Preclinical development of tumor-infiltrating lymphocyte (TIL) based adoptive cell transfer (ACT) immunotherapy for patients with sarcoma and the potential benefit of anti-CD137 stimulation.

Abstract

e14545 Background: Tumor specific TILs can be in vitro expanded and have the ability to induce complete and durable tumor regression in some patients following ACT. In this preclinical study we investigated the feasibility of expanding TILs from sarcomas, as well as performing functional in vitro analyses on these. Methods: Fresh tumor samples from sarcoma patients were obtained, and TILs were isolated and expanded in growth medium containing IL-2. In a sub study, we investigated the effect of adding an agonistic CD137 antibody (Urelumab, BMS) and/or an anti-CD3 antibody (OKT3) to the medium. Phenotype and functional analyses was performed using flow cytometry and IFNγ-Elispot. Results: Tumor samples from 30 patients with various types of sarcomas were obtained, and we were able to expand a minimum of 40 million TILs from 27 of these. Mean expansion times were 32 days (14 - 61). 87,7 % (36,4 – 99,1) of these cells were CD3+, and of these, 66,7 % (16,3 – 99,1) were CD4+, and 21,8 % (0,1 – 50,6) were CD8+. A sub study revealed that adding anti-CD137 and/or OKT3 increased total yield of TILs; anti-CD137 skewed the phenotype significantly towards more CD8+ TILs and in some cases NK cells and γδ T cells. TILs from 8 of 17 tested tumor samples from four different sarcoma subtypes (undifferentiated pleomorphic sarcoma, myxofibrosarcoma, myxoid liposarcoma and osteosarcoma) demonstrated reactivity against autologous tumor cells using IFNγ-Elispot (40 – 500 spots per 100.000 TILs). In TILs stimulated with anti-CD137 the reactivity increased. Conclusions: We were able to expand TILs from 90 % of the acquired tumor samples to numbers needed for possible future clinical ACT implementation. Expanded TILs were a mix of CD4+ and CD8+ with CD4+ being predominant. Approximately half of the TIL cultures showed some degree of in vitro tumor reactivity as determined by Elispot. Early analyses suggest that addition of anti-CD137 could influence expansion time, phenotype, and functional capacity of the expanded TILs. Based on these results, we conclude that it is feasible to translate TIL based ACT into clinical testing in sarcoma patients.