Abstract 623: Immunological aging slows triple-negative breast cancer progression and impedes response to therapy

Understanding how aging impacts cancer progression is critical to improving therapeutic responses. As we age our risk of developing most forms of cancer increases. Conversely, our immune function declines, and though over half of breast cancer patients are over the age of 60, fewer than 25% of clinical trial enrollees are patients in this age range. This is concerning given the expanding use of immunotherapies that rely on immune function, with early clinical trial results suggesting there may be age-associated responses to treatment. Here, we utilize a preclinical model of aging to understand how age impacts immune responses to triple negative breast cancer (TNBC). Immunologically young (~8 week old) and aged (~12 month old) FVB mice were orthotopically injected with syngeneic Met1 TNBC cells. To mimic first-line therapies using chemotherapy combined with anti-PDL1, young and aged FVB mice were treated with paclitaxel or vehicle control and/or anti-PDL1 once tumors became palpable. Tumors in young control mice grew significantly faster than in aged mice, resulting in shorter survival in young mice. Aged control mouse tumors exhibited infiltration of more CD8+ cytotoxic Tcells, but also more FOXP3+ inhibitory T-regulatory cells compared to young mice, despite aged mice having fewer circulating CD8+ and CD4+ lymphocytes. Tumor burden is reduced in young and aged mice on monotherapy, however only young mice receive a further benefit of combination versus monotherapy. Aged mice receive no benefit of combo therapy. Tumors in young mice have a significant increase in infiltration of both CD8+ and inhibitory Tregs with treatment, while aged mice experience no increase in Tcell infiltration with any treatment. GSEA of bulk RNA sequencing reveals that tumors in aged mice are significantly enriched for inflammatory and immune response programs compared to young mice - interferon alpha, interferon gamma, IL6, IL2, inflammatory response. Furthermore, tumors in aged mice have significant enrichment of the immune exhaustion markers PDL1, CTLA4, TIM3, and LAG3. Analysis of published single cell RNAseq data of human TNBC patients reveals the same signatures enriched with age as in our murine model. Furthermore, these pathways are predominantly enriched in the Tcell and fibroblast compartments. Our model mimics both the chronological and immunological age spectra of breast cancer patients and illustrates differential responses to tumor progression, immune responses, and r