Enabling stem cell therapies through synthetic stem cell–niche engineering

Enabling stem cell–targeted therapies requires an understanding of how to create local microenvironments (niches) that stimulate endogenous stem cells or serve as a platform to receive and guide the integration of transplanted stem cells and their derivatives. In vivo, the stem cell niche is a complex and dynamic unit. Although components of the in vivo niche continue to be described for many stem cell systems, how these components interact to modulate stem cell fate is only beginning to be understood. Using the HSC niche as a model, we discuss here microscale engineering strategies capable of systematically examining and reconstructing individual niche components. Synthetic stem cell–niche engineering may form a new foundation for regenerative therapies.     

T cell–independent B cell activation induces immunosuppressive sialylated IgG antibodies

Antigen-specific Abs are able to enhance or suppress immune responses depending on the receptors that they bind on immune cells. Recent studies have shown that pro- or antiinflammatory effector functions of IgG Abs are also regulated through their Fc N-linked glycosylation patterns. IgG Abs that are agalactosylated (non-galactosylated) and asialylated are proinflammatory and induced by the combination of T cell–dependent (TD) protein antigens and proinflammatory costimulation. Sialylated IgG Abs, which are immunosuppressive, and Tregs are produced in the presence of TD antigens under tolerance conditions. T cell–independent (TI) B cell activation via B cell receptor (BCR) crosslinking through polysaccharides or via BCR and TLR costimulation also induces IgG Abs, but the Fc glycosylation state of these Abs is unknown. We found in mouse experiments that TI immune responses induced suppressive sialylated IgGs, in contrast to TD proinflammatory Th1 and Th17 immune responses, which induced agalactosylated and asialylated IgGs. Transfer of low amounts of antigen-specific sialylated IgG Abs was sufficient to inhibit B cell activation and pathogenic immune reactions. These findings suggest an immune regulatory function for TI immune responses through the generation of immunosuppressive sialylated IgGs and may provide insight on the role of TI immune responses during infection, vaccination, and autoimmunity.     

TGF-β prevents T follicular helper cell accumulation and B cell autoreactivity

T follicular helper (Tfh) cells contribute to the establishment of humoral immunity by controlling the delivery of helper signals to activated B cells; however, Tfh development must be restrained, as aberrant accumulation of these cells is associated with positive selection of self-reactive germinal center B cells and autoimmunity in both humans and mice. Here, we show that TGF-β signaling in T cells prevented Tfh cell accumulation, self-reactive B cell activation, and autoantibody production. Using mice with either T cell–specific loss or constitutive activation of TGF-β signaling, we demonstrated that TGF-β signaling is required for the thymic maturation of CD44⁺CD122⁺Ly49⁺CD8⁺ regulatory T cells (Tregs), which induce Tfh apoptosis and thus regulate this cell population. Moreover, peripheral Tfh cells escaping TGF-β control were resistant to apoptosis, exhibited high levels of the antiapoptotic protein BCL2, and remained refractory to regulation by CD8⁺ Tregs. The unrestrained accumulation of Tfh cells in the absence of TGF-β was dependent on T cell receptor engagement and required B cells. Together, these data indicate that TGF-β signaling restrains Tfh cell accumulation and B cell–associated autoimmunity and thereby controls self-tolerance.     

Do automated red cell exchanges relieve priapism in patients with sickle cell anemia?

Priapism is a dramatic, painful complication for some men afflicted by sickle cell anemia. Although the natural history remains unclear, many believe replacing the patient's abnormal red blood cells (RBCs) with normal RBCs by apheresis is effective. However, no controlled trials have demonstrated its effectiveness. We exchanged 7 men after medical management failed. All procedures reduced sickle hemoglobin levels to < 30%. Two patients underwent emergency automated red cell exchanges without any detumescence or reduction of pain. The remaining 5 patients were exchanged non-emergently; 4 experienced no detumescence or relief of pain. One adult experienced resolution 8 h postexchange. However, he had a history of "stuttering" priapism. All required decompression procedures. Automated RBC exchanges were not effective in achieving detumescence or reducing pain.     

