Zoriamin Rivera,Carlos Escutia,Mary Beth Madonna,Kajal H. Gupta
Biological Insight and Recent Advancement in the Treatment of Neuroblastoma
high-risk neuroblastoma,immunotherapy,tumor microenvironment
One of the most frequent solid tumors in children is neuroblastoma, which has a variety of clinical behaviors that are mostly influenced by the biology of the tumor. Unique characteristics of neuroblastoma includes its early age of onset, its propensity for spontaneous tumor regression in newborns, and its high prevalence of metastatic disease at diagnosis in individuals older than 1 year of age. Immunotherapeutic techniques have been added to the previously enlisted chemotherapeutic treatments as therapeutic choices. A groundbreaking new treatment for hematological malignancies is adoptive cell therapy, specifically chimeric antigen receptor (CAR) T cell therapy. However, due to the immunosuppressive nature of the tumor microenvironment (TME) of neuroblastoma tumor, this treatment approach faces difficulties. Numerous tumor-associated genes and antigens, including the MYCN proto-oncogene (MYCN) and disialoganglioside (GD2) surface antigen, have been found by the molecular analysis of neuroblastoma cells. The MYCN gene and GD2 are two of the most useful immunotherapy findings for neuroblastoma. The tumor cells devise numerous methods to evade immune identification or modify the activity of immune cells. In addition to addressing the difficulties and potential advancements of immunotherapies for neuroblastoma, this review attempts to identify important immunological actors and biological pathways involved in the dynamic interaction between the TME and immune system.
Biological Insight and Recent Advancement in the Treatment of Neuroblastoma

One of the most frequent solid tumors in children is neuroblastoma, which has a variety of clinical behaviors that are mostly influenced by the biology of the tumor. Unique characteristics of neuroblastoma includes its early age of onset, its propensity for spontaneous tumor regression in newborns, and its high prevalence of metastatic disease at diagnosis in individuals older than 1 year of age. Immunotherapeutic techniques have been added to the previously enlisted chemotherapeutic treatments as therapeutic choices. A groundbreaking new treatment for hematological malignancies is adoptive cell therapy, specifically chimeric antigen receptor (CAR) T cell therapy. However, due to the immunosuppressive nature of the tumor microenvironment (TME) of neuroblastoma tumor, this treatment approach faces difficulties. Numerous tumor-associated genes and antigens, including the MYCN proto-oncogene (MYCN) and disialoganglioside (GD2) surface antigen, have been found by the molecular analysis of neuroblastoma cells. The MYCN gene and GD2 are two of the most useful immunotherapy findings for neuroblastoma. The tumor cells devise numerous methods to evade immune identification or modify the activity of immune cells. In addition to addressing the difficulties and potential advancements of immunotherapies for neuroblastoma, this review attempts to identify important immunological actors and biological pathways involved in the dynamic interaction between the TME and immune system.

Neuroblastoma is a common childhood tumor that mainly affects young children, especially toddlers, and, with a survival rate in high-risk patients of less than 50%, and is responsible for 15% of all childhood cancer deaths [1,2]. Neuroblastoma originates from neural crest tissue and most commonly manifests on the adrenal glands or thoracic, abdominal, or cervical paraspinal ganglia within the first few years of life [3]. The presenting symptoms are dependent on the degree of involvement of the surrounding tissue, with two thirds of patients experiencing metastasis to the regional lymph nodes [4]. Disease progression varies widely between patients, within a range that includes spontaneous recovery without treatment (age < 1 year) to the development of high-risk metastatic tumors with poor prognosis [5]. Disease progression can be characterized by four stages: localized disease without image-defined risk factors (L1); localized disease with image-defined risk factors (L2); metastatic disease (M); and metastatic disease in children <18 mos with disease spread limited to specific sites (MS) [6]. Further, patients are deemed low-risk and high-risk based on multiple factors including age, tumor histology, and other molecular characteristics regarding the tumor microenvironment (TME) [7]. Notably, less than 10% of high-risk neuroblastoma patients have achieved long term cure, mainly due to the way in which high rates of metastasis and minimal residual disease (MRD) in the bone marrow cause late disease relapse [8]. Over the