Following the fate of genetically modified T cells in melanoma patients

In an open clinical trial for Stage IV melanoma patients, we are testing a promising new therapy in which the patient’s own T cells are genetically engineered with a T cell receptor (TIL 1383I TCR) targeting the melanoma antigen tyrosinase. Included in the TIL 1383I TCR vector is a nonfunctional CD34 marker that can be readily tracked by flow cytometry. These transgenic T cells are infused into the patient with the goals of killing tumor cells and promoting anti-tumor inflammatory responses. We find that the transgenic T cells persist at low levels for at least twenty months in vivo . Many of the transgenic T cells are activated in the patient, indicating that they are responding to antigen. A subset of activated cells express inhibitory receptors, including PD-1 and CTLA-4. Upon further analysis of patient samples, we found that the percent of transgene-expressing T cells can be increased up to three-fold with either cytokine stimulation and/or CD3/CD28-bead stimulation. When cultured in vitro , transduced T cells lose transgene expression over time, and culturing in the absence of cytokines dramatically increases the rate of transgene expression loss. As seen ex vivo , restimulation of in vitro cultured T cells restores transgene expression. Cells undergoing division express substantially more transgene than resting cells. These data suggest that mitogenic factors causing cell division may promote transgene expression. We next plan to test mitogenic (high dose IL-2, IL-15) and anti-inhibition (PD-1 and CTLA-4 blockade) therapies with T cell transfer utilizing murine mouse models and potentially amend our protocol in the future to reduce the effects of exhaustion and transgene loss on transgenic anti-tumor T cells.