TSHR-based chimeric antigen receptor T cell specifically deplete auto-reactive B lymphocytes for treatment of autoimmune thyroid disease, 2023, Huang+

TSHR-based chimeric antigen receptor T cell specifically deplete auto-reactive B lymphocytes for treatment of autoimmune thyroid disease

Highlights

• Graves disease (GD), a typical organ-specific, antibody-mediated autoimmune disease, is caused by stimulating antibody which recognizes TSHR (TRAb)
  
• Therefore, specifically, eliminating TRAb producing B lymphocytesmay be an effective therapeutic strategy for GD.
  
• In this study, we developed a chimeric receptor TSHR-CAR, which fused TSHR extracellular domain to the CD8 transmembrane and intracellular signal domain (4-1BB)
  
• TSHR-CAR-T cells can specifically recognize and exert a cytotoxic effect on TRAb producing B lymphocytes of mice in vivo and in vitro.
  
• The chimeric receptor CAR-T based on autoantigen may provide promising immunotherapy for antibody-mediated autoimmune diseases.

Abstract
Graves' disease (GD) is a prominent antibody-mediated autoimmune disorder characterized by stimulating antibodies (TRAb) that target the thyroid-stimulating hormone receptor (TSHR). Targeting and eliminating TRAb-producing B lymphocytes hold substantial therapeutic potential for GD. In this study, we engineered a novel chimeric antigen receptor T cell (CAR-T) therapy termed TSHR-CAR-T. This CAR-T construct incorporates the extracellular domain of the TSH receptor fused with the CD8 transmembrane and intracellular signal domain (4-1BB). TSHR-CAR-T cells demonstrated the ability to recognize and effectively eliminate TRAb-producing B lymphocytes both in vitro and in vivo. Leveraging this autoantigen-based chimeric receptor, our findings suggest that TSHR-CAR-T cells offer a promising and innovative immunotherapeutic approach for the treatment of antibody-mediated autoimmune diseases, including GD.

https://www.sciencedirect.com/science/article/pii/S1567576923011980

 

@Pibee are you aware of anything upcoming for Graves diseases and CAR-T cells, respectively have you heard of this group of researchers?

Graves seems like a potentially easier target (in the sense that permanent damage is less common in Graves) but I would guess it's harder to justify treatments if there's no long-term data, especially on safety and currently ridiculously high costs to conduct CAR-T cell studies rather than just cutting out someones Thyroid and putting them on cheap hormone therapy which has high efficacy and is safe cannot justify a trial, especially when similarly effective treatments don't exist in other autoimmune diseases and as such focus should be put on these?

 

No, I haven't heard anything for Graves, except maybe running into the same study you shared here. It seems definitely far from happening for diseases like Graves, as you said because it's relatively easy to control comparing to others, and also preconditioning chemotherapy is still too high for that... ( they think is needed for now, but aren't sure, maybe can be reduced further)
But I guess they might try just regular CD19 CAR-T (if Chinese haven't already) or TSHR-CAR-T in some rare patients with super severe Graves.

 

Thyroidectomy does not deal with Graves ophthalmopathy, which can be progressive and lead to loss of sight. The ophthalmopathy is mediated by antibodies independent of thyroid hormone levels.

My thyroid endocrine colleague was one of the first to ask me to help with a rituximab trial in 2000 for this reason. Rituximab worked for Graves even if I suspect it was not an ideal strategy even in these cases. If there was a way to get long term antibody clearance I think there would be a good case for something like antigen specific CAR-T.

 

This is probably a very naive and stupid question because I don't have close enough knowledge to even ask any sensible questions, but what is generally viewed as the "main problem", if such a thing exists:
That B-cells produce autoantibodies or that these B-cells for some reason survive deletion/evade immunological tolerance mechanisms?

 

Most strategies just kill mid-maturation B cells but the bulk of autoantibody is produced by more mature plasma cells some of which live for months, some for decades.

If autoantibody is produced by short lived plasma cells then depleting B cells starves the system of new plasma cells and antibodies go down. They often do, but then come back up, either pretty soon after B cells return or sometimes a year or more later.

The situation is complicated by the fact that B cells can only make antibody to something if there is already some antibody to that something. That might seem odd but it works very well because new B cells are constantly being generated that produce a bit of broad affinity antibody to everything - mostly IgM. It allows for a chain reaction positive feedback loop when you need rapid expansion of antibody during infection.

In autoimmunity it is likely that the long term problem is that once a few B cell clones have got going producing autoantibody to X their antibodies help further B cell clones to make antibody to X. That means that even if a few long term plasma cells are left behind making antibody that may be enough to prime new B cells to do the same.