years, significant attempts have been made to identify somatic mutations in human tumors. Cancer treatment that targets tumor-specific mutations holds the promise of accuracy and efficacy while sparing patients from the short- and long-term side effects of chemotherapy and radiotherapy [9]. However, genome-wide searches have been revealing remarkable variations in the occurrence of mutations among tumor types, from melanomas with relatively frequent alterations to pediatric malignancies such as neuroblastoma with rare abnormalities [10]. Chromosomal aberration is frequent in NB, with segmental chromosomal gains or losses and somatic mutations being linked to high-risk disease. Numerical full chromosomal gains are often detected in low-risk tumors. The lack of mutations is a major setback for those exploring tumor-specific immunity and a huge obstacle for those searching for actionable targets from gene alterations [11]. Treatment for high-risk neuroblastoma involves a combination of induction chemotherapy, most commonly doxorubicin, surgical tumor resection, stem cell transplantation, radiotherapy, and, more recently, immunotherapy [7], as depicted in Table 1. The introduction of immunotherapy in neuroblastoma treatment regimens, specifically the anti-disialoganglioside 2 (GD2) antibody dinutuximab, has significantly improved prognosis and patient outcomes [12]. Still, the unique tumor microenvironment poses challenges in the development of novel and effective immunotherapies [13]. The majority of neuroblastoma tumors are immunologically “cold” and devoid of antitumor immune cells and/or they are infiltrated by immune-suppressive cell types, rather than being ‘hot” tumors which are infiltrated by effector immune cells, such as the cytotoxic T cells that can kill tumors cells [14]. As a result, it is difficult to develop therapies that target specific immunologic mechanisms [15]. Dysregulated cellular signaling and metabolism within tumor cells would affect the TME and the response to immunotherapy. However, demonstrating an active adaptive immunity against neuroblastoma has been challenging, particularly in patients at high risk. Given the unusually high tumor size (both primary and metastatic) and its fast multiplication, which might overwhelm a child’s developing immune system, this is not surprising. Insufficient somatic mutations make neuroblastoma weakly immunogenic. A sophisticated immunosuppressive milieu has also been developed by neuroblastoma, which hinders the maturation of functional T cell immunity [16]. This is a complicated and heterogeneous disease, and a variety of factors, including the patient’s age at diagnosis and the disease’s stage, as well as the tumor’s molecular, cellular, and genetic characteristics, determine whether it will spontaneously regress or spread and become resistant to treatment [11]. Despite advances in therapeutic options for patients, there is an urgent need for the further investigation and development of novel immunotherapy treatments that can target the minimally-immunogenic neuroblastoma tumor microenvironment. The aim of this review is to explore advances in the treatment of neuroblastoma, highlight the key immunologic mechanisms that characterize these pediatric tumors, and, finally, draw attention to the role novel immunotherapy treatments can have on improving prognosis for neuroblastoma patients.

The pediatric immune system has a wide variety of efficient mechanisms in place to detect and destroy foreign pathogens and malignancies that pose a threat to the host. Many cancers, including neuroblastoma, have developed unique abilities to suppress and/or evade the host immune system. The type of tumor and the extent of its infiltration into the immune cells has been associated with prognosis [12,30]. High-risk (HR) neuroblastoma tumors are characterized as immunologically “cold” and devoid of antitumor immune cells and/or have been infiltrated by immune-suppressive T-regulatory cell types rather than being “hot” and thus infiltrated by effector immune cells such as cytotoxic T cells and natural killer (NK) cells, which can kill tumors cells, and dendritic cells (DC), which are antigen-presenting and activate T cells [31,32,33]. HR neuroblastoma tumors have less tumor-infiltrating lymphocytes [34] than low-risk (LR) and medium-risk (MR) tumors [9]. These findings are supported by studies that show that HR tumors display lower levels of tumor infiltrating lymphocytes (TIL), NK and DC genetic signatures; higher levels of T-regulatory cells; and worse patient outcomes compared with LR tumors [35]. Importantly, LR patients, characterized by higher TIL density, have demonstrated higher disease-free survival (DFS), event-free survival (EFS) and overall survival (OS) [7]. Neuroblastoma