Outcomes of acute leukemia patients transplanted with naive T cell–depleted stem cell grafts

BACKGROUND. Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HCT). In mice, naive T cells (T_N) cause more severe GVHD than memory T cells (T_M). We hypothesized that selective depletion of T_N from human allogeneic peripheral blood stem cell (PBSC) grafts would reduce GVHD and provide sufficient numbers of hematopoietic stem cells and T_M to permit hematopoietic engraftment and the transfer of pathogen-specific T cells from donor to recipient, respectively.METHODS. In a single-arm clinical trial, we transplanted 35 patients with high-risk leukemia with T_N-depleted PBSC grafts following conditioning with total body irradiation, thiotepa, and fludarabine. GVHD prophylactic management was with tacrolimus immunosuppression alone. Subjects received CD34-selected PBSCs and a defined dose of T_M purged of CD45RA⁺ T_N. Primary and secondary objectives included engraftment, acute and chronic GVHD, and immune reconstitution.RESULTS. All recipients of T_N-depleted PBSCs engrafted. The incidence of acute GVHD was not reduced; however, GVHD in these patients was universally corticosteroid responsive. Chronic GVHD was remarkably infrequent (9%; median follow-up 932 days) compared with historical rates of approximately 50% with T cell–replete grafts. T_M in the graft resulted in rapid T cell recovery and transfer of protective virus-specific immunity. Excessive rates of infection or relapse did not occur and overall survival was 78% at 2 years.CONCLUSION. Depletion of T_N from stem cell allografts reduces the incidence of chronic GVHD, while preserving the transfer of functional T cell memory.TRIAL REGISTRATION. ClinicalTrials.gov ({"type":"clinical-trial","attrs":{"text":"NCT 00914940","term_id":"NCT00914940"}}NCT 00914940).FUNDING. NIH, Burroughs Wellcome Fund, Leukemia and Lymphoma Society, Damon Runyon Cancer Research Foundation, and Richard Lumsden Foundation.     

Bystander tumoricidal effect and cell apoptosis of mouse mammary carcioma cell transduced with HSV-tk gene

To apply gene therapy to breast carcinoma wepropose a model for in vitro gene transfer of the herpessimplex thymidine kinase (HSV-tk) gene using Stkvector-producing cells. In this study the HSV-tk gene wastransferred to mouse mammary carcinoma cell line 4Tlwith the method of infection. The HSV-tk gene in thegenome of transduced cells (4Tl/tk) was demonstratedby the method of DNA-PCR. Using a modified XTT     

Type I IFN enhances follicular B cell contribution to the T cell–independent antibody response

