Background/Purpose: Hematopoietic stem and progenitor cells (HSPC) are responsible for the lifelong production of immune cells. Accumulation of DNA damage occurs in HSPC during normal ageing, impacts immune regeneration and has been implicated in the increased risk of malignant transformation. Similarly, age-independent premature accumulation of DNA damage occurs in HSPC from rheumatoid arthritis (RA) patients. Among HSPC the CD34⁺CD38^–immunophenotype defines a rare primitive subpopulation of progenitor cells, enriched in their colony forming unit ability, and which numbers are increased in the elderly. In this study we characterized the frequency, phenotype and function of HSPC subpopulations in treatment naïve rheumatoid arthritis (RA) patients.

Methods: Peripheral blood circulating CD34⁺ cells were isolated from treatment naïve, recent onset, ACPA positive RA patients (n=19) and from age/sex matched healthy controls (HC, n=19). The frequency of viable HSPC subpopulations (7AAD^–/CD34⁺/CD38^+/-) and their proliferative responses (CFSE) were assessed by FACS. Clonogenicity was assessed in colony-forming cell (CFC) assays and DNA damage was quantified by single cell gel electrophoresis assay (comet assay). All results are shown as mean ± SEM, non-parametric tests were used for group comparisons.

Results: Treatment naïve RA patients have an increased proportion of circulating CD34⁺CD38^– HSPC (5.30 ± 0.84 % vs 2.83 ± 0.76 % respectively, p<0.05, n=9). The frequency of CD34⁺CD38^– does not change following 6 months of methotrexate treatment (5.21 ± 2.39 % vs 5.49 ± 2.20 %, p=0.375, n=3). Compared to HC, RA-CD34 produced fewer colonies  (n=7) [CFU-GEMM (1.82 ± 0.37 vs 4.71 ± 1.10 respectively, p<0.05), CFU-GM (6.89 ± 1.01 vs 18.54 ± 3.97 respectively, p<0.05) and BFU-E (10.71 ± 1.95 vs 15.43 ± 3.57 respectively, p>0.05)]; accrued DNA damage (32.25 ± 5.27% vs 7.63 ± 2.57% DNA in tail respectively, p<0.0001), and had impaired proliferative responses to hematopoietins (Day 4 expansion index (EI): 3.21 ± 0.20 vs 4.28 ± 0.28, p<0.01, n=11); and increased number of CD34⁺ that remained non-proliferating (generation 0: 27.42 ± 4.06 % vs 18.65 ± 2.74 % respectively, p<0.05, n=11).  The EI of RA-CD34⁺CD38^–HSPC was significantly reduced (3.61 ± 0.48 vs 5.00 ± 0.62 expansion index respectively, p<0.05, n=10).

Conclusion: The function of the most primitive HSPC subpopulations in treatment naïve RA patients is impaired mimicking the HSPC phenotype of healthy elderly individuals. The disruption of HSPC homeostasis is an early event in RA with potential implications in immune-regeneration and carcinogenesis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/increased-frequency-of-dysfunctional-hematopoietic-stem-and-progenitor-cell-subpopulations-in-treatment-naive-rheumatoid-arthritis-patients/