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Lee MS, Tuohy PJ, Kim CY, Yost PP, Lichauco K, Parrish HL, Van Doorslaer K, Kuhns MS. The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-LCK interactions. eLife 2024; 12:RP88225. [PMID: 38639990 PMCID: PMC11031086 DOI: 10.7554/elife.88225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2024] Open
Abstract
CD4+ T cell activation is driven by five-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3γε, CD3δε, and CD3ζζ) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3ζ, ZAP70, and PLCγ1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.
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Affiliation(s)
- Mark S Lee
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
| | - Peter J Tuohy
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
| | - Caleb Y Kim
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
| | - Philip P Yost
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
| | - Katrina Lichauco
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
| | - Heather L Parrish
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
| | - Koenraad Van Doorslaer
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
- School of Animal and Comparative Biomedical Sciences, The University of ArizonaTucsonUnited States
- Cancer Biology Graduate Interdisciplinary Program and Genetics Graduate Interdisciplinary Program, The University of ArizonaTucsonUnited States
- The BIO-5 Institute, The University of ArizonaTucsonUnited States
- The University of Arizona Cancer CenterTucsonUnited States
- The Arizona Center on Aging, The University of Arizona College of MedicineTucsonUnited States
| | - Michael S Kuhns
- Department of Immunobiology, The University of Arizona College of MedicineTucsonUnited States
- Cancer Biology Graduate Interdisciplinary Program and Genetics Graduate Interdisciplinary Program, The University of ArizonaTucsonUnited States
- The BIO-5 Institute, The University of ArizonaTucsonUnited States
- The University of Arizona Cancer CenterTucsonUnited States
- The Arizona Center on Aging, The University of Arizona College of MedicineTucsonUnited States
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2
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Lee MS, Tuohy PJ, Kim CY, Yost P, Lichauco K, Parrish HL, Van Doorslaer K, Kuhns MS. The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-LCK interactions. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.05.539613. [PMID: 37214965 PMCID: PMC10197521 DOI: 10.1101/2023.05.05.539613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
CD4+ T cell activation is driven by 5-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3γε, CD3δε, and CD3ζζ) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee, et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3ζ, ZAP70, and PLCγ1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.
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Affiliation(s)
- Mark S Lee
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Peter J Tuohy
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Caleb Y Kim
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Philip Yost
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Katrina Lichauco
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Heather L Parrish
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Koenraad Van Doorslaer
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
- School of Animal and Comparative Biomedical Sciences, The University of Arizona, Tucson, AZ 85724, USA
- Cancer Biology Graduate Interdisciplinary Program and Genetics Graduate Interdisciplinary Program, The University of Arizona, Tucson, AZ 85724, USA
- The BIO-5 Institute, The University of Arizona, Tucson, AZ 85724, USA
- The University of Arizona Cancer Center, Tucson, AZ, USA
- The Arizona Center on Aging, The University of Arizona College of Medicine, Tucson, AZ, USA
| | - Michael S Kuhns
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
- Cancer Biology Graduate Interdisciplinary Program and Genetics Graduate Interdisciplinary Program, The University of Arizona, Tucson, AZ 85724, USA
- The BIO-5 Institute, The University of Arizona, Tucson, AZ 85724, USA
- The University of Arizona Cancer Center, Tucson, AZ, USA
- The Arizona Center on Aging, The University of Arizona College of Medicine, Tucson, AZ, USA
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3
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Role of the membrane anchor in the regulation of Lck activity. J Biol Chem 2022; 298:102663. [PMID: 36372231 PMCID: PMC9763865 DOI: 10.1016/j.jbc.2022.102663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 10/10/2022] [Accepted: 10/12/2022] [Indexed: 11/13/2022] Open
Abstract
Theoretical work suggests that collective spatiotemporal behavior of integral membrane proteins should be modulated by boundary lipids sheathing their membrane anchors. Here, we show evidence for this prediction while investigating the mechanism for maintaining a steady amount of the active form of integral membrane protein Lck kinase (LckA) by Lck trans-autophosphorylation regulated by the phosphatase CD45. We used super-resolution microscopy, flow cytometry, and pharmacological and genetic perturbation to gain insight into the spatiotemporal context of this process. We found that LckA is generated exclusively at the plasma membrane, where CD45 maintains it in a ceaseless dynamic equilibrium with its unphosphorylated precursor. Steady LckA shows linear dependence, after an initial threshold, over a considerable range of Lck expression levels. This behavior fits a phenomenological model of trans-autophosphorylation that becomes more efficient with increasing LckA. We then challenged steady LckA formation by genetically swapping the Lck membrane anchor with structurally divergent ones, such as that of Src or the transmembrane domains of LAT, CD4, palmitoylation-defective CD4 and CD45 that were expected to drastically modify Lck boundary lipids. We observed small but significant changes in LckA generation, except for the CD45 transmembrane domain that drastically reduced LckA due to its excessive lateral proximity to CD45. Comprehensively, LckA formation and maintenance can be best explained by lipid bilayer critical density fluctuations rather than liquid-ordered phase-separated nanodomains, as previously thought, with "like/unlike" boundary lipids driving dynamical proximity and remoteness of Lck with itself and with CD45.
