Tumor-infiltrating mast cells are associated with resistance to anti-PD-1 therapy

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 IL2Rγ^null (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.

Immune checkpoint therapies (ICT) are promising for treating various cancers, but response rates vary. Here the authors show, in mouse models, that tumor-infiltrating mast cells colocalize with regulatory T cells, coincide with local reduction of MHC-I and CD8 T cells, and is associated with resistance to ICT, which can be reversed by c-kit inhibitor treatment.

Targeting Notch enhances the efficacy of ERK inhibitors in BRAF-V600E melanoma

The discovery of activating BRAF mutations in approximately 50% of melanomas has led to the development of MAPK pathway inhibitors, which have transformed melanoma therapy. However, not all BRAF-V600E melanomas respond to MAPK inhibition. Therefore, it is important to understand why tumors with the same oncogenic driver have variable responses to MAPK inhibitors. Here, we show that concurrent loss of PTEN and activation of the Notch pathway is associated with poor response to the ERK inhibitor SCH772984, and that co-inhibition of Notch and ERK decreased viability in BRAF-V600E melanomas. Additionally, patients with low PTEN and Notch activation had significantly shorter progression free survival when treated with BRAF inhibitors. Our studies provide a rationale to further develop combination strategies with Notch antagonists to maximize the efficacy of MAPK inhibition in melanoma. Our findings should prompt the evaluation of combinations co-targeting MAPK/ERK and Notch as a strategy to improve current therapies and warrant further evaluation of co-occurrence of aberrant PTEN and Notch activation as predictive markers of response to therapy.

A slow-cycling subpopulation of melanoma cells with highly invasive properties

Melanoma is a heterogeneous tumor with different subpopulations showing different proliferation rates. Slow-cycling cells were previously identified in melanoma, but not fully biologically characterized. Using the label-retention method, we identified a subpopulation of slow-cycling cells, defined as label-retaining cells (LRC), with strong invasive properties. We demonstrate through live imaging that LRC are leaving the primary tumor mass at a very early stage and disseminate to peripheral organs. Through global proteome analyses, we identified the secreted protein SerpinE2/protease nexin-1 as causative for the highly invasive potential of LRC in melanomas.

Tumor-associated B-cells induce tumor heterogeneity and therapy resistance

In melanoma, therapies with inhibitors to oncogenic BRAFV600E are highly effective but responses are often short-lived due to the emergence of drug-resistant tumor subpopulations. We describe here a mechanism of acquired drug resistance through the tumor microenvironment, which is mediated by human tumor-associated B cells. Human melanoma cells constitutively produce the growth factor FGF-2, which activates tumor-infiltrating B cells to produce the growth factor IGF-1. B-cell-derived IGF-1 is critical for resistance of melanomas to BRAF and MEK inhibitors due to emergence of heterogeneous subpopulations and activation of FGFR-3. Consistently, resistance of melanomas to BRAF and/or MEK inhibitors is associated with increased CD20 and IGF-1 transcript levels in tumors and IGF-1 expression in tumor-associated B cells. Furthermore, first clinical data from a pilot trial in therapy-resistant metastatic melanoma patients show anti-tumor activity through B-cell depletion by anti-CD20 antibody. Our findings establish a mechanism of acquired therapy resistance through tumor-associated B cells with important clinical implications.Resistance to BRAFV600E inhibitors often occurs in melanoma patients. Here, the authors describe a potential mechanism of acquired drug resistance mediated by tumor-associated B cells-derived IGF-1.

Abstract PR02: Humanized mouse melanoma model using patient-derived xenografts

Melanoma patients develop resistance to both chemo- and targeted-therapy drugs. Promising pre-clinical and clinical results with immune checkpoint inhibitors using antibodies directed against CTLA4 and PD1 have re-energized the field of immune-based therapies in melanoma. However, similar to chemo- or targeted-therapies only subsets of melanoma patients respond to immune checkpoint blockade. Currently available immunodeficient mouse xenograft and transgenic mouse melanoma models have a number of short comings and are unable to address the basis of drug resistance and immune non-responsiveness frequently observed in melanoma patients treated either with chemo- and targeted-therapy drugs or immune checkpoint inhibitors. Thus there is an urgent need to establish a mouse model with an immune microenvironment that can address the above issues encountered in melanoma patients. For this, our laboratory has developed a humanized mouse melanoma model using patient-derived xenograft (PDX). Immunodeficient (NOD/Shi-SCID/IL-2Rgnull [NOG; Taconic]/ NOD.Cg-Prkdcscid IL2rgtm1Wjl/SzJ [NSG; Jackson Laboratory]) mice were reconstituted with human CD34+ cells and after 12 weeks, mature human CD45+ cells are observed in mouse peripheral blood and in the lymphoid organs. Humanized mice with optimum number of mature human CD45+ cells in peripheral blood were challenged with HLA-matched melanoma PDX and the immune response to melanoma associated antigens were monitored. Lymphoid cells derived from humanized mice that are challenged with human leukocyte antigen (HLA) matched melanoma cells in vivo showed enhanced cytokine expression to in vitro stimulation with peptides derived from melanoma antigens. In addition, cytotoxic T-cells were able to functionally lyse tumor cells in vitro, infiltrate and restrict in vivo tumor growth. We are currently refining our model to establish an autologous mouse melanoma model. Our innovative humanized mouse melanoma model will enable one to understand the causes of therapy resistance and immune non-responsiveness in patients.

