Immunogenicity Review Exam 3 PDF

WHAT IS IMMUNOGENICITY? FDA Definition: Host immune response against a therapeutic protein  Typically studied in the context of the formation of Anti-Drug Antibodies (ADA)  All biotherapeutics include a section on immunogenicity in their FDA-approved label (Section 6.2)  This is w...

WHAT IS IMMUNOGENICITY? FDA Definition: Host immune response against a therapeutic protein  Typically studied in the context of the formation of Anti-Drug Antibodies (ADA)  All biotherapeutics include a section on immunogenicity in their FDA-approved label (Section 6.2)  This is within the Adverse Reactions section of the label  TYPES OF ANTI-DRUG ANTIBODIES Know the two main classes of ADA: 1. Binding: Interacts with the drug molecule but does not inhibit its binding to the pharmacologic target a) May impact pharmacokinetics b) May impact safety 2. Neutralizing: Directly blocks interaction of drug with its pharmacologic target a) Loss of efficacy b) May impact pharmacokinetics c) May impact safety GR Gunn, DCF Sealey et al. Clin Exp Immunol. 184(2);137-146 (2016).  ‘CLEARING’ ADA  Both binding and neutralizing ADA can be categorized as ‘clearing’  ‘Clearing’ ADA are detected based on their effects on pharmacokinetics  Non-clearing ADA are also referred to as ‘sustaining’ ADA  Typical expectations:  Rapid decrease in plasma drug concentrations upon ADA development  Decreased plasma concentrations following multiple dosing (typical expectation is accumulation on L Liu. Protein Cell. 9;15-32 (2018).  PHYSIOLOGIC DRIVERS OF Immunogenicity is largely thought to be a T-cell dependent IMMUNOGENICITY phenomenon  The context of presentation to T- cells is likely a driver of ultimate response  Presentation to Thelper cells leads to ADA generation  Presentation to Treg cells limits ADA generation  Amino acid sequences in proteins known as ‘T cell epitopes’ and ‘Tregitopes’ are thought to drive whether an immunogenic response occurs V Jawa, F Terry et al. Front Immunol. 11;1301 (2020).  ‘HUMAN-NESS’ DRIVES Increasing the human content of the primary (amino acid) sequence decreases IMMUNOGENICITY immunogenicity  Non-human IgG sequences are more readily recognized as ‘non- self’ by the immune system  All mAbs being developed now are either humanized or fully human  mAbs with mouse Fc are eliminated more rapidly and need more frequent dosing  Dosing frequency seems to correlate with immunogenicity as well M Sauerborn. Handbook of Therapeutic Antibodies, 2e. (2014).  ROUTE OF ADMINISTRATION IMPACTS Subcutaneous and intramuscular injections are often more immunogenic than IMMUNOGENICITY intravenous dosing.  Injection into these spaces puts the drug near antigen- presenting cells, namely dendritic cells  Proteins must travel through lymph nodes to reach the systemic circulation following SC/IM dosing  Injections may lead to local inflammation, which further primes the immune system for response N Jarvi, SV Balu-Iyer. BioDrugs. 35(2):125-146 (2021). Mirikizumab as Induction and Maintenance Therapy for Ulcerative Colitis Introduction  Drug name: Mirikizumab-mrkz  Brand name: OMVOH  Developed by: Eli Lilly and Company  Initial U.S. Approval: October 2023  M.O.A: Mirikizumab is humanized immunoglobulin G4 (IgG4) monclonal antibody, an interleukin-23 antagonist  Indications: for treatment of moderately to severely active ulcerative colitis in adults  Available doses:  Intravenous Infusion- Injection: 300 mg/15 mL (20 mg/mL) solution in a single-dose vial  Subcutaneous Injection- Injection: 100 mg/mL solution in a single-dose prefilled pen Omvoh - accessdata.fda.gov 7 Hammerhøj, Alexander, et al. "Mirikizumab (Omvoh™) for ulcerative colitis." Trends in Pharmacological Sciences (2024).  Causes of Ulcerative Colitis Porter, Ross J., Rahul Kalla, and Gwo-Tzer Ho. "Ulcerative colitis: Recent advances in the understanding of disease pathogenesis." F1000Research 9 8 (2020).  Pathogenesis of Ulcerative Colitis Ordás I, et al. Ulcerative colitis. Lancet. 2012 Nov 3;380(9853):1606-19 9  Mirikizumab- Mechanism of Action  IL-23 is produced by APCs in intestinal mucosa and is involved in the amplification of inflammatory cascade in ulcerative colitis  IL-23 continually stimulates Th17 cell activation and cytokine production  Mirikizumab (LY3074828) is a humanized immunoglobulin G4 (IgG4) binds to p19 subunit of the interleukin-23 (IL-23) cytokine, and inhibits the interaction between IL-23 and its receptor  Blocks the release of pro-inflammatory cytokines and chemokines  This reduces the activity of Th17 cells and improves clinical outcomes Steere, Boyd, et al. "Generation and characterization of mirikizumab, a humanized monoclonal antibody targeting the p19 subunit of IL- 10 23." Journal of Pharmacology and Experimental Therapeutics 387.2 (2023): 180-187.  Clinical Trial Outcomes  Trial Phase: phase 3, randomized, double-blind, placebo-controlled  Trail design  Induction phase: 1281 adults with moderately to severely active ulcerative colitis, a 3:1 ratio to receive mirikizumab (300 mg) or placebo, administered intravenously, every 4 weeks for 12 weeks.  