Biomedical subjects

Jens Geginat

Publications and source records attributed to Jens Geginat.

6 recordsLinked to original sources

PubMed2005

Toll-like receptor-dependent activation of several human blood cell types by protamine-condensed mRNA.

We reported that RNA condensed on protamine is protected from RNase-mediated degradation and can be used for vaccination. Here, we show that such complexes are also danger signals that activate mouse cells through a MyD88-dependent pathway. Moreover, mRNA-protamine complexes stimulate human blood cells. They strongly activate DC and monocytes, leading to TNF-alpha and IFN-alpha secretion. In addition, protamine-RNA complexes directly activate B cells, NK cells and granulocytes. The detailed analysis of the activated cell types, the study of the cytokines released from PBMC cultured with protamine-RNA complexes and recently published results suggest that TLR-7 and TLR-8 may be involved in the recognition of protamine-stabilized RNA. Our data indicate that protamine-stabilized RNA, which may be similar to RNA condensed in the nucleocapsids of RNA viruses, is a strong danger signal. Thus, similarly to plasmid DNA, protamine-RNA combines antigen production and non-specific immunostimulation. The studies presented here explain the capacity of protamine-RNA to act as a vaccine, and pave the way towards the development of safe and efficient mRNA-based immunotherapies.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Chemokine receptor expression identifies Pre-T helper (Th)1, Pre-Th2, and nonpolarized cells among human CD4+ central memory T cells.

We previously reported that central-memory T cells (T(CM) cells), which express lymph node homing receptors CCR7 and CD62L, are largely devoid of effector functions but acquire characteristics of effector-memory T cells (T(EM) cells) (i.e., CCR7(-) T helper [Th]1 or Th2 cells) after stimulation with T cell receptor agonists or homeostatic cytokines. Here we show that three chemokine receptors identify functional subsets within the human CD4(+) T(CM) cell pool. T(CM) cells expressing CXCR3 secreted low amounts of interferon gamma, whereas CCR4(+) T(CM) cells produced some interleukin (IL)-4, but not IL-5. In response to IL-7 and IL-15, CXCR3(+) T(CM) and CCR4(+) T(CM) cells invariably generated fully differentiated CCR7(-) Th1 and Th2 cells, respectively, suggesting that they represent pre-Th1 and pre-Th2 cells. Conversely, CXCR5(+) T(CM) cells lacking CXCR3 and CCR4 remained nonpolarized and retained CCR7 and CD62L expression upon cytokine-driven expansion. Unlike naive cells, all memory subsets had a low T cell receptor rearrangement excision circle content, spontaneously incorporated bromodeoxyuridine ex vivo, and contained cells specific for tetanus toxoid. Conversely, recall responses to cytomegalovirus and vaccinia virus were largely restricted to CXCR3(+) T(CM) and T(EM) cells. We conclude that antigen-specific memory T cells are distributed between T(EM) cells and different subsets of T(CM) cells. Our results also explain how the quality of primary T cell responses could be maintained by T(CM) cells in the absence of antigen.

Cell Differentiation↗

PubMed2004

Central memory and effector memory T cell subsets: function, generation, and maintenance.

The memory T cell pool functions as a dynamic repository of antigen-experienced T lymphocytes that accumulate over the lifetime of the individual. Recent studies indicate that memory T lymphocytes contain distinct populations of central memory (TCM) and effector memory (TEM) cells characterized by distinct homing capacity and effector function. This review addresses the heterogeneity of TCM and TEM, their differentiation stages, and the current models for their generation and maintenance in humans and mice.

Animals↗

PubMed2003

T cell fitness determined by signal strength.

Two potential outcomes confront proliferating antigen-stimulated naive T cells: differentiation to effector and memory cells, or deletion. How stimulation affects cell fate is unclear. Autonomous CD8+ T cell differentiation has been proposed, but this does not explain the abortive proliferation of T cells induced by immature dendritic cells. Here we show that human and mouse CD4+ and CD8+ T cells receiving short or weak stimulation of the T cell receptor proliferate in response to interleukin 2 (IL-2) but are not 'fit' because they die by neglect, fail to proliferate in response to IL-7 and IL-15 and disappear in vivo. Conversely, prolonged or strong stimulation promotes 'fitness' by enhancing survival and cytokine responsiveness. Our results are consistent with the concept that signal strength drives progressive T cell differentiation and the acquisition of fitness.

CD4-Positive T-Lymphocytes↗

PubMed2003

Proliferation and differentiation potential of human CD8+ memory T-cell subsets in response to antigen or homeostatic cytokines.

Four human CD8+ T-cell subsets, naive (CCR7+CD45RA+), central memory (TCM, CCR7+CD45RA-), effector memory (TEM, CCR7-CD45RA-), and CD45RA+ effector memory cells (TEMRA, CCR7-CD45RA+) were compared for their capacity to proliferate and differentiate in response to antigen or homeostatic cytokines. Cytokine responsiveness and interleukin-15 receptor expression were low in naive T cells and progressively increased from TCM to TEM and TEMRA. In contrast, the capacity to accumulate in response to T-cell receptor (TCR) or cytokine stimulation showed a reciprocal pattern and was associated with resistance to cell death and Bcl-2 expression. Whereas all TCR-stimulated cells acquired a CD45RA-CCR7- phenotype, cytokine-stimulated cells maintained their phenotype with the exception of TCM cells, which expressed CCR7, CD45RA, and perforin in various combinations. Single CD8+ TCM cells, but not TEM cells, could be expanded with cytokines, and the obtained clones displayed several distinct phenotypes, suggesting that TCM cells are heterogeneous. Consistently, CCR4 expression in the CD8+ TCM pool discriminated CCR4+ type 2 polarized cells (Tc2) and CCR4-CTL precursors. Finally, ex vivo bromodeoxyuridine (BrdU) incorporation experiments revealed that memory subsets have different in vivo proliferation rates, with CCR4-TCM having the highest turnover and TEMRA the lowest. These results show that human CD8+ memory T-cell subsets have different proliferation and differentiation potentials in vitro and in vivo. Furthermore, they suggest that TEMRA cells are generated from a TCM subset upon homeostatic proliferation in the absence of antigen.

Antigen Presentation↗

PubMed2002

TCR-independent proliferation and differentiation of human CD4+ T cell subsets induced by cytokines.

Naïve and memory T cells can divide in an antigen-independent manner in vivo maintaining independently a constant pool size. While naïve T cells require TCR tickling by self-MHC for homeostatic proliferation in lymphopenic mice, memory cells do not but respond to cytokines. Human naive and memory CD4+ T cell subsets can be selectively expanded in vitro with different cytokine combinations. Responsiveness of T cells to homeostatic cytokines is associated with the differentiation state. Thus, while memory cells respond directly to IL-7 and IL-15, naïve T cells require costimulation by dendritic cell-derived cytokines, and selectively respond to IL-4. This differential cytokine responsiveness is associated with the expression and modulation of the relevant cytokine receptors. Cytokine-driven proliferation is independent of TCR-stimulation and shows distinct signal transduction requirements. While cytokine-expanded naive T cells maintain a naive phenotype, memory cells differentiate acquiring new effector functions and switching expression of chemokine receptors. Thus human naïve and memory T cell pools can be maintained with homeostatic cytokines in the absence of TCR stimulation.

CD4-Positive T-Lymphocytes↗