Overexpression of CTLA-4 in the Bone Marrow of Patients with Multiple Myeloma As a Sign of Local Accumulation of Immunosuppressive Tregs – Perspectives for Novel Treatment Strategies

Multiple myeloma (MM) development involves a series of genetic alterations and changes in the bone marrow (BM) microenvironment, favoring the growth of the tumor and failure of local immune control. T regulatory (Treg) cells play an important role in the maintenance of self-tolerance and modulation of overall immune responses against infections and tumor cells. T-helper-17 (Th17) cells, on the other hand, have a critical function in eradicating extracellular pathogens and tumor cells. The balance between Treg and Th17 cells may be essential for maintaining homeostasis of anti-tumor immunity. The aim of our study was to characterize the expression of Treg- (FOXP3 and CTLA-4) and Th17-related (RORγt) genes in total MM bone marrow samples to assess the local immune milieu as a potential therapeutic target in this still incurable disease. Material and Methods: Expression of FOXP3, CTLA-4 and RORγt was determined by quantitative real-time PCR (qPCR) in BM aspirates of 55 MM patients, 4 patients with monoclonal gammopathy of undetermined significance (MGUS), and 5 healthy BM donors. Genes were considered overexpressed when their expression was at least two times higher in myeloma BM than in normal samples. Results:RORγt showed a non-significant overexpression in MM patients compared to controls. FOXP3, on the other hand, showed a 3.6-fold higher expression in MM patients compared to controls but the difference was not significant and was overexpressed in 63% of MM cases. CTLA-4 expression was 14.6-fold higher in MM patients compared to controls (p=0.03, Mann-Whitney test) and was overexpressed in 70% of MM cases. Importantly the CTLA-4/RORyt ratio was significantly higher in MM samples compared to controls (p = 0.009) while this difference was not significant when controls were compared to MGUS patients, suggesting that the immunological imbalance worsens with the progression of disease. Conclusions: CTLA-4 (cytotoxic T-lymphocyte antigen-4), an intracellular and membrane inhibitory protein expressed on Treg cells, modulates T-cell activation and is critical in maintaining immune tolerance to self-antigens. Monoclonal antibodies targeting CTLA-4 have improved the survival of patients with metastatic melanoma in clinical trials. The myeloma-related overexperssion of CTLA-4 and the increased CTLA-4/RORyt ratio suggest an accumulation of immunosuppressive Tregs in the tumor microenvironment and/or an immediate involvement of this gene in the development and progression of myeloma. If protein expression confirms gene expression imbalance between Treg and Th17 subpopulations, therapeutic approaches that specifically target CTLA-4-expressing Treg myeloma cases may provide a new treatment strategy for this disease. (Supported by CNPq, Brazil).

No relevant conflicts of interest to declare.