Gerald A. Colvin

Akt Signaling Regulates Side Population Cell Phenotype via Bcrp1 Translocation

Akt is an important regulator of cell survival, growth, and glucose metabolism in many cell types, but the role of this signaling molecule in hematopoietic stem cells is poorly defined. Side population (SP) cells are enriched for hematopoietic stem cell activity and are defined by their ability to efficiently efflux Hoechst 33342. Bone marrow from Akt1-null mice exhibited a reduced SP fraction. However, bone marrow cellularity, growth factor-responsive progenitor cultures, and engraftable stem cells were normal in these mice. Treatment of bone marrow with LY294002, an inhibitor of the Akt effector protein phosphatidylinositol 3-kinase, led to a reversible loss of the SP fraction. Bcrp1, which encodes the Hoechst dye transporter, was translocated from the membrane to the intracellular compartment under conditions that promote the SP-depleted state. Lentivirus-mediated overexpression of Akt1 in bone marrow markedly increased the SP fraction, whereas there was no effect on bone marrow from Bcrp-/- mice. These data suggest that Akt signaling modulates the SP cell phenotype by regulating the expression of Bcrp1.

Alteration of marrow cell gene expression, protein production, and engraftment into lung by lung-derived microvesicles: a novel mechanism for phenotype modulation.

Numerous animal studies have demonstrated that adult marrow‐derived cells can contribute to the cellular component of the lung. Lung injury is a major variable in this process; however, the mechanism remains unknown. We hypothesize that injured lung is capable of inducing epigenetic modifications of marrow cells, influencing them to assume phenotypic characteristics of lung cells. We report that under certain conditions, radiation‐injured lung induced expression of pulmonary epithelial cell‐specific genes and prosurfactant B protein in cocultured whole bone marrow cells separated by a cell‐impermeable membrane. Lung‐conditioned media had a similar effect on cocultured whole bone marrow cells and was found to contain pulmonary epithelial cell‐specific RNA‐filled microvesicles that entered whole bone marrow cells in culture. Also, whole bone marrow cells cocultured with lung had a greater propensity to produce type II pneumocytes after transplantation into irradiated mice. These findings demonstrate alterations of marrow cell phenotype by lung‐derived microvesicles and suggest a novel mechanism for marrow cell‐directed repair of injured tissue.

Clinical and pathological differences between human immunodeficiency virus-positive and human immunodeficiency virus-negative patients with plasmablastic lymphoma

Plasmablastic lymphoma (PBL) is a distinct variant of diffuse large B-cell lymphoma initially described in HIV-positive patients. Several studies have reported the occurrence of PBL in HIV-negative patients, but comparative data are lacking. The goal of this study was to compare the characteristics of HIV-positive and HIV-negative patients with PBL. A MEDLINE search was undertaken through August 2009 for cases of PBL in HIV-positive and HIV-negative patients. Cases were identified and clinicopathological data were gathered. χ2 was used to compare categorical and t-test to compare continuous variables between groups. Calculated Kaplan–Meier survival estimates were compared using the log-rank test. Cox proportional-hazard regression was used for multivariate analysis. From 228 identified cases of PBL, 157 were HIV-positive and 71 HIV-negative. HIV-positive patients were younger, and more likely to be men, present with oral involvement, respond to chemotherapy, and express CD20, CD56, and EBV-encoded RNA than HIV-negative patients. In univariate analysis, age ≥60, advanced stage, bone marrow involvement, no chemotherapy, Ki-67 expression >80%, and HIV-negative status were associated with worse overall survival. In multivariate analysis, advanced stage and no chemotherapy were independent adverse prognostic factors. In conclusion, HIV-positive and HIV-negative patients with PBL have different clinicopathological characteristics, including a better response to chemotherapy and longer survival in HIV-positive patients.

Quick sex determination of mouse fetuses.

We designed a rapid, simple and accurate PCR method to determine sexual identity of mouse fetuses collected on embryonic day 15. A multiplex PCR amplification was used to detect male-specific sequence (Sry) in DNA extracted from fetal livers through SDS denaturation followed by high salt extraction and precipitation. This extraction method resulted in sufficiently purified DNA in < 1 h and was suitable for PCR. The DNA obtained was amplified using a robot thermal cycler for 33 cycles. The reaction was performed in 50 microl, using two sets of primers specific for Sry gene (chromosome Y) and IL3 gene (chromosome 11). Amplification duration was 1.5 h. The assessment of the results was done by electrophoresis in 3% agarose run at high voltage. The 402 bp band (Sry) obtained identifies the male fetuses and the 544 bp product (IL3) confirms the correct amplification of the template DNA. The entire procedure took < 4 h. The specificity of the method was confirmed by fluorescent in situ hybridization using a specific male probe on cultured male and female neural stem cells. This method allowed the preparation and culture of pure male and female neural stem cells from fetal tissue.

