Combination of Cy and AdIL-12 enhances in vivo antitumor immune response by reversion of Tregs and MDSC-driven immunosuppression

MALVICINI M; INGOLOTTI M; FLAVIA PICCIONI; GARCIA M; JUAN BAYO; ATORRASAGASTI C; ALANIZ LAURA; O GRACIELA SCHAROVSKY

Congreso; First French-Argentine Immunology Congress; 2010

We have previously demonstrated the synergistic antitumoreffect of the sequential administration of low-dose cyclophosphamide(Cy) followed by sub-therapeutic doses of adenovirusexpressing IL-12 genes (AdIL-12) in a mouse colorectal carcinoma(CRC) model (CT26). Our results suggested that the combinedtreatment allowed the generation of strong antitumor immuneresponses. The aim of this work was to investigate the immunologicalmechanisms responsible for the therapeutic effect ofthe combination. Methods: Balb/c mice were s.c injected withCT26 cells (day 0), distributed in experimental groups (day 7)and treated with: saline; Cy 50 mg/Kg i.p (day 7); AdIL-12 109TCID50 i.t (day 8) or Cy + AdIL-12. Tumor volume was measuredand samples of peripheral blood, spleen and tumor were taken.CD4+CD25+ and CD4+CD25- T lymphocytes were isolatedby magnetic separation. Results: We observed that mice nonresponderto the combined treatment showed a proportion ofregulatory T cells (Tregs) higher than in responder mice, bothin peripheral blood and spleen, as well as in tumor samples(p<0.05). Also, the antitumor effect of combined therapy wasreverted by in vivo administration of Tregs. The combinationCy+AdIL-12 inhibited Tregs ability to secrete IL-10 and TGF-βand their capacity to inhibit dendritic cells maturation. We alsoobserved that a subpopulation of immature cells with myeloidand suppressive phenotype (MDSCs) was recruited in the spleenof mice during tumor progression. Cy + AdIL-12 induced a significantdecrease in the percentage of MDSCs with respect tountreated mice (4.5 % vs 16 %; p<0.05). Importantly, depletionof Tregs and MDSCs by combined therapy leads to developmentof specific IFNg secreting CD4+ T lymphocytes response, able toeradicate CRC tumors followed to their adoptive transfer. Conclusion:Our results suggest that Cy + AdIL-12 induces a synergisticantitumor immune response against CRC by reversion ofTregs and MDSCs number and function.