Chemokines as novel and versatile reagents for flow cytometry and cell sorting.

Cell therapy regimens are frequently compromised by low-efficiency cell homing to therapeutic niches. Improvements in this regard would enhance effectiveness of clinically applicable cell therapy. The major regulators of tissue-specific cellular migration are chemokines, and therefore selection of therapeutic cellular populations for appropriate chemokine receptor expression would enhance tissue-homing competence. A number of practical considerations preclude the use of Abs in this context, and alternative approaches are required. In this study, we demonstrate that appropriately labeled chemokines are at least as effective in detecting their cognate receptors as commercially available Abs. We also demonstrate the utility of biotinylated chemokines as cell-sorting reagents. Specifically, we demonstrate, in the context of CCR7 (essential for lymph node homing of leukocytes), the ability of biotinylated CCL19 with magnetic bead sorting to enrich for CCR7-expressing cells. The sorted cells demonstrate improved CCR7 responsiveness and lymph node-homing capability, and the sorting is effective for both T cells and dendritic cells. Importantly, the ability of chemokines to detect CCR7, and sort for CCR7 positivity, crosses species being effective on murine and human cells. This novel approach to cell sorting is therefore inexpensive, versatile, and applicable to numerous cell therapy contexts. We propose that this represents a significant technological advance with important therapeutic implications.

Treatment of inflammatory bowel disease by chemokine receptor-targeted leukapheresis.

Leukapheresis removes circulating leukocytes en route to the target organ. Hitherto unspecific matrixes have been used to remove leukocytes in inflammatory bowel disease (IBD). This report describes a novel selective leukapheresis column based on chemokine-chemokine receptor interaction. We found an increased expression of the gut homing chemokine receptor CCR9 on CD14(+) monocytes and on CD3(+) T lymphocytes from IBD patients. Biologically active CCL25 was coupled to a Sepharose matrix and demonstrated to selectively remove CCR9-expressing cells leaving other cell populations largely unaffected. A patient with active ulcerative colitis, was subjected to CCL25-column leukapheresis. Four days after treatment, he experienced clinical improvement and stable disease improvement ensued. The study illustrates that specific cells can be targeted using high affinity interactions, i.e., CCL25-CCR9 interactions to remove pathogenic gut-homing cells. Leukapheresis using the bCCL25 column should be investigated in a clinical phase I trial of patients with inflammatory bowel disease.

Structural and kinetic characterization of quinolinate phosphoribosyltransferase (hQPRTase) from homo sapiens.

Human quinolinate phosphoribosyltransferase (EC 2.4.2.19) (hQPRTase) is a member of the type II phosphoribosyltransferase family involved in the catabolism of quinolinic acid (QA). It catalyses the formation of nicotinic acid mononucleotide from quinolinic acid, which involves a phosphoribosyl transfer reaction followed by decarboxylation. hQPRTase has been implicated in a number of neurological conditions and in order to study it further, we have carried out structural and kinetic studies on recombinant hQPRTase. The structure of the fully active enzyme overexpressed in Escherichia coli was solved using multiwavelength methods to a resolution of 2.0 A. hQPRTase has a alpha/beta barrel fold sharing a similar overall structure with the bacterial QPRTases. The active site of hQPRTase is located at an alpha/beta open sandwich structure that serves as a cup for the alpha/beta barrel of the adjacent subunit with a QA binding site consisting of three arginine residues (R102, R138 and R161) and two lysine residues (K139 and K171). Mutation of these residues affected substrate binding or abolished the enzymatic activity. The kinetics of the human enzyme are different to the bacterial enzymes studied, hQPRTase is inhibited competitively and non-competitively by one of its substrates, 5-phosphoribosylpyrophosphate (PRPP). The human enzyme adopts a hexameric arrangement, which places the active sites in close proximity to each other.