Marrow Stem Cells Shift Gene Expression and Engraftment Phenotype with Cell Cycle Transit

We studied the genetic and engraftment phenotype of highly purified murine hematopoietic stem cells (lineage negative, rhodamine-low, Hoechst-low) through cytokine-stimulated cell cycle. Cells were cultured in interleukin (IL)-3, IL-6, IL-11, and steel factor for 0 to 48 h and tested for engraftment capacity in a lethally irradiated murine competitive transplant model. Engraftment showed major fluctuations with nadirs at 36 and 48 h of culture and recovery during the next G1. Gene expression of quiescent (0 h) or cycling (48 h) stem cells was compared with lineage positive cells by 3′ end PCR differential display analysis. Individual PCR bands were quantified using a 0 to 9 scale and results were visually compared using color-coded matrices. We defined a set of 637 transcripts expressed in stem cells and not expressed in lineage positive cells. Gene expression analyzed at 0 and 48 h showed a major shift from “stem cell genes” being highly expressed at 0 h and turned off at 48 h, while “cell division” genes were turned on at 48 h. These observations suggest stem cell gene expression shifts through cell cycle in relation to cell cycle related alterations of stem cell phenotype. The engraftment defect is related to a major phenotypic change of the stem cell.

Prognostic Factors in Chemotherapy-Treated Patients with HIV-Associated Plasmablastic Lymphoma

BACKGROUND Plasmablastic lymphoma (PBL) is a variant of diffuse large B-cell lymphoma commonly seen in the oral cavity of HIV-infected individuals. PBL has a poor prognosis, but prognostic factors in patients who have received chemotherapy have not been adequately evaluated. METHODS An extensive literature search rendered 248 cases of PBL, from which 157 were HIV(+). Seventy cases with HIV-associated PBL that received chemotherapy were identified. Whenever possible, authors of the original reports were contacted to complete clinicopathological data. Univariate analyses were performed calculating Kaplan-Meier estimates and compared using the log-rank test. RESULTS The mean age was 39 years, with a male predominance. The mean CD4(+) count was 165 cells/mm(3). Advanced clinical stage was seen in 51% and extraoral involvement was seen in 43% of the cases. The expression levels of CD20 and Epstein-Barr virus-encoded RNA were 13% and 86%, respectively. The overall survival duration was 14 months. In a univariate analysis, early clinical stage and a complete response to chemotherapy were associated with longer survival. There was no apparent difference in survival with regimens more intensive than cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP). CONCLUSIONS Patients with HIV-associated PBL have a poor prognosis. Prognosis is strongly associated with achieving a complete clinical response to CHOP or CHOP-like chemotherapy. The role of more intensive regimens is currently unclear. Further research is needed to improve responses using novel therapeutic agents and strategies.

Murine marrow cellularity and the concept of stem cell competition: geographic and quantitative determinants in stem cell biology

In unperturbed mice, the marrow cell numbers correlate with the stem cell numbers. High levels of long-term marrow engraftment are obtained with infusion of high levels of marrow cells in untreated mice. To address the issue of stem cell competition vs ‘opening space’, knowledge of total murine marrow cellularity and distribution of stem and progenitor cells are necessary. We determined these parameters in different mouse strains. Total cellularity in BALB/c mice was 530±20 million cells; stable from 8 weeks to 1 year of age. C57BL/6J mice had 466±48 million marrow cells. Using these data, theoretical models of infused marrow (40 million cells) replacing or adding to host marrow give chimerism values of 7.5 and 7.0%, respectively; the observed 8-week engraftment of 40 million male BALB/c marrow cells into female hosts (72 mice) gave a value of 6.91±0.4%. This indicates that syngeneic engraftment is determined by stem cell competition. Our studies demonstrate that most marrow cells, progenitors and engraftable stem cells are in the spine. There was increased concentration of progenitors in the spine. Total marrow harvest for stem cell purification and other experimental purposes was both mouse and cost efficient with over a four-fold decrease in animal use and a financial saving.

