Tumor necrosis factor-alpha (TNF-alpha) inhibitors were the first biologic drugs approved for inflammatory diseases and remain among the most widely prescribed biologics globally. Five agents are in clinical use, spanning three structural classes that differ in antigen specificity, placental transfer, and granulomatous disease efficacy. Understanding these structural distinctions is essential for individualized prescribing and for anticipating differential toxicity across indications.
TNF Biology and Pharmacological Rationale. TNF-alpha is a pleiotropic pro-inflammatory cytokine produced primarily by macrophages and T cells in response to infection, tissue damage, and immune activation. It signals through two receptors: TNF receptor 1 (TNFR1), which is constitutively expressed on virtually all nucleated cells and mediates most inflammatory and apoptotic effects, and TNF receptor 2 (TNFR2), expressed predominantly on immune cells and mediating proliferative and survival signals in T cells. TNF-alpha exists in two biologically active forms: the membrane-bound trimeric form (mTNF, membrane TNF) anchored to the plasma membrane of producer cells, and the soluble trimeric form (sTNF) shed by metalloprotease (ADAM17/TACE) cleavage. Both forms are pharmacologically relevant: soluble TNF drives systemic inflammation, while membrane-bound TNF mediates local macrophage activation critical for granuloma maintenance and host defense against intracellular pathogens. This distinction underlies key mechanistic differences among the TNF inhibitor structural classes.1
Structural Classes: Monoclonal Antibodies vs. Fusion Protein. The five approved TNF inhibitors fall into two structural categories. The first category consists of monoclonal antibodies and an antibody fragment that bind TNF-alpha directly: infliximab is a chimeric immunoglobulin G1 (IgG1) monoclonal antibody (approximately 25% murine, 75% human sequence); adalimumab is a fully human IgG1 monoclonal antibody; golimumab is a fully human IgG1 monoclonal antibody; and certolizumab pegol is a humanized polyethylene glycol (PEG)-conjugated Fab fragment that lacks the Fc region. The second category is etanercept, a dimeric fusion protein that combines the extracellular domain of TNFR2 fused to the Fc region of human IgG1; it binds both TNF-alpha and lymphotoxin-alpha (TNF-beta), which is not targeted by the monoclonal antibodies. These structural differences create clinically meaningful pharmacological distinctions.12
Certolizumab Pegol: Pregnancy Safety and the Fc-Region Distinction. Certolizumab pegol (CZP) is the only TNF inhibitor that lacks an Fc region, a consequence of its Fab fragment structure. This structural feature has two important clinical implications. First, because transplacental transfer of immunoglobulins from mother to fetus occurs primarily via neonatal Fc receptor (FcRn)-mediated active transport of the IgG Fc region during the second and third trimesters, certolizumab pegol does not undergo significant FcRn-mediated placental transfer; pharmacokinetic studies have demonstrated minimal or undetectable certolizumab concentrations in cord blood and breast milk compared to substantially higher concentrations with Fc-containing agents. This makes certolizumab pegol the preferred TNF inhibitor when biologic therapy for conditions such as rheumatoid arthritis (RA), inflammatory bowel disease (IBD), or psoriatic arthritis is required during pregnancy. Second, certolizumab pegol cannot mediate antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC) through the Fc pathway, which may contribute to subtle differences in mechanism.
Etanercept and Granulomatous Disease: The TNFR2 Fusion Protein Distinction. Etanercept differs in a clinically meaningful way from the anti-TNF monoclonal antibodies in its mechanism of action in granulomatous disease. While all five agents effectively neutralize soluble TNF and are approved for RA, psoriasis, psoriatic arthritis, and ankylosing spondylitis, etanercept has consistently shown inferior or absent efficacy in granulomatous inflammatory conditions including Crohn's disease, sarcoidosis, and Wegener's granulomatosis (granulomatosis with polyangiitis, GPA), indications where the monoclonal antibodies infliximab and adalimumab are effective. The mechanistic basis for this difference is incompletely understood but is believed to relate to differences in binding to membrane-bound TNF versus soluble TNF: the anti-TNF monoclonal antibodies bind both membrane-bound and soluble forms of TNF and induce reverse signaling through mTNF, which may be necessary for granuloma dissolution. Etanercept, as a soluble receptor fusion protein, binds TNF predominantly in its soluble form and may be less effective at disrupting the granulomatous macrophage activation driven by mTNF. This mechanistic principle means that etanercept should not be used as a substitute for infliximab or adalimumab in IBD or sarcoidosis.12
TNF Inhibitor Indications and Clinical Applications. The five TNF inhibitors collectively are approved for: rheumatoid arthritis (RA), juvenile idiopathic arthritis (JIA), ankylosing spondylitis (AS) and non-radiographic axial spondyloarthropathy (nr-axSpA), psoriatic arthritis (PsA), plaque psoriasis, inflammatory bowel disease (Crohn's disease and ulcerative colitis, for infliximab, adalimumab, and golimumab), and other indications including hidradenitis suppurativa (adalimumab) and uveitis (adalimumab). Biosimilars for infliximab, adalimumab, etanercept, and golimumab are widely available and clinically interchangeable with reference biologics for most approved indications, representing a major opportunity for cost reduction without compromising efficacy or safety. The choice among TNF inhibitors for a given patient is determined by indication (Crohn's disease excludes etanercept), frequency and route of administration (subcutaneous weekly or biweekly vs. intravenous monthly or bimonthly), pregnancy status (certolizumab preferred), immunogenicity considerations (highest with infliximab due to its chimeric structure), and formulary access.23
TNF Inhibitor Safety: Infectious Risks and Contraindications. The most clinically consequential safety concern with all TNF inhibitors is the increased risk of serious infections, particularly reactivation of latent infections. Tuberculosis (TB) reactivation is the most important: TNF-alpha is essential for the maintenance of the granulomatous immune response that contains latent Mycobacterium tuberculosis; disruption of this response by TNF inhibitors dramatically increases the risk of active TB, often manifesting as extrapulmonary or disseminated disease rather than the typical pulmonary presentation. Screening for latent TB with tuberculin skin testing (TST) or interferon-gamma release assay (IGRA) is mandatory before initiating any TNF inhibitor, and chemoprophylaxis with isoniazid for at least 9 months must be completed or substantially underway before starting the TNF inhibitor. Hepatitis B virus (HBV) reactivation is another critical concern: HBV surface antigen (HBsAg) and core antibody (anti-HBc) testing is mandatory pre-treatment; patients with HBsAg-positive hepatitis B should receive anti-HBV prophylaxis with entecavir or tenofovir throughout TNF inhibitor therapy and for 12 months after completion. Other infectious risks include fungal infections (histoplasmosis, coccidioidomycosis, aspergillosis, pneumocystis), listeriosis, and opportunistic infections with intracellular pathogens.3
Active infection (including untreated latent TB, active HBV, active fungal infection). Moderate-to-severe heart failure (New York Heart Association, NYHA class III/IV) — TNF inhibitors worsen cardiac function. Active demyelinating disease (multiple sclerosis, optic neuritis). Active malignancy (except adequately treated basal or squamous cell skin carcinoma). Pregnancy: certolizumab pegol preferred; infliximab and adalimumab should be discontinued by week 22–24 if possible. Biologic agents should never be combined with other biologics due to additive immunosuppression and serious infection risk.
