Regulatory T cells (Tregs) are key mediators of immune tolerance and feature prominently in cancer. Depletion of CD25+ FoxP3+ Tregs in vivo may promote T cell cancer immunosurveillance, but no strategy to do so in humans while preserving immunity and preventing autoimmunity has been validated. We evaluated the Food and Drug Administration–approved CD25-blocking monoclonal antibody daclizumab with regard to human Treg survival and function. In vitro, daclizumab did not mediate antibody-dependent or complement-mediated cytotoxicity but rather resulted in the down-regulation of FoxP3 selectively among CD25high CD45RAneg Tregs. Moreover, daclizumab-treated CD45RAneg Tregs lost suppressive function and regained the ability to produce interferon-γ, consistent with reprogramming. To understand the impact of daclizumab on Tregs in vivo, we performed a clinical trial of daclizumab in combination with an experimental cancer vaccine in patients with metastatic breast cancer. Daclizumab administration led to a marked and prolonged decrease in Tregs in patients. Robust CD8 and CD4 T cell priming and boosting to all vaccine antigens were observed in the absence of autoimmunity. We conclude that CD25 blockade depletes and selectively reprograms Tregs in concert with active immune therapy in cancer patients. These results suggest a mechanism to target cancer-associated Tregs while avoiding autoimmunity.

Flow cytometric cell sorting of biological specimens has become prevalent in basic and clinical research laboratories. These specimens may contain known or unknown infectious agents, necessitating precautions to protect instrument operators and the environment from biohazards arising from the use of sorters. To this end the International Society of Analytical Cytology (ISAC) was proactive in establishing biosafety guidelines in 1997 (Schmid et al., Cytometry 1997;28:99–117) and subsequently published revised biosafety standards for cell sorting of unfixed samples in 2007 (Schmid et al., Cytometry Part A J Int Soc Anal Cytol 2007;71A:414–437). Since their publication, these documents have become recognized worldwide as the standard of practice and safety precautions for laboratories performing cell sorting experiments. However, the field of cytometry has progressed since 2007, and the document requires an update. The new Standards provides guidance: (1) for laboratory design for cell sorter laboratories; (2) for the creation of laboratory or instrument specific Standard Operating Procedures (SOP); and (3) on procedures for the safe operation of cell sorters, including personal protective equipment (PPE) and validation of aerosol containment.

Comprehensive molecular analysis of rare circulating tumor cells (CTCs) and cell clusters is often hampered by low throughput and purity, as well as cell loss. To address this, we developed a fully integrated platform for flow cytometry-based isolation of CTCs and clusters from blood that can be combined with whole transcriptome analysis or targeted RNA transcript quantification. Downstream molecular signature can be linked to cell phenotype through index sorting. This newly developed platform utilizes in-line magnetic particle-based leukocyte depletion, and acoustic cell focusing and washing to achieve >98% reduction of blood cells and non-cellular debris, along with >1.5 log-fold enrichment of spiked tumor cells. We could also detect 1 spiked-in tumor cell in 1 million WBCs in 4/7 replicates. Importantly, the use of a large 200μm nozzle and low sheath pressure (3.5 psi) minimized shear forces, thereby maintaining cell viability and integrity while allowing for simultaneous recovery of single cells and clusters from blood. As proof of principle, we isolated and transcriptionally characterized 63 single CTCs from a genetically engineered pancreatic cancer mouse model (n = 12 mice) and, using index sorting, were able to identify distinct epithelial and mesenchymal sub-populations based on linked single cell protein and gene expression.

