In vivo proliferation of adoptively transferred tumor-infiltrating lymphocytes in mice

The adoptive transfer of tumor-infiltrating lymphocytes (TILs) in conjunction with interleukin-2 (IL-2) administration can mediate a reduction in established pulmonary and hepatic metastases of a variety of murine tumors as well as in patients with metastatic melanoma. To characterize further the fate of adoptively transferred TILs, the uptake of the thymidine analog 5-[¹²⁵I]iodo-2-deoxyuridine ([¹²⁵I]UdR) into the DNA of dividing cells was used to study the in vivo proliferation and migration patterns of transferred TILs in C57BL/6N mice. Animals received 500 rad of total body irradiation prior to cell transfer to separate incorporation of radiolabel into endogenous lymphoid cells from that into transferred TILs. Mice were subsequently treated with i.v. injections of TILs or no cells followed by i.p. injections of Hanks' balanced salt solution or IL-2. At various time points, mice received [¹²⁵I]UdR, and 20 h later tissues were removed and counted on a gamma analyzer. A proliferation index (PI) was calculated by dividing the mean cpm of organs of experimentally treated mice by the mean cpm of organs of control mice. Animals receiving TILs alone demonstrated small increases in [¹²⁵1]UdR in the lungs, liver, and spleen of saline-treated controls (PI = 1.4, 1.6, and 1.7, respectively, on day 4), while animals treated with 50,000 U of IL-2 alone showed greater increases in the lungs, liver, kidneys, and spleen (PI = 3.9, 6.1, 3.3, and 15.8). Mice receiving TILs plus IL-2 demonstrated the highest levels of radiolabel incorporation in the same organs (PI = 10.5, 19.4, 10.2, and 22.4). Over a period of 10 days, TIL plus IL-2 treated animals continued to incorporate significantly greater amounts of [¹²⁵I]UdR for as long as high-dose IL-2 was administered. Animals treated with TILs demonstrated increased incorporation of radiolabel with increasing doses of IL-2. Injection of irradiated TILs did not result in an increased uptake of [¹²⁵1]UdR into these tissues, thus confirming that TIL proliferation is responsible for the radiolabel uptake in animals receiving TILs alone or TILs plus IL-2. Additionally, fluorescein-labeled anti-Thy-1.1 anti-body identified proliferating TILs derived from congenic B6.PL Thy l^a/Cy (Thy-1.1) animals in the lungs, spleen, and liver of recipient C57BL/6N (Thy 1.2) mice. In summary, we have demonstrated that adoptively transferred TILs distribute widely after i.v. injection and can proliferate in various tissues especially under the influence of exogenous IL-2.