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We present improved protocols for retroviral transduction of trafficking receptors and competitive homing to study receptor-mediated organ- and microenvironment-specific lymphocyte positioning. This method offers valuable insights into immune cell trafficking mechanisms and has potential applications in future basic and therapeutic research.
Understanding how G-protein coupled receptor (GPCR) expression affects cell positioning within diverse tissue microenvironments is essential for elucidating immune cell trafficking mechanisms. We present a competitive homing assay designed to study GPCR-mediated T-cell localization to organs expressing their cognate chemoattractant ligands, applicable for both short-term and long-term studies. The approach involves an improved protocol for recombinant murine stem cell virus (MSCV) transduction of T cells to express the GPCR of interest or a control construct, followed by competitive homing in recipient mice. Cell distribution across different organs is analyzed using flow cytometry and/or confocal microscopy. In short-term experiments (10-12 h), confocal microscopy revealed distinct cell localization patterns, including to alveoli, bronchi submucosa, venous sites, and interstitium in the lung, as well as the epithelium lining the trachea, stomach, and uterine horn. In long-term studies (1-7 weeks), flow cytometry provided insights into preferential cell accumulation, revealing dynamic changes and potential maturation or repositioning within tissues over time. This competitive homing assay is a robust tool for studying GPCR-mediated cell positioning, offering valuable insights into tissue-specific distribution and potential applications in immunology and therapeutic research.
G-protein coupled receptors (GPCRs) are fundamental in regulating a variety of cellular processes, including signal transduction, neurotransmission, hormone regulation, and immune cell migration1. They play a crucial role in the spatiotemporal control of lymphocyte migration and localization2. During the priming phase of immune responses, the local microenvironment and cellular interactions prompt T lymphocytes to express a unique set of adhesion molecules and chemokine receptors known as homing receptors. This adaptation enables antigen-experienced T cells to engage with organ-specific endothelial cells (ECs) and migrate to distinct target tissues. The ability of T cells to acquire tissue tropism is vital for effective recall responses, particularly in the context of recurrent infections affecting the same organ3,4.
GPCRs guide immune cells to specific tissues and organs where they perform critical functions -- such as directing CD8+ T and NK cells to tumor sites for cytotoxic action or aiding CD4+ T cells in orchestrating immune responses by supporting the activation of other immune cells. Understanding how GPCRs direct T cells to their precise locations is essential for advancing targeted immunotherapies5,6. The challenge, however, lies in modeling these complex interactions in vitro, as replicating both spatially restricted cues and directional chemotactic signals simultaneously is difficult.
Elucidating the roles of specific leukocyte receptors is also often challenging due to their limited frequency of expression in endogenous populations and the fact that these receptors typically decorate distinct cell types. This complexity makes it difficult to isolate the role of a specific receptor from other cell subset-specific mechanisms. Ideally, methods should compare similar populations, differing only in the receptor of interest to provide clear insights.
To overcome these challenges, we have adopted a competitive homing assay that employs recombinant MSCV retroviral transduction for efficient GPCR expression in T cells. MSCV retroviral vectors, which combine elements from the myeloproliferative sarcoma virus (PCMV)-based MESV vectors and the Moloney murine leukemia virus (MMLV)-based LN vectors, incorporate an extended hybrid packaging signal derived from the LN vectors7. This modification enhances the efficiency of gene delivery, enabling both short-term and long-term studies of T-cell localization in vivo. By utilizing high-titer retroviral particles and confocal microscopy, the approach allows for precise visualization of T-cell positioning and interactions within complex tissue environments. We present detailed protocols for the retroviral transduction of trafficking receptors and the performance of internally controlled (so-called competitive) homing assays to study receptor-mediated organ- and microenvironment-specific lymphocyte positioning. The overall goal of this method is to provide valuable insights into immune cell trafficking mechanisms and to enable future applications in both basic research and therapeutic development.
