Anti-PD-1 therapy is used as a front-line treatment for many cancers, but mechanistic insight into this therapy resistance is still lacking. Here we generate a humanized (Hu)-mouse melanoma model by injecting fetal liver-derived CD34+ cells and implanting autologous thymus in immune-deficient NOD-scid IL2Rγnull (NSG) mice. Reconstituted Hu-mice are challenged with HLA-matched melanomas and treated with anti-PD-1, which results in restricted tumor growth but not complete regression. Tumor RNA-seq, multiplexed imaging and immunohistology staining show high expression of chemokines, as well as recruitment of FOXP3+ Treg and mast cells, in selective tumor regions. Reduced HLA-class I expression and CD8+/Granz B+ T cells homeostasis are observed in tumor regions where FOXP3+ Treg and mast cells co-localize, with such features associated with resistance to anti-PD-1 treatment. Combining anti-PD-1 with sunitinib or imatinib results in the depletion of mast cells and complete regression of tumors. Our results thus implicate mast cell depletion for improving the efficacy of anti-PD-1 therapy.

Recent genetic analysis has identified frequent mutations in ten-eleven translocation 2 (TET2), DNA methyltransferase 3A (DNMT3A), isocitrate dehydrogenase 2 (IDH2) and ras homolog family member A (RHOA) in nodal T-cell lymphomas, including angioimmunoblastic T-cell lymphoma and peripheral T-cell lymphoma, not otherwise specified. We examined the distribution of mutations in these subtypes of mature T-/natural killer cell neoplasms to determine their clonal architecture. Targeted sequencing was performed for 71 genes in tumor-derived DNA of 87 cases. The mutations were then analyzed in a programmed death-1 (PD1)-positive population enriched with tumor cells and CD20-positive B cells purified by laser microdissection from 19 cases. TET2 and DNMT3A mutations were identified in both the PD1+ cells and the CD20+ cells in 15/16 and 4/7 cases, respectively. All the RHOA and IDH2 mutations were confined to the PD1+ cells, indicating that some, including RHOA and IDH2 mutations, being specific events in tumor cells. Notably, we found that all NOTCH1 mutations were detected only in the CD20+ cells. In conclusion, we identified both B- as well as T-cell-specific mutations, and mutations common to both T and B cells. These findings indicate the expansion of a clone after multistep and multilineal acquisition of gene mutations.

The activities of non-haematopoietic cells (NHCs), including mesenchymal stromal cells and endothelial cells, in lymphomas are reported to underlie lymphomagenesis. However, our understanding of lymphoma NHCs has been hampered by unexplained NHC heterogeneity, even in normal human lymph nodes (LNs). Here we constructed a single-cell transcriptome atlas of more than 100,000 NHCs collected from 27 human samples, including LNs and various nodal lymphomas, and it revealed 30 distinct subclusters, including some that were previously unrecognized. Notably, this atlas was useful for comparative analyses with lymphoma NHCs, which revealed an unanticipated landscape of subcluster-specific changes in gene expression and interaction with malignant cells in follicular lymphoma NHCs. This facilitates our understanding of stromal remodelling in lymphoma and highlights potential clinical biomarkers. Our study largely updates NHC taxonomy in human LNs and analysis of disease status, and provides a rich resource and deeper insights into LN and lymphoma biology to advance lymphoma management and therapy.

◥ Recurrent hotspot (p.Gly17Val) mutations in RHOA encoding a small GTPase, together with loss-of-function mutations in TET2 encoding an epigenetic regulator, are genetic hallmarks of angioimmunoblastic T-cell lymphoma (AITL). Mice expressing the p.Gly17Val RHOA mutant on a Tet2-null background succumbed to AITL-like T-cell lymphomas due to deregulated T-cell receptor (TCR) signaling. Using these mice to investigate therapeutics for AITL, we found that dasatinib, a multikinase inhibitor prolonged their survival through inhibition of hyperactivated TCR signaling. A phase I clinical trial study of dasatinib monotherapy in 5 patients with relapsed/refractory AITL was performed. Dasatinib was started at a dose of 100 mg/body once a day and continued until days 10-78 (median day 58). All the evaluable patients achieved partial responses. Our findings suggest that AITL is highly dependent on TCR signaling and that dasatinib could be a promising candidate drug for AITL treatment. Significance: Deregulated T-cell receptor signaling is a critical molecular event in angioimmunoblastic T-cell lymphoma and can be targeted with dasatinib.

Activating mutations in the Vav guanine nucleotide exchange factor 1 (VAV1) gene are reported in various subtypes of mature T-cell neoplasms (TCN). However, oncogenic activities associated with VAV1 mutations in TCN remain unclear. To define them, we established transgenic mice expressing VAV1 mutants cloned from human TCN. Although we observed no tumors in these mice for up to a year, tumors did develop in comparably-aged mice on a p53-null background (p53-/- VAV1-Tg), and p53-/- VAV1-Tg mice died with shorter latencies than did p53-null (p53-/-) mice. Notably, various TCN with tendency of maturation developed in p53-/- VAV1-Tg mice, while p53-/- mice exhibited only immature TCN. Mature TCN in p53-/- VAV1-Tg mice mimicked human peripheral T-cell lymphoma (PTCL)-GATA3 and exhibited features of type2 T helper (TH2) cells. Phenotypes seen following transplantation of either p53-/- VAV1 or p53-/- tumor cells into nude mice were comparable, indicating cell-autonomous tumor-initiating capacity. Whole transcriptome analysis (WTA) showed enrichment of multiple Myc-related pathways in TCN from p53-/- VAV1-Tg mice relative to p53-/- or wild-type T cells. Remarkably, amplification of Myc locus were found recurrently in TCN of p53-/- VAV1-Tg mice. Finally, treatment of nude mice transplanted with p53-/- VAV1-Tg tumor cells with JQ1, a bromodomain inhibitor, which targets the Myc pathway, prolonged survival of mice. We conclude that VAV1 mutations function in malignant transformation of T cells in vivo and that VAV1-mutant expressing mice could provide an efficient tool for screening new therapeutic targets in TCN harboring these mutations. We conclude that VAV1 mutations function in malignant transformation of T cells in vivo and that VAV1-mutant expressing mice could provide an efficient tool for screening new therapeutic targets in TCN harboring these mutations.