Checkpoint Antibodies but not T Cell–Recruiting Diabodies Effectively Synergize with TIL-Inducing γ-Irradiation

Abstract

T cell-recruiting bispecific antibodies (bsAb) show promise in hematologic malignancies and are also being evaluated in solid tumors. In this study, we investigated whether T cell-recruiting bsAbs synergize with hypofractionated tumor radiotherapy (hRT) and/or blockade of the programmed death-1 (PD-1) immune checkpoint, both of which can increase tumor-infiltrating lymphocyte (TIL) numbers. Unexpectedly, large melanomas treated with hRT plus bsAb (AC133ÂCD3) relapsed faster than those treated with hRT alone, accompanied by massive TIL apoptosis. This fast relapse was delayed by the further addition of anti-PD-1. Mechanistic investigations revealed restimulation-induced cell death mediated by BIM and FAS as an additional cause of bsAb-mediated TIL depletion. In contrast, the double combination of hRT and anti-PD-1 strongly increased TIL numbers, and even very large tumors were completely eradicated. Our study reveals the risk that CD3-engaging bsAbs can induce apoptotic TIL depletion followed by rapid tumor regrowth, reminiscent of tolerance induction by CD3 mAb-mediated T-cell depletion, warranting caution in their use for the treatment of solid tumors. Our findings also argue that combining radiotherapy and anti-PD-1 can be quite potent, including against very large tumors.

Hypofractionated Irradiation Has Immune Stimulatory Potential and Induces a Timely Restricted Infiltration of Immune Cells in Colon Cancer Tumors

“…Later on, the amount of the cytotoxic T cells dropped again (32). Our data also reveal that CD8 + T cells do migrate in solid tumors that have been irradiated with a hypofractionated protocol.…”

Abscopal Effects With Hypofractionated Schedules Extending Into the Effector Phase of the Tumor-Specific T-Cell Response

“…It has been shown that hRT can elevate CD8 þ tumorinfiltrating lymphocytes (TILs) between days 5 and 8 after hRT (20)(21)(22), which corresponds to the peak of the acute T-cell response against microbial antigens (23). Because T lymphocytes (including TILs) are usually regarded as highly radiosensitive (24,25), it is conceivable that hRT schedules extending into the period during which RT/ICB-induced T cells infiltrate the irradiated tumor might be less immunogenic than shorter schedules.…”

Immunomodulation by ionizing radiation—impact for design of radio‐immunotherapies and for treatment of inflammatory diseases

“…The presence of the cytotoxic T cells in the tumor was, however, limited since later on the amount of these adaptive immune cells dropped again. 134 In the CT26 colon cancer model in BAlb/c mice, we observed a peak of CD8+ T cells in the tumor 5 days after the last irradiation with 2×5 Gy at day zero and four. 90 From the clinical point of view, a re-irradiation on these days with higher single doses of RT should be counter-productive since the beneficial immune cells would be hit by the irradiation.…”

“…Hettich and colleagues demonstrated that irradiation with 2×12 Gy on consecutive days of B16 melanoma tumors induces a high infiltration of CD8+ T cells at day 5 after the last irradiation. The presence of the cytotoxic T cells in the tumor was, however, limited since later on the amount of these adaptive immune cells dropped again . In the CT26 colon cancer model in BAlb/c mice, we observed a peak of CD8+ T cells in the tumor 5 days after the last irradiation with 2×5 Gy at day zero and four .…”