Pieces of a Puzzle: T Cell Activation • iBiology

Duration: 00:15:14
Transcript

00:00:09:00 - I love science.
00:00:10:05 I love the world of discovery.
00:00:13:05 I love the possibility of imagining how things might be.
00:00:19:04 And I feel that the field of science is a ennobling.
00:00:24:16 (gentle music)
00:00:29:16 When I started in university
00:00:31:14 I began to read about the immune system
00:00:34:09 and one of the intriguing aspects of the immune system
00:00:38:20 was its ability to distinguish
00:00:41:16 between self and non-self
00:00:44:08 to distinguish between you and me.
00:00:48:12 (gentle music)
00:00:58:04 What I loved about immunology
00:01:00:10 and it may seem a little counterintuitive
00:01:02:20 and maybe not very scientific
00:01:05:03 was you spend a lot of your time hypothesizing
00:01:09:23 coming up with models.
00:01:11:15 This could be this because of this
00:01:13:03 and ABC goes to here DO doesn't fit okay.
00:01:17:03 So really it was a bit like pieces of a puzzle
00:01:22:01 and really lovely because it stimulated
00:01:26:00 so much the imagination.
00:01:28:10 And T cells seem to be the big players.
00:01:31:06 They seem to be the orchestrators of the immune response.
00:01:34:15 (gentle music)
00:01:40:07 So when we think for example in the case of COVID-19
00:01:44:14 all these antibody responses
00:01:46:24 well the ability of the B cell
00:01:49:13 to produce antibody for sure depends
00:01:52:15 on its ability to recognize the foreign antigen
00:01:55:19 in this case it's SARS COV-2
00:01:58:20 but they require help from T cells.
00:02:01:10 So already you can see T cells
00:02:03:03 are helping B cells do what they do.
00:02:09:00 But T cells also are endowed
00:02:11:11 with their own ability to differentiate.
00:02:14:11 (gentle music)
00:02:42:02 Like B cells T cells become activated
00:02:44:22 by recognizing foreign antigen.
00:02:50:00 Now for a T cell to react against a foreign antigen
00:02:55:09 it has to interact with an antigen presenting cells
00:02:57:19 such as a dendritic cell.
00:03:00:21 Dendritic cells process and present antigen
00:03:03:16 on the cell surface.
00:03:06:17 The antigen is presented
00:03:08:05 by the major histocompatibility complex.
00:03:12:13 The T cell makes initial contact most probably
00:03:15:10 because the dendritic cell releases chemoattractants
00:03:19:00 that bring the T cell into close proximity with itself.
00:03:24:05 A receptor called the T cell receptor binds
00:03:27:24 to the MHC complex
00:03:31:03 but this is then followed by various events
00:03:33:23 that cause the T cell contact
00:03:36:18 with the antigen presenting cell to become reinforced.
00:03:40:22 And that reinforcement of binding
00:03:43:07 is accompanied by a rearrangement of receptors
00:03:46:24 that are needed to generate signals in T cells.
00:03:50:09 (gentle music)
00:03:57:18 What was not known at the time
00:03:59:23 was how these receptors were transmitting signals
00:04:03:16 into T cells
00:04:05:19 to activate the T cells one
00:04:08:03 and secondly to induce the differentiation of T cells.
00:04:13:13 And in 1984 it was clear that the T cell receptor
00:04:17:15 recognizing for an antigen could mediate signals
00:04:21:14 leading to the activation of T cells
00:04:23:24 and at the same time were identified the CD4
00:04:27:14 and CD8 co-receptors that define subsets of cells.
00:04:32:09 So these co-receptors bind to
00:04:35:04 the major histocompatibility antigens
00:04:37:16 that present foreign antigen to T cells
00:04:41:02 reinforcing the ability of the T cell
00:04:44:14 to bind to the MHC peptide complex.
00:04:49:19 There were still big questions.
00:04:52:09 And the most basic was how does
00:04:55:10 this T cell receptor complex actually activate cells?
00:04:59:18 And secondly was there any role at all
00:05:02:22 for tyrosine phosphorylation in T cells
00:05:06:09 that might accompany the activation of these cells?
00:05:10:01 Many receptors very clearly inside the cell
00:05:13:19 there is a domain structure that is a kinase domain.
00:05:17:13 The activity of these kinase domains
00:05:19:11 were shown by many people to be needed for the activation
00:05:23:02 of cells induced by these receptors.
00:05:25:19 But nothing of the kind existed for the T cell receptor.
00:05:29:23 And because of my interest in the SRC family
00:05:33:17 what about SRC family members SRC kinases
00:05:38:03 induced cancer via these SRC family members?
00:05:41:13 And at the time it was really unclear
00:05:44:04 how these SRC kinases operated in normal cells.
00:05:47:16 They had been implicated
00:05:49:13 and retrovirally induced transformation of cells.
00:05:53:11 At this point a role for cellular forms
00:05:56:08 of SRC hadn't been identified.
00:05:59:01 Here's the T cell receptor.
00:06:01:18 The big question is why in heaven's name
00:06:04:02 is it so complicated?
00:06:06:07 You have the inner part
00:06:07:09 which has the T cell receptor
00:06:09:03 that binds to the peptide as presented by the MHC complex.
00:06:14:14 It had been shown to associate with the CD3 sub units
00:06:18:08 as well as a primarily intercellular chain
00:06:21:20 called the zeta chain.
00:06:23:03 But there was no evidence of the involvement
00:06:25:08 of kinase domains within this complex.
00:06:28:22 And we had various scenarios we imagined.
00:06:31:11 Well if the T cell receptor isn't inducing
00:06:35:10 a phosphorylation cascade
00:06:37:05 well maybe there's some mysterious cytokine receptor
00:06:40:18 hanging about somewhere that no one has discovered before
00:06:43:13 that has this kind of classic intercellular kinases domain
00:06:47:20 that may proceed TCR ligation.
00:06:50:06 And we even thought well perhaps
00:06:52:10 given that the T cell receptor
00:06:54:08 and it's associated chains have unique structures
00:06:57:13 maybe they don't even employ tyrosine phosphorylation
00:07:00:14 as a mechanism.
00:07:02:02 Maybe T cells just are fundamentally different
00:07:04:12 from other cells.
00:07:05:21 But always in the back of my mind
00:07:07:18 was maybe during evolution
00:07:10:23 there was also co-evolution
00:07:13:05 of immune cell specific signaling proteins in immune cells
00:07:17:09 that adapted itself to the unique structures
00:07:20:04 on the cell surface
00:07:21:12 that knowing that T-cells become activated
