Exosomes, microvesicles, and other extracellular vesicles-a Keystone Symposia report.

Extracellular vesicles (EVs) are small, lipid-bilayer-bound particles released by cells that can contain important bioactive molecules, including lipids, RNAs, and proteins. Once released in the extracellular environment, EVs can act as messengers locally as well as to distant tissues to coordinate tissue homeostasis and systemic responses. There is a growing interest in not only understanding the physiology of EVs as signaling particles but also leveraging them as minimally invasive diagnostic and prognostic biomarkers (e.g., they can be found in biofluids) and drug-delivery vehicles. On October 30-November 2, 2022, researchers in the EV field convened for the Keystone symposium "Exosomes, Microvesicles, and Other Extracellular Vesicles" to discuss developing standardized language and methodology, new data on the basic biology of EVs and potential clinical utility, as well as novel technologies to isolate and characterize EVs.

DNA Barcoding in Nonhuman Primates Reveals Important Limitations in Retrovirus Integration Site Analysis.

In vivo tracking of retrovirus-tagged blood stem and progenitor cells is used to study hematopoiesis. Two techniques are used most frequently: sequencing the locus of retrovirus insertion, termed integration site analysis, or retrovirus DNA barcode sequencing. Of these, integration site analysis is currently the only available technique for monitoring clonal pools in patients treated with retrovirus-modified blood cells. A key question is how these two techniques compare in their ability to detect and quantify clonal contributions. In this study, we assessed both methods simultaneously in a clinically relevant nonhuman primate model of autologous, myeloablative transplantation. Our data demonstrate that both methods track abundant clones; however, DNA barcode sequencing is at least 5-fold more efficient than integration site analysis. Using computational simulation to identify the sources of low efficiency, we identify sampling depth as the major factor. We show that the sampling required for integration site analysis to achieve minimal coverage of the true clonal pool is likely prohibitive, especially in cases of low gene-modified cell engraftment. We also show that early subsampling of different blood cell lineages adds value to clone tracking information in terms of safety and hematopoietic biology. Our analysis demonstrates DNA barcode sequencing as a useful guide to maximize integration site analysis interpretation in gene therapy patients.

Rapid immune reconstitution of SCID-X1 canines after G-CSF/AMD3100 mobilization and in vivo gene therapy.

Hematopoietic stem-cell gene therapy is a promising treatment of X-linked severe combined immunodeficiency disease (SCID-X1), but currently, it requires recipient conditioning, extensive cell manipulation, and sophisticated facilities. With these limitations in mind, we explored a simpler therapeutic approach to SCID-X1 treatment by direct IV administration of foamy virus (FV) vectors in the canine model. FV vectors were used because they have a favorable integration site profile and are resistant to serum inactivation. Here, we show improved efficacy of our in vivo gene therapy platform by mobilization with granulocyte colony-stimulating factor (G-CSF) and AMD3100 before injection of an optimized FV vector incorporating the human phosphoglycerate kinase enhancerless promoter. G-CSF/AMD3100 mobilization before FV vector delivery accelerated kinetics of CD3+ lymphocyte recovery, promoted thymopoiesis, and increased immune clonal diversity. Gene-corrected T lymphocytes exhibited a normal CD4:CD8 ratio and a broad T-cell receptor repertoire and showed restored γC-dependent signaling function. Treated animals showed normal primary and secondary antibody responses to bacteriophage immunization and evidence for immunoglobulin class switching. These results demonstrate safety and efficacy of an accessible, portable, and translatable platform with no conditioning regimen for the treatment of SCID-X1 and other genetic diseases.

Identification of Salmonella Typhimurium Deubiquitinase SseL Substrates by Immunoaffinity Enrichment and Quantitative Proteomic Analysis.

Ubiquitination is a key protein post-translational modification that regulates many important cellular pathways and whose levels are regulated by equilibrium between the activities of ubiquitin ligases and deubiquitinases. Here, we present a method to identify specific deubiquitinase substrates based on treatment of cell lysates with recombinant enzymes, immunoaffinity purification, and global quantitative proteomic analysis. As a model system to identify substrates, we used a virulence-related deubiquitinase, SseL, secreted by Salmonella enterica serovar Typhimurium into host cells. Using this approach, two SseL substrates were identified in the RAW 264.7 murine macrophage-like cell line, S100A6 and heterogeneous nuclear ribonuclear protein K, in addition to the previously reported K63-linked ubiquitin chains. These substrates were further validated by a combination of enzymatic and binding assays. This method can be used for the systematic identification of substrates of deubiquitinases from other organisms and applied to study their functions in physiology and disease.