Adoptively transferred tumor-infiltrating lymphocytes can cure established metastatic tumor in mice and persist long-term in vivo as functional memory T lymphocytes

Tumor infiltrating lymphocytes (TILs) are derived from solid tumors by culturing single cell suspensions of the tumors in low dose interleukin- 2 (IL-2) and intermittent tumor stimulation. We have investigated the survival of TILs after intravenous injection into tumor-bearing mice. Using several murine transplantable sarcomas, we examined the in vivo survival of TILs derived from B6.PL Thy l^a/CY mice (Thy-1.1), which were used to treat established experimental metastases in C57BL/6N (Thy-1.2) mice. Donor and host lymphoid cells could be clearly distinguished by fluorescence-activated cell sorting. We found that TILs or TILs + IL-2 could extend the survival of and, in some instances, cure established experimental hepatic and pulmonary metastases. Donor TILs could be recovered from treated animals at all time points tested; in mice cured of pulmonary metastases donor TILs could be detected as late as 119 days after intravenous injection even in the absence of exogenous IL-2. The administration of a relatively low dose of IL-2 in vivo to mice receiving TILs increased the number of donor TILs recovered from the lungs of cured animals 5-10-fold at all time points but did not change the period of time during which donor TILs could be detected in vivo. Additionally, TILs could be recovered from animals cured of established metastases and such cells retained their antitumor activity in vivo. Finally, when mice cured of pulmonary metastases by TILs or TILs + IL-2 were rechallenged with tumor, donor TILs specifically accumulated at the site of tumor rechallenge up to 4 months after adoptive transfer of TILs. The data demonstrate that adoptively transferred TILs survive for prolonged periods in cured mice and that these cells retain functional memory T cell characteristics. The data are relevant to ongoing trials of TIL therapy for patients with cancer.