Changes in thymic function with age and during the treatment of HIV infection
TL;DR: It is found that, although thymic function declines with age, substantial output is maintained into late adulthood and this results indicate that the adult thymus can contribute to immune reconstitution following HAART.
Abstract: The thymus represents the major site of the production and generation of T cells expressing alphabeta-type T-cell antigen receptors. Age-related involution may affect the ability of the thymus to reconstitute T cells expressing CD4 cell-surface antigens that are lost during HIV infection; this effect has been seen after chemotherapy and bone-marrow transplantation. Adult HIV-infected patients treated with highly active antiretroviral therapy (HAART) show a progressive increase in their number of naive CD4-positive T cells. These cells could arise through expansion of existing naive T cells in the periphery or through thymic production of new naive T cells. Here we quantify thymic output by measuring the excisional DNA products of TCR-gene rearrangement. We find that, although thymic function declines with age, substantial output is maintained into late adulthood. HIV infection leads to a decrease in thymic function that can be measured in the peripheral blood and lymphoid tissues. In adults treated with HAART, there is a rapid and sustained increase in thymic output in most subjects. These results indicate that the adult thymus can contribute to immune reconstitution following HAART.
Citations
More filters
TL;DR: These Guidelines were developed by the Panel* on Clinical Practices for Treatment of HIV Infection convened by the Department of Health and Human Services and the Henry J. Kaiser Family Foundation.
Abstract: SUMMARY The availability of an increasing number of antiretroviral agents and the rapid evolution of new information has introduced extraordinary complexity into the treatment of HIV-infected persons. In 1996, the Department of Health and Human Services and the Henry J. Kaiser Family Foundation convened the Panel on Clinical Practices for the Treatment of HIV to develop guidelines for the clinical management of HIV-infected adults and adolescents. This report recommends that care should be supervised by an expert, and makes recommendations for laboratory monitoring including plasma HIV RNA, CD4 cell counts and HIV drug resistance testing. The report also provides guidelines for antiretroviral therapy, including when to start treatment, what drugs to initiate, when to change therapy, and therapeutic options when changing therapy. Special considerations are provided for adolescents and pregnant women. As with treatment of other chronic conditions, therapeutic decisions require a mutual understanding between the patient and the health care provider regarding the benefits and risks of treatment. Antiretroviral regimens are complex, have major side effects, pose difficulty with adherence, and carry serious potential consequences from the development of viral resistance due to non-adherence to the drug regimen or suboptimal levels of antiretroviral agents. Patient education and involvement in therapeutic
4,321 citations
Cites background from "Changes in thymic function with age..."
...cell receptor V repertoires [110], and evidence of residual thymic function in patients receiving HAART [111, 112] demonstrate that partial immune reconstitution occurs in these patients....
[...]
TL;DR: NOD-scid IL2Rγnull mice engrafted with human mobilized blood stem cells provide a new in vivo long-lived model of robust multilineage human HSC engraftment.
Abstract: Ethical considerations constrain the in vivo study of human hemopoietic stem cells (HSC). To overcome this limitation, small animal models of human HSC engraftment have been used. We report the development and characterization of a new genetic stock of IL-2R common gamma-chain deficient NOD/LtSz-scid (NOD-scid IL2Rgamma(null)) mice and document their ability to support human mobilized blood HSC engraftment and multilineage differentiation. NOD-scid IL2Rgamma(null) mice are deficient in mature lymphocytes and NK cells, survive beyond 16 mo of age, and even after sublethal irradiation resist lymphoma development. Engraftment of NOD-scid IL2Rgamma(null) mice with human HSC generate 6-fold higher percentages of human CD45(+) cells in host bone marrow than with similarly treated NOD-scid mice. These human cells include B cells, NK cells, myeloid cells, plasmacytoid dendritic cells, and HSC. Spleens from engrafted NOD-scid IL2Rgamma(null) mice contain human Ig(+) B cells and lower numbers of human CD3(+) T cells. Coadministration of human Fc-IL7 fusion protein results in high percentages of human CD4(+)CD8(+) thymocytes as well human CD4(+)CD8(-) and CD4(-)CD8(+) peripheral blood and splenic T cells. De novo human T cell development in NOD-scid IL2Rgamma(null) mice was validated by 1) high levels of TCR excision circles, 2) complex TCRbeta repertoire diversity, and 3) proliferative responses to PHA and streptococcal superantigen, streptococcal pyrogenic exotoxin. Thus, NOD-scid IL2Rgamma(null) mice engrafted with human mobilized blood stem cells provide a new in vivo long-lived model of robust multilineage human HSC engraftment.
1,563 citations
Cites background from "Changes in thymic function with age..."
...Formation of TRECs results from intrathymic TCR rearrangement (45)....
[...]
TL;DR: A long-lived human memory T cell population that has an enhanced capacity for self-renewal and a multipotent ability to derive central memory, effector memory and effector T cells is described.
Abstract: Immunological memory is thought to depend on a stem cell–like, self-renewing population of lymphocytes capable of differentiating into effector cells in response to antigen re-exposure. Here we describe a long-lived human memory T cell population that has an enhanced capacity for self-renewal and a multipotent ability to derive central memory, effector memory and effector T cells. These cells, specific to multiple viral and self-tumor antigens, were found within a CD45RO−, CCR7+, CD45RA+, CD62L+, CD27+, CD28+ and IL-7Rα+ T cell compartment characteristic of naive T cells. However, they expressed large amounts of CD95, IL-2Rβ, CXCR3, and LFA-1, and showed numerous functional attributes distinctive of memory cells. Compared with known memory populations, these lymphocytes had increased proliferative capacity and more efficiently reconstituted immunodeficient hosts, and they mediated superior antitumor responses in a humanized mouse model. The identification of a human stem cell–like memory T cell population is of direct relevance to the design of vaccines and T cell therapies.
1,526 citations
Cites background from "Changes in thymic function with age..."
...Naive T cells have high levels of T cell receptor (TCR) rearrangement excision circles (TRECs), which are diluted during clonal proliferatio...
[...]
TL;DR: Ex vivo gene therapy with gamma(c) can safely correct the immune deficiency of patients with X-linked severe combined immunodeficiency and allow patients to have a normal life.
Abstract: Background X-linked severe combined immunodeficiency due to a mutation in the gene encoding the common γ (γc) chain is a lethal condition that can be cured by allogeneic stem-cell transplantation. We investigated whether infusion of autologous hematopoietic stem cells that had been transduced in vitro with the γc gene can restore the immune system in patients with severe combined immunodeficiency. Methods CD34+ bone marrow cells from five boys with X-linked severe combined immunodeficiency were transduced ex vivo with the use of a defective retroviral vector. Integration and expression of the γc transgene and development of lymphocyte subgroups and their functions were sequentially analyzed over a period of up to 2.5 years after gene transfer. Results No adverse effects resulted from the procedure. Transduced T cells and natural killer cells appeared in the blood of four of the five patients within four months. The numbers and phenotypes of T cells, the repertoire of T-cell receptors, and the in vitro pro...
1,111 citations
TL;DR: It is found that a large proportion of HIV-specific CD8(+) T cells that produce cytokines in response to cognate antigen are unable to divide and die during a 48-hour in vitro culture.
950 citations
References
More filters
TL;DR: In this article, a three-phase T cell reconstitution was demonstrated after HAART, with an early rise of memory CD4(+) cells, a reduction in T cell activation correlated to the decreasing retroviral activity together with an improved CD4+ T cell reactivity to recall antigens.
Abstract: Highly active antiretroviral therapy (HAART) increases CD4(+) cell numbers, but its ability to correct the human immunodeficiency virus (HIV)-induced immune deficiency remains unknown. A three-phase T cell reconstitution was demonstrated after HAART, with: (i) an early rise of memory CD4(+) cells, (ii) a reduction in T cell activation correlated to the decreasing retroviral activity together with an improved CD4(+) T cell reactivity to recall antigens, and (iii) a late rise of "naive" CD4(+) lymphocytes while CD8(+) T cells declined, however, without complete normalization of these parameters. Thus, decreasing the HIV load can reverse HIV-driven activation and CD4(+) T cell defects in advanced HIV-infected patients.
1,839 citations
"Changes in thymic function with age..." refers background in this paper
...Adult HIV-infected patients treated with highly active antiretroviral therapy (HAART) show a progressive increase in their number of naive CD4-positive T cell...
[...]
TL;DR: Quantitation of HIV-1 in plasma by QC-PCR may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative.
Abstract: Quantitative competitive polymerase chain reaction (QC-PCR) methods were used to quantify virion-associated human immunodeficiency virus type-1 (HIV-1) RNA in plasma from 66 patients with Centers for Disease Control stage I to IVC1 infection. HIV-1 RNA, ranging from 100 to nearly 22,000,000 copies per milliliter of plasma (corresponding to 50 to 11,000,000 virions per milliliter), was readily quantified in all subjects, was significantly associated with disease stage and CD4+ T cell counts, and decreased by as much as 235-fold with resolution of primary infection or institution of antiretroviral therapy. Plasma virus levels determined by QC-PCR correlated with, but exceeded by an average of 60,000-fold, virus titers measured by endpoint dilution culture. Quantitation of HIV-1 in plasma by QC-PCR may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative.
1,309 citations
"Changes in thymic function with age..." refers methods in this paper
...We used this internal standard to quantify signal-joint TRECs in thymocytes and PBMCs by quantitative competitive (QC)-PC...
[...]
TL;DR: In this paper, the role of LFA-1 has been highlighted, and several factors in addition to endogenous viral regulatory proteins have been reported as capable of modulating the state of viral latency and expression in vitro.
Abstract: Infection with human immunodeficiency virus (HIV) causes AIDS. As a consequence of the interaction of gp120 envelope with the CD4 receptor molecule expressed by a subset of T lymphocytes and by mononuclear phagocytes (MPs), a second envelope protein (gp41) mediates fusion of the virion membrane with the target membrane. In these events the role of adhesion molecules such as LFA-1 has recently been highlighted. Following viral entry, reverse transcription of the virion-associated RNA and integration of proviral DNA into the host genome are crucial steps in HIV infection, which can lead to expression of high levels of new HIV or to silent infection for indefinite periods, a condition defined as viral latency. Several factors in addition to endogenous viral regulatory proteins have been reported as capable of modulating the state of viral latency and expression in vitro, including the cytokine network that normally modulates immune homeostasis as well as the immune response to inflammatory stimuli. Finally, recent studies have underscored the observation that the CD4+ T lymphocytes are the major reservoir of HIV in the peripheral blood compartment and in the lymphoid tissues, which are characterized by a greater viral burden, whereas in nonlymphoid organs such as the brain and the lung, local infection is predominantly sustained by MPs.
1,090 citations
TL;DR: Thymus-dependent regeneration of CD4+ T lymphocytes occurs primarily in children, whereas even young adults have deficiencies in this pathway, and the results suggest that rapid T-cell regeneration requires residual thymic function in patients receiving high-dose chemotherapy.
Abstract: Background Inadequate reconstitution of CD4+ T lymphocytes is an important clinical problem complicating chemotherapy, human immunodeficiency virus infection, and bone marrow transplantation, but relatively little is known about how CD4+ T lymphocytes regenerate. There are two main possibilities: bone marrow–derived progenitors could reconstitute the lymphocyte population using a thymus-dependent pathway, or thymus-independent pathways could predominate. Previous studies have suggested that the CD45RA glycoprotein on CD4+ T lymphocytes is a marker for progeny generated by a thymus-dependent pathway. Methods We studied 15 patients 1 to 24 years of age who had undergone intensive chemotherapy for cancer. The absolute numbers of CD4+ T lymphocytes in peripheral blood and the expression of CD45 isoforms (CD45RA and CD45RO) on these lymphocytes were studied serially during lymphocyte regeneration after the completion of therapy. Radiographic imaging of the thymus was performed concomitantly. Results There was ...
1,044 citations
TL;DR: It is shown, using mathematical modeling, that redistribution of T cells to the blood can explain the striking correlation between the initial CD4+ and CD8+ memory T-cell repopulation and the observation that 3 weeks after the start of treatment memory CD4-cell numbers reach a plateau.
Abstract: The origin of CD4+ T cells reappearing in the blood following antiretroviral therapy in human immunodeficiency virus type-1 (HIV-1) infection is still controversial. Here we show, using mathematical modeling, that redistribution of T cells to the blood can explain the striking correlation between the initial CD4+ and CD8+ memory T-cell repopulation and the observation that 3 weeks after the start of treatment memory CD4+ T-cell numbers reach a plateau. The increase in CD4+ T cells following therapy most likely is a composite of initial redistribution, accompanied by a continuous slow repopulation with newly produced naive T cells.
735 citations
Additional excerpts
...Recent data indicate that the initial increase in CD4 p cells after HAART may result from release of sequestered cells from lymph node...
[...]