Another famous (among the pharma peptide community) case was Erythropoietin.
People developed immunity to proteins critical to production of red blood
cells, resulting in severe, life threatening immunity,
This wasn't discovered until they'd been using it for years, because at the clinical level, no one can check for antibodies like this. Only the trials were monitoring for immunogenicity, since it's expensive and complex.
It took over a decade to figure out what happened. The manufacturer of prefilled syringes started using tungsten pins to make holes in the syringe. This left behind atomic level traces of tungsten particles. The particles caused the protein to aggregate, and the immune system responded to these aggregates, developing an immunity to them, which unfortunately, looked very similar to the natural protein critical to red blood cell production.
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