Potent antitumor activity of a tumor-specific soluble TCR/IL-2 fusion protein.

We previously have generated a single-chain T cell receptor-cytokine fusion protein (264scTCR/IL-2) comprising interleukin-2 genetically linked to a soluble HLA-A2.1-restricted TCR recognizing a peptide of human p53 protein. In this report, we show that 264scTCR/IL-2 inhibits the growth of primary tumors derived from the A375 (p53+/HLA-A2.1+) human melanoma and exhibits significantly better antitumor activity than recombinant human IL-2 alone. Moreover, treatment with 264scTCR/IL-2 results in tumor growth retardation in mice bearing large A375 tumors and other p53+/HLA-A2.1+ human tumors but does not affect tumor outgrowth of HLA-A2.1-negative tumors. This suggests that antigen targeting plays a substantial role in the efficacy of 264scTCR/IL-2 against p53+/HLA-A2+ tumors. Further, the antitumor activity of 264scTCR/IL-2 was found to be likely mediated by NK cell activation and tumor infiltration. A biologically active chimeric version of the molecule (c264scTCR/IL-2) also exhibits favorable pharmacokinetic properties required of a clinical candidate for this novel class of potent antitumor activities and targeted anticancer immunotherapeutics.

In vitro and in vivo characterization of a novel antibody-like single-chain TCR human IgG1 fusion protein.

We have constructed a protein composed of a soluble single-chain TCR genetically linked to the constant domain of an IgG1 H chain. The Ag recognition portion of the protein binds to an unmutated peptide derived from human p53 (aa 264-272) presented in the context of HLA-A2.1, whereas the IgG1 H chain provides effector functions. The protein is capable of forming dimers, specifically staining tumor cells and promoting target and effector cell conjugation. The protein also has potent antitumor effects in an in vivo tumor model and can mediate cell killing by Ab-dependent cellular cytotoxicity. Therefore, single-chain TCRs linked to IgG1 H chains behave like Abs but possess the ability to recognize Ags derived from intracellular targets. These fusion proteins represent a novel group of immunotherapeutics that have the potential to expand the range of tumors available for targeted therapies beyond those currently addressed by the conventional Ab-based approach.

A soluble single-chain T-cell receptor IL-2 fusion protein retains MHC-restricted peptide specificity and IL-2 bioactivity.

Antibody-based targeted immunotherapy has shown promise as an approach to treat cancer. However, many known tumor-associated antigens are not expressed as integral membrane proteins and cannot be utilized as targets for antibody-based therapeutics. In order to expand the limited target range of antibodies, we have constructed a soluble single-chain T-cell receptor (TCR) fusion protein designated 264scTCR/IL-2. This fusion protein is comprised of a three-domain HLA-A2-restricted TCR specific for a peptide epitope of the human p53 tumor suppressor protein, which is overexpressed in a broad range of human malignancies. The 264scTCR/IL-2 fusion protein has been expressed at high levels in mammalian cells, and milligram quantities have been purified. MHC-restricted antigen-specific binding properties are maintained in the single-chain, three-domain TCR portion of the fusion protein, and the IL-2 portion retains bioactivity similar to that of free recombinant IL-2. Moreover, this fusion protein is capable of conjugating target and effector cells, remains intact in the blood and substantially increases the half life of the IL-2 portion of the molecule. Finally, the 264scTCR/IL-2 fusion protein can be used to stain tumor cells and is capable of reducing lung metastases in an experimental model of metastasis. Thus, TCR-based fusion proteins may provide a novel class of targeted immunotherapeutics for cancer.