A simpler story is that some autoreactive B cells hide away and just get going again once the rituximab or whatever has gone. That doesn't explain why it can take up to five years for autoantibody elves to start rising in some cases but it is very likely that the residual drive to antibody production depends on a bit of everything - feedback and re-emergence.

 

Thank you for this simple layman explanation.

Seems like there's potentially quite a few positive feedback loops involved or at least one feedback mechanism that is sufficiently hard to completely eradicate which would be necessary.

It would seem to me that this would have to mean that generally there's also sufficiently many negative signals or things that destroy these above positive feedback loops in healthy people to prevent these things from happening, and that these things are also present in people with autoimmunity to prevent things such as an ever increasing autoantibody production and in some cases of autoimmunity even produce naturally relapsing-remitting cases. Shouldn't there be therapeutics to strengthen these processes?

If the antibodies that are supposed to be targeted go down temporarily, shouldn't a continous/chronic treatment (if not too dangerous) with Rituximab do the job? Especially when it comes to things like stopping diseases progression (which RTX appears to be ineffective in for example in MS)?

Furthermore why isn't there more focus on combination treatments, be it combinations of things like Rituximab and Belimumab or even a whole range of different things trying to target different points of these feedback loops (combining things such as B-cell depleting drugs with FcRn inhibitors, cyclophosphamide, immunadsorption, Car-T cells or therapeutics targeted at those mechanisms that prevent things like continous expansion of antibody producing B-cells)?

 

A smorgasbord of excellent questions, @EndME. In fact that is pretty much exactly as we thought when I left off fifteen years ago and almost nothing has changed other than the appearance of CAR-T now.

For RA we identified four crucial positive cycles, one of which was dependent on random effects of individual antibody species and could tip the whole process of 55 steps into action. The others are involved in normal functions like localisation - so that inflammation is maximally focused at a site of antigen. Winding back the clock on the one dependent on random antibody generation is the key to long term remission,

Yes, the balancing negative signals are quite easily identified. They include the negative signalling FcRII receptor and also competitive inhibition between different antibodies trying to bind to the same antigen. Complement mediated deletion of early bone marrow B cell precursors is also likely important - or at least a signal for receptor editing and re-programming antibody species. That process is dependent on PTPN22, which is linked to RA risk.

Yes, this may relate to the competition between antibodies. Once antibody is totally dominant over antigen availability the process will lose drive. The weird case is RA where the antigen is antibody itself. That might lead to the entire B cell pool being taken over by autoreactive cells. In the old days we had Felty's syndrome patients in which that looked to be near the case. Huge levels of circulating complexes were documented. Life expectancy was a few years at best.

This is the most tantalising thing. In the 1980s I learnt from practical experience that in about 20% of patients intramuscular gold thiomalate would induce complete remission over a period of about three months. Toxicity was a problem but I had several patients who remained in remission life long. Nobody has any idea what gold does. Penicillamine did the same but was even more toxic. Both contain thiol groups.

The best guess I had was that these drugs were decoupling complement at the stage of generation of the C3d fragment involved in a positive feedback to the B cell through complexes. Interestingly both drugs were capable of inducing immune complex nephritis which is also seen in lupus and is a sign of decoupling of complement activation. (The feedback loop story for lupus includes some loops the same as RA but some loops almost opposite, relating to the specific role of complement in lupus.)

So there might be drugs that could alter the balance of positive and negative loops but I strongly suspect that they would be good for some diseases and bad for others.

It does, repeating rituximab just before you think it is going to wear off and B cell come back keeps most autoimmune disease in remission. But you get a gradual fall in immunoglobulin levels so we always used the minimum we could get away with. A number of my RA patients continued on regular rituximab for the rest of their lives and never relapsed, but for some it was not an option.

Because research funding bodies expected drug companies to pay for the trials and the drug companies were not interested in either 1. combining with someone else's drug or 2. cure. They were happy to have their drug used repeatedly for ever. The commercial aspect of it all was very ugly. Not just from drug companies but in the USA from physicians wanting to maximise their fees - something we did not se in the UK.

The only caveat is that when we did try combinations, which we did, we never seemed to get a synergistic effect on remission time. We never saw 'breaking through' to really long remission. We could see why that might be but organising ethical trials likely to be productive was just too hard. In many ways that is why I left clinical research. I could not see how I could make the next step without new agents in the prevailing political climate. There was still a lot of resistance to B cell therapies 15 years ago. Now I think finally people have realised it is the way to go.