Flow cytometric measurement of DNA S-phase in human bone marrow cells: correcting for peripheral blood contamination

Identification of critical hemodilution by artificial intelligence in bone marrow assessed for MRD analysis in acute myeloid leukemia: the Cinderella method

Minimal residual disease (MRD) detection is a strong predictor for survival and relapse in acute myeloid leukemia (AML). MRD can be either determined by molecular assessment strategies or via multiparameter flow cytometry. The degree of bone marrow (BM) dilution with peripheral blood (PB) increases with aspiration volume causing consecutive underestimation of the residual AML blast amount. In order to prevent false-negative MRD results, we developed Cinderella, a simple automated method for one-tube simultaneous measurement of hemodilution in BM samples and MRD level. The explainable artificial intelligence (XAI) Cinderella was trained and validated with the digital raw data of a flow cytometric "8-color" AML-MRD antibody panel in 126 BM and 23 PB samples from 35 patients. Cinderella predicted PB dilution with high accordance compared to the results of the Holdrinet formula (Pearson's correlation coefficient r = 0.94, R2 = 0.89, p < 0.001). Unlike conventional neuronal networks Cinderella calculated the distributions of 12 different cell populations that were assigned to true hematopoietic counterparts as a Human in the Loop (HIL) approach. Besides characteristic BM cells such as myelocytes and myeloid progenitor cells the XAI identified discriminating populations, which were not specific for BM or PB (e.g., T cell/ NK cell subpopulations, CD45 negative cells) and considered their frequency differences. Thus, Cinderella represents a HIL-XAI algorithm capable to calculate the degree of hemodilution in bone marrow samples with an AML MRD immunophenotype panel. It is explicable, transparent and paves a simple way to prevent false negative MRD reports. This article is protected by copyright. All rights reserved.

Rhythms in human bone marrow and blood cells

In 24h studies of bone marrow (BM), circadian stage-dependent variations were demonstrated in the proliferative activity of BM cells from subsets of 35 healthy diurnally active men. On an average, the percentage of total BM cells in deoxyribonucleic acid (DNA) synthesis phase was 188% greater at midday than at midnight (circadian rhythm: p = 0.018; acrophase or peak time of 13: 16h). Patients with malignant disease (n = 15) and a normal cortisol circadian rhythm showed higher fractions of BM cells in S-phase at midday. Colony-forming units--granulocyte/macrophage (CFU-GM), an indicator of myeloid progenitor cells, showed the same circadian variation as DNA S-phase (average range of change or ROC = 136%; circadian rhythm: p < 0.001; acrophase of 12:09h). Deoxyribonucleic acid S-phase and CFU-GM in BM both showed a circannual rhythm (p = 0.015 and 0.008) with an identical acrophase of August 12. The daily peak in BM glutathione content, a tripeptide involved in cellular defense against cytotoxic damage, preceded BM proliferative peaks by 4-5 h (ROC = 31-90%; circadian rhythm: p = 0.05; acrophase of 08:30h). Myeloid (ROC = 57%; circadian rhythm: p = 0.056; acrophase at 08:40h) and erythroid (ROC = 26%; circadian rhythm: p = 0.01; acrophase of 13:01h) precursor cells were positively correlated (r = 0.41; p < 0.001), indicating a circadian temporal relationship and equal influence on S-phase of total BM cells. Yield of positive selected CD34+ progenitor stem cells also showed significant circadian variation (ROC = 595%; circadian rhythm: p = 0.02; acrophase of 12:40h). Thus, the temporal synchrony in cell cycling renders BM cells more sensitive at specific times to hematopoietic growth factors and cell cycle-specific cytotoxic drugs. Moreover, proper timing of BM harvesting may improve progenitor cell yield. When using marker rhythms in the blood to allow for individualized timing of BM procedures, the times of low values in white blood corpuscles, neutrophils, and lymphocytes and high values in cortisol were predictive of the times of highest BM erythroid, myeloid, and total S-phase numbers occurring in the following 12 h.

Variation in cell yield and proliferative activity of positive selected human CD34+ bone marrow cells along the circadian time scale

Variations in cell yield and proliferative activity of human bone marrow (BM) progenitor cells were determined with flow cytometry along the 24-h (circadian) time scale. Equal volumes of BM were aspirated every 5 h, altogether 5 times in 5 healthy men. An average 6-fold higher yield of positive selected CD34+ cells occurred in each subject when BM was aspirated during the daytime and late afternoon, while a lower yield occurred during the night. Using all CD34+ cell yield data normalized to percentage of mean, a significant time-effect was found by ANOVA (p = 0.02) and a significant circadian rhythm was detected by the least-squares fit of a 24 h cosine (p = 0.02). The 95% confidence limits of the acrophase (time of highest values) were computed to be at midday between 10:24 and 14:48 h. A highly significant correlation (p = 0.001) was found between proliferation of positive selected CD34+ cells and the more mature myeloid precursor cells from the same BM aspirates, suggesting a common temporal pattern along the circadian time scale. However, no correlation was demonstrated between proliferation and cell yield of CD34+ selected cells, suggesting that mechanisms other than variation in proliferation may cause the circadian rhythm in stem cell yield. These circadian variations in stem cell yield and proliferation suggest that proper timing within 24 h may potentially be important regarding outcome from progenitor cell harvesting and treatment with haematopoietic growth factors.

Circadian cell cycle variations of erythro- and myelopoiesis in humans

By use of a multiparameter flow cytometric method with specific surface markers, circadian (24-h) variations in cell cycle distribution have been studied in 19 healthy male volunteers by sampling bone marrow (BM) every 4-5 h during 24-h periods. Admixture of peripheral blood during the sampling was specifically adjusted for, and the fractions of cells in DNA synthetic phase were measured for different hemopoietic cell lineages. Significant circadian variations in DNA S-phase were demonstrated both in myelo- and erythropoiesis of the human BM, with 75% (myeloid) and 80% (erythroid) of the volunteers showing highest activity (values) of DNA S-phase during the day and lowest activity (values) between midnight and 04:00 h. A temporal relationship in the circadian variation of S-phase and G2/M-phase was demonstrated between the myeloid and erythroid cell lineages. The highest fractions of S-phase cells were found in erythropoiesis, while the highest circadian stage dependent variation was found in myelopoiesis. The existence of a similar phasing in DNA synthetic activity for myelopoietic and erythropoietic cells in the human bone marrow indicates that the circadian rhythmicity of hemopoiesis may be caused by a common regulatory mechanism. These findings may be relevant with regard to optimizing the use of cytotoxic drugs and hemopoietic growth factors by taking into consideration the intrinsic (endogenous) circadian variation in proliferative activity of human BM subpopulations.