Membrane-bound KIT ligand-targeting DNA vaccination inhibits mammary tumor growth

Abstract

We have recently demonstrated that a DNA vaccine targeting membrane-bound KIT ligand (KITL) inhibits tumor growth by interfering with vessel stabilization/permeability and by disrupting the recruitment of inflammatory cells and regulatory T cells, the latter being an essential mechanism by which tumors resist available treatments. Combining KITL-targeting vaccines with conventional chemotherapy might avert drug resistance and improve the efficacy of standard-of-care therapeutic interventions.

Keywords: DNA vaccination; membrane-bound KITL; non-functional angiogenesis.

Figure 1. Non-functional angiogenesis and other consequences of a DNA-based vaccine targeting membrane-bound KITL. BALB/c mice were immunized every 2 weeks for a total of 3 applications by the intradermal injection of a plasmid encoding human membrane-bound KIT ligand (pVAX-mbKITL; vaccinated mice) or the empty vector (pVAX; control mice). Immediately after each injection, 2 25-ms low-voltage electric pulses were generated at the injection site, with a 300 ms interval between each pulse (Step 1). The presence of mbKITL-specific antibodies was assessed 1 wk after the last immunization. One week later control mice as well as mice generating polyclonal mbKITL-targeting antibodies received into the mammary fat pad a lethal dose of syngeneic TSA mammary cancer cells (Step 2). Tumor size was measured and immunohistochemical and biochemical analyses were performed. Only about 60% of vaccinated mice that exhibited a serological positive reaction developed tumors, and these lesions were smaller and displayed a lower proliferative rate when compared with those developing in control animals, as determined by proliferating cell nuclear antigen (PCNA) staining. In addition, these tumors were characterized by (1) hyper-dense non-functional vessels with scant pericyte coverage and altered permeability, (2) limited recruitment of myeloid cells and regulatory T cells (Tregs), (3) strongly decreased production of vascular endothelial growth factor (VEGF) and (4) inhibited AKT1 activation (Step 3).