title: Sub-lethal radiation enhances anti-tumor immunotherapy in a transgenic mouse model of pancreatic cancer.
abstract: BACKGROUND
  It is not uncommon to observe circulating tumor antigen-specific T lymphocytes in cancer patients despite a lack of significant infiltration and destruction of their tumors. Thus, an important goal for tumor immunotherapy is to identify ways to modulate in vivo anti-tumor immunity to achieve clinical efficacy. We investigate this proposition in a spontaneous mouse tumor model, Rip1-Tag2.
  
  
  METHODS
  Experimental therapies were carried out in two distinctive trial designs, intended to either intervene in the explosive growth of small tumors, or regress bulky end-stage tumors. Rip1-Tag2 mice received a single transfer of splenocytes from Tag-specific, CD4+ T cell receptor transgenic mice, a single sub-lethal radiation, or a combination therapy in which the lymphocyte transfer was preceded by the sub-lethal radiation. Tumor burden, the extent of lymphocyte infiltration into solid tumors and host survival were used to assess the efficacy of these therapeutic approaches.
  
  
  RESULTS
  In either intervention or regression, the transfer of Tag-specific T cells alone did not result in significant lymphocyte infiltration into solid tumors, not did it affect tumor growth or host survival. In contrast, the combination therapy resulted in significant reduction in tumor burden, increase in lymphocyte infiltration into solid tumors, and extension of survival.
  
  
  CONCLUSIONS
  The results indicate that certain types of solid tumors may be intrinsically resistant to infiltration and destruction by tumor-specific T lymphocytes. Our data suggest that such resistance can be disrupted by sub-lethal radiation. The combinatorial approach presented here merits consideration in the design of clinical trials aimed to achieve T cell-mediated anti-tumor immunity.
authors.affiliation: Department of Biochemistry, Diabetes and Comprehensive Cancer Centers, University of California at San Francisco, San Francisco, CA 94143-0534, USA. alex_cao001@hotmail.com
authors.forename: Zhu Alexander
authors.initials: ZA
authors.lastname: Cao
authors.forename: Dylan
authors.initials: D
authors.lastname: Daniel
authors.forename: Douglas
authors.initials: D
authors.lastname: Hanahan
mesh_terms: D019264:Adoptive Transfer / Q000379:methods; D000818:Animals; D003131:Combined Modality Therapy / Q000379:methods; D004195:Disease Models, Animal; D006801:Humans; D016219:Immunotherapy, Adoptive / Q000379:methods*; D016246:Lymphocytes, Tumor-Infiltrating / Q000528:radiation effects; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010190:Pancreatic Neoplasms / Q000401:mortality / Q000532:radiotherapy* / Q000628:therapy*; D016019:Survival Analysis