Immune escape of DNMT3A R882 mutant hematopoietic stem and progenitor cells in clonal hematopoiesis

• Applicant: Dr. Patrick Stelmach
• Subject Area: Hematology, Oncology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540450219

Hematopoietic stem cells (HSCs) acquire somatic mutations in an age-dependent manner. Some of these mutations confer a Darwinian fitness advantage to the cell and fuel clonal outgrowth. The presence of driver mutations in blood cells from otherwise healthy individuals characterizes the common age-related phenomenon termed clonal hematopoiesis (CH). CH predisposes individuals to an increased risk of developing blood cancer and also to a number of other diseases including atherosclerotic cardiovascular disease. It is unknown how driver mutations confer a fitness advantage to mutant blood cells promoting competitive clonal outgrowth. DNMT3A (DNA methyltransferase 3A) mutations are the most common drivers of this state. To date, no specific surface marker patterns have been identified to enrich for such mutant blood cells. Since the clone size is often small with variant allele frequencies between 1-10%, mutated hematopoietic stem- and progenitor cells (HSPCs) are rare compared to the wealth of healthy wildtype (WT) cells. This condition hampers the characterization of clonal populations with CH-related driver mutations using any type of bulk analysis. In our prior work we used single-cell multi-omics to analyze CH in G-CSF mobilized peripheral blood samples from patients with multiple myeloma. The preliminary results indicate that DNMT3A R882 mutant HSPCs are characterized by lower HLA-DR expression compared to WT HSPCs within the same patient. This was demonstrated in the transcriptome and also on the surface protein level. The lower expression of HLA-DR may represent a mechanism of immune evasion potentially altering the T cell compartment. Starting from these descriptive results, the mechanisms will be comprehensively studied in FACS-sorted DNMT3A R882 mutant primary patient samples and also in model systems for clonal hematopoiesis (CRISPR/Cas9 engineered mutant HSCs and PDX models). Also, there will be a special focus on the T cell compartment in both, primary patient samples and PDX models. The aim is to understand whether and how the reduced HLA-DR expression can result in a survival advantage for mutated cells and which cell types are primarily affected. Ultimately, the aim is to study how CH mutant HSCs gain a competitive growth advantage and how CH-related driver mutations affect different progenitor cell subtypes. These studies will pave the way towards the identification of robust and specific surface protein expression patterns enabling the enrichment of mutant cell populations. This would be highly valuable not only for experimental settings but also for diagnostic and therapeutic purposes.

• DFG Programme: WBP Position