Adjuvant engineering for cancer immunotherapy: Development of a synthetic TLR2 ligand with increased cell adhesion

Abstract

The development of effective immunoadjuvants for tumor immunotherapy is of fundamental importance. The use of Mycobacterium bovis bacillus Calmette-Gué rin cell wall skeleton (BCG-CWS) in tumor immunotherapy has been examined in various clinical applications. Because BCG-CWS is a macromolecule that cannot be chemically synthesized, the development of an alternative synthetic molecule is necessary to ensure a constant supply of adjuvant. In the present study, a new adjuvant was designed based on the structure of macrophage-activating lipopeptide (MALP)-2, which is a Toll-like receptor (TLR)-2 ligand similar to BCG-CWS. Macrophage-activating lipopeptide-2, [S-(2,3-bispalmitoyloxypropyl)Cys (P2C) -GNNDESNISFKEK], originally identified in a Mycoplasma species, is a lipopeptide that can be chemically synthesized. A MALP-2 peptide was substituted with a functional motif, RGDS, creating a novel molecule named P2C-RGDS. RGDS was selected because its sequence constitutes an integrin-binding motif and various integrins are expressed in immune cells including dendritic cells (DCs). Thus, this motif adds functionality to the ligand. P2C-RGDS activated DCs and splenocytes more efficiently than MALP-2 over short incubation times in vitro, and the RGDS motif contributed to their activation. Furthermore, P2C-RGDS showed higher activity than MALP-2 in inducing migration of DCs to draining lymph node, and in inhibiting tumor growth in vivo. This process of designing and developing synthetic adjuvants has been named ''adjuvant engineering,'' and the evaluation and improvement of P2C-RGDS constitutes a first step in the development of stronger synthetic adjuvants in the future. (Cancer Sci 2010; 101: 1596-1603 B acterial adjuvants that were used as biological response modifiers (BRM) for cancer immunotherapy in the 1970s have recently been re-evaluated.(1-3) Cancer antigens that had been identified in many laboratories were tested as peptide vaccines for clinical applications, but the peptides alone were not sufficient to fully activate the immune system.(4) These results suggested that the activation of the innate immune system, including dendritic cells (DCs), by a supporting adjuvant was important.(5-8) In peptide vaccine therapy, the T cells of the acquired immune system play an important role in recognizing and attacking tumor cells.(9) Dendritic cells play a key role in the regulation of the acquired immune system by presenting antigen and inducing a primary immune response. The identification of the Toll-like receptor (TLR) family advanced the understanding of DC function and of the role of adjuvants, because almost all microbial adjuvants work as TLR ligands and activate DCs.(10-12) These findings provide the basis for the understanding of the mechanism of adjuvant therapy.Dr Azuma developed BCG-CWS, a cell-wall skeleton preparation of Mycobacterium bovis bacillus Calmette-Guérin, (13,14) as an antitumor immunotherapeutic adjuvant. Although many BRM studies have been discontinued, basic and clinical research on BCG-CWS has...

Interaction of Mycoplasma hominis PG21 with Human Dendritic Cells: Interleukin-23-Inducing Mycoplasmal Lipoproteins and Inflammasome Activation of the Cell

“…Synthetic lipopeptides derived from Braun's lipoprotein were shown to exhibit stimulatory activity comparable to that of native lipoproteins (24). It was also shown that a TLR2 agonist, which is the hDC TLR that recognizes M. hominis (8), required a hydrophilic N-terminal part (25). The DSL-1 peptide chosen had seven N-terminal amino acid residues (CGGEKFN), which conferred a negative grand average of hydropathy (GRAVY) score close to that of the bioactive mycoplasmal lipopeptides FSL-1 and MALP-2 (11, 12) ( Table 2).…”

Overview and Outlook of Toll-like Receptor ligand–antigen Conjugate Vaccines

“…future science group adjuvants and novel therapeutic agents targeting cancer [32][33][34] and allergy [35].…”

Failure of mycoplasma lipoprotein MALP-2 to induce NK cell activation through dendritic cell TLR2

“…2A). In this context, three markers for NK activation (19) were assessed with this system, IFN-γ production, up-regulation of NK activation markers and target cell (B16D8) cytotoxicity by NK cells (Fig. 2).…”