Interleukin-1 (IL-1) and interleukin-6 (IL-6) are both acute-phase cytokines produced predominantly by activated macrophages in response to inflammasome activation and Toll-like receptor (TLR) signaling. Pharmacological inhibition of these cytokines has proven highly effective in conditions where pathological IL-1 or IL-6 signaling drives disease, including crystal arthropathies, autoinflammatory syndromes, cytokine release syndrome, and rheumatoid arthritis.
IL-1 Antagonists: Anakinra, Canakinumab, and Rilonacept. Three pharmacologically distinct agents target the IL-1 pathway. Anakinra is a recombinant non-glycosylated form of the naturally occurring IL-1 receptor antagonist (IL-1Ra), which competitively blocks IL-1 alpha and IL-1 beta from binding to the IL-1 receptor type 1 (IL-1RI); because it competes with the endogenous IL-1 ligands for receptor occupancy, it requires daily subcutaneous injection to maintain sufficient receptor occupancy for clinical effect, and its short plasma half-life of approximately 4 to 6 hours necessitates consistent daily dosing. Anakinra is approved for rheumatoid arthritis (RA), neonatal-onset multisystem inflammatory disease (NOMID), and adult-onset Still's disease (AOSD) and is used off-label for gout flares, pericarditis, and patients with hyperferritinemic states including macrophage activation syndrome. Canakinumab is a fully human monoclonal antibody that selectively targets IL-1 beta (not IL-1 alpha), with a half-life of approximately 26 days allowing subcutaneous dosing every 4 to 8 weeks. It is approved for cryopyrin-associated periodic syndromes (CAPS), systemic juvenile idiopathic arthritis (sJIA), adult-onset Still's disease, gouty arthritis, and familial Mediterranean fever (FMF). Rilonacept is a dimeric fusion protein (IL-1 trap) consisting of the extracellular domains of both IL-1RI and the IL-1 receptor accessory protein (IL-1RAcP) linked to an IgG Fc region; it binds both IL-1 alpha and IL-1 beta with high affinity and is approved for recurrent pericarditis and CAPS.4
Clinical Applications of IL-1 Blockade. The most dramatic and consistent responses to IL-1 blockade are seen in diseases driven by cryopyrin inflammasome hyperactivation. The cryopyrin sensor protein belongs to the NLR (nucleotide-binding and oligomerization domain-like receptor) family and is encoded by the gene designated NLRP3 (NLR family, pyrin domain-containing 3). CAPS (cryopyrin-associated periodic syndromes), caused by gain-of-function mutations in the NLRP3 gene encoding cryopyrin (the NLRP3 inflammasome sensor protein), comprises a spectrum of three severity-graded autoinflammatory disorders: familial cold autoinflammatory syndrome (FCAS), Muckle-Wells syndrome (MWS), and neonatal-onset multisystem inflammatory disease (NOMID)/chronic infantile neurological cutaneous and articular syndrome (CINCA). All three respond dramatically to canakinumab or rilonacept, with near-complete resolution of fever, rash, and systemic inflammation. Gout flares represent another IL-1 beta-driven condition: monosodium urate (MSU) crystals activate the NLRP3 inflammasome in macrophages, generating IL-1 beta that drives the acute articular inflammatory response; canakinumab is approved for acute gouty arthritis flares in patients who cannot tolerate or have contraindications to colchicine, non-steroidal anti-inflammatory drugs (NSAIDs), or corticosteroids. IL-1 blockade is also highly effective in FMF and periodic fever syndromes where pyrin or other inflammasome-activating mutations generate dysregulated IL-1 beta output.4
IL-6 Receptor Inhibitors: Tocilizumab and Sarilumab. Tocilizumab and sarilumab are humanized monoclonal antibodies directed against the IL-6 receptor alpha chain (IL-6Ra, also called gp80), blocking both membrane-bound and soluble IL-6 receptor (IL-6R). By blocking the shared gp130 signaling receptor complex, they suppress all downstream IL-6 signaling through the Janus kinase 1/2 (JAK1/2)-STAT3 (signal transducer and activator of transcription 3) axis, MAPK (mitogen-activated protein kinase), and PI3K (phosphoinositide 3-kinase) pathways, inhibiting acute-phase protein synthesis (C-reactive protein (CRP), fibrinogen, hepcidin, serum amyloid A), Th17 cell differentiation, and platelet production. The IL-6R alpha chain blockade, rather than IL-6 ligand blockade, is mechanistically advantageous because it blocks signaling from both membrane-bound and soluble IL-6R; by contrast, siltuximab, a chimeric anti-IL-6 ligand antibody, blocks only free soluble IL-6 and is approved only for multicentric Castleman disease (MCD), where viral IL-6 plays a pathogenic role. Tocilizumab is available in intravenous formulation (for RA, sJIA, pJIA, GCA) and subcutaneous formulation (for RA and GCA); sarilumab is subcutaneous only. Both are approved for RA following inadequate response to methotrexate and other disease-modifying antirheumatic drugs (DMARDs).5
