**3. NPs' function in oncolytic virotherapy**

Oncolytic virotherapy infects tumors with viruses, which kills cancer cells. Only attacking cancer cells is a capability of many distinct virus types. Along with this underlying effect, there is also significant inflammation in the cancer microenvironment. The tumor primarily targets the virus with the recruitment of inflammatory cells. The production of cancer-associated antigens as a result of virus-mediated cell lysis, however, may trigger an immune response that targets the tumor, such as by activating macrophages and T cells. The latter produce cytokines that actively stimulate the production of new immune cells as well as cancer cells. Both innate and adaptive immune responses produce an immunological memory that works in conjunction with the oncolytic action of the viruses to prevent cancer from coming back. Oncolytic virotherapy's effectiveness has been evaluated in a large number of preclinical and clinical investigations, mostly in patients with melanoma and brain tumors. Oncolytic virotherapy-induced intratumoral inflammation can be found using MRI. The effectiveness of oncolytic virotherapy may be monitored, virus sites can be indirectly identified and quantified, and new therapeutic virus strains can be improved utilizing 19F MRI [24] and iron oxide NPs [25].

Perfluorocarbon nanoemulsions (PFC) and 19F MRI were used by Weibel and colleagues [26] to establish a longitudinal, noninvasive monitoring of intratumoral inflammation during oncolytic virotherapy. By comparing in vivo and ex vivo 19F/1H MRI with histology, the authors demonstrated the potential of this imaging modality for the localization of the host immune response and for sentinel lymph node detection. Tumor viral colonization significantly altered the 19F signal distribution and intensity in solid tumors as well as in the nearby lymph nodes. Compared to virally infected tumors, which only displayed 19F-positive hot patches along the tumor margin, the mock-infected tumors had a uniform distribution of both the 19F signal and CD68 + -macrophages. The population of CD68+ macrophages displayed a similar pattern of distribution. According to our research, PFC NPs are more likely than intratumoral TAMs to detect circulating immune cells that enter the tumor after viral infection.
