Dysregulated CD4⁺CD25⁺ T- Regulatory Cells and TLRs in Myeloma.

Although current vaccine strategies have achieved anti-myeloma immune responses, meaningful clinical responses have not been observed. This may be related with the significant immune dysfunction observed in myeloma that may interfere with the development of effective anti-myeloma immune responses. The initiation of immune response is controlled by CD4⁺CD25⁺ T regulatory (T_reg) cells, which can suppress anti-tumor immune responses. This property of T_reg cells to modulate anti-tumor immune responses may function as a barrier to cancer immunotherapy. In order to overcome such suppression, signaling through Toll-like receptors (TLRs) can induce adjuvant effect by increasing local production of chemokines, and pro-inflammatory cytokines, and by enhancing antigen-presentation by APCs. Here, we have evaluated the role of T_reg cells and the effects of TLRs in myeloma. We observed significant increase in CD4⁺CD25⁺ T_reg cells in MM patient samples compared to normal donors (23±4% vs 6±3%). Proliferation of T cells depleted of T_reg cells with anti-CD3 antibody was significantly lower in MGUS (n=9, SI=12±2) and MM (n=9, SI=28±8) compared with normal donors (n=9, SI=74±9, p<0.01). As expected addition of T_reg cells was able to suppress T cell proliferation in normal donors (↓31%), however, their effects were less suppressive in MGUS (↓26%), and in fact, they increased T cell proliferation in MM (↑29%). Additionally, LPS which functions through Toll-like receptor 4 (TLR4), is able to overcome suppression of T cell proliferation by T_reg cells in normal controls (110%), however, it had significantly limited influence in MGUS (49%) and MM (24%). Expression profile of myeloma cells (n=15) showed up-regulation of TLR4 (7.4 folds) and its related gene MD2 (2.5 folds) in all the MM cells tested compared to normal plasma cells indicating a possible modulation of immune responses by myeloma cells through TLR4 or its soluble agent. This is the first demonstration of dysregulated T_reg cells and TLRs in myeloma. Understanding of the molecular basis of T_reg cell dysfunction is underway with a view to eventually target these mechanisms to improve immuno-therapeutic strategies in myeloma.