Cytokine Release Syndrome and the IL-6 Pathway. Cytokine release syndrome (CRS) is a life-threatening systemic inflammatory reaction originally characterized in hematopoietic stem cell transplantation and subsequently recognized as the major dose-limiting toxicity of cluster of differentiation 19 (CD19)-directed chimeric antigen receptor T-cell (CAR-T) therapy, bispecific T-cell engaging antibodies (BiTEs, e.g., blistering and blinatumomab), and anti-CD3 antibody administration. CRS manifests as fever, hypotension, hypoxia, and end-organ dysfunction driven by supraphysiological levels of circulating IL-6, interferon-gamma (IFN-gamma), macrophage inflammatory protein-1 alpha (MIP-1 alpha), and other cytokines released from activated T cells and macrophages. Tocilizumab has been approved by the US Food and Drug Administration (FDA) for the treatment of severe or life-threatening CRS in patients 2 years and older, representing a major therapeutic advance; intravenous tocilizumab at 8 mg/kg rapidly reverses the fever and hemodynamic instability of CRS in most patients, with response typically within 24 hours. CRS grading systems (Lee or ASTCT criteria) are used to guide the decision to initiate tocilizumab, with corticosteroids reserved for steroid-responsive or refractory cases. An important clinical caveat is that CRP, the standard biomarker for infection surveillance in inflammatory disease patients, is suppressed to near-zero by IL-6R blockade; clinicians must rely on procalcitonin, clinical assessment, and microbiological investigation rather than CRP to detect concurrent infections in patients receiving tocilizumab or sarilumab.56
Tocilizumab and sarilumab suppress hepatic CRP synthesis so completely that CRP becomes unreliable as an infection biomarker. Patients with intercurrent infections may have normal or low CRP despite active sepsis. Use procalcitonin (PCT), blood cultures, clinical assessment, and imaging to detect infection in patients on IL-6R inhibitors. This caveat also applies to monitoring disease activity in RA: disease activity scores using CRP will be artificially low; use clinical examination and ultrasound to assess synovitis.
The interleukin-17 (IL-17) and interleukin-23 (IL-23) cytokine axis is the principal driver of neutrophilic mucosal and skin inflammation in psoriasis, psoriatic arthritis, and ankylosing spondylitis. Biologics targeting IL-17A (interleukin-17A), the IL-17 receptor, and the p19 or p40 subunit of IL-23 have transformed the treatment of these conditions, with efficacy superior to tumor necrosis factor (TNF) inhibitors for plaque psoriasis and comparable or superior in spondyloarthritis.
The IL-23/Th17 Axis: Pharmacological Framework. Interleukin-23 (IL-23) is a heterodimeric cytokine consisting of a unique p19 subunit and a shared p40 subunit (also shared with IL-12). IL-23 is produced by dendritic cells and macrophages in response to microbial pattern recognition and acts on Th17 cells and type 3 innate lymphoid cells (ILC3 cells) through the IL-23 receptor (IL-23R) and IL-12 receptor beta-1 subunit heterodimer complex, signaling via Janus kinase 2 (JAK2) and tyrosine kinase 2 (TYK2) to activate signal transducer and activator of transcription 3 (STAT3). IL-23 drives the differentiation and survival of Th17 cells, which produce IL-17A, IL-17F (interleukin-17F), IL-22 (interleukin-22), and TNF. IL-17A and IL-17F bind the heterodimeric IL-17RA (IL-17 receptor A subunit)/IL-17RC (IL-17 receptor C subunit) heterodimeric receptor on keratinocytes, fibroblasts, and stromal cells, inducing production of chemokines including IL-8 (C-X-C motif chemokine ligand 8, CXCL8), G-CSF, and pro-inflammatory cytokines that recruit neutrophils and amplify tissue inflammation. Pharmacological targeting at the IL-23 level (upstream) versus the IL-17 level (downstream) has different clinical consequences: blocking IL-23 preserves IL-17-independent effector immune functions, while blocking IL-17 more directly suppresses mucosal neutrophil recruitment.7
IL-17A Inhibitors: Secukinumab, Ixekizumab, and Bimekizumab. Secukinumab is a fully human monoclonal IgG1 antibody that selectively binds and neutralizes IL-17A, preventing its interaction with the IL-17RA (IL-17 receptor A)/IL-17RC (IL-17 receptor C) heterodimeric receptor subunit. It is approved for plaque psoriasis, psoriatic arthritis (PsA), AS (ankylosing spondylitis, a seronegative spondyloarthropathy), and non-radiographic axial spondyloarthropathy (nr-axSpA). In psoriasis, secukinumab achieves Psoriasis Area and Severity Index 90 (PASI 90, a 90% reduction in PASI score) in approximately 60 to 70% of patients, substantially superior to TNF inhibitors and ustekinumab. Ixekizumab is a humanized IgG4 monoclonal antibody that also selectively targets IL-17A with similar indications. Bimekizumab is a humanized IgG1 monoclonal antibody that uniquely inhibits both IL-17A and IL-17F (IL-17 isoform F) simultaneously; dual IL-17A and IL-17F blockade achieves PASI 90 in approximately 85 to 90% of patients at week 16, the highest response rates for any approved biologic in plaque psoriasis.7
IL-17 Inhibitor Safety and Bowel Disease Caution. A key safety consideration shared by all IL-17A inhibitors is an increased risk of mucocutaneous candidiasis (oral and esophageal candidiasis), reflecting the physiological role of IL-17A in mucosal antifungal immunity at barrier surfaces; inflammatory bowel disease (IBD) is a further concern because IL-17A has a protective role in intestinal barrier integrity. Candidiasis occurs in approximately 3 to 4% of patients on IL-17 inhibitors and typically responds to topical antifungal therapy without requiring drug discontinuation. Clinical trials of secukinumab in Crohn's disease showed unexpected disease worsening, and IL-17A inhibitors are therefore contraindicated in active IBD and should be used with caution in patients with a history of IBD.78
IL-23 p19 Inhibitors: Guselkumab, Risankizumab, and Tildrakizumab. The selective IL-23 p19 inhibitors represent a mechanistically refined approach: by blocking the unique p19 subunit of IL-23 rather than the shared p40 subunit, they selectively suppress the IL-23/Th17 axis without affecting IL-12 (which shares p40 with IL-23) and the Th1/interferon-gamma (IFN-gamma) axis. Guselkumab is a fully human IgG1 antibody targeting IL-23 p19, approved for plaque psoriasis and PsA. Risankizumab is a humanized IgG1 antibody targeting IL-23 p19 with high affinity, approved for plaque psoriasis, PsA, Crohn's disease, and ulcerative colitis, making it one of the few biologics approved for both dermatological and gastrointestinal inflammatory diseases. Tildrakizumab is a fully human IgG1 antibody targeting IL-23 p19 approved for plaque psoriasis. The selective IL-23 p19 inhibitors generally show excellent efficacy in psoriasis (PASI 90 rates of 70 to 85%) with a favorable safety profile, lower rates of candidiasis than IL-17 inhibitors, and with no signal for worsening IBD, making them preferred over IL-17 inhibitors in patients with concurrent inflammatory bowel disease.78
Ustekinumab: Combined IL-12 and IL-23 p40 Blockade. Ustekinumab is a fully human IgG1 monoclonal antibody directed against the p40 subunit shared by both IL-12 and IL-23, thus blocking both IL-12-driven Th1 differentiation and IFN-gamma production and IL-23-driven Th17 responses. It is approved for plaque psoriasis (including in children 6 years and older), PsA, Crohn's disease, and ulcerative colitis. Because ustekinumab blocks IL-12 in addition to IL-23, it has a theoretical disadvantage compared to selective IL-23 p19 inhibitors in terms of preserving Th1 immunity, which is important for host defense against intracellular pathogens; in practice, the safety profile of ustekinumab is favorable with a lower infection rate than TNF inhibitors in registry data. Ustekinumab is administered subcutaneously every 12 weeks after induction (including an optional intravenous loading dose for IBD), which is the least frequent maintenance dosing schedule among the approved biologics for psoriasis and IBD, and is an important factor in drug selection for adherence-challenged patients. Subcutaneous biosimilars for ustekinumab are now available in multiple markets and are recommended in guidelines as equivalent alternatives.9
Prefer IL-17 inhibitors: Patients with severe plaque psoriasis prioritizing maximum skin clearance; PsA with peripheral joint disease; AS/nr-axSpA. Prefer IL-23 p19 inhibitors: Patients with concurrent IBD (or IBD history); patients at higher candidiasis risk; Crohn's disease or UC requiring a biologic. Prefer ustekinumab: Every-12-week maintenance preferred for adherence; Crohn's disease and UC (non-TNF naïve); pediatric psoriasis. Mucocutaneous candidiasis with IL-17 inhibitors: Treat with topical antifungal; systemic antifungal if refractory; dose reduction or switch rarely required. IBD flare on IL-17 inhibitor: Discontinue immediately and reassess; switch to IL-23 inhibitor or ustekinumab.
B cells contribute to autoimmune disease through antibody production (autoantibody-mediated tissue damage), antigen presentation to T cells, cytokine secretion, and formation of ectopic lymphoid structures in inflamed tissues. Pharmacological targeting of B cells through depletion, survival factor deprivation, or suppression of the type I interferon axis that drives B-cell hyperactivation has proven effective in a range of systemic autoimmune diseases.
