Abstract 4057: Gender and the immune system in lung and liver colonization of murine melanoma in a B16 metastatic model

Introduction: Until age 45, incidence rates of melanoma are higher in woman than men, but by age 60, rates in men are more than double and by age 80, they are almost triple. With the low rate of survival for distant metastatic patients with melanoma, especially in men, studies aimed at elucidating the mechanisms underlying metastasis and the gender disparity are warranted. The purpose of this study is to identify the immune cells and cellular interactions that are crucial for initial colonization of metastatic melanoma in a gender dependent manner. Experimental Procedures: We used a B16 melanoma metastatic model in which 2×105 cells are injected via the tail vein of B6 mice and allowed to colonize for 14 days. Positive organs are analyzed by visual counting of the metastases, extraction of the melanin pigment and measurement by spectrophotometry, and by flow cytometry. To investigate the role of innate immunity, we injected ip either anti-Ly6G, 1A8 (neutrophil depletion), anti NK1.1, PK136 (natural killer [NK] cell depletion) or control IgG every 3 days, starting 1 day before tumor injection. For hormone ablation studies, an LHRH antagonist was injected. Data: Naive mice injected with B16 cells revealed that females have higher lung tumor burden than males. Previous castration studies indicate that this may be dependent on androgens. Intriguingly, neutrophil depletion increases tumor burden only in male mice when compared to male IgG and does not significantly affect tumor burden in female mice, indicating a potential gender difference in neutrophils. Neutrophil depletion in male mice also reduced NK activation and IFN-γ production, indicating a stimulatory relationship between neutrophils and NK cells. A subsequent NK depletion study revealed significantly increased tumor burden in both male and female NK-depleted mice when compared to the gender-matched controls. However, the increased tumor burden normally seen in lungs of females compared to males was still apparent when comparing lungs of NK depleted male mice to NK depleted female mice. This study also revealed that NK cells are crucial for the prevention of liver metastasis as both genders of NK depleted mice revealed multiple melanoma tumor nodules on the surface of the liver. Conclusion: Our data indicates that both neutrophils, and to a greater extent, NK cells are important for the initial response against B16 melanoma colonization of the lung and may be necessary to prevent metastasis. For the liver, NK cells were absolutely crucial for the prevention of melanoma colonization in this organ. Neutrophil depletion, as well as our previous castration data, indicated that there is a gender specific differential response of these cells, which may contribute to the gender disparity seen in human incidence and survival. Further, the importance of NK cells in killing of tumor cells indicates a population of patients that may benefit from ex vivo NK expansion therapy currently in clinical trials. Citation Format: Janet L. Markman, Daiko Wakita, Timothy R. Crother, Moshe Arditi. Gender and the immune system in lung and liver colonization of murine melanoma in a B16 metastatic model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4057. doi:10.1158/1538-7445.AM2015-4057