CD38 ligation in peripheral blood mononuclear cells of myeloma patients induces release of protumorigenic IL-6 and impaired secretion of IFNγ cytokines and proliferation

Abstract

CD38, a surface receptor that controls signals in immunocompetent cells, is densely expressed by cells of multiple myeloma (MM). The immune system of MM patients appears as functionally impaired, with qualitative and quantitative defects in T cell immune responses. This work answers the issue whether CD38 plays a role in the impairment of T lymphocyte response. To this aim, we analyzed the signals implemented by monoclonal antibodies (mAb) ligation in peripheral blood mononuclear cells (PBMC) obtained from MM patients and compared to benign monoclonal gammopathy of undetermined significance (MGUS). PBMC from MM both failed to proliferate and secrete IFNγ induced by CD38 ligation while it retained the ability to respond to TCR/CD3. The impaired CD38-dependent proliferative response likely reflects an arrest in the progression of cell cycle, as indicated by the reduced expression of PCNA. CD38 signaling showed an enhanced ability to induce IL-6 secretion. PBMC from MM patients displays a deregulated response possibly due to defects of CD38 activation pathways and CD38 may be functionally involved in the progression of this pathology via the secretion of high levels of IL-6 that protects neoplastic cells from apoptosis.

Figure 1

Proliferation, IFNγ, and IL-6 induction by CD38 mAb engagement in PBMC obtained from MM patients or healthy individuals. PBMC (2 × 10⁵ cells/well in 0.2 mL) obtained from MM patients or healthy controls were cultured in the presence of agonistic anti-CD38 IB4 (20 μg/mL). Proliferation (SI) was measured after 5 days by ³H-Thymidine incorporation. IFNγ (pg/mL) and IL-6 (pg/mL) were measured by ELISA after 18 hours of culture. (a) Dispersion of proliferation (SI) respect IFNγ (pg/mL) values in each of all PBMC donors tested. (b) Dispersion of proliferation (SI) respect to IL-6 (pg/mL) values in each of all PBMC donors tested. For the definition of SI and technical details, see text.

Figure 2

IL-6 and PCNA induction by CD38 molecules engagement in PBMC obtained from MM, MGUS patients, or healthy individuals. (a) PBMC (1 × 10⁶/mL) obtained from MM, MGUS patients, or healthy controls were cultured in the presence of agonistic anti-CD38, anti-CD3, or unstimulated (none). Taqman Real Time quantitative RT-PCR for IL-6 gene expression was performed at 18 hours time-point. mRNA transcript levels were expressed as fold increase over the unstimulated PBMC. (b) PBMC (1 × 10⁶/mL) obtained from MGUS, MM patients, or healthy individuals were cultured in the presence of agonistic anti-CD38, anti-CD3, or unstimulated (none). Taqman Real Time quantitative RT-PCR for PCNA gene expression was performed at 18 hours time-point. mRNA transcript levels were expressed as fold increase over the unstimulated PBMC. For further technical details, see text.