Immune response to human papillomavirus 16 L1E7 chimeric virus-like particles: Induction of cytotoxic T cells and specific tumor protection

Expression of human papillomavirus type 16 (HPV 16) fusion proteins LI Delt a CE7(1-55) and LI Delta CE7(1-60), (carboxy-terminal deletion of LI replac ed by 55 or 60 amino-terminal amino acids of E7) leads to formation of chim eric papillomavirus-like particles (CVLPs), After "infection" of cells by C VLPs, the chimeric proteins can be detected in the cytosol and the endoplas mic reticulum (ER), suggesting that they are intracellularly processed via the MHC class I pathway and, therefore, able to activate cytotoxic T lympho cytes (CTLs), To investigate the cytotoxic immune response against HPV 16 L I Delta CE7(1-60), and LI Delta CE7(1-55) CVLPs, we immunized C57B1/6 mice with various CVLP doses without adjuvant, Two weeks after immunization, spl een cells were prepared and stimulated in vitro using HPV 16 E7-expressing transfectants of the tumor cell line RMA, In Cr-51-release cytotoxicity ass ays, spleen cells of mice vaccinated with LI Delta CE7(1-60) CVLPs specific ally lysed the RMA-E7 transfectants as well as RMA cells loaded with the pe ptide E7(49-57), which represents an H2-D-b-restricted CTL epitope, This de monstrates that CVLPs induce an E7-specific CTL response in mice in the abs ence of an adjuvant, Furthermore, immunization with CVLPs prevented outgrow th of E7-expressing tumor cells even if inoculation of cells was performed 2 weeks before vaccination, We conclude from our data that CVLPs show promi se for therapy of HPV-associated lesions. (C) 1999 Wiley-Liss, Inc.