title: Tumor radiation therapy creates therapeutic vaccine responses to the colorectal cancer antigen GUCY2C.
abstract: OBJECTIVE
  Radiation therapy (RT) is thought to produce clinical responses in cancer patients, not only through direct toxicity to cancer cells and supporting tumor stroma cells, but also through activation of immunologic effectors. More recently, RT has potentiated the local and systemic effects of cancer immunotherapy (IT). However, combination regimens that maximize immunologic and clinical efficacy remain undefined.
  
  
  METHODS
  We evaluated the impact of local RT on adenoviral-mediated vaccination against the colorectal cancer antigen GUCY2C (Ad5-GUCY2C) in a murine subcutaneous tumor model using mouse CT26 colon cancer cells (CT26-GUCY2C). Immune responses were assessed by ELISpot, and clinical responses were assessed by tumor size and incidence.
  
  
  RESULTS
  The specific sequence of tumor-directed RT preceding Ad5-GUCY2C IT transformed inactive therapeutic Ad5-GUCY2C vaccination into a curative vaccine. GUCY2C-specific T cell responses were amplified (P<.05), tumor eradication was maximized (P<.01), and tumor volumes were minimized (P<.001) in mice whose tumors were irradiated before, compared with after, Ad5-GUCY2C vaccination. The immunologic and antitumor efficacy of Ad5-GUCY2C was amplified comparably by unfractionated (8 Gy × 1), or biologically equivalent doses of fractionated (3.5 Gy × 3), RT. The antitumor effects of sequential RT and IT (RT-IT) depended on expression of GUCY2C by tumor cells and the adenoviral vaccine vector, and tumor volumes were inversely related to the magnitude of GUCY2C-specific T cell responses. Moreover, mice cured of CT26-GUCY2C tumors by RT-IT showed long-lasting antigen-dependent protection, resisting tumors formed by GUCY2C-expressing 4T1 breast cancer cells inoculated 50 days after CT26 cells.
  
  
  CONCLUSIONS
  Optimal sequencing of RT and IT amplifies antigen-specific local and systemic immune responses, revealing novel acute and long-term therapeutic antitumor protection. These observations underscore the importance of modality sequence optimization before the initiation of clinical trials of RT and IT to maximize immune and antitumor responses.
authors.affiliation: Department of Radiation Oncology, Kimmel Cancer Center; Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: Matthew
authors.initials: M
authors.lastname: Witek
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: Erik S
authors.initials: ES
authors.lastname: Blomain
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Magee
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: Bo
authors.initials: B
authors.lastname: Xiang
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Waldman
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, Philadelphia, Pennsylvania. Electronic address: adam.snook@jefferson.edu.
authors.forename: Adam E
authors.initials: AE
authors.lastname: Snook
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000737:chemistry; D000970:Antineoplastic Agents / Q000737:chemistry; D019496:Cancer Vaccines / Q000737:chemistry*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000737:chemistry / Q000276:immunology* / Q000532:radiotherapy*; D003131:Combined Modality Therapy / Q000379:methods; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000737:chemistry; D006801:Humans; D007167:Immunotherapy / Q000379:methods*; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D019496:Cancer Vaccines; D000939:Epitopes; D018000:Receptors, Peptide; C000613654:GUCY2C protein, human; C000613655:Gucy2c protein, mouse; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled