Fig. 2.

Abscopal effect of combined localized radiation and systemic anti–PD-L1 immunotherapy. (A) Depiction of experimental strategy of bilateral mouse glioblastoma to measure abscopal effect in Tg(NTva);Ink4a-Arf^-/-;Pten^-/-; LoxP-Stop-LoxP luciferase mice with left-sided PDGF-Pten^-/- luciferase tumor and right-sided PDGF-shPten tumor. The right hemisphere contains a non-luciferase tumor and is irradiated. The left side contains neoplastic cells harboring luciferase expression and is not irradiated. Tumor viability (photons second⁻¹) and MRI tumor volume (mm³) are obtained from the left-sided, non-irradiated tumor only. (B) Association between tumor viability (photons second⁻¹) and MRI tumor volume (mm³) for all treatment groups. The growth pattern of each individual animal is shown as black lines and the linear regression summation of all the animals in the treatment group are depicted as colored wide arrows. Mice receiving combination imaging included IgG control (n = 8, red), whole brain radiation (n = 4, purple), non-luciferase tumor radiation alone (n = 4, magenta), anti–PD-L1 alone (n = 4, blue), and non-luciferase tumor radiation with anti–PD-L1 (n = 8, green). Tumor viability (luciferase activity in photons second⁻¹) and MRI T2 signal volume (mm³) are shown relative to pretreatment starting point that was normalized to 100% for all mice. (C) Response of unirradiated tumor to treatment is categorized as transient tumor regression (TTR) or sustained tumor regression (STR). TTR represents any decrease in unirradiated tumor viability (luciferase activity) that is followed by unirradiated tumor regrowth. STR represents any decrease in unirradiated tumor viability that is not followed by unirradiated tumor regrowth prior to reaching endpoint. Relative to IgG treated animals (red), whole brain radiation (10 Gy) or radiation positive control induces TTR in 7 of 7 mice, with STR in 0 of 7 mice. Anti–PD-L1 antibody alone does not induce TTR or STR in any mice (0 of 7 mice). Unilateral radiation of non-luciferase expressing tumor induces TTR in 2 of 7 mice, with STR in 0 of 7 mice. Unilateral radiation of non-luciferase tumor and anti–PD-L1 antibodies induces TTR in 6 of 8 mice, with STR in 2 of 8 mice. All posttreatment viability is shown relative to the original tumor viability, with growth showing increase and treatment response showing decrease on a log₁₀ scale. IgG isotype control is the same for all treatment groups and is shown in red, relative to experimental group shown in blue.