Cytotoxic T Lymphocytes (CTL) are known to play an important role in clearing infectious virus from infected hosts in a variety of viral infections. Depending on the type of virus and mode of virus entry both class I and class II restricted CTL can contribute to protection from virus-induced disease. Although CD8 positive CTL are associated with virus elimination and control in many viral infections, elimination of neurotropic viruses from the Central Nervous system (CNS) is more complex due to the lowered expression of MHC antigens on neuronal cells. This failure to constitutively express high levels of MHC antigens by neurons could serve as an advantage to avoid damage to this differentiated and non-renewable tissue. However, abnormal induction of MHC antigens in the CNS mediated by CD4 positive lymphocytes or by astrocytes have also been shown to cause destructive inflammation in the CNS. The present study deals with CTL responses against one such neurotropic virus called Japanese Encephalitis Virus (JEV). JEV is a positive-stranded RNA virus that belongs to the flavivirus group, a group that is among the most important agents causing human encephalitis worldwide. Although passive transfer of monoclonal antibodies against this virus has been shown to confer protection of mice from lethal challenge with virus, neither the presence of CTL against this virus nor its role in conferring protection has been reported so far. Understanding the CTL responses against these viruses acquired importance in light of recent reports that neurovirulence of JEV and yellow fever viruses can be enhanced by the administration of virus specific antibodies. Hence this study was undertaken to examine the possibility of raising CTL specific to JEV. The specificity of the CTL raised, their therapeutic value and the ability of different lymphocyte subsets to mediate protection in vivo are dealt with in this study. Generation of CTL against JEV The generation of CTL against JEV in BALB/c mice, requires MHC defined cell lines that not only support virus infection but are also histocompatible. Several cell lines were initially examined for their ability to support JEV infection as a prc-rcquisitc before their utilization in in vivo and in vitro stimulation protocols aimed at generating JEV-specific CTL. Virus infection was monitored by immunofluorescence using JEV envelope-specific monoclonal antibodies as well as by titration of virus produced from infected cells by plaque assays. These different cell lines that were characterised for their ability to support JEV infection were then utilised to generate and monitor antiviral CTL. Several in vivo immunisation protocols were examined initially find out which of these infected cells prime BALB/c mice efficiently for generation of virus-specific CTL upon secondary stimulation in vitro with infected syngeneic cells. Immunisation of mice with infected cells per se was preferred over free virus since this was thought to facilitate priming against some viral non-structural proteins preferentially found on infected cells in addition to other viral structural proteins. It was observed that not only infected syngeneic and allogeneic cells but also infected xenogeneic cells prime BALB/c mice for the generation of JEV- specific CTL upon secondary restimulation in vitro. An optimal protocol was standardised for the generation of CTL against JEV. This included primary in vivo immunisation of mice followed by secondary in vitro restimulation of splenocytes with infected syngeneic cells. Either immunisation alone or in vitro stimulation of naive splenocytes alone was unsuccessful. The effector cells generated specifically lysed JEV-infccted P388D1 targets but not uninfected P388D1 or YAC-1 targets suggesting that the lysis on infected targets is not mediated by Natural Killer activity. Specificity and MHC restriction of anti JEV Effectors Cell depletion studies using complement mediated lysis were performed to examine the phenotype of the cells mediating virus specific lysis of infected targets. Depletion of Lyt 2.2+ or Thy 1+ but not L3T4+ sub-populations of effector cells inhibited lysis of infected targets showing that the effectors mediating virus-specific lysis were Lyt-2+ T cells. Examination of target specificities and MHC restriction of the antiviral CTL generated showed that although infected xenogeneic cells were used for immunisation, the effector cells recognised only infected syngeneic (P388D1, Sp2/0) and semisyngeneic (Neuro 2a, YAC-1) cells. Virus-specific recognition was found to be class I Kd and class I Dd restricted. These effector cells were also found to recognise cells infected with a closely related flavivirus, West Nile Virus (WNV) suggesting that they were crossreactive to some degree. Based on the consensus motif that has been established for H-2Kd associated peptides, several nonamers were predicted as possible CTL epitopes by scanning the deduced amino acid sequences of three strains of JEV and WNV. Among several predicted