Rituximab: Anti-CD20 B-Cell Depletion. Rituximab is a chimeric human-murine IgG1 monoclonal antibody directed against the CD20 (cluster of differentiation 20) antigen, a cell-surface phosphoprotein expressed on pre-B cells, mature B cells, and memory B cells, but not on plasma cells or hematopoietic stem cells. This expression pattern means that rituximab depletes the B-cell compartment from pre-B through memory B-cell stages while preserving pre-existing plasma cells (which lack CD20) and their antibody production, and sparing hematopoietic stem cells, allowing B-cell reconstitution over months. The mechanism of B-cell depletion involves three effector pathways: complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC) mediated by natural killer (NK) cells and macrophages via Fc-gamma receptor binding, and direct induction of apoptosis. Rituximab is approved for RA (combined with methotrexate, second-line after TNF inhibitor failure), granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), pemphigus vulgaris, and multiple hematological malignancies. Off-label use in autoimmune conditions includes systemic lupus erythematosus (SLE), myositis, anti-NMDA receptor encephalitis, neuromyelitis optica spectrum disorder (NMOSD), and immune thrombocytopenia (ITP).10
Rituximab Safety: Infections and Progressive Multifocal Leukoencephalopathy. The most serious infectious complication of rituximab is progressive multifocal leukoencephalopathy (PML), a potentially fatal demyelinating brain infection caused by reactivation of JC (John Cunningham) virus, a polyomavirus, in profoundly immunosuppressed patients. PML risk with rituximab is substantially lower than with natalizumab (used in multiple sclerosis) but is non-negligible in patients receiving rituximab for autoimmune indications, particularly when combined with other immunosuppressants or after multiple courses. JC virus antibody serology (JCV index) monitoring is recommended in long-term rituximab users. Other significant infectious risks include hypogammaglobulinemia (from cumulative B-cell depletion reducing plasma cell precursor replenishment over multiple courses), leading to reduced production of new immunoglobulins and increased susceptibility to encapsulated bacteria; prolonged B-cell depletion with below-normal IgG requiring immunoglobulin replacement therapy; hepatitis B virus (HBV) reactivation (screening and prophylaxis as for TNF inhibitors); and late-onset neutropenia. Infusion reactions (fever, chills, hypotension, bronchospasm) are common with the first infusion and managed by pre-medication with antihistamine, acetaminophen, and corticosteroid and by slowing the infusion rate.10
Obinutuzumab: Next-Generation Anti-CD20. Obinutuzumab is a glycoengineered humanized anti-CD20 IgG1 monoclonal antibody with enhanced ADCC activity relative to rituximab, achieved through modification of Fc region glycosylation that increases affinity for Fc-gamma receptor III (CD16) on NK cells and macrophages. Its superior B-cell depletion compared to rituximab has been demonstrated in clinical trials in chronic lymphocytic leukemia (CLL) and follicular lymphoma. In lupus nephritis, obinutuzumab combined with mycophenolate demonstrated superior renal outcomes compared to mycophenolate alone in the NOBILITY (Novel Obinutuzumab In Lupus Nephritis Trial Investigating Efficacy and Safety) trial, supporting its emerging role in severe lupus nephritis refractory to standard therapy. The safety profile parallels rituximab with enhanced depletion depth increasing the risk of hypogammaglobulinemia and infections over time.10
Belimumab: Anti-BAFF/BLyS Therapy in Systemic Lupus Erythematosus. Belimumab is a fully human IgG1 monoclonal antibody that targets B lymphocyte stimulator (BLyS, also called B-cell activating factor (BAFF)), a TNF superfamily cytokine critical for B-cell survival, maturation, and differentiation to plasma cells. BLyS levels are elevated in SLE and correlate with disease activity and anti-double-stranded DNA (anti-dsDNA) antibody titers; BLyS signaling through its three receptors (BAFF-R, TACI, and BCMA) on B cells prevents apoptosis and promotes B-cell survival and antibody production. Belimumab is approved for active, autoantibody-positive SLE in patients who are on standard therapy (antimalarials, corticosteroids, and immunosuppressants) and is the first new drug approved for SLE in over 50 years. It is available as a weekly subcutaneous injection or monthly intravenous infusion. A second indication is active lupus nephritis in patients receiving standard background therapy. Clinical trials demonstrated reductions in SLE disease activity index (SLEDAI) scores, reduction in severe flares, and steroid-sparing effects, though the magnitude of response is modest compared to that seen with biologics in RA or psoriasis, reflecting the complexity of SLE pathogenesis beyond B-cell activation alone.11
Anifrolumab: Type I Interferon Receptor Blockade in SLE. Anifrolumab is a fully human IgG1 monoclonal antibody that blocks the type I interferon receptor subunit 1 (IFNAR1), preventing signaling by all type I interferons (IFN-alpha subtypes and IFN-beta). Type I interferons are produced in large quantities by plasmacytoid dendritic cells (pDCs) in response to nucleic acid-containing immune complexes in SLE; upregulation of interferon-stimulated genes (ISGs), collectively known as the interferon signature detected on gene expression profiling, is present in 60 to 80% of SLE patients and correlates with disease severity and organ involvement. By blocking IFNAR1, anifrolumab suppresses the entire type I interferon response, including the activation of dendritic cells, enhancement of B-cell activation and autoantibody production, and upregulation of pro-inflammatory gene programs. Anifrolumab is approved for moderate-to-severe SLE in adults who are on standard therapy. Clinical trials (TULIP-1 and TULIP-2) demonstrated reductions in BICLA (British Isles Lupus Assessment Group Index-based Composite Lupus Assessment) response rates, organ domain improvement, and reduced oral corticosteroid use. Anifrolumab is generally well tolerated; herpes zoster reactivation occurs at a slightly higher rate, reflecting the role of type I interferons in antiviral defense, and influenza and shingles vaccination before initiation is recommended.12
Background therapy for all SLE: Hydroxychloroquine 5 mg/kg/day (organ-protective, reduces flares, cardiovascular benefit). Add belimumab: Active, autoantibody-positive SLE (anti-dsDNA, anti-Sm) with ongoing disease activity on standard immunosuppression; preferred when B-cell hyperactivation and high BLyS are prominent. Add anifrolumab: Moderate-to-severe SLE with prominent interferon signature; useful for mucocutaneous and musculoskeletal manifestations. Rituximab (off-label): Severe organ-threatening SLE (lupus nephritis class III/IV, CNS lupus, cytopenias) refractory to standard immunosuppression. Not recommended in SLE: TNF inhibitors (may paradoxically induce or worsen lupus-like disease through drug-induced lupus mechanisms).
