Mortality and burden of post-COVID-19 syndrome have reduced with time across SARS-CoV-2 variants in haematology patients.

Haematology patients contracting SARS-CoV-2 were identified at the start of the pandemic to be at higher risk of death or of persistent symptoms (post-COVID-19 syndrome). As variants with altered pathogenicity have emerged, uncertainty remains around how that risk has changed. We prospectively set up a dedicated post-COVID-19 clinic to monitor haematology patients infected with COVID-19 from the start of the pandemic. In total, 128 patients were identified and telephone interviews were conducted with 94 of 95 survivors. Ninety-day mortality attributed to COVID-19 has fallen sequentially from 42% for the Original and Alpha strains to 9% and to 2% for the Delta and Omicron variants respectively. Furthermore, the risk of post-COVID-19 syndrome in survivors has fallen from 46% for the Original or Alpha strains to 35% for Delta and 14% for the Omicron strain. Since vaccine uptake has been nearly universal in haematology patients, it is not possible to determine whether improved outcomes reflect the reduced pathogenicity of the virus, or widespread vaccine deployment. Whilst mortality and morbidity remain higher in haematology patients than in the general population, our data suggest that the absolute risks are now significantly lower. Given this trend, we believe clinicians should initiate conversations about risk with their patients on whether to maintain any self-imposed social isolation.

In utero origin of myelofibrosis presenting in adult monozygotic twins.

The latency between acquisition of an initiating somatic driver mutation by a single-cell and clinical presentation with cancer is largely unknown. We describe a remarkable case of monozygotic twins presenting with CALR mutation-positive myeloproliferative neoplasms (MPNs) (aged 37 and 38 years), with a clinical phenotype of primary myelofibrosis. The CALR mutation was absent in T cells and dermal fibroblasts, confirming somatic acquisition. Whole-genome sequencing lineage tracing revealed a common clonal origin of the CALR-mutant MPN clone, which occurred in utero followed by twin-to-twin transplacental transmission and subsequent similar disease latency. Index sorting and single-colony genotyping revealed phenotypic hematopoietic stem cells (HSCs) as the likely MPN-propagating cell. Furthermore, neonatal blood spot analysis confirmed in utero origin of the JAK2V617F mutation in a patient presenting with polycythemia vera (aged 34 years). These findings provide a unique window into the prolonged evolutionary dynamics of MPNs and fitness advantage exerted by MPN-associated driver mutations in HSCs.

Impact of isolated germline JAK2V617I mutation on human hematopoiesis.

The association between somatic JAK2 mutation and myeloproliferative neoplasms (MPNs) is now well established. However, because JAK2 mutations are associated with heterogeneous clinical phenotypes and often occur as secondary genetic events, some aspects of JAK2 mutation biology remain to be understood. We recently described a germline JAK2V617I mutation in a family with hereditary thrombocytosis and herein characterize the hematopoietic and signaling impact of JAK2V617I. Through targeted sequencing of MPN-associated mutations, exome sequencing, and clonality analysis, we demonstrate that JAK2V617I is likely to be the sole driver mutation in JAK2V617I-positive individuals with thrombocytosis. Phenotypic hematopoietic stem cells (HSCs) were increased in the blood and bone marrow of JAK2V617I-positive individuals and were sustained at higher levels than controls after xenotransplantation. In signaling and transcriptional assays, JAK2V617I demonstrated more activity than wild-type JAK2 but substantially less than JAK2V617F. After cytokine stimulation, JAK2V617I resulted in markedly increased downstream signaling compared with wild-type JAK2 and comparable with JAK2V617F. These findings demonstrate that JAK2V617I induces sufficient cytokine hyperresponsiveness in the absence of other molecular events to induce a homogeneous MPN-like phenotype. We also provide evidence that the JAK2V617I mutation may expand the HSC pool, providing insights into both JAK2 mutation biology and MPN disease pathogenesis.