Search

CN-122029199-A - Cysteine engineered antibodies and immunoconjugates

CN122029199ACN 122029199 ACN122029199 ACN 122029199ACN-122029199-A

Abstract

An antibody engineered with reactive cysteine residues is provided, and more particularly, an antibody having therapeutic or diagnostic applications is provided. Immunoconjugates comprising the engineered antibodies are also provided. Further provided are medicaments or pharmaceutical compositions comprising the antibodies or antibody-drug conjugates, as well as methods and uses of the antibodies or immunoconjugates for the treatment of diseases such as tumors.

Inventors

  • ZHAO MENGHUI
  • ZHU CHENCHEN
  • GAO CHANGSHOU

Assignees

  • 信达生物制药(苏州)有限公司

Dates

Publication Date
20260512
Application Date
20240906
Priority Date
20230908

Claims (20)

  1. A cysteine engineered antibody or antigen binding fragment thereof, wherein (I) The antibody or antigen binding fragment thereof comprises a modified lambda light chain constant region, wherein the amino acid of the modified lambda light chain constant region at position 160 compared to the parent lambda constant region is mutated to a cysteine; (ii) The antibody or antigen binding fragment thereof comprises a modified lambda light chain constant region, wherein the amino acids at positions 160 and 166 of the modified lambda light chain constant region compared to the parent lambda constant region are mutated to cysteines; (iii) The antibody or antigen binding fragment thereof comprises a modified lambda light chain constant region and a modified heavy chain constant region, wherein the amino acid of the modified lambda light chain constant region at position 160 compared to the parent lambda constant region is mutated to a cysteine and the amino acid of the modified heavy chain constant region at position 152 or 155 compared to the parent heavy chain constant region is mutated to a cysteine; (iv) The antibody or antigen binding fragment thereof comprises a modified lambda light chain constant region and a modified heavy chain constant region, wherein the amino acid of the modified lambda light chain constant region at position 166 compared to the parent lambda constant region is mutated to a cysteine and the amino acid of the modified heavy chain constant region at position 152 or 155 compared to the parent heavy chain constant region is mutated to a cysteine; (v) The antibody or antigen binding fragment thereof comprises a modified Kappa light chain constant region and a modified heavy chain constant region, wherein the amino acid at position 165 of the modified Kappa light chain constant region compared to the parent Kappa light chain constant region is mutated to a cysteine and the amino acid at position 152 or 155 of the modified heavy chain constant region compared to the parent heavy chain constant region is mutated to a cysteine; (vi) The antibody or antigen binding fragment thereof comprises a modified Kappa light chain constant region, wherein the modified Kappa light chain constant region is mutated to a cysteine at amino acids 160 and 166 and a tyrosine at amino acid 178 as compared to the parent Kappa constant region; (vii) The antibody or antigen binding fragment thereof comprises a modified Kappa light chain constant region and a modified heavy chain constant region, wherein the amino acid of the modified Kappa light chain constant region at position 166 compared to the parent Kappa light chain constant region is mutated to a cysteine and the amino acid of the modified heavy chain constant region at position 375 compared to the parent heavy chain constant region is mutated to a cysteine, or (Viii) The antibody or antigen binding fragment thereof comprises a modified heavy chain constant region, wherein the amino acids at positions 239 and 375 of the modified heavy chain constant region are mutated to cysteines as compared to the parent heavy chain constant region.
  2. The antibody or antigen binding fragment thereof of claim 1, wherein the parent heavy chain constant region is a heavy chain constant region of human IgG1, e.g., comprising the amino acid sequence set forth in SEQ ID No. 3 or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence set forth in SEQ ID No. 3 and comprising NO cysteine mutation.
  3. The antibody or antigen-binding fragment thereof of claim 1 or 2, wherein the parent lambda light chain constant region is a human lambda light chain constant region, e.g., comprising the amino acid sequence set forth in SEQ ID No. 6 or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence set forth in SEQ ID No. 6 and comprising NO cysteine mutation, or Wherein the parental kappa light chain constant region is a human kappa light chain constant region, e.g., comprising the amino acid sequence shown in SEQ ID No. 5 or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID No. 5 and comprising NO cysteine mutations.
