Antibodies as therapeutics

• Technologies available to produce antibodies

  Mouse, chimeric, humanized, and fully human antibodies
• Oncology is the primary therapeutic area for antibodies, but immune-mediated disorders and others have also been successfully targeted
• Antibody structure: Specificity is determined by one part of the antibody, while non-specific binding is determined by another part
• Function of therapeutic antibodies

  1. Antagonise ligand or receptor

  2. Agonist at receptor

  3. CDC - complement-dependent toxicity - formation of MAC on cell surface

  4. ADCC - Antibody-dependent cellular toxicity - recruitment of T cells to promote cell lysis

  5. ADCP - Antibody-dependent cellular phagocytosis - binds to target and Fc portion binds to Fcγ receptors on phagocytes
• Limitations of mouse monoclonal antibodies: Short serum half-life and limited ability to produce ADCC response
• Example of mouse monoclonal antibody: Muromonab - CD3 (T cell receptor) - leading to apoptosis - treatment of organ transplant rejection
• Example of chimeric antibody: Abciximab - GPIIb/IIIa inhibitor - found on platelets - required for clot formation
• Issues with integrating mouse IgG and human IgG

  • Inappropriate human framework
  • Inaccurate identification of CDR
  • Low homology between Mouse IgG and human IgG
• Choice of human framework

  • Important as adjacent residues affect conformation of antigen binding site (include Vernier zone residues)
• Alternative approaches for integrating specificity determining regions (SDR)

  Grafting critical residues for antigen-Ab binding (potential to reduce anti-idiotypic response)
• Anti-idiotype Ab binds to antibody drug and possesses specificity for unique V region, leading to loss of efficacy
• Idiotope

  The region of an antibody that binds to the paratope of another antibody
• Fully Human antibodies production methods

  1. Phage display

  2. Transgenic mouse
• Safety concerns of monoclonal antibodies include immune reactions, serum sickness, immune complex formation, tumour lysis syndrome, cytokine release syndrome
• Anti-TNF therapies


  Used for various diseases like RA, Psoriasis, Crohns, with different drugs targeting TNF in different ways
• Drugs with the same target may not be licensed for the same disease due to different mechanisms of action or safety profiles
• Forms of TNF and receptors

  • Soluble TNF
  • Transmembrane TNF
  • TNFR1
  • TNFR2
• Incidence of infection and mAbs can be correlated
• Incidence of infection and mAbs

  Correspond to reactivation of latent TB
• TmTNF required for granuloma formation
• Bispecific antibodies bind to 2 different antigens
• Bispecific antibodies

  • Catumaxomab
  • Blinatumomab
• Catumaxomab


  • Described as trifunctional as Fc region can also bind to Fc receptors
• Catumaxomab is designed to recruit immune cells to pathogenic cells
• Blinatumomab is approximately 1/3 the size of IgG Ab and lacks Fc portion with a short linker sequence
• Antibody drug conjugates have specific antigen requirements
• Linkers for ADCs can be cleavable or non-cleavable
• Linkers

  • Lysosomal protease-sensitive linkers (peptide linkers)
  • β-glucuronide linkers
  • Chemically cleavable linkers
  • Non-cleavable linkers
• Cytotoxic drugs in ADCs must be stable in systemic circulation, potent, have low immunogenicity, low MW, long half-life, suitable aqueous solubility, and not interfere with mAb internalization
• Cytotoxic drugs in ADCs inhibit tubulin polymerization, leading to cell cycle arrest/apoptosis and DNA replication inhibition
• Bystander killing

  1. Free drug diffuses out of target cell and diffuses into neighbouring ‘bystander’ cells

  2. Surrounding tumor cells or TAMs release extracellular enzymes to generate diffusible drug from the ADC

  3. ADC bound target tumor phagocytosed through FC mediated phagocytosis – as cell degrades diffusible drug is released
• Antibodies as therapeutics have seen a dramatic rise in usage over the last few years, particularly in oncology and immune-mediated diseases
• Majority of antibodies on the market are humanized or fully human to improve safety/efficacy profile
• Antibodies targeting inflammation/immune pathways may have potential side effects of infection
• Antibodies used in cancer have cytotoxic drugs attached via linkers for delivery of payload resulting in cancer cell toxicity