I will try to address the important issues you brought up:

Regarding the homogenicity issue, obviously the more homogenous a drug is the better, but I am not sure how crucial it is when comparing SGEN’s ADC technology to that of IMGN’s. I think that eventually both companies tend to use around 4 drug molecules per antibody. In fact, I believe SGEN came to the conclusion that an ADC with 4 drug molecules has a better therapeutic window than and ADC armed with 8 drug molecules.

Regarding the different linkers, u said you are not the best of chemist, well, that makes two of us ;).
To the best of my knowledge, IMGN cannot fully control to which lysine residues the drug is conjugated, but i m no expert on this front.
Although the two ADCs it has in the clinic utilizes the vc peptide linker, SGEN also uses non-peptide linkers, similiar to the SMCC (thioether) linker used by IMGN.

thioether linkers are not cleaveable. The disulfide linkers are cleaved by the reducing environment in the lysosome while the peptide based linkers are cleaved by lysosomal proteases, mainly cathepsin B.
From what I see, Genentech prefers thioether linkers (which are noncleavable, of course) from both companies, but I could be wrong.

I hold both SGEN and IMGN believe both have a bright future ahead of them, although there will surely be many frustrating failures down the road. Right now, I am more excited about SGEN’s pipeline as a whole, but Herceptin-DM1 is still the most important ADC out there, imo.

You raise an interesting point that I was not aware of, that SGEN have more homogenous ADC populations than IMGN.

You say SGEN use peptide-linkers, while IMGN use non-peptide linkers, the disulfide linker (SPDB-DMx) and the thioester linker (SMCC-DMx).

I’m not the best chemist, but are you saying that, IMGN attach the linker to any-old amine residue (lysine) on the MAb, as shown in the Figure below:

http://cancerres.aacrjournals.org/cgi/content/full/66/8/4426/FIG5

One other thing, you mention that DNA appear to prefer uncleavable linkers, once again I’m not the best chemist, but which of the above linkers are cleavable and which are uncleavable.

Herceptin-DM1 seems to use the thioester linker (SMCC-DMx).

Lastly, in your very informative articles you mention you are long IMGN, but you do not mention being long SGEN. I’m in the same boat, but wondered the reasons for your preference.