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4
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Lee MS, Tuohy PJ, Kim CY, Lichauco K, Parrish HL, Van Doorslaer K, Kuhns MS. Enhancing and inhibitory motifs regulate CD4 activity. eLife 2022; 11:79508. [PMID: 35861317 PMCID: PMC9333989 DOI: 10.7554/elife.79508] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 07/20/2022] [Indexed: 11/15/2022] Open
Abstract
CD4+ T cells use T cell receptor (TCR)–CD3 complexes, and CD4, to respond to peptide antigens within MHCII molecules (pMHCII). We report here that, through ~435 million years of evolution in jawed vertebrates, purifying selection has shaped motifs in the extracellular, transmembrane, and intracellular domains of eutherian CD4 that enhance pMHCII responses, and covary with residues in an intracellular motif that inhibits responses. Importantly, while CD4 interactions with the Src kinase, Lck, are viewed as key to pMHCII responses, our data indicate that CD4–Lck interactions derive their importance from the counterbalancing activity of the inhibitory motif, as well as motifs that direct CD4–Lck pairs to specific membrane compartments. These results have implications for the evolution and function of complex transmembrane receptors and for biomimetic engineering.
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Affiliation(s)
- Mark S Lee
- Department of Immunobiology, University of Arizona College of Medicine, Tucson, United States
| | - Peter J Tuohy
- Department of Immunobiology, University of Arizona College of Medicine, Tucson, United States
| | - Caleb Y Kim
- Department of Immunobiology, University of Arizona College of Medicine, Tucson, United States
| | - Katrina Lichauco
- Department of Immunobiology, University of Arizona College of Medicine, Tucson, United States
| | - Heather L Parrish
- Department of Immunobiology, University of Arizona College of Medicine, Tucson, United States
| | - Koenraad Van Doorslaer
- School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson, United States
| | - Michael S Kuhns
- Department of Immunobiology, University of Arizona College of Medicine, Tucson, United States
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5
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Van Laethem F, Bhattacharya A, Craveiro M, Lu J, Sun PD, Singer A. MHC-independent αβT cells: Lessons learned about thymic selection and MHC-restriction. Front Immunol 2022; 13:953160. [PMID: 35911724 PMCID: PMC9331304 DOI: 10.3389/fimmu.2022.953160] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 06/24/2022] [Indexed: 12/02/2022] Open
Abstract
Understanding the generation of an MHC-restricted T cell repertoire is the cornerstone of modern T cell immunology. The unique ability of αβT cells to only recognize peptide antigens presented by MHC molecules but not conformational antigens is referred to as MHC restriction. How MHC restriction is imposed on a very large T cell receptor (TCR) repertoire is still heavily debated. We recently proposed the selection model, which posits that newly re-arranged TCRs can structurally recognize a wide variety of antigens, ranging from peptides presented by MHC molecules to native proteins like cell surface markers. However, on a molecular level, the sequestration of the essential tyrosine kinase Lck by the coreceptors CD4 and CD8 allows only MHC-restricted TCRs to signal. In the absence of Lck sequestration, MHC-independent TCRs can signal and instruct the generation of mature αβT cells that can recognize native protein ligands. The selection model thus explains how only MHC-restricted TCRs can signal and survive thymic selection. In this review, we will discuss the genetic evidence that led to our selection model. We will summarize the selection mechanism and structural properties of MHC-independent TCRs and further discuss the various non-MHC ligands we have identified.
