Introduction: Human amniotic epithelial cells (hAEC) are among placenta-derived cells with known immunomodulatory properties. We showed earlier that vaccination of mice with hAEC induced cross-protective immune responses and conferred effective protection in a mice model of colon cancer. Here, we extended our previous observation by examining the potential anti-cancer effects of hAEC-derived exosomes in murine models of colon (CT26), breast (4T1) and melanoma cancers (B16F10).

Methods: hAEC were isolated from term placentas and characterized by immunophenotyping with a panel of stem cells markers. Different sets of experiments were performed to assess anti-cancer effects of hAEC including vaccination with live hAEC and hAEC lysate followed by orthotopic and heterotopic administration of tumor cells. Exosomes were derived from cultured hAEC (ADE) and their anti-proliferative and pro-apoptotic properties were performed by colorimetric and flow cytometric assays, respectively. Protective and therapeutic effects of ADE were also assessed in cancer models mentioned above. Enhancement of CTL responses in mice and percentage of CD4+ and CD8+ splenocytes following exosome injection was evaluated by Calcein AM (cAM) assay and flow cytometry.

Results: Isolated hAEC showed high purity and expressed stem cells markers. Live hAEC conferred effective protection against colon cancer and melanoma but not in breast cancer in orthotopic administration. AEC induced strong cross-reactive antibody response to CT26 cells, but not against B16F10 cells.  Heterotopic injection of tumor cells abolished the anti-cancer effect of hAEC vaccination. Mice vaccinated with hAEC lysate also showed no protection against melanoma or colon cancer. ADE induced apoptosis in CT26 cells and inhibited their proliferation. Co-administration of ADE with tumor cells substantially inhibited tumor development and increased CTL responses in vaccinated mice. ADE did not alter the frequency of spleen CD4+ and CD8+ cells. 

Conclusion: The results of the current study clearly demonstrated that although hAEC triggers cross-reactive humoral immune responses against tumor cells, these immune responses are not necessarily the major player in cancer preventive effects of AEC. Instead, it is the ADE that mediate most activity of AEC in prevention of cancer development. These findings highlighted the potential therapeutic application of ADE for cancer immunotherapy in the future.