Transloading of tumor cells with foreign major histocompatibility complex class I peptide ligand: a novel general strategy for the generation of potent cancer vaccines.

The major hurdle to be cleared in active immunotherapy of cancer is the poor immunogenicity of cancer cells. In previous attempts to overcome this problem, whole tumor cells have been used as vaccines, either admixed with adjuvant(s) or genetically engineered to express nonself proteins or immunomodulatory factors before application. We have developed a novel approach to generate an immunogeneic, highly effective vaccine: major histocompatibility complex (MHC) class I-positive cancer cells are administered together with MHC class I-matched peptide ligands of foreign, nonself origin, generated by a procedure we term transloading. Murine tumor lines of the H2-Kd or the H2-Db haplotype, melanoma M-3 and B16-F10, respectively, as well as colon carcinoma CT-26 (H2-Kd), were transloaded with MHC-matched influenza virus-derived peptides and applied as irradiated vaccines. Mice bearing a deposit of live M-3 melanoma cells were efficiently cured by this treatment. In the CT-26 colon carcinoma and the B16-F10 melanoma, high efficacies were obtained against tumor challenge, suggesting the universal applicability of this new type of vaccine. With foreign peptide ligands adapted to the requirements of a desired MHC class I haplotype, this concept may be used for the treatment of human cancers.

Induction of intracellular cAMP by a synthetic retroviral envelope peptide: a possible mechanism of immunopathogenesis in retroviral infections.

A synthetic heptadecapeptide, CKS-17, represents the highly conserved amino acid sequences occurring within the transmembrane envelope protein of many animal and human retroviruses. CKS-17 has been demonstrated to exhibit suppressive properties for numerous immune functions. We have recently shown that CKS-17 acts as an immunomodulatory epitope causing an imbalance of human type 1 and type 2 cytokine production and suppression of cell-mediated immunities. cAMP, an intracellular second messenger, plays an important role in regulation of cytokine biosynthesis--i.e., elevation of intracellular cAMP levels selectively inhibits type 1 cytokine production but has no effect or enhances type 2 cytokine production. Here, we demonstrate that CKS-17 induces dramatic rises in the intracellular cAMP levels of a human monocyte cell line and of human peripheral blood mononuclear cells in a time- and dose-dependent manner. A peptide corresponding to the reverse sequence of CKS-17, used as control, has no effect on intracellular cAMP levels. The cAMP-inducing ability of CKS-17 is significantly blocked by SQ-22536, an inhibitor of adenylate cyclase. These results indicate that CKS-17, a highly conserved component of the transmembrane proteins of immunosuppressive retroviruses, induces increased intracellular levels of cAMP via activation of adenylate cyclase and suggest that this retroviral envelope peptide may differentially modulate type 1 and type 2 cytokine production through elevation of intracellular cAMP levels.

Differential modulation of Th1- and Th2-related cytokine mRNA expression by a synthetic peptide homologous to a conserved domain within retroviral envelope protein.

The influence of a synthetic retroviral peptide, CKS-17, on T helper type 1 (Th1)- or Th2-related cytokines was investigated in human blood mononuclear cells. Cells were stimulated with staphylococcal enterotoxin A, anti-CD3 plus anti-CD28 monoclonal antibodies, or lipopolysaccharide to induce cytokine mRNA. mRNA was detected by a reverse transcription-polymerase chain reaction or Northern blot analysis. CKS-17 down-regulated stimulant-induced mRNA accumulation for interferon gamma (IFN-gamma), interleukin (IL)-2, and p40 heavy and p35 light chains of IL-12, a cytokine that mediates development of Th1 response. CKS-17 up-regulated stimulant-induced mRNA accumulation of IL-10 and did not suppress Th2-related cytokine (IL-4, IL-5, IL-6, or IL-13) mRNA expression. A reverse sequence of CKS-17 peptide, used as a control, showed no such action. Anti-human IL-10 monoclonal antibody blocked ability of CKS-17 to inhibit mRNA accumulation for IFN-gamma but not the CKS-17 suppressive activity of IL-12 p40 heavy chain mRNA. Thus, CKS-17-mediated suppression of IFN-gamma mRNA expression is dependent upon augmentation of IL-10 production by CKS-17. This conserved component of several retroviral envelope proteins, CKS-17, may act as an immunomodulatory epitope responsible for cytokine dysregulation that leads to suppression of cellular immunity.