Fetal exposure to oncoantigen elicited antigen-specific adaptive immunity against tumorigenesis

Background: Envisioned as a similar process to tumorigenesis in terms of biological behaviors and molecular basis, embryogenesis necessitates an immune surveillance system to eliminate erratically transformed cells. Our previous study demonstrated that fetal macrophage-like phagocytes triggered Th2-skewed immunity following endocytosing prenatally administered ovalbumin to facilitate postnatal allergic airway responses, highlighting the critical role fetal phagocytes played in dealing with antigens present in developing fetuses and shaping subsequent immune responses. It prompted us to examine whether fetuses could mount Th1 tumoricidal immunity against tumorigenesis following in utero exposure to tumor antigens.

Methods: Gestational day 14 murine fetuses underwent in utero injection of Th1-promoting human papilloma virus (HPV) E7 peptides. Postnatally, recipients were examined for immunological consequences and the resistance to TC-1 tumorigenesis.

Results: Fetal exposure to HPV E7 did not cause tolerance but rather immunization in the recipients, characterized by proinflammatory Th1 polarization of their lymphocytes. Fetal macrophage-like phagocytes were responsible for taking up HPV E7 and triggering HPV E7-specific T-cell cytotoxicity and humoral immunity that rendered recipients resistant to TC-1 tumorigenesis in postnatal life. Adoptive transfer of HPV E7-loaded fetal phagocytes also elicited Th1 immunity with rapid expansion of HPV E7-specific cytotoxic CD8⁺ T-cell clones in response to TC-1 cell challenge so as to protect the recipients from TC-1 tumorigenesis, but failed to completely eliminate pre-existing TC-1 cells despite perceptible attenuation of local TC-1 tumor growth.

Conclusions: Our study revealed that Th2-biasing fetus was not immune-privileged to foreign peptides, but competent to mount Th1 cytotoxic immunity and generate immunoglobulins against tumorigenesis following in utero exposure to Th1-promoting oncoantigen. It shed light on the role of fetal macrophage-like phagocytes in bridging toward tumor antigen-specific cellular and humoral immunity potentially as an immune surveillance system to eliminate transformed cells that might be egressing during embryogenesis and leftover until postnatal life.