The treatment of melanoma has been revolutionized by the discovery of immune check-point inhibitors, antibodies that act at the level of the immunological synapsis or at the tumor level. Active immunotherapy involves the reactivation of the patient’s immune system against the tumor. Vaccines against tumor antigens are regarded as a mean to prime the immune system against the tumor cells. Some of the challenges associated with the efficacy of the cancer vaccine are related to the poor adjuvancy of the antigenic peptides. Thereby, newer adjuvants, in the form of particulate (micro or nano) systems, have been investigated.
In this context, thermally oxidized porous silicon (TOPSi) nanoparticles (NPs) induce the activation of antigen presenting cells, with a potential function as adjuvants. In order to increase the efficacy of the adjuvant particles, we employed glass capillary microfluidics to encapsulate TOPSi NPs in a polymeric layer composed of acetalated dextran (AcDEX). AcDEX is a biocompatible polymer derived from the modification of dextran, with innate immunostimulative properties. TOPSi@AcDEX particles were able to induce the maturation of antigen presenting cells, as signified by the increased expression of co-stimulatory signals (CD80 and CD86; Figure 1) and by the secretion of pro-inflammatory cytokines (interferon gamma). We added the antigenic component to the system by coating, through a process of membrane extrusion, the NPs with cellular membranes derived from cancer cells of interest, thereby formulating biohybrid nanovaccines.[7, 8]
Figure 1. Percentage of CD86+ peripheral blood monocytes after incubation with nanosystems at two different concentrations (100 and 500 µg/mL). The results are presented as mean±s.d. (n=3) and have been analyzed with one-way ANOVA, followed by Bonferroni post-test. The level of significance was set at ***p<0.001.
We then evaluated the efficacy of the particles in vivo, in an immunologically relevant murine model (B16.OVA). As shown in Figure 2, the administration of the complete vaccine (NanoCCM) enables a higher control of the growth of established tumors, when compared to the single components (adjuvant nanoparticles or cancer cell membranes).
Figure 2. Tumor growth single curves after the administration of a) mock, b) adjuvant component, particles only, c) antigenic component only, cell membranes, and d) the final vaccine formulation, subcutaneously.
Furthermore, a synergistic effect between the nanovaccines and checkpoint inhibitors (anti CTLA-4) was also established (Figure 3), with promising results for a future translation of the biohybrid nanovaccines to the clinic, in a personalized medicine optic.
Figure 3. Tumor growth curves after treatment with mock, checkpoint inhibitor (aCTLA4) or combination therapy (checkpoint inhibitor and nanovaccines). The results are presented as mean±s.d. (n=6) and were analyzed with two-way ANOVA with Tukey’s multiple comparison correction. The levels of significance were set at **p<0.01 and ****p<0.0001.
In conclusion, we developed an innovative biohybrid nanovaccine and investigated its efficacy both in vitro and in vivo. The vaccine controls tumor growth when used in monotherapy and improves the efficacy of the standard of care (treatment with immune checkpoint inhibitor).
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