Development Programs

Project Abstract : Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas and a leading cause of mortality in individuals with Neurofibromatosis type 1 (NF1). MPNST are difficult to treat because of their relative resistance to chemotherapy and radiotherapy. No available therapies have shown efficacy in clinical trials and patient outcomes remain poor. Thus, novel therapeutic approaches are urgently needed. Our laboratory group demonstrated that inhibition of SHP2, a protein phosphatase necessary in RAS activation, is a crucial antitumor strategy in NF1-MPNST. Our studies were done in immunocompromised models, but it has been shown that SHP2 plays a vital role in macrophages development within other cancers. The immunomodulatory effects of targeted therapies suggest the potential for combinatorial approaches with more durable responses. One strategy is to target intratumoral immunosuppressive macrophages, which have been shown to contribute to immune evasion in NF1-MPNST. Therefore, we propose using a combination of drugs that target MPNST tumor cells AND activate an antitumor immunity through targeting immunosuppressive macrophages within the tumor immune microenvironment (TIME). Our preliminary data show additive effects of SHP2 and CSF1R inhibitors in an immunocompetent mouse model. CSF1R is a receptor tyrosine kinase that is associated with macrophage development but has emerged as a oncogenic driver in various tumors. We aim to uncover the mechanism in which SHP2 plus CSF1R inhibitors target MPNST cells and intratumoral pathogenic macrophages. To do this, we will identify the effects of CSF1R modulation in MPNST cell growth and responsiveness to SHP2 inhibition in a panel of genomically diverse patient-derived cell lines. We will then test the combination in an immunocompetent mouse model to evaluate the effects on the TIME of MPNST. Tumor cells and intratumoral immune cells will be isolated from treated tumors, and their functionality will be evaluated using flow cytometric, single-cell RNA sequencing, and immune cell functional suppression assays. These data will establish how the targeted agents alter tumor cells and intratumoral immune cells as well as their interactions within the TIME. This results from this project will provide the preclinical rationale for advancing the combination to clinical trials for patients with NF1-MPNST.

Clinical Impact : The leading cause of mortality in individuals with NF1 is the development of malignant peripheral nerve sheath tumors (MPNST). Patient outcomes have not been shown to improve following chemotherapy and/or radiotherapy. The only definitive treatment for localized disease is surgery with wide margins, although this is often not feasible due to tumor size, location, or presence of metastatic disease. Therefore, the development of effective therapeutics for MPNST will fill an unmet clinical need. We aim to define the antitumor efficacy and antitumor immunity generated by the therapeutic combination of SHP2 and CSF1R inhibitors in preclinical models of MPNST. Understanding the interactions between targeted therapies and the tumor immunobiology will undoubtedly aid in developing strategies to activate the immune system against the tumor. We anticipate that the successful completion of our scientific aims will result in promising preclinical data that will serve as the basis to design effective, novel combinations of molecularly targeted agents for patients with NF1-MPNST. Furthermore, the successful development of novel therapeutics and targets for MPNST has additional potential application to other chemotherapy-refractory soft-tissue sarcomas and NF1-deficient malignancies.

Project Abstract : Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive sarcomas that arise from pre-existing plexiform and atypical neurofibromas in individuals with neurofibromatosis type 1 (NF1). We have recently uncovered a critical role of altered T cell immune surveillance programs in governing the evolutionary trajectory of these precursor lesions. Spatially resolved immune profiling demonstrates progressive T cell exclusion and upregulation of immune checkpoints as neurofibromas transform to MPNST, with regulatory T cells (Tregs) constituting 60–80% of all CD4+ T cells within the tumor microenvironment. Functional studies with neutralizing antibodies and Foxp3-DTR mice confirmed that selective ablation of Tregs significantly prolongs MPNST-free survival, implicating Tregs as a critical driver of immunosuppression in MPNST. Further, we find that the TGFβ signaling pathway, which promotes Treg recruitment and function, is hyperactivated in MPNST. While treatment with the TGFβ receptor I (TGFβRI) inhibitor galunisertib reduced intratumoral Tregs and enhanced CD8+ T cell infiltration, compensatory PD-1 upregulation led to T cell exhaustion and no survival benefit, suggesting that monotherapy is insufficient for durable immune reactivation. Based on these findings, we hypothesize that combined inhibition of TGFβ and PD-1 is required to overcome dual mechanisms of immune evasion: TGFβ- driven Treg expansion and extracellular matrix (ECM) remodeling, and PD-1–mediated CD8+ T cell exhaustion. To test this hypothesis, we will employ orthotopic, immunocompetent MPNST models using syngeneic Nf1-p53 and Nf1-Ink4a cell lines to evaluate the therapeutic efficacy of vactosertib (a next-generation TGFβRI inhibitor), and anti-PD-1, alone and in combination. Tumor growth, survival, and pharmacodynamic markers of target engagement (p-SMAD2/3) will be assessed. High-dimensional immunophenotyping via flow cytometry and 3’ single-cell RNA sequencing (scRNA-seq) will define changes in T cell states, myeloid populations, and cell-cell communication networks in response to single agent and combination therapy. Multiplex immunohistochemistry and spatial analysis will quantify CD8+ T cell infiltration depth relative to TGFβ activity and ECM density. These studies will determine whether dual blockade reprograms the MPNST immune microenvironment to enable sustained cytotoxic T cell function, providing critical proof of concept data for a translatable immunotherapeutic strategy for MPNST.

Clinical Impact : This project directly advances the translational mission of the DHART SPORE to develop a rationally-designed immunotherapy for MPNSTs. Our previous work established that Tregs, driven by hyperactive TGFβ signaling, play a critical role in driving immune suppression in the MPNST microenvironment. Here we propose to test a combination therapy: vactosertib + anti-PD-1, targeting two non-redundant immunosuppressive mechanisms identified through our prior CEP-funded research. These findings align with and extend the goals of DHART SPORE Project 1 by elucidating how the immune microenvironment shapes tumor evolution across the neurofibroma-to-MPNST continuum. This study bridges discovery and translation by integrating high- dimensional immunophenotyping and cutting-edge single cell analytics (supported by the Omics Core) with clinically relevant orthotopic models. Furthermore, vactosertib’s efficacy and safety in ongoing phase 2 trials, alone and in combination with pembrolizumab (anti-PD-1), and FDA fast track designation in pediatric osteosarcoma offers a direct path to translation. Successful completion of this work will not only define a new combination immunotherapy approach for MPNST but also generate robust preclinical data to launch a SPORE- driven clinical trial, fulfilling the program’s mandate to accelerate bench-to-bedside innovation for NF1-related tumors.