B cell–Derived IL35 Drives STAT3-Dependent CD8+ T-cell Exclusion in Pancreatic Cancer

Abstract

Pancreatic ductal adenocarcinoma (PDA) is an aggressive malignancy characterized by a paucity of tumor-proximal CD8 þ T cells and resistance to immunotherapeutic interventions. Cancer-associated mechanisms that elicit CD8 þ T-cell exclusion and resistance to immunotherapy are not well-known. Here, using a Kras-and p53-driven model of PDA, we describe a mechanism of action for the protumorigenic cytokine IL35 through STAT3 activation in CD8 þ T cells. Distinct from its action on CD4 þ T cells, IL35 signaling in gp130 þ CD8 þ T cells activated the transcription factor STAT3, which antagonized intratumoral infiltration and effector function of CD8 þ T cells via suppression of CXCR3, CCR5, and IFNg expression. Inhibition of STAT3 signaling in tumor-educated CD8 þ T cells improved PDA growth control upon adoptive transfer to tumor-bearing mice. We showed that activation of STAT3 in CD8 þ T cells was driven by B cell-but not regulatory T cell-specific production of IL35. We also demonstrated that B cell-specific deletion of IL35 facilitated CD8 þ T-cell activation independently of effector or regulatory CD4 þ T cells and was sufficient to phenocopy therapeutic anti-IL35 blockade in overcoming resistance to anti-PD-1 immunotherapy. Finally, we identified a circulating IL35 þ B-cell subset in patients with PDA and demonstrated that the presence of IL35 þ cells predicted increased occurrence of phosphorylated (p)Stat3 þ CXCR3 À CD8 þ T cells in tumors and inversely correlated with a cytotoxic T-cell signature in patients. Together, these data identified B cell-mediated IL35/gp130/ STAT3 signaling as an important direct link to CD8 þ T-cell exclusion and immunotherapy resistance in PDA.

IL-12 Family Cytokines in Cancer and Immunotherapy

“…Additionally, IL-35 restricted CD8 + T cell activation by suppressing the expression of the costimulatory surface molecule CD28, and Th1 cytokine production, and reduced cytolytic functions by repressing the expression of perforins [ 167 , 168 ]. Furthermore, IL-35 converted effector T cells into IL-35-producing T cells known as iT35 cells and activated IL-35 production and the proliferation of Treg cells [ 163 , 169 , 170 ]. A subset of mouse and human regulatory B cells can be a major source of IL-35 in certain malignant tumor types [ 167 , 171 , 172 ].…”

“…A specialized subset of B cells marked by CD21 hi CD1d hi CD5 + was identified as the main source of IL-35 in pancreatic cancer. The B cell-specific production of IL-35 promoted the expansion of Treg cells and blocked the anti-tumor activity of effector CD4 + T cells [ 169 ]. Furthermore, IL-35 directly acted on CD8 + T cells and suppressed their infiltration and effector function by downregulating the expression of IFN-γ and CXCR3 in a STAT3-dependent manner [ 169 ].…”

“…The B cell-specific production of IL-35 promoted the expansion of Treg cells and blocked the anti-tumor activity of effector CD4 + T cells [ 169 ]. Furthermore, IL-35 directly acted on CD8 + T cells and suppressed their infiltration and effector function by downregulating the expression of IFN-γ and CXCR3 in a STAT3-dependent manner [ 169 ]. IL-35-producing B cells were also elevated in the peripheral blood of gastric cancer (GC) patients and were responsible for the accumulation of immune suppressive Treg cells, MDSCs, IL-10-producing B cells and CD14 + monocytes [ 170 ].…”

“…Turnis et al showed that anti-PD-1 therapy combined with the depletion of IL-35 and/or deletion of Treg cell-specific IL-35 expression significantly limited murine melanoma and colon cancer growth by promoting cytotoxic T cell proliferation, effector function and long-term memory formation [ 166 ]. Similarly, the loss of B cell-specific IL-35 expression or antibody-based IL-35 blockade synergized with anti-PD1 treatment in a CD8 + T cell-dependent manner to inhibit pancreatic cancer growth in preclinical models [ 169 ]. A similar approach of combining IL-35 blockade with the immune checkpoint inhibition of PD1 or PD-L1 was effective in NSCLC [ 185 ].…”

Mechanisms Governing Immunotherapy Resistance in Pancreatic Ductal Adenocarcinoma

“…Recent studies suggest that B cells in PDA have regulatory functions. In both PDA patients and mouse models, B cell production of IL-35 correlated with reduced T cell tumor infiltration and increased Tregs ( 90 , 134 ). Interfering with IL-35 increased T cell infiltration and cytokine production while reducing tumor weight and PanIN lesion formation ( 90 , 102 , 134 ).…”