Abstract 4083: Opposing roles of B cells in Ras-driven squamous tumor development dependent on tissue compartment of oncogene expression and tumor phenotype

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Studies in mouse models and human cancers show that B cells can both promote and inhibit cancer development, but the mechanisms generating these alternate outcomes are not well understood. Here we have developed a mouse model of Ras-driven epidermal tumor development in which opposite effects of B cells are manifest, dependent on the differentiation state of cells expressing oncogenic Ras. We used a doxycycline regulatable bitransgenic system to target oncogenic H-RasV12G to either the basal/stem cell (Keratin14-rTAxtetORasV12G, K14Ras) or differentiating (Involucrin-tTA x tetORasV12G, InvRas) compartment of the epidermis. K14Ras mice develop focal squamous cell carcinoma while InvRas mice develop squamous papillomas within 30 days on threshold levels of doxycycline resulting in ∼10 tumors/mouse. On a Rag1-/- background we observed opposite tumor responses, with InvRasRag1-/- mice developing fewer tumors and K14RasRag1-/- mice developing more tumors with shorter latency than Rag1+/+ controls. Depletion of CD4+ T cells caused an overall increase in tumor burden compared to isotype controls in both models, while adoptive transfer of naive CD4+ T cells (purity ≥ 93%) increased tumor burden in K14RasRag1-/- mice, but suppressed tumors in InvRasRag1-/- mice. Tumors from CD4 transferred K14RasRag1-/- mice had a predominant Th1 infiltrate with few Tregs and increased tumor-infiltrating neutrophils compared to mock transferred controls. Conversely, CD4+ T cells adoptively transferred to InvRasRag1-/- mice displayed a regulatory phenotype with low IFNγ and high Foxp3, which was associated with a decrease in neutrophilic infiltration. In contrast, B cell depletion with anti-CD20 caused a significant suppression of tumor outgrowth in InvRas mice but enhanced tumor burden in K14Ras mice. Furthermore, adoptive transfer of magnetically purified splenic B cells into K14RasRag1-/- mice suppressed tumor formation, and co-transfer of B cells with CD4+ T cells reduced tumor development to a greater extent than B cells alone. Tumor-infiltrating B cells from co-transferred mice had greater percentage of B regulatory cells, and increased costimulatory molecule expression compared to B cells alone, resembling K14RasRag1+/+ controls. B cell co-transfer significantly increased Foxp3+ Treg percentage to levels similar to K14RasRag1+/+ mice as measured by flow cytometry. Taken together these results show that B cells are the critical lymphocyte driving both tumor suppression or promotion in this model, that the differentiation state of the tumor initiating cell determines the B cell response, and that interactions between CD4+ T cells and B cells may be important for the development of a proper anti-tumor immune response. Citation Format: Michael A. Podolsky, Andrew Gunderson, Kyle Breech, Adam B. Glick. Opposing roles of B cells in Ras-driven squamous tumor development dependent on tissue compartment of oncogene expression and tumor phenotype. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4083. doi:10.1158/1538-7445.AM2014-4083