Exhaustion of the bone marrow progenitor cell reserve is associated with major events in severe limb ischemia

Lower numbers of progenitor cells (PCs) in peripheral blood (PB) have been associated with cardiovascular events in high-risk populations. Therapies aiming to increase the numbers of PCs in circulation have been developed, but clinical trials did not result in better outcomes. It is currently unknown what causes the reduction in PB PC numbers: whether it is primary depletion of the progenitor cell reserve, or a reduced mobilization of PCs from the bone marrow (BM). In this study, we examine if PB and BM PC numbers predict Amputation-Free Survival (AFS) in patients with Severe Limb Ischemia (SLI). We obtained PB and BM from 160 patients enrolled in a clinical trial investigating BM cell therapy for SLI. Samples were incubated with antibodies against CD34, KDR, CD133, CD184, CD14, CD105, CD140b, and CD31; PC populations were enumerated by flow cytometry. Higher PB CD34⁺ and CD133⁺ PC numbers were related to AFS (Both Hazard Ratio [HR_event] = 0.56, p = 0.003 and p = 0.0007, respectively). AFS was not associated with the other cell populations in PB. BM PC numbers correlated with PB PC numbers and showed similar HRs for AFS. A further subdivision based on relative BM and PB PC numbers showed that BM PC numbers, rather than mobilization, associated with AFS. Both PB and BM PC numbers are associated with AFS independently from traditional risk factor and show very similar risk profiles. Our data suggest that depletion of the progenitor cell reserve, rather than decreased PC mobilization, underlies the association between PB PC numbers and cardiovascular risk.