by Claire Baldock © Boult Wade Tennant 2011 Therapeutic Antibodies – Technical Introduction AIPPI Forum Hyderabad Pharma Workshop Oct 2011

What is an antibody? Produced by B-Lymphocytes Immunoglobulin family Bind antigen; in particular, specific sequences or structures within the antigen termed epitopes 5 major classes: IgG, IgM, IgA, IgE and IgD

Structure of an antibody – (1) An archetypal IgG antibody has 2 heavy chains and 2 light chains, linked by disulphide bonds Each heavy chain consists of 4 immunoglobulin (Ig) domains; each light chain consists of two Ig domains Each heavy and each light chain have constant (C; Blue) and variable (V; Red) domains Ig domain Adapted from Janeway 4 th edition

Structure of an antibody – (2) The variable domains of each Ab chain (V H and V L ) combine to create the site of antigen recognition Each variable domain can be divided into 3 hypervariable (HV) regions situated on the outer surface of each variable region The HV regions of V H and V L combine in 3 areas termed complementarity- determining regions (CDRs) to determine antigen specificity VHVH VLVL HV region

Fab and Fc fragments Antibody structure is often also divided into the antigen-binding and crystallisable fragments, or Fab and Fc respectively Fab or F(ab) 2 consist of the V H and V L regions from one or both arms of the antibody respectively, along with the corresponding C H and C L regions. Fabs are able to bind antigen The Fc fragment consists only of the 2 nd and 3 rd C H domains and is recognised by effector molecules and cells carrying an Fc receptor (FcR) FabF(ab) 2 Fc Adapted from Janeway 4 th edition

Monoclonal antibodies Antibodies produced from a single B-cell clone following immunisation with a target antigen All antibodies specific to the same epitope on the target antigen Much work on and production of monoclonals has been performed using mice, whether by inducing ascites or making hybridomas

Chimeric, humanised and “fully human” monoclonals Murine antibodies often suffer from immune rejection Chimeric antibodies consisting of human constant domains and murine variable domains fare better but unwanted immunogenicity is still a problem Humanised monoclonals, where only the CDRs are of murine origin, demonstrate a further reduction in immunogenicity Murine Chimeric Humanised

“Fully human” monoclonals In recent years so-called “fully human” antibodies have been developed Technologies such as MedImmune’s phage display library or Amgen’s transgenic XenoMouse, carrying most of the human antibody genes, allow production of monoclonals containing only human sequences In theory such technologies are able to generate antibodies with high specificity, optimal affinity and with the desired effector functions, but without any of the unwanted immunogenicity of chimeric or humanised monoclonals

Monoclonal product development Herceptin – Genentech anti-HER-2/Neu antibody for use in cancer treatment 1987Parent mouse anti-HER-2 antibody developed by Genentech 1990 Parent mouse HER-2 antibody humanised to generate Herceptin 1998 Phase III clinical trial completed and FDA approval received 2000EC approval received 2008$1.8 billion worth of sales of Herceptin Total R&D costs for the same year were $2.8 billion Other Genentech monoclonals include Avastin and Rituxan, each with higher $ sales than Herceptin

by Claire Baldock © Boult Wade Tennant 2011 Therapeutic Antibodies – Technical Introduction AIPPI Forum Hyderabad Pharma Workshop October 2011