Maintenance phase: 544 patients who responded to mirikizumab in induction trial, a 2:1 ratio to receive mirikizumab (200 mg) or placebo, administered subcutaneously, every 4 weeks for 40 weeks  The primary end points: clinical remission  Major secondary end points: clinical response, endoscopic remission, and improvement in bowel-movement urgency D’Haens, Geert, et al. "Mirikizumab as induction and maintenance therapy for ulcerative colitis." New England Journal of Medicine 388.26 (2023): 11 2444-2455.  Adverse Drug Reactions  Adverse drug reactions(≥2%) are:  Induction: upper respiratory tract infections and arthralgia  Maintenance: upper respiratory tract infections, injection site reactions, arthralgia, rash, headache, and herpes viral infection https://omvoh.lilly.com/hcp/safety-profile 12 Effector Functions of Antibodies 13 Humoral Immunity  The main functions of antibodies are to neutralize and eliminate infectious microbes and microbial toxins  Antibodies are produced by plasma cells in peripheral (secondary) lymphoid organs, inflamed tissues, and bone marrow, and antibodies perform their effector functions at sites distant from their production.  Many of the effector functions of antibodies are mediated by Fc regions of immunoglobulin (Ig) molecules, and different Ig heavy chain isotypes serve distinct effector functions.  The effector functions of antibodies that are mediated by the Fc regions are triggered by the binding of antigens to the variable regions. 14 Vaccine-Induced Humoral Immunity 15 Functions of Antibody Isotypes 16 Neutralization of microbes and toxins by antibodies 17 Subunit composition of Fcγ receptors 18 Fc receptors 19 Antibody-mediated opsonization and phagocytosis of microbes 20 Antibody-dependent cell-mediated cytotoxicity 21 Summary  Humoral immunity is mediated by antibodies and is the effector arm of the adaptive immune system responsible for defense against extracellular microbes and microbial toxins.  The antibodies that provide protection against infection may be produced by long-lived antibody-secreting cells generated by the first exposure to microbial antigen or by reactivation of memory B cells by the antigen.  Antibodies block, or neutralize, the infectivity of microbes by binding to the microbes and sterically hindering interactions of the microbes with cellular receptors. Antibodies similarly block the pathologic actions of toxins by preventing binding of the toxins to host cells.  Antibody-coated (opsonized) particles are phagocytosed by binding of the Fc portions of the antibodies to phagocyte Fc receptors. There are several types of Fc receptors specific for different subclasses of IgG and for IgA and IgE antibodies, and different Fc receptors bind the antibodies with varying affinities. Attachment of antigen-complexed Ig to phagocyte Fc receptors also delivers signals that stimulate the microbicidal activities of phagocytes. 22 Complement Activation 23 The classical pathway of complement activation 24 The alternative pathway of complement activation. 25 The alternative pathway of complement activation. 26 Complement Activation Regulatory Mechanisms 27  Complement Activation Regulatory Mechanisms Complement activation needs to be regulated because:  Low-level complement activation goes on spontaneously, and if such activation is allowed to proceed, the result can be damage to normal cells and tissues.  Even when complement is activated where needed, such as on microbial cells or antigen-antibody complexes, it needs to be controlled because degradation products of complement proteins can diffuse to adjacent cells and injure them.  Different regulatory mechanisms include:  Inhibition of the formation of C3 convertases in the early steps of complement activation.  Break down and inactivate C3 and C5 convertases.  Inhibition of the formation of the MAC in the late steps of the complement pathway. 28 Molecules and Receptors That Inhibit Complement Activation 29 Functions of complement 30 Complement Deficiencies Paroxysmal nocturnal hemoglobulinuria (PNH) Individuals with PNH are missing both DAF and CD59 and have increased sensitivity to complement lysis. This results in intravascular red cell hemolysis and hematoglobinuria (loss of iron) that is characteristic of the disease. The absence of CD59 on platelets also contributes to recurrent thrombosis that is often fatal in individuals with PNH. PNH Treatment:  Transfusion of packed red blood cells can replace lost cells.  Androgens and recombinant erythropoietin are commonly used to accelerate erythropoiesis.  Thrombotic complications are reduced by standard therapy, including heparin and maintenance doses of common anticoagulants.  Iron loss is corrected by the administration of supplemental iron.  To reduce complement activation, eculizumab can be used to block the activation of C5 and the generation of the MAC. 31 Complement Deficiencies Hereditary angioneurotic edema (HANE) is caused Hereditary Angioedema by C1 INH deficiency. Inherited (normal levels of nonfunctional C1 INH) and acquired (low serum levels of C1 INH) forms of HANE exist. During a clinical episode, well-circumscribed edema is localized to the face, tongue, and larynx. HANE Treatment:  Oral androgens, anabolic steroids, and antifibrinolytic agents are commonly used to treat HANE.  