Dexamethasone and Daratumumab Impair T-Cell Mediated Killing in Multiple Myeloma: Implications for Sequential Therapies

Background

For elderly patients the combination Daratumumab-lenalidomide-dexamethasone (D-Rd) is an emerging standard-of-care regimen, able to improve long-term outcomes in MM patients. Nevertheless, CD38 is ubiquitously expressed on both MM cells and immune cells, and the effect of daratumumab on MM microenvironment are still under investigation. Thus, we investigated the potential immunomodulatory effect of D-Rd on T-cells function in patients with newly diagnosed MM.

Material and methods

PB samples were collected from newly diagnosed MM patients receiving D-Rd (n=8) at baseline and after 2 months of therapy. PBMCs were obtained using Ficoll-Paque (GE Healthcare, Piscataway Township, NJ) and then used for in vitro experiments and flow cytometry analysis (T lymphocytes populations were identified as CD3+, CD4+/CD8+ cells). T-cells' activation was evaluated by flow cytometry (using a CD25, CD38, CD71, HLA-dr cocktail); mitochondrial mass was evaluated after cell staining with MitoTracker Green (Life Technologies); cell lysis was estimated by Annexin v FITC/7-ADD kit assay.

Results

Our data showed a redistribution of T cell subsets with decreased pool of terminal differentiated and highly differentiated end-stage CD8+ cells after 2 months of D-Rd (p<0.05) (n=4), associated with a loss of mitochondrial mass (p<0.0005) and an increase in percentage of dysfunctional mitochondria (p<0.05) in T lymphocytes compared to baseline (n=8). Additionally, we observed that both CD4+ and CD8+ cells from MM patients who received D-Rd therapy lose their ability to activate when stimulated in vitro with phytohemagglutinin (n=8), while no differences in proliferation capacity were observed (n=4). Thus, to explore the impact of D-Rd therapy on T lymphocyte fitness, we treated T lymphocytes from healthy donors and newly diagnosed MM patients in vitro with single agent (daratumumab, lenalidomide, dexamethasone) and their combinations, evaluating mitochondrial functionality, activation capacity, and proliferation in vitro. Our results showed that T lymphocyte fitness was negatively affected only in conditions with dexamethasone (p<0.0001). Furthermore, the tumor cell lysis capacity of T lymphocytes treated with dexamethasone, or its combinations, was significantly reduced. Finally, we observed that the negative effects on T lymphocyte functionality induced by dexamethasone were reversed by using a bispecific antibody, which enhanced tumor cell lysis capacity in vitro in T lymphocytes from healthy donor and newly diagnosed MM patients (p<0.0001).

Conclusions

Taken together, our data suggest an impairment in T-cell function occurring upon up-front treatment that should be considered when new combinations and sequential treatments are designed.

No relevant conflicts of interest to declare.