Type 2 inflammation is a systemic inflammatory state driven by T helper 2 (Th2) cells and type 2 innate lymphoid cells (ILC2 cells), producing the cytokines interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-13 (IL-13), and interleukin-33 (IL-33) that orchestrate IgE production, eosinophilia, mast cell activation, and mucus hypersecretion. Targeted biological therapies against the key mediators of this pathway have transformed the management of severe atopic diseases, demonstrating that precision cytokine targeting can produce dramatic clinical responses in conditions previously treatable only with broad immunosuppression or escalating corticosteroids.
Dupilumab: Mechanism and Approved Indications. Dupilumab is a fully human IgG4 monoclonal antibody that binds the IL-4 receptor alpha chain (IL-4R alpha), which is shared by the type I IL-4 receptor (IL-4R alpha/gamma-c chain, used by IL-4) and the type II receptor (IL-4R alpha/IL-13 receptor alpha 1 (IL-13R alpha-1), used by both IL-4 and IL-13). By targeting this shared subunit, dupilumab simultaneously blocks signaling by both IL-4 and IL-13, the two principal Th2 cytokines driving IgE (immunoglobulin E) class switching, goblet cell metaplasia, smooth muscle hyperreactivity, fibrosis, and barrier dysfunction in atopic disease. The downstream signaling pathway blocked is JAK1/TYK2 (Janus kinase 1/tyrosine kinase 2) to STAT6 (signal transducer and activator of transcription 6). Dupilumab is approved for moderate-to-severe atopic dermatitis (AD), moderate-to-severe asthma, chronic rhinosinusitis with nasal polyps (CRSwNP), eosinophilic esophagitis (EoE), prurigo nodularis, and COPD (chronic obstructive pulmonary disease) with type 2 inflammation.13
Dupilumab Safety Profile. Dupilumab is administered subcutaneously every two weeks with a loading dose for most indications. Unlike conventional immunosuppressants, it does not cause significant immunosuppression, increased infection risk, or malignancy. The most common adverse effects are injection site reactions and conjunctivitis, which occurs in approximately 10% of patients with atopic dermatitis; the mechanism of conjunctivitis is not fully established but may involve unopposed IL-4 signaling in conjunctival goblet cells when IL-13-mediated suppression is blocked, altering conjunctival mucus composition and immune homeostasis.13
Anti-IL-5 Therapies: Mepolizumab, Reslizumab, and Benralizumab. IL-5 is the principal cytokine for eosinophil production in the bone marrow, maturation, survival, and priming for activation. Three approved agents target the IL-5 pathway at different points. Mepolizumab is a humanized IgG1 monoclonal antibody that binds IL-5 ligand, preventing it from signaling through the IL-5 receptor complex (IL-5R alpha/beta-c). Reslizumab is a humanized IgG4 antibody directed against the IL-5 ligand with a slightly different binding epitope; it is administered intravenously in weight-based dosing. Benralizumab is a humanized IgG1 monoclonal antibody directed against the IL-5 receptor alpha chain (IL-5R alpha), blocking IL-5 binding and additionally mediating rapid and profound eosinophil depletion through ADCC (natural killer (NK) cells expressing CD16 (Fc-gamma receptor III) bind the Fc region of benralizumab-opsonized eosinophils), resulting in near-complete depletion of blood and tissue eosinophils within weeks. All three agents are approved for severe eosinophilic asthma (mepolizumab also in eosinophilic granulomatosis with polyangiitis (EGPA), hypereosinophilic syndrome, and chronic rhinosinusitis with nasal polyps). In severe eosinophilic asthma with high blood eosinophil counts (usually greater than 300 eosinophils per microliter), these agents reduce exacerbation rates by approximately 50%, reduce oral corticosteroid (OCS) requirements, and improve lung function and quality of life measures.1314
Tezepelumab: Thymic Stromal Lymphopoietin Blockade. Tezepelumab is a fully human IgG2 monoclonal antibody that blocks thymic stromal lymphopoietin (TSLP), an epithelial-derived alarmin cytokine produced in response to environmental triggers (allergens, pollutants, viruses, and cigarette smoke) that acts on dendritic cells, mast cells, and type 2 innate lymphoid cells (ILC2 cells) to initiate and amplify type 2 inflammation. By blocking TSLP at the most upstream position in the type 2 inflammatory cascade, tezepelumab has a broader mechanism of action than the downstream cytokine-targeted agents: it reduces eosinophils, IgE, TSLP, IL-5, IL-13, and FeNO (fractional exhaled nitric oxide) across patients regardless of baseline eosinophil count, and is effective in both eosinophilic and non-eosinophilic severe asthma phenotypes. This distinguishes tezepelumab from the anti-IL-5 agents, which are primarily effective in patients with blood eosinophil counts above 300 per microliter. Tezepelumab is approved for add-on maintenance treatment of severe asthma in adults and children 12 years and older; clinical trials demonstrated a 56% reduction in annualized exacerbation rate versus placebo across unselected severe asthma patients, including those with low eosinophil counts.14
Omalizumab: Anti-IgE Therapy. Omalizumab is a humanized IgG1 monoclonal antibody that selectively binds the Fc region of free IgE (immunoglobulin E), preventing IgE from binding to its high-affinity receptor (Fc epsilon RI) on mast cells and basophils. By depleting free IgE and downregulating surface Fc epsilon RI expression on mast cells, omalizumab reduces the cellular machinery for IgE-mediated allergic responses without inducing mast cell degranulation. Omalizumab is approved for moderate-to-severe allergic asthma with perennial allergen sensitization inadequately controlled by inhaled corticosteroids and long-acting beta-agonists (IgE 30 to 700 international units (IU) per mL and weight-dependent dosing), chronic spontaneous urticaria (CSU) refractory to antihistamines, chronic rhinosinusitis with nasal polyps, and food allergy (for peanut allergy in children). The dosing interval (every 2 or 4 weeks subcutaneously) is determined by baseline IgE level and patient weight using a dosing table. Patients with CSU show dramatic responses to omalizumab regardless of IgE level, suggesting IgE-independent mechanisms in this indication. Anaphylaxis occurs rarely but unpredictably with omalizumab; patients should be observed for 30 minutes after the first three injections, with injectable epinephrine available.13
High eosinophils (≥300/μL) + allergic: Dupilumab, mepolizumab, benralizumab, or tezepelumab all appropriate; benralizumab most rapidly depletes eosinophils (near-complete within 4 weeks). High eosinophils + non-allergic: Anti-IL-5 agents preferred. Low eosinophils (<300/μL): Tezepelumab preferred (effective regardless of phenotype). Allergic (IgE 30–700 IU/mL) + sensitization confirmed: Omalizumab. Nasal polyps co-morbidity: Dupilumab, benralizumab, mepolizumab, or omalizumab all have nasal polyp approval data. OCS-dependent: All agents reduce OCS; benralizumab fastest onset of OCS reduction. Biologics should not be combined; switch rather than add.
