br Focal therapies that modulate local immune
Focal therapies that modulate local immune responses may also enhance the efficacy of NP vaccines. Gao and colleagues developed a pH-sensitive endosomolytic polymeric NP that efficiently delivered OVA peptide to APCs called PC7A55. These NPs increased APC activation through the stimulator of interferon gene (STING) pathway. While tumor growth delay was enhanced, resistance to therapy was problematic for tumors > 100 mm2 at the time of treatment. One of the principle activators of STING is cytosolic DNA. Radiation enhances the generation of cytosolic DNA and activation of STING is believed to be one of the central mechanisms by which radiation enhances systemic immunity following radiation68. Dr. Gao’s group recently demonstrated that tumor rejection and systemic immunity could be enhanced in larger tumors by combining PC7A particles and focal radiotherapy and that this effect was mediated by enhanced STING activation by combination therapy69.
RNA-based vaccine strategies delivering neoantigen mRNAs and immune adjuvants directly to APCs have also demonstrated promise. Lipid calcium phosphate NPs have been used to deliver mRNA and induce PF-06424439 of tumor neoantigens such as MUC1 to successfully induce class-restricted cytotoxic T-cells and improve responses to checkpoint inhibitors in preclinical studies70. Liu et al. confirmed efficient delivery and translation of a modified MUC1 mRNA in 4T1 tumors and draining lymphoid tissues using mannose decorated lipid calcium phosphate NPs. The modified protein product was easily distinguished from endogenously expressed antigen. Importantly, the validity of this approach has also been demonstrated in early phase clinical trials. The systemic delivery of neoantigen mRNA using DOTMA/DOPE liposomes induced strong systemic INF responses and the generation of tumor-specific neoantigens in three patients71.
3.1.2 Enhancing Antigenic Presentation of Endogenous Tumor Neoantigens
At present, a major rate-limiting step to the clinical translation of efficient nanovaccines is the identification of specific tumor neoantigens for individual patients. A priori knowledge of targetable, specific tumor peptides in many spontaneous human tumors is rare. Additionally, clinical experience with targeted biologic therapies suggests that the stimulation of monoclonal populations of T-cells targeting a single tumor peptide may be suboptimal. Most tumor-directed biologics, including EGFR and ALK inhibitors, stimulate robust initial responses and improve progression-free survival (PFS). However, the development of resistance is inevitable and these drugs have minimal effect on overall survival (OS)72,73. Some mechanisms of resistance to targeted biologics, such as the upregulation of redundant signaling pathways, may not be relevant to immune vaccines. However, tumor heterogeneity and downregulation of the targeted peptides could be very problematic for monoclonal vaccines. Wang and colleagues recently demonstrated that cationic antigen-capturing NPs and ionizing radiation can stimulate robust polyclonal immune responses74. They generated polymeric PLGA NPs with various surface modifications (decoration with DOTAP, maleimide, NH2, mPEG, or unmodified PLGA) to determine the effects of NP surface chemistry on antigen capture efficiency. All of the particles except for those decorated with mPEG efficiently captured tumor neoantigens following in silico radiation of B16F10 tumor cells. Importantly, these particles also captured immune adjuvants including various DAMPs and alarmins that are necessary for APC co-stimulation and avoidance of immune tolerance. They then used a bilateral flank-tumor model to assess systemic immunity. Intratumoral injection of particles into the unilaterally-radiated tumor significantly enhanced abscopal responses in the unirradiated contralateral tumor compared to radiation and anti-PD-1 antibodies alone. Intratumoral injection of unmodified PLGA NPs stimulated complete regression of bilateral tumors in 20% of mice compared to 0% without any NPs. Using fluorescent-labeled NPs, they were able to confirm that the NPs were efficiently internalized by APCs and trafficked to lymphoid tissues. Figure 3 shows how antigen-capturing NPs can improve the efficiency of T-cell activation by improving the simultaneous presentation of neoantigens and danger signals to APCs. r> Cell membrane-coated NPs have also been used to improve endogenous neoantigen recognition by APCs. In this technique, NP carriers are decorated with disrupted cell membranes and their associated cell surface proteins. Kroll et al. coated CpG-loaded PLGA NPs with B16F10 surface membranes75. They showed that the surface of the membrane-coated NPs contained multiple established tumor neoantigens including gp100, TRP-2, and melanin A. Significantly more (86%) mice were successfully vaccinated with these particles than with whole cells and CpG. Another group demonstrated similarly encouraging results with membrane-coated PLGA NPs encapsulating the TLR-7 agonist imiquimod76. These novel approaches demonstrate that it may be possible to stimulate polyclonal systemic immune responses without any upfront identification of specific tumor neoantigens in individual patients using novel nanomedicines.