In the tumor microenvironment there may be present T cells that are recognizing the cancer and trying to fight it. Theconcept behind TILs is, if possible, harvest cells that want to attack the cancer. If you stimulate these cells and grow more outside the body, then re-infuse them to the patient, they may be powerful enough to eliminate the cancer. It is a reasonable concept that is already showing some success. This technique is gaining more attention now because of research published by Dr. Steven Rosenberg in Nature Medicine, June 2018, demonstrating complete regression in an advanced breast cancer patient using this technique. They selected out TILs that reacted against 4 different mutant proteins of the cancer, growing those and infusing them into the patient. This therapy, though promising, still has some drawbacks. One is that you have to deplete the patient’s immune system with chemotherapy; the other is that this technique is extremely expensive. I do not want to downplay too much the benefits of this type of therapy, but it is still my belief that intra-tumoral immunotherapy has better potential, both in terms of success and practicality.

Reference: Jason R. Williams, 15 Oct 2019, The Immunotherapy Revolution: The Best New Hope For Saving Cancer Patients’ Lives, https://williamscancerinstitute.com/the-immunotherapy-revolution