  4. The antibody or antigen-binding fragment thereof of any one of claims 1-3, wherein (I) Wherein the modified lambda light chain constant region comprises the amino acid sequence set forth in SEQ ID NO. 7; (ii) Wherein the modified lambda light chain constant region comprises the amino acid sequence set forth in SEQ ID NO. 28; (iii) Wherein the modified lambda light chain constant region comprises the amino acid sequence set forth in SEQ ID NO. 7 and the modified heavy chain constant region comprises the amino acid sequence set forth in SEQ ID NO. 10 or 11; (iv) Wherein the modified lambda light chain constant region comprises the amino acid sequence set forth in SEQ ID NO. 8 and the modified heavy chain constant region comprises the amino acid sequence set forth in SEQ ID NO. 10 or 11; (v) Wherein the modified kappa light chain constant region comprises the amino acid sequence shown in SEQ ID NO. 9 and the modified heavy chain constant region comprises the amino acid sequence shown in SEQ ID NO. 10 or 11; (vi) Wherein said modified kappa light chain constant region comprises the amino acid sequence shown as SEQ ID NO. 62; (vii) Wherein the modified Kappa light chain constant region comprises the amino acid sequence depicted in SEQ ID NO. 66 and the modified heavy chain constant region comprises the amino acid sequence depicted in SEQ ID NO. 67, or (Viii) The modified heavy chain constant region comprises the amino acid sequence shown in SEQ ID NO. 67 and the amino acid sequence shown in SEQ ID NO. 68.
  5. The antibody or antigen-binding fragment thereof of any one of claims 1-4, wherein (I) The modified light chain constant region comprising or consisting of the amino acid sequence shown in SEQ ID NO. 16, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 16 and being substituted at position 160 with a cysteine, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 16 and comprising the amino acid sequence shown in SEQ ID NO. 7, or (Ii) The modified light chain constant region comprising or consisting of the amino acid sequence shown in SEQ ID NO. 18, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 18 and being substituted at positions 160 and 166 with cysteine, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 18 and comprising the amino acid sequence shown in SEQ ID NO. 28, or (Iii) The modified light chain constant region comprises or consists of the amino acid sequence shown in SEQ ID NO. 16, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 16 and being substituted at position 160 with a cysteine, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 16 and comprising the amino acid sequence shown in SEQ ID NO. 7, and The modified heavy chain constant region comprises or consists of the amino acid sequence: an amino acid sequence shown in SEQ ID NO. 25, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 25 and substituted with cysteine at position 152, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 25 and comprising the amino acid sequence shown in SEQ ID NO. 10, or An amino acid sequence shown in SEQ ID NO. 26, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 26 and substituted with cysteine at position 155, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 26 and comprising the amino acid sequence shown in SEQ ID NO. 11, or The modified heavy chain constant region comprises a modified CH1, the modified CH1 comprising or consisting of the amino acid sequence: An amino acid sequence shown in SEQ ID NO. 22, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 22 and substituted with cysteine at position 152, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 22 and comprising the amino acid sequence shown in SEQ ID NO. 10, or An amino acid sequence shown in SEQ ID NO. 23, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 23 and substituted with cysteine at position 155, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 23 and comprising the amino acid sequence shown in SEQ ID NO. 11; (iv) The modified light chain constant region comprising or consisting of the amino acid sequence shown in SEQ ID NO. 17, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 17 and being substituted at position 166 with a cysteine, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 17 and comprising the amino acid sequence shown in SEQ ID NO. 8, and The modified heavy chain constant region comprises or consists of the amino acid sequence: an amino acid sequence shown in SEQ ID NO. 25, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 25 and substituted with cysteine at position 152, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 25 and comprising the amino acid sequence shown in SEQ ID NO. 10, or An amino acid sequence shown in SEQ ID NO. 26, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 26 and substituted with cysteine at position 155, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 26 and comprising the amino acid sequence shown in SEQ ID NO. 11, or The modified heavy chain constant region comprises a modified CH1, the modified CH1 comprising or consisting of the amino acid sequence: An amino acid sequence shown in SEQ ID NO. 22, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 22 and substituted with cysteine at position 152, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 22 and comprising the amino acid sequence shown in SEQ ID NO. 10, or An amino acid sequence shown in SEQ ID NO. 23, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 23 and substituted with cysteine at position 155, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 23 and comprising the amino acid sequence shown in SEQ ID NO. 11, or (V) The modified light chain constant region comprising or consisting of the amino acid sequence shown in SEQ ID NO. 20, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 20 and being substituted at position 165 with cysteine, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 20 and comprising the amino acid sequence shown in SEQ ID NO. 9, and The modified heavy chain constant region comprises or consists of the amino acid sequence: an amino acid sequence shown in SEQ ID NO. 25, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 25 and substituted with cysteine at position 152, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 25 and comprising the amino acid sequence shown in SEQ ID NO. 10, or An amino acid sequence shown in SEQ ID NO. 26, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 26 and substituted with cysteine at position 155, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 26 and comprising the amino acid sequence shown in SEQ ID NO. 11, or The modified heavy chain constant region comprises a modified CH1, the modified CH1 comprising or consisting of the amino acid sequence: An amino acid sequence shown in SEQ ID NO. 22, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 22 and substituted with cysteine at position 152, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 22 and comprising the amino acid sequence shown in SEQ ID NO. 10, or An amino acid sequence shown in SEQ ID NO. 23, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 23 and substituted with cysteine at position 155, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 23 and comprising the amino acid sequence shown in SEQ ID NO. 11; (vi) The modified light chain constant region comprises or consists of the amino acid sequence shown in SEQ ID NO. 60, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 60 and being substituted with a cysteine at positions 160 and 166 and a tyrosine at position 178, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 60 and comprising the amino acid sequence shown in SEQ ID NO. 62; (vii) The modified light chain constant region comprises or consists of the amino acid sequence shown in SEQ ID NO. 44, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 44 and being substituted at position 166 with a cysteine, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 44 and comprising the amino acid sequence shown in SEQ ID NO. 66; And the modified heavy chain constant region comprises or consists of the amino acid sequence shown in SEQ ID NO. 61, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 61 and substituted with cysteine at position 375, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 61 and comprising the amino acid sequence shown in SEQ ID NO. 67, or the modified heavy chain constant region comprises or consists of the amino acid sequence shown in SEQ ID NO. 63, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 63 and substituted with amino acid sequence at position 92%, 93%, 94%, 95%, 96%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 63, or an amino acid sequence shown in at least 92%, 93%, 95% or 95% and comprising the amino acid sequence shown in SEQ ID NO. 67; (viii) The modified heavy chain constant region comprising or consisting of the amino acid sequence shown in SEQ ID NO. 64, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 64 and substituted with cysteine at positions 239 and 375, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 64 and comprising the amino acid sequence shown in SEQ ID NO. 67 and SEQ ID NO. 68, or the modified heavy chain constant region comprising or consisting of the amino acid sequence shown in SEQ ID NO. 65, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the amino acid sequence shown in SEQ ID NO. 65 and substituted with amino acid sequence shown in positions 67, 68, or an amino acid sequence shown in SEQ ID NO. 65 and comprising at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%.