nonamers, three peptides were examined for their ability to reconstitute lysis of uninfected targets by polyclonal anti JEV CTL populations. Results demonstrate that peptides derived from NS1 and NS3 but not NS5 protein of JEV were able to partially reconstitute lysis of uninfected targets by effectors when pulsed with the appropriate peptide. Protective ability of the CTL raised against JEV To examine whether anti-JEV effectors raised in vitro could confer protection from intracerebral challenge with JEV, these effectors were adoptively transferred into adult BALB/c mice intracerebrally along with 10 x LDJ0 dose of JEV. More than 55% of these animals were protected from death and survived beyond 100 days after JEV challenge demonstrating that adoptively transferred anti-JEV effectors could indeed confer protection from lethal challenge with JEV. However, adoptive transfer of effectors by either intravenous or intraperitoneal routes did not protect adult mice from the lethal effects of intracerebral challenge with JEV. In contrast to adult mice, newborn mice were not protected from death by the adoptively transferred effector cells. This was also supported by experiments where a correlation was observed with the increasing age of mice and the success of protection conferred by the adoptively transferred effector cells. To establish the identity of cell subsets responsible for protection, Lyt 2, L3T4 or Thy 1 positive cells were specifically depleted from the polyclonal CTL by multiple cycles of complement mediated lysis and the remaining cells were adoptively transferred intracerebrally along with 10 x LD of JEV. These results demonstrate that both Lyt 2 and L3T4 positive T cells present in the effector population were necessary to confer protection of adult mice. Examination of virus-specific neutralising antibodies in the sera of protected and unprotected mice revealed that presence of L3T4 positive cells in the adoptively transferred population increases virus-specific neutralising antibodies. However presence of neutralising antibodies alone was not sufficient to confer protection. The protection required both Lyt-2 and L3T4 positive cells together. These studies could in the long term throw some light on similar observations about age dependant susceptibility to JEV in humans.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 100-117).

Το CD40L είναι ένα συνδιεγερτικό μόριο και αποτελεί πρώιμο δείκτη ενεργοποίησης του Τ λεμφοκυττάρου. Υπάρχουν δεδομένα που υποστηρίζουν την υπόθεση ότι τα ενεργοποιημένα Τ λεμφοκύτταρα πιθανώς παίζουν ρόλο στην παθογένεια της ψωριασικής αρθρίτιδας (ΨΑ). Μελετήσαμε συνολικά 12 ασθενείς με ΨΑ, 6 ασθενείς με ρευματοειδή αρθρίτιδα (ΡΑ) και 4 υγιείς εθελοντές. Υπολογίσαμε την έκφραση του CD40L στην επιφάνεια των Τ λεμφοκυττάρων με κυτταρομετρία ροής σε κατάσταση ηρεμίας και μετά από διέγερση με ΡΜΑ/ιονομυκίνη. Επίσης μελετήσαμε την ανασταλτική δράση της κυκλοσπορίνης στην επαγόμενη έκφραση του CD40L. Η έκφραση του CD40L ήταν σημαντικά αυξημένη στην επιφάνεια των Τ λεμφοκυττάρων των ασθενών με ΨΑ, ειδικότερα αυτών με ενεργό νόσο, σε σύγκριση με τους υγιείς εθελοντές και τους ασθενείς με ΡΑ (μέσο ποσοστό των CD3+CD40L+ κυττάρων: 23.74%, 11.59% και 9.57% για τους ασθενείς με ενεργό ΨΑ, ασθενείς με ΡΑ και υγιείς εθελοντές αντίστοιχα). Η αναστολή από την κυκλοσπορίνη της επαγόμενης έκφρασης του CD40L ήταν εξίσου αποτελεσματική και στις 3 ομάδες μελέτης. Συμπερασματικά αναφέρουμε ότι το CD40L υπερεκφράζεται στη επιφάνεια των Τ λεμφοκυττάρων ασθενών με ενεργό ΨΑ μετά από in vitro διέγερση. Το γεγονός αυτό ενισχύει την άποψη ότι ο άξονας CD40- CD40L παίζει σημαντικό ρόλο στη παθογένεια της ΨΑ και κατά συνέπεια θεραπείες που να στοχεύουν εκλεκτικά αυτόν τον άξονα θα μπορούσαν να δοκιμαστούν στην ΨΑ. / CD40L is a costimulatory molecule and an early activation marker of T lymphocytes. Evidence supports the hypothesis that activated T cells may play a role in the pathogenesis of psoriatic arthritis (PsA). We examined the levels of CD40L expression on resting T cells from 12 patients with PsA, 6 patients with rheumatoid arthritis (RA) and 4 healthy volunteers, and following stimulation with phorbol myristate acetate (PMA)/ionomycin. The inhibitory effect of cyclosporine A (CsA) on the induced expression of CD40L was also evaluated. This expression was significantly increased on the cell surface of T cells from patients with PsA, particularly those with active disease, when compared to normal individuals and patients with RA (mean percentages of CD3+ CD40L+ cells: 23.74%, 11.59% and 9.57% for patients with active PsA, patients with RA and healthy volunteers, respectively). CsA-mediated inhibition of CD40L induction was equally effective in all study groups. In conclusion, we report herein that CD40L is overexpressed in patients with active PsA. This may indicate that CD40L with its counter-receptor may be crucially involved in the pathogenesis of PsA. Consequently, therapies specifically targeting this pair may be worth testing.

