PO-430 Natural killer cell-based adoptive immunotherapy is effective in the eradication of chemoresistant stem-like cells in bladder cancer

Introduction Bladder cancer is the most common malignancy of the urinary tract, and one of the leading causes of cancer death in Western countries. Non-muscle invasive bladder cancer (NMIBC) has high risk of recurrence and progression to muscle-invasive forms, which seems to be largely related with the presence of stem-like cell populations known as cancer stem cells (CSCs) that are refractory to conventional therapies. Here, we evaluated the anti-tumoral activity of Natural Killer (NK) cell-based adoptive immunotherapy against competent bladder CSCs in a pre-clinical relevant orthotopic bladder cancer model, using NK cells from healthy donors and NMIBC patients. Material and methods NK cells collected from healthy donors and NMIBC patients and activated with IL-2/IL-15 were phenotypically characterised and assayed in vitro against CSCs and bulk differentiated bladder cancer cells, using the CD107a degranulation or Cr-51 release assays. CSCs were isolated using the matrigel sphere-forming assay. The in vivo therapeutic efficacy was evaluated in mice bearing a CSC-induced orthotopic model. Animals were treated twice a week by intravesical instillation of activated-NK cells during two weeks. Tumour response was evaluated longitudinally by non-invasive bioluminescence imaging. Results and discussions NK cells from healthy donors, but not from NMIBC patients, upon IL-2/IL-15 activation, kill indiscriminately both stem-like and differentiated tumour cells, via stress ligands recognition. Moreover, NK cells shifted CSCs towards a more differentiated phenotype rendering them more susceptible to cisplatin, highlighting the benefits of a possible combined therapy. The locoregional administration, via intravesical instillation of healthy activated-NK cells provides an efficient tumour infiltration and subsequent massive decrease in the tumour burden ranging from 80% to complete remission, with high selective cytolytic activity against CSCs. Conclusion Although pre-clinical, our results strongly suggest that an immunotherapeutic strategy using allogeneic activated-NK cells is effective against bladder cancer by targeting both stem and non-stem cell populations and should be exploited as a complementary approach in high-risk bladder cancer patients to prevent tumour recurrence and progression. Aknowldgements Astellas European Foundation Uro-Oncology Grant 2013 and FCT (Portugal): PEst-UID/NEU/04539/2013 and FEDER-COMPETE (FCOMP-01–0124-FEDER-028417 and POCI-01–0145-FEDER-007440).