Data from Cancer Immunotherapy Targeting the High Molecular Weight Melanoma-Associated Antigen Protein Results in a Broad Antitumor Response and Reduction of Pericytes in the Tumor Vasculature

Abstract

<div>Abstract<p>The high molecular weight melanoma-associated antigen (HMW-MAA), also known as melanoma chondroitin sulfate proteoglycan, has been used as a target for the immunotherapy of melanoma. This antigen is expressed on the cell surface and has a restricted distribution in normal tissues. Besides its expression in a broad range of transformed cells, this antigen is also found in pericytes, which are important for tumor angiogenesis. We generated a recombinant <i>Listeria monocytogenes</i> (<i>Lm</i>-LLO-HMW-MAA-C) that expresses and secretes a fragment of HMW-MAA (residues 2,160–2,258) fused to the first 441 residues of the listeriolysin O (LLO) protein. Immunization with <i>Lm</i>-LLO-HMW-MAA-C was able to impede the tumor growth of early established B16F10-HMW-MAA tumors in mice and both CD4<sup>+</sup> and CD8<sup>+</sup> T cells were required for therapeutic efficacy. Immune responses to a known HLA-A2 epitope present in the HMW-MAA<sub>2160-2258</sub> fragment was detected in the HLA-A2/K<sup>b</sup> transgenic mice immunized with <i>Lm</i>-LLO-HMW-MAA-C. Surprisingly, this vaccine also significantly impaired the <i>in vivo</i> growth of other tumorigenic cell lines, such as melanoma, renal carcinoma, and breast tumors, which were not engineered to express HMW-MAA. One hypothesis is that the vaccine could be targeting pericytes, which are important for tumor angiogenesis. In a breast tumor model, immunization with <i>Lm</i>-LLO-HMW-MAA-C caused CD8<sup>+</sup> T-cell infiltration in the tumor stroma and a significant decrease in the number of pericytes in the tumor blood vessels. In conclusion, a <i>Lm</i>-based vaccine against HMW-MAA can trigger cell-mediated immune responses to this antigen that can target not only tumor cells but also pericytes in the tumor vasculature. [Cancer Res 2008;68(19):8066–75]</p></div>