Successful adoptive cellular immunotherapy is dependent on induction of a host immune response triggered by cytokine (IFN-γ and granulocyte/macrophage colony-stimulating factor) producing donor tumor- infiltrating lymphocytes

Adoptive immunotherapy with tumor-infiltrating lymphocytes (TIL) and systemic low dose rIL-2 effectively eradicates pulmonary metastases of the murine MCA-105 sarcoma. We described earlier that host CD8⁺ T cells are critical for tumor eradication and that successful treatment is associated with production of high levels of IFN-γ and granulocyte/macrophage (GM)-CSF by donor TIL in vitro. Here, we propose the mechanism through which adoptively transferred Thy-1.1⁺ TIL induce a host antitumor response in congenic Thy-1.2⁺ tumor-bearing mice. Donor Thy-1.1⁺ TIL were detected at the tumor site 12 h after transfer. These Thy-1.1⁺ cells produced IFN-γ and GM-CSF in situ. The percentage of Thy-1.1⁺ TIL at the tumor site increased up to 16.4 ± 4.9% 24 h after transfer but decreased to undetectable levels thereafter. In contrast, the percentages of host cells producing IFN-γ and GM-CSF continued to increase at the tumor site. These increases were significantly higher in TIL + rIL-2-treated mice compared with untreated mice and rIL-2-treated mice 48 h after TIL transfer. The appearance of IFN-γ⁺ and GM-CSF⁺ cells was followed by a large influx of host CD4⁺, CD8⁺, and Thy-1.2⁺ TIL and eventually by tumor eradication. This response was tumor specific since TIL obtained from MCA-205 did not induce high levels of IFN- γ and GM-CSF and did not induce tumor eradication of MCA-105 tumor. Coinjection of Thy-1.1⁺ TIL and anti-IFN-γ or anti-GM-CSF mAb significantly inhibited antitumor efficacy of the TIL + rIL-2 treatment. We conclude that successful adoptive immunotherapy in this model is mediated through cytokine production by adoptively transferred TIL that induce a host T cell-dependent antitumor response.