Humoral immunity to viruses and encapsulated bacteria is comprised of T cell–independent type 2 (TI-2) antibody responses that are characterized by rapid antibody production by marginal zone and B1 B cells. We demonstrate that toll-like receptor (TLR) ligands influence the TI-2 antibody response not only by enhancing the overall magnitude but also by skewing this response to one that is dominated by IgG isotypes. Importantly, TLR ligands facilitate this response by inducing type I interferon (IFN), which in turn elicits rapid and significant amounts of antigen-specific IgG2c predominantly from FO (follicular) B cells. Furthermore, we show that although the IgG2c antibody response requires B cell–autonomous IFN-α receptor signaling, it is independent of B cell–intrinsic TLR signaling. Thus, innate signals have the capacity to enhance TI-2 antibody responses by promoting participation of FO B cells, which then elaborate effective IgG anti-pathogen antibodies.The peripheral pool of mature B cells in adults is composed of several subpopulations, each of which is generally thought to make a distinct contribution to humoral immunity. As an example, natural serum IgM functions as a first line of defense against pathogens and is produced primarily by B1a B cells before exposure (Baumgarth et al., 1999; Haas et al., 2005). Upon bacterial or viral infection, marginal zone (MZ) and B1 B cell subsets respond rapidly, constituting the immediate acquired antibody response (Martin et al., 2001). Finally, FO (follicular) B cells dominate the delayed highly specific antibody response comprised by somatically mutated higher affinity class-switched antibodies and memory B cells. These latter processes occur in germinal center reactions that occur after productive interactions between responding B cells and antigen-specific helper T cells (Martin and Kearney, 2002; McHeyzer-Williams, 2003).The nature of the antigen itself can also dictate which B cell subset is recruited into an antibody response. Using model antigens in rodents, B cell antigens have been classified as either T cell independent (TI) or T cell dependent (TD). TI antigens promote B cell proliferation, differentiation, and antibody production in the absence of T cells and are further classified into two subgroups: type I (TI-1) or type 2 (TI-2). TI-1 antigens are mitogens that stimulate all B cells to produce antibody in a polyclonal manner and irrespective of antigen specificity. Physiological TI-1 antigens include Toll-like receptor (TLR) ligands, such as LPS which is expressed by gram negative bacteria (Coutinho et al., 1974), or certain viral coat proteins (Berberian et al., 1993; Blutt et al., 2004). TI-2 antigens are instead composed of repetitive epitopes displayed on a backbone that simultaneously engage multiple antigen receptors on the surface of antigen-specific B cells. TI-2 antigens elicit robust IgM and IgG3 antibody production in a TI fashion, although the presence of noncognate T cell help promotes production of other IgG isotypes (Mongini et al., 1984). These TI antigens include polysaccharides found on encapsulated bacteria and highly organized viral capsid proteins such as those found on vesicular stomatitis virus and poliovirus (Bachmann et al., 1995; Bachmann and Zinkernagel, 1997; Fehr et al., 1998). In contrast to TI antigens, TD antigens are generally monomeric soluble proteins that display single or few epitopes to antigen-specific B cells and require cognate T cell help for induction of highly specific antibody responses generated through germinal center reactions.Although not absolute, a general division of labor is also acknowledged between B cell subsets and the response to TI-2 and TD antigens. B1 and MZ B cell subpopulations have been considered to be primarily responsible for the antibody response to TI-2 