The design, construction and function of a new chimeric anti-CD20 antibody

Multimerization is required for antigen binding activity of an engineered IgM/IgG chimeric antibody recognizing a skin-related antigen

Monoclonal antibodies offer great tools for research. We encountered a potentially useful mouse IgM monoclonal antibody whose antigen is expressed in normal skin but lost in human skin cancer. Because IgM is difficult to work with and the antigen was unknown, we decided to convert the IgM (µ) to IgG (γ) version. After cDNA for the antibody was obtained by RACE PCR, we made a series of molecules with different combinations of IgM and IgG domains. Whereas V_H-Cµ1-Cµ2-Cγ3 and V_H-Cµ1-Cµ2-Hinge-Cγ2-Cγ3 functionally bound to the antigen, V_H-Cγ1-Hinge-Cγ2-Cγ3, V_H-Cµ1-Hinge-Cγ2-Cγ3, and V_H-Cµ1-Cµ2-Cγ2-Cγ3 did not. Gel filtration analyses revealed that the functional molecules tend to form multimers and the multimeric forms retained antigen binding activity. Furthermore, the mutation of amino acid residue p.309Q > C of mouse IgG and addition of IgM tailpiece to the C-terminus of the molecules induced multimer formation, dramatically enhanced antibody functionality and all non-functional molecules became strongly functional. The functional molecules could be bound by protein A/protein G and other IgG specific reagents and therefore should be useful for further characterization of the antigen. Our study revealed that multimerization of converted IgM is functionally important for antigen binding activity of engineered IgM/IgG chimeric antibodies.

Successful construction and massive expression of a novel Anti-CD19 human-mouse chimeric antibody Hm2E8b

CD19 antigen is a major target for human B cell malignancies. Many studies have shown that the antibodies recognizing this antigen hold clinical therapeutic potential, while CD19 antibody of mouse origin requires genetic engineering to reduce the potential side effects of the antibody for their clinical use. There are many clones of CD19 antibodies available with different subclasses of immunoglobulin. IgM type antibody holds a high affinity and high complement activating capacities facilitating the targeting efficacy when it is used in targeting therapy. However, engineering the murine IgM antibody into a functional humanized antibody remains a challenge. The aim of this study was to construct a chimeric antibody composed of a CD19 specific murine IgM antibody 2E8 single-chain antibody fragment (scFv) and human IgG1 Fc region, which was named 2E8scFv-Fc or Hm2E8b. The function and the biological activities of this engineered antibody were characterized using a variety of approaches including cellular, immunological, flow cytometric, and molecular biological approaches. After switching from IgM- to IgG-like type antibody, Hm2E8b retained full antigen-binding activity to membrane CD19 antigen as its parental antibody 2E8, and the immune effector function analysis revealed that it could mediate complement-dependent cytotoxicity (CDC) to kill the target cells via IgG1 Fc domain. The yield of the engineered antibody Hm2E8b in the supernatant was 13.3 μg/mL expressed and secreted in the CHO cell system, which reached the secretory quantity of a regular mouse hybridoma cells. Our conclusion is that the IgM type of CD19 mouse antibody can be successfully engineered into an IgG1 type human-mouse chimeric antibody with similar affinity and biological activity. The yield of the Hm2E8b expression and secretion in CHO cell system was adequate to facilitate further development for therapeutic purpose.

Construction and expression of a human/mouse chimeric CD19 monoclonal antibody: Successful modification of a murine IgM to a chimeric IgG

CD19 is a specific surface marker of B cells. A murine IgM-subtype antibody, 2E8, was generated previously and assigned to the CD19 category by the 6th International Workshop and Conference on Human Leukocyte Differentiation Antigens in 1996. In the present study, the 2E8 Fv gene was inserted into a baculovirus shuttle vector and novel protein was expressed in an IgG1 form in the Sf9 insect cell line. VH_2E8 and VL_2E8 genes were cloned and inserted into the baculovirus shuttle vector pAc-κ-CH3 to form pAc-κ-CH3-VH_2E8-VL_2E8. Sf9 cells were then transfected with the reconstructed baculovirus shuttle vector. Novel protein expressed by the Sf9 cells was identified by immunofluorescence and western blot analysis, while activity levels were analyzed by flow cytometry (FCM). Sequencing demonstrated that the VH_2E8 and VL_2E8 fragments were inserted into pAc-κ-CH3 correctly. The immunofluorescence, western blot analysis and FCM results indicated that active recombinant antibody was expressed in the cytoplasm of Sf9 cells, but not in the culture supernatant. Thus, functional recombinant antibody was expressed successfully in the cytoplasm of Sf9 cells, but was not secreted into the culture supernatant. Therefore, the present study demonstrates that it is possible to modify mouse IgM to mouse-human chimeric IgG1 while retaining reasonable biological activity.

Prophylactic and therapeutic efficacy of a chimeric monoclonal antibody specific for H5 haemagglutinin against lethal H5N1 influenza

BACKGROUND

Recent outbreaks of highly pathogenic H5N1 viruses in humans indicate that no endogenous protection exists in the general population. Vaccination programmes against this new pathogen require synthesis of endogenous antibodies and cannot provide any immediate protection in the event of a pandemic. Passive immunization with humanized neutralizing monoclonal antibodies can prove to be promising in preventing a catastrophic pandemic.

METHODS

A murine monoclonal antibody (mAb) 3B1 of immunoglobulin M isotype was switched to a chimeric immunoglobulin G1. BALB/c mice were used to study the protective efficacy of the chimeric mAbs against a lethal H5N1 virus challenge with strains from clades 1 and 2.1. Kinetics of the viral load were determined during the course of the treatment.

RESULTS

The chimeric mAb, in passive administration, was able to protect 100% of the mice when challenged with H5N1 strains from clades 1 or 2.1. Prophylaxis at 1 day prior to challenge and treatment at 1 day after challenge with this mAb resulted in the clearance of the virus from the lungs of the infected mice within 6 days post-viral challenge.

CONCLUSIONS

Passive immunotherapy using chimeric mAb 3B1 can be an effective tool in both the prophylaxis and treatment of highly pathogenic H5N1 infection, providing the immediate immunity needed to contain a future influenza pandemic.