00:07:24:01 to elicit really different kinds of functions
00:07:28:04 that you don't find in other cell types
00:07:30:13 that there must be some kind of immune specific component
00:07:34:18 to all of this.
00:07:35:21 And in the back of my mind always
00:07:37:10 I was thinking of CD8 and CD4
00:07:40:18 which had been thought previously
00:07:42:10 just to reinforce the presentation of antigen
00:07:45:19 that this would be an excellent way to activate cells
00:07:49:02 if indeed the rest of the T cell receptor complex
00:07:52:19 had no clear link to tyrosine phosphorylation.
00:07:57:13 In the early days
00:07:58:14 in comparing the cytoplasmic tails of CD4 and CD8
00:08:02:02 I identified a motif that was shared between the two.
00:08:05:13 So that gave me a hint that something might be going on.
00:08:09:22 (gentle music)
00:08:17:18 The Eureka experiment was so exciting at the time.
00:08:22:05 We used anti CD4 and CD8
00:08:25:03 we would precipitate out of lysates from T cells.
00:08:28:19 We would add B32 a substrate for kinases
00:08:32:06 to the purified immuno precipitate.
00:08:34:16 Also enolase was included in the immuno precipitates.
00:08:38:17 We let it incubate for a period of time
00:08:40:16 and then we could run it out on a gel.
00:08:43:02 We saw a very strong band at about 55-60.
00:08:47:06 In addition as you can see in lane one
00:08:50:21 the enolase band below.
00:08:53:20 When I first saw that result I was stunned.
00:08:57:16 But of course we repeated it many many times.
00:09:00:18 It was clear there was lots of kinase activity associated
00:09:04:13 with CD4 and CD8.
00:09:06:14 We just didn't know what kind of kinase was there.
00:09:11:03 But what we did notice when we looked
00:09:13:13 at the phosphoryl signatures
00:09:16:06 that all of the phosphorylation was in tyrosine
00:09:20:03 on the tyrosine residue.
00:09:21:15 We could see nothing on threonine serine.
00:09:25:05 (gentle music)
00:09:31:17 So at the time given my interest in SRC kinases
00:09:36:01 I was aware that PB60 SRC
00:09:38:14 had a molecular weight around 60 kD.
00:09:41:19 And here we had these heavily labeled bands
00:09:44:13 at about 55 to 60 kD.
00:09:49:05 So that really suggested
00:09:50:24 that we might be dealing with a SRC kinase.
00:09:56:07 So the next step was for us to take an antibody
00:09:59:06 of a SRC-like kinase called lystra
00:10:02:07 roughly in that molecular range
00:10:04:22 and again we ran the assays.
00:10:06:17 And as you'll see in panel B in lanes 3 and 4
00:10:10:01 it was very clear.
00:10:11:23 A SRC family member tyrosine kinase called the Lck
00:10:15:24 was precipitated associated with CD4 and CD8.
00:10:21:09 So this was really exciting
00:10:24:22 because for the first time
00:10:27:07 it implicated a tyrosine kinase linked
00:10:30:11 to a surface receptor on T cells
00:10:33:04 which in turn was active in reinforcing contact
00:10:37:07 during antigen presentation with the T cell receptor
00:10:41:06 while it was responding and generating signals.
00:10:44:00 So it made great sense.
00:10:47:02 We then ran a second experiment
00:10:49:02 where in this case what we did is we added two antibodies
00:10:52:12 one against the T cell receptor one against CD4
00:10:56:12 and we then carried out a precipitation
00:10:59:19 and then ran it on a 2D gel.
00:11:01:24 And what we were able to see was a CD3 gamma delta
00:11:05:22 and epsilon chains as well as a zeta chain.
00:11:08:24 So each of these chains was being phosphorylated by Lck.
00:11:13:19 So that was the next step. It made sense.
00:11:16:18 Here you have CD4 coming in or CD8
00:11:19:07 phosphorylating the T cell receptor.
00:11:22:09 And subsequent analysis of the sequence
00:11:25:03 of these chains identified a conserved motif
00:11:28:21 which has two tyrosines separated by 10 to 12 amino acids
00:11:33:24 which is now called an immuno receptor tyrosine based
00:11:38:10 activation motif or an ITAM motif.
00:11:41:15 (gentle music)
00:11:44:03 And here you can see how the model unfolds.
00:11:48:02 We have CD4 or could be CD8 binding to Lck.
00:11:53:03 Lck then phosphorylates ITAMs within the CD3 chains
00:11:58:05 as well as within the zeta chain.
00:12:00:24 This then allows for the recruitment
00:12:02:19 of a second immune specific protein tyrosine kinase.
00:12:08:08 So here we now have two immune specific tyrosine kinase
00:12:12:13 is one Lck a second ZAP-70.
00:12:16:04 (gentle music)
00:12:28:00 The work that we did
00:12:29:08 identifying tyrosine phosphorylation cascade in T cells
00:12:34:17 leading to the identification of specific motifs
00:12:39:08 that are needed to generate signals in cells
00:12:42:02 led to their being used in something
00:12:46:19 called chimeric antigen receptors.
00:12:49:02 And these are receptors that have a outside domain
00:12:52:24 which is essentially an antibody
00:12:55:09 that will recognize a tumor associated antigen.
00:12:59:14 (gentle music)
00:13:05:15 You can take these designer molecules
00:13:07:22 you can put them in T cells and put them back into patients.
00:13:12:22 (gentle music)
00:13:15:00 And they proved very effective in certain cancers
00:13:18:23 saving thousands of lives.
00:13:21:13 And the race is on to make new kinds of CARs
00:13:25:16 that are more and more effective
00:13:27:11 in particular able to penetrate solid tumors
00:13:30:22 because this is where the real challenge lies.
00:13:34:07 So in summary the work we defined a role
00:13:38:08 for SRC family kinases in normal receptor signaling.
00:13:43:13 In the case of CD4 and CD8-p56lck
00:13:48:00 these initiate T cell activation
00:13:50:18 and are responsible for initiating
00:13:53:02 a phosphorylation cascade.
00:13:56:02 And the discovery that SRC kinases
00:13:59:03 can interact with receptors led to a renewed interest
00:14:03:07 on behalf of pharmaceutical companies
00:14:05:14 to design new drugs
00:14:07:10 in particular drugs that were inhibitory
00:14:09:19 with the idea in mind that these would be useful
00:14:12:13 in treating autoimmune diseases.
00:14:16:21 And as I just mentioned
00:14:18:17 I believe our early work has led to new therapies
00:14:23:02 that have helped to cure patients of cancer.
00:14:26:11 So I'm very much motivated by the hope
00:14:29:18 that some of the things that we discover
00:14:32:00 will make the world a better place.
00:14:35:03 (gentle music)

