BackgroundH5N1 influenza vaccines, including live intranasal, appear to be relatively less immunogenic compared to seasonal analogs. The main influenza virus surface glycoprotein hemagglutinin (HA) of highly pathogenic avian influenza viruses (HPAIV) was shown to be more susceptible to acidic pH treatment than that of human or low pathogenic avian influenza viruses. The acidification machinery of the human nasal passageway in response to different irritation factors starts to release protons acidifying the mucosal surface (down to pH of 5.2). We hypothesized that the sensitivity of H5 HA to the acidic environment might be the reason for the low infectivity and immunogenicity of intranasal H5N1 vaccines for mammals.Methodology/Principal FindingsWe demonstrate that original human influenza viruses infect primary human nasal epithelial cells at acidic pH (down to 5.4), whereas H5N1 HPAIVs lose infectivity at pH≤5.6. The HA of A/Vietnam/1203/04 was modified by introducing the single substitution HA2 58K→I, decreasing the pH of the HA conformational change. The H5N1 reassortants containing the indicated mutation displayed an increased resistance to acidic pH and high temperature treatment compared to those lacking modification. The mutation ensured a higher viral uptake as shown by immunohistochemistry in the respiratory tract of mice and 25 times lower mouse infectious dose50. Moreover, the reassortants keeping 58K→I mutation designed as a live attenuated vaccine candidate lacking an NS1 gene induced superior systemic and local antibody response after the intranasal immunization of mice.Conclusion/SignificanceOur finding suggests that an efficient intranasal vaccination with a live attenuated H5N1 virus may require a certain level of pH and temperature stability of HA in order to achieve an optimal virus uptake by the nasal epithelial cells and induce a sufficient immune response. The pH of the activation of the H5 HA protein may play a substantial role in the infectivity of HPAIVs for mammals.

Human endogenous retroviruses (HERVs) represent a cellular reservoir of potentially pathogenic retroviral genes. A growing body of evidence indicates that the activation of endogenous retroviral sequences might be involved in the transformation of melanocytes. In this study, we investigated the effects of ultraviolet radiation (UVR) on the expression of human endogenous retrovirus type K (HERV-K) in melanoma cells and non-melanoma cells in vitro. Solely in melanoma cell lines, irradiation with UVB (200 mJ/cm(2)) resulted in a significant transcriptional activation of the retroviral pol gene as well as in an enhanced expression of the retroviral envelope protein (env). In addition, UVB treatment induced the production of retroviral particles in the supernatants of melanoma cell lines. These data indicate that HERV-K expression can be activated by UVB irradiation and suggest an involvement of HERV-K in UVR-related melanoma pathogenesis.

We previously described the expression of melanomaassociated endogenous retrovirus (MERV) proteins and viral particles in human melanomas and metastases. The objective of the present study was to determine whether a humoral immune response to MERV proteins occurs in melanoma. Candidate B-cell epitopes on MERV proteins were predicted using bioinformatic screening. The reactivity of MERV peptides corresponding to the predicted epitopes with antibodies prevalent in sera of melanoma patients was analyzed. An immunodominant peptide located in the env protein of MERV was identified. Subsequent analyzes using 81 samples from stage I to stage IV melanoma patients and 95 sera from healthy subjects revealed statistically significant differences in seroprevalence of antibodies in melanoma sera samples when compared with reference samples from healthy subjects. The prevalence of anti-MERV antibodies in melanoma patient sera was confirmed by immunofluorescence on env-transfected cells. These data indicate the potential of this candidate peptide as target for diagnosis and immunotherapy.

Azidothymidine (AZT), currently used for HIV treatment, was also shown to induce cell growth inhibition and apoptosis in different human tumors. The objective of this study was to investigate the ability of AZT to inhibit the growth of human melanoma cells in vitro and in vivo. In cytotoxicity assays, treatment of cells with varying concentrations of AZT-induced inhibition of cell growth and apoptosis in three human melanoma cell lines without affecting the growth of nontumorigenic cells. AZT-dependent inhibition of proliferation was accompanied by a significant S-phase arrest of the cell cycle. Coexposure of cells to AZT during cisplatin treatment showed a synergistic effect on cytotoxicity. Moreover, AZT monotreatment of melanoma in a severe combined immunodeficiency-mouse xenotransplantation model resulted in significant tumor reduction. These results demonstrate for the first time the antimelanoma activity of AZT, suggesting its clinical utilization either as a sole agent or in combination with other chemotherapeutic agents.

No abstract