Haematopoietic stem cells (HSCs) reside atop of the blood hierarchy and localise in the bone marrow (BM). Acute myeloid leukaemia (AML) is caused by accumulation of mutations in the stem cell compartment, which blocks the differentiation of the myeloid lineage. AML also modulates the BM microenvironment but the mechanisms of action are largely unknown. We and others, demonstrated recently that BM marrow vasculature is damaged in AML engrafted mice (Passaro et al. 2017; Duarte et al. 2018). The arterioles are increased, while the sinusoidal endothelial cells are vastly decreased. In order to understand the mechanism underlining this change, we previously performed RNA-sequencing of CD31+ endothelial cells (ECs) extracted from healthy and leukemic mice.
This project aims to identify key processes that play a role in the crosstalk between AML cells and BM microenvironment and test whether modulating these niche factors can improve the current therapeutic regimen. Thus, herein we focused on the potential role of CD276 on ECs of AML engrafted mice.
RNAseq of BM ECs from non-transplanted or AML Patients’ Derived Xenograft (PDX) mice was performed. Flow cytometry and immunostaining of BM ECs were performed. ShRNA against CD276 is being used to define the effect of its knockdown in ECs on leukaemia engraftment in our 3D humanised scaffold model. Blocking antibodies against CD276 will also be tested in vivo.
Analysis of the RNAseq data showed that CD276 (B7-H3) gene is among the top 100 differentially expressed genes and is particularly upregulated in ECs of AML engrafted mice. It has been demonstrated that CD276 is overexpressed specifically in ECs of solid tumours and its blockade leads to tumour shrinkage (Seaman et al. 2017). The protein network map of CD276 indicated that it can participate in immune responses as well as adhesion signalling pathways. Indeed, there are several such genes deregulated in the leukemic ECs suggesting that CD276 might have a functional role in transforming the BM niche. CD276 overexpression was validated in ECs PDX and murine AML models. Moreover, we also observed this upregulation in human ECs by using our humanised scaffolds seeded with AML cell lines.
So far, our RNAseq analysis of healthy and leukemic PDX mice shows that CD276 is being upregulated in ECs. We confirmed this upregulation at the protein level both using mouse and human ECs. Our next step is to determine the consequence of CD276 downregulation on leukaemia engraftment.