Stem cell properties of GT101, a tumor infiltrating lymphocyte (TIL) product with multiple indications.

e14506 Background: Tumor infiltrating lymphocyte (TIL) is a kind of adoptive T cell therapy that has demonstrated clinical benefits in several types of solid tumors. GT101 is an autologous TIL therapy for the treatment of multiple solid tumors. Previous studies showed that in vitro expansion resulted in over 80% terminally differentiated effector T cells in the final TIL products, which may show good cytotoxicity but weak capability of persistence and proliferation in vivo. Herein we present phenotype and function characterization of our TIL product GT101 with a focus on its stemness attributes. Methods: We have produced more than 30 batches of GT101 TIL samples from 10 different cancer indications and analyzed their proliferation, cytokine production and phenotype at preREP and/or REP stage. Results: GT101 products keep a consistent T cell phenotype and good proliferation capacity, and are capable of secreting large amounts of cytokines after stimulation by anti-CD3/CD28 antibody, reflecting its good functionality. The residues in the final products, such as feeder cells and tumor cells, are below the detection limit. In contrast to equivalent TIL products previously reported across the world, we find that GT101 features a manufacturing process that preserves the stem cell characteristics of T cells. Analysis of all the 30 GT101 TIL samples demonstrates that the average percentage of central memory T cells (Tcm) and naïve T cells is 40-50% and 10-20% respectively in both CD8 + and CD4 + populations at the end of preREP stage. Meanwhile, CD8 + TCF1 + cells are close to 50%, mainly in the form of PD-1 - . In the phase of REP, the stemness of T cell is still well maintained—the average proportion of both Tcm and naïve T cells only decreases by about 5%, and that of CD8 + TCF1 + cells down by about 10%. Conclusions: In general, GT101 demonstrates good stemness with a higher percentage of Tcm and TCF1 + than equivalent products previously reported across the world, suggesting better performance in persistence and proliferation in clinic.