Immunopharmacology: Foundations and Cytokine Pharmacology

Correct Answer

A — Infliximab

Rationale

Infliximab is classified as a chimeric immunoglobulin G1 monoclonal antibody, meaning it contains both human and murine protein sequences — approximately 75% human and 25% murine. This chimeric structure makes it the most immunogenic of the tumor necrosis factor inhibitors. Adalimumab and golimumab are fully human immunoglobulin G1 monoclonal antibodies. Certolizumab pegol is a humanized polyethylene glycol-conjugated Fab fragment that lacks the Fc region entirely.

Correct Answer

C — Rituximab

Rationale

Rituximab is classified as an anti-CD20 monoclonal antibody that depletes B cells from the pre-B through memory B-cell stages. Basiliximab targets CD25, the interleukin-2 receptor alpha chain, and is used as transplant induction therapy. Belimumab targets B lymphocyte stimulator (BLyS/BAFF) and is approved for systemic lupus erythematosus. Anifrolumab targets the type I interferon receptor subunit 1 (IFNAR1) and is approved for systemic lupus erythematosus.

Correct Answer

B — Omalizumab

Rationale

Omalizumab is classified as a humanized anti-immunoglobulin E monoclonal antibody. It binds free immunoglobulin E in circulation, preventing it from binding high-affinity Fc epsilon receptors on mast cells and basophils. Mepolizumab is an anti-interleukin-5 monoclonal antibody. Dupilumab targets the interleukin-4 receptor alpha chain. Tezepelumab targets thymic stromal lymphopoietin, an upstream epithelial alarmin cytokine.

Correct Answer

D — Belimumab

Rationale

Belimumab is classified as a fully human monoclonal antibody targeting B lymphocyte stimulator, also called B-cell activating factor or BLyS/BAFF, a tumor necrosis factor superfamily cytokine critical for B-cell survival. Rituximab targets CD20 on B cells. Anifrolumab targets the type I interferon receptor subunit 1 (IFNAR1). Tocilizumab targets the interleukin-6 receptor alpha chain.

Correct Answer

C — Tezepelumab

Rationale

Tezepelumab is classified as a monoclonal antibody targeting thymic stromal lymphopoietin, an upstream epithelial alarmin cytokine released in response to airway irritants and allergens. Omalizumab targets immunoglobulin E. Benralizumab targets the interleukin-5 receptor alpha chain. Mepolizumab targets interleukin-5 itself.

Correct Answer

A — Benralizumab

Rationale

Benralizumab is classified as an anti-interleukin-5 receptor alpha chain monoclonal antibody. By binding the receptor rather than the cytokine, benralizumab also recruits natural killer cells to deplete eosinophils through antibody-dependent cellular cytotoxicity, producing near-complete blood eosinophil depletion. Mepolizumab and reslizumab both target interleukin-5 itself, not the receptor. Dupilumab targets the interleukin-4 receptor alpha chain and is not an eosinophil-specific agent.

Correct Answer

B — Plasma cells, which are the primary source of autoantibodies, do not express CD20 and are therefore not depleted by rituximab

Rationale

CD20 is expressed from the pre-B cell stage through memory B cells, but is downregulated as B cells undergo terminal differentiation into plasma cells. Because plasma cells are the primary long-lived autoantibody-secreting cells in systemic lupus erythematosus and other autoimmune diseases, rituximab-mediated depletion of CD20-positive cells leaves the plasma cell compartment intact. Long-lived plasma cells residing in bone marrow niches can continue producing autoantibodies for months to years after rituximab treatment. This limitation is the rationale for developing agents that target the plasma cell compartment or B-cell survival factors such as BLyS/BAFF.

Correct Answer

B — Infliximab

Rationale

Infliximab is the most immunogenic of the approved tumor necrosis factor inhibitors because it is a chimeric monoclonal antibody containing approximately 25% murine protein sequence. Patients can generate anti-drug antibodies against this foreign sequence, which reduce clinical efficacy and shorten duration of response. Co-prescribing methotrexate reduces anti-drug antibody formation and preserves therapeutic drug concentrations over time. Adalimumab, golimumab, and certolizumab pegol are fully human or humanized agents and are less immunogenic; methotrexate co-prescription is less obligatory with these agents, though it still improves response rates in rheumatoid arthritis through additive immunosuppression.

