Not quite transmogrification
After there were enough of Matthews’ cells, they put the T cells through transduction. Using a neutered virus as a carrier, they injected a gene into the white blood cells.
This gene rewrites part of the genetic code of the cells, effectively reprogramming them into seeking out a different target. This target is CD19, a protein, which makes up part of the cellular surface of the lymphoma.
Now they had a squad of trained killers. But they needed an army. So the modified T cells went back into the incubator until their number rose to two million.
A battery of tests, sort of like boot camp, ensured that the T cells were healthy and in fighting shape. Then they were sent back to Boston to be launched into the battlefield.