Genetic Ablation of CD33 in HSC to Broaden the Therapeutic Index of CD33-directed Immunotherapy in Patients with AML

CRISPR/Cas9-mediated inactivation of CD33 in hematopoietic stem cells (HSC) may broaden the therapeutic index of CD33-directed immunotherapy for patients with AML by rendering healthy hematopoietic stem and progenitor cells (HSPC) resistant to escalating doses and/or shorter dosing intervals of the CD33-specific antibody-drug conjugate (ADC) Gemtuzumab-ozogamicin (GO).

In this proof of concept trial, we will develop a platform for genome editing of CD34+ HSC and demonstrate the feasibility, safety and efficacy of this approach for targeted therapy of AML.

Upon implementation, the platform shall be used for innovative clinical trials in diverse types of cancer. Outside of leukemias, autologous HSC could be used to ease the procedure.

Patients with relapsed AML after allogeneic hematopoietic stem cell transplantation will be transplanted with CD33-deleted CD34+ HSC derived from the initially matched family donor.

Upon HSC engraftment, patients will be treated with escalating doses of the anti-CD33 antibodydrug conjugate Gemtuzumab-Ozogamicin (GO). A conditioning regimen containing GO (d-14, d-11, d-8),Fludarabine 30 mg/m2 (d-6 to d-3) and Melphalan 140mg/m2 (d-2) is used prior to transplantation.

The clinical trial will be conducted at two trial sites in the University Hospitals in Heidelberg and Dresden.

25 patients will be assessed for eligibility and 12 patients will be allocated into the trial.

Key Inclusion Criteria:

• confirmed AML according to the WHO classification
• relapsed disease after allo-SCT from an HLA-identical family donor (≥ 2 months after allo-SCT at time of inclusion)
• ≤ 29% of bone marrow blasts as detected by cytomorphology or immunohistochemistry
• age ≥ 18 years
• confirmed CD33 expression on leukemic blasts at current relapse (as detected by flow cytometry)
• adequate organ function:

• Renal function defined as: serum creatinine of ≤ 2x ULN or eGFR ≥ 30 mL/min/1.73 m2
• Liver function defined as:

• ALT ≤ 3 times the ULN for the respective age
• Bilirubin ≤ 2.0 mg/dl with the exception of patients with hyperbilirubinemia explained by Gilbert-Meulengracht syndrome (may be included if total bilirubin is ≤ 3.0 x ULN and direct bilirubin ≤ 1.5 x ULN) or extrahepatic disease (e.g. chronic hemolytic anemia)
• Minimum level of pulmonary reserve defined as ≤ grade 1 dyspnea and pulse oxygenation > 90% on room air
• Hemodynamic stability and LVEF ≥ 40% as confirmed by echocardiogram
• Absolute lymphocyte count (ALC) ≥ 100/mm3

Key Exclusion Criteria:

• ECOG performance status >2
• Confirmed CNS involvement
• Acute or chronic Graft versus Host disease (GvHD)
• Availability of other curative standard treatment options
• Prior treatment with GO
• Prior hepatic veno-occlusive disease (VOD) or sinusoidal obstruction syndrome (SOS)
• Uncontrolled active hepatitis B or C
• HIV-positivity
• Uncontrolled bacterial, viral or fungal infection
• Participation in another clinical trial at the time of screening
• Organ dysfunction (liver, kidney, lung, heart) that is a contraindication for conditioning therapy
• Severe concomitant disease (e.g. uncontrolled arterial hypertension, heart failure NYHA III-IV, uncontrolled diabetes mellitus, uncontrolled hyperlipidemia)
• Unstable angina and/or myocardial infarction within 3 months prior to screening
• Pregnant or nursing (lactating) women