Clearing and replacing tissue-resident myeloid cells with an anti-CD45 antibody–drug conjugate

Tissue-resident myeloid (TRM) cells in adults have highly variable lifespans, and may be derived from early embryonic yolk sac, fetal liver, or bone marrow. Some of these TRM cells are known pathogenic participants in congenital and acquired diseases. Myeloablative conditioning and hematopoietic stem cell transplantation can replace long-lived brain TRM cells, resulting in clinical improvements in metabolic storage diseases. With the advent of antibody–drug conjugate (ADC)-targeted cell killing as a cell-selective means of transplant conditioning, we assessed the impact of anti-CD45–ADC on TRM cells in multiple tissues. Replacement of TRM cells ranged from 40% to 95% efficiencies in liver, lung, and skin tissues, after a single anti-CD45–ADC dose and bone marrow hematopoietic cell transfer. Of note, the population size of TRM cells in tissues returned to pretreatment levels, suggesting a regulated control of TRM cell abundance. As expected, brain microglia were not affected, but brain monocytes and macrophages were 50% replaced. Anti-CD45–ADC and adoptive cell transfer were then tested in the chronic acquired condition, atherosclerosis exacerbated by Tet2 mutant clonal hematopoiesis. Plaque-resident myeloid cells were efficiently replaced with anti-CD45–ADC and wild-type bone marrow cells. Notably, this reduced existent atherosclerotic plaque burden. Overall, these results indicate that the anti-CD45–ADC clears both hematopoietic stem and TRM cells from their niches, enabling cell replacement to achieve disease modification in a resident myeloid cell–driven disease.