Among cytomegalovirus (CMV) tegument proteins, phosphoprotein 65 (pp65) has been identified as the important target antigen of the cytotoxic T lymphocyte (CTL) response against the virus. We synthesized seven CMV-pp65-derived peptides carrying an HLA-A24-binding motif, and investigated the ability of these peptides to induce CMV-specific CTL. We identified one nonamer peptide (pp65113-121; VYALPLKML) able to bind HLA-A24 and induce CTL responses in vitro in peripheral blood mononuclear cells (PBMC) from CMV-seropositive individuals. The peptide-specific CTLs generated were capable of recognizing pp65 expressed on CMV-infected fibroblasts as well as pp65113-121 peptide bound to the surface of C1R-A*2402 cells in an HLA-A24-restricted manner. The pp65113-121 peptide thus might be considered a synthetic peptide vaccine in HLA-A24-positive individuals.
Summary: We demonstrated transmission of human cytomegalovirus (HCMV) from the human lung fibroblast MRC-5 to peripheral blood leukocytes (PBLs). mRNA of the HCMV immediately early (IE) antigen was detected in PBLs cultured with IL-2 or IL-2+ IL-4 that made direct contact with HCMV-infected MRC-5, whereas it was not detected in PBLs prevented from making cell-to cell contact. However, mRNA of HCMV IE was not detected in PBLs cultured with IL-2 and IFN gamma that made direct contact with HCMV-infected MRC-5. Transmission of the pp65 antigen was increased in culture medium containing IL-4. At a higher viral infection titer, cell-free HCMV infected adherent PBLs cells. The subset, which did not adhere, did not infect cell-free viruses even at a very high multiplicity of infection. Moreover, the adhered subset of PBLs infected with HCMV was able to transmit HCMV to non-infected fibroblasts. Our results suggest that cell-to-cell contact (when PBLs make direct contact with HCMV-infected cells) is important in the mechanism of HCMV transmission and that the adherent cells of PBLs are one of the most important vehicles for HCMV infection. Moreover, we suggest that type 2 cytokines such as IL-4 enhance the transmission of HCMV to PBLs.
It has been proven that interleukin-15 (IL-15) has structural and functional features similar to those of interleukin-2 (IL-2). In this study we examined the anti-tumor effect of IL-15 using an adenoviral vector in a mouse model. We constructed an adenoviral vector expressing the IL-15 gene, and introduced it into a mouse Lewis lung carcinoma (LLC) cell line. Then we inoculated pulmonary tissue of a syngeneic mouse strain (C57BL/6 CR) with the IL-15 gene-expressing LLC cells (LLC/IL-15). At the early phase (Day 14), a large number of NK cells accumulated around the IL-15 expressing tumors. At the late phase (Day 28), a much larger number of NK cells had accumulated around the tumors and quite a few NK cells had invaded the IL-15 expressing tumors. The LLC/IL-15-inoculated group survived significantly longer compared to the control groups, i.e., a group inoculated with LacZ gene-expressing LLC cells or a group inoculated with IL-2 gene-expressing LLC cells. After 60 days, the surviving mice of the LLC/IL-15-inoculated group were re-challenged with an additional inoculation of LLC cells alone. Tumor growth was significantly inhibited in the rechallenged LLC/IL-15 group. Induction of cytotoxic T cells was confirmed by interferon-gamma production by splenocytes. We concluded that the IL-15 expressed in the IL-15 expressing tumor cells enhanced the accumulation of NK cells and activated them, leading to suppression of proliferation of the tumor cells.
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