American universities accept PhD students to work with departments rather than individual faculty. You apply to graduate programs, not individual labs, and if you are accepted, you do two month rotations in 3-4 labs, looking for a mutual fit that will lead to a PhD project.
Here is the link to the Graduate School of Arts and Sciences (GSAS) and programs within the life sciences: https://gsas.harvard.edu/programs-of-study/divisions/harvard-integrated-life-sciences. You can learn more about the graduate programs that Andrew is associated with here:
Systems, Synthetic, and Quantitative Biology Ph.D. program