Cellular therapies for IBD

CAR-T cells

Initial cellular therapy studies used autologous stem cell transplantation in the presence or absence of immunotherapy with vedolizumab to induce clinical remission in refractory CD.20 21 While this approach held the promise of an immune reset in CD, the rather non-selective approach of stem cell transplantation is associated with a potentially high burden of adverse events. This gave rise to the concept that new cellular immunotherapies that focus on immune cell subsets, and not the modulation of the entire immune system, could be more selective and well-tolerated immune interventions. Cellular immunotherapies encompass a range of treatments that employ anti-inflammatory autologous or allogeneic cells, including T lymphocytes. One of these cellular immunotherapies with innovative potential for IBD therapy is CAR-T cell therapy.

In this therapy, CD4+ or CD8+ T cells are obtained from patients via leukapheresis and genetically reprogrammed to recognise and fight target cells based on defined target structures, such as the CD19 surface molecule22 (figure 2). Subsequently, ex vivo gene transfer is employed, during which a genetically modified virus (eg, via a lentiviral vector) is introduced into the cells, thereby enabling them to produce the chimeric antigen receptor and express this designer molecule on their surface.22 Following the expansion of the CAR-T cells, a space is created in the patient’s blood system for the transfer of the cells via lymphodepletion (eg, via cyclophosphamide and fludarabine) in preparation for infusion of the cells. Subsequently, the modified CAR-T cells are infused into the patient in a final step following lymphodepletion.23 After administration, these CAR-T cells are capable of replicating within the body, thereby enabling long-term therapeutic effects to be achieved through the use of living CAR-T cells (figure 2). Following initial successes in the treatment of haematological tumours,22 23 major therapeutic successes with CAR-T cell therapy have now also been achieved in chronic inflammatory and autoimmune diseases such as lupus erythematosus.24

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Figure 2

New approaches for therapy: schematic of CAR-T cell therapy from cell generation to application is shown (left side). Furthermore, the mode of action of T regulatory cells (Treg) and Tr1 cells is shown (upper right side). In addition, cell depleting antibody therapies are shown (lower right side). IL, interleukin; TNF, tumour necrosis factor. Image was created with Biorender.

A key target structure of CAR-T cell therapy in cancer is currently CD19+ B cells, which can be selectively depleted by therapy (eg, via tisagenlecleucel, lisocabtagene maraleucel, brexucabtagene autoleucel, axicabtagene ciloleucel).22 23 Although this approach has been highly effective in B cell-mediated diseases and even led to a complete cure of the disease in individuals with lupus erythematosus,24 the potential of a CD19+ B cell approach in IBD remains unclear. This is primarily due to the fact that studies in IBD patients have thus far failed to demonstrate a positive effect when using CD20 antibodies such as rituximab.25 However, recent data on B cells in the pathogenesis of IBD indicate that mucosal B cells appear to play an important role in therapy resistance in IBD.11 Activated B cells and plasma cells are enriched in therapy-refractory disease in IBD patients and are capable of producing pro-inflammatory cytokines and autoantibodies against epithelial cells, which can contribute to the inflammatory process observed in IBD.11 26 Therefore, the effective depletion of mucosal B cells could have a greater impact on the inflammatory process in IBD than peripheral B cell depletion with rituximab. It is necessary to conduct controlled studies in order to assess the clinical benefit of CD19+ CAR-T cell therapy in IBD and to determine the extent to which target cells are depleted in different compartments.

Nevertheless, numerous additional potential targets for CAR-T cell therapies in IBD remain to be explored. A Chinese study is currently investigating the significance of CD7 CAR-T cells in chronic inflammatory diseases, including CD and UC (NCT05239702). CD7 is a transmembrane glycoprotein expressed on T cells, natural killer cells and their precursors. Consequently, CAR-T cells targeting CD7 have the potential to eliminate a specific subpopulation of immune cells such as T cells, which may result in the suppression of tissue inflammation and damage in IBD. Another potential avenue for CAR-T cell therapies in IBD is the targeting of IL-23R cells.27 In a recent study, an approach was taken to engineer regulatory T cells (Tregs) expressing an interleukin 23 receptor (IL-23R)-chimeric antigen receptor in order to create IL-23R-CAR-Tregs for the treatment of CD.27 As IL-23R signalling and IL-23R-expressing mucosal cells play a pivotal role in IBD pathogenesis,28 29 targeting IL-23R by CAR-T cells is a plausible new concept for IBD therapy. The study demonstrated that IL23R-CAR-Treg cells exhibited CAR-dependent suppressive activity against target cells in cell culture and protected mice from experimental colitis.27 Furthermore, these cells demonstrated activation following exposure to intestinal biopsy-derived cells from CD, indicating the potential efficacy of IL23R-CAR cells in human disease. Despite these encouraging preclinical findings, the therapeutic efficacy of these cells in human IBD remains to be established.

