according to claim 10 , wherein the first CH3 sequence and the second CH3 sequence each comprise one or more amino acid modifications that promote formation of a heterodimeric CH3 domain compared to a homodimeric CH3 domain.

12. The antibody construct according to claim 10 , wherein the Fc region further comprises a first constant domain 2 (CH2) sequence and a second CH2 sequence.

13. The antibody construct according to claim 10 , wherein the Fc region is a human Fc, a human IgG1 Fc, a human IgA Fc, a human IgG Fc, a human IgD Fc, a human IgE Fc, a human IgM Fc, a human IgG2 Fc, a human IgG3 Fc, or a human IgG4 Fc.

14. The antibody construct of claim 5 , wherein the linkers are one or more polypeptide linkers.

15. The antibody construct of claim 14 , wherein the linkers comprise one or more antibody hinge regions.

16. The antibody construct of claim 15 , wherein the linkers comprise one or more IgG1 hinge regions.

17. The antibody construct according to claim 5 , wherein the antibody construct is conjugated to a drug.

18. The antibody construct according to claim 6 , wherein the first heterodimer comprises:

a) 83F, 85T and 105E;

b) 83V and 85T;

c) 83V, 85T, 105E and 106I;

d) 83I and 85T;

e) 83I, 85T, 105E and 106I;

f) 83A and 85T; or

g) 83A, 85T, 105E and 106I.

19. A pharmaceutical composition comprising the chimeric heterodimer of claim 1 , and a pharmaceutically acceptable carrier.

20. A polynucleotide or set of polynucleotides encoding the chimeric heterodimer of claim 1 .

21. A vector or set of vectors comprising one or more of the polynucleotides or sets of polynucleotides according to claim 20 .

22. An isolated cell comprising the polynucleotide or set of polynucleotides according to claim 20 .

23. A method of preparing a chimeric heterodimer of claim 1 , comprising the steps of: (a) obtaining a host cell comprising a polynucleotide or set of polynucleotides encoding the chimeric heterodimer; (b) culturing the host cell in a host cell culture under conditions that allow expression of the chimeric heterodimer, and (c) collecting the chimeric heterodimer from the host cell culture.

24. A chimeric heterodimer comprising:

a) a first immunoglobulin heavy chain polypeptide construct (H1) comprising a human heavy chain constant domain 1 (CH1) sequence and a human or mouse heavy chain variable domain (VH) sequence, and

b) a first chimeric immunoglobulin light chain polypeptide construct (L1) comprising a human kappa light chain constant domain (Ckappa) IGKC*01 sequence having the amino acid sequence set forth in SEQ ID NO: 31 and a human or mouse lambda light chain variable domain (Vlambda) sequence,

the Vlambda sequence comprising one or more stabilizing amino acid modifications that increase the melting temperature of the chimeric heterodimer compared to a corresponding wild-type chimeric heterodimer without the stabilizing amino acid modifications, as measured by differential scanning calorimetry (DSC) or differential scanning fluorimetry (DSF),

wherein H1 and L1 form a first Fab region that binds to a first epitope,

wherein the melting temperature of the first Fab region without the stabilizing amino acid modifications is decreased compared to the Fab region of a corresponding parental wild-type antibody, and wherein the stabilizing amino acid modifications comprise:

a) 83F, 105E and 106AK;

b) 83F, 105E, 106I and 106AK;

c) 80A, 83F, 105E and 106AK;

d) 80A, 83F, 105E, 106I and 106AK;

e) 80A, 83F, 85T, 105E and 106AK;

f) 80A, 83F, 85T, 105E, 106I and 106AK;

g) 80P, 83F, 85T, 105E, 106I and 106AK; or

h) 83F, 85T, 105E, 106I and 106AK.

25. A method of preparing an antibody construct of claim 5 , comprising the steps of: (a) obtaining a host cell comprising a polynucleotide or set of polynucleotides encoding the antibody construct; (b) culturing the host cell in a host cell culture under conditions that allow expression of the antibody construct, and (c) collecting the antibody construct from the host cell culture.