Targeted lymphodepletion with a CD45-directed antibody radioconjugate as a novel conditioning regimen prior to adoptive cell therapy

Chimeric antigen receptor (CAR) T cell therapies, and adoptive cell therapy (ACT) in general, represent one of the most promising anti-cancer strategies. Conditioning has been shown to improve the immune homeostatic environment to enable successful ACT or CAR-T engraftment and expansion in vivo following infusion, and represents potential point of intervention to decrease serious toxicities following CAR-T treatment. In contrast to relatively non-specific chemotherapy-derived lymphodepletion, targeted lymphodepletion with radioimmunotherapy (RIT) directed to CD45 may be a safer and more effective alternative to target and deplete immune cells. Here we describe the results of preclinical studies with an anti-mouse CD45 antibody 30F11, labeled with two different beta-emitters 131Iodine ((131)I) and 177Lutetium ((177)Lu), to investigate the effect of anti-CD45 RIT lymphodepletion on immune cell types and on tumor control in a model of adoptive cell therapy. Treatment of mice with 3.7 MBq (131)I-30F11 or 1.48 MBq (177)Lu-30F11 safely depleted immune cells such as spleen CD4+ and CD8+ T Cells, B and NK cells as well as Tregs in OT I tumor model while sparing RBC and platelets and enabled E. G7 tumor control. Our results support the application of CD45-targeted RIT lymphodepletion with a non-myeloablative dose of (131)I-30F11 or (177)Lu-30F11 antibody prior to adoptive cell therapy.