At the Raritan, New Jersey, facility where Legend Biotech and Johnson & Johnson manufacture Carvykti, a multiple myeloma patient named Colleen met some of the employees who had worked on the CAR-T cell therapy she received while battling for her life.

It was a meeting that showcased the deep personal connection patients have to CAR-T therapies, Legend said. And for the company, it also laid bare the therapy’s unique operating model: A commercial dose is not just tied to a product. It is tied to one patient.

Carvykti’s commercial footprint is expanding quickly. First approved in 2022, the treatment notched $657 million in second-quarter net trade sales, 50% above the year-earlier period, and is available at 348 sites across 19 markets.

But years into Carvykti’s launch, the fundamental constraint has not changed: Growth still means adding thousands of individualized manufacturing runs rather than simply producing larger batches.

As demand grows, the manufacturing challenge is not simply making a bigger batch. Patient cells, manufacturing slots, quality testing, release dates, logistics and treatment center schedules all have to move together.