antigens (Fagarasan and Honjo, 2000; Martin et al., 2001; Balázs et al., 2002), whereas FO B cells dominate antibody responses to soluble protein TD antigens. In accord with generating rapid antibody responses, MZ and B1 B cells have lower thresholds for activation compared with FO B cells and are physically poised at sites either in tissues or at the blood–lymphoid interface that facilitates these early responses (Martin and Kearney, 2002). B1 and MZ B cells are described as innate B cells in that they express a restricted repertoire of germline-encoded BCRs with polyreactive specificities (Bendelac et al., 2001). Responding MZ B cells produce antigen-specific antibody at extrafollicular splenic sites early during the antibody response that is low affinity and predominantly IgM but also includes limited IgG subclasses. Although evidence exists that MZ B cells can also mount TD responses and initiate germinal center reactions (Song and Cerny, 2003; Phan et al., 2005), the ability of FO B cells to directly participate in rapid extrafollicular TI-2 antibody responses is minor (Ron and Sprent, 1985; Goud et al., 1988; Liu et al., 1988).Characterization of the TI-2 antibody response has predominantly relied on hapten-coupled carbohydrates as model antigens. However, physiological TI-2 antigens would rarely be encountered in isolation but, rather, are typically associated with pathogen-associated molecular patterns (PAMPs) recognized by pattern recognition receptors (PRRs; Janeway, 1989; Snapper, 2006). TLRs are one family of innate immune PRRs that have been shown to enhance the antibody response (Coutinho et al., 1974; Seppälä and Mäkelä, 1984; Sen et al., 2005; Heer et al., 2007; Rubtsov et al., 2008; Eckl-Dorna and Batista, 2009). However, whether this regulation is physiologically relevant has been controversial (Pasare and Medzhitov, 2005; Gavin et al., 2006).A major consequence of signaling by many PRRs is the rapid elaboration of inflammatory type I IFN cytokines (Baccala et al., 2007; McCartney and Colonna, 2009), and many viral and bacterial infections lead to IFN-α/β production (Bogdan, 2000; Mancuso et al., 2009). Type I IFN has been previously characterized to modulate antibody production both in vitro and in vivo, including promoting class-switch recombination and polarizing antibody responses toward IgG2a/c production (Finkelman et al., 1991; Le Bon et al., 2001, 2006; Coro et al., 2006; Heer et al., 2007). How IFN-α/β acts to effect these changes in humoral immunity is not well established, nor is whether the type I IFN produced as a result of innate immune receptor signaling contributes to regulating the antibody response.It has been proposed that in addition to their antigen-specific BCR, B cells may also use innate mechanisms for pathogen recognition. However, it is still unclear which of the innate receptors are used by B cells or what the consequence of these signals is to the B cell antibody response. The rapid TI-2 antibody response provides a temporal bridge between the early innate and late adaptive immune responses. Thus, we were interested to investigate how innate signals would augment the TI-2 antibody response and influence the different B cell populations during this response.In this paper, we show that TLR agonists significantly enhance the TI-2 antibody response through the elaboration of type I IFN that promotes production of IgG2c by FO B cells. This contribution elicited by FO B cells is shown to accelerate the kinetics and enhance the magnitude and quality of the TI-2 antibody response. Thus, these data not only provide a mechanistic example of how innate immunity influences adaptive immunity but also define how humoral immunity counters physiological pathogens that present TI-2 antigens in the presence of ligands for innate immune receptors.     

