Abstract PL01-03: TIL therapy in the era of immune checkpoint blockade
Authors: Haanen John B.A.G. , Berg Joost Van den , Zon Maaike Van , Bakker Noor , Geukes Marnix , Thienen Hans Van , Blank Christian , Kvistborg Pia , Schumacher Ton 
Published: May 2016

Abstract
Infusion of tumor-infiltrating T-lymphocytes was developed as treatment for metastatic melanoma by Dr. S. Rosenberg (Surgery Branch, NIH, Bethesda, MD, USA) in the late 90's of the past century. This therapy was based on the finding that melanomas oftentimes have infiltrates of CD8 T cells that show recognition of melanoma cells. Many tumor antigens have been characterized for which specific T cells can be found within the tumor or in peripheral blood. As tumors may use mechanisms to induce local T cell unresponsiveness, isolation of TILs and in vitro activation and expansion was shown to overcome this anergic state both in preclinical models and in clinical trials. In order for the TILs to survive, persist, and be cytolytic after infusion, culture time should be as short as possible (to obtain cells with a less terminally differentiated phenotype), patients should receive lymphodepleting treatment (chemotherapy +/- TBI) prior to infusion and interleukin-2 as a survival factor post infusion. Up to date several hundreds of metastatic melanoma patients have been treated with TIL therapy in centers within the US, Europe and Israel. Objective response rates vary between 38 and 72% depending on the phase I/II trial with 10-20% of patients acquiring a CR, which were most often very durable. Many of these oftentimes heavily pretreated patients have benefitted from TIL therapy.
As melanomas are heavily mutated cancers, the idea that T cells may react to epitopes derived from mutated proteins could be investigated with new technologies developed at NKI. Using whole exome sequencing, the total mutational burden could be measured for each melanoma. Only those mutations present in expressed genes were used for epitope prediction for every MHC class I molecule of the patient using validated prediction algorithms. Filters were used to select those epitopes with high enough binding affinity for MHC that were subsequently synthesized for production of peptide-MHC multimers that could be used to screen for neo-antigen specific T cells among peripheral blood T- cells or TIL using a multiplex flow cytometric technology. Together with the NCI, using a somewhat different approach, we were able to show that in the vast majority of melanoma TIL, CD8 T cells specific for epitopes resulting from UV light induced DNA damage can be found, sometimes in high frequencies (up to 25-30%), strongly suggesting that neo-antigen-specific T cells play an important role in the success of TIL therapy and possibly other immunotherapies, including checkpoint inhibitors. So far TIL therapy has been mostly used in metastatic melanoma patients pretreated with BRAF inhibitors, anti-CTLA4, high-dose IL-2, and demonstrated activity irrespective of these treatments, although isolation of TIL appeared less successful in patients progressing upon BRAFi. Early results in patients pretreated with PD1 blocking antibodies are promising as well, although the objective response rate is still unknown.
Next to metastatic melanoma, TIL can be grown from other cancers as well and promising results have been obtained in patients with cervical cancer and in a patient with cholangiocarcinoma. Trials are planned for patients with epithelial ovarian cancer as well.
Citation Format: John B.A.G. Haanen, Joost Van den Berg, Maaike Van Zon, Noor Bakker, Marnix Geukes, Hans Van Thienen, Christian Blank, Pia Kvistborg, Ton Schumacher. TIL therapy in the era of immune checkpoint blockade. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr PL01-03.