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Affiliation(s)
- François Van Laethem
- Lymphocyte Development Section, Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, United States
- Department of Biological Hematology, Centre Hospitalier Universitaire (CHU) Montpellier, Montpellier, France
- *Correspondence: François Van Laethem, ,
| | - Abhisek Bhattacharya
- Lymphocyte Development Section, Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, United States
| | - Marco Craveiro
- Lymphocyte Development Section, Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, United States
| | - Jinghua Lu
- Structural Immunology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD, United States
| | - Peter D. Sun
- Structural Immunology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD, United States
| | - Alfred Singer
- Lymphocyte Development Section, Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, United States
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6
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An Amino Acid Polymorphism within the HIV-1 Nef Dileucine Motif Functionally Uncouples Cell Surface CD4 and SERINC5 Downregulation. J Virol 2021; 95:e0058821. [PMID: 34037423 DOI: 10.1128/jvi.00588-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Serine incorporator 5 (SERINC5) reduces the infectivity of progeny HIV-1 virions by incorporating into the outer host-derived viral membrane during egress. To counter SERINC5, the HIV-1 accessory protein Nef triggers SERINC5 internalization by engaging the adaptor protein 2 (AP-2) complex using the [D/E]xxxL[L/I]167 Nef dileucine motif. Nef also engages AP-2 via its dileucine motif to downregulate the CD4 receptor. Although these two Nef functions are related, the mechanisms governing SERINC5 downregulation are incompletely understood. Here, we demonstrate that two primary Nef isolates, referred to as 2410 and 2391 Nef, acquired from acutely HIV-1 infected women from Zimbabwe, both downregulate CD4 from the cell surface. However, only 2410 Nef retains the ability to downregulate cell surface SERINC5. Using a series of Nef chimeras, we mapped the region of 2391 Nef responsible for the functional uncoupling of these two antagonistic pathways to the dileucine motif. Modifications of the first and second x positions of the 2410 Nef dileucine motif to asparagine and aspartic acid residues, respectively (ND164), impaired cell surface SERINC5 downregulation, which resulted in reduced infectious virus yield in the presence of SERINC5. The ND164 mutation additionally partially impaired, but did not completely abrogate, Nef-mediated cell surface CD4 downregulation. Furthermore, the patient infected with HIV-1 encoding 2391 Nef had stable CD4+ T cell counts, whereas infection with HIV-1 encoding 2410 Nef resulted in CD4+ T cell decline and disease progression. IMPORTANCE A contributing factor to HIV-1 persistence is evasion of the host immune response. HIV-1 uses the Nef accessory protein to evade the antiviral roles of the adaptive and intrinsic innate immune responses. Nef targets SERINC5, a restriction factor which potently impairs HIV-1 infection by triggering SERINC5 removal from the cell surface. The molecular determinants underlying this Nef function remain incompletely understood. Recent studies have found a correlation between the extent of Nef-mediated SERINC5 downregulation and the rate of disease progression. Furthermore, single-residue polymorphisms outside the known Nef functional motifs can modulate SERINC5 downregulation. The identification of a naturally occurring Nef polymorphism impairing SERINC5 downregulation in this study supports a link between Nef downregulation of SERINC5 and the rate of plasma CD4+ T cell decline. Moreover, the observed functional impairments of this polymorphism could provide clues to further elucidate unknown aspects of the SERINC5 antagonistic pathway via Nef.
