Gene therapy for cancer using single-chain Fv fragments specific for 4-1BB

Area of Science:

• Immunology
• Oncology
• Vaccine Development

Background:

• Monoclonal antibodies targeting the T-cell activation molecule 4-1BB have shown efficacy in treating established mouse tumors.
• Developing vaccines that mimic the immune-stimulating effects of anti-4-1BB antibodies is a promising therapeutic strategy.
• The K1735 melanoma model, characterized by low immunogenicity and MHC class I expression, was chosen for its relevance to challenging tumor types.

Purpose of the Study:

• To construct a vaccine vector encoding cell-bound single-chain variable fragment (scFv) of the anti-4-1BB antibody 1D8.
• To evaluate the vaccine's ability to elicit an anti-tumor immune response and mediate tumor rejection.
• To assess the potential of this approach for treating established tumors, including those with low MHC class I expression.

Main Methods:

• Construction of a vector encoding cell-bound single-chain Fv fragments from the anti-4-1BB antibody 1D8.
• Transfection of the vector into K1735 melanoma cells.
• Assessment of the induced immune response, including T-helper cell type 1 (Th1) response, CD4+ and CD8+ T lymphocyte involvement, and natural killer (NK) cell activity.
• Evaluation of tumor rejection in mice bearing established K1735 tumors (subcutaneous and lung nodules).

Main Results:

• Transfected K1735 melanoma cells induced a potent type 1 T-helper cell response.
• The anti-tumor immunity was dependent on CD4+ T lymphocytes but not CD8+ T lymphocytes, and involved natural killer cells.
• Vaccinated mice demonstrated rejection of established wild-type K1735 tumors, both as subcutaneous nodules and lung metastases.
• The vaccine strategy showed efficacy against tumors with low immunogenicity and low MHC class I expression.

Conclusions:

• A vaccine strategy utilizing cell-bound single-chain Fv fragments of anti-4-1BB antibody can effectively stimulate anti-tumor immunity.
• This approach successfully mediated the rejection of established tumors in a preclinical mouse model.
• The findings suggest that this vaccination method holds promise for treating human micrometastases, particularly in tumors with low MHC class I expression.