Recurrent IL4R Somatic Mutations in Diffuse Large B-Cell Lymphoma Lead to an Altered Gene Expression Profile and Changes in Tumor Microenvironment Composition

The Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway is an important and conserved pathway in lymphocytes which is activated by extracellular stimuli such as cytokines and growth factors. Aberrant activation of the JAK-STAT pathway is a hallmark of a variety of lymphomas which leads to increased proliferation/survival as well as immune evasion. Regarding the latter, it has been previously described that activation of the JAK-STAT signaling pathway can alter the secretome of lymphoma cells and the composition of the tumor microenvironment (TME). Specifically, our group reported PTPN1 loss-of-function as well as IL4R gain-of-function (p.I242N) mutations up-regulate the expression of the immune regulatory chemokine CCL17 through a STATs-dependent mechanism in primary mediastinal B cell lymphoma (PMBCL). Here, we assembled a cohort of 340 diffuse large B cell lymphoma (DLBCL) patients uniformly treated with R-CHOP to investigate JAK-STAT signaling mutations (targeted gene sequencing), copy number alteration (SNP arrays), gene expression (RNAseq) and TME composition (Cibersort, IHC). We confirmed the presence of mutations in SOCS1, STAT6 and 9p24 amplification with a frequency of 13.8%, 2.5%, 11.4%, respectively. Interestingly, we also identified the presence of somatic IL4R mutations in DLBCL, including the hotspot p.I242N mutation previously reported in PMBCL. Similarly to what was reported for other alterations in the JAK-STAT pathway, IL4R mutations were significantly enriched in GCB-DLBCL as compared to the ABC subtype, unclassified or double hit lymphomas with DLBCL morphology (p=0.045). Within the GCB group, patients carrying mutations in IL4R showed inferior disease-specific survival (p=0.029) and time to progression (p=0.023) after R-CHOP therapy. Mutational analysis revealed IL4R mutation being significantly concurrent together with mutations in ACTB, KLML6, MYC, STAT6, NLRC5, TNFAIP3 and mutually exclusive with EZH2 mutations (p<0.05). However, among those gene mutations, only mutations in IL4R risk-stratified patients with GCB DLBCL and showed inferior patient outcomes. Moreover, mutations in the extracellular and transmembrane domains of IL4R resulted in gain-of-function leading to constitutive activation of the JAK-STAT pathway in vitro. Gene expression analysis of primary patient samples carrying IL4R mutations displayed increased CCL17 expression (p=0.027), which positively correlated with the level of the T-regulatory marker FOXP3 by IHC (p=0.005). In addition, in silico TME composition analysis revealed a role of IL4R mutations in inducing changes in macrophage polarization. Specifically, we observed an enrichment of an M2-like macrophage phenotype in primary patient specimens carrying IL4R mutations (p=0.01) and a high M2/M1 ratio was significantly associated with inferior patient outcomes (time to progression, log rank p=0.027).

In summary, our data suggest a common mechanism between PMBCL and DLBCL where aberrant JAK-STAT activation mediated by mutations in IL4R plays a significant role in altering chemokine expression profiles and TME changes.