What happened

ImmunoGen (NASDAQ:IMGN) ended Monday up 12.5%, after presenting phase 1 data for its anti-CD33 antibody-drug conjugate IMGN779 at the European Hematology Association on Saturday.

So what

Like ImmunoGen's other antibody-drug conjugates, IMGN779 delivers a toxic drug payload using an antibody to tumor cells -- in this case, to acute myeloid leukemia cells that express CD33. IMGN779 uses ImmunoGen's novel indolino-benzodiazepine payload DGN462 that damages DNA by alkylating it without cross-linking, helping to kill tumor cells while causing less damage to the normal progenitor cells that give rise to healthy blood cells.

As with most phase 1 trials, the main purpose of the study was to measure safety at increasing doses of the drug. As of the data cutoff, ImmunoGen had gotten through seven increasing doses, with no dose limiting toxicities. At dose levels 6 and 7, the drug appears to be staying in the bloodstream, with CD33 becoming saturated.

Most importantly for IMGN779's potential, ImmunoGen observed initial anti-leukemia activity at dose levels 6 and 7 in patients who had failed intensive front-line therapy.

Stained blood cells seen under a microscope

Image source: Getty Images.

Now what

ImmunoGen continues to try higher doses of IMGN779 to determine the best dose to take into phase 2 development.

While the phase 1 data is trending in the right direction, it's debatable whether this preliminary data justifies a double-digit increase in the biotech's valuation. Of course, it's better than ImmunoGen's going up for no apparent reason.

Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends ImmunoGen. The Motley Fool has a disclosure policy.