Abstract 4913: Engineering dendritic cell-based vaccines as targeted immunotherapy against medulloblastoma, neuroblastoma, and Ewing sarcoma
Authors: Zahler Stacey , Luo Wen , Ayello Janet , Cairo Mitchell S. 
Published: July 2016

Medulloblastoma (MB), Neuroblastoma (NB), and Ewing Sarcoma (ES) are malignant pediatric neuroectodermal solid tumors. Current treatments are highly intensive but toxic and subsets of patients such as metastatic and/or relapsed patients have a dismal outcome (Esiashvili N et al, 2008; Leavey PJ et al, 2008; Bernstein ML et al, 2006). Targeted treatments with reduced side effects are urgently needed. Immunotherapy is a promising approach to inducing tumor control. Among various strategies of immunotherapy, dendritic cell-based vaccines have shown promising preliminary activity in the setting of minimal residual disease (Lasky JL et al, 2013; Westers TM et al, 2011; Shumway NM et al, 2009). To evaluate the feasibility of dendritic cell based vaccine in pediatric solid tumors, we incubated HLA A02+ human peripheral blood mononuclear cells (PBMC) with monocyte-derived autologous dendritic cells (DCs) pulsed with or without whole tumor cell lysates in interferon-ã (INFã) ELISPOT assays. We demonstrated that the number of spots detected in test wells (Daoy: 141.6±3, SKPNDW: 233.3±33.5, EWS502: 157.6±22.3, TC71: 249.6±24.5) is significantly (p&lt;0.05) greater than control wells (PBS: 42±2), suggesting successful tumor antigen presenting of DCs and specific immune response from PBMC. To test T-cell responses, we isolated CD8+ T cells from PBMC and incubated them with tumor cell lysate pulsed mature DCs. Interestingly, we observed a similar trend in activation but fewer number of spots (PBS: 27±9, Daoy: 52.6±14.5, SKPNDW: 76.6±30.1, EWS502: 44.6±8.3, TC71: 68.6±19) in ELISPOT assays. Further analysis using HLA-DR blocking antibody (L243) showed that CD4+ T cell function is required for the responsive activity of PBMC because the number of spots was significantly (p = 0.03) reduced in test wells with the antibody (45.5±4.9) compared to that in control wells (352.5±17.6). These data indicate that both CD4+ and CD8+ T cells are required for the T-cell immune response to tumor antigens in whole tumor cell lysate presented by DCs. We next tested in vitro cytotoxic activity of DC-activated PBMCs to MB, NB, and ES cells by DELFIA cytotoxicity assay. PBMCs incubated with tumor lysate pulsed DCs induced significantly increased cell lysis compared to control PBMCs in Daoy (78±4.8% vs. 46.5±3.5% at E:T = 10:1, p = 0.019), SKPNDW (80±14.1% vs. 15±2.3% at E:T = 10:1, p = 0.016), and TC71 (82.5±3.5% vs. 39.5±13.4% at E:T = 20:1, p = 0.036). Taken together, our proof-of-principle studies demonstrated the efficacy of DC-based vaccines using whole tumor cell lysate as antigens in pediatric neuroectodermal solid tumors. Further investigation in the preclinical setting in a xenograft NSG model is warranted.

Citation Format: Stacey Zahler, Wen Luo, Janet Ayello, Mitchell S. Cairo. Engineering dendritic cell-based vaccines as targeted immunotherapy against medulloblastoma, neuroblastoma, and Ewing sarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4913.