Person:

Ho, Li-Lun

Despite initial responses, most melanoma patients develop resistance to immune checkpoint blockade (ICB). To understand the evolution of resistance, we studied 37 tumor samples over 9 years from a metastatic melanoma patient with exceptional response followed by delayed recurrence and death. Phylogenetic analysis revealed co-evolution of 7 lineages with multiple convergent, but independent resistance-associated alterations (RAAs). All recurrent tumors emerged from a lineage characterized by loss of chromosome 15q, with post-treatment clones acquiring additional genomic driver events. Deconvolution of bulk RNAseq and highly-multiplexed immunofluorescence (t-CyCIF) revealed differences in immune composition amongst different lineages. Imaging revealed a vasculogenic mimicry phenotype in NGFR-High tumor cells with high PD-L1 expression in close proximity to immune cells. Rapid autopsy demonstrated 2 distinct NGFR spatial patterns with high polarity and proximity to immune cells in subcutaneous tumors versus a diffuse spatial pattern in lung tumors, suggesting different roles of this neural crest-like program in different tumor microenvironments. Broadly, this study establishes a high-resolution map of the evolutionary dynamics of resistance to ICB, characterizes a de-differentiated, neural crest tumor population in melanoma immunotherapy resistance, and describes site specific differences in tumor-immune interactions via longitudinal analysis of a melanoma patient with an unusual clinical course.

Brown adipose tissue (BAT) and related beige fat function in energy expenditure in part due to their role in thermoregulation. The prominent capacity of thermogenic fat to enhance fuel utilization and energy expenditure makes it an attractive target for treating obesity and metabolic disorders. While prolonged cold exposure increases BAT mass through de novo recruitment of brown adipocytes, the exact sources of cold-induced thermogenic adipocytes are not completely understood. Here, we sought to investigate the cellular origin of cold-induced brown adipocytes using single-cell RNA sequencing. We identify two distinct types of adipocyte progenitors that contribute to de novo recruitment of brown adipocytes in response to cold challenge. One population is the previously-known Pdgfr-expressing mesenchymal progenitors, while the other is a previously-unidentified vascular smooth muscle-derived adipocyte progenitor (VSM-APC) population, which expresses the temperature-sensitive ion channel transient receptor potential cation channel subfamily V member 1 (Trpv1). Using flow cytometry and lineage tracing, we demonstrate that the Trpv1-positive VSM-APCs are distinct from the Pdgfr-positive progenitors, and can give rise to thermogenic adipocytes in response to cold. Together, these findings illustrate the landscape of the thermogenic adipose niche at the single cell resolution and identify a new cellular origin for the development of brown and beige adipocytes.