Biomedical subjects

Mikael Jondal

Publications and source records attributed to Mikael Jondal.

9 recordsLinked to original sources

PubMed2006

Interference with O-glycosylation in RMA lymphoma cells leads to a reduced in vivo growth of the tumor.

Carbohydrate processing in cancer cells can influence the growth, metastatic potential, vascularization and immune recognition of such cells. Interference with N-glycosylation has been shown both to reduce the membrane expression of MHC class I and to increase the in vitro sensitivity of tumor cells to NK cell killing. We investigated the effect of O-glycosylation inhibition on the in vivo growth, phenotype and NK sensitivity of RMA lymphoma cells using benzyl N-acetyl-alpha-D-galactosamide (BAG). BAG-treated cells were found to have a strongly reduced local growth potential in vivo. However, inhibition of O-glycosylation caused this effect without any significant downregulation of MHC-I and increase in sensitivity to NK killing as seen after inhibition of N-glycosylation using Castanospermine. BAG treatment of RMA cells resulted in the removal of larger O-linked glycans and a high expression of the T-antigen (GalGalNAc), a target for natural antibodies (NAs) induced by the gastrointestinal bacterial flora. Whether the loss of larger O-linked glycans, and associated functions, or of biological effects of NA contributed to the antitumor effect remains to be established. The results support the idea that inhibitors of O- as well as N-linked glycosylation may be useful for the treatment of cancer, given that they can be specifically targeted to the tumor tissue.

Acetylgalactosamine↗

PubMed2005

Conditional expression of a glucocorticoid receptor transgene in thymocytes reveals a role for thymic-derived glucocorticoids in thymopoiesis in vivo.

We and others have previously reported that thymic epithelial cells produce glucocorticoids (GCs). In vitro studies have also suggested that thymic-derived GCs play a role in the development of thymocytes. However, until now it has not yet been established whether thymic-derived GCs play a role in thymopoiesis in vivo. To investigate this, we conditionally overexpressed the GC receptor (GR) in thymocytes using transgenic mice with a tetracycline-inducible expression system. The influence of systemic GCs was excluded by adrenalectomizing the transgenic mice before the GR induction. Conditional expression of transgenic GR in the thymocytes of adrenalectomized transgenic mice led to a decrease in the thymocyte number. This was associated with increased thymocyte apoptosis. The effect of thymic-derived GCs on the thymocytes was confirmed after transgenic GR induction in a thymic organ culture system. Finally, the GR antagonist RU486 increased thymocyte number in adrenalectomized mice in vivo and prevented a reduction in thymocyte number in thymic organ culture after transgenic GR induction. These observations further confirmed a role for the thymic-derived GCs in regulating thymocyte homeostasis in vivo.

Adrenalectomy↗

PubMed2005

High expression of bfl-1 contributes to the apoptosis resistant phenotype in B-cell chronic lymphocytic leukemia.

In order to identify regulatory genes involved in the development of an apoptosis-resistant phenotype in patients with chemotherapy refractory B-cell chronic lymphocytic leukemia (B-CLL) expression of apoptosis-regulating genes in B-CLL cells was quantified using cDNA arrays and RT-PCR. Data were obtained from and compared between 2 groups of B-CLL patients with either nonprogressive, indolent, previously untreated disease and with leukemic cells sensitive to in vitro fludarabine-induced apoptosis, referred to as sensitive B-CLL (sB-CLL) or with progressive, chemotherapy refractory disease and with leukemic cells resistant to in vitro fludarabine-induced apoptosis, referred to as resistant B-CLL (rB-CLL). By performing a supervised clustering of genes that most strongly discriminated between rB-CLL vs. sB-CLL a small group of genes was identified, where bfl-1 was the strongest discriminating gene (p < 0.05), with higher expression in rB-CLL. A group of apoptosis-regulating genes were modulated during induction of apoptosis by serum deprivation in vitro in a similar manner in all cases studied. However, bfl-1 was preferentially downregulated in sB-CLL as compared to rB-CLL (p < 0.05). We conclude that bfl-1 may be an important regulator of B-CLL apoptosis, which could contribute to disease progression and resistance to chemotherapy, and as such represent a future potential therapeutic target.

