TRLS-02 CEREBROSPINAL FLUID-DERIVED TUMOR REACTIVE T CELLS (CSF-TRT CELLS) FOR THE TREATMENT OF MELANOMA LEPTOMENINGEAL DISEASE.

Abstract BACKGROUND Leptomeningeal disease (LMD), a devastating complication of metastatic cancers, has a median survival of weeks to a few months. LMD incidence is highest in melanoma (5-25%), carrying the worst prognosis. Adoptive cell therapy (ACT) using tumor-infiltrating lymphocytes (TILs) has demonstrated complete and durable responses in patients with advanced metastatic melanoma, including regression of brain metastases. We are optimizing the rapid expansion of CSF-TRT cells as a potential source of T cells for ACT. We aim to evaluate CSF-TRT cells and determine their tumor reactivity ex vivo/in vivo to develop a novel therapeutic approach. METHODS Cells from the CSF from M-LMD patients (n=26; via lumbar puncture/Ommaya) were plated following established TIL culture protocols (high-dose IL-2): 1) OKT3, 2) anti-4-1BB-agonist, 3) IL-7+IL-15+IL-21, 4) anti-CD3/CD28-T-activator, 5) anti-CD3/CD28/CD137-T-activator, 6) anti-CD3/CD28-T-expander. After 4-6 weeks, reactivity was assessed with HLA-matched or autologous tumor cells. We are investigating tumor-based genomic correlates with whole exome sequencing (WES) by interrogating tumor samples initially collected from extracranial disease, and response to therapy in vivo in our LMD mouse model. RESULTS After initial culture in IL-2, 53.4% of samples showed increased cell yield with an average 165.29-fold expansion. PreREP resulted in 37.6% CD8+ T cells. REP was completed with a 96.8% success rate (mean 589.87-fold expansion). Post-REP flow cytometry revealed expansion of CD4+ T cells. Additional cultures produced similar yields with reduced T cell input requirement and demonstrated the potential to enrich for CD8+ T cells. Out of five M-LMD samples tested for reactivity to HLA-matched melanoma cell lines, three produced varying levels of IFN-y. Results from WES and our in vivo experiments are ongoing with pending results. CONCLUSION Results demonstrate successful expansion of T cells ex vivo from CSF in M-LMD, raising the potential to use autologous CSF-derived T cells as therapeutic strategy for patients with LMD.