AUTHOR=Muraro Elena , Furlan Carlo , Avanzo Michele , Martorelli Debora , Comaro Elisa , Rizzo Aurora , Fae’ Damiana A. , Berretta Massimiliano , Militello Loredana , Del Conte Alessandro , Spazzapan Simon , Dolcetti Riccardo , Trovo’ Marco 

TITLE=Local High-Dose Radiotherapy Induces Systemic Immunomodulating Effects of Potential Therapeutic Relevance in Oligometastatic Breast Cancer

JOURNAL=Frontiers in Immunology

VOLUME=Volume 8 - 2017

YEAR=2017

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2017.01476

DOI=10.3389/fimmu.2017.01476

ISSN=1664-3224

ABSTRACT=Local irradiation of cancer through radiotherapy can induce spontaneous regression of non-directly irradiated lesions, suggesting the involvement of systemic anti-tumor immune responses. In oligometastatic Breast Cancer (BC) patients, the use of Stereotactic ablative Radiotherapy (SBRT) favors the local control of treated lesions and may contribute to break local tolerance and release tumor-associated antigens (TAAs), improving host anti-tumor immunity. We performed a detailed immunomonitoring of BC patients undergoing SBRT to verify its ability to “switch on” the anti-tumor immunity both systemically, in peripheral blood, and locally, employing in vitro BC models. 
Twenty-one BC patients with ≤ 6 metastases were treated with 3 daily doses of 10 Gy with SBRT. Blood samples for immune profiling were collected before and after treatment. One month after treatment a third of patients displayed the boosting or even the de novo appearance of polyfunctional CD4+ and CD8+ T cell responses against known BC TAAs (survivin, mammaglobin-A, Her2), through intracellular staining in flow cytometry. Half of patients showed increased numbers of activated NK cells, measured with multispectral flow cytometry, immediately after the first dose of SBRT. Interestingly, high levels of activated NK cells at diagnosis correlated with a longer PFS. BC in vitro models, treated with the same SBRT modality, showed enhanced expression of MHC class-I and class-II, MICA/B, and Fas molecules, and increased release of pro-inflammatory cytokines, such as IL-1 and TNF-. Consistently, we noticed enhanced production of perforin by CD4+ T cells when patients lymphocytes were cultured in the presence of irradiated BC cell line, compared to untreated targets. Besides immunogenic effects, SBRT also enhanced the percentages of circulating regulatory T cells, and increased IDO and PD-L1 expression in BC in vitro models. 
These results suggest that SBRT may boost host anti-tumor immune responses also in an advanced disease setting such as oligometastatic BC, by inducing immunomodulating effects both locally and systemically. However, the concomitant induction of immunosuppressive pathways suggests that a combination with immunotherapy could further enhance the in situ vaccination ability of RT, possibly further improving the curative potential of SBRT in this subset of patients.