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Abstract

Clinical outcomes of adoptive cell therapy (ACT) are less favorable in solid tumors compared to those in hematological malignancies due to the higher complexity and immunosuppressive characteristics of their tumor microenvironment (TME). The extracellular matrix (ECM) barrier represents a significant limitation for ACT success, since targeting and killing of cancer cells by the immune system requires immune cell extravasation, infiltration and progression through the ECM. Heparan sulfate proteoglycans (HSPGs) are one of the major ECM components and Heparanase (HPSE) is the only known endoglycosidase which cleaves the side chains of HSPGs, therefore participating in the ECM remodeling. HPSE is highly expressed by immune cells, and it has been described to facilitate the migration and infiltration of macrophages, T cells and dendritic cells. This suggests that HPSE plays an important role in immune cell migration and infiltration through tissues. Nevertheless, tumor cells also express high HPSE levels and require its activity for all stages of tumor progression. It seems that HPSE has a dual role in cancer progression and, while being necessary for immune cells infiltration, an increase in HPSE in the tumor ECM would be detrimental. While T cells have been the primary focus of ACT, Natural killer (NK) cells are emerging as a promising alternative due to their antigen independent killing capacity, low toxicity risk and “off-the-shelf” manufacturing feasibility. However, the ECM limitation for infiltration still poses as an issue to be solved. The main goal of my thesis was to investigate the effects of the expression of a constitutively active, membrane-bound HPSE (GS3TM) on the ability of human NK cells to infiltrate tumors, using the NK-92CD3/CD8 cells as a model. NK-92CD3/CD8/GS3TM cells displayed significantly enhanced infiltration capability into tumor spheroids, as well as into xenograft tumors in immunodeficient mice. This enhanced infiltration was translated into significant tumor growth suppression without detectable adverse effects. Moreover, I assessed the expression of HPSE upon NK cell activation and the role of this enzyme in NK infiltration capacity. My results could show that HPSE surface expression decreases upon activation of primary human NK cells and upon co-culture of NK-92CD3/CD8 cells with target cells. Moreover, HPSE-KO (knockout) NK cells presented a significant lower capacity to infiltrate tumor spheroids, suggesting that HPSE is required for NK cell infiltration capacity. These findings suggest that HPSE is important for NK cell infiltration and that the constitutive expression of a surface-bound active HSPE on immune effector cells enhances their capability to access and eliminate tumor cells while limiting the supply of free HPSE in the TME. This approach opens new possibilities for improving adoptive immune treatments using NK cells.