LILRB4 expression in CMML and MDS based on response to hypomethylating agents.

e18550 Background: Leukocyte immunoglobulin-like receptor B4 (LILRB4) is expressed on M4 and M5 monocytic acute myeloid leukemia (AML) cells and leads to negative regulation of immune cell activation via T cell suppression. Its expression and role in chronic myelomonocytic leukemia (CMML) and myelodysplastic syndrome (MDS) are unknown. We investigated LILRB4 expression in patients with CMML and MDS and correlated it with response to hypomethylating agent (HMA) therapy. Methods: We evaluated bone marrow samples from 19 patients with CMML and 27 patients with MDS from 2008-2014. Transcriptomic and splicing analysis by RNA sequencing were performed on CD34-positive cells in CMML and MDS patient samples in addition to AML or MDS cell lines (n = 6). Gene set enrichment analysis was used to identify pathways associated with increased LILRB4 expression. Results: By the WHO 2016 classification for CMML, there were 8 CMML-0, 5 CMML-1, and 6 CMML-2 patients, and there were 2 low-risk, 8 intermediate-1-risk, 12 intermediate-2-risk, and 5 high-risk MDS patients by IPSS. A total of 12 CMML patients and 27 MDS patients received HMA, with 6 and 12 showing response, respectively. RNA expression of LILRB4 was increased in CMML patients when compared to MDS patients and healthy controls (q < 0.1) with no difference in expression based on risk groups. Pathway analysis revealed upregulation of PD-1 signaling (p = 0.004), CTLA-4 signaling (p = 0.004), and inflammatory response (p = 0.004), and gene correlates revealed a positive association with CTLA-4 expression (p = 0.05). LILRB4 expression was slightly increased in CMML patients who responded to HMAs (q > 0.1). In cell lines, LILRB4 was expressed in MOLM13 (AML M5), SKM1 (AML M5), and U937 (histiocytic lymphoma), with an increase in HMA-sensitive MOLM13 cells compared to HMA-resistant MOLM13 cells (q < 0.01) and no difference based on HMAs seen in other cell lines. Conclusions: LILRB4 expression is increased in CMML, with further increase in those exhibiting response to HMA therapy. It is positively correlated with immune checkpoint signaling pathways, particularly CTLA-4 expression. This may set the basis for exploring the possibility of anti-LILRB4 and anti-CTLA-4 combinations.