Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment for patients with non-malignant or malignant blood disorders. Its success has been limited by graft-versus-host disease (GVHD). Current genotoxic conditioning regimens mediate tissue injury and potentially incite and amplify GVHD, limiting use of this potentially curative treatment beyond malignant disorders. Minimizing genotoxic conditioning while achieving alloengraftment without global immune suppression is highly desirable. Antibody-drug-conjugates (ADCs) targeting hematopoietic cells can specifically deplete host stem and immune cells and enable alloengraftment. Here we report an anti-mouse CD45-targeted-ADC (CD45-ADC) that facilitates stable murine multi-lineage donor cell engraftment. Conditioning with CD45-ADC (3mg/kg) was effective as a single agent in both congenic and minor-mismatch transplant models resulting in full donor chimerism comparable to lethal total body irradiation (TBI). In an MHC-disparate allo-HSCT model, pre-transplant CD45-ADC (3mg/kg) combined with low-dose TBI (150cGy) and a short course of costimulatory blockade with anti-CD40 ligand antibody enabled 89% of recipients to achieve stable alloengraftment (mean value: 72%). When CD45-ADC was combined with pre-transplant TBI (50cGy) and post-transplant Rapamycin, Cytoxan or a JAK inhibitor, 90-100% of recipients achieved stable chimerism (mean: 77%, 59%, 78%, respectively). At a higher dose (5mg/kg), CD45-ADC as a single agent was sufficient for rapid, high level multi-lineage chimerism sustained through the 22 weeks observation period. Therefore, CD45-ADC has potential utility to confer the benefit of fully myeloablative conditioning but with substantially reduced toxicity when given as a single agent or at lower doses in conjunction with reduced intensity conditioning.
Innate Immune Activation by Tissue Injury and Cell Death in the Setting of Hematopoietic Stem Cell Transplantation