Biologic immunosuppressants, while highly targeted in mechanism, share a set of class-wide safety considerations that apply regardless of the specific cytokine or cell target. Universal application of pre-treatment screening, vaccination optimization, and ongoing monitoring protocols is essential for safe biologic prescribing across all indications and patient populations.
Mandatory Pre-Treatment Screening for All Biologics. Before initiating any biologic immunosuppressant, a standardized pre-treatment evaluation must be completed. Tuberculosis screening is required for all patients receiving immunosuppressive biologics: the choice between tuberculin skin test (TST) and IGRA (interferon-gamma release assay; e.g., QuantiFERON-TB Gold or T-SPOT.TB) should account for prior bacille Calmette-Guerin (BCG) vaccination (which causes false-positive TST but not IGRA) and immunosuppression status (which may cause false-negative results in severely immunocompromised patients). Positive TST or IGRA in the absence of active TB requires at least 4 weeks of isoniazid prophylaxis before biologic initiation, with the full 9-month course continued concurrently. Hepatitis B serology (HBsAg, anti-HBs, anti-HBc total) is mandatory; HBsAg-positive patients require antiviral prophylaxis (entecavir or tenofovir) before biologic initiation, and anti-HBc-positive/HBsAg-negative patients (occult HBV carriers) should be monitored with HBV deoxyribonucleic acid (DNA) testing every 3 months. Human immunodeficiency virus (HIV) testing is recommended in at-risk individuals. A complete blood count (CBC), comprehensive metabolic panel, and hepatic function tests form the baseline laboratory evaluation. Chest imaging is indicated in high-risk patients to evaluate for pulmonary TB, histoplasmosis, or other endemic mycoses.315
Vaccination Strategy Before and During Biologic Therapy. Vaccination strategy must be individualized based on the specific biologic and the degree of immunosuppression it produces. The fundamental principle is that live attenuated vaccines are contraindicated once biologic therapy is initiated, because impaired immune surveillance may allow vaccine-strain organisms to cause disseminated infection. Live vaccines include live-attenuated influenza vaccine (intranasal), yellow fever vaccine, oral typhoid vaccine, varicella-zoster live vaccine (Zostavax, now largely superseded), and the MMR (measles-mumps-rubella) vaccine. Inactivated and subunit vaccines, including inactivated influenza, pneumococcal vaccines (PCV15, PCV20, PPSV23), zoster subunit vaccine (Shingrix, the preferred zoster vaccine for immunocompromised patients), hepatitis A, hepatitis B, and coronavirus disease 2019 (COVID-19) vaccines may be administered during biologic therapy, though immunogenicity may be reduced. Ideally, all recommended vaccines should be completed at least 2 to 4 weeks before biologic initiation. The recombinant zoster vaccine (Shingrix, two-dose series) is strongly recommended before initiating biologics that increase herpes zoster risk (Janus kinase (JAK) inhibitors, rituximab, anifrolumab) and is preferred over the live-attenuated Zostavax in immunocompromised patients, as it is an inactivated vaccine safe for use in this population.15
Immunogenicity and Biosimilars. All biologic agents are immunogenic to varying degrees, capable of inducing the formation of anti-drug antibodies (ADAs) that reduce drug efficacy and may cause hypersensitivity reactions. Immunogenicity is highest with chimeric biologics (infliximab, rituximab, which contain more murine protein sequence) and lower with humanized and fully human agents. Concurrent immunosuppressive therapy, particularly methotrexate and azathioprine, substantially reduces anti-drug antibody (ADA) formation by suppressing the adaptive immune response to the biologic, which is the pharmacological rationale for combining methotrexate with infliximab or adalimumab in rheumatoid arthritis (RA) and inflammatory bowel disease (IBD). Loss of efficacy during sustained biologic therapy is often due to ADA formation; therapeutic drug monitoring (TDM) of biologic trough levels and ADA titers is increasingly used to guide decisions about dose escalation, interval shortening, or switching. Biosimilars are biological medicines that have been approved on the basis of demonstrated similarity to a reference biologic in terms of structure, quality, safety, and efficacy; multiple biosimilars are now approved for infliximab, adalimumab, etanercept, rituximab, and ustekinumab and are recommended as equivalent, cost-effective alternatives to reference biologics by major clinical guidelines.15
