Jiayi He

Yujia Xia

Hongji Zhang

Dmitry Genkin

George Tetz

Methods: Subcutaneous MC38 (MSI-H adenocarcinoma of the colon) tumors were established in 6-week-old mice. Treatment was initiated six days after tumor inoculation with daily intraperitoneal (i.p) injections of DNase I followed by i.p anti-PD-1 treatment administered every 3 days. Animals were divided into treatment groups: control, DNase alone, anti-PD-1 alone and combination of DNase I with anti-PD-1 (n = 6 mice/ group).

Results: Tumors were successfully established after 6 days of inoculation. These tumors expressed high neutrophil infiltration and NETs. To determine the effects of combination therapy on tumor progression, we measured tumor volume and time to progression (TTP). We found that mice treated with combination DNase I and anti-PD-1 had significantly lower mean tumor volume compared to anti-PD-1 alone (1372.68mm³ vs 2193.20 mm³, p-value = 0.043). TTP was higher in the combination group compared to anti-PD-1 treatment alone (median time to progression 22 vs 17 days, p-value = 0.004). Next we sought to determine the mechanism behind this effect by investigating if NETs blockade modulated the tumor microenvironment. We found that treatment with DNase I decreased exhaustion of CD8+ T-cells in the tumor compared to no treatment.

Conclusions: Targeting NETs in combination with immune checkpoint inhibition may be an option to improve response rate to immune checkpoint inhibitors through decreasing exhausted CD8+ T-cells.