**Acknowledgements**

We wish to thank Dr. Antonello Villa (Università Milano Bicocca, Milan, Italy) for his outstanding contribution in generating confocal, immunohistochemistry and electron-microscopy images; Dr. Daniela Belloni (Division of Experimental Oncology, San Raffaele Scientific Institute, Milan, Italy) for developing the 3D model in bioreactor and performing experiments; Prof Federico Caligaris-Cappio (Italian Association for Cancer Research-AIRC) and Dr. Giovanni Tonon (Division of Experimental Oncology, San Raffaele Scientific Institute, Milan, Italy) for helpful discussion and unceasing support; Prof. Paolo Ghia (Division of Experimental Oncology, San Raffaele Scientific Institute, Milan, Italy) for precious insights.