Aged↗

PubMed2004

Loading of the antigen-presenting protein CD1d with synthetic glycolipids.

CD1 proteins present mammalian and microbial lipid and glycolipid antigens to different subsets of T cells. Few such antigens have been identified and the binding of these to CD1 molecules has mainly been studied by using responding T cells in cellular assays or recombinant solid-phase CD1 proteins. In the present study we use four different glycolipids, some of which contain tumor-associated carbohydrate antigens, to develop a procedure to easily detect binding of glycolipids to CD1 proteins on viable cells. Two of these glycolipids are novel glycoconjugates containing alpha-D-N-acetylgalactosamine (alpha-GalNAc) that were prepared by a combined solution and solid-phase approach. The key step, a Fischer glycosylation of 9-fluorenylmethoxycarbonylaminoethanol with GalNAc, furnished the alpha-glycoside 4 in 34% yield. Cells were incubated with glycolipids and stained with monoclonal antibodies specific for the carbohydrate part. The level of glycolipid bound to cells was then determined by flow cytometry with a secondary antibody labeled with fluorescein isothiocyanate. All four glycolipids were found to bind to CD1d but with different selectivity. The loading was dose dependent and could be inhibited by an established CD1d ligand, alpha-galactosylceramide. Through use of this procedure, glycolipids were selectively loaded onto CD1d expressed on professional antigen-presenting cells for future use as cellular vaccines. Moreover, the glycolipids described in this study represent novel CD1d-binding ligands that will be useful derivatives in the study of CD1d-dependent immune responses, for example, against tumors.

Animals↗

PubMed2004

Glucocorticoids delay age-associated thymic involution through directly affecting the thymocytes.

After puberty, the thymus undergoes a dramatic loss in size, resulting in a reduction in the number of thymocytes, a phenomenon termed age-associated thymic involution. The factors regulating this process are poorly understood. We investigated the role of endogenous glucocorticoids (GCs) in this process by studying transgenic mice with increased GC sensitivity restricted to the T-cell lineage due to overexpression of a GC-receptor transgene under the control of the proximal lck promoter. Surprisingly, in these transgenic mice, the age-associated thymic involution did not start until after 6 months of age, demonstrating that endogenous GCs through directly affecting the thymocytes delay the age-associated thymic involution process. The delayed age-associated thymic involution resulted in a significantly higher number of thymocytes in transgenic mice, compared with wild-type mice at 6 months of age or older. The higher number of thymocytes was associated with increased percentage of cycling double-negative and single-positive thymocytes, whereas thymic apoptosis was unaffected. The above effects of GCs were restricted to the thymocytes and were not reflected on the peripheral T cells, in which GCs suppressed the number of peripheral T cells in aged transgenic mice, demonstrating that thymocytes and T cells are differentially regulated by GCs. Furthermore, CD4(+) T cells were more affected than CD8(+) T cells, resulting in a decrease in the CD4/CD8 T-cell ratio. In summary, our results reveal novel biological effects of endogenous GCs on thymic involution and T-cell homeostasis in aged mice.

Aging↗

PubMed2004

Alternative processing for MHC class I presentation by immature and CpG-activated dendritic cells.

Exogenous proteins can be processed by antigen-presenting cells for the generation of MHC class I-restricted T cell responses. Where this occurs is not clear, although both transfer of internalized antigen into the cytosol and alternative processing in endolysosomes and phagosomes have been reported. Here we have studied the capacity of bone marrow-derived mouse myeloid dendritic cells (DC) to process the OVA protein for peptide presentation by H2-K(b). We have found that immature DC (iDC), both wild-type and transporter associated with antigen processing (TAP)-deficient cells, can transiently process OVA in a pathway which is resistant to inhibitors of the classical MHC class I pathway including the Golgi inhibitor Brefeldin A (BFA) and the proteasome inhibitor lactacystin. This alternative pathway is not found in subcultured DC with an intermediate maturity (imDC) or in resting, IL-3 expanded macrophages but can be re-expressed in imDC if these are activated by an immunostimulatory CpG oligonucleotide. Both iDC and CpG-activated DC were found to process OVA by regurgitation. In addition, we found that iDC secrete proteolytic enzymes into the supernatant, which can process OVA in the extracellular phase. These results suggest that multiple pathways exist for the processing of exogenous protein antigens into MHC class I-binding peptides.

