With TGN1412, it wasn't that the right work wasn't done, or that results ignored, but rather that the regulations in place at the time weren't right to deal with that sort of drug. Following what happened, the regulations were changed around the world to be more cautious and suitable.

The article says that they did do this:

> Qiu’s team had engineered mice to have a human version of the CHD3 gene with their daughter’s mutation, R1025W, which results in a protein with the amino acid tryptophan where there should be an arginine. The mutant pups developed autismlike traits and didn’t squeak as much as normal mice when separated from their mothers. When the researchers repaired that mutation, the pups developed normally.

They did animal experiments first. But according to the article they didn't really look at the serious side effects observed in monkeys, or ignored them. But animal experiments can only provide warning signs here, they can't tell you what will really happen in a human.