Engraftment of gene-edited hematopoietic stem cells after antibody-drug conjugate conditioning in nonhuman primates Open Access

• Antibody-based conditioning for HCT was directly compared against busulfan chemotherapy in a nonhuman primate model.

• Targeting CD117 or CD45 with antibody drug conjugates enables autologous transplant of CCR5-edited HSCs.

Hematopoietic stem cell (HSC) gene therapies provide lifelong benefit in numerous hematological diseases and disorders, but safety and toxicity remain a critical barrier for routine application. In the setting of immunodeficiency syndromes and infectious diseases such as human immunodeficiency virus (HIV) infection, conditioning regimens may exacerbate immune dysfunction, blunting or impairing overall efficacy. Here, we conduct a head-to-head comparison of two novel antibody drug conjugates (ADC) with a pyrrolobenzodiazepine (PDB) payload for autologous transplantation in rhesus macaques: ADCs targeting either CD117 or CD45 and benchmarked against the clinical standard busulfan. We quantified extent of myeloablation and immunosuppression, time to hematopoietic recovery, long-term engraftment of CCR5 CRISPR-edited autologous HSC, and resistance to infection when challenged with increasing concentrations of an HIV-like virus. Both ADCs enabled engraftment of CRISPR-edited HSCs, although with lower levels of long-term editing compared to busulfan. We observed myeloablation with similar times to hematopoietic recovery and preserved lymphocyte counts with all three conditioning regimens, but neither ADC conditioning nor busulfan enabled sufficient CCR5 editing for viral immunity. While these results only apply to the specific ADC conditioning protocols tested here, they are a step towards developing targeted strategies to engraft cells with therapeutic edits and highlight the need for further refinement of antibody-based selection.