No abstract

The apicoplast is a distinctive organelle associated with apicomplexan parasites, including Plasmodium sp. (which cause malaria) and Toxoplasma gondii (the causative agent of toxoplasmosis). This unusual structure (acquired by the engulfment of an ancestral alga and retention of the algal plastid) is essential for long-term parasite survival. Similar to other endosymbiotic organelles (mitochondria, chloroplasts), the apicoplast contains proteins that are encoded in the nucleus and post-translationally imported. Translocation across the four membranes surrounding the apicoplast is mediated by an N-terminal bipartite targeting sequence. Previous studies have described a recombinant "poison" that blocks plastid segregation during mitosis, producing parasites that lack an apicoplast and siblings containing a gigantic, nonsegregating plastid. To learn more about this remarkable phenomenon, we examined the localization and processing of the protein produced by this construct. Taking advantage of the ability to isolate apicoplast segregation mutants, we also demonstrated that processing of the transit peptide of nuclear-encoded apicoplast proteins requires plastid-associated activity.

We hypothesized that human hematopoietic cells displaying a CD34 + , kit + , rhodamine123 low phenotype would be highly enriched for cells with stem-like properties. To test this hypothesis, we employed fluorescence activated cell sorting (FACS) to isolate cells with this phenotype from normal light density marrow mononuclear cells (MNC). CD34 + , kit + , rhodamine123 low cells comprised from 0.05-0.01% of the total MNC population. They were small, had scant cytoplasm, and contained nuclei with dense, hyperchromatic chromatin and inconspicuous nucleoli. Additional immunophenotyping revealed that these cells were CD33 − , CD38 − , CD20 − , and glycophorin A − . When plated in semisolid cultures containing optimal concentrations of IL-3, GM-CSF, KL, EPO, IL-6, and IL-1 these cells did not form colonies. However, when cultured over irradiated stromal cells, cobblestone areas were observed to form after 3 weeks, and harvested cells were able to initiate long-term cultures. To further demonstrate that these cells were indeed stem like, we also tested their ability to engraft and mature in immunocompromised (SCID) mice. Irradiated (400 cGy) SCID mice were transplanted with 2 × 10 3 candidate stem cells which were then injected with recombinant human growth factors every other day. Two months post-transplant the animals were sacrificed. PCR and FACS analysis of marrow and spleen cell samples revealed the presence of cells expressing human CD45 consistent with engraftment of human stem cells and the establishment of murine-human chimerism. Moreover, MNC isolated from transplanted mice formed unambiguously human BFU-E, CFU-GM and B cell colonies when stimulated with the appropriate growth factors. Accordingly, we have identified a relatively rapid and simple mechanism for isolating primitive human hematopoietic cells with stem cell-like properties. We anticipate that this strategy will be useful for experimental and therapeutic applications that require human stem cells in quantity.

No abstract

Summary. Thrombopoietin (TPO) has been reported to stimulate erythropoiesis, but the stimulatory mechanism has not been defined. To address this issue, we performed serum-free cell-culture experiments with recombinant human TPO and purified human progenitor cells. We found that TPO alone was able to stimulate the megakaryocyte colony formation in serum-free cultures, but erythroid colonies were never observed. Only in the presence of EPO (erythropoietin) þIL-3 was TPO able to stimulate a small increase (ϳ25%) in erythroid colony formation. Accordingly, we hypothesized that TPO might have an effect on erythroid progenitor cell viability, rather than a direct stimulatory effect. To test this idea, CD34 þ cells were cultured for 7 d in serum-free methylcellulose in the presence or absence of TPO, after which time KL+ EPO was added to the cultures. Cells which were pre-cultured for 7 d in the presence of TPO gave rise to approximately 6 times as many burst forming unit-erythroid (BFU-E) colonies as cells which were pre-cultured in the absence of TPO. Further, when primitive CD34 þ , Kit þ MNC were cultured for 3-7 d under serum-free conditions in the presence or absence of TPO, significantly fewer cells cultured in the presence of TPO displayed apoptotic changes when compared to cells cultured in the absence of TPO. Taken together, these results suggest that TPO has little direct stimulatory effect on erythroid progenitor cells, but might indirectly enhance erythropoiesis by preventing very early erythroid progenitor cells from undergoing apoptotic cell death.