Circulating CD34 Positive Cells and Immunological Responses in Extremely Preterm Infants.

Abstract

Background: The dynamic changes of the hematopoietic system during fetal development may be disrupted by preterm birth. Hematopoietic stem and progenitor cell (CD34⁺) levels are poorly investigated in preterm infants, particularly in relation to immune responses and morbidities. This is partly because of low blood volumes, which raise ethical concerns and limit specific sampling for research studies. To overcome this problem, we used residual blood from routine clinical testing to monitor CD34⁺ cell counts in the first months of life. Our aim was to characterize the dynamics of circulating CD34⁺ cells and explore associations with prenatal and postnatal clinical events.

Methods: We retrieved residual blood samples from nine infants born <28 weeks gestational age (GA), collected from birth through eight postnatal weeks. CD34⁺ cell count was assessed using flow cytometry. The number of nucleated red and white blood cells, and hemoglobin concentration were also measured.

Results: Median (min-max) GA was 25+0 (22+3─27+5) weeks. CD34⁺ cell counts at birth ranged from 19 to 284 x 10⁶ cells/L. Between days 0 and 1, CD34⁺ cell count increased in four infants and decreased in four. By day 7, the proportion of CD34⁺ of total nucleated blood cells was significantly lower than at birth (p=0.018). High inter- and intra-individual variability in CD34⁺ cell count was observed. Notably, the highest CD34⁺ cell levels coincided with maternal or infant infections.

Conclusion: This pilot study demonstrates the feasibility of longitudinal monitoring of CD34⁺ hematopoietic stem and progenitor cells in extremely preterm infants using residual clinical blood samples. While limited by a small sample size, the study provides preliminary insights into early immune function and highlights directions for future research in larger cohorts.