Extrafollicular B cell activation by marginal zone dendritic cells drives T cell–dependent antibody responses

Dendritic cells (DCs) are best known for their ability to activate naive T cells, and emerging evidence suggests that distinct DC subsets induce specialized T cell responses. However, little is known concerning the role of DC subsets in the initiation of B cell responses. We report that antigen (Ag) delivery to DC-inhibitory receptor 2 (DCIR2) found on marginal zone (MZ)–associated CD8α⁻ DCs in mice leads to robust class-switched antibody (Ab) responses to a T cell–dependent (TD) Ag. DCIR2⁺ DCs induced rapid up-regulation of multiple B cell activation markers and changes in chemokine receptor expression, resulting in accumulation of Ag-specific B cells within extrafollicular splenic bridging channels as early as 24 h after immunization. Ag-specific B cells primed by DCIR2⁺ DCs were remarkably efficient at driving naive CD4 T cell proliferation, yet DCIR2-induced responses failed to form germinal centers or undergo affinity maturation of serum Ab unless toll-like receptor (TLR) 7 or TLR9 agonists were included at the time of immunization. These results demonstrate DCIR2⁺ DCs have a unique capacity to initiate extrafollicular B cell responses to TD Ag, and thus define a novel division of labor among splenic DC subsets for B cell activation during humoral immune responses.Upon recognition of T cell–dependent (TD) or T cell–independent (TI) antigen (Ag), B cells differentiate into short-lived antibody (Ab)-forming cells (AFCs), which are critical for providing frontline protection against the spread of blood-borne pathogens such as Salmonella typhimurium and influenza (Gerhard et al., 1997; Cunningham et al., 2007; Rothaeusler and Baumgarth, 2010). Alternatively, cognate interaction of B cells with CD4⁺ T cells results in the formation of germinal centers (GCs) and selection of high-affinity clones for differentiation to memory B cells and long-lived plasma cells (Jacob et al., 1991).  Although GC responses and affinity maturation have been extensively studied, much less is known concerning the early events that govern B cell activation and how they influence the decision to produce extrafollicular AFC responses versus GC B cell differentiation.The context in which B cells encounter Ag is highly influenced by the size, nature, and form of the Ag itself (Roozendaal et al., 2009). Although direct recognition of small, soluble Ag by the BCR can occur in vivo (Pape et al., 2007), acquisition of membrane-associated Ag is also an efficient means to trigger B cell activation (Carrasco and Batista, 2006; Depoil et al., 2008). Multiple APCs can present Ag to B cells including follicular DCs, subcapsular sinus and marginal zone (MZ) macrophages, and DCs (Wykes and MacPherson, 2000; Huang et al., 2005; Qi et al., 2006; Phan et al., 2009; Roozendaal et al., 2009; Suzuki et al., 2009). Among these, DCs in particular have been shown in vitro to influence a range of B cell processes including proliferation, differentiation, and Ig class-switch recombination (CSR; Dubois et al., 1998; Fayette et al., 1998; Litinskiy et al., 2002; Craxton et al., 2003). DC-mediated presentation of Ag to B cells in vivo has been shown to enhance TI Ab responses to immune complexes internalized by FcγRIIb on splenic DCs, as well as TI responses against Streptococcus pneumoniae mediated by blood-derived DCs (Balázs et al., 2002; Bergtold et al., 2005; Dubois and Caux, 2005).In contrast, it is unclear what, if any, role DC–B cell interactions may have during humoral responses to TD Ag. Some evidence has suggested that DCs directly present Ag to B cells during TD immune responses. Qi et al. (2006) showed that adoptively transferred DCs can transfer hen egg lysozyme (HEL) to Ag-specific B cells in the lymph node; however, neither the DC subset responsible for the Ag presentation nor the subsequent B cell response was evaluated. Earlier studies showed that adoptive transfer of Ag-bearing DCs was sufficient to induce TD Ab responses; however, because adoptive transfer strategies were used, the role of Ag uptake in situ by resident DC subsets remained unclear (Wykes et al., 1998; Berney et al., 1999). More recent studies using mAbs to deliver Ag directly to APCs in vivo demonstrated Ab responses after Ag uptake by several C-type lectin receptors (CLRs) including FIRE (F4/80-like receptor), CIRE (C-type lectin immune receptor), Dectin-1, Clec12a, and Clec9a (Corbett et al., 2005; Caminschi et al., 2008; Lahoud et al., 2009). Because the CLRs targeted in these studies are also expressed on macrophages, plasmacytoid DCs (pDCs), and/or B cells, it is again unclear which APC populations were required for the observed Ab induction. In sum, many questions remain concerning the induction of Ab responses by DCs.Here, we describe a novel mechanism underlying DC-mediated induction of Ab responses after Ag uptake by DC-inhibitory receptor 2 (DCIR2), a CLR found exclusively on a subset of MZ-associated CD8α⁻ DCs (Dudziak et al., 2007). Using mAbs to deliver Ag in vivo, we show that Ag uptake by DCIR2, but not DEC205 found on CD8α⁺ DCs, induces robust IgG1-restricted TD Ab responses without the addition of any adjuvant. Although DCIR2⁺ DCs are known to preferentially present peptide–MHCII complexes to CD4 T cells after Ag delivery to DCIR2 (Dudziak et al., 2007), we found that DCIR2⁺ DCs also present Ag to B cells and facilitate their rapid activation in vivo. As early as 24 h after immunization, activated Ag-specific B cells accumulated in extrafollicular splenic bridging channels, coincident with the location of DCIR2⁺ DCs in situ. Importantly, DC-primed Ag-specific B cells were highly efficient APCs for driving naive CD4 T cell proliferation, suggesting that B cell–mediated Ag presentation is a key component to sustaining CD4 T cell responses after Ag delivery to DCs. In the absence of adjuvants, DCIR2 DCs induced extrafollicular Ab responses that did not involve GC formation or affinity maturation of serum Ab. Instead, inclusion of agonists for toll-like receptor (TLR) 7 or TLR9 (but not TLR3, TLR5, or RIG-I) shifted the B cell differentiation program toward GC formation and affinity maturation. Thus, our data show that DCIR2⁺ MZ-associated DCs are uniquely equipped and/or positioned to prime B cells and initiate extrafollicular Ab responses to TD Ag.     

