Macrophages in multiple myeloma: emerging concepts and therapeutic implications

Leuk Lymphoma. 2013 Oct;54(10):2112-21. doi: 10.3109/10428194.2013.778409. Epub 2013 Apr 11.

Abstract

Multiple myeloma, a clonal plasma cell malignancy, has long provided a prototypic model to study regulatory interactions between malignant cells and their microenvironment. Myeloma-associated macrophages have historically received limited scrutiny, but recent work points to central and non-redundant roles in myeloma niche homeostasis. The evidence supports a paradigm of complex, dynamic and often mutable interactions between macrophages and other cellular constituents of the niche. We and others have shown that macrophages support myeloma cell growth, viability and drug resistance through both contact-mediated and non-contact-mediated mechanisms. These tumor-beneficial roles have evolved in opposition to, or in parallel with, intrinsic pro-inflammatory and tumoricidal properties. Thus, simple blockade of protective "don't eat me" signals on the surface of myeloma cells leads to macrophage-mediated myeloma cell killing. Macrophages also enhance the tumor-supportive role of mesenchymal stem/stromal cells (MSCs) in the niche: importantly, this interaction is bidirectional, producing a distinct state of macrophage polarization that we termed "MSC-educated macrophages." The intriguing pattern of cross-talk between macrophages, MSCs and tumor cells highlights the myeloma niche as a dynamic multi-cellular structure. Targeted reprogramming of these interactions harbors significant untapped therapeutic potential, particularly in the setting of minimal residual disease, the main obstacle toward a cure.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Cell Communication
  • Cell Survival
  • Humans
  • Immunotherapy
  • MAP Kinase Kinase Kinases / metabolism
  • Macrophage Activation / immunology
  • Macrophages / immunology*
  • Macrophages / metabolism
  • Mesenchymal Stem Cells / immunology
  • Mesenchymal Stem Cells / metabolism
  • Multiple Myeloma / immunology*
  • Multiple Myeloma / metabolism*
  • Multiple Myeloma / therapy
  • Neovascularization, Pathologic
  • Phenotype
  • Proto-Oncogene Proteins / metabolism
  • Tumor Microenvironment

Substances

  • Proto-Oncogene Proteins
  • MAP Kinase Kinase Kinases
  • MAP3K8 protein, human