06/15/22 12:42 1 Monoclonal Antibodies - Antibodies (Abs). Also known as immunoglobulins (Ig). - Comprised of 2 heavy chains and 2 light chains - Monoclonal Abs bind specifically to a single site (epitope) on a particular antigen - Abs are produced by B lymphocytes - Because of their specificity and ease of generation, they are extensively used as therapeutics (“passive immunotherapy”) and as diagnostic and research tools -They can be generated in large (unlimited) amounts in vitro
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04/12/23 07:02 1
Monoclonal Antibodies
- Antibodies (Abs). Also known as immunoglobulins (Ig).
- Comprised of 2 heavy chains and 2 light chains
- Monoclonal Abs bind specifically to a single site (epitope) on a particular antigen
- Abs are produced by B lymphocytes
- Because of their specificity and ease of generation, they are extensively used as therapeutics (“passive immunotherapy”) and as diagnostic and research tools
-They can be generated in large (unlimited) amounts in vitro
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B cells develop in the bone marrow hematopoietic stem cells and lymphoid stem cells T-cells and B-cells
progenitor = pro-B cell (B220+)
precursor = pre-B cells: heavy-chain rearranged
immature B cell: IgM + light-chain rearranged
mature B cell: IgM + IgD + an antigen encounter in spleen or lymph nodes; goes to periphery
Opsonization: Direct uptake of bacteria coated with antibody molecules
Complement activation: Activated complement proteins lyse cells by making holes in their mebranes(e.g. bacteria)
Antibody-dependent cell-mediated cytotoxicity (ADCC):Killer T-cells use antibodies on their surface to target cells with an antigen and kill them.
Transcytosis:Antibody-antigen complexes are taken up (endocytosed) on on side of an epithelial cell and directed to theother side, where they are exocytosed
Fc functions
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Multigene organization of Ig genes
–light chains: V, J (variable) and C (constant)–heavy chain: V, D, J, (variable) C (constant)
Mechanism of Ab gene rearrangement
Recombination signal sequences (RSS)–flank V, D, J gene segments
–V-RSS------RSS-D-RSS---------RSS-J
11IgGkappa gene rearrangement
SPLICING
SPLICING
+ SOMATIC HYPERMUATION
+ SOMATIC HYPERMUATION
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Antibodies can participate in host defense in three main ways
Other protein-binding proteins: natural receptors in soluble form
Analogous to MAbs and make use of the Fc portion of the antibody molecule:
Example: Enbrel (etanercept):Anti-rheumatoid arthritis drug Soluble TNF receptor fused to the Fc IgG1 domain (TNF= tumor necrosis factor)
Ties up TNF, blocking its inflammatory functionFc domain dimerizes the receptor, which increases its affinity for TNF.Fc domain increases the half-life of the protein in the bloodstreamAmgen + Wyeth
Still experimental: anti HIV drug PRO 542 Soluble CD4 (HIV receptor) fused to IgG2.
Tetrameric (4 V-regions replaced)Reduced Fc function (since IgG2 < IgG1), Better half-lifeProgenics
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Single chain antibodies (scFv)
Ag binding site
15 AA linker
Phage display selection of scFvSource of sequence:PCR from genome or mRNA, add randomization