(OA-15) S100A8/A9 Promotes T Cell Exhaustion and Impairs Response to Bispecific Therapy in Multiple Myeloma

S100A8/A9 is a calcium-binding alarmin released during cellular stress and inflammation. In cancer, it plays a critical role in modulating the immune microenvironment, including in multiple myeloma (MM). Previously, our group implicated S100A8/A9 in resistance to anti-BCMA CAR-T therapy by suppressing cytotoxic function, and we demonstrated that cytotoxicity could be rescued by a monoclonal antibody against S100A8/A9. Here, we explore its role in MM patients treated with bispecific antibodies (BsAb) targeting BCMA and GPRC5D.

Methods:

Peripheral blood serum was collected from 19 MM patients before and during BsAb therapy. S100A8/A9 protein levels were measured and correlated with depth of response (DOR) and progression-free survival (PFS). To study mechanistic effects, patient and healthy donor T cells were exposed to S100A8/A9 in vitro, followed by multiparameter spectral flow cytometry to investigate phenotypic composition, antigen-specific cytokine production, and cytotoxic activity. In addition, we examined the signaling pathways affected by S100A8/A9 using Western blot analysis.

Results:

MM patients achieving less than a very good partial response to bsAb therapy (< VGPR) had significantly higher serum S100A8/A9 levels at baseline and during therapy (p < 0.05). Elevated levels were inversely correlated with PFS (r=-0.53, p< 0.05). When split in two groups, median PFS was ~400 days in patients with low levels of S100A8/A9, vs. ~100 days in patients with high levels (p=0.02). In vitro, S100A8/A9 impaired bispecific antibody-mediated cytotoxicity in a coculture assay. Incubation with S100A8/A9 was associated with an increase in exhausted T cells, as denoted by augmentation of TOX+CD4+ and TOX+CD8+ cells (p< 0.05), which could be reversed with the use of a monoclonal antibody against S100A8/A9. Antigen-specific stimulation resulted in less TNF-α production in S100A8/A9-treated T cells. T cell pathway analysis of S100A8/A9-incubated T cells shows a dose-dependent decrease in pERK, pZAP70, and pNF-κB. 

Conclusions:

S100A8/A9 promotes T cell exhaustion and impairs T cell function, limiting the efficacy of BsAb therapy in MM. Elevated serum S100A8/A9 is associated with inferior clinical responses and shorter PFS after BsAb therapy. Incubation with S100A8/A9 increased the number of T cells expressing TOX and decreased the phosphorylation of T cell signaling pathways, which corresponded to a reduction in the functional production of cytokines and cytotoxicity in vitro. Our findings support S100A8/A9 as a biomarker of resistance and a potential therapeutic target to enhance the efficacy of T cell-engaging therapies.