Types Of Memory Cells Research Articles

CD8 T cell memory: it takes all kinds

Understanding the mechanisms that regulate the differentiation and maintenance of CD8+ memory T cells is fundamental to the development of effective T cell-based vaccines. Memory cell differentiation is influenced by the cytokines that accompany T cell priming, the history of previous antigen encounters, and the tissue sites into which memory cells migrate. These cues combine to influence the developing CD8+ memory pool, and recent work has revealed the importance of multiple transcription factors, metabolic molecules, and surface receptors in revealing the type of memory cell that is generated. Paired with increasingly meticulous subsetting and sorting of memory populations, we now know the CD8+ memory pool to be phenotypically and functionally heterogeneous in nature. This includes both recirculating and tissue-resident memory populations, and cells with varying degrees of inherent longevity and protective function. These data point to the importance of tailored vaccine design. Here we discuss how the diversity of the memory CD8+ T cell pool challenges the notion that “one size fits all” for pathogen control, and how distinct memory subsets may be suited for distinct aspects of protective immunity.

Combined mTOR Inhibition and OX40 Agonism Enhances CD8+ T Cell Memory and Protective Immunity Produced by Recombinant Adenovirus Vaccines

The memory CD8(+) T cell population elicited by immunization with recombinant human adenovirus serotype 5 (rHuAd5) vaccines is composed primarily of effector and effector memory cells (T(EM)) with limited polyfunctionality. In this study, we investigated whether treatment with immunomodulators could enhance and/or redistribute the CD8(+) memory population elicited by rHuAd5. Vaccination in combination with both rapamycin (to modulate differentiation) and an OX40 agonist (to enhance costimulation) increased both the quantity and polyfunctionality of the CD8(+) memory T cell population, with expansion of the T(EM) and memory precursor populations. Furthermore, this intervention enhanced protection against multiple virus challenges. Attenuation of adenovirus transgene expression was required to enable the combination rapamycin + OX40 agonist immunomodulatory treatment to further enhance skewing towards central memory formation, indicating that persistence of antigen expression ultimately limits development of this memory population following rHuAd5 immunization. These results demonstrate that during the expansion phase following adenovirus immunization, the level of mammalian target of rapamycin (mTOR) activity, the amount of costimulation and the duration of antigen availability act together to define the magnitude, phenotype, and functionality of memory CD8(+) T cells. Modulation of these factors can be used to selectively manipulate memory formation.

B‐lymphocyte biology

B‐lymphocyte biology

Memory CD8. + T Cells Specific for Minor Histocompatibility Antigen H60 Can Mediate the Graft-Versus-Leukemia Effect.

Abstract 1332Poster Board I-354In allogeneic hematopoietic stem cell transplantation (alloSCT), donor T cells mediate graft-vs-leukemia (GVL) but also cause graft-vs.-host disease (GVHD). Our previous studies indicate that memory T cells (TM) induce less GVHD than do naïve T cells (TN). Therefore the selective infusion of memory T cells could improve immune reconstitution with less GVHD. However, human memory T cells have a more restricted TCR repertoire than do TN and therefore may be less effective in mediating GVL. One approach for addressing this concern would be to vaccinate donors against a single miHA expressed by host leukemic cells. Then the selective transfer of memory T cells could improve both GVL and immune reconstitution with less GVHD. Questions remain about how best to apply this strategy. For example, differences in target antigen distribution could affect the re-expansion of transferred memory cells and determine whether vaccination augments GVHD. Also, different types of memory cells could behave differently. To begin to optimize this approach in mouse models we chose as our target antigen the H-2Kb-restricted minor histocompatibility antigen (miHA) H60. We cloned the H60 peptide sequence (LTFNYRNL) into a genetic construct encoding the heavy chain of a monoclonal antibody against DEC205. Donor C3H.SW (H-2b, H60-) mice were vaccinated with a single injection of anti-DEC205-H60 plus an agonist antibody against CD40 (FGK45). By two months post vaccination, H60-reactive memory cells were a stable population that comprised approximately 4-8% of splenic and peripheral blood CD8 cells. Approximately 50% of H60-tetramer+ cells had central memory phenotype, which could be ideal as central memory T cells mount strong anti-tumor responses. Similar results were obtained by using a prime/boost approach with H60-pulsed DCs. To test their function, CD44+ memory CD8 cells from H60-vaccinated mice were sort-purified and transferred into recipient B6 mice congenic for H60 (B6.H60; expression hematopoietically restricted ). By day 7 post transplant, H60-specific CD8+ TM from vaccinated mice comprised 70-90% of total splenic and blood CD8 cells, as compared to 1-5% in recipients of TM from unvaccinated mice. In contrast to anti-H60 responses by naïve CD8 cells, expansion of H60-tetramer+ cells from H60-vaccinated mice did not require CD4 help. To test whether target antigen distribution affects the re-expansion of H60-reactive cells from H60-vaccinated mice, expansion was compared in B6.H60 and B6.H60<right arrow>B6.actH60 (ubiquitous expression of H60 driven by an actin promoter) bone marrow chimeras. Approximately 60% of splenic and lymph node CD8 cells in both recipient groups were H60-tetramer+, though there was a trend towards increased overall numbers of tetramer+ cells in B6.H60 recipients. We are currently testing the GVL potency of TM from H60-vaccinated against mouse models of chronic phase (CP-CML) and blast crisis chronic myelogenous leukemia (BC-CML). In an ongoing experiment, very low numbers of CD8+ TM from H60-vaccinated mice mediate potent GVL against CP-CML relative to CD8+ TM from unvaccinated donors. Small numbers of CD8+ TM cells from vaccinated mice also mediated GVL against BC-CML, which is typically GVL resistant. Future studies will better define the potency of TM from H60-vaccinated mice and test these cells against CP-CML and BC-CML that do or do not express H60 but are otherwise identical. GVHD effect will also be tested. DisclosuresNo relevant conflicts of interest to declare.

Acquired immunity: immunosenescence and physical activity

AbstractSeveral lines of evidence indicate that infectious diseases, cancer, and autoimmune disorders occur more frequently in elderly people, thus suggesting that altered function of immune organs and cells, such as thymus and T and B lymphocytes are of primary importance in the pathogenesis of these diseases. Furthermore, old subjects are less responsive to vaccine than younger because of immune changes. The most common changes accompanying the adaptive immune system include decrement of T and B cells proliferation, repertoire degeneracy, increase of the memory cell type, decreased numbers of naive cells, and shift from T helper1(Th1) to T helper2(Th2) response. Regular exercise in the elderly may improve the alterations in acquired immunity which follow the physiological process of aging, allowing a major resistance against external pathogens and a better quality of life.

HIV infection destabilizes a targeted subset of the gamma/delta T cell repertoire

The mature gamma/delta T cell receptor repertoire arises by a process of positive selection and amplification of cells expressing the Vg2Vd2 TCR, with further skewing to TCR with the Vg2-Jg1.2 rearrangement. Once formed, the Vg2 repertoire is stable in healthy adults showing more than 50% sequence conservation over intervals of up to 7 years. The Vg2-Jg1.2 chains are among the most conserved elements in healthy individuals and even the balance among naive and memory cell types is maintained. This situation is altered by HIV infection. We showed previously that HIV disease was associated with the targeted loss of cells expressing the Vg2-Jg1.2 rearrangement. In longitudinal studies with specimens from the MACS cohort, we showed that peripheral blood Vg2Vd2 T cell has a high frequency of staining with the vital dye 7-AAD, in most specimens the Vg2Vd2 T cells were twice as likely to be 7-AAD positive compared with CD4+ T cells. The lower viability of circulating Vg2Vd2 T cells was reflected in the repertoire characteristics. We observed a high degree of repertoire conservation in HIV+ individuals, with values consistent with the lower range found in healthy adults. However, stability was confined largely to Vg2 cells with rearrangements using J segments other than Jg1.2. In most cases, any Jg1.2 sequences that were found in HIV+ individuals were not seen in subsequent specimens collected at 6 monthly intervals. The pattern of instability among only the Vg2-Jg1.2+ cells, shows that the effect of HIV on repertoire is a process of rapid turn-over among cells that may be reacting to viral antigens while cells without known responses to HIV (Vg2 with all other Jg rearrangements) are relatively unaffected. Even in this population of cells that are not susceptible to direct infection, owing to the lack of CD4 receptor, depletion is confined to the virus reactive cells.

Homeostasis of memory T cells

The pool of memory T cells is regulated by homeostatic mechanisms to persist for prolonged periods at a relatively steady overall size. Recent work has shown that two members of the common gamma chain (gammac) family of cytokines, interleukin-7 (IL-7) and IL-15, govern homeostasis of memory T cells. These two cytokines work in conjunction to support memory T-cell survival and intermittent background proliferation. Normal animals contain significant numbers of spontaneously arising memory-phenotype (MP) cells, though whether these cells are representative of true antigen-specific memory T cells is unclear. Nevertheless, it appears that the two types of memory cells do not display identical homeostatic requirements. For antigen-specific memory CD8+ T cells, IL-7 is primarily important for survival while IL-15 is crucial for their background proliferation. For memory CD4+ T cells, IL-7 has an important role, whereas the influence of IL-15 is still unclear.

