Bone marrow mesenchymal stem cells regulate the dysfunction of NK cells via the T cell immunoglobulin and ITIM domain in patients with myelodysplastic syndromes

TIGIT: Will it be the next star therapeutic target like PD-1 in hematological malignancies?

Research on the mechanism and application of checkpoint inhibitory receptors in hematologic diseases has progressed rapidly. However, in the treatment of relapserefractory (R/R) hematologic malignancies and anti-programmed cell death protein 1 (PD-1), patients who are resistant to anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) are in urgent need of alternative therapeutic targets. T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) has a broad prospect as an inhibitory receptor like PD-1, but its more specific mechanism of action and application in hematologic diseases still need to be further studied. In this review, we discuss the mechanism of TIGIT pathway, combined effects with other immune checkpoints, immune-related therapy, the impact of TIGIT on hematopoietic stem cell transplantation (HSCT) and the tumor microenvironment (TME) provides a potential therapeutic target for hematologic malignancies.

Downregulating LKB1 in bone marrow mesenchymal stem cells could inhibit CD4+ T cell proliferation via the PD-1/PD-L1 signaling pathway

BACKGROUND

Our previous research has shown that LKB1 in amniotic mesenchymal stem cells (MSCs) serves as a vital regulator of regulatory T cell differentiation and T cell proliferation, which may have a similar role in bone marrow MSCs (BMMSCs). Therefore, we investigated the role of LKB1 in BMMSCs for regulating CD4+ T cell proliferation in the bone micro-environment of AML.

METHODS

RT-PCR was used to assessed LKB1 expression in BMMSCs derived from AML patients and healthy controls. Subsequently, LKB1 was knocked down in the BMMSCs line HS-5 (HS-5-LKB1KD). Co-cultures in vitro were established to analyze the effect of HS-5-LKB1KD on CD4+ T cell. Flow cytometry was employed to measure PD-L1 and CD4+ T cell proliferation levels. Western blot was utilized to detect related proteins.

RESULTS

The expression of LKB1 in BMMSCs derived from AML patients was decreased. Knockdown of LKB1 in HS-5 resulted in upregulation of PD-L1 expression. Co-culture of peripheral blood CD4+ T cell with HS-5-LKB1KD exhibited reduced CD4+ T cell proliferation compared to co-culture with HS-5-LKB1con. Furthermore, blocking PD-L1 in the co-culture conditions could restore the reduced CD4+ T cell proliferation. Additionally, it was found that upregulation of the Wnt signaling pathway-related proteins following LKB1 knockdown in HS-5, indicating that downregulating LKB1 could promote PD-L1 expression through activation of the Wnt signaling pathway.

CONCLUSIONS

The decreased expression of LKB1 in BMMSCs may activate the Wnt signaling pathway, leading to increased PD-L1 expression. This inhibited CD4+ T cell proliferation, which might lead to impaired anti-tumor immunity in AML patients and promote AML progression.

Therapeutic and immunomodulatory potentials of mesenchymal stromal/stem cells and immune checkpoints related molecules

Mesenchymal stromal/stem cells (MSCs) are used in many studies due to their therapeutic potential, including their differentiative ability and immunomodulatory properties. These cells perform their therapeutic functions by using various mechanisms, such as the production of anti-inflammatory cytokines, growth factors, direct cell-to-cell contact, extracellular vesicles (EVs) production, and mitochondrial transfer. However, mechanisms related to immune checkpoints (ICPs) and their effect on the immunomodulatory ability of MSCs are less discussed. The main function of ICPs is to prevent the initiation of unwanted responses and to regulate the immune system responses to maintain the homeostasis of these responses. ICPs are produced by various types of immune system regulatory cells, and defects in their expression and function may be associated with excessive responses that can ultimately lead to autoimmunity. Also, by expressing different types of ICPs and their ligands (ICPLs), tumor cells prevent the formation and durability of immune responses, which leads to tumors' immune escape. ICPs and ICPLs can be produced by MSCs and affect immune cell responses both through their secretion into the microenvironment or direct cell-to-cell interaction. Pre-treatment of MSCs in inflammatory conditions leads to an increase in their therapeutic potential. In addition to the effect that inflammatory environments have on the production of anti-inflammatory cytokines by MSCs, they can increase the expression of various types of ICPLs. In this review, we discuss different types of ICPLs and ICPs expressed by MSCs and their effect on their immunomodulatory and therapeutic potential.

Targeting TIGIT for cancer immunotherapy: recent advances and future directions

As a newly identified checkpoint, T cell immunoreceptor with immunoglobulin and tyrosine-based inhibitory motif (ITIM) domain (TIGIT) is highly expressed on CD4+ T cells, CD8+ T cells, natural killer (NK) cells, regulatory T cells (Tregs), and tumor-infiltrating lymphocytes (TILs). TIGIT has been associated with NK cell exhaustion in vivo and in individuals with various cancers. It not only modulates NK cell survival but also mediates T cell exhaustion. As the primary ligand of TIGIT in humans, CD155 may be the main target for immunotherapy due to its interaction with TIGIT. It has been found that the anti-programmed cell death protein 1 (PD-1) treatment response in cancer immunotherapy is correlated with CD155 but not TIGIT. Anti-TIGIT alone and in combination with anti-PD-1 agents have been tested for cancer immunotherapy. Although two clinical studies on advanced lung cancer had positive results, the TIGIT-targeted antibody, tiragolumab, recently failed in two new trials. In this review, we highlight the current developments on TIGIT for cancer immunotherapy and discuss the characteristics and functions of TIGIT.

Myeloid-derived suppressor cells inhibit natural killer cells in myelodysplastic syndromes through the TIGIT/CD155 pathway

OBJECTIVE

This experiment will explore the role of TIGIT/PVR signaling pathway in the pathogenesis of MDS immune tolerance through in vitro co-culture of NK cells and MDSC cells.

METHODS

Flow cytometry was used to detect the expression percentage of MDSCs and CD155 on MDSCs in the bone marrow of MDS patients and controls. The expression of NK cell surface receptors (NKG2D, NKp30, NKp46), secreted cytokines (perforin, granzyme B, CD107a, IFN-γ) and NK cell apoptosis rate were detected by flow cytometry to evaluate the effect of MDSCs on NK cell function.

RESULTS

The number of MDSCs in bone marrow of MDS patients was notably higher than that of the control group (8.39 ± 7.01 vs 2.31 ± 1.65, P = 0.0001). Compared with the control group, the expression of CD155 on MDSCs in MDS group was increased (31.81 ± 21.33 vs. 10.49 ± 6.53, P < 0.0001). After NK cells were co-cultured with MDSCs, NKG2D, NKp30, NKp46, CD107a, IFN-γ, perforin and granzyme B were decreased, and the NK function partially recovered after the addition of inhibitors.

CONCLUSION

Compared with the normal control, MDSCs and CD155 on MDSCs were highly expressed in MDS patients. After co-culture with MDSCs, the expression of NK cells' surface receptors decreased, the secretion of cytokines decreased and the apoptosis rate increased. After blocking TIGIT/CD155 pathway, NK cell function was reversed, but NK cell apoptosis was not reduced.