Abstract IA16: Immune suppression in cancer and strategies for its reversal

Abstract

Abstract The microenvironment is involved in multiple aspect of cancer progression. Tumor metastasis is a critical step in the progression of solid tumors that is associated with patient mortality, and the metastatic microenvironment is key regulator of this process. The pre-metastatic niche is the microenvironment important for metastatic initiation that is established at distant sites in response to primary tumor factors during cancer progression. We characterized this microenvironment which involves changes in both stromal and immune populations in the lungs of sarcoma-bearing mice and in the liver in pancreatic- bearing mice by flow cytometry and RNA sequencing approaches. We identified a gene signature in pre-metastatic niche formation that demonstrates upregulation of immune suppression genes that is consistent across different metastatic tissue including lung and liver as well as across species with commonalities in murine and human early metastatic microenvironments. Performing single cell RNA sequencing of the pre-metastatic niche revealed key immune suppressive genes were found in the myeloid cell clusters. In addition to the increase of myeloid cells and immunosuppressive pathways, we discovered that T cell populations are reduced in pre-metastatic lungs. We hypothesized that reversing this immunosuppressive environment would restore T cell function and antitumor immunity. We designed a novel approach in which we generated Genetically-Engineered Myeloid cells (GEMys) to deliver IL-12, a potent antitumor molecule, into the pre-metastatic microenvironment. We evaluated the lungs by flow cytometry and observed that IL12-GEMy-treated mice had increased numbers of T cells and enhanced expression of activation markers, resulting in reduced metastasis and increased survival. This model was effective in an aggressive experimental metastasis model of pancreatic liver metastasis and was not only able to limit metastatic progression but was able to cure a subset of mice compared to rapid metastatic progression in the liver within a month in the untreated pancreatic cancer mice. When combined with chemotherapy pre-conditioning, IL12-GEMys cured mice of established tumors and generated long-lived T cell memory, as these mice were immune to subsequent tumor challenge. These studies demonstrate that IL12-GEMys can functionally modulate the core program of immune suppression in the pre-metastatic niche to successfully rebalance the dysregulated metastatic microenvironment in cancer. Citation Format: Rosandra N. Kaplan. Immune suppression in cancer and strategies for its reversal [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr IA16.