CD8 + T-Cell Subpopulations in Human Abdominal Aortic Aneurysm Lesion

To the Editor: We read with interest the article by Duftner et al1 reporting the prevalence of peripheral interferon-γ (IFN-γ)–producing CD4+CD28− and CD8+CD28− T cells in patients with small abdominal aortic aneurysm (AAA). Along with the recent description that Th1-type immune responses predominate in human end-stage AAA lesion,2,3 their observation further supports preference toward polarized type 1 T-cell responses in aneurysm disease. The potential involvement of Th1 cells in the pathogenesis of the disorder is also suggested by the convincing demonstration that absence of CD4+ T cells or targeted deletion of IFN-γ prevents the induction of experimental AAA in a calcium chloride–induced mouse model,4 AAA formation being reconstituted by administration of IFN-γ into CD4−/− mice or infusion of competent splenocytes from wild-type mice into IFN-γ−/− mice. In their study, Duftner et al further established that both circulating CD4+CD28− and CD8+CD28− T cells are highly differentiated cells that display extensive CD45RO to CD45RA reversion and produce large amounts of IFN-γ and perforin. Surprisingly, low percentages of CD8+CD28− T cells were identified in AAA tissue sections using immunohistochemistry compared with flow cytometric analysis of peripheral blood mononuclear cells. In a series of our …

The Influence of Migration, Alloreactive Repertoire and Memory Subset on the Differential Ability of Naive and Memory T Cells To Induce GVHD.

Allogeneic stem cell transplantation (alloSCT) can cure many hematologic malignancies and hematopoietic stem cell disorders but is frequently complicated by graft vs. host disease (GVHD). We and others have published that memory phenotype (CD62LloCD44hi) T cells do not cause GVHD but can engraft and mount immune responses, including graft-vs.-tumor (GVT) effects. Importantly, these findings apply to GVHD induced by CD4 or CD8 T cells, and across major MHC differences. Thus, the inability to induce GVHD seems a fundamental property of memory phenotype (M) cells. We are investigating several hypotheses to explain why naïve cells (N) cause potent GVHD but M cells do not, including: 1. M cells lack CD62L and fail to traffic to LN and PP, two sites that may be essential for initial priming to allogeneic antigens and 2. M cells have a restricted alloreactive repertoire. There are at least two types of memory cells: central memory (CM) and effector memory (EM). EM cells (CD62LloCCR7neg) quickly express effector functions upon restimulation, preferentially migrate to tissues and spleen (bypassing LNs) and have relatively lower proliferative potential. CM cells (CD62LhiCCR7pos) have hybrid properties of both N and effector cells. Like N cells, their adhesion and chemokine receptors promote migration to LNs; however, their effector functions are more vigorous than N cells, yet slower than EM cells. It is of clinical interest for the design of M cell transfusion to determine the contributions of CM vs. EM cells in GVHD, but prior studies have not clearly investigated CM cells. We therefore compared GVHD initiated by N, EM and CM CD4 cells in the B6 (H-2b) ->BALB/c (H-2d) model. CM cells caused severe GVHD, similar to that induced by N cells. This suggests that LN homing enables M cells to initiate GVHD and/or that CM cells have unique functional properties required to initiate GVHD which are lacking in EM cells. We next asked whether LN entry was required for donor cells to initiate GVHD. N cells induced GVHD, albeit less severe than in WT recipients, in recipients lacking all secondary lymphoid organs (LN, PP and spleen), suggesting that priming in tissues is sufficient. Both of these findings support those of Beilhack, et al. ( Blood 2005; 106:1113) that migration affects T cell initiation of GVHD. However, we also found that N cells from CD62L-deficient donors caused GVHD. Thus, because CD62L function and even secondary lymphoid tissue are dispensable for GVHD induction, we conclude that homing differences alone do not control GVHD and that critical functional properties other than homing must limit EM cells' ability to induce GVHD. To address the role of repertoire, we increased the alloreactive precursor frequency of M cells. We isolated Thy1.1 (B6.C) (H-2d) effector T cells from mice with active GVHD (BALB/c recipients), and therefore with expanded anti-BALB/c repertoire, and parked them in syngeneic RAG1-/- (B6.C) recipients to allow them to differentiate into M cells. After 4 weeks we re-isolated the alloreactive M cells and transplanted them into new BALB/c recipients. The alloreactive M cells engrafted and caused transient skin GVHD without gut GVHD, unlike the more severe chronic GVHD induced by fresh N cells. This muted GVHD argues that although M cells can cause limited GVHD if their repertoire is artificially increased, they are still lacking in other functional properties required for optimal GVHD induction.

