TGN1412 worked in monkeys — in 6 humans it caused catastrophic organ failure

TGN1412 was a monoclonal antibody developed by TeGenero, a spin-off of the University of Würzburg, Germany. The drug was designed to treat autoimmune diseases by stimulating T cells through the CD28 receptor — a novel approach that made it a 'superagonist'. Pre-clinical testing in cynomolgus macaques showed no serious adverse effects, and the drug was approved for a Phase I first-in-human trial at a Parexel-run facility in Northwick Park Hospital, London.

On 13 March 2006, eight volunteers were enrolled in a trial. Six received a single intravenous dose of TGN1412 at 0.1 mg/kg — 500 times lower than the highest safe dose tested in monkeys. Within 50 minutes, the first participant complained of headache, fever and a burning sensation. Within hours, all six drug recipients were in intensive care with catastrophic cytokine release syndrome. Their immune systems had gone into overdrive, causing organ failure, angioedema, and the near-total loss of lymphocytes. One volunteer was described as having a ballooned head; another lost fingers and toes.

All six survived after treatment. Five were discharged within a month; the last left hospital on 26 June 2006. TeGenero went bankrupt later that year. The reason the animal model failed: cynomolgus macaques do not express CD28 on their effector memory T cells, so the drug could not trigger the same catastrophic reaction. The UK's expert group on Phase I trials made 22 recommendations, including sequential dosing and expert review for high-risk studies. The case permanently changed how first-in-human trials of immune-targeting drugs are conducted worldwide.

Cynomolgus macaques lack CD28 on effector memory T cells, so TGN1412 seemed safe in animals but was a maximum immunostimulatory dose in humans, bankrupting TeGenero.

The animal model was not predictive — cynomolgus macaques lack CD28 on effector memory T cells, so TGN1412 appeared safe in monkeys while being catastrophic in humans.

The starting dose of 0.1 mg/kg, though 500 times below the safe animal dose, resulted in 86–91% CD28 receptor occupancy — essentially a maximum immunostimulatory dose in humans.

TeGenero was a small biotech with no margin for error — a single failed trial bankrupted the company because it had no other products or revenue.

A drug that looks safe in monkeys can kill in humans when the animal model does not express the target receptor — and a biotech with one product goes bankrupt when the trial fails.