Radiotherapy-activated NBTXR3 nanoparticles modulate cancer cell immunogenicity and TCR repertoire

Radiotherapy is a powerful and widely used technique for the treatment of solid tumors. Beyond its ability to destroy tumor cells, it has been demonstrated that radiotherapy can stimulate the anti-tumor immune response. Unfortunately, this effect is mainly restricted to the irradiated lesion, as tumor control outside the treated field (called the 'abscopal effect') is rarely obtained. In addition, many pro-tumoral factors prevent this anti-tumor immune response from being sustained and efficient. We previously reported that radiotherapy-activated NBTXR3 produced a significant CD8-dependent abscopal effect in immunocompetent mice bearing CT26.WT tumors, while radiotherapy failed to generate such a response. To identify the mechanisms that may explain this response, we evaluated the capacity of radiotherapy-activated NBTXR3 to modulate the immunogenicity of tumor cells by analysis of immunogenic cell death biomarkers and immunopeptidome sequencing. In vivo, we analyzed treated tumors for CD4+, CD8 + and CD68 + cell infiltrates by immunohistochemistry and digital pathology and sequenced the T cell receptor (TCR) repertoire in both treated and untreated distant tumors. We showed that NBTXR3 activated by radiotherapy both increased immunogenic cell death biomarkers and modulated the immunopeptidome profile of CT26.WT cells. Immunohistochemistry analysis of treated tumors revealed a significant increase in CD4+, CD8 + and CD68 + cell infiltrates for NBTXR3 activated by radiotherapy group, compared to radiotherapy. We also measured significant modifications in TCR repertoire diversity in the radiotherapy-activated NBTXR3 group, both in treated and distant untreated tumors, compared to radiotherapy alone. These results indicate that radiotherapy-activated NBTXR3 can act as an effective immunomodulator, modifying tumor cell immunogenicity and impacting the lymphocyte population.