This Talk

Speaker: Christopher E. Rudd

Audience:

Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: November 2021

Talk Overview

Researchers are harnessing the power of the human immune system to create new treatments for challenging diseases, such as cancer and autoimmune disorders. In this video, meet one such researcher, Christopher Rudd, Ph.D., an immunologist whose seminal experiments in understanding how T cells respond to diseases in the immune system have led to the development of cancer immunotherapies.

Rudd was the first to identify the role of tyrosine kinases and phosphorylation cascades in the activation of T cells via the T cell receptor. His discovery has led to the development of many different therapies, including chimeric antigen receptor (CAR) T cells which are designed to treat and cure certain cancers.

Please head to the Science Communication Lab’s website for more films like this along with educator resources, full video transcript, and most up to date content.

View Educator Resources & Transcript on SCL Website →

More Health & Medicine Films →

Speaker Bio

Christopher E. Rudd

Chris Rudd

Christopher E. Rudd, Ph.D. is a professor of medicine at the Université de Montréal where his research focuses on deciphering the signal transduction pathways in T-cells, and how these pathways control immune functions. He received his BSc from McGill University (Canada) and his Ph.D. and D.Sc. degrees from University College London (UK). Rudd began his… Continue Reading

Credits

Producers: Brittany Anderton, Shannon Behrman, Lee Rossoff
Cinematographer & Sound: Productions Albédo Inc.
Editor: Lee Rossoff
Graphics: Chris George, Maggie Hubbard
Associate Producer: Shelley Elizabeth Carter
Executive Producers: Shannon Behrman, Sarah Goodwin, Elliot Kirschner

Leave a Reply Cancel reply