It's "Marketplaces Week" for us at a16z, thanks to our consumer team releasing a new index of the next industry-defining marketplaces, the Marketplace 100.   But what happens as such marketplaces and other platforms evolve over time, as do their users? This episode is a rerun of a popular conversation from a couple years ago -- featuring general partners Andrew Chen and Jeff Jordan (in conversation with Sonal Chokshi) -- on what comes after user acquisition: retention.  It's all about engagement. So what are the key metrics? And if different kinds of users join a  platform over time -- what does that mean for engagement, and where do cohort analyses come in?

with @OzAzamTmunity1, @JorgeCondeBio, and @omnivorousread CAR T therapy, the groundbreaking new medicines that uses engineered T-cells to attack cancer, has been so effective in childhood leukemias that we believe it may actually be a potential cure. But this isn't just one new medicine, it's an entirely new therapeutic tool—and a total paradigm shift from most traditional medicines we've seen before. Tmunity CEO Usman "Oz" Azam was previously the head of Cell and Gene Therapies at Novartis, in many ways the first CAR T company and the team brought us blood cancer CAR T-cell therapy Kymriah—the first cell-based gene therapy to be approved in the US. In this conversation, Azam discusses with a16z's general partner Jorge Conde and Hanne Tidnam what CAR T therapy really is and how it all works. The conversation begins with the “patient and cell journey” of this treatment and how this medicine is developed, manufactured, delivered to patients; why exactly it's so different traditional medicines; what it will take to make these new medicines work on more kinds of cancer, scale to more patients, and cost less; and finally, what company building lessons can be learned from building the first CAR T company of its kind from the ground up. This episode was recorded at the annual a16z Summit.