To characterize the growth of cord blood progenitor cells, single nonadherent, low-density, T-lymphocyte-depleted CD34 cells were sorted by flow cytometer with an autoclone device into single wells containing culture medium and cytokines. These cells were evaluated for proliferation and for replating ability of their progeny. This latter effect is used as a measure of self-renewal capacity. Colony formation was assessed in 1 degree wells containing various cytokines, alone and in combination, and single colonies deriving after 21 days in semisolid medium were replated into 2 degree wells in the presence of the combination of purified preparations of recombinant human steel factor (SF, a c-kit ligand), granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), interleukin-3 (IL-3), and erythropoietin (Epo). Replating of single colonies was performed also for 3 degrees, 4 degrees, and 5 degrees cultures. In the presence of serum, colony formation was observed in > 66% of the wells stimulated with the combination of Epo, SF, GM-CSF, G-CSF, and IL-3, and more than 39% of the colonies formed in these 1 degree wells were very large in size (> 2.5 mm in diameter, dense in the center, and containing > 10(4) cells/colony). The replating efficiency of these large colonies was up to 93% with generation of subsequent colonies of very large size. Replating could be shown for up to five generations. The cells in these colonies were large, nonspecific esterase positive, and contained large amounts of cytoplasm with one or more nuclei containing several nucleoli per nucleus. Smaller colonies (1 to 2.5 mm in diameter and dense in the center) containing similar cells and making up an additional 14% of the colonies formed in 1 degree wells also showed extensive replating capacity, including generation of larger colonies. These colony-forming cells are likely similar to the murine macrophage high-proliferative potential colony-forming cells. The cells giving rise to these colonies are present in about eightfold higher frequency in cord blood than in adult bone marrow. These cells may at least in part be associated with the successful hematopoietic repopulating capacity of umbilical cord blood cells.

In the absence of conclusive assays capable of determining the functionality of ex vivo expanded human hematopoietic progenitor cells, we combined cell tracking with the membrane dye PKH2, immunostaining for CD34, and limiting dilution analysis to estimate the frequency of long-term hematopoietic culture-initiating cells (LTHC-ICs) among de novo-generated CD34+ cells. Umbilical cord blood (CB) and bone marrow (BM) CD34+ cells were stained with PKH2 on day 0 and cultured with stem cell factor (SCF) and interleukin-3 (IL-3) in short-term stromal cell-free suspension cultures. Proliferation of CD34+ cells in culture was tracked through their PKH2 fluorescence relative to day 0 and the continued expression of CD34. As such, it was possible to identify cells that had divided while maintaining the expression of CD34 (CD34+PKH2dim) and others that expressed CD34 but had not divided (CD34+PKH2bright). In all such cultures, a fraction of both BM and CB CD34+ cells failed to divide in response to cytokines and persisted in culture for up to 10 days as CD34+PKH2bright cells. Between days 5 and 7 of culture, CD34+PKH2bright and CD34+PKH2dim cells were sorted in a limiting dilution scheme into 96-well plates prepared with medium, SCF, IL-3, IL-6, granulocyte-macrophage colony-stimulating factor, and erythropoietin. Cells proliferating in individual wells were assayed 2 weeks later for their content of clonogenic progenitors and the percentage of negative wells was used to calculate the frequency of LTHC-ICs in each population. Among fresh isolated BM and CB CD34+ cells, the frequencies of LTHC-ICs were 2.01% +/- 0.98% (mean +/- SEM) and 7.56% +/- 2.48%, respectively. After 5 to 7 days in culture, 3.00% +/- 0.56% of ex vivo-expanded BM CD34+PKH2bright cells and 4.46% +/- 1.10% of CD34+PKH2dim cells were LTHC-ICs. In contrast, the frequency of LTHC-IC in ex vivo expanded CB CD34+ cells declined drastically, such that only 3.87% +/- 2.06% of PKH2bright and 2.29% +/- 1.75% of PKH2dim cells were determined to be initiating cells after 5 to 7 days in culture. However, when combined with a calculation of the net change in the number of CD34+ cells in culture, the sum total of LTHC-ICs in both BM and CB cells declined in comparison to fresh isolated cells, albeit to a different degree between the two tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Interleukin-9 receptor (IL-9R) complex consists of a ligand-specific ␣ chain and IL-2R ␥ chain. In this study, two regions in the cytoplasmic domain of human IL-9R␣ were found to be important for IL-9-mediated cell growth. A membrane-proximal region that contains the BOX1 consensus sequence is required for IL-9-induced cell proliferation and tyrosine phosphorylation of Janus kinases (JAKs). Deletion of this region or internal deletion of the BOX1 motif abrogated IL-9-induced cell proliferation and signal transduction. However, substitution of the Pro-X-Pro in the BOX1 motif with Ala-X-Ala failed to abolish IL-9-induced cell proliferation but decreased IL-9-mediated tyrosine phosphorylation of JAK kinases, insulin receptor substrate-2, and signal transducer and activator of transcription 3 (STAT3) and expression of c-myc and junB. Another important region is downstream of the BOX1 motif and contains a STAT3 binding motif YLPQ. Deletion of this region significantly impaired IL-9-induced cell growth, activation of JAK kinases, insulin receptor substrate-2, and STAT3 and expression of early response genes. A point mutation changing YLPQ into YLPA greatly reduced IL-9-induced activation of STAT3 and expression of c-myc but did not affect cell proliferation. These results suggest that cooperation or cross-talk of signaling molecules associated with different domains of IL-9R␣ other than STAT3 is essential for IL-9-mediated cell growth. Interleukin 9 (IL-9)1 is a T cell-derived multifunctional growth factor that exerts its effects on activated T cells, B cells, mast cells, and hematopoietic progenitors (1, 2). The in vitro biological functions of IL-9 include its ability to stimulate proliferation of activated T cells, to enhance production of immunoglobulin in B cells, and to promote proliferation and differentiation of mast cells and hematopoietic progenitors (3-7). The involvement of IL-9 in lymphomagenesis has been suggested by in vivo studies (8) in which a higher susceptibility to T cell lymphoma was observed in transgenic mice expressing IL-9 constitutively and by in vitro experiments (9) in which IL-9 has been shown to protect mouse lymphoma cells from dexamethasone-induced apoptosis. The functions of IL-9 are mediated by the IL-9 receptor (IL-9R), which consists of a ligand-specific ␣ chain and IL-2 receptor (IL-2R) ␥ chain. IL-2R ␥ chain, normally referred to as the common ␥ chain (␥ c chain), is shared by receptors for IL-2, IL-4, IL-7, IL-9, and IL-15 (10 -13). Some of the signaling pathways elicited by these cytokines are quite similar, which probably explains in part the functional redundancy of these cytokines.IL-9R ␣ chain (IL-9R␣) is IL-9-specific and is responsible for IL-9 binding. The cDNAs encoding mouse and human IL-9R␣ have been cloned (14 -15). IL-9R␣ belongs to the hematopoietic receptor superfamily and has no intrinsic tyrosine kinase motif in its cytoplasmic region. Several homologous sequences, such as the BOX1 consensus sequence and a serine-rich region, which were demonstrated to be import...