IL-21 regulates germinal center B cell differentiation and proliferation through a B cell–intrinsic mechanism

Germinal centers (GCs) are sites of B cell proliferation, somatic hypermutation, and selection of variants with improved affinity for antigen. Long-lived memory B cells and plasma cells are also generated in GCs, although how B cell differentiation in GCs is regulated is unclear. IL-21, secreted by T follicular helper cells, is important for adaptive immune responses, although there are conflicting reports on its target cells and mode of action in vivo. We show that the absence of IL-21 signaling profoundly affects the B cell response to protein antigen, reducing splenic and bone marrow plasma cell formation and GC persistence and function, influencing their proliferation, transition into memory B cells, and affinity maturation. Using bone marrow chimeras, we show that these activities are primarily a result of CD3-expressing cells producing IL-21 that acts directly on B cells. Molecularly, IL-21 maintains expression of Bcl-6 in GC B cells. The absence of IL-21 or IL-21 receptor does not abrogate the appearance of T cells in GCs or the appearance of CD4 T cells with a follicular helper phenotype. IL-21 thus controls fate choices of GC B cells directly.The immunological memory that develops during T cell–dependent (TD) immune responses comprises populations of plasma cells and recirculating antigen-experienced B and T lymphocytes (Tarlinton, 2006). Two compartments of humoral memory, plasma cells and memory B cells, are generated in germinal centers (GCs) that develop within the secondary lymphoid organs during TD responses (Tarlinton, 2006). Although composed primarily of B lymphocytes, GCs contain small numbers of CD4⁺ T cells, dendritic cells, and macrophages and develop in association with antigen localized on the surface of follicular dendritic cells (Haberman and Shlomchik, 2003; Allen et al., 2007). After a period of B cell proliferation, several processes are initiated within the GC that affect affinity maturation whereby the mean binding affinity of antigen-specific antibody increases as a function of time (MacLennan, 1994; Allen et al., 2007). Affinity maturation is driven in large part by the somatic hypermutation (SHM) of the immunoglobulin V genes of proliferating GC B cells, a process which is mediated by the enzyme activation-induced cytidine deaminase (AID). B cells expressing antigen receptors of improved affinity, usually as a result of SHM, are preserved preferentially. Iterations of proliferation, mutation, and avidity-based selection improve the mean affinity of the responding B cell population (MacLennan, 1994; Allen et al., 2007).Normally, in an immune response to a protein antigen the vast majority of memory B cells and bone marrow plasma cells arise from the somatically diversified affinity-matured population of GC B cells (Tarlinton, 2006). It is inferred that avidity for antigen is a major determinant in plasma cell differentiation of GC B cells, whereas memory B cell formation is more influenced by survival (Lanzavecchia and Sallusto, 2002; Phan et al., 2006; Tarlinton, 2006). It also appears that both types of post-GC B cell are produced throughout the GC reaction rather than being released into the circulation in a single event (Blink et al., 2005). The persistence and continued activity of GC, which is indicated by the continued production of plasma cells and memory B cells and the increasing frequency of V gene mutation, implies that a proportion of GC B cells remain within the GC and undergo additional rounds of proliferation, mutation, and selection (MacLennan, 1994; Allen et al., 2007). B cells within GC therefore have several possible fates: death, division with or without SHM, or differentiation into either the memory B cell or plasma cell compartments.GC persistence, development, and function absolutely require CD4⁺ T cells. T cells activated by antigen-presenting dendritic cells migrate into the B cell area in part as a result of their up-regulation of CXCR5, a chemokine receptor normally restricted to B cells (Allen et al., 2007). Indeed, the expression of CXCR5 contributes to the definition of what are now called T follicular helper (Tfh) cells (Vinuesa et al., 2005). In addition to CXCR5, Tfh cells are distinguished from other CD4 T cells by their elevated expression of ICOS and CD40L (Vinuesa et al., 2005), both of which are critical for the initiation and maintenance of the GC (Tarlinton, 2006). Intriguingly, up-regulation of many of the molecules that define the Tfh phenotype appears to be mediated by Bcl-6, which is required for their development in a cell-intrinsic manner (Johnston et al., 2009). Tfh cells are also enriched for secretion of IL-21 (Chtanova et al., 2004; Nurieva et al., 2008) and IL-4 (Reinhardt et al., 2009). IL-21 is associated with growth and differentiation of many types of lymphocytes, including B and T cells (Ettinger et al., 2008). The effects of IL-21 on B cells vary depending on the context. In vivo, IL-21R deficiency leads to a state of pan-hypogammaglobulinaemia while promoting high titers of IgE (Ozaki et al., 2002). In vitro, IL-21 has been shown to increase both Blimp-1 and Bcl-6 in B cells (Ozaki et al., 2004; Arguni et al., 2006), suggesting an ability for IL-21 to influence multiple aspects of B cell differentiation. Recent data support the notion that IL-21 has a critical, possibly obligatory, role in the development of Tfh cells and, through this, on the formation of GC (Nurieva et al., 2008; Vogelzang et al., 2008), whereas other data suggest a less universal association (Linterman et al., 2009). IL-21 has also been shown to augment the formation of Th17 cells (Korn et al., 2007; Nurieva et al., 2007; Zhou et al., 2007), which have been shown to both secrete IL-21 and promote GC formation in a mouse model of autoimmunity (Hsu et al., 2008), strengthening the view that the effects of IL-21 on GC activity are T cell mediated. An earlier study, however, using IL-21R–deficient mice reported GC and memory development to be normal (Ozaki et al., 2002), raising uncertainty as to exactly what the requirement of IL-21 may be in the GC reaction, on which cell types it may act, and what its activities might be. This uncertainty has been heightened by recent publications suggesting that IL-4 is a key mediator of Tfh activity (King and Mohrs, 2009; Reinhardt et al., 2009).Given the multitude of potential roles for IL-21 on lymphocyte behavior (Ettinger et al., 2008), we wished to assess the development of a humoral immune response in mice lacking IL-21 or the IL-21R. These experiments confirmed a role for IL-21 in the formation of plasma cells, contradicted a mandatory autocrine role for IL-21 in Tfh development or function, and revealed a previously undefined role for this cytokine in the GC reaction and the regulation of their output. These actions of IL-21 on B cells were direct, as they were replicated by the selective absence of the IL-21R on B cells and not on T cells, suggesting that the major activity of IL-21 in the GC is on B cells and is not to establish or maintain cells of a Tfh phenotype.     

