The biotech industry is a VERY close knit group, especially the scientists. Follow them from company to company and you will see our partners being lined up as well over time.
It wouldn't surprise me a bit to find out that BI recommended IMGN's technology to Biotest.
After all, BI worked with us for a while in trials, before they figured out the antibody target they had was also found in skin cells. According to BI, they were perfectly happy with the conjugate's performance, just not with the skin reaction, as far as I understand it.