Abstract A018: Cancer Associated Fibroblasts regulate Humoral Immunity and B Cell Education within Tertiary Lymphoid Structures

Abstract

Pancreatic ductal adenocarcinoma (PDAC) has a 5-year survival rate of just 13%. Immune checkpoint blockade (ICB) has revolutionized cancer therapy, yet has shown limited efficacy in PDAC, benefiting fewer than 1% of patients to date. Contributing to this, the PDAC tumor microenvironment (TME) is desmoplastic and composed of cancer associated fibroblasts (CAFs) that physically and metabolically impede immune cell infiltration, leading to ineffective immunotherapeutic intervention. Despite this, B cell infiltration and tertiary lymphoid structures (TLS) in the PDAC TME are associated with enhanced survival in patients. B cells become functional as they differentiate into memory B cells or plasma cells through either an extrafollicular or germinal center (GC) response, with the GC response occurring within tertiary lymphoid structures (TLS), which are associated with enhanced response rates to ICB. However, different CAF subtypes have been shown to limit antitumor immunity, particularly at the level of TLS formation, where myofibroblastic CAFs (myCAFs) specifically have been shown to be suppressive. Together, these findings illuminate a need to further understand how different subtypes of CAFs regulate these prognostic features. We hypothesized that CAF localization regulates TLS activity in a subtype-specific manner, with myCAFs suppressing and inflammatory CAFs (iCAFs) promoting TLS activity, and that CAFs can directly modulate the humoral response. We assessed this axis in PDAC patients both ex vivo and in vitro via multispectral imaging of patient samples and B cell modulation by patient-derived CAFs. We found that CAFs cultured in conditions representative of the physiologic stromal and metabolic landscape of PDAC can suppress the GC response of B cells. We have also demonstrated that myofibroblastic CAFs (myCAFs) and inflammatory CAFs (iCAFs) differentially localize within the TME, with myCAFs localizing in tumor-rich zones with sparse immune infiltration and iCAFs localizing adjacent to and within immune structures like TLS. Together, these findings suggest that CAF subtypes differentially regulate the humoral immune response in PDAC, and that myCAFs are likely to suppress this response. Future work will focus on polarizing CAFs into myCAFs and iCAFs in vitro to investigate their distinct interactions with B cells. Further, we will pair our multispectral imaging of CAFs with TLS state and activity to correlate these metrics with varying CAF subsets. Finally, as nearly all PDAC patients receive standard-of-care chemotherapy, we are extending this work to determine how regimen-specific CAF reprogramming, particularly by platinum-based FOLFIRINOX, further modulates this CAF: B cell axis and may inform future immunotherapeutic strategies.