All mice in this study were maintained in specific pathogen-free (SPF) facilities at the Veterans Affairs Palo Alto Health Care System (VAPAHCS). B6/SJL Prprc Pep3BoyJ (CD45.1), C57B6/J (CD45.2), and Rag1-/- mice were purchased from Jackson Laboratories. While we used PepBoy to obtain CD45.1 cells, we recommend using JAXBoy (C57BL/6J-Ptprcem6Lutzy/J). JAXBoy is a fully coisogenic strain generated through CRISPR instead of traditional backcrossing, which improves genetic consistency. Historically, CD45 allotype-marked studies using PepBoy mice (CD45.1), which are not fully congenic, have included control homing and recirculation assays with wild-type (WT/WT) comparisons to address potential variability. With JAXBoy mice now available as a fully isogenic alternative, these additional controls may no longer be necessary. Researchers should still consider that differences between CD45.1 and CD45.2 variants-such as their roles as protein tyrosine phosphatases-can influence cellular behavior and homing patterns. All protocols discussed in theΒ text and below have been approved or meetΒ the guidelines of the accredited Department ofΒ Laboratory Animal Medicine and theΒ Administrative Panel on Laboratory Animal CareΒ at the VA Palo Alto Health Care SystemΒ (VAPAHCS). Animals were sacrificed usingΒ approved procedures.Β Mice of both sexes, aged 8-12 weeks, were included in the experiments.
1. MSCV vector preparation
2. Establishing packaging cell line culture
NOTE: We used Platinum E (Plat-E) cells from Cell Biolabs. Plat-E cells are a 293T-based cell line with an EF1Ξ± promoter, which provides a stable and high-yield expression of retroviral structural proteins (gag, pol, and env genes), enabling retroviral packaging with a single plasmid transfection8. Although other cell lines, such as NIH-3T3 or 293T, might be used, we have not tested these alternatives.
3. Production of transduced cells
In this study, we present a detailed protocol for investigating the ability of specific receptors to direct T-cell localization in vivo. As a demonstration of this protocol, we used GPR2513. We are able to achieve 30%-40% transduction efficiency using this protocol, as assessed by Thy1.1 staining by flow cytometry. We performed in vitro transwell-based chemotaxis assays using GPR25-transduced cells alongside stuffer controls, testing their migration towards hCXCL17, mCXCL17, and CXCL12 as...
The internally controlled homing assay outlined in this study is a comprehensive method for examining GPCR-mediated T cell trafficking and positioning within diverse organs and tissue microenvironments. This approach integrates several critical optimizations to enhance reproducibility, accuracy, and efficiency.
A critical aspect of this protocol is the efficient transduction of T cells using MSCV retroviral vectors, which is facilitated by the use of Plat-E cells for viral production. Key opti...
The authors have nothing to disclose.
Supported by NIH grants R01 AI178113 and R01 AI047822, Grant 1903-03787 from The Leona M. & Harry B. Helmsley Charitable Trust, and Tobacco-Related Disease Research Program (TRDRP) grants T31IP1880 and T33IR6609 to E.C.B.; Y.B. was supported by a Research Fellows Award of the Crohn's and Colitis Foundation of America (835171). B.O. was supported by a postdoctoral fellowship of the Ramon Areces Foundation (Madrid, Spain) and a Research Fellows Award of the Crohn's and Colitis Foundation of America (574148). A.A. was supported by the California Institute for Regenerative Medicine (CIRM) - EDUC2-12677.
Name | Company | Catalog Number | Comments |
AF647 anti mouse CD90.1-Thy1.1 (OX-7) | BiolegendΒ | 202507 | |
anti-CD31 (DyLight 633, clone 390) | InvivoMabΒ | BE0377 | |
anti-mouse CD28 37.51 | eBiosciencesΒ | ||
anti-mouse CD3 145-2c11 | eBiosciencesΒ | ||
APCCy7 anti mouse CD3 (145-2c11) | BiolegendΒ | 100329 | |
BV421 anti mouse CD8bΒ (Ly-3) | BiolegendΒ | 126629 | |
BV711 anti mouse CD4 (RM4-5)Β | BiolegendΒ | 100549 | |
CD90.1 microbeadsΒ | MiltenyiΒ | 130-121-273 | |
CFSEΒ | ThermoscientificΒ | C34554 | |
FITC anti mouse CD45.2 (104) | BD | AB_395041 | |
mouse IL2Β | PeprotechΒ | 200-02-50UG | |
mouse IL7Β | PeprotechΒ | Β 217-17-10UG | |
Mouse T CD4 isolation kitΒ | STEMCELL technologiesΒ | 18000 | |
MSCV-IRES- Thy1.1 GPR25 | VectorbuilderΒ | ||
MSCV-IRES- Thy1.1 Stuffer | VectorbuilderΒ | ||
PE-CD45 (30-F11) antibodyΒ | BiolegendΒ | 103105 | |
PECy7 anti mouse TCRbΒ (H57-597) | Tonbo | ||
PercpCy5.5 anti mouse CD45.1 (A20) | eBiosciencesΒ | ||
Platinum-E (Plat-E)Β | cell Biolabs. IncΒ | RV-101 | |
Yellow fluorescent dyeΒ | ThermoscientificΒ |
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