Altered Quantity and Function of Follicular T Helper Cell Subsets in Multiple Myeloma and MGUS

Introduction

Almost all Multiple myeloma (MM) cases were progressed from a premalignant condition called monoclonal gammopathy of undetermined significance (MGUS). So far, the pathogenesis of myeloma is not yet clear. The immune cells, especially T cells in the tumor microenvironment, play an important role in myelomagenesis. Follicular helper T cells (Tfh) primarily assist in plasma cell activation and antibody secretion, potentially contributing to abnormal plasma cell generation. Previous studies showed a significant increase in circulating Tfh cell numbers in MM patients. However, the specific changes in quantity and function, as well as their correlation with disease status, remain unclear. In this study, we performed a comprehensive analysis of Tfh cell subsets in untreated MM patients and individuals with MGUS, which might help further elucidate mechanisms of immune dysfunction during myelomagenesis.

Methods

Our study included 20 MGUS patients and 45 newly diagnosed MM (NDMM) patients. Flow cytometry was applied to determine the proportion of Tfh cell subsets in PB. Flow sorting technology was used to separate Tfh cells and follicular regulatory T cells (Tfr) in MGUS and MM patients. The immune function was indirectly calculated by detecting proliferation rate of plasmablasts differentiated from B cells which were cocultured with Tfh cells. Concentration of IL-10, IL-21 from the culture supernatants of proliferation assay was measured using ELISA.

Results

The proportion of Tfh (CD4⁺CXCR5⁺PD-1⁺) in CD4⁺ T cells was significantly higher in NDMM patients than healthy controls (P<0.001); there was no difference in the proportion of Tfh between MGUS and healthy adults (P=0.37). The proportion of Tfh1 subset (CD3⁺CD4⁺CXCR5⁺PD-1⁺CXCR3⁺CCR6⁻) in Tfh cells was gradually increased in MGUS, NDMM patients than healthy controls (P=0.012, P<0.001); while the number of Tfh2 subset (CD3⁺CD4⁺CXCR5⁺PD-1⁺CXCR3^-CCR6⁻) in Tfh cells showed a trend of decrease in MGUS, NDMM patients than healthy controls. The proportions of Tfr cells in CD4⁺ T cells in MGUS and NDMM patients were no difference from healthy adults.

The immune function of Tfh cells was also altered in MGUS and NDMM patients. The ability of induced differentiation from B cells into plasmablasts (CD19⁺CD27⁺CD38^hiIgD⁻) was significantly enhanced in MGUS and NDMM patients compared with healthy controls (P=0.047, P=0.011). The levels of IL-10 and IL-21 secreted by Tfh cells in untreated MM patients was notably higher than that of healthy adults (P<0.001, P=0.001).

Conclusions

There were significant changes in the frequencies of Tfh cell subsets in MGUS and MM patients, suggesting that immunomodulatory abnormality has existed in patients at premalignant stage. The induced differentiation and cytokine secretory functions of Tfh cells in MGUS and NDMM patients were also impaired to promote myeloma cell proliferation and disease progression.

No relevant conflicts of interest to declare.