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7
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Johnson DK, Magoffin W, Myers SJ, Finnell JG, Hancock JC, Orton TS, Persaud SP, Christensen KA, Weber KS. CD4 Inhibits Helper T Cell Activation at Lower Affinity Threshold for Full-Length T Cell Receptors Than Single Chain Signaling Constructs. Front Immunol 2021; 11:561889. [PMID: 33542711 PMCID: PMC7851051 DOI: 10.3389/fimmu.2020.561889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 11/30/2020] [Indexed: 11/13/2022] Open
Abstract
CD4+ T cells are crucial for effective repression and elimination of cancer cells. Despite a paucity of CD4+ T cell receptor (TCR) clinical studies, CD4+ T cells are primed to become important therapeutics as they help circumvent tumor antigen escape and guide multifactorial immune responses. However, because CD8+ T cells directly kill tumor cells, most research has focused on the attributes of CD8+ TCRs. Less is known about how TCR affinity and CD4 expression affect CD4+ T cell activation in full length TCR (flTCR) and TCR single chain signaling (TCR-SCS) formats. Here, we generated an affinity panel of TCRs from CD4+ T cells and expressed them in flTCR and three TCR-SCS formats modeled after chimeric antigen receptors (CARs) to understand the contributions of TCR-pMHCII affinity, TCR format, and coreceptor CD4 interactions on CD4+ T cell activation. Strikingly, the coreceptor CD4 inhibited intermediate and high affinity TCR-construct activation by Lck-dependent and -independent mechanisms. These inhibition mechanisms had unique affinity thresholds dependent on the TCR format. Intracellular construct formats affected the tetramer staining for each TCR as well as IL-2 production. IL-2 production was promoted by increased TCR-pMHCII affinity and the flTCR format. Thus, CD4+ T cell therapy development should consider TCR affinity, CD4 expression, and construct format.
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Affiliation(s)
- Deborah K Johnson
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Wyatt Magoffin
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Sheldon J Myers
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Jordan G Finnell
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT, United States
| | - John C Hancock
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Taylor S Orton
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Stephen P Persaud
- Division of Laboratory and Genomic Medicine, Department of Pathology and Immunology, Washington University in St. Louis, St. Louis, MO, United States
| | - Kenneth A Christensen
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT, United States
| | - K Scott Weber
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
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8
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Barber-Axthelm IM, Barber-Axthelm V, Sze KY, Zhen A, Suryawanshi GW, Chen IS, Zack JA, Kitchen SG, Kiem HP, Peterson CW. Stem cell-derived CAR T cells traffic to HIV reservoirs in macaques. JCI Insight 2021; 6:141502. [PMID: 33427210 PMCID: PMC7821595 DOI: 10.1172/jci.insight.141502] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Accepted: 11/25/2020] [Indexed: 12/12/2022] Open
Abstract
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) with CCR5– donor cells is the only treatment known to cure HIV-1 in patients with underlying malignancy. This is likely due to a donor cell–mediated graft-versus-host effect targeting HIV reservoirs. Allo-HSCT would not be an acceptable therapy for most people living with HIV due to the transplant-related side effects. Chimeric antigen receptor (CAR) immunotherapies specifically traffic to malignant lymphoid tissues (lymphomas) and, in some settings, are able to replace allo-HSCT. Here, we quantified the engraftment of HSC-derived, virus-directed CAR T cells within HIV reservoirs in a macaque model of HIV infection, using potentially novel IHC assays. HSC-derived CAR cells trafficked to and displayed multilineage engraftment within tissue-associated viral reservoirs, persisting for nearly 2 years in lymphoid germinal centers, the brain, and the gastrointestinal tract. Our findings demonstrate that HSC-derived CAR+ cells reside long-term and proliferate in numerous tissues relevant for HIV infection and cancer.
