What was the first monoclonal antibody approved for medical use in humans?

Muromonab-CD3 was the first monoclonal antibody approved for medical use in humans.

The U.S. Food and Drug Administration approved muromonab-CD3 in 1986 under the brand name Orthoclone OKT3. It was used to treat acute rejection after organ transplantation by targeting CD3, a protein associated with T cells. Suppressing activated T cells could help protect a transplanted organ from immune attack.

The drug represented a landmark for biotechnology because monoclonal antibodies can be designed to recognize a specific molecular target. It was a laboratory-produced version of an antibody rather than a conventional broad-acting medicine.

Muromonab-CD3 is often confused with rituximab, infliximab, or trastuzumab, which were approved later for cancer, inflammatory disease, and other conditions. Its use declined because of side effects and the development of newer antibody treatments with improved properties.