Biologic Therapy in Special Populations: Pregnancy and Perioperative Management. The use of biologic drugs during pregnancy requires careful individualized risk-benefit assessment. The general principle is that disease activity during pregnancy carries risks to both mother and fetus that may outweigh the risks of continued biologic therapy. Most biologic monoclonal antibodies with intact Fc regions undergo active placental transfer via FcRn during the second and third trimesters, resulting in neonatal drug levels that may exceed maternal levels; infants born to mothers who received Fc-containing biologics in the third trimester should not receive live vaccines for the first 6 to 12 months of life, as their immune function is transiently impaired by transplacentally transferred drug. Certolizumab pegol, lacking an Fc region, is the preferred tumor necrosis factor (TNF) inhibitor in pregnancy and can be continued throughout gestation. The IL-17 (interleukin-17) and IL-23 (interleukin-23) inhibitors have limited safety data in pregnancy, though animal studies are reassuring; the prescribing decision should be made with the patient in full consultation with rheumatology and maternal-fetal medicine. Perioperative biologic management: guidelines generally recommend withholding biologics for one to two half-lives before elective surgery to reduce infection risk, then restarting when wound healing is complete and there is no active infection; these recommendations carry low-quality evidence and must be balanced against the risk of disease flare.215
TNF inhibitors: Infliximab ~9.5 days (IV q8wk); adalimumab ~14 days (SQ q2wk); etanercept ~4 days (SQ weekly); certolizumab ~14 days (SQ q2wk); golimumab ~14 days (SQ monthly). IL-1 axis: Anakinra ~4–6 hours (SQ daily); canakinumab ~26 days (SQ q4–8wk); rilonacept ~8.6 days (SQ weekly). IL-6 axis: Tocilizumab ~11–13 days (IV/SQ); sarilumab ~10 days (SQ q2wk). IL-17/23 axis: Secukinumab ~27 days (SQ monthly maintenance); ixekizumab ~13 days (SQ q4wk); bimekizumab ~23 days; guselkumab ~18 days; risankizumab ~28 days; ustekinumab ~21 days (SQ q12wk). B-cell/type 2: Rituximab ~18–22 days (IV q6mo); belimumab ~19 days (SQ weekly/IV monthly); anifrolumab ~21 days (IV monthly); dupilumab ~20 days (SQ q2wk); mepolizumab ~16–22 days (SQ monthly); benralizumab ~15 days (SQ q8wk); tezepelumab ~26 days (SQ monthly); omalizumab ~26 days (SQ q2–4wk).
Tracey D, Klareskog L, Sasso EH, Salfeld JG, Tak PP. Tumor necrosis factor antagonist mechanisms of action: a comprehensive review. Pharmacol Ther. 2008;117(2):244-279.
doi:10.1016/j.pharmthera.2007.10.001Keystone EC, Genovese MC, Klareskog L, et al. Golimumab, a human antibody to tumour necrosis factor alpha given by monthly subcutaneous injections, in active rheumatoid arthritis despite methotrexate therapy. Ann Rheum Dis. 2009;68(6):789-796.
doi:10.1136/ard.2008.099010Singh JA, Saag KG, Bridges SL Jr, et al. 2015 American College of Rheumatology guideline for the treatment of rheumatoid arthritis. Arthritis Rheumatol. 2016;68(1):1-26.
doi:10.1002/art.39480Martinon F, Mayor A, Tschopp J. The inflammasomes: guardians of the body. Annu Rev Immunol. 2009;27:229-265.
doi:10.1146/annurev.immunol.021908.132715Tanaka T, Narazaki M, Kishimoto T. IL-6 in inflammation, immunity, and disease. Cold Spring Harb Perspect Biol. 2014;6(10):a016295.
doi:10.1101/cshperspect.a016295Le RQ, Li L, Yuan W, et al. FDA approval summary: tocilizumab for treatment of chimeric antigen receptor T cell-induced severe or life-threatening cytokine release syndrome. Oncologist. 2018;23(8):943-947.
doi:10.1634/theoncologist.2018-0028Miossec P, Kolls JK. Targeting IL-17 and TH17 cells in chronic inflammation. Nat Rev Drug Discov. 2012;11(10):763-776.
doi:10.1038/nrd3794Gordon KB, Strober B, Lebwohl M, et al. Efficacy and safety of risankizumab in moderate-to-severe plaque psoriasis (UltIMMa-1 and UltIMMa-2). Lancet. 2018;392(10148):650-661.
doi:10.1016/S0140-6736(18)31713-6Feagan BG, Sandborn WJ, Gasink C, et al. Ustekinumab as induction and maintenance therapy for Crohn's disease. N Engl J Med. 2016;375(20):1946-1960.
doi:10.1056/NEJMoa1602773Pescovitz MD. Rituximab, an anti-cd20 monoclonal antibody: history and mechanism of action. Am J Transplant. 2006;6(5 Pt 1):859-866.
doi:10.1111/j.1600-6143.2006.01288.xFurie R, Rovin BH, Houssiau F, et al. Two-year, randomized, controlled trial of belimumab in lupus nephritis. N Engl J Med. 2020;383(12):1117-1128.
doi:10.1056/NEJMoa2001180Morand EF, Furie R, Tanaka Y, et al. Trial of anifrolumab in active systemic lupus erythematosus. N Engl J Med. 2020;382(3):211-221.
doi:10.1056/NEJMoa1912196Gandhi NA, Bennett BL, Graham NMH, Pirozzi G, Stahl N, Yancopoulos GD. Targeting key proximal drivers of type 2 inflammation in disease. Nat Rev Drug Discov. 2016;15(1):35-50.
doi:10.1038/nrd4624Menzies-Gow A, Corren J, Bourdin A, et al. Tezepelumab in adults and adolescents with severe, uncontrolled asthma. N Engl J Med. 2021;384(19):1800-1809.
doi:10.1056/NEJMoa2034975Furst DE, Keystone EC, Fleischmann R, et al. Updated consensus statement on biological agents for the treatment of rheumatic diseases, 2012. Ann Rheum Dis. 2013;72(Suppl 2):ii2-ii34.
doi:10.1136/annrheumdis-2013-203348