Effect of CD34⁺ Total/Myeloid CD34⁺ Cell Progenitors and B-Lymphoid Progenitors Within the Bone Marrow Grafts on the Hematopoietic Recovery After Hematopoietic Stem Cell Transplantation.

OBJECTIVES: The influence of CD34⁺ cells on transplant outcomes following hematopoietic stem cell transplantation remains controversial. A minimum of 2.0 to 2.5 million CD34⁺ cells/kg of patient weight is requested for a rapid and durable engraftment. The aim of this study was to detect the ratio of CD34+ B-lymphoid progenitors (hematogones) in bone marrow grafts and investigate their effects on hematopoietic recovery after transplant. MATERIALS AND METHODS: Our study included 41 patients who received a bone marrow graft from their HLA-matched donor from 2016 through 2019. The CD34⁺ cell numbers within the graft were detected using Stem-Kit (Beckman Coulter). The ratio of CD34⁺ hematogones was determined either by their light scatter characteristics or by the detection of CD34, CD19, or CD10 coexpressing cells in a separate tube. RESULTS: The median number of CD34⁺ cells was 5.9 × 106/kg (0.8-14.3 × 106/kg). The CD34⁺ cells consisted of 71% (range, 35.7%-100%) and 29% (range, 5.7%-64.3%) myeloid and B-lymphoid progenitors, respectively. Percentage of CD34⁺ (P < .001) and total (P < .001) hematogones in correlation with donor age. Time of neutrophil engraftment was significantly longer (P = .039) when total infused CD34⁺ cell content was <3 × 106/kg. CONCLUSIONS: A remarkable population of hematogones within the CD34⁺ cell pool was detected in bone marrow grafts. Detection of the ratio of hematogones and most primitive stem cells (CD34⁺CD90⁺CD38⁻) may overall provide more information to build a better correlation between CD34⁺ cell content and the recovery of bone marrow.

Leukemic stem cells shall be searched in the bone marrow before "tyrosine kinase inhibitor-discontinuation" in chronic myeloid leukemia.

BACKGROUND: Leukemic stem cells (LSCs) of chronic myeloid leukemia (CML), persisting in the bone marrow (BM) niche, could be responsible for the relapses within the patients of whom the treatment-free remission (TFR) had been attempted. We assessed the presence of the CML LSCs in the peripheral blood (PB) and concurrently in the BM in the patients with chronic-phase CML (CP CML). PATIENTS AND METHODS: Thirty-eight patients with CP CML were included into the study. CD45+ /CD34+ /CD38- cells with positive CD26 expression were considered as CML LSCs (CD26+ LSC) by using multiparameter flow cytometry (FCM). RESULTS: Mean BCR-ABL, PB LSC, and BM LSC were 58.528 IS (37.405-83.414 IS), 237.5 LSC/µL (16-737.5 LSC/µL), and 805 LSC/106  WBCs (134.6-2470 LSC/106  WBCs), respectively, in newly diagnosed CML patients. In the patients with BCR-ABL positive hematopoiesis, mean BCR-ABL, PB LSCs, and BM LSCs were 30.09 IS (0.024-147.690 IS), 13.5 LSC/µL (0-248.7 LSC/µL) and 143.5 LSC/106  WBCs (9-455.2 LSC/106  WBCs), respectively. No CML LSCs were detected in PB of patients who achieved deep molecular response (DMR). BM LSCs of the patients who were in DMR were 281.1 LSC/106  WBCs (3.1-613.7 LSC/106  WBCs). The amount of PB LSCs was highest in patients with newly diagnosed CML (P < .001). CONCLUSION: LSCs persisted in the BM of the patients with DMR, whereas there was no LSCs in the peripheral blood. The investigation of the CML LSCs in bone marrow before deciding TKI discontinuation could be justified to achieve and maintain stable TFR.