Do Any FDA-Approved Protein Drugs Still Carry a His or SUMO Tag? The Answer Is More Nuanced Than You Think

2. Approved therapeutic fusion proteins (the real examples)

• Etanercept / Enbrel: FDA label describes it as a dimeric fusion protein: the extracellular ligand-binding portion of human p75 TNF receptor linked to the Fc portion of human IgG1.
• Literature lists etanercept as an FDA-approved TNFR-Fc fusion, approved in 1998.
• Romiplostim / Nplate: a thrombopoietin-binding peptide fused to human IgG1 Fc, FDA approved in 2008.
• A review identifies eight fusion proteins that received regulatory approval for human therapy: etanercept, belatacept, abatacept, alefacept, rilonacept, romiplostim, aflibercept, and denileukin-diftitox.
• All of these except denileukin-diftitox use IgG1 Fc as the fusion partner; denileukin-diftitox uses a modified diphtheria toxin effector.

3. The key difference

• His-tag and SUMO-tag are "expression/purification/solubility tags." Their job is to help make the protein in the lab or factory — they are usually removed before final formulation.
• Fc fusions, receptor fusions, and peptibodies are "therapeutic fusions." The fusion partner stays in the drug intentionally to improve half-life, dimerization, stability, or pharmacological activity.

So the correct answer is: Yes, there are FDA-approved protein drugs that carry a fusion partner as part of the final product — etanercept and romiplostim are clear examples. But there is insufficient evidence that any approved drug retains a His-tag or SUMO-tag in the finished medicine.