This abstract is also being presented as Poster B33.

Citation Format: Clemens Krepler, Michela Perego, Mizuho Kalabis, Marilda Beqiri, Denitsa Hristova, Min Xiao, Nicholas J. Petrelli, Rajasekharan Somasundaram, Meenhard Herlyn. Humanized mouse melanoma model using patient-derived xenografts. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr PR02.

Abstract 1508: UV-induced Wnt7a in the human skin microenvironment specifies the fate of neural crest -like cells via suppression of Notch

Multipotent stem cells with neural crest-like properties have been identified in the dermis of human skin. These neural crest stem cell (NCSC)-like cells display self-renewal capacity and differentiate into neural crest derivatives including epidermal pigment-producing melanocytes. NCSC-like cells share many properties with aggressive melanoma cells, such as high migratory capabilities and expression of the neural crest markers. However, little is known about which intrinsic or extrinsic signals determine the proliferation or differentiation of these neural crest-like stem cells. Here, we show that in NCSC-like cells, Notch signaling is highly activated, similar to melanoma cells. Inhibition of Notch signaling reduced proliferation of NCSC-like cells, induced cell death, and down-regulated non-canonical Wnt5a, suggesting that the Notch pathway contributes to the maintenance and motility of these stem cells. In three-dimensional skin reconstructs, canonical Wnt signaling promoted the differentiation of NCSC-like cells into melanocytes. This differentiation was triggered by the endogenous Notch inhibitor Numb, which is up-regulated in the stem cells by Wnt7a derived from UV-irradiated keratinocytes. Together, these data reveal a novel crosstalk between the two conserved developmental pathways in postnatal human skin, and highlight the role of the skin microenvironment in specifying the fate of stem cells.

Citation Format: Mizuho Fukunaga-Kalabis, Denitsa Hristova, Joshua Wang, Ling Li, Markus Heppt, Zhi Wei, Alexandra Gyurdieva, Marie Webster, Masahiro Oka, Ashani Weeraratna, Meenhard Herlyn. UV-induced Wnt7a in the human skin microenvironment specifies the fate of neural crest -like cells via suppression of Notch. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1508. doi:10.1158/1538-7445.AM2015-1508

Variability of the N-protein and the intergenic region of the S RNA of tomato spotted wilt tospovirus (TSWV)

The genetic heterogeneity of the N protein gene and the intergenic region (IGR) of the S RNA from tomato spotted wilt virus (TSWV) isolates, collected in Bulgaria, were compared with isolates from other parts of the world. The results substantiated the highly conserved nature of the N protein. Twenty six independent sequences revealed only seven variable amino acid positions, common to all isolates. The type of amino acids present in these positions seems to be independent of the geographical origin. In contrast to the structural N protein, comparisons of the related IGR-sequences led to clusters correlated with the geographical origin of the isolates. Although the overall sequence homology in the IGRs was much lower than for the N proteins, three conserved parts within this region were identified. The outstanding part was a central area of 31 nucleotides with a significantly increased GC-content. This was located in both viral- and viral-complement RNA at structures with similar foldings, which led to the assumption that this stabilised structure, rather than a sequence motive, might serve as a transcription terminator during the synthesis of the two mRNAs from the ambisense segments.

Immunohistological localization of regenerating protein in ocular structures

PURPOSE

To investigate the presence of pancreatic stone protein (PSP)/reg (regenerating) protein in eyes and extraocular structures of rabbits, monkeys and man, according to species and age.

METHODS

Rabbit eyes, with normal or de-epithelialized corneas, were taken from albino and pigmented animals. Monkey eyes were taken from cynomolgus monkeys, 2 years old. Stillborn and adult human eyes were obtained after autopsy. They were studied by immunohistochemistry methods, using a monoclonal antibody raised against human PSP.

RESULTS

On rabbit ocular structures, the anti-PSP monoclonal antibody showed a strong reactivity at the level of basement membranes and basal poles of the cells of corneal and conjunctival epithelia and on basement membranes of skin and palpebral conjunctiva in eyelids. On de-epithelialized rabbit eyes, the remaining basement membrane was labeled while, along the re-epithelialization, the anti-PSP reactivity appeared with the migrating cells which cover the denuded cornea. On young monkeys, the whole corneal epithelium was reactive. Similar results were obtained from stillborn eyes, whereas no reactivity was detected on autopsy specimens from aged persons.

CONCLUSIONS

As in other tissues and organs, the reg protein, in the eye, is found in structures known for their continuous and rapid renewal. This protein seems not to exist (or persist) in eyes from aged donors while it is strongly expressed in young donor eyes (monkey, stillborn baby) as well as in regenerating corneal epithelium. These findings enforce the hypothesis about the involvement of reg protein in cell proliferation and differentiation phenomena and its probable correlation with aging.