Targeted macrophage cytotoxicity using a nonreplicative live vector expressing a tumor-specific single-chain variable...

Area of Science:

• Immunology
• Oncology
• Virology

Background:

• Cancer immunotherapy aims to eliminate tumor cells via antigen-specific cytotoxic T lymphocytes (CTLs).
• Tumor growth can persist due to insufficient CTLs, T-cell anergy, or reduced MHC class I (MHC-I) expression on tumor cells.
• Previous work demonstrated vaccinia virus expressing tumor antigen-specific monoclonal antibodies can enable macrophages to kill antigen-positive tumor cells.

Purpose of the Study:

• To express a membrane-anchored single-chain variable fragment (scFv) of the MUC1 antibody (SM3) on activated macrophages using the modified vaccinia Ankara (MVA) poxvirus vector.
• To evaluate if macrophages expressing the membrane-bound scFv can specifically recognize and lyse MUC1-expressing tumor cells.

Main Methods:

• Gene transfer of a membrane-anchored scFv construct targeting MUC1 into activated macrophages using the MVA vector.
• Confirmation of scFv expression and antigen binding using Western blot, FACS analysis, and BIAcore.
• Assessment of MUC1-specific tumor cell recognition and lysis by MVA-scFv-infected macrophages through IL-12 release and cytotoxicity assays.

Main Results:

• Macrophages successfully expressed the membrane-anchored MUC1-specific scFv.
• Cells expressing the membrane-bound scFv demonstrated specific binding to the MUC1 antigen.
• GM-CSF-activated macrophages infected with the MVA-scFv construct specifically recognized MUC1-expressing tumor cells, evidenced by IL-12 release.
• These modified macrophages specifically lysed MUC1-positive tumor cells while sparing MUC1-negative cells.

Conclusions:

• Modified vaccinia Ankara (MVA) can serve as an effective vector for delivering genes encoding membrane-bound antibody fragments to macrophages.
• Activated macrophages engineered to express MUC1-specific scFv can specifically target and destroy MUC1-expressing tumor cells.
• This approach represents a promising strategy for developing novel cancer immunotherapies by enhancing macrophage-mediated tumor cell killing.