Supplementary Figures 1-12. Figure S1-S2 demonstrates survival in TA3-Ha-challenged mice treated with cyclophosphamide + MPL/TDCM (S1) or TDB and MPL individually (S2). Figures S3-S4 demonstrate B cell purification strategies. Figures S5-S6 demonstrate the effect of memory B-1a cells (S5) and IL-10 deficiency (S6) on survival following TA3-Ha challenge. Figures S8-S10 demonstrate MPL/TDCM treatment induces the production of TA3-Ha- and GD2-reactive IgM both in vivo (S8, S10) and TA3-Ha reactive IgM in vitro (S9). Figure S11 shows MPL/TDCM treatment following primary EL4 challenge generates memory that provides protection during rechallenge. Figure S12 shows the effect of passive transfer of serum from MPL/TDCM-treated mice into naïve mice on survival following TA3-Ha challenge.
ARTICLE ABSTRACT
Metastatic cancer involving spread to the peritoneal cavity is referred to as peritoneal carcinomatosis and has a very poor prognosis. Activating the antitumor immune response in the characteristically immune-suppressive peritoneal environment presents a potential strategy to treat this disease. In this study, we show that a toll-like receptor (TLR) and C-type lectin receptor (CLR) agonist pairing of monophosphoryl lipid A (MPL) and trehalose-6,6′-dicorynomycolate (TDCM) effectively inhibits tumor growth and ascites development in a mouse model of aggressive mammary cancer–induced peritoneal carcinomatosis. MPL/TDCM treatment similarly inhibited peritoneal EL4 tumor growth and ascites development. These effects were not observed in mice lacking B cells or mice lacking CD19, which are deficient in B-1a cells, an innate-like B-cell population enriched in the peritoneal cavity. Remarkably, adoptive transfer of B-1a cells, but not splenic B cells from WT mice, restored MPL/TDCM-induced protection in mice with B-cell defects. Treatment induced B-1 cells to rapidly produce high levels of natural IgM reactive against tumor-associated carbohydrate antigens. Consistent with this, we found significant deposition of IgM and C3 on peritoneal tumor cells as early as 5 days post-treatment. Mice unable to secrete IgM or complement component C4 were not protected by MPL/TDCM treatment, indicating tumor killing was mediated by activation of the classical complement pathway. Collectively, our findings reveal an unsuspected role for B-1 cell–produced natural IgM in providing protection against tumor growth in the peritoneal cavity, thereby highlighting potential opportunities to develop novel therapeutic strategies for the prevention and treatment of peritoneal metastases.
This work identifies a critical antitumor role for innate-like B cells localized within the peritoneal cavity and demonstrates a novel strategy to activate their tumor-killing potential.See related commentary by Tripodo, p. 5
