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. Their structural differences carry clinically meaningful consequences for pregnancy safety, mechanism of action in granulomatous disease, and immunogenicity.
Four of the five agents are monoclonal antibodies or antibody fragments that bind TNF-alpha directly. Infliximab is a chimeric immunoglobulin G1 monoclonal antibody (approximately 25% murine sequence), making it the most immunogenic of the class. 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. Etanercept is structurally distinct from the others: it is a dimeric fusion protein combining the extracellular domain of TNF receptor 2 with the Fc region of human immunoglobulin G1, and it binds both TNF-alpha and lymphotoxin-alpha (also called TNF-beta), which the monoclonal antibodies do not target.
The absence of the Fc region in certolizumab pegol has two important clinical consequences. First, transplacental transfer of immunoglobulins from mother to fetus occurs primarily through neonatal Fc receptor-mediated active transport of the Fc region during the second and third trimesters. Certolizumab pegol, lacking the Fc region, does not undergo this transport and produces minimal or undetectable drug concentrations in cord blood, making it the preferred TNF inhibitor when biologic therapy is required during pregnancy. Second, certolizumab pegol cannot mediate antibody-dependent cellular cytotoxicity or complement-dependent cytotoxicity through the Fc pathway.
Etanercept is consistently less effective than the anti-TNF monoclonal antibodies in granulomatous inflammatory diseases including Crohn's disease, sarcoidosis, and granulomatosis with polyangiitis. The mechanistic basis is believed to relate to differences in binding membrane-bound TNF: the monoclonal antibodies bind both membrane-bound and soluble TNF and induce reverse signaling through membrane-bound TNF, which may be necessary for granuloma dissolution. Etanercept, as a soluble receptor decoy, preferentially binds soluble TNF and appears less effective at disrupting granulomatous macrophage activation. Etanercept must not be substituted for infliximab or adalimumab in Crohn's disease or sarcoidosis.
The five TNF inhibitors collectively are approved for rheumatoid arthritis, juvenile idiopathic arthritis, ankylosing spondylitis, psoriatic arthritis, plaque psoriasis, and inflammatory bowel disease (infliximab, adalimumab, and golimumab for Crohn's disease and ulcerative colitis; etanercept is not approved for inflammatory bowel disease). Biosimilars for infliximab, adalimumab, etanercept, and golimumab are widely available and clinically interchangeable for approved indications.
TNF-alpha is essential for maintaining the granulomatous immune response that contains latent Mycobacterium tuberculosis. TNF inhibitor therapy dramatically increases the risk of active tuberculosis, often as extrapulmonary or disseminated disease. Screening with tuberculin skin test (TST) or an interferon-gamma release assay (IGRA) is mandatory before initiating any TNF inhibitor; confirmed latent tuberculosis requires at least four weeks of isoniazid prophylaxis before starting the biologic, with the full nine-month course continued concurrently. Hepatitis B virus reactivation is a second critical concern: hepatitis B surface antigen and core antibody testing is mandatory before treatment; surface antigen-positive patients require antiviral prophylaxis (entecavir or tenofovir) throughout therapy.
Active infection including untreated latent tuberculosis, active hepatitis B virus, and active serious fungal infection. Moderate-to-severe heart failure (New York Heart Association class III or IV) — TNF inhibitors worsen cardiac function. Active demyelinating disease including multiple sclerosis and optic neuritis. Active malignancy (except adequately treated skin cancers). Never combine two biologic agents — additive immunosuppression causes unacceptable serious infection risk. Pregnancy: certolizumab pegol is preferred; other Fc-containing agents should be discontinued by week 22 to 24 of pregnancy when possible.
