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In this randomized, controlled trial involving women in South Africa and Uganda, twice-yearly subcutaneous lenacapavir was superior to daily oral emtricitabine–tenofovir disoproxil fumarate in preventing HIV infection.

HIV infection has been difficult to cure because of uncharacterized reservoirs of infected cells that are resistant to antiretroviral therapy. This study shows that some hematopoietic stem cells are latently infected and may therefore constitute such a reservoir. HIV causes a chronic infection characterized by depletion of CD4 + T lymphocytes and the development of opportunistic infections. Despite drugs that inhibit viral spread, HIV infection has been difficult to cure because of uncharacterized reservoirs of infected cells that are resistant to highly active antiretroviral therapy (HAART) and the immune response. Here we used CD34 + cells from infected people as well as in vitro studies of wild-type HIV to show infection and killing of CD34 + multipotent hematopoietic progenitor cells (HPCs). In some HPCs, we detected latent infection that stably persisted in cell culture until viral gene expression was activated by differentiation factors. A unique reporter HIV that directly detects latently infected cells in vitro confirmed the presence of distinct populations of active and latently infected HPCs. These findings have major implications for understanding HIV bone marrow pathology and the mechanisms by which HIV causes persistent infection.

The mechanistic target of rapamycin (mTOR) functions in two distinct complexes: mTORC1, and mTORC2. mTORC1 has been implicated in the pathogenesis of flaviviruses including dengue, where it contributes to the establishment of a pro-viral autophagic state. Activation of mTORC2 occurs upon infection with some viruses, but its functional role in viral pathogenesis remains poorly understood. In this study, we explore the consequences of a physical protein-protein interaction between dengue non-structural protein 5 (NS5) and host cell mTOR proteins during infection. Using shRNA to differentially target mTORC1 and mTORC2 complexes, we show that mTORC2 is required for optimal dengue replication. Furthermore, we show that mTORC2 is activated during viral replication, and that mTORC2 counteracts virus-induced apoptosis, promoting the survival of infected cells. This work reveals a novel mechanism by which the dengue flavivirus can promote cell survival to maximize viral replication.

Retrotransposons and genomic integrity The ability of retrotransposons to mobilize and insert into genes presents a challenge to a cell needing to maintain its genomic integrity. Garcia-Perez et al . have studied retrotransposition in embryonic carcinoma-derived cells. On insertion into the DNA, the retrotransposon is quickly silenced by a chromatin-dependent mechanism. However, this process is specific for certain retrotransposons, implying that multiple silencing mechanisms may exist. Once cells differentiate, the ability to silence newly introduced retrotransposons is lost, but previously inactivated retrotransposons remain inactive. This suggests that either a crucial silencing factor is not expressed in differentiated cells, or that a repressor of silencing is activated in differentiated cells. The ability of retrotransposons to mobilize and insert into genes presents a challenge to a cell needing to maintain its genomic integrity. These authors have studied retrotransposition in embryonic carcinoma-derived cells. On insertion into DNA, the retrotransposon is quickly silenced, but the retrotransposon-specificity of this process implies that multiple silencing mechanisms may exist. Once cells differentiate, the ability to silence newly introduced retrotransposons is lost but previously inactivated retrotransposons remain inactive. Long interspersed element-1 (LINE-1 or L1) retrotransposition continues to affect human genome evolution 1 , 2 . L1s can retrotranspose in the germline, during early development and in select somatic cells 3 , 4 , 5 , 6 , 7 , 8 ; however, the host response to L1 retrotransposition remains largely unexplored. Here we show that reporter genes introduced into the genome of various human embryonic carcinoma-derived cell lines (ECs) by L1 retrotransposition are rapidly and efficiently silenced either during or immediately after their integration. Treating ECs with histone deacetylase inhibitors rapidly reverses this silencing, and chromatin immunoprecipitation experiments revealed that reactivation of the reporter gene was correlated with changes in chromatin status at the L1 integration site. Under our assay conditions, rapid silencing was also observed when reporter genes were delivered into ECs by mouse L1s and a zebrafish LINE-2 element, but not when similar reporter genes were delivered into ECs by Moloney murine leukaemia virus or human immunodeficiency virus, suggesting that these integration events are silenced by distinct mechanisms. Finally, we demonstrate that subjecting ECs to culture conditions that promote differentiation attenuates the silencing of reporter genes delivered by L1 retrotransposition, but that differentiation, in itself, is not sufficient to reactivate previously silenced reporter genes. Thus, our data indicate that ECs differ from many differentiated cells in their ability to silence reporter genes delivered by L1 retrotransposition.

Twice-yearly subcutaneous lenacapavir has been shown to be efficacious for prevention of human immunodeficiency virus (HIV) infection in cisgender women. The efficacy of lenacapavir for preexposure prophylaxis (PrEP) in cisgender men, transgender women, transgender men, and gender-nonbinary persons is unclear. In this phase 3, double-blind, randomized, active-controlled trial, we randomly assigned participants in a 2:1 ratio to receive subcutaneous lenacapavir every 26 weeks or daily oral emtricitabine-tenofovir disoproxil fumarate (F/TDF). The primary efficacy analysis compared the incidence of HIV infection in the lenacapavir group with the background HIV incidence in the screened population. The secondary efficacy analysis compared the incidence of HIV infection in the lenacapavir group with that in the F/TDF group. Among 3265 participants who were included in the modified intention-to-treat analysis, HIV infections occurred in 2 participants in the lenacapavir group (0.10 per 100 person-years; 95% confidence interval [CI], 0.01 to 0.37) and in 9 participants in the F/TDF group (0.93 per 100 person-years; 95% CI, 0.43 to 1.77). The background HIV incidence in the screened population (4634 participants) was 2.37 per 100 person-years (95% CI, 1.65 to 3.42). The incidence of HIV infection in the lenacapavir group was significantly lower than both the background incidence (incidence rate ratio, 0.04; 95% CI, 0.01 to 0.18; P<0.001) and the incidence in the F/TDF group (incidence rate ratio, 0.11; 95% CI, 0.02 to 0.51; P = 0.002). No safety concerns were identified. A total of 26 of 2183 participants (1.2%) in the lenacapavir group and 3 of 1088 (0.3%) in the F/TDF group discontinued the trial regimen because of injection-site reactions. The HIV incidence with twice-yearly lenacapavir was significantly lower than the background incidence and the incidence with F/TDF. (Funded by Gilead Sciences; PURPOSE 2 ClinicalTrials.gov number, NCT04925752.).

In recent studies, strains of non-dysenteriae 1 Shigella (NDS) expressing Shiga toxin have been reported. In this study, we report a novel stx1a-converting bacteriophage of Shigella sonnei associated with travel to Mexico. Phylogenetic comparison between this and other stx-converting phages suggests that toxigenic NDS strains have arisen through separate horizontal transfer events from toxigenic Escherichia coli.