  6. The antibody or antigen-binding fragment thereof of any one of claims 1-5, wherein the antigen-binding fragment is selected from the group consisting of Fab, fab ', F (ab') 2, or diabody antibody (diabody).
  7. The antibody or antigen-binding fragment thereof of any one of claims 1-6, wherein the antibody or antigen-binding fragment thereof specifically binds an antigen, such as a tumor-associated antigen, such as an immune checkpoint molecule, such as HER2.
  8. The antibody or antigen-binding fragment thereof of claim 7, wherein the antibody or antigen-binding fragment thereof that specifically binds HER2 comprises 3 heavy chain variable region CDRs and 3 light chain variable region CDRs of an antibody that specifically binds HER2, such as trastuzumab, or comprises heavy chain variable region and light chain variable region of an antibody that specifically binds HER2, such as trastuzumab.
  9. The antibody or antigen-binding fragment thereof of claim 7, wherein the parent antibody or antigen-binding fragment thereof is trastuzumab or antigen-binding fragment thereof.
  10. An isolated nucleic acid molecule encoding the antibody or antigen-binding fragment thereof of any one of claims 1-9.
  11. An expression vector comprising the nucleic acid molecule of claim 10.
  12. A host cell comprising the isolated nucleic acid molecule of claim 10 or the expression vector of claim 11.
  13. A method of making a cysteine engineered antibody or antigen binding fragment thereof comprising: Introducing a nucleic acid encoding each strand of the antibody or antigen-binding fragment thereof of any one of claims 1-9 or an expression vector comprising said nucleic acid into a host cell, and Expressing and assembling the antibody or antigen binding fragment thereof in a host cell; Optionally, the antibody or antigen binding fragment thereof is purified, e.g., by Protein a.
  14. An immunoconjugate comprising the antibody or antigen binding fragment thereof of any one of claims 1-9 and a payload.
  15. The immunoconjugate of claim 14, wherein the payload is selected from a drug such as a small molecule drug, radionuclide, DNA, RNA, enzyme, or polypeptide, such as a cytotoxic agent, chemotherapeutic agent, innate immune agonist (e.g., toll-like receptor agonist (TLR) class ISAC drug SBT6050, SBT6290, BDC-1001; sting agonist ISAC drug XMT-2056, treg cell modulating ISAC drug ADCT-301, etc.), immune modulator, therapeutic oligonucleotide (siRNA, PMO, etc.), or radionuclide, etc.
  16. The immunoconjugate of claim 14, wherein the immunoconjugate is selected from an Antibody Drug Conjugate (ADC), an antibody immunostimulatory conjugated drug (ISAC), an Antibody Oligonucleotide Conjugate (AOC), an antibody polypeptide conjugated drug (APC), an antibody nuclide conjugated drug (RDC), or an antibody degrading conjugated drug (ADeC).
  17. The immunoconjugate of claim 16, wherein the immunoconjugate is an Antibody Drug Conjugate (ADC), and wherein the payload is a drug moiety selected from topoisomerase I inhibitors, such as camptothecin derivatives or camptothecins (e.g., DXd), anti-tubulin agents, such as auristatins (MMAF, MMAE), taxane analogs (e.g., epothilones a and B), maytansinoids (DM 1, DM 4), tubulysins and analogs thereof, DNA-acting drugs, such as PBD, and the like.
  18. The immunoconjugate of claim 16 or 17, wherein the immunoconjugate is an antibody drug conjugate, and wherein the average DAR value of the ADC is 1 to 4.
  19. The immunoconjugate of any one of claims 14-18, wherein the antibody or antigen binding fragment thereof is linked to a payload by a mutation-introduced cysteine, e.g., with or without a linker.
  20. The immunoconjugate of claim 19, wherein the linker comprises a functional group capable of reacting with a thiol group on a cysteine residue present on the antibody or antigen binding fragment thereof to form a covalent bond, e.g. a group selected from maleimide, iodoacetamide, bromoacetamide, vinylpyridine, disulfide, pyridyl disulfide, haloacetamide, a-haloacetyl, active esters such as succinimidyl ester, 4-nitrophenyl ester, pentafluorophenyl ester, tetrafluorophenyl ester, anhydride, acid chloride, sulfonyl chloride, isocyanate and isothiocyanate, preferably maleimide.

