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Hsp70-Like Protein 1 Fusion Protein Enhances Induction of Carcinoembryonic Antigen–Specific CD8⁺ CTL Response by Dendritic Cell Vaccine

¹ Institute of Immunology, Second Military Medical University, Shanghai, People's Republic of China and ² Institute of Immunology, Zhejiang University, Hangzhou Zhejiang, People's Republic of China

Requests for reprints: Xuetao Cao, Institute of Immunology Second Military Medical University, 800 Xiangyin Road, Shanghai 200433, People's Republic of China. Phone: 86-21-2507-0316; Fax: 86-21-6538-2502; E-mail: caoxt{at}public3.sta.net.cn.

Heat shock proteins (HSP) have been revealed to interact with antigen-presenting cells and have potent adjuvant capability to induce antigen-specific CD8⁺ CTL and Th1 responses. Our previous work shows how Hsp70-like protein 1 (Hsp70L1), as a new member of the Hsp70 subfamily, acts as potent Th1 adjuvant. Here, we report the efficient induction of tumor antigen-specific immune response by dendritic cells pulsed with recombinant fusion protein of Hsp70L1 and CEA_576-669 fragment of the carcinoembryonic antigen (CEA) containing CAP-1 (a HLA-A2–restricted CTL epitope). Fusion protein CEA_576-669-Hsp70L1 can promote dendritic cell maturation and activate dendritic cells to produce cytokines, such as interleukin-12, interleukin-1ß, and tumor necrosis factor-, and chemokines, such as macrophage inflammatory protein-1, macrophage inflammatory protein-1ß, and regulated on activation, normal T expressed and secreted, indicating the adjuvant ability of Hsp70L1 in the fusion protein. CEA-specific HLA-A2.1–restricted CD8⁺ CTLs either from patients with CEA⁺/HLA-A2.1⁺ colon carcinoma or from splenocytes of immunized HLA-A2.1/K^b transgenic mice can be generated more efficiently after stimulations or immunizations with dendritic cells pulsed by CEA_576-669-Hsp70L1 than with dendritic cells pulsed by CEA_576-669 alone, resulting in secreting more Th1 cytokine IFN- and killing target cells more potently in an antigen-specific and HLA-A2.1–restricted manner. Adoptive transfer of splenocytes from transgenic mice immunized with CEA_576-669-Hsp70L1–pulsed dendritic cells can inhibit tumor growth and prolong survival in nude mice bearing CEA⁺/HLA-A2.1⁺ human colon carcinoma more markedly. Therefore, Hsp70L1 has potent adjuvant effect in form of fusion protein, indicating that Hsp70L1 may be widely used as Th1 adjuvant to prepare antigenic fusion protein for the therapeutics of cancer or infectious diseases.