There are currently an estimated 33.2 million people living with human immunodeficiency virus (HIV) worldwide. For these individuals, long-term use of combination antiretroviral therapy (cART) is not feasible for a variety of reasons including major adverse complications, multi-drug resistance, poor adherence, and high cost. Hence, development of novel therapeutic strategies that can reduce the life-long dependency on cART is highly desired. In order to develop effective therapeutic strategies such as a therapeutic vaccine, we need to have a greater understanding of the immune correlates of viral control in chronic HIV infection. In this thesis, we used treatment interruption (TI) as a tool to test the efficacy of several therapeutic approaches and immune parameters for their association with effective control of viral replication. / In Chapter 2 we showed that cART intensification and Remune vaccination resulted in reduced viral load (VL) plateau during sequential TIs. Although HIV-specific immune responses measured by interferon-gamma (IFN-gamma) enzyme-linked immunospot assay (ELISPOT) increased in the same time frame, neither their breadth nor magnitude correlated with the decrease in VL plateau. In Chapter 3 the effect of ALVAC-vCP1425 plus Remune vaccination on HIV proteome-wide HIV-specific responses was monitored using a dual color IFN-gamma/interleukin-2 (IL-2) ELISPOT assay. We observed an increase in the magnitude of HIV-specific IFN-gamma/IL-2 responses, as well as in the breadth of Gag-specific IFN-gamma responses in the vaccinated groups compared to placebo groups. A shift towards an increased contribution of Gag-specific responses to total HIV-specific vaccine induced immune response was associated with longer delay to viral rebound during TI. In Chapters 4 and 5, we examined baseline pre-TI immune parameters and their association with viral rebound and CD4 count change during TI in HIV-infected individuals in the chronic phase of infection experiencing virologic failure before TI (Chapter 4) or with different levels of VL control while on therapy prior to TI (Chapter 5). We saw that chronic antigen stimulation from persistent viremia as well as co-infections such as with cytomegalovirus are associated with T-cell senescence, which may result in less favourable clinical outcomes during TI. / Consequently, results from this thesis contribute to further understanding of immune correlates of viral control in chronic HIV infection. New therapeutic vaccines and interventions should induce polyfunctional HIV-specific immune responses, broad Gag-specific immune responses, as well as reducing chronic antigen stimulation to prevent irreversible T-cell exhaustion. Taken together, these insights could potentially lead to the development of novel treatment interventions that could effectively control viral replication off cART.

The peripheral naive CD4 T cell pool is homeostatically regulated through a balance of thymic production, delivery of survival signals and homeostatic proliferation. CD4 recent thymic emigrants (RTEs) have a high T cell receptor excision circle (TREC) content and express high levels of CD31. We report premature thymic involution in RRMS, initiated by reduced numbers of naive CD4 T cells and various naive CD4 T cell subsets in peripheral blood. Further, CXCR4, a receptor involved in emigration from the thymus, and CD127 and Bcl-2 (survival signals) are upregulated in various naive CD4 T cell subsets in RRMS. As a compensatory process, naive CD4 T cells undergo homeostatic proliferation. This proliferation is a form of peripheral positive selection through self-MHC/self-antigen interaction and thus can contribute to the expansion of autoreactive T cells and predispose to development of RRMS.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 122-140).

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.