Antibody subclass deficiency accelerates tumorigenesis in genetically engineered mouse models of pancreatic cancer.

Antibody production by B cells has emerged as an important factor in regulating antitumor immunity with both suppressive and promotive roles in cancer. However, the specific effect of antibody deficiency during development of pancreatic ductal adenocarcinoma (PDAC) has not been explored. To address this question, we crossed the well-established KPC mouse model to mice lacking all circulating immunoglobulin (Ig) due to genetic ablation of both Ig secretion and Ig class switching (KPC-μSAID mice). KPC-μSAID mice exhibited a two-fold acceleration in tumor formation, a two-fold reduction in median survival, and increased liver metastases versus KPC-WT control mice. Immunofluorescence analysis of pancreatic tissues from antibody-sufficient KC- and KPC-WT mice showed that IgG was predominantly localized within the extracellular matrix (ECM). Furthermore, in both KC- and KPC-μSAID mice, ECM density and podoplanin+ cancer-associated fibroblasts (CAFs) were significantly reduced. In the KPC-μSAID tumor microenvironment (TME), intratumoral myeloid-derived suppressor cells (MDSC) were also increased, while CD4+ and CD8+ T cells decreased, relative to tumor-bearing KPC-WT mice, with macrophage exhibiting a mixed polarization phenotype. These findings were recapitulated in antibody subclass-deficient, KPC-AID mice, suggesting a potentially novel function of IgG in suppressing PDAC progression by directly or indirectly regulating pancreatic fibrosis and the density of the ECM.