The biology and phenotypic consequences of B-cell clonality driven by mosaic chromosomal alterations

/ABSTRACT B-cell clones in blood are commonly detectable in individuals over the age of 40 years, categorized as high- count monoclonal B-cell lymphocytosis (HC-MBL) when present at a clone size of 500 to 5000 cells/μl. HC-MBL predisposes to chronic lymphocytic leukemia (CLL), other cancers, and infections, but the full spectrum of its phenotypic consequences is unknown due to the limited scale of studies thus far, which have relied on flow cytometric screening. CLL-initiating chromosomal alterations can arise in hematopoietic stem and progenitor cells (HSPCs) and penetrate into both the myeloid and lymphoid lineages. Immune dysfunction is a major source of morbidity in CLL and may underlie phenotypic consequences of HC-MBL. While miR-15/16 is a well- characterized CLL driver in del (13q) and its role in myeloid malignancies and T-cells has been studied, comprehensive, lineage-spanning studies of del (13q) and trisomy 12 in patient samples to uncover novel pathogenic mechanisms and potential therapeutic targets have been lacking. The applicant’s preliminary studies have identified a strong relationship of HC-MBL with mosaic chromosomal alterations (mCAs) – large somatic deletions and duplications of DNA segments – leading to a model for detecting HC-MBL using existing genetic and hematologic data in large biobanks. Preliminary studies have also revealed the presence of del (13q) and trisomy 12 beyond the B-cell lineage and the ability to detect these mCAs and their transcriptomic output in single-cell RNA-sequencing (scRNA-seq) of patient samples. Aim 1 will determine phenotypic consequences of HC-MBL in two large biobanks (n = 402,973) by performing a phenome-wide association study and test the hypothesis that immune-related diseases are more common in those with HC-MBL. Aim 2 will determine the impact of del (13q) and trisomy 12 on HSPC and mature blood cell biology through scRNA-seq analyses of bone marrow and blood samples from untreated CLL patients and test the hypothesis that these mutations exert cell- intrinsic effects on the biology of hematopoietic cells beyond their roles as drivers in the B-cell lineage. Successful completion of these aims will lay the foundation for developing risk mitigation strategies for HC-MBL, a common precancerous condition, and provide a deeper molecular understanding of initiating events and immune dysfunction in CLL, which could uncover novel therapeutic opportunities. The applicant, Dr. Aswin Sekar, is an oncologist at Dana-Farber Cancer Institute (DFCI), where he spends 80% of his time in research and 20% caring for patients with MBL, CLL and lymphomas. His five-year career development plan draws upon mentorship, collaborations, conferences, coursework, and seminars. Dr. Sekar’s primary mentor is Dr. Benjamin Ebert, a leader in hematologic malignancies and premalignant states with a long track record of mentoring trainees to independent positions. Dr. Sekar has assembled a committee of internationally recognized experts in MBL, CLL, hematopoiesis, and genetics to provide scientific and career mentorship. Dr. Sekar will leverage the exceptional environment at DFCI and Harvard to achieve his career goal of becoming an independent physician-scientist. Project Number: 1K08CA300940-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Aswin Sekar | Institution: DANA-FARBER CANCER INST, BOSTON, MA | Award Amount: $235,491 | Activity Code: K08 | Study Section: Special Emphasis Panel[ZRG1 CTH-K (83)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11299731