Macrophages and Natural Killer cells in the tumor microenvironment: towards novel immunotherapeutic approaches for neuroblastoma patients

Cancer represents one of the main causes of death in both adults and children. Immunotherapy has significantly advanced cancer treatment, improving survival rates and quality of life for a considerable proportion of patients. However, continued research is essential to enhance outcomes for those who remain resistant to current therapies. The tumor microenvironment (TME) plays a pivotal role in disease progression, driving malignant cell growth and contributing to treatment resistance. In neuroblastoma (NB), the most common extracranial solid tumor in childhood, bone marrow (BM) infiltration by tumor cells represents a major clinical challenge. The BM TME might support tumor cell survival and resistance to conventional therapies, emphasizing the need for a deeper understanding of this niche to develop effective treatments. My research focused on the heterogeneity of innate immune cells within the human TME, aiming to propose innovative strategies for enhancing immunotherapeutic efficacy. Specifically, I examined macrophages, which are key players in cancer immune evasion, and natural killer (NK) cells, potent cytotoxic effectors against tumors. I contributed to the study of a novel macrophage population highly represented in the peritoneal fluid of adult cancer patients and BM of NB patients, distinguished by a surface expression of a membrane-bound interleukin-18 (mIL-18). I worked on the characterization of this population in terms of proteomic profile, metabolic activity, and ultrastructural properties. Additionally, I analysed the phenotypic and functional characteristics of NK cells in the BM of NB patients at diagnosis, following autologous hematopoietic stem cell transplantation (aHSCT), and during maintenance therapy. A subset of NK cells with intermediate CD56 expression and low or absent CD16 levels was consistently observed in all BM samples. This subset may impair the effectiveness of current anti-GD2 immunotherapies. In this context, preliminary data are presented showing that tetra-specific engineered molecules engaging NK cells and tumor cells can efficiently activate all BM-NK cell subsets, including the CD16low/neg population. These innovative molecules represent a promising and feasible immunotherapeutic strategy alternative to anti-GD2 IgG antibody. Finally, I introduced preliminary findings on a novel humanized mouse model mimicking the human immune system and providing a valuable platform for testing existing and new immunotherapies.