Acetylcysteine↗

PubMed2004

Different roles for glucocorticoids in thymocyte homeostasis?

Glucocorticoids (GCs) have important immunoregulatory effects on thymocytes and T cells. Ectopic production of GCs has been demonstrated in thymic epithelial cells (TECs) but the role of GCs in thymocyte homeostasis is controversial. Studies in several different mouse models, genetically modified for the GC receptor (GR) expression or function, have demonstrated conflicting results in terms of the effect of the hormone on thymocytes. Here, we summarize these data and suggest that GCs can mediate both positive and negative effects in the organ depending on the local hormonal concentration. Basal GC levels might promote growth of early thymocytes in young mice, and increased levels, generated through a stress reaction, apoptosis in these cells. A gradual loss of GC synthesis in TECs during aging might contribute to thymic involution, a process so far unexplained.

Animals↗

PubMed2002

Immunotherapy with recombinant SFV-replicons expressing the P815A tumor antigen or IL-12 induces tumor regression.

Replicons based on alphaviruses are emerging as candidate vectors for vaccination and gene therapy purposes. We have reported previously that mice vaccinated with a recombinant Semliki Forest virus (a member of the alphavirus genus) carrying the gene encoding the P815A tumor antigen (rSFV/E-P1A) were protected against a lethal challenge with the P815 tumor. In this study we investigated the anti-tumor therapeutic efficacy of rSFV/E-P1A or rSFV expressing the cytokine interleukin 12 (rSFV/IL12) on Day 5-established tumors. The results show that both antigen-specific and cytokine-mediated rSFV treatments exhibited a significant effect on P815 tumor growth, by delaying tumor progression and even inducing complete tumor regressions in several mice. The therapeutic potency of these vectors was dependent on the size of the treated tumor, as treatment of mice bearing larger tumors showed lower efficacy. In addition, rSFV treatment resulted in long-term immunity as observed by the lack of tumor recurrence in the majority of tumor-regressing mice after rechallenge with the tumor. Furthermore, the anti-tumor therapeutic effect was only achieved by local intratumoral injection of rSFV, as treatment by injection in the contralateral site resulted in tumor progression comparable to control-untreated mice. Accordingly, expression of a rSFV-RNA was localized to the tumor and draining lymph node. These results further demonstrate the potential of rSFV replicons as tumor therapeutic agents.

Animals↗

PubMed2002

Effects of altered glucocorticoid sensitivity in the T cell lineage on thymocyte and T cell homeostasis.

The homeostatic regulation that controls total thymocyte and peripheral T-cell numbers is not clearly understood. We describe here a direct hormonal influence of endogenous levels of glucocorticoids (GCs) on thymocyte and peripheral T-cell homeostasis independent of indirect systemic effects of GCs. The results were obtained by generating transgenic mice with an altered GC sensitivity targeted to thymocytes and peripheral T cells by increasing or decreasing glucocorticoid receptor (GR) expression specifically in thymocytes and peripheral T cells. A twofold increase in GC sensitivity resulted in a major decrease in thymocyte number, affecting all subpopulations, although single-positive CD8+ cells were less influenced. In the thymus, this was due to increased apoptosis in the organ, whereas proliferation of thymocyte populations was unaffected. In the periphery, a pronounced reduction in T-cell number was seen, demonstrating an effect of endogenous GCs also on T-cell homeostasis. The effects were confirmed in transgenic mice with reduced GR expression, which showed increased thymocyte and T-cell numbers. Thus, our data demonstrate that physiological GC levels are directly involved in controlling the size of both thymocyte and T-cell pools.

Animals↗