The focus of this review is to examine the role of ITK signaling in multiple diseases and investigate the clinical potential of ITK inhibition. The diseases and potential interventions reviewed include T cell-derived malignancies as well as other neoplastic diseases, allergic diseases such as asthma and atopic dermatitis, certain infectious diseases, several autoimmune disorders such as rheumatoid arthritis and psoriasis, and finally the use of ITK inhibition in both solid organ and bone marrow transplantation recipients.

Allogeneic hematopoietic stem cell transplantation is a potentially curative procedure for many malignant diseases. Donor T cells prevent disease recurrence via graft-versus-leukemia (GVL) effect. Donor T cells also contribute to graft-versus-host disease (GVHD), a debilitating and potentially fatal complication. Novel treatment strategies are needed which allow preservation of GVL effects without causing GVHD. Using murine models, we show that targeting IL-2-inducible T cell kinase (ITK) in donor T cells reduces GVHD while preserving GVL effects. Both CD8⁺ and CD4⁺ donor T cells from Itk^-/- mice produce less inflammatory cytokines and show decrease migration to GVHD target organs such as the liver and small intestine, while maintaining GVL efficacy against primary B-cell acute lymphoblastic leukemia (B-ALL). Itk^-/- T cells exhibit reduced expression of IRF4 and decreased JAK/STAT signaling activity but upregulating expression of Eomesodermin (Eomes) and preserve cytotoxicity, necessary for GVL effect. Transcriptome analysis indicates that ITK signaling controls chemokine receptor expression during alloactivation, which in turn affects the ability of donor T cells to migrate to GVHD target organs. Our data suggest that inhibiting ITK could be a therapeutic strategy to reduce GVHD while preserving the beneficial GVL effects following allo-HSCT treatment.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for hematological malignancies, due to graft-versus-leukemia (GVL) activity mediated by alloreactive donor T cells. However, graft-versus-host disease (GVHD) is also mediated by these cells. Here, we assessed the effect of attenuating TCR-mediated SLP76:ITK interaction in GVL vs. GVHD effects after allo-HSCT. CD8+ and CD4+ donor T cells from mice expressing a Y145F mutation in SLP-76 did not cause GVHD but preserved GVL effects against B-ALL cells. SLP76Y145FKI CD8+ and CD4+ donor T cells also showed less inflammatory cytokine production and migration to GVHD target organs. We developed a novel peptide to specifically inhibit SLP76:ITK interactions, resulting in decreased phosphorylation of PLCγ1 and ERK, decreased cytokine production in human T cells, and separation of GVHD from GVL effects. Altogether, our data suggest that inhibiting SLP76:ITK interaction could be a therapeutic strategy to separate GVHD from GVL effects after allo-HSCT treatment.

Regulatory T cells (Tregs) play an important role in controlling autoimmunity and limiting tissue damage and inflammation. IL2‐inducible T cell kinase (Itk) is part of the Tec family of tyrosine kinases and is a critical component of T cell receptor mediated signaling. Here, we showed that either genetic ablation of Itk signaling or inhibition of Itk signaling pathways resulted in increased frequency of “noncanonical” CD4⁺CD25⁻FOXP3⁺ Tregs (ncTregs), as well as of “canonical” CD4⁺CD25⁺FOXP3⁺ Tregs (canTregs). Using in vivo models, we showed that ncTregs can avert the formation of acute graft‐versus‐host disease (GVHD), in part by reducing conventional T cell proliferation, proinflammatory cytokine production, and tissue damage. This reduction in GVHD occurred without disruption of graft‐versus‐leukaemia (GVL) effects. RNA sequencing revealed that a number of effector, cell adhesion, and migration molecules were upregulated in Itk^–/− ncTregs. Furthermore, disrupting the SLP76: ITK interaction using a specific peptide inhibitor led to enhanced Treg development in both mouse and primary human cells. This peptide inhibitor also significantly reduced inflammatory cytokine production in primary GVHD patient samples and mouse T cells without causing cell death or apoptosis. We provide evidence that specifically targeting Itk signaling could be a therapeutic strategy to treat autoimmune disorders.

The transcription factor T cell factor-1 (TCF-1) is encoded by Tcf7 and plays a significant role in regulating immune responses to cancer and pathogens. TCF-1 plays a central role in CD4 T cell development; however, the biological function of TCF-1 on mature peripheral CD4 T cell-mediated alloimmunity is currently unknown. This report reveals that TCF-1 is critical for mature CD4 T cell stemness and their persistence functions. Our data show that mature CD4 T cells from TCF-1 cKO mice did not cause graft versus host disease (GvHD) during allogeneic CD4 T cell transplantation, and donor CD4 T cells did not cause GvHD damage to target organs. For the first time, we showed that TCF-1 regulates CD4 T cell stemness by regulating CD28 expression, which is required for CD4 stemness. Our data showed that TCF-1 regulates CD4 effector and central memory formation. For the first time, we provide evidence that TCF-1 differentially regulates key chemokine and cytokine receptors critical for CD4 T cell migration and inflammation during alloimmunity. Our transcriptomic data uncovered that TCF-1 regulates critical pathways during normal state and alloimmunity. Knowledge acquired from these discoveries will enable us to develop a target-specific approach for treating CD4 T cell-mediated diseases.

Cancer immunotherapy relies on improving T cell effector functions against malignancies, but despite the identification of several key transcription factors (TFs), the biological functions of these TFs are not entirely understood. We developed and utilized a novel, clinically relevant murine model to dissect the functional properties of crucial T cell transcription factors during anti-tumor responses. Our data showed that the loss of TCF-1 in CD8 T cells also leads to loss of key stimulatory molecules such as CD28. Our data showed that TCF-1 suppresses surface NKG2D expression on naïve and activated CD8 T cells via key transcriptional factors Eomes and T-bet. Using both in vitro and in vivo models, we uncovered how TCF-1 regulates critical molecules responsible for peripheral CD8 T cell effector functions. Finally, our unique genetic and molecular approaches suggested that TCF-1 also differentially regulates essential kinases. These kinases, including LCK, LAT, ITK, PLC-γ1, P65, ERKI/II, and JAK/STATs, are required for peripheral CD8 T cell persistent function during alloimmunity. Overall, our molecular and bioinformatics data demonstrate the mechanism by which TCF-1 modulated several critical aspects of T cell function during CD8 T cell response to cancer. Graphical Summary Figure: TCF-1 is required for persistent function of CD8 T cells but dispensable for anti-tumor response. Here, we have utilized a novel mouse model that lacks TCF-1 specifically on CD8 T cells for an allogeneic transplant model. We uncovered a molecular mechanism of how TCF-1 regulates key signaling pathways at both transcriptomic and protein levels. These key molecules included LCK, LAT, ITK, PLC-γ1, p65, ERK I/II, and JAK/STAT signaling. Next, we showed that the lack of TCF-1 impacted phenotype, proinflammatory cytokine production, chemokine expression, and T cell activation. We provided clinical evidence for how these changes impact GVHD target organs (skin, small intestine, and liver). Finally, we provided evidence that TCF-1 regulates NKG2D expression on mouse naïve and activated CD8 T cells. We have shown that CD8 T cells from TCF-1 cKO mice mediate cytolytic functions via NKG2D.