tumors employ a variety of methods in which they suppress TILs and NK and DC cells while increasing the levels of regulatory T cells (Tregs). The immunosuppressive tumor microenvironment (TME) comprises myeloid-derived suppressor cells (MDSCs), stromal cells, tumor-associated macrophages [8] and neuroblastoma cancer cells [36]. MDSCs induce several immunoregulatory mechanisms including disialoganglioside (GD2), transforming growth factor (TGF-B), and the transcriptional coactivator TAZ (transcriptional coactivator with PDZ-binding motif) [1,36]. GD2 suppresses DC antigen presentation and the expression of MHC-I and MHC-II molecules, rendering neuroblastoma tumor cells invisible to cytotoxic CD8+ T lymphocytes, and repressing the ability of CD4+ helper T lymphocytes to mount an immune response via cytokine signaling inhibition [12,36]. Neuroblastoma tumors also express reduced levels of interferon (IFNγ), interleukin (IL-6), IL-8, IL-10, IL-12, and IL-21 [12,36,37]. Table 2 summarizes few of the cytokines and there interactions with the ICIs. Under normal conditions, these cytokines function by amplifying the host’s immune responses against pathogens and cancerous cells [38]. Their reduction in neuroblastoma tumors impedes TIL activation and infiltration, contributing to the low immunogenicity of the neuroblastoma TME [12,36,37]. Treatments that target GD2, such as the anti-GD2 antibody dinutuximab, have been developed and have undergone phase trials in neuroblastoma patients with promising results [7]. This discovery has marked an important breakthrough in pediatric solid tumor research and represents promising potential for further investigation in immunotherapy treatments in oncology. Transforming growth factor beta (TGF-β) is responsible for cell growth, proliferation, differentiation, and apoptosis [37] in various cancers. Although it has been shown that TGF-β plays an inhibitory, anti-tumor role in early cancer stages, recent studies have revealed that TGF-β also displays cancer-promoting properties, including the impairment of NK function, which in turn enhances tumorigenesis and metastasis while inducing immunosuppression and drug resistance [12,37]. This makes TGF-β a promising target in the development of novel immunotherapies. Additionally, TAZ has a major impact on the NB TME’s immunosuppressive environment. Increased TAZ expression induces the expression of immune checkpoint programmed death-1 (PD-1) in both T lymphocytes and NK cells. It has been established that the interaction between programmed death-ligand 1 (PD-L1) and PD1 is linked to decreased lymphocyte proliferation, downregulation of NK function, and the survival of cancer cells [36,39]. Importantly, studies have shown that higher expression of PD-1 and PDL-1 is related to poor prognosis [24]. From a therapeutic point of view, it would be beneficial to silence TAZ expression with Food and Drug Administration-approved drugs that target TAZ signaling [36]. Further, inhibition of the PD-1/PD-L1 immunomodulatory checkpoints molecule (ICMS) mechanism has been used to successfully treat some chemotherapy-resistant cancers in adults [36]. Neuroblastoma cells may not be recognized by CTL due to their poor MHC-I expression, but they should be vulnerable to NK cells as a result [40,41]. NK cells can kill neuroblastoma cells, though in some circumstances pre-activation of isolated NK cells is necessary [42]. Nonetheless, neuroblastoma appears to be shielded from NK-mediated death in patients by additional escape mechanisms that adjust the harmony between activating and inhibitory impulses on NK cells. For instance, the ligands (PVR, nectin-2, MICA, MICB, and ULBPs) for the NK cell activating receptors DNAM-1 and NKG2D are not expressed at high levels in neuroblastoma tumors. Thus, NK cell therapies may prove useful in both stand-alone and combination treatments for NB [43]. As previously mentioned, the combined immunosuppressive mechanisms of neuroblastoma cancer cells create an immunologically “cold” environment devoid of activated T lymphocytes and NK cells, with T-regulatory cells upregulated. Under normal circumstances, NK cells and cytotoxic T cells play a prominent role in preventing tumor progression and metastasis by inducing tumor cell lysis and inflammation [12]. T-regulatory (Tregs) cells function to modulate the immune system by inhibiting other immune effector cells to prevent the over activation of the immune system. The overexpression of Tregs further inhibits the already immunologically inactive TME by suppressing NK and cytotoxic T cell functioning [51,52]. This is especially seen in high-risk neuroblastoma tumors where there are increasingly higher levels of immunosuppressive stromal cancer cells, MDSCs and Tregs [36,52].