Although sustained production of committed human hematopoietic progenitor cells in long-term bone marrow cultures (LTBMC) is well documented, evidence for the generation and expansion of human primitive hematopoietic progenitor cells (PHPC) in such cultures is lacking. For that purpose, we attempted to determine if the human high proliferative potential colony-forming cell (HPP-CFC), a primitive hematopoietic marrow progenitor cell, is capable of generation and expansion in vitro. To that effect, stromal cell-free LTBMC were initiated with CD34+ HLA-DR-CD15- rhodamine 123dull bone marrow cells and were maintained with repeated addition of c-kit ligand and a synthetic interleukin-3/granulocyte-macrophage colony-stimulating factor fusion protein. By day 21 of LTBMC, a greater than twofold increase in the number of assayable HPP-CFC was detected. Furthermore, the production of HPP-CFC in LTBMC continued for up to 4 weeks, resulting in a 5.5-fold increase in HPP-CFC numbers. Weekly phenotypic analyses of cells harvested from LTBMC showed that the number of CD34+ HLA-DR- cells increased from 10(4) on day 0 to 56 CD34+ HLA-DR- cells increased from 10(4) on day 0 to 56 x 10(4) by day 21. To examine further the nature of the in vitro HPP-CFC expansion, individual HPP- CFC colonies were serially cloned. Secondary cloning of individual, day 28 primary HPP-CFC indicated that 46% of these colonies formed an average of nine secondary colony-forming unit--granulocyte-macrophage (CFU-GM)--derived colonies, whereas 43% of primary HPP-CFC gave rise to between one and six secondary HPP-CFC colonies and 6 to 26 CFU-GM. These data show that CD34+ HLA-DR- CD15- rhodamine 123dull cells represent a fraction of human bone marrow highly enriched for HPP-CFC and that based on their regeneration and proliferative capacities, a hierarchy of HPP-CFC exists. Furthermore, these studies indicate that in the presence of appropriate cytokine stimulation, it is possible to expand the number of PHPC in vitro.

Some people remain healthier throughout life than others but the underlying reasons are poorly understood. Here we hypothesize this advantage is attributable in part to optimal immune resilience (IR), defined as the capacity to preserve and/or rapidly restore immune functions that promote disease resistance (immunocompetence) and control inflammation in infectious diseases as well as other causes of inflammatory stress. We gauge IR levels with two distinct peripheral blood metrics that quantify the balance between (i) CD8+ and CD4+ T-cell levels and (ii) gene expression signatures tracking longevity-associated immunocompetence and mortality-associated inflammation. Profiles of IR metrics in ~48,500 individuals collectively indicate that some persons resist degradation of IR both during aging and when challenged with varied inflammatory stressors. With this resistance, preservation of optimal IR tracked (i) a lower risk of HIV acquisition, AIDS development, symptomatic influenza infection, and recurrent skin cancer; (ii) survival during COVID-19 and sepsis; and (iii) longevity. IR degradation is potentially reversible by decreasing inflammatory stress. Overall, we show that optimal IR is a trait observed across the age spectrum, more common in females, and aligned with a specific immunocompetence-inflammation balance linked to favorable immunity-dependent health outcomes. IR metrics and mechanisms have utility both as biomarkers for measuring immune health and for improving health outcomes.