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.