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J Immunother Cancer. 2019 Aug 13;7(1):216. doi: 10.1186/s40425-019-0698-6.

Immune microenvironment modulation unmasks therapeutic benefit of radiotherapy and checkpoint inhibition.

Author information

1
Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, Houston, TX, USA.
2
Interdepartmental Program in Translational Biology and Molecular Medicine, Houston, TX, USA.
3
Department of Pediatrics, Division of Pediatric Hematology/Oncology, Columbia University Irving Medical Center/New York Presbyterian, New York, NY, USA.
4
Department of Medicine, Division of Hematology/Oncology, Columbia University Irving Medical Center/New York Presbyterian, New York, NY, USA.
5
Laboratory of Cellular and Molecular Immunology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.
6
Laboratory of Myeloid Cell Immunology, VIB Center for Inflammation Research, Brussels, Belgium.
7
Department of Oral and Maxillofacial Surgery, School of Dentistry, The University of Texas Health Science Center at Houston, Houston, TX, USA.
8
Department of Surgery, University of South Dakota, Sanford School of Medicine, Vermillion, SD, USA.
9
Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, Houston, TX, USA. Andrew.Sikora@bcm.edu.
10
Department of Cell and Gene Therapy, Baylor College of Medicine, Houston, TX, USA. Andrew.Sikora@bcm.edu.

Abstract

BACKGROUND:

Immune checkpoint inhibitors (ICIs) for solid tumors, including those targeting programmed cell death 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), have shown impressive clinical efficacy, however, most patients do not achieve durable responses. One major therapeutic obstacle is the immunosuppressive tumor immune microenvironment (TIME). Thus, we hypothesized that a strategy combining tumor-directed radiation with TIME immunomodulation could improve ICI response rates in established solid tumors.

METHODS:

Using a syngeneic mouse model of human papillomavirus (HPV)-associated head and neck cancer, mEER, we developed a maximally effective regimen combining PD-1 and CTLA-4 inhibition, tumor-directed radiation, and two existing immunomodulatory drugs: cyclophosphamide (CTX) and a small-molecule inducible nitric oxide synthase (iNOS) inhibitor, L-n6-(1-iminoethyl)-lysine (L-NIL). We compared the effects of the various combinations of this regimen on tumor growth, overall survival, establishment of immunologic memory, and immunologic changes with flow cytometry and quantitative multiplex immunofluorescence.

RESULTS:

We found PD-1 and CTLA-4 blockade, and radiotherapy alone or in combination, incapable of clearing established tumors or reversing the unfavorable balance of effector to suppressor cells in the TIME. However, modulation of the TIME with cyclophosphamide (CTX) and L-NIL in combination with dual checkpoint inhibition and radiation led to rejection of over 70% of established mEER tumors and doubled median survival in the B16 melanoma model. Anti-tumor activity was CD8+ T cell-dependent and led to development of immunologic memory against tumor-associated HPV antigens. Immune profiling revealed that CTX/L-NIL induced remodeling of myeloid cell populations in the TIME and tumor-draining lymph node and drove subsequent activation and intratumoral infiltration of CD8+ effector T cells.

CONCLUSIONS:

Overall, this study demonstrates that modulation of the immunosuppressive TIME is required to unlock the benefits of ICIs and radiotherapy to induce immunologic rejection of treatment-refractory established solid tumors.

KEYWORDS:

Cyclophosphamide (CTX); Cytotoxic T lymphocyte associated antigen-4 (CTLA-4); Head and neck cancer; Human papillomavirus (HPV); Immune checkpoint inhibitors; Immunotherapy; L-n6-(1-iminoethyl)-lysine (L-NIL); Programmed cell death protein-1 (PD-1); Radiotherapy; Tumor immune microenvironment

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