Low propidium iodide intensity in flow cytometric white blood cell counting as a marker of cell destruction?

BACKGROUND: Residual white blood cells (WBC) in filtered blood products were investigated with flow cytometry. Frequently two distinct populations with different propidium iodide (PI) intensities can be found. The aim of this study was to specify a population with low PI intensity and discuss it as a marker of ongoing cell destruction and their possible impact on cytomegalovirus safety. STUDY DESIGN AND METHODS: Buffy coat-depleted red blood cells were filtered with an in-line filtration set (LCR5, MacoPharma) after 4 hours (LCR5/4 hr) and 16 hours (LCR5/16 hr) of storage, and whole blood was filtered with a whole-blood filtration set (LST1, MacoPharma [LST1/4 hr]). The population with low PI intensity was sorted with a flow cytometer and prepared for transmission electron microscopy. RESULTS: The absolute count obtained in the low-PI-intensity area before filtration was significantly different comparing LCR5/4 hr (11.5 x 10(6) +/- 6.84 x 10(6) and 0.12 x 10(6) +/- 0.1 x 10(6)/unit) and LCR5/16 hr (69.3 +/- 42.12 and 0.06 +/- 0.05; p < 0.002). By use of LST1/4 hr no difference was found compared to LCR5/4 hr after filtration (0.12 +/- 0.09 vs. 0.12 +/- 0.1), but a significant difference was found when comparing the results before filtration (1.25 +/- 0.41 vs. 11.5 +/- 6.84; p < 0.02). Electron microscopy revealed that the sorted population consisted of predominantly cell and nuclear fragments. CONCLUSIONS: Events found in the low-PI-intensity area are not WBCs but partially degraded DNA coming from ongoing cell destruction during extended storage. Our results provide evidence that the absolute count of events found in the low-PI-intensity area can be used as a semiquantitative marker of WBC destruction.     

Stem cell‐based therapy for Parkinson's disease

Motor dysfunctions in Parkinson's disease are considered to be primarily due to the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Pharmacological therapies based on the principle of dopamine replacement are extremely valuable, but suffer from two main drawbacks: troubling side effects (e.g. dyskinesia) and loss of efficacy with disease progression. Transplantation of embryonic dopaminergic neurons has emerged as a therapeutic alternative. Enthusiasm following the success of the initial open‐label trials has been dampened by the negative outcome of double‐blind placebo controlled trials. Additionally, the emergence of graft‐related dyskinesia indicates that the experimental grafting procedure requires further refinement before it can be developed into a therapy. Shortage of embryonic donor tissue limits large‐scale clinical transplantation trials. We review three of the most attractive tissue sources of dopaminergic neurons for cell replacement therapy: human embryonic ventral mesencephalic tissue, embryonic and adult multipotent region‐specific stem cells and embryonic stem cells. Recent developments in embryonic stem cell research and on their implications for a future transplantation therapy in Parkinson's disease are described. Finally, we discuss how human embryonic stem cells can be differentiated into dopaminergic neurons, and issues such as the numbers of dopaminergic neurons required for success and the risk for teratoma formation after implantation.