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Page 8 of 38 J Cancer Metastasis Treat 2020;6:5 I http://dx.doi.org/10.20517/2394-4722.2020.13

The bone marrow (BM) constitutes the home niche for leukemic cells. Tumor microenvironment (TME) is
defined as the cellular environment in which the tumor exists. This environment is made up of endothelial,
stromal, and immune cells and plays a key role in the development, propagation, and survival of cancer
cells. The immune microenvironment has been well described in several hematologic malignancies,
including Hodgkin lymphoma, acute lymphoblastic leukemia, chronic myeloid leukemia, and chronic
lymphocytic leukemia, but less is known about the microenvironment in AML.

We studied the myeloid subsets in bone marrow tissues of normal and AML patients using MultiOmyx
technique. We aimed to clarify the clinical significance of these cells in the AML patients.

Experimental procedure: MultiOmyx is an exclusive proprietary multiplex immunofluorescent technology
that overcome the challenges for immuno-oncology biomarker profiling. It enables detection and
visualization of up to 60 biomarkers on a single formalin-fixed paraffin-embedded (FFPE) slide and
co-expression analysis of up to 25 stains on a single cell, which is unattainable with the conventional
immunohistochemistry (IHC) technique. Other advantages include: quantitative single cell classification,
measures of marker intensity (mean, median, and total), and full spatial context for measuring the distances
between cells with different immunophenotypes.

Results: Myeloid subsets present in tumors are heterogeneous and play a crucial role in promoting cancer
development and metastasis. Tumor associated macrophages (TAMs) and myeloid-derived suppressor
cells (MDSCs) all contribute to an immunologically permissive microenvironment for cancer cells. Based
on surface markers expression, MDSC can be further subdivided into granulocytic MDSC (G-MDSC,
polymorphonuclear MDSC) and monocytic MDSC (M-MDSC). MDSC have also been shown to express
immune checkpoint ligands such as programmed death-ligand 1 (PD-L1) that can suppress T cell
responses in vitro. There is little information regarding MDSCs in AML. TAMs can be polarized by signals
from their environment into two major subsets, called M1 and M2 macrophages. Acute myeloid leukemia
blasts have been shown to differentiate monocytes from healthy donors into an M2-like phenotype in
transwell coculture assays. In our study, we were able to highlight the immune landscape of AML and
compared it with the landscape for normal bone marrow. We observed that both M-MDSC and G-MDSC
accumulated within the TME in AML BM samples, with higher frequency of G-MDSCs over M-MDSCs.
The data also reveal abundant M2 macrophages present in the TME of the AML samples. The detection
of both MDSCs and M2 macrophages in these samples supports the hypothesis that these cells contribute
to the establishment of an immunosuppressive TME. Using the MultiOmyx proprietary algorithm, which
takes into account the staining patterns, we quantified the counts and density of different tumor-resident
myeloid subsets and measured the spatial distance from the different subsets of tumor-resident myeloid
cells to CD34+ blasts in AML samples. We highlighted the correlations between the immunosuppressive
myeloid cells and the different subsets of T cells including T-regulatory cells in AML clinical biopsy
samples. TAMs and MDSCs are emerging as potential biomarkers for diagnosis and prognosis of cancer as
well as therapeutic targets of many immunomodulating agents. As demonstrated in this study, MultiOmyx
multiplexed panel has the potential to monitor the changes of immunosuppressive myeloid cells in
response to immune modulating drugs such as MDSC-targeting drugs (e.g., PDE-5 inhibitors and COX-2
inhibitors), TAM-targeting agents (e.g., anti-CSF1R), and combination therapy in treatment of AML.

11. Radiation oncology updates in treatment of prostate cancer

Lauren Layer Mayo

The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.