Radiation induces iatrogenic immunosuppression by indirectly affecting hematopoiesis in bone marrow
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Vaishali Kapoor1, Andrea Collins1, Kaylan Griffith1, Subhajit Ghosh1, Nathan Wong1, Xiaowei Wang1, Grant A. Challen3, Joseph Krambs5, Dan Link3,4, Dennis E. Hallahan1,2 and Dinesh Thotala1,2
1 Department of Radiation Oncology, St. Louis School of Medicine, Washington University, St. Louis, Missouri, USA
2 Siteman Cancer Center, St. Louis School of Medicine, Washington University, St. Louis, Missouri, USA
3 Department of Medicine, St. Louis School of Medicine, Washington University, St. Louis, Missouri, USA
4 Department of Pathology & Immunology, St. Louis School of Medicine, Washington University, St. Louis, Missouri, USA
5 Medical Scientist Training Program, St. Louis School of Medicine, Washington University, St. Louis, Missouri, USA
Keywords: radiation; lymphopenia; mass cytometry RNA sequencing
Received: October 14, 2019 Accepted: April 03, 2020 Published: May 12, 2020
The immune system plays a vital role in cancer therapy, especially with the advent of immunotherapy. Radiation therapy induces iatrogenic immunosuppression referred to as radiation-induced lymphopenia (RIL). RIL correlates with significant decreases in the overall survival of cancer patients. Although the etiology and severity of lymphopenia are known, the mechanism(s) of RIL are largely unknown. We found that irradiation not only had direct effects on circulating lymphocytes but also had indirect effects on the spleen, thymus, and bone marrow. We found that irradiated cells traffic to the bone marrow and bring about the reduction of hematopoietic stem cells (HSC) and progenitor cells. Using mass cytometry analysis (CyTOF) of the bone marrow, we found reduced expression of CD11a, which is required for T cell proliferation and maturation. RNA Sequencing and gene set enrichment analysis of the bone marrow cells following irradiation showed down-regulation of genes involved in hematopoiesis. Identification of CD11a and hematopoietic genes involved in iatrogenic immune suppression can help identify mechanisms of RIL.
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