445 Analysis and feasibility of cerebrospinal fluid (CSF) lymphocyte expansion from patients with melanoma leptomeningeal disease (M-LMD)

<h3>Background</h3> Leptomeningeal disease (LMD), the spread of tumor cells to the subarachnoid space and CSF, is a devastating, fatal complication of metastatic cancers. LMD has a dismal prognosis with patients living 4–8 weeks after diagnosis. The incidence of LMD has been increasing with improved patient survival with advances in immunocellular and targeted therapies as well as with enhanced diagnostic studies. There are currently no FDA-approved treatments for this disease. Adoptive cell therapy (ACT) with tumor-infiltrating lymphocytes (TIL) was recently approved for melanoma patients. Here we explore the feasibility of utilizing CSF as a novel source of tumor reactive T cells to develop a similar modality and offer hope to patients with M-LMD. <h3>Methods</h3> CSF was collected from 19 patients with M-LMD via lumbar puncture or Ommaya reservoir tap. T cells were cultured directly from CSF in the following conditions: 1) 6000 IU/mL of IL-2 only, 2) IL-2 + OKT3, 3) IL-2 + anti-4-1BB agonistic antibody, 4) IL-2 + IL-7/15/21, 5) IL-2 + CD3/CD28 T-activator dynabeads, 6) IL-2 + CD3/CD28/CD137 dynabeads, and 7) IL-2 + CD3/CD28 T-expander dynabeads. Cultures were evaluated after 4–8 weeks, and T cells were further propagated via the rapid expansion protocol (REP). The final T cell product was phenotyped by flow cytometry and T cell reactivity was determined via co-culture with melanoma tumor cells. <h3>Results</h3> An average of 6.1 mL of CSF was collected from patients with LMD, resulting in an average yield of 1.017e4 viable cells available for expansion (range: 5e2–2.4e6). After initial culture in IL-2, 60% demonstrated an increased cell yield, with an average of 211-fold expansion (range 2.4–3512.6). Phenotypic analysis of preREP TILs revealed approximately 55.6% of the samples were predominantly CD8+ T cells. Growth kinetics were accelerated with the addition of dynabeads and maintained a predominantly CD8+ population. Twenty-nine samples underwent a REP, with an average of 339.1-fold expansion (range 4.0–1202.4). PostREP phenotypic analysis revealed heterogeneity, with both CD4+ and CD8+ dominant populations. CSF T cell reactivity to HLA-matched tumor was detected for two samples and varied by expansion condition. An autologous tumor cell line was established from the CSF of one patient and reactivity results are currently pending. <h3>Conclusions</h3> Expansion of T cells from the CSF of M-LMD is feasible. Ongoing experiments seek to optimize expansion of reactive CD8+ T cells. Long term, we hope to apply our findings to a possible model in order to see if our research can translate to applied studies. <h3>Ethics Approval</h3> This study was approved by the Ethics Committee and Internal Review Board (protocol MCC 19332). Tissue collected for analyses was performed after patient‘s approval and consent. <h3>Consent</h3> This study does not require consent to participate or publish the study.