Safety is important when developing new IBD treatments. CAR-T cell therapy for haematological neoplasms has been associated with the potential for life-threatening side effects, including cytokine release syndrome (CRS).22 23 CRS is a condition that arises when CAR-T cells are activated in the human body, leading to the death of target cells and the subsequent release of cytokines. Another serious complication is immune effector cell-associated neurotoxicity syndrome (ICANS). These potentially serious complications have thus far been observed with minimal frequency in the treatment of chronic inflammatory diseases.24 This is likely due to the significantly lower number of CD19+ target cells that are eliminated by the therapy as compared with haematological cancers. Nevertheless, further controlled studies are necessary to assess the safety of CAR-T cell therapy in inflammatory diseases. In addition, CAR-T cell therapy for the treatment of cancer has been linked to the potential for secondary cancers.30 While these cases appear to be rare, and are still under investigation, such important adverse events would need to be weighed carefully in the risk-benefit considerations of CAR-T for IBD.

Regulatory T cells

Studies in an experimental model of colitis have identified a protective role for regulatory CD4+CD25+FoxP3 T cells (Treg) in suppressing mucosal inflammation caused by polarised, pathogenic effector T cells.31 In this context, the generation of additional Treg cells may provide new avenues for therapeutic intervention (figure 2). Specifically, transfer of these Treg cells has been shown to ameliorate T cell transfer colitis, which is associated with reduced production of pro-inflammatory cytokines such as interferon-gamma (IFN-γ) and TNF.31 Moreover, it was demonstrated that the adoptive transfer of inducible Tregs generated ex vivo in cell culture in the presence of TGF-β has the capacity to ameliorate mucosal inflammation.32 These studies provided the basis for the development of translational concepts using cellular therapies with T-regulatory cells for IBD.

A pilot study on the use of cellular therapy with autologous Tregs in patients with active CD employed ovalbumin-specific T cells (derived from peripheral blood cells on ovalbumin exposure).33 A 12-week, open-label, single-injection, escalating-dose, phase I/IIa clinical study was conducted in 20 patients with refractory CD. The administration of Treg cells was well tolerated and exhibited a dose-related efficacy, as evidenced by a 40% reduction in Clinical Disease Activity Index scores in patients at weeks 5 and 8. However, this approach was ultimately abandoned due to manufacturing challenges associated with the cellular product. Subsequently, other research groups employed autologous, ex vivo expanded polyclonal Treg cells for cellular therapy in IBD (NCT04691232; NCT03185000). A phase I, fast-track dose-escalation clinical trial was recently completed in UC and demonstrated clinical responses in subgroups of patients with active disease following a single infusion of Treg cells34 (Voskens et al, unpublished data). Treg administration was well tolerated. Ex vivo expansion of Treg cells prior to infusion may however not be necessary as shown by a recent study using low-dose subcutaneous IL-2 therapy (Proleukin) to expand Treg cells in vivo and ameliorate the activity of UC in an open-label phase Ib/IIa induction trial.35

T regulatory cells type 1 (Tr1) cells are a defined group of regulatory, tolerogenic T cells that are distinct from Treg cells and are characterised by the production of IL-10 and the lack of FoxP3 expression.36 37 While FoxP3-Tr1 cells express c-Maf and Blimp-1 and produce IL-10 and TGF-β, eomesodermin-expressing Tr1-like cells produce IL-10 and IFN-γ and exhibit marked cytotoxicity. In IBD patients, a reduction in IL-10 production by mucosal Tr1-like cells was observed, suggesting a potential defect in Tr1 cells that could be overcome by the exogenous administration of these cells in order to suppress inflammation.37 38 In experimental colitis, mucosal Tr1 cells were postulated to fill a tolerogenic niche under suboptimal conditions for Foxp3+ Treg-mediated suppression39 and were demonstrated to suppress experimental colitis in vivo.40

A cell product enriched in Tr1 cells was recently employed in patients with leukaemia and allogeneic hematopoietic stem cell transplantation. In this study, Tr1 cells exhibited high expression of CTLA4 and PD1 and were detectable in the peripheral blood of patients up to 1 year after cell transfer.41 These findings suggest that the administration of Tr1 cells could be exploited for future therapy of IBD. Indeed, a phase I programme is currently being prepared for CD therapy using polyclonal, allogeneic ex vivo expanded Tr1 cells (TRX103; www.tr1x.bio/our-programs). It is anticipated that these cells will be able to migrate to sites of mucosal inflammation via chemokine receptors, where they will suppress pro-inflammatory immune responses and stimulate the local production of antigen-specific Tr1 cells, thereby resetting the mucosal immune system and restoring homeostasis. The allogeneic nature of these Tr1 cells offers a significant advantage in that it allows for rapid cell expansion without the need to isolate and expand patient cells. This is in contrast to the previously described autologous Treg cell transfer concepts that require a significant local infrastructure, and which bear challenges of poor scaleability and significant patient burden. However, it remains to be determined whether the tolerogenic nature of these Tr1 cells is sufficient to prevent any undesired allogeneic T cell responses in the host. Controlled clinical trials are needed to ascertain the efficacy and safety of allogeneic Tr1 cell therapy in the treatment of IBD.

