During embryogenesis the hematopoietic system develops through distinct waves that generate progenitors with increasing lineage potential, ultimately producing haematopoietic stem cells (HSCs). In vitro differentiation of human pluripotent stem cells (hPSCs) follows the early steps of haematopoietic development but the production of HSCs has proven more challenging. To study the dynamics and heterogeneity of hematopoietic progenitor cells generated in vitro from hPSCs, we performed RNA sequencing of over 10000 CD235a - CD43 + single cells. We identified the transcriptome of naïve progenitors and those primed toward erythroid, megakaryocyte and leukocyte lineages, and revealed their markers by clustering, trajectory analyses and functional assays. CD44 marks naïve clonogenic progenitors that express the transcription factor, LMO4 and can be expanded upon BMP4 stimulation. Naïve progenitors give rise to primed CD326 + erythroid, ICAM2 + CD9 + megakaryocyte, and monocyte, neutrophil and eosinophil progenitors. We have generated an online dataset of human hematopoietic progenitors and their transcriptional remodelling upon lineage priming.

The two sides of trauma-induced coagulopathy, the hypocoagulable and the hypercoagulable states, are poorly understood. To identify potential mechanisms for venous thromboembolism and bleeding after acute trauma, we estimated changes in circulating procoagulant microparticles (MPs) and thrombin activity during hospitalization for trauma.
Whole blood was collected by venipuncture into 3.2% trisodium citrate at 0, 6, 12, 24, and 72 hours after injury and discharge. Platelet-poor plasma was harvested and stored at -80°C until analysis. Thrombin generation was determined using the calibrated automated thrombogram (CAT), reported as lag time (minutes), peak height (nM thrombin), and time to reach peak height (ttPeak, minutes). The concentration of total procoagulant MPs (number/μL) was measured by flow cytometry. Data are presented as median (interquartile range [IQR]).
Among 443 trauma patients (1,734 samples; Injury Severity Score [ISS], 13.0 [IQR, 6.0-22.0]; hospital length of stay, 4.0 days [IQR, 2.0-10.0]; age, 48 years [IQR, 28-65]; 70.7% male; 95% with blunt mechanism; mortality, 3.2%), no discernable patterns in thrombin generation or MP concentration were observed over time. The peak height and MPs were significantly different from healthy volunteers and were 337 nM (IQR, 285-395) and 400/μL plasma (IQR, 211-772), respectively. Extreme (defined as highest or lowest 5%) values reflecting a possible "hypercoagulable state" (lag time ≤ 1.98, peak height ≥ 486.2, ttPeak ≤ 3.61, and total procoagulant MP ≥ 2,278) were reached within 12 hours after acute trauma, while extreme values representing a possible "hypocoagulable state" (lag time ≥ 18.6, peak height ≤ 17.8, and ttPeak ≥ 29.45) were not reached until 1 day to 3 days.
Although there was no predictable pattern of coagulopathy observed in each patient after trauma, those who reached extreme values did so relatively early after injury. These findings should be taken into account when designing risk model tools involving coagulation laboratory parameters.
Epidemiologic study, level III.