title: The timing of TGF-β inhibition affects the generation of antigen-specific CD8+ T cells.
abstract: BACKGROUND
  Transforming growth factor (TGF)-β is a potent immunosuppressive cytokine necessary for cancer growth. Animal and human studies have shown that pharmacologic inhibition of TGF-β slows the growth rate of established tumors and occasionally eradicates them altogether. We observed, paradoxically, that inhibiting TGF-β before exposing animals to tumor cells increases tumor growth kinetics. We hypothesized that TGF-β is necessary for the anti-tumor effects of cytotoxic CD8+ T lymphocytes (CTLs) during the early stages of tumor initiation.
  
  
  METHODS
  BALB/c mice were pretreated with a blocking soluble TGF-β receptor (sTGF-βR, TGF-β-blockade group, n=20) or IgG2a (Control group, n=20) before tumor inoculation. Tumor size was followed for 6 weeks. In vivo lymphocyte assays and depletion experiments were then performed to investigate the immunological basis of our results. Lastly, animals were pretreated with either sTGF-βR (n=6) or IgG2a (n=6) prior to immunization with an adenoviral vector encoding the human papillomavirus E7 gene (Ad.E7). One week later, flow cytometry was utilized to measure the number of splenic E7-specific CD8+ T cells.
  
  
  RESULTS
  Inhibition of TGF-β before the injection of tumor cells resulted in significantly larger average tumor volumes on days 11, 17, 22, 26 and 32 post tumor-inoculation (p < 0.05). This effect was due to the inhibition of CTLs, as it was not present in mice with severe combined immunodeficiency (SCID) or those depleted of CD8+ T cells. Furthermore, pretreatment with sTGF-βR inhibited tumor-specific CTL activity in a Winn Assay. Tumors grew to a much larger size when mixed with CD8+ T cells from mice pretreated with sTGF-βR than when mixed with CD8+ T cells from mice in the control group: 96 mm3 vs. 22.5 mm3, respectively (p < 0.05). In addition, fewer CD8+ T cells were generated in Ad.E7-immunized mice pretreated with sTGF-βR than in mice from the control group: 0.6% total CD8+ T cells vs. 1.9%, respectively (p < 0.05).
  
  
  CONCLUSIONS
  These studies provide the first in vivo evidence that TGF-β may be necessary for anti-tumor immune responses in certain cancers. This finding has important implications for our understanding of anti-tumor immune responses, the role of TGF-β in the immune system, and the future development of TGF-β inhibiting drugs.
authors.affiliation: Division of Thoracic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA. jonq@mail.med.upenn.edu
authors.forename: Jon G
authors.initials: JG
authors.lastname: Quatromoni
authors.forename: Eiji
authors.initials: E
authors.lastname: Suzuki
authors.forename: Olugbenga
authors.initials: O
authors.lastname: Okusanya
authors.forename: Brendan F
authors.initials: BF
authors.lastname: Judy
authors.forename: Pratik
authors.initials: P
authors.lastname: Bhojnagarwala
authors.forename: Ollin
authors.initials: O
authors.lastname: Venegas
authors.forename: Evgeniy
authors.initials: E
authors.lastname: Eruslanov
authors.forename: Jarrod D
authors.initials: JD
authors.lastname: Predina
authors.forename: Steven M
authors.initials: SM
authors.lastname: Albelda
authors.forename: Sunil
authors.initials: S
authors.lastname: Singhal
mesh_terms: D000818:Animals; D051940:B7-2 Antigen / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002452:Cell Count; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004195:Disease Models, Animal; D000939:Epitopes / Q000276:immunology*; D005260:Female; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D007114:Immunization; D007074:Immunoglobulin G; D008198:Lymph Nodes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008212:Lymphocyte Depletion; D051379:Mice; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000276:immunology / Q000473:pathology; D050725:Papillomavirus E7 Proteins / Q000276:immunology; D018125:Receptors, Transforming Growth Factor beta / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology; D012995:Solubility; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D051940:B7-2 Antigen; D000939:Epitopes; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G; D050725:Papillomavirus E7 Proteins; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta