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PubMed2005

Transplanting stem cells: potential targets for immune attack. Modulating the immune response against embryonic stem cell transplantation.

The curative promise of stem cells and their descendants for tissue regeneration and repair is currently the subject of an intense research effort worldwide. If it proves feasible to differentiate stem cells into specific tissues reliably and safely, this approach will be invaluable in the treatment of diseases that lead to organ degeneration or failure, providing an alternative or supplementary source of tissue for transplantation. Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass of a pre-implantation blastocyst that can produce all cells and tissues of the foetus. In recent years, several laboratories have described the directed differentiation of ES cells into multiple mature cell types including: cardiomyocytes; haemopoietic cells; hepatocytes; neurones; muscle cells and both endocrine and exocrine cells of the pancreas. How the immune system of the host will respond when these ES cell-derived mature cells are transplanted is ill defined. This review will focus on the potential mechanisms that the immune system could use to target ES cell-derived transplants and how unwanted responses might be prevented.

Animals↗
PubMed2005

Kinetics of T lymphocyte responses to persistent antigens.

Long term sequential study of immune responses in the same individuals is difficult from the time commitment required and the problem of maintaining enough subjects to provide for comparative analysis. We closely studied one hundred women with silicone mammary devices through cross sectional analysis up to 26 years post implantation and a similar sample of women to 6 years post explantation. The T cell index, calculated from tritiated thymidine incorporation during lymphoblast transformation, rose to a post implant peak at 10.5-12.0 years, falling progressively over the next 14.0-15.5 years to values indicative of probable immune quiescence. Post explantation, the index rose over the first 3 years and then sharply declined to within the range for unexposed controls. The shape of these time curves contains considerable information referent cell dynamics for both stimulatory and inhibitory factors and for demonstrating net group effects, appropriate to analysis in the cross sectional perspective. When a subset of four women was studied frequently and sequentially up to 8 years, an internal oscillatory pattern emerged, focusing attention on both the stimulatory and the inhibitory aspects of long term clonal expansion. IL-2 has stimulatory and inhibitory properties at different levels of production and is considered a prime candidate as the essential cytokine. The equations have details, however, which require exploration beyond any such provisional conclusion. The analytic process was aided by normalization of oscillatory data to eliminate subject variability and by Pareto optimization to assess the trend shown by normalization. Pareto analysis revealed two minimally coordinated oscillations, one over time and the other along net clonal expansion or decline of the siloxane specific T lymphocyte clone. The segments of the time related oscillation greatly exceeded the reaction times of cytokines currently known to be active in T cell regulation. Although the ultimate controlling factor(s) may be cytokine or chemokine combinations, the data are compatible with some more basic regulatory factor(s) of cell integrity, including limits on the number of cell divisions which can be sustained in long term immunopathic lesions, among other processes.

Antigens↗
PubMed2001

Immune reconstitution after hematopoietic stem cell transplantation: gaining experience without losing naivety.

In addition to lymphocyte phenotyping and functional assays, new tools are now available to monitor specific aspects of the immune response in the follow-up of hematopoietic stem cell transplantation: reconstitution of T-cell diversity (spectratyping or immunoscope), ex vivo thymic function by measuring "T-cell receptor rearrangement excision DNA circles" and antigen-specific T-cell responses (HLA tetramers). Combining these methods should contribute to improve our current knowledge of how the immune system is reconstituted in different settings of hematopoietic stem cell transplantation and how we could improve this recovery process.

Antigens↗
PubMed2003

Presence of functional dendritic cells in patients chronically infected with hepatitis C virus.

The absence of expanded numbers of hepatitis C virus (HCV)-reactive CD8(+) T lymphocytes (CTLs) in patients chronically infected with HCV has led to the investigation of dendritic cell (DC) function in this population as a potential cause for this defect. Several studies have shown evidence for impaired monocyte-derived DCs in chronically infected patients. As it is difficult to reconcile these data with the fact that patients with chronic HCV are immune competent, we re-evaluated this finding, carefully assessing phenotypic markers and functional activity of patient DCs as compared with noninfected controls. In contrast to these prior studies, DCs from 13 of 13 chronic HCV patients expressed typical maturation markers. These mature DCs were capable of priming allogeneic T lymphocytes, as well as stimulating influenza-specific memory T cells. This finding is consistent with clinical and immunologic data that the deficit in the patient's immune repertoire is HCV-specific and suggests that refined models are required for understanding the role of DCs in HCV pathogenesis.

Adult↗
PubMed2002

A mathematical model for germinal centre kinetics and affinity maturation.

We present a mathematical model which reproduces experimental data on the germinal centre (GC) kinetics of the primed primary immune response and on affinity maturation observed during the reaction. We show that antigen masking by antibodies which are produced by emerging plasma cells can drive affinity maturation and provide a feedback mechanism by which the reaction is stable against variations in the initial antigen amount over several orders of magnitude. This provides a possible answer to the long-standing question of the role of antigen reduction in driving affinity maturation. By comparing model predictions with experimental results, we propose that the selection probability of centrocytes and the recycling probability of selected centrocytes are not constant but vary during the GC reaction with respect to time. It is shown that the efficiency of affinity maturation is highest if clones with an affinity for the antigen well above the average affinity in the GC leave the GC for either the memory or plasma cell pool. It is further shown that termination of somatic hypermutation several days before the end of the germinal centre reaction is beneficial for affinity maturation. The impact on affinity maturation of simultaneous initiation of memory cell formation and somatic hypermutation vs. delayed initiation of memory cell formation is discussed.

Antibody Affinity↗
PubMed2000

Immune system protects integrity of tissues.

The immune system neither discriminates between "Self" and "Nonself", nor it acts when confronting "Danger", rather, it reacts to disruption of tissue integrity allowing its renewal. The "integrity" hypothesis proposes three groups of signals that coordinate actions of dendritic cells and immunocytes during the initiation of the specific immune response, and suggests explanations for tolerance, memory formation, and repertoire selection, including differences with other theories.

Biological Evolution↗
PubMed2005

Specific memory within innate immune systems.

Research into immune defense has been considerably enriched by the increasing focus on innate immunity. This type of immunity is still considered to lack specific memory, largely because there is no evidence of mechanisms that could provide such memory (such as acquired immunity). However, recent experimental data demonstrate specific memory phenomena in invertebrates: these organisms are thought to rely solely on innate defense. Here, I argue that a clear definition of the terms 'specificity' and 'memory', together with dissection of the evolutionary roots of immune defense, show us that innate immunity should not be, and is probably not, necessarily free of specific memory.

Animals↗
PubMed2003

Kinetics of CD4+ and CD8+ memory T-cell responses during hepatitis C virus rechallenge of previously recovered chimpanzees.

The immunological correlates of hepatitis C virus (HCV)-specific immunity are not well understood. Antibodies to HCV structural proteins do not appear to play a key role in clearance of the virus and do not persist after recovery. Here, we studied the kinetics of the cellular immune responses of three HCV-recovered chimpanzees during rechallenge with increasing doses of homologous HCV. Although HCV envelope antibodies remained undetectable throughout the rechallenge, all animals mounted rapid HCV-specific T-cell responses. The pattern of the cellular immune response in blood and liver correlated with the virological outcome. The animal that most rapidly cleared circulating HCV as determined by nested reverse transcription-PCR (RT-PCR) displayed the most vigorous and sustained response of gamma interferon (IFN-gamma)-producing and proliferating CD4(+) T cells in the blood. Vigorous CD4(+) T-cell proliferation during viremia was followed by an increased frequency and a phenotypic and functional change of the tetramer(+) CD8(+) T-cell population. The second animal cleared HCV initially with strong peripheral and intrahepatic CD4(+) T-cell responses but experienced low-level HCV recrudescence 12 weeks later, when HCV-specific T cells became undetectable. The third animal maintained minute amounts of circulating HCV, detectable only by nested RT-PCR, in the face of a weak IFN-gamma(+) T-cell response. Collectively, the results suggest protective rather than sterilizing immunity after recovery from hepatitis C. The rate of HCV clearance following reexposure depends on the cellular immune response, the quality and quantity of which may vary among chimpanzees that recovered from HCV infection.

Animals↗