Tetraspanins displayed in retrovirus-derived virus-like particles and their immunogenicity.

Virus-like particles (VLPs) are a particular subset of subunit vaccines which are currently explored as safer alternatives to live attenuated or inactivated vaccines. VLPs derived from retrovirus (retroVLPs) are commonly used as scaffolds for vaccine candidates due to their ability to incorporate heterologous envelope proteins. Pseudotyping retroVLPs is however not a selective process therefore, host cellular proteins such as tetraspanins are also included in the membrane. The contribution of these host-proteins to retrovirus immunogenicity remains unclear. In this work, human cells silenced and not silenced for tetraspanin CD81 were used to produce CD81(-) or CD81(+) retroVLPs. We first analyzed mice immune response against human CD81. Despite effective silencing of CD81 in retroVLP producing cells, both humoral and cellular immune responses showed persistent anti-CD81 immunogenicity, suggesting cross reactivity to related antigens. We thus compared the incorporation of related tetraspanins in retroVLPs and showed that decreased CD81 incorporation in CD81(-) retro-VLPs is compensated by an increased incorporation of CD9 and CD63 tetraspanins. These results highlight the dynamic nature of host-derived proteins incorporation in retroVLPs membrane, which should be considered when retrovirus-based biopharmaceuticals are produced in xenogeneic cells.

Selective B-cell expression of the MHV-68 latency-associated M2 protein regulates T-dependent antibody response and inhibits apoptosis upon viral infection.

To better understand the role of the M2 protein of the murine herpes virus strain 68 (MHV-68) in vivo, B-lymphocyte-restricted, M2-transgenic mice were constructed. The transgenic mice contained normal B-cell subpopulations in bone marrow, lymph nodes and spleen. After immunization with sheep red blood cells, spleens from M2-transgenic mice had increased germinal centres. Transgenic mice responded to the T-cell-dependent antigen keyhole limpet haemocyanin (KLH) with higher levels of secondary IgM and IgG2a antibodies than WT mice. Normal and M2-transgenic mice were infected with WT and M2 frame-shift mutant (M2FS) MHV-68 viruses. The pathogenesis of M2-transgenic mice infected with the M2-deficient mutant virus did not revert to that observed upon infection of normal mice with WT virus. However, the higher reactivation levels late after M2-transgenic mice were infected with WT virus reflected the importance of M2 as a target for the immune response, and thus with an impact on the establishment of latency. Finally, there was markedly less apoptosis in B-cells from M2-transgenic mice infected with either WT or M2FS mutant than from similarly infected WT mice, consistent with the published inhibitory influence of M2 on apoptosis in vitro. Thus, M2 provides a strategy to increase the pool of germinal centre B-cells through inhibition of apoptosis in the infected cell.

A novel TLR3 inhibitor encoded by African swine fever virus (ASFV).

African swine fever virus (ASFV) encodes proteins that manipulate important host antiviral mechanisms. Bioinformatic analysis of the ASFV genome revealed ORF I329L, a gene without any previous functional characterization as a possible inhibitor of TLR signaling. We demonstrate that ORF I329L encodes a highly glycosylated protein expressed in the cell membrane and on its surface. I329L also inhibited dsRNA-stimulated activation of NFκB and IRF3, two key players in innate immunity. Consistent with this, expression of I329L protein also inhibited the activation of interferon-ß and CCL5. Finally, overexpression of TRIF reversed I329L-mediated inhibition of both NFκB and IRF3 activation. Our results suggest that TRIF, a key MyD88-independent adaptor molecule, is a possible target of this viral host modulation gene. The demonstration of an ASFV host evasion molecule inhibiting TLR responses is consistent with the ability of this virus to infect vertebrate and invertebrate hosts, both of which deploy innate immunity controlled by conserved TLR systems.

An effective toxoid from tetanus toxin prepared by stepwise iodination of purified toxin.

Purified samples of tetanus toxin were gradually iodinated by stepwise addition of iodine, up to saturation. The residual capacity of each sample to provoke tetanus was tested by injecting sc 25 Lf (Limit of flocculation) in mice. Toxicity diminished in relation to iodine incorporated, and with iodine-saturated samples, doses of up to 100 Lf in mice, or 500 Lf in guinea-pigs, proved innocuous. Mice immunized with two doses of this toxoid adsorbed on Al(OH)3, and challenged with standard lethal toxin, gained protection against 10 MLD (Minimum Lethal Doses). Guinea-pigs were immunized by a single sc dose of 27.5 Lf with fluid toxoid, and all resisted challenge against 10 MLD applied 30 days later. The mice sera gave strong immunoprecipitation lines against the native toxin. The findings indicated that by controlled iodination of tetanus toxin an effective and inexpensive toxoid can be prepared.