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Lymphocyte-specific protein tyrosine kinase (LCK) is essential for T cell antigen receptor (TCR)–mediated signal transduction. Here, we report two siblings homozygous for a novel LCK variant (c.1318C>T; P440S) characterized by T cell lymphopenia with skewed memory phenotype, infant-onset recurrent infections, failure to thrive, and protracted diarrhea. The patients’ T cells show residual TCR signal transduction and proliferation following anti-CD3/CD28 and phytohemagglutinin (PHA) stimulation. We demonstrate in mouse models that complete (Lck−/−) versus partial (LckP440S/P440S) loss-of-function LCK causes disease with differing phenotypes. While both Lck−/− and LckP440S/P440S mice exhibit arrested thymic T cell development and profound T cell lymphopenia, only LckP440S/P440S mice show residual T cell proliferation, cytokine production, and intestinal inflammation. Furthermore, the intestinal disease in the LckP440S/P440S mice is prevented by CD4+ T cell depletion or regulatory T cell transfer. These findings demonstrate that P440S LCK spares sufficient T cell function to allow the maturation of some conventional T cells but not regulatory T cells—leading to intestinal inflammation.

Exosomes are 50‐ to 150‐nm‐diameter extracellular vesicles secreted by all mammalian cells except mature red blood cells and contribute to diverse physiological and pathological functions within the body. Many methods have been used to isolate and analyze exosomes, resulting in inconsistencies across experiments and raising questions about how to compare results obtained using different approaches. Questions have also been raised regarding the purity of the various preparations with regard to the sizes and types of vesicles and to the presence of lipoproteins. Thus, investigators often find it challenging to identify the optimal exosome isolation protocol for their experimental needs. Our laboratories have compared ultracentrifugation and commercial precipitation‐ and column‐based exosome isolation kits for exosome preparation. Here, we present protocols for exosome isolation using two of the most commonly used methods, ultracentrifugation and precipitation, followed by downstream analyses. We use NanoSight nanoparticle tracking analysis and flow cytometry (Cytek^®) to determine exosome concentrations and sizes. Imaging flow cytometry can be utilized to both size exosomes and immunophenotype surface markers on exosomes (ImageStream^®). High‐performance liquid chromatography followed by nano‐flow liquid chromatography–mass spectrometry (LCMS) of the exosome fractions can be used to determine the presence of lipoproteins, with LCMS able to provide a proteomic profile of the exosome preparations. We found that the precipitation method was six times faster and resulted in a ∼2.5‐fold higher concentration of exosomes per milliliter compared to ultracentrifugation. Both methods yielded extracellular vesicles in the size range of exosomes, and both preparations included apoproteins. © 2020 Wiley Periodicals LLC.

Basic Protocol 1: Pre‐analytic fluid collection and processing

Basic Protocol 2: Exosome isolation by ultracentrifugation

Alternate Protocol 1: Exosome isolation by precipitation

Basic Protocol 3: Analysis of exosomes by NanoSight nanoparticle tracking analysis

Alternate Protocol 2: Analysis of exosomes by flow cytometry and imaging flow cytometry

Basic Protocol 4: Downstream analysis of exosomes using high‐performance liquid chromatography

Basic Protocol 5: Downstream analysis of the exosome proteome using nano‐flow liquid chromatography–mass spectrometry