A Charge-Control SPICE Engineering Model for the Parasitic Bipolar Transistor Action in SOI CMOS Single-Event Upsets

An ion strike on an SOI CMOS transistor produces a charge cloud of electron-hole pairs. The subsequent behavior of the charge cloud as it spreads and impinges on the source and drain junctions is explained by 1-D analytical solutions and by 2-D device simulations. By examining the charge cloud from a top view perspective and a side view perspective, it is shown that a 2-D side view simulation gives about the same electrical behavior as would a 3-D simulation, thereby eliminating the necessity for expensive and time-consuming 3-D simulations. It is further shown that the electrical behavior predicted by 2-D simulations can be captured in a simple bipolar SPICE model, which is necessary for practical SEU analysis of large numbers of logic and memory cell types. The SPICE model is based on fundamental physical parameters, not curve-fitting. The predictions of the SPICE model correlate well with experimental SEU sensitivities of a D-type flip-flop and a six-transistor SRAM cell processed in a 0.35 /spl mu/m SOI technology.

Flow cytometric detection of perforin in normal human lymphocyte subpopulations defined by expression of activation/differentiation antigens

We investigated with three-color flow cytometry the expression of perforin (Pf) in normal human lymphocyte subpopulations identified by means of activation and differentiation-related antigens. Interestingly, Pf could be detected in a substantial subset (13±2%) of memory CD4 +CD45RO + cells, on relevant percentages of memory (CD45RO +) and naive (CD45RA +) CD8 + cells and on virtually all CD3 −CD16 +, CD3 −CD56 + and NKB1 + natural killer cells, as expected. The analysis of fluorescence intensity showed higher levels of Pf expression on CD8 dim and NK cells compared to CD8 bright and CD4 + lymphocytes, Pf and CD69, HLA-DR, CD95 and CD25 activation/differentiation-related antigens were never co-expressed. On average, 15±3% of CD3 +CD28 + cells were found to be Pf +, in line with a previously activated or memory cell type. Comparable percentages of CD8 +CD11b − (cytotoxic) and CD8 +CD11b + (suppressor) T cells were Pf +. Multiparameter flow cytometry is a powerful tool to detect minute fractions of Pf-expressing cells in heterogeneous populations.

Test CMOS/SOS RAM for transient radiation upset comparative research and failure analysis

The test Complementary Metal-Oxide-Semiconductor/Silicon-on-Sapphire Random Access Memory (CMOS/SOS RAM) with eight types of memory cells was designed and tested at high dose rates with a flash X-ray machine and laser simulator. The memory cell (MC) design with additional transistors and RC-chain was found to be upset free up to 2/spl times/10/sup 12/ rad(Si)/s. An "inversion" effect was discovered in which almost 100% logic upset was observed in poorly protected memory cell arrays at very high dose rates.

A 20-Gb/s flip-flop circuit using direct-coupled FET logic

A new type of direct-coupled FET logic (DCFL) flip-flop called the memory cell type flip-flop (MCFF) is presented. The MCFF operates faster than conventional DCFL flip-flops and enhances the DCFL's advantages, such as low power consumption and high packing density. A D-flip-flop IC and a 1/8 divider IC were developed using the MCFF. These ICs were fabricated using 0.2- mu m-gate pseudomorphic inverted HEMTs. The D-flip-flop IC is confirmed to operate up to 20 Gb/s. The 1/8 divider is toggled up to a maximum frequency of 25 GHz. These results prove that the MCFF enables DCFL circuits applicable not only to large-scale integration but to small-scale and medium-scale integration operating up to 20 Gb/s as well.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ion implantation challenges in the drive towards 64 Mb and 256 Mb memory cell type devices

Ion implantation techniques will be critical in the production of evermore complex devices, with major challenges for the device designer in utilising available techniques and those that are potentially available. Equally difficult challenges face the equipment designer in judging which technologies are required for future devices and welding these requirements into a reliable, productionworthy fabrication tool, capable of meeting or exceeding the automation and up-time expectations of the wafer fabrication managers. High yield and consistent performance on the wafer continue to be paramount. This paper will review these challenges from the equipment suppliers' viewpoint and in particular the new technology needs and cost of ownership issues.