Homing of Purified Murine Lymphohematopoietic Stem Cells: A Cytokine-Induced Defect

This study was designed to establish a direct homing assay using purified lineage-negative Sca-1-positive (Lin(-) Sca(+)) murine bone marrow cells and to evaluate the effects of cytokines on homing. C57BL/6 Lin(-) Sca(+) marrow stem cells were labeled with 5-(and 6)-carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) and then injected by tail vein into untreated C57BL/6 mice. Marrow was harvested at various times after cell infusion and analyzed on a high-speed MoFlo cell sorter for fluorescent positive events, using a large event analysis, with at least 16 million total events analyzed. We have shown that homing of Lin(-) Sca(+) cells plateaus by 1 h, and at 3 h post-infusion is linear between 50,000 and 1,000,000 infused cells. This forms a base for a homing assay in which 250,000 CFDA-SE labeled Lin(-) Sca(+) marrow cells are infused and then recovered from marrow 3 h later, followed by a large-event fluorescence-activated cell sorting (FACS) analysis. We found that 7.45-9.32% of infused cells homed and that homing of stem cells cultured for 48 h in interleukin-3 (IL-3), IL-6, IL-11, and steel factor cultured cells was defective when compared to noncultured cells. Exposure of marrow stem cells to IL-3, IL-6, IL-11, and steel factor induces a stem cell homing defect, which probably underlies the engraftment defect previously characterized under these conditions.

HIV-negative plasmablastic lymphoma: not in the mouth.

Plasmablastic lymphoma (PBL) is an aggressive variant of non-Hodgkin lymphoma initially reported in the oral cavity of HIV-positive individuals. Since its original description, several cases have been reported in patients who do not have HIV infection. However, despite its recognition as a distinct subtype of diffuse large B-cell lymphoma several years ago, comprehensive reviews of this entity are lacking. A MEDLINE search through June 2010 was performed to identify cases with a pathologic diagnosis of HIV-negative PBL based on morphology and minimal immunohistochemical criteria. Our study included a total of 76 cases. The median age was 57 years (range, 1 to 90 years) with a male-to-female ratio of 1.7. Seventy-four percent of cases did not have an apparent association with immunosuppression, 18% had a concurrent lymphoproliferative or autoimmune disorder and 9% developed PBL after solid organ transplantation. Oral involvement was observed in 21%, advanced stage in 60%, Epstein-Barr virus-encoded RNA expression was positive in 45% and Ki-67 expression of greater than or equal to 80% in 61% of the cases. Chemotherapy was documented in 43 patients, from which 43% received the cyclophosphamide, doxorubicin, vincristine, prednisone (CHOP)-like regimens. The median and the 2-year overall survival for the whole group were 9 months and 10%, respectively. Patients who had HIV-negative PBL have distinct clinicopathological characteristics, such as short overall survival and lower rates of oral involvement and Epstein-Barr virus-encoded RNA expression than the previously reported in HIV-positive patients.

Intrinsic hematopoietic stem cell/progenitor plasticity: Inversions

Traditional concepts indicate that stem cells give rise to progenitor cells in a hierarchical system. We studied murine engraftable stem cells (ESCs) and progenitors in in vitro and found that ESC and progenitors exist in a reversible continuum, rather then a hierarchy. B6.SJL and BALB/c marrow cells were serially cultured with thrombopoietin (TPO), FLT‐3 ligand (FLT‐3L), and steel factor through cell cycle. Progenitors (high‐proliferative potential colony‐forming cells (HPP‐CFC) and colony‐forming unit culture (CFU‐c)) and ESC capacity was determined. The cell cycle status of purified lineagenegativerhodaminelowHoechstlow stem cells was determined under the same conditions using tritiated thymidine incorporation and cell counts. We found an inverse relationship between progenitors and ESC, which occurred during the first cell cycle transit and was reversible. We have termed these progenitor/stem cell inversions and found that these inversions were consistently seen at 28–32 h of culture, representing early S‐phase. We observed 13 major reversible increases in progenitor numbers from one time‐point to another during the first cell cycle transit; this was coupled with 11 major ESC decreases and in 2 instances ESC were at baseline. These studies indicate that primitive marrow cells reversibly shift from ESC to progenitors without differentiation occurring. They exist as a fluctuating continuum. J. Cell. Physiol. 199: 20–31, 2004© 2003 Wiley‐Liss, Inc.