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Affiliation(s)
- Isaac M Barber-Axthelm
- Stem Cell and Gene Therapy Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.,Department of Comparative Medicine, University of Washington, Seattle, Washington, USA
| | - Valerie Barber-Axthelm
- Stem Cell and Gene Therapy Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Kai Yin Sze
- Stem Cell and Gene Therapy Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Anjie Zhen
- Department of Medicine, Division of Hematology and Oncology, David Geffen School of Medicine at University of California, Los Angeles, California, USA.,UCLA AIDS Institute, Los Angeles, California, USA
| | - Gajendra W Suryawanshi
- UCLA AIDS Institute, Los Angeles, California, USA.,Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine at University of California, Los Angeles, California, USA
| | - Irvin Sy Chen
- Department of Medicine, Division of Hematology and Oncology, David Geffen School of Medicine at University of California, Los Angeles, California, USA.,UCLA AIDS Institute, Los Angeles, California, USA.,Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine at University of California, Los Angeles, California, USA
| | - Jerome A Zack
- Department of Medicine, Division of Hematology and Oncology, David Geffen School of Medicine at University of California, Los Angeles, California, USA.,UCLA AIDS Institute, Los Angeles, California, USA.,Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine at University of California, Los Angeles, California, USA
| | - Scott G Kitchen
- Department of Medicine, Division of Hematology and Oncology, David Geffen School of Medicine at University of California, Los Angeles, California, USA.,UCLA AIDS Institute, Los Angeles, California, USA
| | - Hans-Peter Kiem
- Stem Cell and Gene Therapy Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.,Department of Medicine and.,Department of Pathology, University of Washington, Seattle, Washington, USA
| | - Christopher W Peterson
- Stem Cell and Gene Therapy Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.,Department of Medicine and
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9
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Mørch AM, Bálint Š, Santos AM, Davis SJ, Dustin ML. Coreceptors and TCR Signaling - the Strong and the Weak of It. Front Cell Dev Biol 2020; 8:597627. [PMID: 33178706 PMCID: PMC7596257 DOI: 10.3389/fcell.2020.597627] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Accepted: 09/28/2020] [Indexed: 12/02/2022] Open
Abstract
The T-cell coreceptors CD4 and CD8 have well-characterized and essential roles in thymic development, but how they contribute to immune responses in the periphery is unclear. Coreceptors strengthen T-cell responses by many orders of magnitude - beyond a million-fold according to some estimates - but the mechanisms underlying these effects are still debated. T-cell receptor (TCR) triggering is initiated by the binding of the TCR to peptide-loaded major histocompatibility complex (pMHC) molecules on the surfaces of other cells. CD4 and CD8 are the only T-cell proteins that bind to the same pMHC ligand as the TCR, and can directly associate with the TCR-phosphorylating kinase Lck. At least three mechanisms have been proposed to explain how coreceptors so profoundly amplify TCR signaling: (1) the Lck recruitment model and (2) the pseudodimer model, both invoked to explain receptor triggering per se, and (3) two-step coreceptor recruitment to partially triggered TCRs leading to signal amplification. More recently it has been suggested that, in addition to initiating or augmenting TCR signaling, coreceptors effect antigen discrimination. But how can any of this be reconciled with TCR signaling occurring in the absence of CD4 or CD8, and with their interactions with pMHC being among the weakest specific protein-protein interactions ever described? Here, we review each theory of coreceptor function in light of the latest structural, biochemical, and functional data. We conclude that the oldest ideas are probably still the best, i.e., that their weak binding to MHC proteins and efficient association with Lck allow coreceptors to amplify weak incipient triggering of the TCR, without comprising TCR specificity.