Description

Cysteine engineered antibodies and immunoconjugates The present invention relates to antibodies engineered with reactive cysteine residues, and more particularly, to antibodies having therapeutic or diagnostic applications. The invention also relates to immunoconjugates comprising said engineered antibodies. The invention further relates to a medicament or pharmaceutical composition comprising said antibody or immunoconjugate, and to a method and use of applying said antibody or immunoconjugate for the treatment of diseases such as tumors. Background Despite clinical success of therapeutic antibodies, naked antibodies targeting cell surface tumor antigens rarely alone provide adequate efficacy. To increase the low activity of antibodies, new strategies have focused on binding them to toxic molecules. Plant and bacterial toxins, as well as small chemotherapeutic molecules, can be good candidates because they are very effective and active in very small amounts. Therefore, coupling antibodies to other components, constituting new immunoconjugates such as Antibody Drug Conjugates (ADCs), has become a new development strategy for tumor therapy. Most of the current methods for ADC coupling are still random coupling, including cysteine coupling and lysine coupling, and the like, and this coupling mode can cause uneven distribution of ADC products, for example, an ADC with average DAR value of 4 of cysteine coupling can contain multiple components of DAR0-DAR8, and even though the components with the same DAR value still have the difference of coupling at different sites. While these components tend to have different properties, such as the DAR0 component will competitively bind to the target, the DAR8 component is more easily aggregated due to the greater amount of hydrophobic drug coupled and thus more easily cleared in vivo. The different pharmacodynamic and pharmacokinetic characteristics of these components, respectively, make PK/PD analysis of such a mixture of heterogeneous ADCs difficult and require a relatively high manufacturing process to produce a relatively stable batch of ADC products. In order to obtain a product homogeneous ADC, genentech in 2006 (WO 2006034488 A2) tried to mutate one site of the antibody to cysteine, enabling a uniform coupling of the drug to this mutation site. The antibodies screened in this patent have higher thiol reactivity of the introduced cysteine, and the cysteine mutation does not affect the binding capacity of the antibody to the antigen, and in addition, have stronger in vivo efficacy than randomly coupled ADCs. But this technique still has some limitations. With more and more researches in recent years, it is found that only 2 drugs are coupled to some diseases or targets, so that the expected drug effect can not be achieved far, and therefore, the technology of obtaining a uniform product with higher DAR is also important. The screening strategies for the presently disclosed engineered sites are relatively limited, and in order to screen for higher sites with thiol reactions, to obtain higher DAR ADCs, the selection of the existing sites is biased towards exposure to the antibody surface, with higher solvent accessibility. However, other negative effects of sites with higher solvent accessibility, such as ADC stability after drug conjugation, hydrophilicity, PK behaviour, in vivo efficacy, etc. are not considered. Thus, there remains a need in the art for new cysteine engineering techniques for antibodies, based on which antibodies can be obtained that, when constructing an ADC, result in an ADC that has greater stability and greater potency. Summary of The Invention The present invention relates to a modified antibody or antigen binding fragment thereof having a cysteine mutation at a more cryptic site of the constant region, thereby providing better stability and/or hydrophilicity to an immunoconjugate comprising the same. In one embodiment, the cysteine engineered antibodies of the invention, after mutation of one or both amino acids to cysteine on their light or heavy chains, result in two or four cysteine engineered antibody molecules due to the dimerization properties of IgG antibodies. Depending on the thiol group on the cysteine, nucleophilic reactions with toxin small molecules with maleimide linkers can occur, thus preparing site-specifically coupled ADC molecules at four cysteine-coupled toxin small molecules. The choice of mutation site is the key point in the invention, and the quality of the site directly determines the properties of the ADC. After the small molecule drug is connected to the site with higher accessibility of the solvent, the possibility of thiol exchange between the small molecule and protein in the blood plasma is increased due to the fact that the small molecule drug is in a relatively exposed environment, so that the reduced drug effect and toxic and side effects are caused. In addition, the smaller molecules that are more exposed als