Introduction
Neuroblastoma (NB) is the most common pediatric neuroendocrine tumors with high malignancy and early metastasis. The survival rate of children with high-risk NB is still less than 40% although many therapeutic method including surgery, radiotherapy, chemotherapy and stem cell transplantation have been adopted. So, a new therapeutic method is urgently needed to raise curative effect and reduce the recurrence and metastasis for NB 1, 2. Although immunotherapy in children with solid tumors started lately, many studies have shown that immunotherapy of NB can effectively remove the tumor cells and reduce tumor recurrence and metastasis with higher specificity and less toxicity compared with the traditional therapy 3.
However, in the survival microenvironment of NB, all kinds of complicated immunosuppressive factors impede therapeutic effects and result in immune tolerance, including downregulation of HLA-I antigen and accumulation of various immunosuppressive cells such as myeloid-derived suppressor cell (MDSC), regulatory T cell and tumor associated macrophage, etc 4-8. Currently, new approaches targeting the tumor microenvironment hold promise for further improvements in survival and long-term quality of life9. Furthermore, Jales A found high expression of disialoganglioside in surface of NB resulted in increasing of MDSC agglomeration in tumor microenvironment 10, which triggered tumor immunosuppression and promoted the development and metastasis of tumor. So, in these factors, MDSC may be the main impediment to NB immunotherapy. Some studies described MDSCs caused dissociation between T-cell receptor (TCR) and cluster of differentiation 3ζ (CD3ζ) molecules, disrupting TCR complexes on T cells which result in Ag-specific CD8+T cell tolerance in cancer 11. MDSC down-regulate L-selectin levels on naive T cells, decreasing their ability to home to sites where they would be activated 12. Alizadeh D et al pointed out doxorubicin (DOX) can be used as a potent immunomodulatory agent that selectively impair MDSC-induced immunosuppression in breast cancer13. However, whether these mechanisms can explain the inhibitory role of MDSC in NB immunotherapy is still remain unclear.
Therefore, in the present study, we proposed BALB/c mice as the experimental object, successfully prepared NB Ag-specific CTLs, and grouping mixed cultivation of CTL, neuroblastoma cells, MDSC and DOX. Thereafter, the killing rates of CTL to neuroblastoma cells, secretion of Interleukin-2 (IL-2) and interferon-γ (IFN-γ), levels of cluster of differentiation 3ζ chain (CD3ζ) and L-selectin (CD62L) in CTL were detected and compared in different groups respectively in order to explore mechanism of immune tolerance caused by MDSC in NB and provide the new method to enhance the immune therapeutic effects of NB by using doxorubicin to targeted inhibition of myeloid-derived suppressor cells.