title: Episomal expression of truncated listeriolysin O in LmddA-LLO-E7 vaccine enhances antitumor efficacy by preferentially inducing expansions of CD4+FoxP3- and CD8+ T cells.
abstract: Studies have shown that Listeria monocytogenes (Lm)-based vaccine expressing a fusion protein comprising truncated listeriolysin O (LLO) and human papilloma virus (HPV) E7 protein (Lm-LLO-E7) induces a decrease in regulatory T cells (Treg) and complete regression of established, transplanted HPV-TC-1 tumors in mice. However, how the Lm-based vaccine causes a decrease in Tregs remains unclear. Using a highly attenuated Lm dal dat ΔactA strain (LmddA)-based vaccine, we report here that the vector LmddA was sufficient to induce a decrease in the proportion of Tregs by preferentially expanding CD4(+)FoxP3(-) T cells and CD8(+) T cells by a mechanism dependent on and directly mediated by LLO. Episomal expression of a nonhemolytic truncated LLO in Lm (LmddA-LLO) significantly augmented the expansion, thus further decreasing Treg frequency. Although adoptive transfer of Tregs compromised the antitumor efficacy of the LmddA-LLO-E7 vaccine, a combination of LmddA-LLO and an Lm-based vaccine expressing E7 protein (Lm-E7) induced complete regression against established TC-1 tumors. An engineered LLO-minus Lm expressing perfringolysin O (PFO) that enables the recombinant bacteria to exit from the phagolysosome without LLO confirmed that the adjuvant effect was dependent on LLO. These results suggest that LLO may serve as a promising adjuvant by preferentially inducing the expansions of CD4(+)FoxP3(-) T cells and CD8(+) T cells, thus reducing the ratio of Tregs to CD4(+)FoxP3(-) T cells and to CD8(+) T cells favoring immune responses to eradicate tumor.
authors.affiliation: Vaccine Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland;
authors.forename: Zhisong
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Vaccine Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland;
authors.forename: Laurent
authors.initials: L
authors.lastname: Ozbun
authors.affiliation: Vaccine Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland;
authors.forename: Namju
authors.initials: N
authors.lastname: Chong
authors.affiliation: Advaxis Inc., Princeton, New Jersey; and.
authors.forename: Anu
authors.initials: A
authors.lastname: Wallecha
authors.affiliation: Vaccine Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland; skhleif@gru.edu berzofsk@helix.nih.gov.
authors.forename: Jay A
authors.initials: JA
authors.lastname: Berzofsky
authors.affiliation: GRU Cancer Center, Georgia Regents University, Augusta, Georgia skhleif@gru.edu berzofsk@helix.nih.gov.
authors.forename: Samir N
authors.initials: SN
authors.lastname: Khleif
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D019496:Cancer Vaccines / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D005260:Female; D005822:Genetic Vectors; D008089:Listeria monocytogenes / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D009374:Neoplasms, Experimental / Q000628:therapy; D050725:Papillomavirus E7 Proteins / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*
chemical_list: D019496:Cancer Vaccines; D050725:Papillomavirus E7 Proteins