Asxl1 loss cooperates with oncogenic Nras in mice to reprogram the immune microenvironment and drive leukemic transformation

Abstract

Mutations in chromatin regulator ASXL1 are frequently identified in myeloid malignancies, in particular ~40% in chronic myelomonocytic leukemia (CMML). ASXL1 mutations associate with poor prognosis in CMML and significantly co-occur with NRAS mutations. Here, we show that concurrent ASXL1 and NRAS mutations defined a population of CMML patients with shorter leukemia-free survival than those with ASXL1 mutation only. Corroborating this human data, Asxl1-/- accelerated CMML progression and promoted CMML transformation to acute myeloid leukemia (AML) in NrasG12D/+ mice. NrasG12D/+; Asxl1-/- (NA) leukemia cells displayed hyperactivation of MEK/ERK signaling, increased global level of H3K27ac, and Flt3 upregulation. Moreover, we find that NA-AML cells overexpressed all the major inhibitory immune checkpoint ligands, PD-L1/L2, CD155, and CD80/86. Among them, overexpression of PD-L1 and CD86 correlated with upregulation of AP-1 transcription factors (TFs) in NA-AML cells. An AP-1 inhibitor or shRNAs against AP-1 TF Jun decreased PD-L1 and CD86 expression in NA-AML cells. Once NA-AML cells were transplanted into syngeneic recipients, NA-derived T cells were not detectable. Host-derived wildtype T cells overexpressed PD-1 and TIGIT receptors, leading to a predominant exhausted T cell phenotype. Combined inhibition of MEK and BET led to downregulation of Flt3 and AP-1 expression, partial restoration of the immune microenvironment, enhancement of CD8+ T cell cytotoxicity, and prolonged survival in NA-AML mice. Our study suggests that combined targeted therapy and immunotherapy may be beneficial for treating secondary AML with concurrent ASXL1 and NRAS mutations.

Multistep pathogenesis of chronic myelomonocytic leukemia in patients

“…Also, the higher number of WBC and blast cells is in agreement with previous reports since NRAS mutations in CMML have been associated with myeloproliferation 2,20 . Although there was a numerical decline of hemoglobin and platelet values in the TSN group, this difference was not statistically significant.…”

“…25 Also, the higher number of WBC and blast cells is in agreement with previous reports since NRAS mutations in CMML have been associated with myeloproliferation. 2,20 Although there was a numerical decline of hemoglobin and platelet values in the TSN group, this difference was not statistically significant. The relatively low patient numbers in the three cohorts may explain this finding since anemia and thrombocytopenia are established prognostic parameters in larger CMML cohorts.…”

How I diagnose and treat chronic myelomonocytic leukemia

“…CMML is a neoplasm associated with aging, often arising in the background of CH (biallelic TET2, or TET2/SRSF2 mutations), with the subsequent acquisition of mutations involving signaling (RAS pathway or JAK2V617F), epigenetic regulation (SETBP1, DNMT3A, EZH2), transcription factors (RUNX1) and pre mRNA splicing (SF3B1, U2AF1), shaping clinical phenotypes (Figure 1) 2, 3,13 . There do exist pCMML subtypes where oncogenic RAS pathway mutations (NRAS, CBL, KRAS and PTPN11) are clear initiating driver mutations, occurring early in the course of disease, associated with poor outcomes (decreased survival and higher AML transformation rates) (Figure 1) 10,14 . Unlike in MDS, MPN or AML, TP53 mutations are extremely infrequent in CMML (<1%) and are only really encountered at the time of CMML to AML transformation, or in the context of therapy related CMML 11,15,16 .…”

“… 2 , 3 , 13 There are pCMML subtypes in which oncogenic RAS pathway mutations ( NRAS , CBL , KRAS and PTPN11 ) are clear initiating driver mutations, occurring early in the course of disease, associated with poor outcomes (decreased survival and higher rates of transformation to acute myeloid leukemia [AML]) ( Figure 1 ). 10 , 14 Unlike in MDS, MPN or AML, TP53 mutations are extremely infrequent in CMML (<1%), and are only really encountered at the time of CMML to AML transformation, or in the context of therapy-related CMML. 11 , 15 , 16 …”

Srsf2P95H/+ co-operates with loss of TET2 to promote myeloid bias and initiate a chronic myelomonocytic leukemia like disease in mice

“…An alternative is to use genetically modified immunocompetent mice and engineer the relevant mutations, an approach already applied to several of the genes recurrently mutated in CMML [12][13][14][15][16][17] . These predominantly single gene mutation models partially deciphered the consequences of each lesion but have to date not recapitulated the clinical landscape of the multiple dysfunctional pathways occurring in CMML 18,19 .…”