Correct Answer

A — Tocilizumab blocks the interleukin-6 receptor alpha chain, suppressing the interleukin-6-driven inflammatory cascade that causes cytokine release syndrome

Rationale

Cytokine release syndrome is driven predominantly by massive interleukin-6 production from activated macrophages recruited by chimeric antigen receptor T cells or bispecific antibodies. Interleukin-6 signals through the JAK1/2-STAT3 axis to produce fever, acute-phase protein synthesis, vasodilation, and vascular leak. Tocilizumab blocks the interleukin-6 receptor alpha chain, severing this signaling cascade and producing rapid reversal — often within hours — of fever, oxygen requirements, and hemodynamic instability. Intravenous tocilizumab is the standard treatment for grade 2 or higher cytokine release syndrome and is approved for this indication in patients aged 2 and older.

Correct Answer

C — Interleukin-17A normally drives neutrophil recruitment and antimicrobial peptide production at mucosal surfaces, and its blockade impairs antifungal mucosal immunity

Rationale

Interleukin-17A plays a critical physiological role in antifungal defense at epithelial surfaces. It stimulates epithelial cells to produce antimicrobial peptides such as defensins and S100 proteins, and drives neutrophil recruitment to mucosal sites where Candida colonizes. Patients with genetic deficiencies of interleukin-17A signaling develop chronic mucocutaneous candidiasis, which established the pathway's non-redundant role in fungal defense. Secukinumab and ixekizumab block interleukin-17A, removing this mucosal immune defense and producing an increased rate of oral, esophageal, and cutaneous candidiasis compared to placebo. The risk is generally manageable with antifungal therapy and does not usually require discontinuation of the biologic.

Correct Answer

C — Certolizumab pegol

Rationale

Certolizumab pegol is the preferred tumor necrosis factor inhibitor during pregnancy because it results in negligible fetal drug exposure. Unlike infliximab, adalimumab, and golimumab — which are full immunoglobulin G monoclonal antibodies that are actively transported across the placenta in increasing amounts through the second and third trimesters — certolizumab pegol does not undergo significant placental transfer. Studies have confirmed minimal or undetectable drug concentrations in cord blood and neonatal samples. Etanercept is also transported across the placenta to some degree. Certolizumab pegol is therefore the agent of choice when a tumor necrosis factor inhibitor is clinically necessary and minimizing fetal drug exposure is a priority.

Correct Answer

A — Herpes zoster reactivation; recombinant zoster vaccine recommended before initiation when feasible

Rationale

Anifrolumab blocks the type I interferon receptor and increases the risk of herpes zoster reactivation because type I interferons are a key component of the innate antiviral defenses that normally suppress varicella-zoster virus from reactivating in sensory ganglia. The recombinant zoster vaccine (Shingrix) is a non-live adjuvanted subunit vaccine and is recommended before initiating anifrolumab when feasible; it may also be given during therapy. Invasive aspergillosis, progressive multifocal leukoencephalopathy, and mandatory tuberculosis prophylaxis are not established class risks of anifrolumab. Tuberculosis reactivation and mandatory pre-treatment screening are associated with tumor necrosis factor inhibitors; progressive multifocal leukoencephalopathy risk is associated with rituximab and natalizumab.

Correct Answer

A — Tumor necrosis factor-alpha is required to maintain granuloma integrity, and its inhibition allows latent Mycobacterium tuberculosis to escape granulomatous containment

Rationale

Tumor necrosis factor-alpha is an essential cytokine for both the formation and maintenance of the granulomas that contain Mycobacterium tuberculosis in latent infection. It activates macrophages, promotes macrophage-T-cell interactions within the granuloma, and sustains the structural integrity that prevents bacterial escape. When tumor necrosis factor inhibitors are administered, this containment fails, and latent tuberculosis reactivates — often as extrapulmonary or disseminated disease, reflecting hematogenous spread unchecked by granulomatous defense. Mandatory pre-treatment screening with tuberculin skin test or interferon-gamma release assay, and at least four weeks of isoniazid prophylaxis before biologic initiation when latent tuberculosis is confirmed, are the standards of care for this reason.

Correct Answer

C — Rituximab-induced B-cell depletion impairs immune surveillance of latent JC virus, allowing it to reactivate and infect oligodendrocytes

Rationale

JC virus (John Cunningham virus) is a polyomavirus that establishes latent infection in most adults without causing disease. In severely immunosuppressed patients, impaired immune surveillance allows JC virus to reactivate, travel to the central nervous system, and infect oligodendrocytes, causing the progressive demyelinating brain disease known as progressive multifocal leukoencephalopathy. Rituximab's B-cell depletion indirectly impairs overall immune surveillance, and cumulative immunosuppression from concurrent or prior immunosuppressive therapy compounds the risk. Monitoring of JC virus antibody titers is recommended in long-term rituximab users, particularly those with additional immunosuppressive exposures, to stratify risk.

