6_ T-CELL DEVELOPMENT.pptx

WELCOME! BMS 545 IMMUNOLOGY SEPTEMBER 30, 2024  ANNOUNCEMENTS/SCHEDULE  9/30- T cell development  10/1- Office hours from 4-430 pm virtual  10/2- T cell development & activation  10/3 Office hours from 4-5 pm 316J  10/4- T cell activation & effector functions  10/7- (Flipped classroom)...

WELCOME! BMS 545 IMMUNOLOGY SEPTEMBER 30, 2024  ANNOUNCEMENTS/SCHEDULE  9/30- T cell development  10/1- Office hours from 4-430 pm virtual  10/2- T cell development & activation  10/3 Office hours from 4-5 pm 316J  10/4- T cell activation & effector functions  10/7- (Flipped classroom) Short pre-lecture video posted on CAR-T cells & then CBL during class  10/8- Office hours from 4-5 pm virtual  10/9- In-Class Activity  10/9- Office Hours 4-5 pm  10/10- Exam 2 from 2:30-4:00 (aka second exam that day)- NO OFFICE HOURS  FALL BREAK OCTOBER 12-15 NO class & NO office hours during this  REVIEW OF LAST CLASS αβ TCR α chain- Chromosome 14; Has V & J segments, and 1 constant segment β chain- Chromosome 7; Has V, D, & J segments, & 2 potential constant segments γδ TCR γ chain- Chromosome 7 ; Has V & J segments and TWO constant segments δ chain- Chromosome 14 (within α chain locus); Has V, D, & J segments and ONE constant segment  Gamma is like alpha with the V & J, but like beta with the TWO constants, while delta is like beta with the VDJ, but like alpha with the ONE constant. Make sense now? I saw it and knew there would be confusion WHY SHOULD YOU CARE?  OBJECTIVES (ON-GOING, THIS & NEXT CLASS)  Outline the major events that transform a hematopoietic stem cell into a mature, naïve T-cell  Identify proteins and receptors that aid in the development & drive of hematopoietic stem cells  Describe steps & importance of Notch signaling  Describe the microenvironments of the thymus where each stage of T-cell development takes place  Describe the changes in expression of CD4, CD8, and TCR that occur during T-cell development  Compare & contrast αβ and δγ cells (& start familiarizing yourself with how they are similar/different to B1 & B2 cells- more of a focus next module)  Define and describe the importance of, and the basis for, positive and negative selection.  Describe the relationship between positive selection & MHC restriction, & the relationship between negative selection & central tolerance  Recognize the variety of T cells that are generated in the thymus and articulate a basic understanding of the events that lead to the development of each lineage, particularly the CD4+, CD8+ and δγ!  INTRO TO T-CELL DEVELOPMENT  Epitope-specific T-cell & B-cell receptors (TCRs & BCRs) are randomly generated within individual thymus- & bone marrow–derived lymphocytes by gene rearrangement  Some lymphocytes develop receptors that react with “Self”  Selection mechanism (e.g., negative selection) is in place that removes these cells before they become fully functional & attack the body’s own tissues  Adaptive immune system carefully regulates development & differentiation of lymphocytes to prevent maturation of self-reactive T & B cells  ^This prevents this > T-CELL LINEAGE OVERVIEW  Prothymocytes (T-cell precursors aka immature T-cells) migrate from bone marrow to the thymus  “Interestingly” this process is largely undefined… for now ;)  Thymocytes must then “run a gauntlet” of selective tests as they migrate from the thymic cortex to the medulla  Selection processes are so demanding that only an estimated 1-5% of all thymocytes “graduate” as T cells  Other 95-99% either leave the thymus before undergoing selection (e.g., γδ T cells) OR die an apoptotic death after failing one of the selective tests Figure 7.1 T-cell precursors migrate from the bone marrow to mature in the thymus  The development of T cells in the thymus 7-1 T cells develop in the thymus Thymic epithelial cells form a nurturing network around the thymocytes Figure 7.3 The cellular organization of the thymus Hassall’ s corpuscl es- believed to be sites of cell Figure 7.4 The proportion of thymic tissue that produces T cells decreases with age What is an implication of this?  The development of T cells in the thymus 7-2 Thymocytes commit to the T-cell lineage BEFORE rearranging their T-cell receptor genes Commitment to the T-cell lineage involves changes in the expression of various cell- surface & intracellular proteins To know: CD34, CD44, CD2, CD5, Figure 7.6 T-cell development is driven by the receptor Notch1 1. Notch1 membrane-associated receptor on surface of thymocytes binds to its ligand (Notch1 Ligand) on thymic epithelium (aka thymic stromal cells) 2. Induces a protease to cleave intracellular domain of Notch1, releasing it from plasma membrane 3. Soluble intracellular domain is translocated to nucleus of thymocyte 4. Removes repressive transcription factors & recruits co-activating transcription factors 5. Turns on expression of genes essential for T-cell development Without Notch1, no T cell maturation!  