caesium-137 and Disease-Models--Animal

Murine bone marrow (BM) chimeras are a versatile and valuable research tool in stem cell and immunology research. Engraftment of donor BM requires myeloablative conditioning of recipients. The most common method used for mice is ionizing radiation, and Cesium-137 gamma irradiators have been preferred. However, radioactive sources are being out-phased worldwide due to safety concerns, and are most commonly replaced by X-ray sources, creating a need to compare these sources regarding efficiency and potential side effects. Prior research has proven both methods capable of efficiently ablating BM cells and splenocytes in mice, but with moderate differences in resultant donor chimerism across tissues. Here, we compared Cesium-137 to 350 keV X-ray irradiation with respect to immune reconstitution, assaying complete, syngeneic BM chimeras and a mixed chimera model of autoimmune disease. Based on dose titration, we find that both gamma and X-ray irradiation can facilitate a near-complete donor chimerism. Mice subjected to 13 Gy Cesium-137 irradiation and reconstituted with syngeneic donor marrow were viable and displayed high donor chimerism, whereas X-ray irradiated mice all succumbed at 13 Gy. However, a similar degree of chimerism as that obtained following 13 Gy gamma irradiation could be achieved by 11 Gy X-ray irradiation, about 85% relative to the gamma dose. In the mixed chimera model of autoimmune disease, we found that a similar autoimmune phenotype could be achieved irrespective of irradiation source used. It is thus possible to compare data generated, regardless of the irradiation source, but every setup and application likely needs individual optimization.

Topics: Animals; Autoimmune Diseases; Bone Marrow; Bone Marrow Cells; Bone Marrow Transplantation; Cesium Radioisotopes; Disease Models, Animal; Female; Gamma Rays; Graft vs Host Disease; Male; Mice; Mice, Inbred C57BL; Radiation Chimera; Whole-Body Irradiation; X-Rays

Monoclonal antibodies (mAbs) targeting negative regulators, or checkpoint molecules (e.g. PD1/PD-L1 & CTLA4), of anti-tumoural T cells have demonstrated clinical efficacy in treating several neoplastic diseases. While many patients enjoy remarkable responses to checkpoint inhibitors, a majority show adverse effects. Understanding how checkpoint inhibitors may augment established chemotherapy or radiotherapy regimens or other immunotherapies like oncolytic viruses may lead to better clinical outcomes measured by improved efficacy with reduced toxicity. Here, we assess how Newcastle disease virus (NDV), an oncolytic virus in clinical testing, may interact with radiotherapy to enhance checkpoint inhibitor blockade.. An immunocompetent B16-F10 murine melanoma model, generally considered to be a poorly immunogenic or "cold" tumour, was utilised to query whether combining localised radiotherapy with NDV may be more effective than either therapy alone in controlling tumours in mice treated with anti-PD1 or anti-CTLA4 monoclonal antibodies. We also investigated whether localised administration of a checkpoint inhibitor through an intratumoural injection of NDV that expresses anti-CTLA4 single-chain variable fragment (scFv) is comparable to systemic administration of anti-CTLA4 when combined with radiation in mediating its anti-tumour efficacy. Response rates were characterised by measuring tumour size over time, observation of complete tumour regression, and overall survival.. Our results show that combining NDV plus radiotherapy with checkpoint inhibitors (PD1 or CTLA4 targeted mAbs) results in significantly better complete tumour regression rates with an abscopal effect in a murine model of melanoma than either single therapy combined with checkpoint inhibitors. Finally, we also show that localised administration of a recombinant NDV expressing anti-CTLA4 plus radiation is comparable to systemic anti-CTLA4 plus radiation in mediating its anti-tumour effect as assayed by survival benefit.. Our results show that oncolytic NDV plus radiotherapy work together with checkpoint inhibitors to enhance tumour clearance of murine melanoma. NDV is an effective radiotherapy dose-sparing and immunotherapeutic agent capable of transgenic, in vivo expression of an anti-CTLA4 targeted scFv antibody with the potential to spare systemic exposure.. The National Institutes of Health grant HHSN272201400008C supported the work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Topics: Animals; Cell Line, Tumor; Cesium Radioisotopes; CTLA-4 Antigen; Disease Models, Animal; Female; Immunity; Immunotherapy; Melanoma, Experimental; Mice, Inbred C57BL; Newcastle disease virus; Oncolytic Virotherapy; Oncolytic Viruses; Programmed Cell Death 1 Receptor