Treatment of rat pancreatic islets with reactive PEG.

Covalent attachment of polymers to cells and tissues could be used to solve a variety of problems associated with cellular therapies. Insulin-dependent diabetes mellitus is a disease resulting from the autoimmune destruction of the beta cells of the islets of Langerhans in the pancreas. Transplantation of islets into diabetic patients would be an attractive form of treatment, provided that the islets could be protected from the host's immune system in order to prevent graft rejection. If reaction of polyethylene glycol (PEG) segments with the islet surface did not damage function, the immunogenicity and cell binding characteristics of the islet could be altered. To determine if this process damages islets, rat islets have been isolated and treated with protein-reactive PEG-isocyanate (MW 5000) under mild reaction conditions. An assessment of cell viability using a colorimetric mitochondrial activity assay showed that treatment of the islets with PEG-isocyanate did not reduce cell viability. Insulin release in response to secretagogue challenge was used to evaluate islet function after treatment with the polymer. The insulin response of the PEG-treated islets was not significantly different than untreated islets in a static incubation secretagogue challenge. In addition, PEG-isocyanate-treated islets responded in the same manner as untreated islets in a glucose perifusion assay. Finally, the presence of PEG on the surface of the islets after treatment with the amine-reactive N-hydroxysuccinimide-PEG-biotin (not PEG-isocyanate) was confirmed by indirect fluorescence staining. These results demonstrate the feasibility of treating pancreatic islets with reactive polymeric segments and provide the foundation for further investigation of this novel means of potential immunoisolation.

Cloning and expression of unique murine macrophage colony-stimulating factor transcripts.

Cocultivation of cells from the gamma-irradiated D2XRII murine bone marrow stromal cell line with an interleukin-3/granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent hematopoietic progenitor cell line FDC-P1JL26 stimulates the emergence of factor-independent hematopoietic cell sublines. Several lines of evidence suggested that M-CSF or a protein antigenically related to M-CSF, termed leukemogenic stromal factor (LSF), that was expressed by D2XRII cells may have played a role in the emergence of the factor-independent sublines. In an effort to isolate a factor antigenically related to M-CSF, molecular clones were isolated from a D2XRII cDNA library that hybridized to a mouse M-CSF genetic probe. Two of these molecular clones, designated 60.8.2 and 6452, contained an 885-bp deletion in the M-CSF coding region. Such a cDNA clone has not been previously described in the mouse, but a cDNA clone homologous to it has been isolated from a human pancreatic tumor cell line, MIA-PaCa-2. Three transcripts (4.8, 3.4, and 1.8 kb) were detected that hybridized to an oligonucleotide probe that was specific to RNA transcripts containing the 60.8.2 deletion. The level of the 1.8-kb transcript was not detectably induced by ionizing irradiation; however, the levels of the 4.8-kb and 3.4-kb transcripts and two other M-CSF transcripts of sizes to 4.4 kb and 2.3 kb showed a 1.4- to 2.2-fold increase after gamma irradiation. Reverse transcription-polymerase chain reaction showed that the deletion-specific transcript(s) was detected in multiple mouse bone marrow stromal cell lines and in normal mouse tissues. The present studies establish the existence of an increased spectrum of murine M-CSF transcripts in bone marrow stromal cells and other tissues. This complexity of transcripts along with their increased accumulation after irradiation provides additional evidence for a role of proteins encoded by M-CSF transcripts in the response of bone marrow stromal cells to ionizing irradiation.