Immunotherapy can fall into two different types (Figure 1), one being active immunotherapy and the other being passive. Active immunotherapy relies on directly attacking cancer cells through the stimulation of the immune system [53]. Passive immunotherapy utilizes the acceptance of an organism’s immune system of antibodies, cytokines, and transformed immune cells to act directly on tumor cells [54]. Immunotherapy treatments that can target neuroblastoma cells have been in development over the course of recent decades. Cancer immune surveillance is a mechanism by which immune cells recognize and eliminate tumor cells. Neuroblastomas produce a highly immunosuppressive environment that has an effect on the body as well as locally in the tumor. Neuroblastomas employ indirect immunoregulatory mechanisms by chartering immune suppressive agents to dampen the activity of immune system. TGF, galectin-1, MIF, soluble GD2 (sGD2), and arginase-2 are some of the soluble mediators that neuroblastoma cells produce, and which have the ability to inhibit lymphocyte activation [55]. Neuroblastoma cancer cells also produce several other immunosuppressive molecules such as, sMICA, sB7-H6, sHLA-E, sHLA-G, IL-10 and HMGB1 [56]. Neuroblastoma tumors are intermixed with myeloid and stromal cell populations with defective activating functions or enhanced suppressive functions, which can prevent TIL from effectuating an anti-tumor response. One of the areas in which immunotherapies have become focused is that associated with the passive invocation of the immune system to respond to a tumor in ways that would not occur without outside intervention. These therapies target the activation of immune cells such as T-cells to assist in the aim to provide an anti-tumor effect through the infiltration of the immune cells in the tumor. High-risk neuroblastoma with higher T cell infiltration has been associated with improved survival [57]. Increasing the levels of T cell infiltration into the tumor cells must be a goal for the improvement of patient outcomes. A form of passive treatment for immunotherapy that has shown promising results is the use of monoclonal antibodies (mAbs). One of these immune therapies focuses on the use of mAbs in order to recognize GD2, which is overexpressed relative to a control in neuroblastoma. GD2 is a disialoganglioside that is ubiquitously expressed on the surface of all neuroblastoma cells (source) [29]. This makes GD2 an appealing target due to its specificity for the disease. Adoption of mAbs such as anti-GD2 in both upfront and relapse treatment protocols has dramatically increased survival rates and altered the landscape for children with high-risk neuroblastoma [28]. Even in patients with relapsed disease, dinutuximab may have a treatment value [58]. The success of dinutuximab has sparked investigations into combination therapy with cytotoxic compounds, as well as cellular immunotherapy with (haploidentical) donor NK cells [59,60,61]. Recent technological advancements have made it feasible to analyze the immune response to patient-specific neoantigens that result from tumor-specific mutations. New evidence suggests that clinical immunotherapies may be more effective when these neoantigens are recognized. However, children probably have few, if any, actionable, mutation-generated, immunogenic tumor neoantigens because most juvenile cancers have a very low tumor mutation burden [62,63]. Cancer-testis antigens, as well as other embryonic or differentiation antigens expressed during development and on children’s cancers but not on normal postnatal tissues, may fall under this category [64]. Studies have shown a correlation between the use of these neoantigens and an increase in T cell activity [65]. Recently researchers have identified PHOX2B, a peptide displayed on the surface of neuroblastoma cells, by their MHC molecules [66]. The oncofetal proteins, expressed during embryonic development, though silenced after birth, may be ideal targets for T cell-based immunotherapies in NB due to their restricted expression outside of the tumor. While the comparatively low tumor mutational burden of neuroblastoma may limit neoantigen expression, developmental antigens may be the target of T cell-based immunotherapy. Given the high sensitivity and efficacy of some of these receptors, as has previously been seen with certain modified TCRs, researchers will need to be cautious of the possibility for antigen cross-reactivity. By administering immunomodulating agents that improve the tumor’s immunogenicity, stimulate antigen presentation, increase the patient’s endogenous tumor-reactive T cells, and suppress the tumor’s immunosuppressive microenvironment, it may also be possible to trigger endogenous tumor-reactive T cells in a patient [67,68,69,70]. Tumor-specific neoantigens lead to personalized immunotherapies for patients. Future development of technology involved in the recognition of these neoantigens can help provide an efficient and rapid response. Cytokines released by cancer cells or cells in the tumor microenvironment support angiogenesis, tumor cell migration and metastasis, and the development of an immunosuppressive microenvironment. These tumor-promoting effects of cytokines also apply to NB, as depicted in Table 3. IL-6 and VEGF have been further characterized as cytokines that stimulate tumor growth and metastasis, while others, such as IFN-γ, can exert anti-NB activity by inducing tumor cell apoptosis and by inhibiting angiogenesis (Figure 2 and Table 3).