Selective immune cell depleting therapies for IBD

While current therapies primarily focus on the blockade of individual cytokines or trafficking mechanisms,1 17 selective depletion of immune cells represents an intriguing new concept for therapeutic intervention. Depletion of immune cells has the potential for powerful and durable effects in complex immune mediated disorders such as IBD. Pathogenic subsets of immune and non-immune cells, including T cells, B cells, macrophages, granulocytes and fibroblasts, have been previously defined, particularly in patients refractory to current therapeutic concepts.7 9 Prior attempts to deplete activated immune cells from the peripheral circulation using various techniques of apheresis have not proven to be successful in IBD.42 43 However, new approaches to selective depletion of these cells hold promise as an emerging direction for therapy.

One example is the antibody rosnilimab, which has recently been developed for the selective targeting of PD1-high expressing immune cells.44 45 This antibody is a novel PD1 checkpoint agonist that aims to reduce the activity of overactive T effector cells in the inflamed intestine by facilitating their removal. It is important to note that rosnilimab binds to the membrane-proximal region of PD1, and like other such antibodies is an agonist of PD1. Unlike the PD1 antagonists used in immunotherapy for cancer, rosnilimab has the potential to downregulate the immune response in inflammatory diseases.46

Indeed, PD1-expressing T cells are prevalent in the inflamed mucosa and in the peripheral blood of IBD patients and have been identified as a potential positive predictor of response to vedolizumab therapy.47 Of note, rosnilimab selectively depletes PD1-high T cells and antagonises the function of PD1-intermediate T cells, while sparing the presence or function of PD1-low cells (figure 2). Such an approach may deplete or suppress highly pathogenic effector T cells in the inflamed mucosa in IBD, while maintaining immunocompetence. A phase I study in healthy volunteers demonstrated rosnilimab to be highly efficacious in the depletion of PD1 high T cells in the peripheral circulation.45 The therapy was well tolerated, with no clinically significant safety signals. Hence, a phase II placebo-controlled study in patients with moderate to severe UC (ROSETTA; NCT06127043) has recently been initiated, with the objective to determine the efficacy and safety of rosnilimab. The study will provide first insights into the regulatory role of PD1-expressing mucosal T cells in IBD patients under in vivo conditions and should provide insight, as to whether this approach also affects cell populations within the intestinal mucosa.

A second approach to selective immunodepletion is seen with the bispecific T cell engager blinatumomab.48 This molecule is composed of two immunoglobulin single-chain variable fragments connected via a flexible linker that permits bridging between B and T cells (figure 2). Although this concept was initially employed to facilitate T cell-mediated killing of B cells in acute lymphoblastic leukaemia,49 recent studies have indicated that this molecule may also have therapeutic efficacy in patients with inflammatory diseases such as refractory rheumatoid arthritis through the induction of profound B cell depletion.50 It is assumed that a single blinatumomab-driven T cell can engage several B cells and kill them serially, resulting in the depletion of B cells in the peripheral blood and inflamed tissues. In fact, in rheumatoid arthritis, blinatumomab therapy depleted autoantibody-producing memory B cells, which were replaced by non-class-switched IgD-positive naive B cells, leading to a reset of B cell immunology.50 It can therefore be postulated that blinatumomab therapy may result in a more profound depletion of mucosal B cells than rituximab therapy.25 Consequently, the administration of blinatumomab to patients with IBD may provide a novel approach to investigate the function of mucosal B cells. In contrast to CAR-T cell therapies targeting CD19+ B cells, the effect of blinatumomab on B cell depletion is more transient. This finding may be exploited to more tightly control mucosal B cell numbers in IBD. Nevertheless, prospective, controlled studies will be necessary to determine the efficacy and safety of this drug in the treatment of these diseases.

The third example comprises depletion of monocytes using an antibody directed against the C-C chemokine receptor type 2 (CCR2; GRT-001, GraniteBio) through antibody dependent cellular cytotoxicity (figure 2). CCR2 is mainly expressed on classical monocytes, plasmacytoid dendritic cells and basophils but can also be found on Th1 cells and Th17 cells. Monocyte chemoattractant protein-1, also known as CCL2, is its major ligand. Monocytes are multifunctional cell types central in chronic intestinal inflammation.51 CCR2 is involved in monocyte chemotaxis and hence holds the promise of selective depletion of ‘activated’ or pro-inflammatory monocytes with leaving tissue resident macrophages untouched. A biological rationale is provided by CCR2+ monocyte-derived macrophages expanding in the inflamed IBD mucosa.52 Monocyte depletion and CCR2 knock-out are protective in experimental IBD models in vivo.51 53

Of note, CCR2 antagonism (not depletion) failed to show an effect on clincial improvement and synovial biomarkers in active rheumatoid arthritis therapy in a phase IIa clincial trial with the human CCR2 blocking antibody MLN1202.54 Rather than putting the monocyte depletion strategy into question, this may be due to incomplete receptor occupancy and/or redundancy of the monocyte-attracting chemokine network, in particular functional CCR1/2/5 redundancies. The first participants have now been dosed with GRT-001 in the so called MONOlith Ph1 trial in healthy volunteers and patients with IBD (EU CT 2023-507547-11-00) and outcome data is awaited. This clinical trial will provide insight into the functional relevance of CCR2 expressing monocytes in IBD patients.