iwCLL 2017 | Monocytes and Nurse-Like Cells have immunosuppressive features and support CLL cell survival 

The second session at this year’s iwCLL was titled “Role of Non-Leukemic Cells and the Microenvironment in CLL Development”, and was jointly chaired by Silvia Deaglio (University of Turin, Torino, Italy) and Christopher Pepper (Cardiff University, Wales, UK).

During this session, Martina Seiffert, PhD, from the German Cancer Research Center, Heidelberg, Germany, gave a talk titled “From Monocytes to Nurse-Like Cells: Myeloid Cells Matter in CLL.”

The talk began by giving an update to the hallmarks of cancer; four “next generation” properties:

• Deregulating cellular energetics
• Genome instability and mutation
• Avoiding immune destruction
• Tumor-promoting inflammation

Tumor Associated Macrophages (TAMs) are the “undisputed stars of the inflammatory tumor microenvironment”:

• Decrease apoptosis and increase proliferation of tumor cells
• Increase angiogenesis
• Remodel the matrix
• Encourage metastasis (intravasation)
• Suppress the immune response toward the tumor

CLL monocytes and Nurselike Cells (NLCs) have immunosuppressive features; for example, they decrease effector T-cell proliferation and function as well as decrease phagocytosis by macrophages. NLCs have characteristics similar to that of TAMs. Monocytes and NLCs support survival of CLL cells in vitro.

Cytokine antibody arrays have detected 174 human or 144 murine serum proteins including CCL2, Axl, CXCL13, IL-1ra, L-Selectin and E-Selectin (P-Selectin in mice), and MMP1 (MMP9 in mice).

CLL is associated with a buildup of patrolling monocytes. In TCL1 mice, peritoneal macrophages are skewed towards a M2-like or TAM phenotype. They exhibit M2-like marker expression and signaling (CD206, IL-4Ra, CD86, PD-L2, p-STAT3, and p-STAT6). TCL1 monocytes have an inflammatory and immunosuppressive phenotype: express TREM-1 (regulates inflammatory responses and stimulates cytokine release) and PD-L1 (inhibitory co-stimulator, up-regulated on tumor cells and inhibits T-cell activity).

The effect of immune checkpoint blockade with anti-PD-L1 treatment on CLL has been evaluated in TCL1 mice:

Martina Seiffert then asked what induces the tumor-supportive phenotype in myeloid cells in CLL? CLL exosomes were isolated by serial centrifugation and verified by Electron Microscopy (EM) and immune-gold EM (particle size: 30–350 nm). Uptake of CLL exosomes induces PD-L1 expression and cytokine secretion in monocytes.

Uptake of Y RNA hY4 induces PD-L1 expression, cytokine secretion, and inflammatory response by monocytes:

Increase chemokines	CCL2, CCL4, CCL5, CXCL9, CXCL10, CXCL11
Increase pro-inflammatory genes	IL6, IL12A, TNF
Increase immunosuppressive factors	CD274 (PD-L1), IDO1, PDCD1 (PD-1)
Decrease chemokine receptors	CCR2, CXCR4

 Many of these genes are deregulated in CLL. Response to hY4 in monocytes is TLR7-dependent; hY4 effects are abolished in TLR7 knock-out, but not MAVS knock-out or wild type mice.

Martina Seiffert concluded the talk by outlining a novel proposed mechanism of myeloid phenotype induction in CLL:

• Y RNA are highly enriched in CLL exosomes, which are taken up by monocytes and macrophages
• Exosomes and Y RNA induce PD-L1 expression and cytokine secretion
• Y RNA-mediated response is dependent on endosomal TLR7
• Chloroquine decreases exosome-mediated effects on leukemia development in mice