Endogenous retrovirus expression is required for murine melanoma tumor growth in vivo

Area of Science:

• Oncology
• Immunology
• Virology

Background:

• Tumorigenesis involves genetic and epigenetic alterations.
• Endogenous retroviruses (ERVs) are implicated in immune evasion but lack direct evidence.
• B16 murine melanoma is a model for studying tumor immune evasion.

Purpose of the Study:

• To investigate the role of ERVs in immune evasion of B16 melanoma.
• To determine if ERVs subvert immune surveillance to promote tumor growth.
• To explore therapeutic strategies targeting ERVs in cancer.

Main Methods:

• RNA interference (RNAi) was used to knock down an ERV in B16 melanoma cells.
• Tumor growth was assessed in immunocompetent and immunodeficient mice.
• Cellular transformation was evaluated using soft agar assays.
• Adoptive transfer of regulatory T cells was performed.
• Reexpression of the ERV envelope gene was studied.

Main Results:

• Knockdown of an ERV resulted in B16 melanoma rejection in immunocompetent mice.
• The transformed phenotype of melanoma cells remained unchanged in vitro and in immunodeficient mice.
• Tumor rejection was reversed by regulatory T cell transfer or ERV envelope gene reexpression.
• These findings indicate ERVs mediate immune evasion via regulatory T cells.

Conclusions:

• Endogenous retroviruses are essential for regulatory T cell-mediated immune subversion in B16 melanoma.
• The ERV envelope gene plays a critical role in this immune evasion mechanism.
• Targeting ERVs, particularly their envelope genes, may offer novel cancer immunotherapies for human tumors expressing these elements.