The upcoming 5th edition of the World Health Organization (WHO) Classification of Haematolymphoid Tumours is part of an effort to hierarchically catalogue human cancers arising in various organ systems within a single relational database. This paper summarizes the new WHO classification scheme for myeloid and histiocytic/dendritic neoplasms and provides an overview of the principles and rationale underpinning changes from the prior edition. The definition and diagnosis of disease types continues to be based on multiple clinicopathologic parameters, but with refinement of diagnostic criteria and emphasis on therapeutically and/or prognostically actionable biomarkers. While a genetic basis for defining diseases is sought where possible, the classification strives to keep practical worldwide applicability in perspective. The result is an enhanced, contemporary, evidence-based classification of myeloid and histiocytic/dendritic neoplasms, rooted in molecular biology and an organizational structure that permits future scalability as new discoveries continue to inexorably inform future editions.

Acquired mutations are pervasive across normal tissues. However, our understanding of the processes that drive transformation of certain clones to cancer is limited. Here we study this phenomenon in the context of clonal hematopoiesis (CH) and the development of therapy-related myeloid neoplasms (tMN). We find mutations are selected differentially based on exposures. Mutations in ASXL1 are enriched in current or former smokers, whereas cancer therapy with radiation, platinum and topoisomerase II inhibitors preferentially selects for mutations in DNA damage response (DDR) genes ( TP53, PPM1D, CHEK2 ). Sequential sampling provides definitive evidence that DDR clones outcompete other clones when exposed to certain therapies. Among cases where CH was previously detected, the CH mutation was present at tMN diagnosis. We identify the molecular characteristics of CH that increase risk of tMN. The increasing implementation of clinical sequencing at diagnosis provides an opportunity to identify patients at risk of tMN for prevention strategies.

Genomic analyses of cancer have identified recurrent point mutations in the RNA splicing factor-encoding genes SF3B1, U2AF1, and SRSF2 that confer an alteration of function. Cancer cells bearing these mutations are preferentially dependent on wild-type (WT) spliceosome function, but clinically relevant means to therapeutically target the spliceosome do not currently exist. Here we describe an orally available modulator of the SF3b complex, H3B-8800, which potently and preferentially kills spliceosome-mutant epithelial and hematologic tumor cells. These killing effects of H3B-8800 are due to its direct interaction with the SF3b complex, as evidenced by loss of H3B-8800 activity in drug-resistant cells bearing mutations in genes encoding SF3b components. Although H3B-8800 modulates WT and mutant spliceosome activity, the preferential killing of spliceosome-mutant cells is due to retention of short, GC-rich introns, which are enriched for genes encoding spliceosome components. These data demonstrate the therapeutic potential of splicing modulation in spliceosome-mutant cancers.

Key Points• Key biological features of MDSs are explained by NLRP3 inflammasome activation, which drives pyroptotic cell death and b-catenin activation.• Alarmin signals and founder gene mutations license this redox-sensitive inflammasome platform.Despite genetic heterogeneity, myelodysplastic syndromes (MDSs) share features of cytological dysplasia and ineffective hematopoiesis. We report that a hallmark of MDSs is activation of the NLRP3 inflammasome, which drives clonal expansion and pyroptotic cell death. Independent of genotype, MDS hematopoietic stem and progenitor cells (HSPCs) overexpress inflammasome proteins and manifest activated NLRP3 complexes that direct activation of caspase-1, generation of interleukin-1b (IL-1b) and IL-18, and pyroptotic cell death. Mechanistically, pyroptosis is triggered by the alarmin S100A9 that is found in excess in MDS HSPCs and bone marrow plasma. Further, like somatic gene mutations, S100A9-induced signaling activates NADPH oxidase (NOX), increasing levels of reactive oxygen species (ROS) that initiate cation influx, cell swelling, and b-catenin activation. Notably, knockdown of NLRP3 or caspase-1, neutralization of S100A9, and pharmacologic inhibition of NLRP3 or NOX suppress pyroptosis, ROS generation, and nuclear b-catenin in MDSs and are sufficient to restore effective hematopoiesis. Thus, alarmins and founder gene mutations in MDSs license a common redox-sensitive inflammasome circuit, which suggests new avenues for therapeutic intervention. (Blood. 2016;128(25):2960-2975

Adeno-associated viruses (AAVs) are being developed as gene therapy vectors, and their efficacy could be improved by a detailed understanding of their viral capsid structures. AAV serotype 8 (AAV8) shows a significantly greater liver transduction efficiency than those of other serotypes, which has resulted in efforts to develop this virus as a gene therapy vector for hemophilia A and familial hypercholesterolemia. Pseudotyping studies show that the differential tissue tropism and transduction efficiencies exhibited by the AAVs result from differences in their capsid viral protein (VP) amino acids. Towards identifying the structural features underpinning these disparities, we report the crystal structure of the AAV8 viral capsid determined to 2.6-Å resolution. The overall topology of its common overlapping VP is similar to that previously reported for the crystal structures of AAV2 and AAV4, with an eight-stranded ␤-barrel and long loops between the ␤-strands. The most significant structural differences between AAV8 and AAV2 (the best-characterized serotype) are located on the capsid surface at protrusions surrounding the two-, three-, and fivefold axes at residues reported to control transduction efficiency and antibody recognition for AAV2. In addition, a comparison of the AAV8 and AAV2 capsid surface amino acids showed a reduced distribution of basic charge for AAV8 at the mapped AAV2 heparin sulfate receptor binding region, consistent with an observed non-heparin-binding phenotype for AAV8. Thus, this AAV8 structure provides an additional platform for mutagenesis efforts to characterize AAV capsid regions responsible for differential cellular tropism, transduction, and antigenicity for these promising gene therapy vectors.