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598 Local radiation in combination with CpG and anti-OX40 induces enhanced T cell activation and proliferation
  1. Dan Spiegelman1,
  2. Alexander Pieper1,
  3. Luke Zangl1,
  4. Arika Feils1,
  5. Anna Hoefges1,
  6. Mildred Felder1,
  7. Sritha Moram1,
  8. Alexander Rakhmilevich1,
  9. Amy Erbe1,
  10. Jacquelyn Hank1,
  11. Ravi Patel2,
  12. Zachary Morris1 and
  13. Paul Sondel1
  1. 1University of Wisconsin-Madison, Madison, WI, USA
  2. 2University of Pittsburgh, Pittsburgh, PA, USA


Background We, and others, have previously shown that the in-situ vaccine of hypomethylated CG-enriched oligodeoxynucleotide (CpG) with agonist anti-OX40 antibody (OX40) is effective at curing mice in the A20 lymphoma model [1–4]. In separate preclinical models where CpG+OX40 fails to cause tumor regression, radiation therapy (RT) prior to the in-situ vaccine enhances the anti-tumor effect of CpG+OX40 [4]. We investigated the immune response, and specifically the activity of T cells, following treatment with RT+CpG+OX40 in the B78 melanoma model where CpG+OX40 typically fails to cause tumor regression.

Methods C57BL/6 mice were inoculated with 2x106 B78 melanoma cells on the right flank and allowed to grow until the average tumor size was ~150mm3. In two independent experiments, mice were randomized (n=4–5 per group per experiment) and treated with one of the following: 1) PBS, 2) CpG+OX40, 3) RT, 4) RT+CpG+OX40. 12 Gy external beam RT was dosed to the flank tumor on day 0 and intratumoral CpG (50µg)+OX40 (20 µg) were given on days 5, 7, and 9 after RT. Spleens and tumor draining lymph nodes (TDLNs) were harvested on day 12. T cell activation and proliferation were assessed via flow cytometry.

Results Compared to all other groups in the study, mice treated with RT+CpG+OX40 demonstrated significantly elevated levels of CD4+ and CD8+ T cell activation in the TDLNs, as measured by interferon gamma expression. Similar trends of CD4+ and CD8+ T cell activation were measured in the spleens. Splenic CD8+ T cells from RT+CpG+OX40 treated mice demonstrated significantly elevated levels of proliferation over PBS and RT, as measured by Ki67.

Conclusions In B78 melanoma, a weakly immunologic tumor model, combining RT with the in-situ vaccine CpG+OX40 enhances the activity of T cells, evidenced by significantly increased CD4+ and CD8+ T cell activation in the TDLN and spleen and elevated CD8+ T cell proliferation in the spleen.


  1. Houot, R. and Levy, R. T-cell modulation combined with intratumoral CpG cures lymphoma in a mouse model without the need for chemotherapy. Blood, 2009. 113(15):3546–52.

  2. Marabelle, A., et al. Depleting tumor-specific Tregs at a single site eradicates disseminated tumors. J Clin Invest, 2013. 123(6):2447–63.

  3. Sagiv-Barfi, I., et al. Eradication of spontaneous malignancy by local immunotherapy. Sci Transl Med, 2018. 10(426).

  4. Zangl, LM. Et al. External Beam Radiotherapy Required for Tumor Regression When Using CpG-Oligodeoxynucleotide and Anti-OX40 in an Immunologically Cold Tumor Model. Red Journal. 2019. 105:S88.

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