Depletion of Foxp3+ regulatory T cells but not the absence of CD19+IL‐10+ regulatory B cells hinders tumor growth in a para‐orthotopic neuroblastoma mouse model

Abstract

Adaptive immune cells with regulatory function reportedly mediate immune escape in a variety of tumors. Little is known regarding the relevance of the most prominent regulatory cell populations, namely Foxp3+ T regulatory cells (Tregs) and CD19+IL‐10+ B regulatory cells (Bregs), for neuroblastoma (NB) survival. After establishing a novel immunocompetent syngeneic NB mouse model where orthotopic tumors can be generated after intrarenal injection of NB975A cells, we studied the importance of Tregs and Bregs in Foxp3‐DTR mice whose Tregs can be depleted by diphtheria toxin (DT) application as well as in CD19‐specific IL‐10 deficient mice that lack IL‐10+ Bregs (CD19cre+/− × IL‐10fl/fl mice). We observed Foxp3 Treg cells in tumors from wild type mice. On the contrary, Bregs or B cells were scarce. Specific depletion of Tregs in Foxp3‐DTR mice resulted in an 85% reduction of tumor volume and weight compared to DT‐treated wild type mice and untreated Foxp3‐DTR mice. In contrast, NB tumor growth was not affected in CD19‐specific IL‐10 deficient mice. Similarly, mice lacking mature B cells (μMT mice) and CD19 deficient mice (CD19cre mice) showed no change in growth pattern of NB tumors. In Treg‐depleted mice, reduced tumor growth was associated with an increased concentration of IFN‐gamma, TNF‐alpha, IL‐4, IL‐6, and IL‐10 in isolated splenocytes. In summary, transient ablation of Tregs but not absence of Bregs hindered the growth of NB, strongly suggesting the therapeutic potential of targeting Tregs for this aggressive childhood tumor.

Targeting macrophage Syk enhances responses to immune checkpoint blockade and radiotherapy in high-risk neuroblastoma

“…However, administration of ULTRA-LEAF™ purified mAb depleted B cells, but did not suppress NB9464 tumor growth ( Figures S3A–C ). Taken together, these results suggest that macrophages and not B cells play an important role in the progression of NB, and these results were also validated by other groups ( 19 , 51 ).…”

“…The immune microenvironment of NB plays an important role in disease progression and predicting responses to immunotherapy (12,50). However, limited studies are available which exemplify the presence of immune cells in NB tumors (13,15,16).…”

The dichotomy of regulatory B cells in cancer versus allergic disease

“…Weißenborn et al created a cre‐flox mouse model for inducible deletion of IL‐10 on CD19 cells. However, Breg depletion did not show as significant of a tumor growth reduction in murine neuroblastoma as compared to Treg depletion 78 . Future work will be important to identify targetable cell‐surface markers to allow for selective Breg depletion.…”

“…76 Matsushita et al describe using a monoclonal mouse antibody against CD22 that was shown to selectively deplete splenic B10 cells in an autoimmune encephalitis model, 77 Treg depletion. 78 Future work will be important to identify targetable cell-surface markers to allow for selective Breg depletion.…”