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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

¹ Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania and ² Hillman Cancer Center, Pittsburgh, Pennsylvania

Requests for reprints: Yvonne Paterson, Department of Microbiology, University of Pennsylvania School of Medicine, 323 Johnson Pavilion, 36th Street and Hamilton Walk, Philadelphia, PA 19104-6076. Phone: 215-898-3461; Fax: 215-573-4666; E-mail: yvonne{at}mail.med.upenn.edu.

Key Words: HMW-MAA • immunotherapy • Listeria monocytogenes

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 Listeria monocytogenes (Lm-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 Lm-LLO-HMW-MAA-C was able to impede the tumor growth of early established B16F10-HMW-MAA tumors in mice and both CD4⁺ and CD8⁺ T cells were required for therapeutic efficacy. Immune responses to a known HLA-A2 epitope present in the HMW-MAA_2160-2258 fragment was detected in the HLA-A2/K^b transgenic mice immunized with Lm-LLO-HMW-MAA-C. Surprisingly, this vaccine also significantly impaired the in vivo 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 Lm-LLO-HMW-MAA-C caused CD8⁺ T-cell infiltration in the tumor stroma and a significant decrease in the number of pericytes in the tumor blood vessels. In conclusion, a Lm-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]

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