A Novel Targeted Approach to Achieve Immune System Reset: CD45-Targeted Antibody Drug Conjugates Enable Autologous HSCT and Ameliorate Disease in Preclinical Autoimmune Disease Models

Resetting the immune system through autologous hematopoietic stem cell transplant (autoHSCT) is a highly effective treatment in patients with autoimmune diseases (AID). AutoHSCT achieved long-term remission in patients with relapsed refractory and secondary progressive multiple sclerosis (Muraro 2017), superior to their previous standard of care (Burt 2019). AutoHSCT in scleroderma patients achieved superior outcomes in two randomized studies (Tyndall 2014, Sullivan 2018). These impressive results are achieved by both eradication of autoreactive immune effector cells and re-establishment of a self-tolerant immune system, i.e., immune system reset. However, only a fraction of eligible patients undergo autoHSCT, in part due to toxicity associated with current conditioning regimens that remove the disease-causing cells. To enable more patients to benefit from immune reset without debilitating chemotherapy, we generated novel anti-human CD45 ADCs that cross react with NHP and evaluated these for the ability to deplete hematopoietic cells in vitro and in vivo (Fig.1). In vitro the CD45-ADC efficiently killed human CD34+ progenitors and peripheral CD3+ T cells from both healthy donors and MS patients. In vivo in humanized NSG mice, single doses of the CD45-ADCs were well-tolerated and led to depletion of human hematopoietic cells in BM (Fig. 1A) and periphery. In NHPs, single doses of CD45-ADCs were well tolerated and depleted BM HSCs and peripheral lymphocytes (Fig.1B). CD45-ADC treatment of hNSGs with sclerodermatous xenoGVHD resulted in resolution of symptoms (Fig. 1C). To model the complete immune reset approach in mouse models of AID, we generated a tool anti-mouse CD45 ADC. A single-dose enabled full myeloablation (>99% depletion of LT-HSCs) and complete donor chimerism with congenic HSCT (>90% chimerism at 16 weeks). In an adoptive transfer model of type I diabetes, treatment with a single dose of CD45-ADC and congenic HSCT led to disease prevention. In a murine model of MS EAE, a single dose of the CD45-ADC followed by congenic HSCT enabled full donor chimerism; treatment prior to disease onset significantly delayed disease onset and reduced disease severity; treatment after disease onset also halted progression of symptoms. These data demonstrate that CD45-ADC conditioning followed by congenic HSCT is sufficient for full myeloablation and immune reset. Experiments are ongoing, and evaluation of this ADC in murine models of diabetes and arthritis will be presented. These results indicate that targeted immune depletion with a single dose of CD45-ADC may be sufficient to enable auto-HSCT and immune reset in multiple AID indications. Targeted conditioning with CD45-ADC may enable more patients to benefit from immune reset through removal of pathogenic cells and autoHSCT without the morbidity and mortality associated with current chemotherapeutic conditioning.