Numerous cancers exhibit deregulation of the MYC family of oncogenes, which includes c-MYC, MYCN, and MYCL, and this is frequently correlated with a poor outcome [87]. MYCN amplification is a significant driver in neuroblastoma and is indicative of a poor prognosis in early-stage tumors [88]. Numerous studies have investigated the relationship between MYCN amplification and TIL infiltration and composition. Given the tight relationship between MYCN amplification status and tumor stage, it is unclear which factor is responsible for the correlation between MYCN amplification and TIL infiltration [89]. Inverse correlation between MYCN amplification and leukocyte infiltration has been reported, demonstrating lesser infiltration of MYCN-A tumors by CD8+ and CD4+ T cells, NK cells, NKT cells, B cells, macrophages, and monocytes [90,91]. The presence of iNKT cells has also been predicted by MYCN overexpression at the RNA level in combination with low CCL2 expression [74]. It is significant to note that, even within the group of HR-neuroblastomas, T cell and cytotoxic cell signatures, as well as CD8+ infiltration, were lower in MYCN-A than in MYCN-NA tumors, indicating that low TIL infiltration is at least partially linked to MYCN amplification [92]. A possible cause of decreased TILs infiltration in MYCN-A could be reduced lymphocyte attraction and activation or reduced immunogenicity. It has been previously shown that there is greater TIL infiltration and cytotoxicity in tumors with a higher mutational load, with tumor mutational load being a significant determinant of tumor immunogenicity [74]. Neuroblastomata are typically known to have a low mutational burden and therefore low immunogenicity [63,93]. As an outcome, it is possible to infer that MYCN-A neuroblastoma may be less susceptible to T cell immune monitoring on a variety of levels. In recent years, novel approaches in the treatment of neuroblastoma have undergone clinical trials. Recently, multi step treatments have been recommended. These involve treatment with granulocyte-macrophage colony stimulating factor gene (GM-CSF), which enhances the immune activation and enhancement of antibody cell-mediated cytotoxicity (ADCC). Several other clinical trials are in progress in which combinational therapy, including drugs and newly defined immunotherapies, are in progress. Table 4 depicts some of these clinical trials, including those that evaluate CAR T cells that target CD171 [94] in patients with NB, clinical trial using novel combinations like 131-I-MIBG and ch14.18/CHO, targeting GD2, GM-CSF, and GD2-CAR NKT cells are also discussed.

Immune response to a tumor is associated with a positive response to immunotherapies, a type of medical treatment that aids your body in fighting cancer. Numerous cancer types now routinely receive immunotherapy as a treatment, but little is known regarding the question of how juvenile patients’ immune systems react to malignancies and how they compare to those of adults. Although many treatments have been developed that successfully combat solid cancers in adult patients, many of those treatments cannot be applied in a pediatric setting. This is due to important differences between adult and pediatric immune systems that occur as the body grows and develops. Further, neuroblastoma is a cancer that is rarely diagnosed in adults; almost 90% of cases are diagnosed in children younger than age 5 [1]. For this reason, it is difficult to apply successful cancer treatments in adults to a cancer that predominantly affects young children. The explanation behind this overrepresentation in younger age groups is due to the origin of the cancerous cells. Neuroblastoma originates from abnormally proliferating neural crest cells in-utero due to spontaneous genetic mutations [52]. These cells mature and become part of the newborn’s sympathetic nervous system, with the tumor developing most commonly in the adrenal glands within the first few years of life [1,52], thus explaining why adults do not develop this specific cancer. The TME that then thrives in young children can be explained by the relative immaturity of the young immune system. At birth, nearly all T cells in the body are naive T cells that have yet to encounter foreign antigens; there is also a larger quantity of Tregs during this earlier time of life [95]. As the body grows, the immune system matures and gradually develops memory during a life-course of exposure to multiple foreign antigens [52,96]. Additionally, pediatric cancers are known to have a lower mutational burden [97]. Combined with the abundance of Tregs relative to cytotoxic T cells, young children foster a susceptible environment for neuroblastoma tumor cells to thrive within. Importantly, the immunological differences between pediatric and adult patients explain why pediatric tumors are less responsive than adult tumors to immunotherapeutic tumor treatments, particularly treatments that utilize immune checkpoint inhibitors (ICI) such as anti-PD-1/PD-L1 [97]. For example, a study in melanoma patients found that younger patients exhibited higher levels of resistance to anti-PD1 inhibition therapy when compared with adults [98]. The same study also showed younger melanoma patients exhibit higher amounts of Treg genetic signatures and a decreased level of cytotoxic CD8+ T cell populations