Cytotoxic CD8 T lymphocytes kill virus-infected cells and are critical for viral clearance from the body. Cytokines, particularly those sharing the common gamma receptor chain (gamma c), play a key role in this cytotoxic function as well as in the growth, differentiation and homeostasis of CD8 T lymphocytes. In order to exert these biological effects, cytokine-dependent signal transduction via the Janus kinase (Jak) / Signal Transducers and Activators of Transcription (STAT) pathway, the phosphoinositide 3-kinase (PI3-K) and mitogen-activated protein kinase (MAPK) pathways is required. In HIV infection however, the CD8 T lymphocytes become defective and are characterized by impaired cytotoxicity, altered differentiation patterns, and increased susceptibility to apoptosis. I hypothesized that impaired cytokine responsiveness resulting from defects in cytokine-dependent signal transduction contributes to the CD8 T cell impairment observed in HIV+ patients. I investigated the activation of the Jak/STAT signaling pathway to cytokines in CD8 T cells from HIV+ patients. Interestingly, these cells were responsive to IL-2, IL-4, IL-10, IL-15, and IL-21 at the level of their respective STAT activation. However, impairment of the IL-7 / IL-7Ralpha signaling axis was identified and characterized by a defect in STAT5 signaling. The impaired STAT5 activation correlated with a low IL-7Ralpha surface expression. The expanded population of IL- 7Ralphalow-expressing CD8 T cells, found particularly in viremic HIV+ patients, expressed higher levels of the transcriptional repressor Growth Factor Independent-1 (GFI1) compared to their IL-7Ralphahigh counterparts. This prompted further investigations into the role of GFI1 in IL-7Ralpha regulation in primary human CD8 T cells as a model. Though silencing of GFI1 did not modulate basal IL-7Ralpha expression, exogenous overexpression negatively regulated IL-7Ra surface levels. The gc cytokines, IL-2, IL-4, IL-7, and IL-15, but not IL-21, were found to efficiently suppress IL-7Ralpha expression however, only IL-4 simultaneously upregulated GFI1 expression. RNA interference studies targeting GFI1 in IL-4 stimulated CD8 T cells established a specific role for GFI1 in sustaining the suppression of IL-7Ralpha expression. Furthermore, transient downregulation of GFI1 in CD8 T cells subjected to IL- 4-dependent proliferation reduced their proliferative capacity. Other functions identified for GFI1 were in the suppression of CXCR4 and Bax expression in CD8 T cells. Studies aimed at identifying the signal transduction pathways responsible for regulating GFI1 and IL-7Ralpha expression revealed that IL-4-mediated downregulation of IL-7Ralpha expression required activation of the Jak/STAT and the PI3K pathways. On the other hand, IL-4-induced upregulation of GFI1 expression was mediated via the PI3K pathway. The JNK and P38 MAPK pathways appeared to be important as regulators of basal IL-7Ralpha expression levels, but had no statistically significant effects on GFI1 expression. To conclude, these studies have clarified the important biological effects of GFI1 in mature human CD8 T lymphocytes. Furthermore, exposure to IL-4 may generate CD8 T cell populations with an exhausted phenotype similar to those found in chronically-infected HIV+ patients, characterized by reduced cytotoxic activity and increased IL-4 production. Thus, the IL-4 study model may prove valuable for investigating the activity of human CD8 T cells in such chronic diseases and those characterized by a type 2 cytokine profile.

