Evaluating myeloid cells as targets to promote anti-tumor immunity in undifferentiated pleomorphic sarcoma

Anusha Kalbasi, MD,  University of California, Los Angeles
Recipient of the: Jay Vernon Jackson Memorial Research Award

The vast majority of patients with soft tissue sarcoma present with localized disease, yet nearly half of these patients develop incurable distant metastases. Chemotherapy has been marginally effective in reducing the rate of metastasis or prolonging survival. However, undifferentiated pleomorphic sarcomas (UPS) appear to respond well to immune checkpoint blockade, which has sparked interest in immune based approaches to improve outcomes in these curable patients.

Still, the majority of patients with UPS do not respond to immune checkpoint blockade and long-lasting responses are sparse. We have observed that the immune microenvironment of UPS is dominated by myeloid cells. Although macrophages can suppress T cell anti-tumor function, the identity and function of myeloid cells within the sarcoma microenvironment is not well-studied. We have established a workflow to characterize, grow and expand tumor-infiltrating lymphocytes (TIL) from soft tissue sarcomas. Leveraging this pipeline at our high-volume sarcoma center, we will evaluate how macrophages affect TIL ex vivo. These studies will provide insight that will allow rationale design of approaches targeting myeloid cells combined with anti-PD1 therapy.

In Aim 1, we seek to determine the phenotype and function of myeloid cells within the UPS environment using the TIL platform. First, we will examine the impact of tumor derived macrophages on the phenotype and proliferative capacity of ex vivo stimulated peripheral blood monocytes. We will also assess the proliferation, phenotype and cytokine production of ex vivo TIL grown in culture with and without macrophage targeting strategies (inhibition, repolarization or immune checkpoint neutralization). Lastly, using flow and mass cytometry we will examine the expression of immune regulatory molecules on each myeloid cell subset.

In our second aim we evaluate the impact of a condensed preoperative RT approach on myeloid-driven T cell immunosuppression in UPS. This aim builds on a novel clinical trial I am leading at our institution studying 5-day preoperative radiotherapy for soft tissue sarcoma, instead of traditional 5-week preoperative radiotherapy. Condensed radiation may have an in situ vaccination effect that promotes anti-tumor immunity. However, condensed RT can also cause recruitment of immunosuppressive myeloid cells to the tumor microenvironment. We will use IHC and IF to characterize changes in myeloid and T cell populations within the tumor microenvironment. Second, we will compare the proliferation, phenotype and cytokine production of ex vivo TIL from UPS patients treated on the 5-day preoperative RT protocol with TIL from non-irradiated patients.

Together, we envision that Aim 1 and 2 will provide the framework to propose a clinical trial combining immune checkpoint blockade with macrophage targeting strategies in the context of 5-day preoperative radiotherapy.