Targeting of interleukin 2 to human ovarian carcinoma by fusion with a single-chain Fv of antifolate receptor antibody.

To provide a new tool for the immunotherapy of human ovarian carcinoma, we constructed a fusion protein between interleukin-2 (IL-2) and the single-chain Fv (scFv) of MOV19, a monoclonal antibody directed against alpha-folate receptor (alpha-FR), known to be overexpressed on human nonmucinous ovarian carcinoma. This was accomplished by fusing the coding sequences in a single open reading frame and expressing the IL-2/MOV19 scFv chimera under the control of the murine immunoglobulin K promoter in J558L plasmacytoma cells. The design allowed the construction of a small molecule combining the specificity of MOV19 with the immunostimulatory activity of IL-2. This might improve the tissue penetration and distribution of the fusion protein within the tumor, reduce its immunogenicity, and avoid the toxicity related to the systemic administration of IL-2. The IL-2/MOV19 fusion protein was stable on purification from the cell supernatant and was biologically active. Importantly, this construct was able to target IL-2 onto the surface of alpha-FR-overexpressing tumor cells and stimulated the proliferation of the IL-2-dependent CTLL-2 cell line as well as that of human resting peripheral blood lymphocytes. In a syngeneic mouse model, IL-2/MOV19 scFv specifically targeted a-FR gene-transduced metastatic tumor cells without accumulating in normal tissues, due to its fast clearance from the body. Prolonged release of IL-2/MOV19 scFv by in vivo transplanted J558-EF6.1 producer cells protected 60% of mice from the development of lung metastases caused by an i.v. injection of a-FR gene-transduced tumor cells. Moreover, treatment with IL-2/MOV19 scFv, but not with recombinant IL-2, significantly reduced the volume of s.c. tumors. The pharmacokinetics and biological characteristics of IL-2/NMOV19 scFv might allow us to combine the systemic administration of this molecule with the adoptive transfer of in vitro retargeted T lymphocytes for the treatment of ovarian cancer, thereby providing local delivery of IL-2 without toxicity.