Abstract LB-105: Combining CD4+ T cell transfer and immune checkpoint blockade demonstrates the power of combined immunotherapies for treatment of progressed solid carcinomas in mice
2018-07-01

Abstract Tumor and immune cells express inhibitory immune checkpoints (ICP) that paralyze tumor infiltrating T cells. ICP-specific antibodies (mAbs) can block and restore T cell functions and promote anti-tumoral effects. Also, tumor-antigen specific IFN-y secreting CD4+ T cells (TA-Th1) mediate strong anti-tumoral effects and can induce senescence in cancer cells. Here, we report on the development and immunological characterization of a highly efficient TA-Th1 and checkpoint-inhibitor based combined immunotherapy (CIT) in a progressed endogenous cancer model. Mice bearing progressed pancreatic islet carcinomas (RIP1-Tag2) and symptomatic low blood glucose levels (BGL; ~80 mg/dl) were treated weekly with TA-Th1 and αPD-L1+αLAG-3 mAbs (PDL1/LAG3) after an initial preparative 2 Gy-whole body radiation. Therapy was monitored by BGL measurements. Additionally, we conducted baseline and follow-up 18F-FDG PET/MRI scans to uncover the splenic glucose metabolism as a consequence of immune cell activation. We performed ex vivo flow cytometry (FC), immunohistochemistry (IHC), and fluorescent microscopy (FM) of tumor tissue and lymphatic organs at early (1 wk) and late (3-4 wks; endpoint of SHAM treated mice) time point of treatment focusing on the immune cell composition, activation patterns and senescence induction. Treatment exclusively with TA-Th1 prolonged the median survival of the mice from 14 to 18 wks (n=14) while ICP blockade without TA-Th1 cells was not efficient at all (PDL1/LAG3; median survival=14wks, n=11). The combination of TA-Th1 and PDL1/LAG3 (CIT) was highly efficient and significantly extended the median survival to 20 wks (n=15, p=0.001). Thus, exclusively CIT-treated mice revealed very small tumors and a strong lymphocytic infiltrate. FC analysis demonstrated early and specific homing of highly activated (CD69) TA-Th1 into the draining LN without impairment of the endogenous CD8+ T cell population. After 4 wks of treatment, we determined an increase in endogenous effector CD4+ and CD8+ T cells exclusively in mice receiving TA-Th1, indicating cross-priming as a possible mechanism of T cell activation. Analysis of p16/Ki67 expression in tumors revealed a strongly enhanced p16 and reduced Ki67 expression exclusively in CIT-treated mice indicating tumor senescence which was not observed in control groups. 18F-FDG-PET/MRI of the spleen showed a significantly increased glucose metabolism in CIT treated mice when compared to SHAM-treatment. In conclusion, our newly developed CIT (2 Gy+TA-Th1+PDL1/LAG3) strongly promoted an anti-tumor immune response in mice with progressed solid cancer. Most importantly, only CIT was able to induce TA-Th1 mediated tumor senescence whereas TA-Th1 or PDL1/LAG3 mAbs alone were inefficient. Moreover, 18F-FDG-PET/MRI of the spleen might represent a novel powerful tool to stratify ICP-blocked responders. Thus, ICP-blockade is applicable to reinforce Th1-cell based immunotherapies and to prolong the lifespan of mice with progressed solid carcinomas. Citation Format: Barbara F. Schörg, Dominik Sonanini, Johannes Schwenck, Christoph Griessinger, Birgit Fehrenbacher, Martin Schaller, Ursula Kohlhofer, Leticia Quintanilla-Martinez, Christian La Fourgère, Martin Röcken, Bernd J. Pichler, Manfred Kneilling. Combining CD4+ T cell transfer and immune checkpoint blockade demonstrates the power of combined immunotherapies for treatment of progressed solid carcinomas in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-105.