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Affiliation(s)
- Alexander M. Mørch
- The Kennedy Institute of Rheumatology, University of Oxford, Oxford, United Kingdom
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Štefan Bálint
- The Kennedy Institute of Rheumatology, University of Oxford, Oxford, United Kingdom
| | - Ana Mafalda Santos
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Simon J. Davis
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Michael L. Dustin
- The Kennedy Institute of Rheumatology, University of Oxford, Oxford, United Kingdom
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10
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Chandler NJ, Call MJ, Call ME. T Cell Activation Machinery: Form and Function in Natural and Engineered Immune Receptors. Int J Mol Sci 2020; 21:E7424. [PMID: 33050044 PMCID: PMC7582382 DOI: 10.3390/ijms21197424] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 10/05/2020] [Accepted: 10/07/2020] [Indexed: 12/15/2022] Open
Abstract
The impressive success of chimeric antigen receptor (CAR)-T cell therapies in treating advanced B-cell malignancies has spurred a frenzy of activity aimed at developing CAR-T therapies for other cancers, particularly solid tumors, and optimizing engineered T cells for maximum clinical benefit in many different disease contexts. A rapidly growing body of design work is examining every modular component of traditional single-chain CARs as well as expanding out into many new and innovative engineered immunoreceptor designs that depart from this template. New approaches to immune cell and receptor engineering are being reported with rapidly increasing frequency, and many recent high-quality reviews (including one in this special issue) provide comprehensive coverage of the history and current state of the art in CAR-T and related cellular immunotherapies. In this review, we step back to examine our current understanding of the structure-function relationships in natural and engineered lymphocyte-activating receptors, with an eye towards evaluating how well the current-generation CAR designs recapitulate the most desirable features of their natural counterparts. We identify key areas that we believe are under-studied and therefore represent opportunities to further improve our grasp of form and function in natural and engineered receptors and to rationally design better therapeutics.
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Affiliation(s)
- Nicholas J Chandler
- Structural Biology Division, Walter and Eliza Hall Institute, Parkville, VIC 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, VIC 3052, Australia
| | - Melissa J Call
- Structural Biology Division, Walter and Eliza Hall Institute, Parkville, VIC 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, VIC 3052, Australia
| | - Matthew E Call
- Structural Biology Division, Walter and Eliza Hall Institute, Parkville, VIC 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, VIC 3052, Australia
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Leddon SA, Fettis MM, Abramo K, Kelly R, Oleksyn D, Miller J. The CD28 Transmembrane Domain Contains an Essential Dimerization Motif. Front Immunol 2020; 11:1519. [PMID: 32765524 PMCID: PMC7378745 DOI: 10.3389/fimmu.2020.01519] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Accepted: 06/09/2020] [Indexed: 12/13/2022] Open
Abstract
CD28 plays a critical role in regulating immune responses both by enhancing effector T cell activation and differentiation and controlling the development and function of regulatory T cells. CD28 is expressed at the cell surface as a disulfide linked homodimer that is thought to bind ligand monovalently. How ligand binding triggers CD28 to induce intracellular signaling as well as the proximal signaling pathways that are induced are not well-understood. In addition, recent data suggest inside-out signaling initiated by the T cell antigen receptor can enhance CD28 ligand binding, possibly by inducing a rearrangement of the CD28 dimer interface to allow for bivalent binding. To understand how possible conformational changes during ligand-induced receptor triggering and inside-out signaling are mediated, we examined the CD28 transmembrane domain. We identified an evolutionarily conserved YxxxxT motif that is shared with CTLA-4 and resembles the transmembrane dimerization motif within CD3ζ. We show that the CD28 transmembrane domain can drive protein dimerization in a bacterial expression system at levels equivalent to the well-known glycophorin A transmembrane dimerization motif. In addition, ectopic expression of the CD28 transmembrane domain into monomeric human CD25 can drive dimerization in murine T cells as detected by an increase in FRET by flow cytometry. Mutation of the polar YxxxxT motif to hydrophobic leucine residues (Y145L/T150L) attenuated CD28 transmembrane mediated dimerization in both the bacterial and mammalian assays. Introduction of the Y145L/T150L mutation of the CD28 transmembrane dimerization motif into the endogenous CD28 locus by CRISPR resulted in a dramatic loss in CD28 cell surface expression. These data suggest that under physiological conditions the YxxxxT dimerization motif within the CD28 transmembrane domain plays a critical role in the assembly and/or expression of stable CD28 dimers at the cell surface.
