Adoptive cell transfer involves removing immune cells from the pt, potentially altering them to target a given cancer, growing them ex vivo and then re-infusing them. There are 3 main sources of tumor-specific immune cells: tumor-infiltrating lymphocytes found in surgical tumor specimens which can be cultured, antigen-specific immune cells that are created through repeated exposure to the antigen of interest or antigen-specific T cells that can be created artificially using genetic engineering.