Adoptive cell therapy has shown great success in treating liquid tumors. While T cells have been most commonly used for these indications, NK cells are emerging as a promising immune effector cell against solid tumors. Solid tumors present a more heterogeneous population of tumor antigens than liquid tumors, and NK cells, unlike T cells, can target multiple antigens to decrease the likelihood of antigen escape. NK cells can also be transplanted allogeneically with a lower risk of inducing graft-versus-host disease than T cells, which makes off-the-shelf NK cell therapy both simpler than T cell therapy and available to leukopenic patients. However, barriers to treating solid tumors with adoptive cell therapy remain, including the physical barrier of the dense stroma, which blocks immune cell infiltration. This project aims to develop an adoptive cell therapy to overcome this barrier. We tested the ability of cord blood-derived NK cells to kill mesothelioma tumor cell lines H226 and H2452 in the presence of heparanase, a heparan sulfate proteoglycan endoglucuronidase that both degrades the tumor stroma and stimulates NK cell invasion. We also conjugated this heparanase to FDA-approved Prussian blue nanoparticles to determine whether these nanoparticles might increase heparanase accumulation in the tumor and protect it from degradation. We used cytotoxicity assays, transwell invasion assays, and spheroid coculture assays to determine whether heparanase or hep-PBNPs aid NK cell cytotoxicity, invasion, and penetration. Surprisingly, our results indicate that PBNPs themselves may have heparanase activity. However, our invasion and penetration assays must be repeated to fully elucidate the effect of PBNPs and hep-PBNPs on NK cell invasion. Citation Format: Nicole F. Bonan, Eric Yvon, Rohan Fernandes. Enhancing NK cell penetration of the tumor stroma using gene modification and nanomedicine [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO051.