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Affiliation(s)
- Scott A Leddon
- Department of Microbiology and Immunology, David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
| | - Margaret M Fettis
- Department of Microbiology and Immunology, David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
| | - Kristin Abramo
- Department of Microbiology and Immunology, David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
| | - Ryan Kelly
- Department of Microbiology and Immunology, David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
| | - David Oleksyn
- Department of Microbiology and Immunology, David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
| | - Jim Miller
- Department of Microbiology and Immunology, David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
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Glatzová D, Cebecauer M. Dual Role of CD4 in Peripheral T Lymphocytes. Front Immunol 2019; 10:618. [PMID: 31001252 PMCID: PMC6454155 DOI: 10.3389/fimmu.2019.00618] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 03/08/2019] [Indexed: 01/07/2023] Open
Abstract
The interaction of T-cell receptors (TCRs) with self- and non-self-peptides in the major histocompatibility complex (MHC) stimulates crucial signaling events, which in turn can activate T lymphocytes. A variety of accessory molecules further modulate T-cell signaling. Of these, the CD4 and CD8 coreceptors make the most critical contributions to T cell sensitivity in vivo. Whereas, CD4 function in T cell development is well-characterized, its role in peripheral T cells remains incompletely understood. It was originally suggested that CD4 stabilizes weak interactions between TCRs and peptides in the MHC and delivers Lck kinases to that complex. The results of numerous experiments support the latter role, indicating that the CD4-Lck complex accelerates TCR-triggered signaling and controls the availability of the kinase for TCR in the absence of the ligand. On the other hand, extremely low affinity of CD4 for MHC rules out its ability to stabilize the receptor-ligand complex. In this review, we summarize the current knowledge on CD4 in T cells, with a special emphasis on the spatio-temporal organization of early signaling events and the relevance for CD4 function. We further highlight the capacity of CD4 to interact with the MHC in the absence of TCR. It drives the adhesion of T cells to the cells that express the MHC. This process is facilitated by the CD4 accumulation in the tips of microvilli on the surface of unstimulated T cells. Based on these observations, we suggest an alternative model of CD4 role in T-cell activation.
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Affiliation(s)
- Daniela Glatzová
- Department of Biophysical Chemistry, J. Heyrovsky Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czechia
- Laboratory of Leukocyte Signaling, Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czechia
| | - Marek Cebecauer
- Department of Biophysical Chemistry, J. Heyrovsky Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czechia
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Glassman CR, Parrish HL, Lee MS, Kuhns MS. Reciprocal TCR-CD3 and CD4 Engagement of a Nucleating pMHCII Stabilizes a Functional Receptor Macrocomplex. Cell Rep 2018; 22:1263-1275. [PMID: 29386113 PMCID: PMC5813697 DOI: 10.1016/j.celrep.2017.12.104] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 12/07/2017] [Accepted: 12/27/2017] [Indexed: 12/24/2022] Open
Abstract
CD4+ T cells convert the time that T cell receptors (TCRs) interact with peptides embedded within class II major histocompatibility complex molecules (pMHCII) into signals that direct cell-fate decisions. In principle, TCRs relay information to intracellular signaling motifs of the associated CD3 subunits, while CD4 recruits the kinase Lck to those motifs upon coincident detection of pMHCII. But the mechanics by which this occurs remain enigmatic. In one model, the TCR and CD4 bind pMHCII independently, while in another, CD4 interacts with a composite surface formed by the TCR-CD3 complex bound to pMHCII. Here, we report that the duration of TCR-pMHCII interactions impact CD4 binding to MHCII. In turn, CD4 increases TCR confinement to pMHCII via reciprocal interactions involving membrane distal and proximal CD4 ectodomains. The data suggest that a precisely assembled macrocomplex functions to reliably convert TCR-pMHCII confinement into reproducible signals that orchestrate adaptive immunity.
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Affiliation(s)
- Caleb R Glassman
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Heather L Parrish
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Mark S Lee
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA
| | - Michael S Kuhns
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724, USA; The BIO-5 Institute, The University of Arizona College of Medicine, Tucson, AZ 85724, USA; The Arizona Center on Aging, The University of Arizona College of Medicine, Tucson, AZ 85724, USA; The University of Arizona Cancer Center, The University of Arizona College of Medicine, Tucson, AZ 85724, USA.
