Pathobiology and Targeting of CD38 in Cutaneous T-Cell Lymphoma

Introduction: Cutaneous T-cell lymphoma (CTCL) is a malignancy of mature CD4+ T-cells that primarily affects the skin. Despite a wide variety of topical and systemic therapies for patients, CTCL remains difficult to treat. Because of its high likelihood of relapse and resistance, new therapeutic approaches are needed. We recently showed strong CD38 expression on neoplastic T-cells from patients with mature T-cell neoplasms, including CTCL. In this study, we evaluated i) the role of CD38 in CTCL pathogenesis ii) strategies to enhance CD38 expression in CTCL and iii) tested efficacy of combination therapy in vivo. Methods: Skin and peripheral blood samples from patients and healthy donors were evaluated for CD38 expression by immunohistochemistry (N=7), microarray (N=82), single-cell RNA-sequencing (N=11), and flow cytometry (N=14). To investigate the role of CD38 in CTCL, we generated CD38 knockout cell lines (H9, HH, and HuT-78) using CRISPR/Cas9-mediated genomic deletion. The CD38 wild-type (CD38 WT) and knockout (CD38 KO) cells were purified, cultured, and used for downstream functional analysis. We evaluated the lines for growth, metabolic capacities (XFe24 Seahorse assay), and engraftment potential in vivo. For in vivo therapeutic studies, we transduced firefly-luciferase gene into H9 CD38 WT and CD38 KO cells, and engrafted them intravenously into immunodeficient NOD Rag -/-γc -/- mice. Mice were treated with anti-CD38 antibody daratumumab or IgG control and disease progression was monitored over time using an in vivo imaging system. For combination studies, we evaluated CD38 expression by flow cytometry in H9 cells treated with increasing doses of HDAC inhibitor, panobinostat (5nM, 10nM, 25nM) for 24, 48, and 72 hours. Next, we tested co-treatment with panobinostat and daratumumab in vivo in mice engrafted with H9 CD38 WT cells with four treatment groups (vehicle/IgG, panobinostat/IgG, vehicle/daratumumab, and panobinostat/daratumumab). Results: Patient skin biopsies showed increased CD38 expression at both protein and RNA levels (log fold change 4.8; p