Therapeutic Immunomodulation of the Lymphoid-like Tumor Environment Using Nanoparticulate Formulations

Cancer is a leading cause of death worldwide. Understanding the underlying mechanisms that lead to tumor escape and evasion is pivotal for the design of new therapeutic applications. This thesis takes an immunobioengineering approach, and navigates through identifying the immunological parameters relevant in the tumor microenvironment, proposing and developing a strategy in response to address these parameters using nanosized drug and antigen carriers. It is widely accepted that changes in the immunological equilibriumof the tumor microenvironment are crucial for the progression, dissemination and metastasis of a developing tumor. Motivated by tumors' natural secretion of CCL21, a chemokine known for dendritic (DC) migration towards the lymphatics, and for attracting DC and T cells in the lymph node (LN), we perturbed the physiological secretion of CCL21 of B16-F10 melanomas, deriving both a knock-down (CCL21low) and an over-expressing (CCL21high) variant. Interestingly, in immunocompetent mice, growth in CCL21-secreting tumors had an advantage over the CCL21low sub-clones and was CCR7 dependent. CCL21low tumors harbored more antigen specific T cells, while CCL21-secreting, more T regulatory cells (Tregs), which also correlated with subsequent biochemical polarization. Moreover, CCL21-secreting tumors formed a reticular fibroblastic (FRC) network (ERTR7+gp38+CCL21+) reminiscent of the lymphoid tissue of the paracortex (T cell zone) within LNs. The lymphoidlike stroma was orchestrated by the recruitment of CCR7+ adult lymphoid tissue inducers (LTis), responsible for LN formation during embryogenesis, present only in the CCL21-secreting tumors. In mice lacking LTis (Rorc(γt)-deficient) control tumors displayed impaired growth, suggesting that tumor growth is stroma dependent. In addition, the stroma of control or CCL21high tumors was infiltrated by more myeloid suppressor cells (MDSCs) than in CCL21low variant. MDSCs are a heterogeneous population of immature myeloid precursor cells that repress T cell activation and antigen presentation in chronic inflammation and cancer, hampering the efficacy of anti-tumoral vaccinations. CCL21's ability to protect allografts was further demonstrated in non-syngeneic recipients and in ectopically CCL21 transduced βTC tumor models. By mimicking secondary lymphoid organs, tumors may hi-jack and modulate the immune response from immunogenic to tolerogenic to allow for growth and metastasis. Intrigued by the excessive stroma infiltration of MDSCs in CCL21-secreting tumors, we performed a detailed spatiotemporal biodistribution analysis of ultrasmall (sub 50 nm) nanoparticles (NPs) in naïve and tumor bearing mice. Intradermally administered NPs rapidly drained to the LNs and spleen and persistently targetedmajor phagocytic populations that play a key role in hosting an immune response in naïve and tumor bearing mice. Furthermore, tumor-induced myeloid compartments, mainlyMDSCs, were highly targeted naturally within t