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Glassman CR, Parrish HL, Deshpande NR, Kuhns MS. The CD4 and CD3δε Cytosolic Juxtamembrane Regions Are Proximal within a Compact TCR-CD3-pMHC-CD4 Macrocomplex. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2016; 196:4713-22. [PMID: 27183595 PMCID: PMC4875830 DOI: 10.4049/jimmunol.1502110] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 03/29/2016] [Indexed: 12/15/2022]
Abstract
TCRs relay information about peptides embedded within MHC molecules (pMHC) to the ITAMs of the associated CD3γε, CD3δε, and CD3ζζ signaling modules. CD4 then recruits the Src kinase p56(Lck) (Lck) to the TCR-CD3 complex to phosphorylate the ITAMs, initiate intracellular signaling, and drive CD4(+) T cell fate decisions. Whereas the six ITAMs of CD3ζζ are key determinants of T cell development, activation, and the execution of effector functions, multiple models predict that CD4 recruits Lck proximal to the four ITAMs of the CD3 heterodimers. We tested these models by placing FRET probes at the cytosolic juxtamembrane regions of CD4 and the CD3 subunits to evaluate their relationship upon pMHC engagement in mouse cell lines. The data are consistent with a compact assembly in which CD4 is proximal to CD3δε, CD3ζζ resides behind the TCR, and CD3γε is offset from CD3δε. These results advance our understanding of the architecture of the TCR-CD3-pMHC-CD4 macrocomplex and point to regions of high CD4-Lck + ITAM concentrations therein. The findings thus have implications for TCR signaling, as phosphorylation of the CD3 ITAMs by CD4-associated Lck is important for CD4(+) T cell fate decisions.
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Affiliation(s)
- Caleb R Glassman
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724
| | - Heather L Parrish
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724
| | - Neha R Deshpande
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724; The Arizona Center on Aging, The University of Arizona College of Medicine, Tucson, AZ 85724; and
| | - Michael S Kuhns
- Department of Immunobiology, The University of Arizona College of Medicine, Tucson, AZ 85724; The Arizona Center on Aging, The University of Arizona College of Medicine, Tucson, AZ 85724; and The BIO5 Institute, The University of Arizona College of Medicine, Tucson, AZ 85724
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Parrish HL, Glassman CR, Keenen MM, Deshpande NR, Bronnimann MP, Kuhns MS. Correction: A Transmembrane Domain GGxxG Motif in CD4 Contributes to Its Lck-Independent Function but Does Not Mediate CD4 Dimerization. PLoS One 2016; 11:e0150876. [PMID: 26930656 PMCID: PMC4773146 DOI: 10.1371/journal.pone.0150876] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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Abstract
How T cells become restricted to binding antigenic peptides within class I or class II major histocompatibility complex molecules (pMHCI or pMHCII, respectively) via clonotypic T-cell receptors (TCRs) remains debated. During development, if TCR-pMHC interactions exceed an affinity threshold, a signal is generated that positively selects the thymocyte to become a mature CD4(+) or CD8(+) T cell that can recognize foreign peptides within MHCII or MHCI, respectively. But whether TCRs possess an intrinsic, subthreshold specificity for MHC that facilitates sampling of the peptides within MHC during positive selection or T-cell activation is undefined. Here we asked if increasing the frequency of lymphocyte-specific protein tyrosine kinase (Lck)-associated CD4 molecules in T-cell hybridomas would allow for the detection of subthreshold TCR-MHC interactions. The reactivity of 10 distinct TCRs was assessed in response to selecting and nonselecting MHCII bearing cognate, null, or "shaved" peptides with alanine substitutions at known TCR contact residues: Three of the TCRs were selected on MHCII and have defined peptide specificity, two were selected on MHCI and have a known pMHC specificity, and five were generated in vitro without defined selecting or cognate pMHC. Our central finding is that IL-2 was made when each TCR interacted with selecting or nonselecting MHCII presenting shaved peptides. These responses were abrogated by anti-CD4 antibodies and mutagenesis of CD4. They were also inhibited by anti-MHC antibodies that block TCR-MHCII interactions. We interpret these data as functional evidence for TCR-intrinsic specificity for MHCII.
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