[The following isn't an answer to your question of which specific companies to invest in with impact in mind; instead, it’s about general pros, cons, and strategies for impact investing. Hopefully that's somewhat useful, and hopefully someone else will also jump in to more directly answer your question.]

The EA researchers John Halstead and Hauke Hillebrandt looked into the pros and cons of impact investing. Here's an EA Forum post from Hillebrandt, which also links to the report they wrote together: Impact investing is only a good idea in specific circumstances. 

Hillebrandt writes in that post: "We find that effective impact investing is very hard and, to maximize social impact, it is usually much more effective to donate." (Though note the "usually"; from memory, there were various caveats/nuances/uncertainties.)

And here's a talk from Halstead: Is impact investing impactful?

Other have also discussed the topic on the Forum, e.g. here. You might find other relevant posts by searching "impact investing" and/or looking at the Investing tag.

Anything in the genomic medicine space, that is to say, the ARKG etf.

A lot of new opportunities opened up in this field recently due to crispr, and they haven't been realized yet, and the stocks are generally too low due to, I dunno, Theranos maybe. Some of the treatments are really amazing. Cures for previously incurable genetic diseases, better cancer treatments.

We should pause, though, and ask whether accelerating the realization of these technologies will accelerate the realization of extinctive biological weapons. I have not paused long enough over this question, myself. I can't really argue that the benefits outweigh the costs.