Streptavidin-drug conjugates streamline optimization of antibody-based hematopoietic stem cell transplant conditioning.

Hematopoietic stem cell transplantation (HSCT) conditioning using antibody-drug conjugates (ADC) is a promising approach to preparing patients for transplant, potentially avoiding the severe toxicities of conventional chemotherapy- and irradiation-based conditioning regimens. The toxic payload determines the efficacy and potential toxicities of an ADC, but comparison of different payloads in conjugates designed for HSCT conditioning has not been reported. Such comparisons would be greatly facilitated by methods enabling efficient screening of many combinations of antibody and payload. Herein, we used Click chemistry to conjugate four different small molecule payloads to a streptavidin backbone, yielding streptavidin-drug conjugates that can be combined with any biotinylated antibody to rapidly and cost-effectively produce an ADC. We vetted this system by evaluating CD45-targeted ADCs, finding pyrrolobenzodiazepine (PBD) dimers to be the most effective payload of those we tested for targeting mouse and human hematopoietic stem cells (HSCs) and acute myeloid leukemia (AML) cells. Single-dose murine CD45-PBD enabled near-complete conversion to donor hematopoiesis in syngeneic HSCT models as well as in autologous transplantation using gene-edited HSCs. Finally, human CD45-PBD targeted human HSCs and provided significant antileukemia benefit in a patient-derived AML xenograft model. Notably, our streptavidin-drug conjugates were produced using routine molecular biology techniques and readily available supplies without requiring complex instrumentation, making production and screening of ADCs for myriad targeting applications accessible to virtually any laboratory.