Elective nodal irradiation attenuates the combinatorial efficacy of stereotactic radiation therapy and immunotherapy

Ariel E. Marciscano, Ali Ghasemzadeh, Thomas R. Nirschl, Debebe Theodros, Christina M. Kochel, Brian J. Francica, Yuki Muroyama, Robert A. Anders, Andrew B. Sharabi, Esteban Velarde, Wendy Mao, Kunal R. Chaudhary, Matthew G. Chaimowitz, John Wong, Mark J. Selby, Kent B. Thudium, Alan J. Korman, David Ulmert, Daniel L.J. Thorek, Theodore L. DeWeeseCharles G. Drake

Research output: Contribution to journalArticlepeer-review

195 Scopus citations


Purpose: In the proper context, radiotherapy can promote antitumor immunity. It is unknown if elective nodal irradiation (ENI), a strategy that irradiates tumor-associated draining lymph nodes (DLN), affects adaptive immune responses and combinatorial efficacy of radiotherapy with immune checkpoint blockade (ICB). Experimental Design: We developed a preclinical model to compare stereotactic radiotherapy (Tumor RT) with or without ENI to examine immunologic differences between radiotherapy techniques that spare or irradiate the DLN. Results: Tumor RT was associated with upregulation of an intratumoral T-cell chemoattractant chemokine signature (CXCR3, CCR5-related) that resulted in robust infiltration of antigen-specific CD8+ effector T cells as well as FoxP3+ regulatory T cells (Tregs). The addition of ENI attenuated chemokine expression, restrained immune infiltration, and adversely affected survival when combined with ICB, especially with anti-CLTA4 therapy. The combination of stereotactic radiotherapy and ICB led to long-term survival in a subset of mice and was associated with favorable CD8 effector-to-Treg ratios and increased intratumoral density of antigen-specific CD8+ T cells. Although radiotherapy technique (Tumor RT vs. ENI) affected initial tumor control and survival, the ability to reject tumor upon rechallenge was partially dependent upon the mechanism of action of ICB; as radiotherapy/anti-CTLA4 was superior to radiotherapy/ anti-PD-1. Conclusions: Our results highlight that irradiation of the DLN restrains adaptive immune responses through altered chemokine expression and CD8+ T-cell trafficking. These data have implications for combining radiotherapy and ICB, longterm survival, and induction of immunologic memory. Clinically, the immunomodulatory effect of the radiotherapy strategy should be considered when combining stereotactic radiotherapy with immunotherapy.

Original languageEnglish
Pages (from-to)5058-5071
Number of pages14
JournalClinical Cancer Research
Issue number20
StatePublished - Oct 15 2018


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