| Summary: | 碩士 === 國立陽明大學 === 生物醫學影像暨放射科學系 === 102 === Significant progress has been made in the field of cancer immunotherapy. American Association for the Advancement of Science (AAAS) had selected cancer immunotherapy as the “breakthrough of the year 2013”. Immunotherapy exerts its function of anticancer effect by enhancing immunity and recognition of tumor antigen. Moreover, it is becoming clear that the mechanisms of immune-suppressing also play an important role in anticancer effects of immune system. Co-stimulatory signaling pathway triggered by the binding of B7.1/B7.2 (CD80/86) of antigen-presenting cells (APCs) to CD28 of T cells is required for optimal T-cell activation. Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is a negative regulator of T cell activation, which competes with CD28 for B7.1/B7.2 binding with a greater affinity. Ipilimumab, a monoclonal antibody against CTLA-4, has shown positive efficacy in a pivotal clinical trial for the treatment of metastatic melanoma and was approved by FDA. However, the cost of monoclonal antibody-based therapeutics might limit the number of patients treated. To develop a novel therapeutics specifically targeting CTLA-4 at a price more affordable to most cancer patients, we constructed a DNA vaccine by cloning the sequence of CTLA-4 fused with a transmembrane domain sequence of placental alkaline phosphatase (PLAP) into a mammalian expression plasmid, pVAC-1. Immunization with the resulting construct, pVAC- 1-hCTLA-4, elicited antibody specific to human CTLA-4 with cross reactivity to murine CTLA-4, which was sufficient for inhibiting B16F10 tumor growth in c57BL/6 mice in the absence of measurable toxicity. Coupling liposome with pVAC-1-mCTLA-4 could break tolerance to self-antigen in BALB/c mice and induce potent immunity against murine CTLA-4, thereby suppressing growth of subcutaneous renal cell carcinoma (Renca).
Our data presents anti-human CTLA-4 serum from mice immunized with DNA vaccine that can suppress binding of human CTLA-4 to B7 and exhibited significant anti-tumor effect in vivo with no measurable toxicity in B16F10 tumor model. Additionally, the tolerance to mCTLA-4 that restricts specific antibody induced by naked pVAC-1-mCTLA-4 DNA can be overcome by coupling pVAC-1-mCTLA-4 with cationic liposome.
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