Analysis and modeling of floating-gate EEPROM cells

Floating-gate MOS devices using thin tunnel oxide are becoming an acceptable standard in electrically erasable nonvolatile memory. Theoretical and experimental analysis of WRITE/ERASE characteristics for this type of memory cell are presented. A simplified device model is given based on the concept of coupling ratios. The WRITE operation is adequately represented by the simplified model. The ERASE operation is complicated due to formation of depletion layers in the transistor's channel and under the tunnel oxide. Experimental investigation of these effects is described, and they are included in a detailed cell model. In certain cell structures, a hole current can flow from the drain into the substrate during the ERASE oepration. This effect is shown to be associated with positive charge trapping in the tunnel oxide and threshold window opening. An experimental investigation of these phenomena is described, and a recommendation is made to avoid them by an appropriate cell design.

Babesia microti in mice. Subpopulations of cells involved in the adoptive transfer of immunity with immune spleen cells.

Protection against a primary Babesia microti infection in mice, induced by the adoptive transfer of immune spleen cells, was abolished when the immune spleen cells were treated with mitomycin C prior to transfer. Since mitomycin C treatment prevents the replication of lymphocytes without affecting other cell functions, these results would suggest that the transferred cells required proliferation in the recipient mice before they could exert their protective effect, and this excludes the already differentiated antibody-forming cells (AFC's), macrophages and sensitised helper T cells. This was partly supported by the finding that Sephadex G-10 non-adherent immune cells, depleted of macrophages and AFC's, still conferred a strong protection after transfer. However, the Sephadex G-10 adherent cells, on a cell to cell basis, initially conferred a better protection against B. microti than did the non-adherent cells or unfractionated immune spleen cells. The possibility of the retention of an intermediate B memory cell type on the Sephadex G-10 columns and the suppression of antibody production are discussed in view of these results.

Lymphoid cell dependence of eosinophil response to antigen. IV. Effects of in vitro x-irradiation on adoptive transfer of anamnestic cellular and humoral responses.

Recently, we have reported the detection of two types of memory cells induced by a priming injection of tetanus toxoid—one memory cell mediating the secondary eosinophil response and a separate memory cell associated with antitoxin production. It was further demonstrated that formation of both memory cells was dependent upon the presence of thymic cells at the time of priming. Memory cells involved in eosinophil responses, however, are formed earlier and become more widely distributed in lymphatic tissues than do memory cells involved in antitoxin responses. Consequently, adoptive transfer of specific lymphoid tissues at selected intervals after priming can demonstrate the presence of one type of memory without the other (1, 2). For example, at 10 days after priming, cells present in the spleen were capable of inducing a secondary rise in eosinophils, but not antitoxin. However, at 30 days, splenic cells were capable of inducing both responses. In the experiments to be described, we have demonstrated differing sensitivities of these memory cells to in vitro X-irradiation. Materials and Methods. The experimental procedure is similar to that utilized in previous studies (1–3). Briefly, adult BAFX (C57BL × A/J) female donor mice were primed with a single subcutaneous injection of 0.2 ml aluminum phosphate-adsorbed tetanus toxoid (National Drug Co., Philadelphia, PA) in an adjuvant of 0.2 ml pertussis vaccine (Eli Lilly Drug Co., Indianapolis, IN) diluted 1:10 with saline (PVTT). Thirty days after priming, the mice were sacrificed and cell suspensions made of the spleen.

Lymphoid Cell Dependence of Eosinophil Response to Antigen

Abstract Priming induced at least two distinct types of memory cells as determined by their capacity after adoptive transfer to elicit secondary type eosinophil or antitoxin responses to a challenging injection of tetanus toxoid. Thymic depletion prevents the formation of both types of memory cells, and injection of thymic cells 1 week before priming restores the capacity of these animals to respond. Memory cells involved in eosinophil responses are formed earlier and become more widely distributed in the blood and lymphatic tissues than do memory cells involved in antitoxin responses. Beginning on or about 6 days after priming and in all periods examined thereafter, eosinophil responses were obtained with cell suspensions of all lymphatic tissues tested. Inflammatory exudates obtained from the peritoneal cavity 7, 11, and 13 days after subcutaneous priming contained cells capable of augmenting the cellular responses but not the secondary type antitoxin responses. Memory cells capable of inducing antitoxin responses were detected in the regional lymph node suspensions 10 days after priming. At 17 days the regional lymph node and, to a lesser extent, other lymph nodes and the spleen induced antitoxin responses. By 30 days all lymphatic tissues tested except the thymus gave good responses. We discuss the possible role of eosinophils in immunologic reactions and suggest that eosinophils are an integral component of the anamnestic responses to antigen.