In cases of acquired C1 INH deficiency, glucocorticosteroids are effective as an The clinical appearance of hereditary angioedema, showing emergency treatment and are usually tapered off the local transient swelling that affects mucous membranes when the patient begins taking androgens. Other Complement Deficiencies  A defect in C2 synthesis is the most commonly identified deficiency and increases the risk for neisserial infections.  Individuals with a C3 deficiency usually have recurrent infections of the respiratory tract, gut, and skin.  Life-threatening meningitis is associated with defects in properdin, factor H, factor I, and the complement MAC. meningococcal vaccination is indicated to create high levels of protective antibodies. 32 Summary  The complement system consists of serum and membrane proteins that interact in a highly regulated manner to produce biologically active products.  The three major pathways of complement activation. All pathways converge on a common pathway that involves the formation of a membrane pore after the proteolytic cleavage of C5.  the alternative pathway, which is activated on microbial surfaces in the absence of antibody; the classical pathway, which is activated by antigen-antibody complexes;  and the lectin pathway, which is initiated by circulating lectins binding to carbohydrates on pathogens.  The biologic functions of the complement system include:  opsonization of organisms and immune complexes by proteolytic fragments of C3, followed by binding to phagocyte receptors for complement fragments and phagocytic clearance,  Activation of inflammatory cells by proteolytic fragments of complement proteins called anaphylatoxins (C3a, C4a, C5a),  Cytolysis mediated by MAC formation on cell surfaces,  Solubilization and clearance of immune complexes, and enhancement of humoral immune responses.  Complement components play critical roles in the immobilization of microbes, opsonization, chemotaxis, and B cell activation. Complement activation is regulated by various plasma and cell membrane proteins that inhibit different steps in the cascades.  Hereditary angioneurotic edema is caused by failure to regulate complement activation.  Paroxysmal nocturnal hemoglobulinuria (PNH) is caused by lack of membrane-bound complement inhibitors.  Complement deficiencies in C2, alternative pathway components, or the membrane attack complex (MAC) increase the risk of life-threatening neisserial infections. 33 The Primary Immunodeficiency Disorders Shields AM, Patel SY. 2017 34 The Primary Immunodeficiency Disorders 35 The Primary Immunodeficiency Disorders Shields AM, Patel SY. 2017 36 The Primary Immunodeficiency Disorders Shields AM, Patel SY. 2017 37 Specialized Immunity at Epithelial Barriers and in Immune Privileged Tissues 38  The Gastrointestinal Immune System  Intestinal epithelial cells lining the small and large bowel are an integral part of the gastrointestinal innate immune system, involved in responses to pathogens and antigen sampling for delivery to the adaptive immune system in the gut.  The gastrointestinal system, like other mucosal tissues, is composed of a tube-like structure lined by a continuous epithelial cell layer sitting on a basement membrane that serves as a physical barrier to the external environment.  Underlying the epithelium is a layer of loose connective tissue called the lamina propria that contains blood vessels, lymphatic vessels, and MALTs. 39 M cells in the small intestine  M cells are located in regions of the gut epithelium called follicle-associated (or dome) epithelium that overlie the domes of Peyer’s patches and other GALT structures.  Antigen may be delivered from the lumen to the GALT through specialized cells within the gut epithelium called M cells.  Although M cells and the more numerous absorptive epithelial cells likely arise from a common epithelial precursor, the M cells are distinguishable by a thin glycocalyx, relatively short, irregular microvilli (referred to as microfolds), and large fenestrations in their membranes, all features that enhance the uptake of antigens from the gut lumen. 40  Homing Properties of Intestinal Lymphocytes  The gut-homing properties of effector lymphocytes are imprinted in the lymphoid tissues, where they have undergone differentiation by naive precursors.  Dendritic cells in gut-associated lymphoid tissues (GALT), are induced by cytokines.  When naive B or T cells are activated by antigen in GALT, they are exposed to retinoic acid produced by the dendritic cells, and this induces the expression of the chemokine receptor CCR9 and the integrin α4β7 on the plasmablasts and effector T cells that arise from the naive lymphocytes.  The effector lymphocytes enter the circulation and home back into the gut lamina propria. 41  IgA class switching in the gut  Immunoglobulin A (IgA) class switching in the gut occurs by both T-dependent and T-independent mechanisms.  