Antibodies are pretty useful. In addition to warding off infections, they're good at sticking to proteins in general, which has allowed drugmakers to use them to make therapies.

Have a protein that treats a disease when it's inhibited? Just develop a therapeutic antibody to it, and when the antibody finds the protein, it'll stick to it and inhibit the function. Abbott Labs' (NYSE: ABT) Humira, for instance, attacks TNF in order to reduce the autoimmune response seen in rheumatoid arthritis and other autoimmune diseases.

The next logical step was to attach a toxic payload to the antibody to kill a tumor cell -- a heat-seeking missile on the cellular level, if you will. Two companies -- Seattle Genetics (Nasdaq: SGEN) and ImmunoGen (Nasdaq: IMGN) -- have developed such systems.

Seattle Genetics calls its system an antibody-drug conjugate, or ADC, which attaches antimicrotubule agents called auristatins to the antibody. Once inside the tumor cell, the auristatin can inhibit microtubules, which are required for cellular division. No cell division, no tumor growth. In fact, cells stopped during cell division tend to die through a process called apoptosis.

ImmunoGen's TAP system is very similar, attaching a tumor-targeting antibody to a cytotoxic agent that can kill the cell once it's inside the cell.

Which company is the better buy? Let's look at a couple of aspects to find out.

Both companies have licensed their technology to multiple partners in order to make payload-containing antibody drugs. Looking at who's interested in the technology is a good way to gauge whether it's worthy of an investment. The scientists at the partner likely get to see more data than what's available to the general public, and they're hopefully more knowledgeable about developing drugs than you and I.

Seattle Genetics has licensed or is co-developing drugs using its ADC technology with 11 different companies, including big names like Takeda, GlaxoSmithKline, and Pfizer (NYSE: PFE).

ImmunoGen has licensed the TAP technology to seven different drugmakers, including Amgen (Nasdaq: AMGN), Biogen Idec (Nasdaq: BIIB), sanofi-aventis, and Novartis (NYSE: NVS).

Technically, Seattle Genetics is leading the list, but both companies are seeing pretty strong interest, and a couple of pharmas -- Roche and Bayer -- count both companies as partners.

Seattle Genetics is leading this category, but only if it can slip in phase 2 clinical trial data where ImmunoGen and partner Roche couldn't.

Roche tried to get an accelerated approval for trastuzumab-DM1, but the Food and Drug Administration said the patients tested in the phase 2 trial hadn't exhausted all their options and therefore the trial wasn't appropriate for seeking an accelerated approval. Roche is running phase 3 trials to support a marketing application. Assuming the data is as good as it was in the phase 2, the companies shouldn't have much problem gaining an approval.

The setback allowed Seattle Genetics to jump ahead with brentuximab vedotin, which treats a different type of cancer. The company submitted a marketing application to the FDA in February and should hear back shortly that the trials were appropriate enough to get the application reviewed. Considering how good the data looked, that seems to be the limited factor to an approval.

Beyond their lead compounds, Seattle Genetics boast four drugs in phase 1 trials, although only two use the antibody-drug conjugate technology. ImmunoGen claims seven phase 1 compounds, with five of those being developed in partnerships with other drugmakers.

Seattle Genetics is nearly three times more expensive than ImmunoGen. That seems completely reasonable considering that Seattle Genetics should have revenue coming in sooner than ImmunoGen. Seattle Genetics also owns full rights to brentuximab vedotin in the U.S. and Canada -- Takeda owns rights in the rest of the world -- while ImmunoGen will only get royalties on the sales of T-DM1.

Given the relative risks and rewards, both appear fairly valued at this point. Valuation at this point isn't that important since both companies will be worth a heck of a lot more if they're able to develop multiple drugs using their technologies.

Buy both?
It's a cop-out answer, but buying both isn't the worst idea. This isn't like buying two competitors, where one's succeeding will cause the other to fail. There are plenty of cancer types with tons of targets for both drugmakers to use their platforms on -- by themselves or through partnerships.

Presumably, one of the technologies will work better and more drugmakers may gravitate toward it, but until there's a clear winner, it might be best to hedge your bet and own both. Please take our Motley Poll, then scroll down to leave a comment on your choice.