Abstract 7051: CCL21 therapy in conjunction with low-dose metronomic cyclophosphamide generates superior responses against neuroblastoma in vivo

Abstract Neuroblastoma is a pediatric malignancy that arises from aberrant neural crest progenitor cell division and proliferation. Relapsed and refractory disease often has a poor prognosis, with the long-term survival rate less than 30%. Neuroblastoma is canonically considered to be an immunologically cold and non-immunogenic tumor type, with dense populations of immune suppressive cell populations that have been shown to impair anti-tumor immunity. Despite the significant clinical response in other tumor types, immune checkpoint inhibitors have only shown limited clinical efficacy in neuroblastoma. Superior treatment modalities are needed to increase overall survival with less severe toxicity in the treatment of neuroblastoma. CCL21 is a chemokine that mediates the migration of immune cell populations such as T cells, NK cells, and dendritic cells, which are key immune cell populations for robust anti-tumor immunity. Prior preclinical studies have highlighted the effectiveness of CCL21 therapy as a potential treatment modality for multiple solid tumor types; however, CCL21’s effectiveness against neuroblastoma is poorly understood. We sought to investigate the effectiveness of intratumoral delivery of CCL21 therapy against neuroblastoma in vivo. We desired to also characterize the immunomodulatory properties of the alkylating agent cyclophosphamide against neuroblastoma both in vitro and in vivo. Cyclophosphamide is part of the standard-of-care treatment protocol for neuroblastoma and has been shown to possess unique immunomodulatory properties at low doses. Herein, we demonstrate that CCL21 therapy in conjunction with metronomic low-dose cyclophosphamide chemotherapy generates superior controlling of neuroblastoma tumor growth in an immunocompetent, syngeneic Neuro2a mouse model. In our in vitro studies, we show that low-dose cyclophosphamide up-regulates cell surface calreticulin expression, as well as cell surface PD-L1 expression on neuroblastoma tumor cells, suggesting that it has potential to facilitate sensitization to anti-PD-L1 checkpoint blockade. In short, this research shows the therapeutic potential of CCL21 and metronomic low-dose cyclophosphamide chemotherapy in the treatment of non-immunogenic tumor types such as neuroblastoma. Furthermore, this research supports the technical feasibility of a novel in situ tumor immunotherapy strategy for neuroblastoma in a preclinical setting. Citation Format: Benjamin Gephart, Gabrielle Brumfield, Donald W. Coulter, Joyce Solheim. CCL21 therapy in conjunction with low-dose metronomic cyclophosphamide generates superior responses against neuroblastoma in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7051.