Page 30 - Haematologica3

J.T. Butler et al.
Diagnostic and therapeutic application of extracellular vesicles in hematologic disorders
Vesicles are continuously shed by a wide range of blood cells.74 In addition to their short-range biological effects, the small size and rapid equilibration of EVs between tis- sues and the bloodstream have fueled interest in develop- ing minimally invasive biomarkers based on EVs and their cargo. Identification of disease-specific markers based on circulating EVs may aid in early detection and post-remis- sion monitoring for several types of hematologic disorders (Figure 4C). A number of studies indicate the feasibility of developing circulating EVs as a minimally invasive plat- form for the analysis of miRNA and protein content pro- files to detect and classify hematologic malignancies and non-malignant hematopoietic disorders.75,76 For example, antibody microarray profiling of the membrane protein content of plasma EVs from patients with chronic lym- phoid leukemia showed elevated levels of CD5, CD19, CD31, CD44, CD55, CD62L, CD82, HLA-A, HLA-B, HLA-C, and HLA-DR and low levels of CD21, CD49c, and CD63.77 The utility of EVs as biomarkers in chronic lymphoid leukemia is also supported by the observation of high levels of CD19 and CD37 relative to the levels in healthy controls.78 In patients with newly diagnosed AML, plasma EVs were rich in myeloblastic markers (CD34, CD33 and CD117), but also TGF-β1 protein, and MHC class I chain-related genes (MICA and MICB).69 The dynamic range of plasma EV-TGF-β1 readily separated AML patients by diagnosis, early and late remission sta- tus. In multiple myeloma, EVs bearing CD38, CD138, CD44 and CD147 allowed stratification of patients by dis- ease phase and therapy response.79 There is a range of plat- forms for RNA amplification and the high incidence of relapse in AML patients has driven efforts to mine EV RNA content for highly sensitive detection of minimal residual disease and emergent drug resistance. EV miRNA appears to be a particularly promising minimally invasive biomarker platform. When EV cargo loading leads to the selective enrichment of some and exclusion of other cellu- lar miRNA, the resulting highly selective vesicle miRNA profiles offer a potentially significant advantage over analysis of more diverse and abundant “free” circulating miRNA, which is often complexed with small lipoprotein particles. This improved signal to noise ratio led a number of groups to survey EV miRNA as a highly dynamic bio- marker tool in hematologic malignancies (Table 3), and several studies have shown that AML EVs contain charac- teristic miRNA profiles.80,81 A particularly intriguing aspect of circulating EV miRNA is that it represents contributions of (occasionally identical) miRNA contained in EVs from multiple cellular sources. Such a compartmental biomarker reflects EV miRNA contributions from leukemic clones and the surrounding BM stromal cells.68,81
The use of EVs as biomarkers is not limited to hemato- logic malignancies; it may also be prognostically useful for benign hematologic disorders such as sickle-cell anemia. Plasma EVs from patients with sickle-cell anemia showed a distinct signature of miRNA that not only distinguished patients from healthy donors, but also coincided with the stage of the disease in the patients.82 In a study of patients with BM failure, investigators showed distinct profiles in patients with aplastic anemia and myelodysplastic syn- drome and a biomarker response to successful immuno- suppressive therapy.83 While many believe that EV miRNA under consideration as hematologic biomarkers may pri-
marily serve a biological role in endocrine cell-cell com- munication between distant tissues and cells, an alterna- tive, and no less intriguing, possibility is the deliberate secretion of protein and RNA into EVs as a way of pre- venting regulation of the originating cell.84
Finally, autologous EVs from any number of accessible and in vitro expandable cells, including MSCs, T cells, and NK cells, can be a potentially exciting prospect for EV ther- apeutics, especially if approaches for selective loading and organ targeting can be developed. Human MSC EVs, for example, were shown in vitro to shuttle miR-155 and miR- 146 that exerted immunomodulatory effects through sup- pression of NK-, B-, and T-cell activity.85 In a murine model, CD73-bearing MSC EVs effectively reversed graft-versus- host disease through the promotion of adenosine metabo- lism that in turn suppressed Th1-mediated inflammation immune suppression.86 As noted earlier, CD34-derived EVs appear to reverse hindlimb ischemia in animal models.53 A recent human study relied on MSC-derived EVs to treat graft-versus-host disease, based on prior successful work using pooled MSCs as a promising therapy for refractory graft-versus-host disease, a complication of allogeneic HSC transplantation.87 Presumably based on the high concentra- tion of interleukin-10, TGF-β, and HLA-G, EV injection resulted in a significant reduction of the patient’s inflamma- tory response and improved the symptoms of graft-versus- host disease in multiple organ systems.
One recent study showed that Rab27 alpha/beta double knockout (RAB27DKO) mice, with impaired exosome release, have increased levels of cytokines and myelopro- liferation, consistent with chronic inflammation. Grafting these mice with wild-type HSCs, or injecting EVs pro- duced by granulocyte-macrophage colony-stimulating fac-
Table 3. Extracellular vesicle miRNA, selective roles in homeostasis and hema- tologic malignancies.
Function
Support erythroid differentiation
Regulate osteogenic differentiation
Regulate HSPC clonogenicity and mobilization
Regulate hematopoietic function
Control HSPC viability and clonogenicity
Biomarker Biomarker
Biomarker
Biomarker
Homeostasis/ disease
Homeostasis Homeostasis AML
AML and MDS MDS AML
CLL
Hodgkin lymphoma
miRNA
Reference
miR-486 63 miR-183-5p 65
miR-150 and miR-155
24,99,100
miR-7977 70
miR-10a, and miR-15a 71
miR-155 and miR-1246 81
MM
miR-20a, miR-29, miR-150, 101 miR-155, and miR-202-3p,
miR-223
miR-21-5p, miR-24-3p, 102 miR-127-3p, miR-155-5p,
and let-7a-5p
miR-15, and miR-18a, miR-21, 103 miR-135b and let-7b
390
AML: acute myeloid leukemia; CLL: chronic lymphocytic leukemia; miR: micro-ribonucleic acid; HSPC: hematopoietic stem and progenitor cell; MDS: myelodysplastic syndrome; MM: multiple myeloma.
haematologica | 2018; 103(3)