Second-generation rabies virus-based vaccine vectors expressing human immunodeficiency virus type 1 gag have greatly reduced pathogenicity but are highly immunogenic.

Rabies virus (RV) vaccine strain-based vectors show great promise as vaccines against other viral diseases such as human immunodeficiency virus type 1 (HIV-1) infection and hepatitis C, but a low residual pathogenicity remains a concern for their use. Here we describe several highly attenuated second-generation RV-based vaccine vehicles expressing HIV-1 Gag. For this approach, we modified the previously described RV vaccine vector SPBN by replacing the arginine at position 333 (R333) within the RV glycoprotein (G) with glutamic acid (E333), deleting 43 amino acids of the RV G cytoplasmic domain (CD), or combining the R333 exchange and the CD deletion. In addition, we constructed a new RV vector that expresses HIV-1 Gag from an RV transcription unit upstream of the RV phosphoprotein gene (BNSP-Gag) instead of upstream of the G gene. As expected and as demonstrated for SPBN-Gag, all vaccine vehicles were apathogenic after peripheral administration. However, the new, second-generation vaccine vectors containing modifications in the RV G were also apathogenic after intracranial infection with 10(5) infectious particles, and BNSP-Gag produced a 50%-reduced mortality in mice. Of note, the observed attenuation of pathogenicity did not result in either the attenuation of the humoral response against the RV G or the previously observed robust cellular response against HIV-1 Gag. These findings demonstrate that very safe and highly effective RV-based vaccines can be constructed and further emphasize their potential utility as efficacious antiviral vaccines.

Both viral transcription and replication are reduced when the rabies virus nucleoprotein is not phosphorylated.

Rabies virus nucleoprotein (N) plays vital roles in regulation of viral RNA transcription and replication by encapsidation of the nascent genomic RNA. Rabies virus N is phosphorylated, and previous studies demonstrated that mutation of the phosphorylated serine at position 389 to alanine resulted in reduction of viral transcription and/or replication of a rabies virus minigenome. In the present study, we mutated the serine (S) at position 389 to alanine (A), glycine (G), aspartic acid (D), asparagine (N), glutamic acid (E), and glutamine (Q) and examined the effects of these mutations on rabies virus transcription and replication in the minigenome. Furthermore, mutations from S to A, S to D, and S to E were also incorporated into the full-length infectious virus. Mutation of the serine to each of the other amino acids resulted in the synthesis of an unphosphorylated N and reduction of viral transcription and replication in the minigenome. Mutations from S to A and S to D also resulted in reduction of both viral transcription and replication in full-length infectious viruses. Growth curve studies indicated that production of the mutant virus with the S-to-A mutation (L16A) was as much as 10,000-fold less than that of the wild-type virus (L16). Northern blot hybridization with rabies virus gene probes revealed that the rates of viral transcription and replication were reduced by as much as 10-fold in the mutant viruses when the N was not phosphorylated. Interpretation of the data from the minigenome system and the full-length infectious virus indicates that phosphorylation of rabies virus N is necessary for replication. Further studies involving cycloheximide treatment of infected cells revealed that viral transcription was also reduced when the N was not phosphorylated. Taken together, these results provide definitive evidence that N phosphorylation plays an important role in the processes of rabies virus transcription and replication.

Rhabdovirus-based vectors with human immunodeficiency virus type 1 (HIV-1) envelopes display HIV-1-like tropism and target human dendritic cells.

We describe replication-competent, vaccine strain-based rabies viruses (RVs) that lack their own single glycoprotein and express, instead, a chimeric RV-human immunodeficiency virus type 1 (HIV-1) envelope protein composed of the ectodomain and transmembrane domains of HIV-1 gp160 and the cytoplasmic domain of RV G. The envelope proteins from both X4 (NL4-3)- and R5X4 (89.6)-tropic HIV-1 strains were utilized. These recombinant viruses very closely mimicked an HIV-1- like tropism, as indicated by blocking experiments. Infection was inhibited by SDF-1 on cells expressing CD4 and CXCR4 for both viruses, whereas RANTES abolished infection of cells expressing CCR5 in addition to CD4 in studies of the RV expressing HIV-1(89.6) Env. In addition, preincubation with soluble CD4 or monoclonal antibodies directed against HIV-1 gp160 blocked the infectivity of both G-deficient viruses but did not affect the G-containing RVs. Our results also indicated that the G-deficient viruses expressing HIV-1 envelope protein, in contrast to wild-type RV but similar to HIV-1, enter cells by a pH-independent pathway. As observed for HIV-1, the surrogate viruses were able to target human peripheral blood mononuclear cells, macrophages, and immature and mature human dendritic cells (DC). Moreover, G-containing RV-based vectors also infected mature human DC, indicating that infection of these cells is also supported by RV G. The ability of RV-based vectors to infect professional antigen-presenting cells efficiently further emphasizes the potential use of recombinant RVs as vaccines.