compared with older patients. These results indicate that modulating the TME in young patients may be key in sensitizing pediatric tumors to PD-1 inhibition and other immune checkpoint inhibitors [98]. Patients are further treated with adoptive chimeric antigen receptor (CAR) T cells, cells that are collected from a donor and engineered to express CAR, which targets a tumor-specific antigen [7,99]. Immune-modulatory drugs, such as lenalidomide, have also been developed; these have a direct or indirect impact on host immune cells [7]. The utilization of cytokines and monoclonal antibody therapies to treat high risk neuroblastomas, in conjunction with consolidation therapy and bone-marrow transplant (BMT), is a novel approach that has improved the long-term survival of neuroblastoma patients [51,100]. The disialoganglioside GD2 is an antigen expressed in different cell types of the nervous system (including neurons, peripheral pain fibers, and melanocytes), and, importantly, is expressed at higher levels in neuroblastoma cells, making it an ideal target for antibody development [51,101]. Anti-GD2 antibodies, such as dinutuximab, have been developed and have undergone phase trials in neuroblastoma patients with promising results [7,51]. Tumor cells are labeled with anti-GD2 antibodies, allowing for their recognition and destruction by immune effector cells. The addition of cytokines to this regimen, such as GM-CSF, has been shown to increase the efficiency of neutrophil-mediated ADCC by lymphocytes in neuroblastoma patients [7,102]. This discovery marked an important breakthrough in pediatric solid tumor research—immunotherapy has given way to a promising era in oncology that will significantly improve the survival and long-term sequelae of neuroblastoma patients.

As previously discussed, the primary challenge in treating high-risk neuroblastoma is the low immunogenicity of neuroblastoma tumors. It has become evident that both the natural immune response and the effectiveness of immunotherapeutic treatments are hindered by the various immunosuppressive characteristics of the neuroblastoma TME. However, the success of dinutuximab is an important example of the promise that immunotherapy has in treating this cancer, as well as other complex childhood cancers [12,103]. Immunotherapies, specifically immune checkpoint inhibitors, may be key in inducing immunologically “hot” TMEs, thereby eliciting T cell reactivity and memory, allowing for more effective and promising anti-cancer treatments. Importantly, utilizing a combination of personalized immunotherapies that target different subjects simultaneously may be required for improved outcomes and prognosis. It has been established that TILs serve an important prognostic role in neuroblastoma [104]. Increased infiltration by T lymphocytes is correlated with the recruitment of DCs and NK cells, which correlates with favorable outcomes for neuroblastoma patients due to their interactions with each other and with other immune cells in the TME [57,105]. Additionally, a key relationship has been identified in which the expression of DC and NK cell signatures (THBD and NCR1) in neuroblastoma samples is significantly correlated with the expression of genes that the encode important immunomodulatory checkpoint molecules (ICMS) PD1 (programmed-death receptor expressed on lymphocytes) and PDL1 (programmed-death ligand expressed on cancer cells) [104]. It has been established that the interaction between PDL1 and PD1 is linked to decreased lymphocyte proliferation, and the survival of cancer cells [104]. Inhibition of this specific ICM mechanism has been used to successfully treat some chemotherapy-resistant cancers in adults [101]. Although research on the inhibition of checkpoint molecules as drug therapy for pediatric solid tumors is limited, recent studies have begun to shed light on the relationship between expression of ICMS and prognosis in neuroblastoma. Mouse models have yielded significant trends relating PDL1 and neuroblastoma. Importantly, expression of PDL1 is correlated with poor prognosis, indicating that inhibition of PDL1 leads to tumor cell death. Further, combining inhibition therapy with other chemotherapeutic agents corresponds to a prolonged response [1]. Although research is limited, these trends lay the foundation for the possibility of ICMS to provide viable treatment regimens in pediatric neuroblastoma. Further investigation is needed to establish a mechanistic link between the DC-NK axis, T lymphocyte infiltration, expression of key genetic signatures, the PDL1-PD1 pathway, and prognosis for neuroblastoma patients. In conclusion, immunotherapy has yielded promising results in the treatment of certain high-risk cancers. In neuroblastoma, however, the low immunogenicity of these tumors combined with the relatively immature immune system makes it challenging to effectively administer treatments with high levels of efficacy. Therefore, future studies must first identify ways in which the immune environment of these pediatric tumors can be characterized and induced to overcome the inhibitory mechanisms at play. Identifying these new therapeutic strategies will therefore allow for the improvement of the long-term efficacy of current treatments and yield novel approaches, thereby improving the long-term prognosis of these young patients.