Dual targeting of cancer and suppressive myeloid cells by tumor-redirected iNKT cells and antigen-carrying microparticles G. Delfanti1, F. Cortesi1,3, G. Antonini1, C.Garavaglia1, M.Consonni1, H. Shen2, G. Casorati1, P. Dellabona1 1Experimental Immunology Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, Milan 20132, Italy 2 Department of Nanomedicine, Houston Methodist Research Institute, Houston, TX 77030,USA 3 present address: University Medical Center Hamburg-Eppendorf, Department of General, Visceral and Thoracic Surgery Campus Forschung N27, Hamburg, Germany Background Adoptive immunotherapy with T cells engineered with tumor-specific TCRs or CARs hold promise for the treatment of hematological and solid malignancies. However, suppressive cues generated by the tumor microenvironment (TME) can dampen the efficacy of engineered T cells. Hence, reprograming the TME is considered critical to optimize the current cell therapy approaches. CD1d-restricted invariant natural killer T (iNKT) cells are active component of the TME and participate in the tumor immunosurveillace by restraining cancer-supporting myeloid populations. Retargeting iNKT cells against cancer cells, by transducing tumor-specific TCR genes, may produce enhanced effectors able to concurrently kill malignant cells and modulate detrimental myeloid cells in TME. Methods Mouse iNKT cells were expanded in vitro, engineered with TCRs specific for MHC-restricted tumor-associate peptide antigens and assessed either in vitro or upon transfer in vivo against tumors expressing the nominal tumor associate antigens. Moreover, the adoptive iNKT cell transfer was combined with their local restimulation with the strong agonist aGalactosylCeramide (αGalCer) delivered using porous silicon microparticle-based nanotherapeutics, which sequentially overcome biological barriers and accumulate at the tumor site. Results iNKT cells engineered with MHC-restricted TCRs specific for tumor-associate peptide antigens are indeed bi-specific for CD1d- and MHC-restricted antigens in vitro. Upon adoptive transfer in vivo, TCR-engineered iNKT cells effectively delay the progression of tumors expressing the cognate antigens and remodel the local myeloid components. These dual anti-tumor functions are further sustained by delivering in vivo αGalCer using porous silicon microparticles resulting in enhanced tumor control. Conclusions Collectively, these results support the use of tumor-retargeted iNKT cells plus local restimulation to enhance adoptive cell transfer efficacy, suggesting a rational for future therapeutic strategies in cancer patients.