Extracellular vesicles (EVs) are mediators of intercellular communication that have been reported to contribute to viral spread and immune evasion. Infection by high-risk human papillomavirus, such as type 16 (HPV16), is causally associated with cervical cancer. Progression from infection to cancer is attributed by persistence linked to the evasion of a host immune response, and continued over-expression of HPV16 oncoproteins, E6 and E7 (E6/E7). This study investigated the effects of HPV16 E6/E7 oncoproteins on EV production by cells and the immune-modifying effects of E6/E7-EVs on Langerhans cells (LCs), implicated in initiation of the adaptive immune response to HPV.
EVs were produced from mouse cell lines expressing the HPV16 E6/E7 proteins (TC-1) or control (PDV) by differential centrifugation. LCs were differentiated from mouse bone-marrow progenitors, activated by lipopolysaccharide (LPS) and the effects of E6/E7-EVs on the maturation of LCs were measured by CD40 and IL-12 following co-culture and flow cytometry.
After sizing bead and phosphatidylserine analysis for EV characterisation, annexin V-positive EVs less than 1 µm in diameter were similar in number between cell lines (P > 0.05, n = 3, Mann-Whitney U pairwise comparison). CD40, but not IL-12, was downregulated on LPS-activated LCs co-cultured with E6/E7-EVs (P < 0.05, n = 3, Two-way ANOVA, followed by Sidak’s multiple comparisons) when compared with control-EVs.
This result is consistent with previous research that EVs produced from cells expressing the HPV16 E7 oncoprotein alone can downregulate CD40 on LCs. EV-associated modulation of the CD40 signaling pathway could be a potential HPV immune evasion strategy from LC function.