Project 4:Targeting M2-like Macrophages and MDSC with Myelolytic-Virotherapy

Abstract - Project 4: Cure rates for pediatric patients with relapsed or metastatic solid tumors remain unacceptably low. Cancer immunotherapies hold great promise, but scores of disappointing studies highlight our relative ignorance in understanding the immunosuppressive microenvironment within solid tumors. Because of their central role in

mediating immunosuppression, tumor associated macrophages (TAMs), typically “polarized” to a so-called M2- like immunosuppressive phenotype, and myeloid-derived suppressor cells (MDSC), are thought to be important therapeutic targets. We have found a clinically viable strategy that simultaneously reduces TAMs/MDSC (we dub

“myelolytic”) and polarizes the microenvironment (via oncolytic virus infection), resulting in significant antitumor efficacy. We hypothesize that targeting TAM and MDSC by combining “myelolytic” therapies with pro- inflammatory therapies activates innate antitumor mechanisms that cause cancer regressions and

reshapes the solid tumor microenvironment to be more permissive to cellular immunotherapies. In aim 1, we will determine the mechanism(s) by which combined myelolytic-virotherapy drives tumor regressions. We will use novel technologies such as fluorescent nanodiamonds to determine effects on innate immune cell phagocytosis of tumor cells. We will utilize the Genomics & Immune Monitoring Shared Resource

Core B directed by Dr. Elaine Mardis to conduct flow cytometry with time-of-flight mass spectrometry and single cell transcriptomics to determine the effects on immune cell composition and polarization. We will also utilize gain- and loss-of-function approaches to determine if loss of MDSC are critical for enabling tumor regressions

with myelolytic-virotherapy. We will also test combination therapies in xenograft and immunocompetent models of other cancer types to confirm its generalizability (osteosarcoma, Ewing sarcoma, rhabdomyosarcoma, neuroblastoma). In aim 2, we will determine the effects of myelolytic-virotherapy on T cell-mediated

immunotherapies. We will examine the effect of myelolysis alone and combined with virotherapy on the efficacy of antitumor T cells in a T cell exhaustion setting and with CAR-T cells (with Project 1 Leader Dean Lee and co- investigator Ruoning Wang, PI-DDN U01 member). We will work with Core B to examine the effects on T cell

clonality using TCR sequencing. In aim 3, we will determine whether combined myelolytic-virotherapy enhances the efficacy of NK-based cellular therapies. We will work with Project 1 Leader Dean Lee and Project 2 Leader Mitch Cairo to study the effects on adoptive NK and CAR-NK cell therapy. Overall, with this

project we will further elucidate, test and develop strategies to modulate the tumor microenvironment to facilitate innate immune cells as cancer therapy. Our findings may be applicable across a broad panel of pediatric cancer types and thus fits well into the aims of the Pediatric Immunotherapy Discovery and Development Network.