Dual roles of IRE1α inhibition in reversing mitochondrial ROS-induced CD8+ T-cell senescence and exerting direct antitumor effects in multiple myeloma.

Background: Multiple myeloma (MM) is characterized by the proliferation of malignant plasma cells within the bone marrow (BM) microenvironment, which significantly contributes to immune suppression of CD8⁺ T cells. Our previous research identified that dysregulation of the IRE1α-XBP1s-SLC38A2 axis leads to decreased glutamine uptake and senescence of CD8⁺ T cells in MM. However, the underlying mechanisms of T-cell senescence remain unclear.

Methods: Single-cell RNA sequencing was used to analyze mitochondrial function in CD8⁺ T cells in MM. The effects of XBP1s and SLC38A2 on mitochondrial reactive oxygen species (mtROS) were evaluated by flow cytometry under loss-of-function experiments. An IRE1α inhibitor (17#) was administered to explore its effects on T-cell senescence and MM cell growth. RNA sequencing was employed to disclose pathway alterations in T cells treated with 17#. The Vk*MYC mouse model was used to assess the impact of 17# on CD8⁺ T cell senescence and anti-myeloma effects.

Results: BM-derived CD8⁺ T cells from patients with MM exhibited downregulated expressions of genes critical for glutamine transport (SLC38A2), mitochondrial respiratory chain, and ATP synthesis, while genes associated with ROS were upregulated. Suppression of XBP1s in CD8⁺ T cells resulted in decreased mtROS levels, whereas inhibition of SLC38A2 increased mtROS levels. Compound 17# significantly reduced senescence marker KLRG1 expression and increased perforin expression in nutrient-deprived BM CD8⁺ T cells from healthy donors and in BM CD8⁺ T cells from patients with MM, while promoting T-cell proliferation. Importantly, 17# did not impair the viability of peripheral blood mononuclear cells from healthy donors or alter the immune phenotypes of healthy CD8⁺ T cells. The NPR2-cGMP-PKG pathway was activated by IRE1α inhibition in restoring T-cell function. Furthermore, 17# exhibited direct inhibitory effects on MM cells. In Vk*MYC mouse model, 17# decreased mtROS levels in BM CD8⁺ T cells, reduced the proportion of senescent (KLRG1⁺CD57⁺CD28^-) T cells, and resulted in a lower tumor burden.

Conclusion: Inhibiting IRE1α represents a promising strategy to reverse the senescence of CD8⁺ T cells by mitigating mtROS production. This dual mechanism not only rejuvenates T cells but also directly targets myeloma cells, offering a novel therapeutic approach for MM treatment.