P742: TRANSCRIPTOMIC ANALYSIS OF ISOLATED CD4+ AND CD8+ T CELLS REVEALS DIFFERENCES IN TCR REPERTOIRE IN PATIENTS WITH HIGH RISK MDS COMPARED TO AML.

Abstract

Background: Myelodysplastic syndrome (MDS) is a group of clonal disorders of hematopoietic progenitor cells, which often progresses towards acute myeloid leukemia (AML). Even though MDS is a clonal hematopoietic disease, bone marrow microenvironment and more specifically inflammation has been linked to its progression. Among other cell types, CD4+ and CD8+ T cells are major players in the regulation of the microenvironment in malignancies. Aims: In this study, we aimed to investigate the molecular signature of bone marrow CD4+ and CD8+ T cells from patients with high-risk MDS, AML and chronic myelomonocytic leukemia (CMML). Methods: RNA sequencing was performed on isolated CD4+ and CD8+ T cells from the bone marrow of six patients with high risk MDS (RAEB-II), six patients with CMML and four patients with AML, using cell sorting. Except from the analysis of gene expression, we performed TCR repertoire analysis using VDJtools, an open-source Java/Groovy-based framework that can analyze immune repertoire sequencing (RepSeq) data and allows applying a diverse set of post-analysis strategies. To do so, RNA sequencing data were used as input for the V-(D)-J junction mapping software and analysis was performed on the MiXCR platform. The output of MiXCR wereused as input for the VDJtools after running a convert routine with -S mixcr argument to prepare datasets in a format for VDJtools analysis. Results: Analysis of CD8+ T cells from patients with high risk MDS and AML identified 38 differentially expressed genes. We observed that the expression of the TCR variants TRAV20 and TRAV13-1 was increased in patients with AML compared to high risk MDS (Figure 1A). Further analysis of the TCR repertoire revealed that the diversity of TCR was higher in CD8+ T cells from patients with AML (Figure 1B), whereas multidimentional scaling analysis revealed a clear separation of the two groups (Figure 1C). To the same direction, clustering of the usage of TRAV-TRAJ further confirmed this finding (Figure 1D). On the other hand, we did not observe any difference in the TCR diversity of the variant usage when we compared CD8+ T cells from patients with CMML and AML (Figure 1E-F), or in the comparison between CD4+ T cells from patients with high risk MDS and AML (Figure 1G-I). Image:Summary/Conclusion: CD8+ T cells are a major cell population that exerts anti-tumour properties in cancer. Herein, we compared the TCR repertoire of CD8+ and CD4+ T cells in the bone marrow of patients with high risk MDS and AML and observed that despite the common features of these two disorders, there are significant differences in the TCR repertoire specifically in CD8+ T cells, especially concerning TCR diversity. These findings imply that there is more active T cell response in the bone marrow in AML compared to MDS. However, it is not clear to what degree this T cell response targets AML neo-antigens.