CD28-mediated pro-survival signaling induces chemotherapeutic resistance in multiple myeloma

Abstract

• CD28 delivers a pro-survival signal to MM cells via regulation of PI3K/Akt, FoxO3a, and Bim.• Blockade of CD28:CD80/ CD86 in vivo resensitizes MM cells to chemotherapy and significantly reduces tumor burden.Chemotherapeutic resistance remains a significant hurdle in the treatment of multiple myeloma (MM) and is significantly mediated by interactions between MM cells and stromal cells of the bone marrow microenvironment. Despite the importance of these interactions, the specific molecules and downstream signaling components involved remain incompletely understood. We have previously shown that the prototypic T-cell costimulatory receptor CD28, which is also expressed on MM cells, is a key mediator of MM survival and apoptotic resistance. Crosslinking CD28 by agonistic antibodies or myeloid dendritic cells (DC; these express the CD28 ligands CD80/CD86) prevents apoptosis caused by chemotherapy or serum withdrawal. We now report that CD28 pro-survival signaling is dependent upon downstream activation of phosphatidyl-inositol 3-kinase/Akt, inactivation of the transcription factor FoxO3a, and decreased expression of the pro-apoptotic molecule Bim. Conversely, blocking the CD28-CD80/CD86 interaction between MM cells and DC in vitro abrogates the DC's ability to protect MM cells against chemotherapyinduced death. Consistent with these observations, in vivo blockade of CD28-CD80/CD86 in the Vk*MYC murine myeloma model sensitizes MM cells to chemotherapy and significantly reduces tumor burden. Taken together, our findings suggest that CD28 is an important mediator of MM survival during stress and can be targeted to overcome chemotherapy resistance. (Blood. 2014;123(24): 3770-3779) IntroductionMultiple myeloma (MM), the bone marrow (BM)-resident plasma cell (PC) neoplasm, is the second most common hematologic malignancy after non-Hodgkin lymphoma.1 Although new therapies have improved survival, MM remains almost uniformly fatal and only curable in a small fraction of patients. 2,3 Initially, patients are responsive to therapy and experience remission; however, relapses result in MM cells that are progressively resistant to therapy. 3,4 Thus, understanding and overcoming resistance mechanisms may lead to development of new therapeutic approaches.Chemotherapies such as the DNA alkylator melphalan and the proteasome inhibitor bortezomib were developed because of their direct apoptotic effects on MM cells. 5,6 However, these agents, thalidomide, and thalidomide derivatives also target the BM microenvironment, pointing to the key role that stroma plays in myeloma survival.6-8 Moreover, primary MM culture in vitro requires stroma, indicating that the BM niche provides essential pro-survival signals.9-11 Thus, identifying key interactions between MM and the microenvironment is essential for understanding and overcoming therapeutic resistance mechanisms.Broadly, MM-stromal interactions fall into 2 categories. The first consists of soluble pro-survival factors induced from stromal niche cells upon MM interaction, and include int...

Myeloma Drug Resistance Induced by Binding of Myeloma B7-H1 (PD-L1) to PD-1

“…These results indicated that B7-H1 expression on myeloma cells is directly associated with their aggressive characteristics, i.e., increased cell proliferation and drug resistance. Although another immune checkpoint pathway, CD28-CD86, was previously reported to prevent cell death induced by melphalan (29)(30)(31), the blockade of B7-H1 on MOSTI-1 cells using anti-B7-H1 did not affect BrdUrd incorporation and the number of apoptotic cells induced by melphalan (Fig. 1F), suggesting that MOSTI-1 cells expressed no functional receptors for B7-H1.…”

Phenotypic and genomic analysis of multiple myeloma minimal residual disease tumor cells: a new model to understand chemoresistance

“…Furthermore, MRD subclones showed enhanced expression of several integrins (eg, CD11a, CD11c, CD29, CD49d, and CD49e), chemokine receptors (eg, CXCR4), adhesion molecules (eg, CD44 and CD54), CD28 (a prosurvival mediator through PC-dendritic cell interaction 39 ), and HLADR. The expression of these class of markers has been shown to be intrinsically related to different PC chemoresistant potential in vitro and in vivo, [40][41][42][43][44][45] as well as to patients' survival, [46][47][48] which would be potentially due to a stronger attachment of MRD clonal PCs to the BM stroma, which provides higher protection from 49,50 In fact, it could be hypothesized that a subset of chemoresistant MRD cells strongly attached to the stroma might be potentially underestimated in BM aspirates.…”

Dendritic cells accumulate in the bone marrow of myeloma patients where they protect tumor plasma cells from CD8+ T-cell killing

“…CD28 expression in MM has been found to be associated with poor prognosis, disease progression, and resistance to chemotherapy. [15][16][17] Thus, its upregulation during the MGUS-to-MM transition may indeed reflect an escalation in the intrinsic plasma cell malignancy, meaning that oncogenic events accumulate in a clone that gains proliferative advantages.…”

“…Different studies have shown that DCs may promote myeloma-specific T-cell responses, 12,13 although they may also support plasma cell proliferation and survival via engagement of their CD80/86 receptors by the ligand CD28 on plasma cells. [14][15][16][17] Moreover, little information is available on DCs in the bone marrow (BM), which is the privileged site of clonal plasma cell proliferation, and therefore the main site of tumor-antigen expression.…”