The development of T cells in the thymus 7-3 The two lineages of T cells arise from a common double-negative (DN) thymocyte progenitor Figure 7.7 αβ and γδ T cells develop from a common double-negative T-cell progenitor 1. T-cell precursors that enter the thymus express HSC marker CD34 but no characteristic marker of mature T cells 2. Common progenitors proliferate then rearrange δ-, γ-, & β-chain genes i. Cells that productively rearrange both a γ- & a δ-chain gene (but not β-chain) commit to γδ T-cell lineage  Once γδ T-cell receptor appears on cell surface, cells exit thymus & travel in blood to other tissues ii. Rearrangement of a β-chain gene shuts down recombination machinery  May already have rearranged a γ- or a δ-chain gene or be cells in which their first rearrangement was a β-chain gene Figure 7.7 αβ and γδ T cells develop from a common double-negative T-cell progenitor  In absence of recombination, β chain is made & is quality tested (shown on slide 30)  If test is passed, cell proliferates to form a clone of β chain–positive cells 3. Recombination machinery is reactivated & targeted at α-, γ-, & δ-chain genes  Can productively rearrange their γ- & δ-chain genes to give rise to additional γδ T cells  In majority of cells a productive α-chain gene rearrangement is made, followed by assembly of an αβ receptor & commitment to αβ lineage = CD4+CD8+ αβ cells OR failure to rearrange α-chain gene (minority of cells) = If test is failed, no successful α chain   The development of T cells in the thymus 7-4 Gene rearrangement in double-negative thymocytes leads to assembly of either a γδ receptor or a pre-T-cell receptor This next slide, is basically a different retelling of the slides we Figure 7.9 T-cell receptor gene rearrangements in double-negative thymocytes  Inor can lead to expression of either a γδ receptor double-negative thymocytes, β, γ, & a pre-T-cell receptor δ genes rearrange (top)  If productive γ- & δ-chain gene rearrangements occur first, then a γδ receptor is expressed & cell is signaled to differentiate into a mature γδ cell (bottom left) OR  If a successful β-chain gene rearrangement is made before γ & δ genes have both made successful rearrangements, a pre-T-cell receptor (pre-TCR, composed of a β chain & a pTα chain) assembles & signals cell to proliferate, express CD4 AND CD8, & become a pre-T cell (bottom right)  Pre-T cell turns on recombination Figure 7.10 Comparison of the structures of the pre-T-cell receptor and the T-cell receptor 1 2 3 4  Testing whether β chain is functional 1. Two heterodimers of a β chain & pTα (pre-T alpha- invariant polypeptide that acts as a surrogate α chain) chain will form pre-T-cell receptor 2. If β chain has capacity to form a functional T-cell receptor, the two heterodimers can form a superdimer 3. Interaction of superdimer with CD3 complex & ζ chain forms a functional pre-T-cell receptor  This generates signals that initiate rearrangement of α-chain genes & stops synthesis of pTα (not shown) 4. When a functional α chain is made, it associates with β chain to form T-cell receptor Figure 7.11 Rescue of nonproductive rearrangements at the β-chain locus  Successive rearrangements can rescue an initial non- productive β-chain gene rearrangement, but ONLY if that rearrangement involves D & J gene segments associated with Cβ1 gene segment  A second rearrangement is then possible → second Vβ gene segment rearranges to a DJ segment associated with Cβ2 gene segment  In the process, Cβ1 & nonproductively rearranged gene segments are deleted Figure 7.8 Immature T cells that undergo apoptosis are ingested by macrophages in the thymic cortex  The development of T cells in the thymus 7-5 Rearrangement of the α-chain gene occurs only in pre-T cells Figure 7.12 Successive gene rearrangements allow the replacement of one T-cell receptor α chain by another  Having multiple V & J gene segments in T-cell receptor α- chain genes allows successive rearrangement events to jump over nonproductively rearranged VJ segments, deleting intervening gene segments  Process continues until either a productive rearrangement occurs or supply of V & J gene segments is exhausted  If V & J gene segments exhausted, the cell dies Figure 7.13 The δ-chain locus is sequestered within the α-chain locus and is deleted during α-chain gene rearrangement  The δ-chain locus lies between V & J gene segments of α- chain locus  During a recombination event that joins a Vα segment to a Jα segment, the intervening region, which contains δ-chain locus, is inevitably deleted as a small circular DNA that is disconnected from genome  The development of T cells in the thymus 7-6 Stages in T-cell development are marked by changes in gene expression Figure 7.14 Stages of αβ T-cell development in the thymus correlate with T-cell receptor gene rearrangement and the expression of particular proteins by the developing T cell  Remember Notch? T-cell development is driven by the receptor Notch 1  RAG proteins- essential for gene rearrangement & are selectively expressed at the 2 stages where β & α gene rearrangements are made  Other enzymes involved in somatic recombination:  TdT- inserts N nucleotides  pTα- defining component of pre-T cell receptor; expressed when rearrangements are made, so β chains can immediately be tested for their capacity to assemble a pre-T-cell receptor  If successful, cell stops recombination & initiates cell division & clonal expansion  Signals from pre-T-cell receptor depend on presence of CD4, CD8, CD3 signaling complex, & tyrosine kinases ZAP70 (zeta chain– associated protein kinase 70) & Lck  CD2- adhesion molecule on T cells; interacts with CD58 on other cells  Th-Pok- transcription factor expressed late in development & necessary for single-positive CD4 T cells to develop from double- positive thymocytes ALSO A SCIENTIST  Andrea Schietinger, PhD  Associate Member, Immunology Program, SKI Wanted to know what is unique about autoreactive T cells and used a mouse model of diabetes to study these cells. They found that a unique population of stem-like cells continually replenishes the self-reactive T cells in diabetes, a finding that has implications for treating both autoimmune diseases and cancer. https://www.mskcc.org/news/discovery- stem-cell-type-1-diabetes-holds-potenti al-improving-cancer-immunotherapy-sl oan-kettering-institute-scientists-say