Summary Senescence is a cellular phenotype present in health and disease, characterized by a stable cell-cycle arrest and an inflammatory response called senescence-associated secretory phenotype (SASP). The SASP is important in influencing the behavior of neighboring cells and altering the microenvironment; yet, this role has been mainly attributed to soluble factors. Here, we show that both the soluble factors and small extracellular vesicles (sEVs) are capable of transmitting paracrine senescence to nearby cells. Analysis of individual cells internalizing sEVs, using a Cre-reporter system, show a positive correlation between sEV uptake and senescence activation. We find an increase in the number of multivesicular bodies during senescence in vivo . sEV protein characterization by mass spectrometry (MS) followed by a functional siRNA screen identify interferon-induced transmembrane protein 3 (IFITM3) as being partially responsible for transmitting senescence to normal cells. We find that sEVs contribute to paracrine senescence.

Defining the earliest virologic events following human immunodeficiency virus type 1 (HIV-1) transmission may be critical for the design of vaccine strategies aimed at blocking acquisition of HIV-1 infection. In particular, the length of the eclipse phase and the number of transmitted virus variants may define the window in which a prophylactic vaccine must act. Here we show that the dose of the virus inoculum affects these key virologic parameters following intrarectal simian immunodeficiency virus (SIV) infection of rhesus monkeys. Low-dose SIV infection resulted in a lengthened eclipse phase, fewer transmitted virus variants, and decreased innate immune activation compared with these parameters in high-dose SIV infection. These data suggest a mechanism by which it may be considerably easier for a vaccine to protect against low-risk HIV-1 transmission than against high-risk HIV-1 transmission. These findings have implications for the design and interpretation of HIV-1 vaccine efficacy studies.

Acinar metaplasia is an initial step in a series of events that can lead to pancreatic cancer. Here we perform single-cell RNA-sequencing of mouse pancreas during the progression from preinvasive stages to tumor formation. Using a reporter gene, we identify metaplastic cells that originated from acinar cells and express two transcription factors, Onecut2 and Foxq1. Further analyses of metaplastic acinar cell heterogeneity define six acinar metaplastic cell types and states, including stomach-specific cell types. Localization of metaplastic cell types and mixture of different metaplastic cell types in the same pre-malignant lesion is shown. Finally, single-cell transcriptome analyses of tumor-associated stromal, immune, endothelial and fibroblast cells identify signals that may support tumor development, as well as the recruitment and education of immune cells. Our findings are consistent with the early, premalignant formation of an immunosuppressive environment mediated by interactions between acinar metaplastic cells and other cells in the microenvironment.

Effective strategies are needed to block mucosal transmission of human immunodeficiency virus type 1 (HIV-1). Here, we address a crucial question in HIV-1 pathogenesis: whether infected donor mononuclear cells or cell-free virus plays the more important role in initiating mucosal infection by HIV-1. This distinction is critical, as effective strategies for blocking cell-free and cell-associated virus transmission may be different. We describe a novel ex vivo model system that utilizes sealed human colonic mucosa explants and demonstrate in both the ex vivo model and in vivo using the rectal challenge model in rhesus monkeys that HIV-1-infected lymphocytes can transmit infection across the mucosa more efficiently than cell-free virus. These findings may have significant implications for our understanding of the pathogenesis of mucosal transmission of HIV-1 and for the development of strategies to prevent HIV-1 transmission. N ovel microbicide and vaccine candidates for human immunodeficiency virus type 1 (HIV-1) are being evaluated preclinically for efficacy by assessing their ability to protect nonhuman primates against cell-free simian immunodeficiency virus (SIV) or simian-human immunodeficiency virus (SHIV) challenges. However, it remains unclear whether cell-associated virus (virus-infected donor mononuclear cells), cell-free virus, or both play the most important roles in initiating mucosal infection by HIV-1 (1-5). This distinction is critical, since effective strategies for blocking cell-free and cell-associated virus transmission may be very different (3, 6, 7). We sought to explore early events in mucosal transmission of HIV-1 and SIV by evaluating the relative efficiency of cell-associated and cell-free virus in initiating mucosal infection. To model these infection events, we developed a novel three-dimensional sealed human colonic mucosa explant system. We utilized this system in association with the SIV distal colon in vivo challenge model in rhesus macaques to evaluate the relative efficiency of initiating mucosal infection using cell-associated virus compared to that of initiating mucosal infection using cell-free virus in vivo. MATERIALS AND METHODS Viruses.A replication-competent CC chemokine receptor type 5 (CCR5)-tropic HIV-1 strain expressing green fluorescence protein (GFP) [HIV-1(R5) NL4.3-BaL-GFP] (8) was utilized for human organ infections, and SIVmac251 (9) was utilized for rhesus monkey tissue infections.TCID 50 for cell-associated virus and cell-free virus. The 50% tissue culture infective dose (TCID 50 ) was determined as previously described (10). Briefly, 4 replicates each of cell-associated virus (starting with 200,000 cells/well) and cell-free virus (starting with concentrated virus) were added to the first column of a 96-well plate. Then, 5-fold dilutions were performed for a total of 9 serial dilutions (1:5 to 1:5 9 ). An additional column with no virus or cells added served as a negative control to measure the background. TZM-bl cells (NIH AIDS Research and Reference Reagent Pr...