Key Points: CTLA-4 is enriched in the microenvironmental niche in cHL, and identifies a T-cell population largely distinct from PD-1 CD86, the natural ligand for CTLA-4, is enriched in the niche and expressed on HRS cells and a subset of TAMs that also express PD-L1

The spatial anatomy of hematopoiesis in the bone marrow (BM) has been extensively studied in mice and other preclinical models, but technical challenges have precluded a commensurate exploration in humans. Institutional pathology archives contain thousands of paraffinized BM core biopsy tissue specimens, providing a rich resource for studying the intact human BM topography in a variety of physiologic states. Thus, we developed an end-to-end pipeline involving multiparameter whole tissue staining, in situ imaging at single-cell resolution, and artificial intelligence–based digital whole slide image analysis and then applied it to a cohort of disease-free samples to survey alterations in the hematopoietic topography associated with aging. Our data indicate heterogeneity in marrow adipose tissue (MAT) content within each age group and an inverse correlation between MAT content and proportions of early myeloid and erythroid precursors, irrespective of age. We identify consistent endosteal and perivascular positioning of hematopoietic stem and progenitor cells (HSPCs) with medullary localization of more differentiated elements and, importantly, uncover new evidence of aging-associated changes in cellular and vascular morphologies, microarchitectural alterations suggestive of foci with increased lymphocytes, and diminution of a potentially active megakaryocytic niche. Overall, our findings suggest that there is topographic remodeling of human hematopoiesis associated with aging. More generally, we demonstrate the potential to deeply unravel the spatial biology of normal and pathologic human BM states using intact archival tissue specimens.

The clinicopathologic features of DNA methyltransferase 3A (DNMT3A)-mutated de novo acute myeloid leukemia (AML), and the significance of variant type, variant allele frequency (VAF), and multiple concomitant DNMT3A mutations, remain poorly defined. We examined 104 DNMT3A-mutated de novo AML patients from 2 major centers. Most (82%) had normal karyotype (NK); R882H variants were frequent(38%). The most commonly comutated genes included nucleophosmin (NPM1; 53%), Fms-related tyrosine kinase 3 (FLT3)–internal tandem duplication (25%), IDH1 (23%), IDH2 (23%), and TET2 (21%). Patients with high DNMT3A VAF at diagnosis (≥44%; DNMT3AHIGH) had more significant leukocytosis and higher blast counts in peripheral blood and bone marrow. DNMT3AHIGH cases were associated with much shorter event-free survival (EFS; 14.1 vs 56.8 months) and overall survival (OS; 18.3 months vs not reached) compared with cases of patients with low DNMT3A (DNMT3ALOW). Thirteen patients had 2 DNMT3A variants and similar VAFs at diagnosis that tracked together at multiple time points after chemotherapy and/or stem cell transplantation (SCT). In multivariable analyses performed in NK patients who received standard induction chemotherapy, presence of 2 DNMT3A mutations (hazard ratio [HR] = 3.192; P = .038) and SCT in first complete remission (HR = 0.295; P = .001) independently affected EFS; increasing marrow blast percentage (HR = 1.026; P = .025), high DNMT3A VAF (HR = 3.003; P = .010), and 2 DNMT3A mutations (HR = 4.816; P = .020) had independent effects on OS. These data support the adverse prognostic significance of DNMT3AHIGH reveal a novel association between 2 concomitant DNMT3A mutations and inferior outcome in DNMT3A-mutated de novo AML with a NK.