Re-Modulation Innate Immune Activity in the Tumor Microenvironment by a Combination of Inducer on Micro-Particles

Targeted cancer immunotherapy is a challenge due to the cellular diversity and imposed immune tolerance in the tumor microenvironment (TME). A possible promising route to overcome those drawbacks is by activation of the innate immune cells (IIC) in the TME, toward tumor destruction. Studies have shown the ability to “re-educate” pro-tumor-activated IIC toward antitumor responses. The current research was aimed to stimulate such activation with a combination of innate activators loaded onto micro-particles (MP). Inducers of Toll-like receptors 4 (TLR-4), the complement C5a receptor (C5aR) and their combinations were loaded on MP, and their influence on immune cell activation was evaluated. Stimulation of immune cell activation by MP was tested in vivo using a subcutaneous B16-F10 melanoma model induced in C57BL6 mice. Exposure to the TLR4 ligand lipopolysaccharide (LPS) bound to MP induced acute inflammatory cytokine and chemokine activity in the TME. Elevation of CD45+ leukocytes, in particular the GR-1+ neutrophils, and F4/80 macrophages in the TME was evident. Nevertheless, LPS alone bound to the MP was insufficient to significantly delay tumor progression. LPS combined with the C5aR ligand C5a-pep on the same MP resulted in a similar pattern of inflammation activation. However, interleukin-10 and TGF-β3 levels were lowered, and tumor growth was significantly delayed. Mixtures of these two ligands on separate MP did not yield the same cytokine activation pattern, indicating the importance of the need for cells’ dual activation to yield the adequate response. The results suggest that delivery of inducers of distinct innate immune activation pathways holds promise for successful redirection of TME-residing IIC toward anti-tumoral activation.