(D) Time-dependent killing assay of DCR-2-PBD on HL-60, with final viability measured at 96 hours. internalizes into target cells. We have generated a highly potent anti-CD300f antibody-drug conjugate (ADC) with a pyrrolobenzodiazepine warhead that selectively depletes AML cell lines and colony forming units in vitroThe ADC synergizes with fludarabine, making it a natural combination to use in a minimal toxicity conditioning regimen. Our ADC prolongs the survival of mice engrafted with human cell lines and depletes primary human AML engrafted with a single injection. In a humanized mouse model, a single injection of the ADC depletes CD34+ HSPCs and CD34+CD38?CD90+ hematopoietic stem cells. This work establishes an anti-CD300f ADC as an attractive potential therapeutic that, if validated in transplant models CHK1-IN-2 using a larger cohort of primary AML samples, will reduce relapse rate and toxicity for patients with AML undergoing allo-HSCT. Visual Abstract Open in a separate window Introduction Relapse after allogeneic hematopoietic stem cell transplant (allo-HSCT) for acute myeloid leukemia (AML) occurs in 24% to 36% of patients, and the outcomes for these patients are poor.1 Disease genetic characteristics can predict for relapse overall and impact postCallo-HSCT relapse rates.2 The rate of relapse after allo-HSCT is higher in adverse-risk groups, particularly in some subgroups such as monosomal karyotypes.3,4 Postinduction factors CHK1-IN-2 that predict relapse include the presence of residual disease. Minimal residual disease (MRD) positivity prior to allo-HSCT, detected by flow cytometry, quantitative polymerase chain reaction, or next-generation sequencing, correlates with relapse.5-7 Although allo-HSCT remains the only potential curative option in patients with refractory disease, relapse rates remain high in that setting.8 The role of the immune response and graft-versus-leukemia effect is well established.9 Evidence demonstrates that the intensity of conditioning plays a clear role in reducing relapse risk. Myeloablative (MA) allo-HSCT conditioning regimens reduce relapse more than reduced-intensity conditioning (RIC) and non-MA regimens.10 The increased relapse rate seen in patients who are MRD positive or undergo non-MA conditioning suggests that reducing the burden of disease by the time of transplant is critical to improving outcomes. The advent of RIC and non-MA regimens has transformed transplantation, making it accessible to older patients and those with comorbidities. RIC regimens demonstrate significantly less treatment-related mortality (TRM) than MA regimens.11 Despite the reduction seen in RIC, TRM remains significant, especially in those 65 years.12 The development of antibody-based therapies depleting hematopoietic stem and progenitor cells (HSPCs) as part of allo-HSCT conditioning is expanding.13 Such therapies may reduce or eliminate traditional methods of depleting HSPC such as alkylating agents and irradiation. Preclinical studies demonstrate that antibody-drug conjugate (ADC)Cbased conditioning limits damage to bone marrow (BM) architecture and accelerates immune recovery compared with traditional conditioning.14 The advent of targeted condition has the potential to further reduce TRM. The CD300f protein (encoded by the gene) is an inhibitory receptor found RXRG on healthy myeloid cells, including antigen-presenting cells (APCs).15,16 CD300f is present on a high proportion of AML cells as well as HSPCs.17,18 Its distribution makes CD300f an excellent target in both AML therapy and targeted allo-HSCT conditioning. CHK1-IN-2 We have completed proof-of-principle work demonstrating how incorporating CHK1-IN-2 an anti-CD300f ADC into conditioning for allo-HSCT in AML may decrease relapse and toxicity by reducing/replacing traditional agents. Methods Preparation of tissue samples Blood and BM CHK1-IN-2 samples from patients with AML or healthy individuals were collected at Concord Repatriation General Hospital (CRGH) or Royal Prince Alfred Hospital (Sydney, Australia). Patient and.
