CAR T-cells meet autoimmune neurological diseases: a new dawn for therapy

Abstract

Autoimmunity and autoimmune diseases arise when the immune system erroneously targets self-antigens leading to tissue damage. Consequently, immunomodulatory and mainly immunosuppressive drugs comprise the conventional treatment in conditions such as systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis. However, many of these agents often fall short of providing a cure and have a limit on symptom management. This underscores the urgent need for even more advanced therapies for patients to constrain progressive disability. Therefore, currently, researchers explore the potential of chimeric antigen receptor (CAR) T-cell therapy for autoimmune diseases considering its success in cancer treatment and specifically in hematological malignancies. This review will examine recent advancements in CAR T-cell therapy for autoimmune disorders, highlighting how CAR T cells can be engineered to precisely target and eliminate autoreactive immune cells that drive these debilitating diseases, particularly those affecting the nervous system such as Multiple sclerosis, Myasthenia gravis, Neuromyelitis optica, Stiff-person syndrome, Autoimmune encephalitis, MOG-antibody disease and Chronic inflammatory demyelinating polyneuropathy. Also, through an analysis of preclinical and clinical data, we will assess the efficacy, safety, potential side effects and limitations of these innovative therapies. Lastly, we will underline the transformative potential of CAR T-cells in Autoimmune Neurology, offering a promising new hope for treatment where conventional therapies have failed.

Keywords: CAR T-cells; CRS; autoimmune neurological diseases; clinical trials; efficacy; limitations; preclinical data; safety.

Figure 1

Central and peripheral tolerance. (A, B) Central tolerance takes place in the primary lymphoid organs, thymus for T cells and bone marrow for B cells. (A) The epithelial cells of the thymus, due to the transcription factor autoimmune regulator (AIRE) can express a wide variety of tissue specific antigens (TSAs) to promote self-tolerance. The T cells undergo selection, either negative, when their T cell receptor (TCR) recognizes strongly the self-antigen resulting in their apoptosis or positive, when the recognition is low. They leave the thymus as single positive (CD4+ or CD8+) T cells. Some T cells that recognize self-antigens with moderate affinity become T regulatory cells (Tregs) expressing forkhead box P3 (FOXP3) and CD4. (B) Regarding B cells, when their B-cell receptor (BCR) recognizes a self-antigen with high affinity, they edit their receptor through recombination of the light chain. If the edited receptor still possesses high affinity, the B cells will be led to negative selection or apoptosis. In case of a moderate affinity BCR, the B cells undergo positive selection and leave the bone marrow as naïve B cells. (C) Peripheral tolerance is orchestrated on peripheral tissues like lymph nodes, to hamper either already autoreactive lymphocytes that “slipped” from central tolerance or possible future autoreactive cells which will merge after they encounter a self-antigen. In periphery, autoreactive cells if they recognize a self-antigen without receiving co-stimulation, can become anergic -which means inactivated- or can be deleted through apoptosis. Tregs can suppress them through different mechanisms, too.

Figure 2

CAR-T cell manufacturing process. (A) Leukapheresis: collection of peripheral blood mononuclear cells (PBMCs); (B) T cell collection: separation of T cells from PBMCs.; (C) Activation: T cells require stimulation from artificial antigen-presenting cells (aAPCs), anti-CD3/anti-CD28 antibodies, and interleukin-2 (IL-2) in order to proliferate and become effector T cells; (D) Transduction: T cells are transduced with lenti- or retroviral vectors to express CAR on their cell membrane; (E) CAR expression: the viral vectors integrate the CAR gene in the T-cell genome so they express it on their surface; (F) Expansion: CAR-T cells proliferate after their treatment with IL-2; (G) Infusion: CAR-T cells, after quality and functional assessments, transferred back to the patient through intravenous infusion.

Figure 3

Generations of CARs. All generations have an extracellular antigen binding domain consisting of variable heavy (VH) and light (VL) chains (scFv). They differ though in the intracellular component. (A) First-generation: one intracellular CD3ζ for signal transduction.; (B) Second-generation: two intracellular domains: CD3ζ and an additional costimulatory domain (e.g., CD28 or 4-1BB).; (C) Third-generation: three intracellular domains: CD3ζ and two additional costimulatory domains (CD28 and 4-1BB or OXO40).; (D) Fourth-generation or T-cells redirected for universal cytokine-mediated killing (TRUCKS): are based on the second generation but with the addition of a cytokine inducer domain which activates the nuclear factor of activated T cells (NFAT). NFAT as a transcription factor induces cytokine production (especially of IL-12) which is secreted from CAR T-cells and thus modulate immune responses.; (E) Fifth or Next generation: based on the second generation but with the addition of intracellular domains of cytokine receptors such as IL-2 receptor β-chain (IL-2Rβ) domain with a binding site for Janus kinase (JAK) and for the transcription factors Signal transducer and activator of transcription 3/5 (STAT3/5). Antigen activation triggers three synergistic signals through CD3ζ, CD28, and cytokine JAK–STAT3/5 signaling, which lead to T-cell activation and proliferation. CD, cluster of differentiation.

Figure 4

Autoreactive cells and CAR T-cells. An antigen-presenting cell (dendritic cell or autoreactive B cell) presents through the MHC class II a self-antigen to an autoreactive T cell (A) which becomes activated after the co-stimulation of CD40-CD40L and the secretion of cytokines IFN-α, IFN-β and IL-12. (B) In parallel, B cell activation is based on the secretion of IL-2, IL-4, IL-5 from T cells. (C) B cells after activation can differentiate into plasma cells (D) producing large quantities of autoantibodies (E) which along with autoreactive TCRs of T cells can directly attack the cells or tissues expressing the self-antigen like the Myelin Basic Protein (MBP) of the myelin sheath of oligodendrocytes which is believed to be the autoantigen in Multiple Sclerosis. (F) As a result, tissue damage occurs. (G) CAR T-cells can eliminate autoreactive T, B and plasma cells targeting CD70 or CD7, (H) CD19 or CD20 (I) and BCMA or CD38, (J) respectively. CAR T-cells through the secretion of Perforin (PFN), Granzyme B (GzmB) and IFN-γ (K) cause the cell death of autoreactive cells (L). IFN, interferon; CD, cluster of differentiation.

Figure 5

Autoreactive cells and CAR Tregs. Two signals are essential for T-cell activation; one is TCR-MHC signaling and the other is CD28-CD80/86 co-stimulation. CAR Tregs can express a TCR which binds to the complex MHC class II-autoantigen of dendritic cells leading to CAR Tregs proliferation (A). Also, through the expression of Cytotoxic T-lymphocyte associated protein 4 (CTLA-4) which binds to the CD80/86 can inhibit the activation and maturation of dendritic cells, so as not to present the self-antigens to T cells (B). In parallel, the CTLA-4 inhibition upregulates the Indoleamine 2, 3-dioxygenase (IDO) expression, an enzyme which converts tryptophan to kynurenine, with the later suppressing T cells (C). Moreover, CAR Tregs either with the immunosuppressive cytokines TGF-β, IL-10, IL-35 (D) or with IL-2 deprivation (E) can cause T cell apoptosis (F). Regarding autoreactive B cells, CAR Tregs expressing the receptor programmed cell death protein 1 (PD-1) which binds to programmed death-ligand 1 (PD-L1) (G), can induce B cell tolerance, inhibiting their activation and differentiation into plasma cells (H). Lastly, through the secretion of Granzyme B and Perforin trigger apoptosis of any autoreactive cell (I).