Priming versus propagating: distinct immune effects of an alpha- versus beta-particle emitting radiopharmaceutical when combined with immune checkpoint inhibition.

Radiopharmaceutical therapy (RPT) enhances tumor response to immune checkpoint inhibitors (ICI) in preclinical models, but the effects of different radioisotopes have not been thoroughly compared. To evaluate mechanisms of response to RPT+ICI, we used NM600, an alkylphosphocholine selectively taken up by most tumors. Effects of Y-, Lu-, and Ac-NM600 + ICIs were compared in syngeneic murine models, B78 melanoma (poorly immunogenic) and MC38 colorectal cancer (immunogenic).

Immunological effects of radiopharmaceutical therapy.

Radiation therapy (RT) is a pillar of cancer therapy used by more than half of all cancer patients. Clinically, RT is mostly delivered as external beam radiation therapy (EBRT). However, the scope of EBRT is limited in the metastatic setting, where all sites of disease need to be irradiated.

Intratumoral radiation dose heterogeneity augments antitumor immunity in mice and primes responses to checkpoint blockade.

Radiation therapy (RT) activates multiple immunologic effects in the tumor microenvironment (TME), with diverse dose-response relationships observed. We hypothesized that, in contrast with homogeneous RT, a heterogeneous RT dose would simultaneously optimize activation of multiple immunogenic effects in a single TME, resulting in a more effective antitumor immune response. Using high-dose-rate brachytherapy, we treated mice bearing syngeneic tumors with a single fraction of heterogeneous RT at a dose ranging from 2 to 30 gray.