Microenvironment-dependent growth of Sezary cells in humanized IL-15 mice

Sezary syndrome (SS) is a rare, aggressive leukemic variant of cutaneous T cell lymphoma (CTCL) that lacks adequate therapeutic options and representative small animal models. Here we demonstrate that IL-15 is a critical CTCL growth and survival factor. Importantly, a genetically engineered immunodeficient mouse model expressing human IL-15 uniquely supported the growth of patient derived Sezary cells relative to conventional immunodeficient mouse strains. Patient derived xenograft (PDX) SS models recapacitated the pathologic features of the human disease, including skin infiltration and spread of leukemic cells to the periphery, and maintained the dependence on human IL-15 upon serial in vivo passaging. Detailed molecular characterization of the engrafted cells by single cell transcriptome analysis revealed tissue specific regulation of gene expression and distinct clonal engraftment patterns. Overall, we document an important dependence of Sezary cell survival and proliferation on IL-15 signaling and the utility of the humanized IL-15, immunodeficient mice for SS PDX model generation. Furthermore, these studies advocate for the thorough molecular understanding of the resultant PDX models to maximize their translational impact. Overall design: Data inludes 7 Sezary patient-derived xenograft (PDX) P3 mice samples. 4 come from spleen and 3 come from skin. These are SRG15 mice modeling humanization of IL15 allele on an SRG immunodeficient background. Samples were enriched for CD4+ cells and subjected to single cell RNA-seq.