Philosophiae Doctor - PhD / Epidemiological studies have highlighted that leukaemia can be considered as the most prominent malignancy after radiation exposure during childhood. The lifetime risk on radiation-induced leukaemia for a given dose is 3 – 5 times higher for children compared to adults. The high risk at a young age is related to the elevated sensitivity of the red bone marrow where haematopoietic stem and progenitor cells (HSPCs) are located. HSPCs self-renewal capacity and long-life span increase their susceptibility to DNA damage accumulation, making them a major target of radiation-induced carcinogenesis. Proton beam therapy (PBT) is increasingly used to treat paediatric brain tumours due to its dose sparing properties compared to conventional X-ray based radiotherapy. However, concerns regarding the carcinogenic potential of secondary neutrons produced during PBT, especially in terms of their effect on HSPCs harboured in the cranial bone marrow of paediatric patients, remain. In this study, the radiobiological differences between 60Co γ-rays and p(66)/Be(40) neutron exposure was investigated to resolve the underlying mechanisms for the high radiosensitivity of HSPCs (CD34+ cells) isolated from umbilical cord blood (UCB). For both radiation qualities, an apparent dose-dependent increase in the frequency of radiation-induced MN was observed in CD34+ cells. Furthermore, increased cytogenetic damage was observed with the CBMN assay after neutron irradiation, which highlights its leukaemogenic potential. In addition, no difference was observed in the nuclear division index of the CD34+ cells post-irradiation between both radiation qualities. The number of DNA DSBs was assessed by microscopic scoring of γ-H2AX foci, 2 and 18 hours after radiation exposure. A significant higher number of DNA DSBs were observed 2 hours after neutron irradiation with 0.5 Gy, but decreased to similar levels for both radiation qualities after 18 hours. Different stages of apoptosis in CD34+ cells were studied at 18 and 42 hours numerous time points post-irradiation by flow cytometry using the Annexin/PI assay. In contrast to the γ-H2AX foci results, a significant difference in late apoptosis was observed at 18 hours and 42 hours between the two radiation qualities. The results point towards a fast error-prone DNA repair in HSPCs after neutron irradiation, which might contribute to genomic instability and leukemogenesis. In the second phase of the PhD project, the impact of age on radiosensitivity was investigated by comparing newborn T-lymphocytes with adult peripheral blood (APB) T-lymphocytes. The major difference between UCB and APB T-lymphocytes, is their immunophenotypic profile. Since it is known that different T-lymphocyte subsets have a difference in radiosensitivity, the fraction of CD4+, CD8+, naïve (CD45RA+) and memory (CD45RO+) T-lymphocytes was determined via flow cytometry in the two groups. The cytokinesis-block micronucleus (CBMN) assay was used to determine the extent to which age influences the frequency of cytogenic damage in response to 60Co γ-rays radiation. For both APB and UCB, an outspoken dose-dependent increase in the frequency of radiation-induced MN was observed at 0.5, 1, 3 and 4 Gy. However, no significant difference was observed at 4 Gy when comparing MN yields of APB and UCB. An increased radiosensitivity of newborn to adult donors of 34%, 42%, 29%, 26% and 16% was observed based on the MN scoring at doses of 0.5, 1, 2, 3 and 4 Gy, respectively. The lowest radiosensitivity was identified at the highest dose, which might explain the non-significant difference at 4 Gy. In addition, there was a clear trend that females were more sensitive to 60Co γ-rays radiation than males in both adults and newborns, even though the difference was not significant. The immunophenotypic study revealed that that both the CD4+ and CD8+ T-lymphocytes of newborns are mainly naïve. This is illustrated by the co-expression of CD45RA+ on 90.70% (range: 80.80% – 98.40%) and 95.90% (range: 89.60% – 98.80%) of CD4+ and CD8+ cells respectively. The composition of adult T-lymphocytes, in contrast, is clearly different with a more equal distribution between CD45RA+ and CD45RO+ subpopulations. This finding demonstrates that there are differences in the radiosensitivity between newborn and adult T-lymphocytes which might be linked to the immunophenotypic change of T-lymphocytes with age.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 122-146).

Disputats, Stockholm : Karolinska institutet, 2006. / Härtill 4 uppsatser. Med populärvetenskaplig sammanfattning på svenska.

The Bar-Or laboratory recently reported that human B cells from normal subjects can produce either pro-inflammatory (TNF-alpha; LT) or regulatory (IL-10) effector cytokines depending on their context of activation. It was of interest to investigate the change in B cell cytokine profiles from normal subjects when activated in the context of a Th1 pro-inflammatory environment or a Th2 anti-inflammatory environment. It was found that the B cell regulatory network of effector cytokines from normal subjects is significantly modulated depending on the local cytokine milieu. In addition, it was of interest to study how MS patients' B cell cytokine network would respond in a Th1 pro-inflammatory and a Th2 anti-inflammatory context. It was found that MS patients' B cell cytokine network was dysregulated compared to B cell responses from normal subjects. The findings define a novel regulatory network involving human B cells from normal subjects and point to a newly discovered abnormality in MS patients' B cells.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 5 uppsatser.