I think they had "only" a target problem with IMGN901:
IMGN901 is an ADC for the treatment of CD56 positive cancer. But a subtype of natural killer cells also regonized CD56.
So, i think, IMGN901 kills cancer zells AND a subtype auf natural killer cells. So the patients are in trouble with infections.
And on the other side, I THINK, immunogen use two or three types of linkers : smcc (Kadcyla, IMGN 289), spp, spdb (IMGN901)