CD133 Epitope Vaccine Using Gp96 As Adjuvant Elicits An Antitumor T Cell Response Against Lymphocytic Leukemia

Leukemia is the most common blood cell cancer.The five-year relative survival rate for leukemia has more than quadrupled since 1960.From 2005 to 2011,the five-year relative survival rate was 62 percent in the US.Despite significant progress achieved over the past decade in the chemotherapy-based and targeted treatments of several leukemia subsets,the relapse and refractory remain common after an initial response,indicating resistance of leukemia stem/progenitor cells to current therapies.Importantly,targeted therapy possesses unique possibilities for the targeting of tumor tissue not obtainable by current cancer therapies,such as chemotherapy and molecular-targeted agents,in which most suffer from off-target toxicity limiting optimal therapeutic dosing of patients.Cytotoxic T lymphocytes(CTLs)are well known for their role in the target of killing tumor cells,especially the CD8+ T cells.It is important to development of an effective tumor immunotherapy vaccine for stimulating of specific CTLs against leukemia.Cancer stem cells are currently under intensive investigation due to their capabilities for tumor initiation,self-renewal,and resistance to chemotherapy.Cancer stem cells are currently under intensive investigation due to their capabilities for tumor initiation,self-renewal,and resistance to chemotherapy and radiation-therapy.CD133 has been defined as a CSC surface antigen marker in various malignancies,including leukemia,hepatic cell carcinoma,lung cancer,breast cancer,brain tumors and prostate cancer.CD133 is implicated in stemness and the malignancy of tumor cells.And it is an ideal target for therapeutic development against cancer.Several recent studies have shown that gp96 can induce the activation of dendritic cells and macrophages though its interaction with Toll-like receptors(TLRs),support the activation of innate immune responses.On the other hand,gp96-peptide complex also could activation both of the innate immune system and cytotoxic T lymphocyte(CTL)response.Here,we explored recombinant-heat shock protein gp96 adjuvanted CD133 epitope vaccine against lymphocytic leukemia.Three H2-Kd-restricted CTL epitopes derived from CD133,namely CD133419-428,CD133702-710 and CD133760-769 were screened and identified in this study.The immunogenicity and antitumor activity of the epitope vaccine using heat shock protein gp96 as adjuvant were further determined in CD133~+ lymphocytic leukemia xenograft mice.In prophylactic model,compared to control peptide,immunization with CD133 epitopes significantly inhibited tumor growth,decreasing tumor volume and weight both by approximately 43%(both P < 0.05).ELISPOT assays revealed that immunization with CD133 epitopes resulted in about 4.6-,0.6-,and 1.2-fold increases in tumor-specific T cells compared to control peptide immunization.Splenocytes from CD133 epitopes-immunized mice exhibited significantly higher cytotoxicity activity towards L1210 cells than those from control peptide-immunized mice(P < 0.05).In therapeutic model,compared to controls,immunization with CD133 epitope vaccine significantly inhibited tumor growth and decreased tumor weight by approximately 31 and 30%,respectively(both P < 0.05).Simillaly,stong T cell-mediated cytotoxic activity against CD133~+ L1210 cells was obverved in mice immunized with CD133 epitope vaccine in therapeutic model(P<0.01).Finally,we demonstrate that adoptive transfer of epitope-specific CTLs led to suppression of lymphocytic leukemia growth.In summary,our data therefore provide the basis for designing a CD133 epitope vaccine to activate specific CTLs against CD133~+ leukemia and other cancers.