In T-dependent IgA class switching, dendritic cells in the subepithelial dome of Peyer’s patches capture bacterial antigens delivered by microfold (M) cells and migrate to the interfollicular zone, where they present antigen to naive CD4+ T cells.  The activated T cells differentiate into helper T cells with a T follicular helper phenotype and engage in cognate interactions with antigen-presenting IgM+ B cells that have also taken up and processed the bacterial antigen. APRIL, A proliferation-inducing ligand; BAFF, B cell–activating factor; PAMP, pathogen-associated molecular pattern. 42 Transport of IgA across epithelial cells  IgA is produced by plasma cells in the lamina propria of mucosal tissue and binds to the poly-Ig receptor at the base of an epithelial cell.  The complex is transported across the epithelial cell, and the bound IgA is released into the lumen by proteolytic cleavage.  The process of transport across the cell, from the basolateral to the luminal surface in this case, is called transcytosis. 43 Transport of IgA across epithelial cells  The abundance of immunoglobulin A (IgA)- producing plasma cells (green) in colon mucosa compared with IgG-secreting cells (red) is shown by immunofluorescence staining.  IgA that is being transcytosed by the crypt epithelial cells is visualized in their cytoplasm (green fluorescent stain). 44 Antigen sampling by intestinal dendritic cells  DCs and macrophages are abundant in the gastrointestinal immune system and can participate in stimulating protective effector T cell responses or inducing regulatory T cell responses that suppress immunity to ingested antigens and commensal organisms.  DCs in the lamina propria take up and process protein antigens from microbes that are in the lumen or have breached the epithelial barrier and transport these antigens via lymphatics to mesenteric lymph nodes 45  Effector and regulatory T cells in the intestinal mucosa  In the gastrointestinal tract, different subsets of effector CD4+ T cells are induced by and protect against different microbial species.  Th17 effector T cells and regulatory T cells are abundant in the intestinal mucosa. Bacterial antigen– specific Th17 cells differentiate from naive CD4+ T cells in gut-associated lymphoid tissues in response to antigens presented by dendritic cells (DCs) and cytokines they secrete, including interleukin-6 (IL-6) and IL-23.  Differentiation of bacterial antigen–specific regulatory T cells (Tregs) is promoted by transforming growth factor-β (TGF-β) and retinoic acid produced by intestinal epithelial cells. Thymic Tregs that migrate to the intestine expand in number under the influence of bacterial metabolites. Regulatory T cells require antigen presentation by DCs; the nature of these antigens is unknown. 46 The Cutaneous Immune System  The epidermis provides a physical barrier to microbial invasion. The epidermis consists of multiple layers of stratified squamous epithelium, made up almost entirely of specialized epithelial cells called keratinocytes.  In addition to forming a physical barrier, keratinocytes actively respond to pathogens and injury by producing antimicrobial peptides, which kill microbes, and various cytokines, which promote and regulate immune responses. 47 The Cutaneous Immune System  The skin-homing properties of effector lymphocytes are imprinted in skin-draining lymph nodes, where they have undergone differentiation from naive precursors.  Ultraviolet rays in sunlight (UVB) stimulate production of vitamin D, which induces expression of CCR10; interleukin-12 (IL-12) induces expression of the E-selectin ligand CLA; and other signals induce CCR4, CCR8, and CCR10 expression.  These homing molecules direct migration of the effector T cells into the skin. CLA, Cutaneous lymphocyte antigen. 48 Immune-Privileged Tissues  Immune responses and associated inflammation in certain parts of the body, including brain, eye, testes, placenta, and fetus, carry a high risk for lethal organ dysfunction or reproductive failure.  These tissues, which have evolved to be protected, to a variable degree, from immune responses, are called immune-privileged sites 49 Immune-Privileged Tissues Testis  Immune privilege in the testis serves to limit inflammation that may impair male fertility.  Many self antigens in the adult testis are first expressed at the time of puberty, well after the development of a competent immune system, so it is unlikely that lymphocytes specific for these antigens are deleted during development.  Therefore, immune privilege in the testis may also serve to prevent autoimmunity. 50  Immune-Privileged Tissues  The fetus expresses paternally inherited genes that are foreign to the mother, but fetuses are not normally rejected by the mother.  The mother is exposed to fetal antigens during pregnancy because maternal antibodies against paternal major histocompatibility complex (MHC) molecules are easily detectable.  Many different special molecular and barrier features of the placenta and local immunosuppression may contribute. 51