Correct Answer

C — Omalizumab binds free immunoglobulin E in the circulation, preventing it from loading onto mast cells and basophils and thereby blunting allergen-triggered release of bronchoconstricting mediators

Rationale

Omalizumab is a humanized monoclonal antibody that binds the constant region of free immunoglobulin E in the circulation, preventing it from binding the high-affinity Fc epsilon receptor I on mast cells and basophils. With fewer immunoglobulin E molecules loaded onto these effector cells, allergen cross-linking triggers a substantially reduced release of histamine, leukotrienes, and prostaglandins — the mediators responsible for bronchoconstriction, mucus secretion, and early-phase allergic symptoms. Over time, receptor downregulation on mast cells further reduces allergic responsiveness. Omalizumab is approved for moderate-to-severe allergic asthma with elevated immunoglobulin E and confirmed allergen sensitization inadequately controlled by inhaled corticosteroids. Depleting eosinophils via the interleukin-5 receptor is the mechanism of benralizumab. Blocking thymic stromal lymphopoietin is the mechanism of tezepelumab. Blocking the interleukin-4 receptor alpha chain is the mechanism of dupilumab.

Correct Answer

D — Belimumab neutralizes B lymphocyte stimulator, depriving autoreactive B cells of the survival signal they require to persist and differentiate into antibody-secreting cells

Rationale

B lymphocyte stimulator, also known as B-cell activating factor or BLyS/BAFF, is a tumor necrosis factor superfamily cytokine that provides a critical survival signal for B cells, promoting their persistence and differentiation into antibody-secreting plasma cells. Autoreactive B cells in systemic lupus erythematosus are particularly dependent on elevated B lymphocyte stimulator levels. Belimumab is a fully human monoclonal antibody that neutralizes soluble B lymphocyte stimulator, thereby withdrawing this survival signal and allowing autoreactive B cells to undergo apoptosis. This reduces the pool of cells available to differentiate into autoantibody-secreting plasma cells, lowering anti-double-stranded deoxyribonucleic acid titers and reducing flare frequency over several months. Belimumab does not bind CD20 or directly deplete B cells — that is the mechanism of rituximab. It does not block the interleukin-6 receptor or the type I interferon receptor.

Correct Answer

C — Live attenuated varicella-zoster vaccine (Zostavax), because live vaccines are contraindicated in immunosuppressed patients and may cause disseminated infection

Rationale

Live attenuated vaccines are contraindicated once any biologic immunosuppressant is initiated, because impaired immune surveillance may allow the vaccine-strain organism to cause disseminated infection. Live vaccines that must be completed before biologic initiation include the live attenuated varicella-zoster vaccine (Zostavax), live attenuated intranasal influenza vaccine, yellow fever vaccine, oral typhoid vaccine, and measles-mumps-rubella vaccine. The recombinant zoster vaccine (Shingrix), by contrast, is a non-live adjuvanted subunit vaccine; it is safe to administer during biologic therapy and does not need to be completed before initiation — though pre-treatment administration produces a stronger immune response. Inactivated influenza and pneumococcal vaccines may also be given during biologic therapy.

Correct Answer

A — Interleukin-17A inhibitors are contraindicated in active inflammatory bowel disease because interleukin-17A contributes to mucosal barrier integrity, and its blockade can precipitate new-onset or worsen existing inflammatory bowel disease

Rationale

Interleukin-17A plays a physiological role in maintaining mucosal barrier defense in the gastrointestinal tract by promoting epithelial integrity and driving antimicrobial peptide production at mucosal surfaces. Secukinumab and ixekizumab, which block interleukin-17A, carry a class-specific risk of new-onset or worsening inflammatory bowel disease and are contraindicated in patients with active Crohn's disease or ulcerative colitis. For this patient who requires biologic therapy for psoriasis and has Crohn's disease, appropriate alternatives include tumor necrosis factor inhibitors such as adalimumab or infliximab — which are approved for both conditions — or ustekinumab, which targets the interleukin-12/23 p40 subunit and is approved for both psoriasis and Crohn's disease. Interleukin-23 p19 inhibitors are also approved for psoriasis and do not carry the inflammatory bowel disease contraindication of interleukin-17A inhibitors.