Antigen-specific precursor frequency impacts T cell proliferation, differentiation, and requirement for costimulation

After a brief period of antigenic stimulation, T cells become committed to a program of autonomous expansion and differentiation. We investigated the role of antigen-specific T cell precursor frequency as a possible cell-extrinsic factor impacting T cell programming in a model of allogeneic tissue transplantation. Using an adoptive transfer system to incrementally raise the precursor frequency of antigen-specific CD8+ T cells, we found that donor-reactive T cells primed at low frequency exhibited increased cellular division, decreased development of multifunctional effector activity, and an increased requirement for CD28- and CD154-mediated costimulation relative to those primed at high frequency. The results demonstrated that recipients with low CD4+ and CD8+ donor-reactive T cell frequencies exhibited long-term skin graft survival upon CD28/CD154 blockade, whereas simultaneously raising the frequency of CD4+ T cells to ∼0.5% and CD8+ T cells to ∼5% precipitated graft rejection despite CD28/CD154 blockade. Antigenic rechallenge of equal numbers of cells stimulated at high or low frequency revealed that cells retained an imprint of the frequency at which they were primed. These results demonstrate a critical role for initial precursor frequency in determining the CD8+ T cell requirement for CD28- and CD154-mediated costimulatory signals during graft rejection

The Psychological Science Accelerator: Advancing Psychology Through a Distributed Collaborative Network

Source at https://doi.org/10.1177/2515245918797607.Concerns about the veracity of psychological research have been growing. Many findings in psychological science are based on studies with insufficient statistical power and nonrepresentative samples, or may otherwise be limited to specific, ungeneralizable settings or populations. Crowdsourced research, a type of large-scale collaboration in which one or more research projects are conducted across multiple lab sites, offers a pragmatic solution to these and other current methodological challenges. The Psychological Science Accelerator (PSA) is a distributed network of laboratories designed to enable and support crowdsourced research projects. These projects can focus on novel research questions or replicate prior research in large, diverse samples. The PSA’s mission is to accelerate the accumulation of reliable and generalizable evidence in psychological science. Here, we describe the background, structure, principles, procedures, benefits, and challenges of the PSA. In contrast to other crowdsourced research networks, the PSA is ongoing (as opposed to time limited), efficient (in that structures and principles are reused for different projects), decentralized, diverse (in both subjects and researchers), and inclusive (of proposals, contributions, and other relevant input from anyone inside or outside the network). The PSA and other approaches to crowdsourced psychological science will advance understanding of mental processes and behaviors by enabling rigorous research and systematic examination of its generalizability

Dendritic Cell Expression of Retinal Aldehyde Dehydrogenase-2 Controls Graft-versus-Host Disease Lethality

Recent studies have underscored the critical role of retinoic acid (RA) in the development of lineage-committed CD4 and CD8 T cells in vivo. We have shown that under acute graft-versus-host disease (GVHD) inflammatory conditions, RA is upregulated in the intestine and is proinflammatory, as GVHD lethality was attenuated when donor allogeneic T cells selectively expressed a dominant negative RA receptor α that blunted RA signaling. RA can function in an autocrine and paracrine fashion, and as such, the host cell lineage responsible for the production of RA metabolism and the specific RA-metabolizing enzymes that potentiate GVHD severity are unknown. In this study, we demonstrate that enhancing RA degradation in the host and to a lesser extent donor hematopoietic cells by overexpressing the RA-catabolizing enzyme CYP26A1 reduced GVHD. RA production is facilitated by retinaldehyde isoform-2 (RALDH2) preferentially expressed in dendritic cells (DCs). Conditionally deleted RA-synthesizing enzyme RALDH2 in host or to a lesser extent donor DCs reduced GVHD lethality. Improved survival in recipients with RALDH2-deleted DCs was associated with increased T cell death, impaired T effector function, increased regulatory T cell frequency, and augmented coinhibitory molecule expression on donor CD4+ T cells. In contrast, retinaldehydrogenase isoform-1 (RALDH1) is dominantly expressed in intestinal epithelial cells. Unexpectedly, conditional host intestinal epithelial cells RALDH1 deletion failed to reduce GVHD. These data demonstrate the critical role of both donor and especially host RALDH2+ DCs in driving murine GVHD and suggest RALDH2 inhibition or CYP26A1 induction as novel therapeutic strategies to prevent GVHD

GvHD-associated, inflammasome-mediated loss of function in adoptively transferred myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are a naturally occurring immune regulatory population associated with inhibition of ongoing inflammatory responses. In vitro generation of MDSC from bone marrow have been shown to enhance survival in an acute model of lethal graft-versus-host disease (GvHD). However, donor MDSC infusion only partially ameliorates GvHD lethality. In order to improve the potential therapeutic benefit and ultimately survival outcomes we set out to investigate the fate of MDSC after transfer in the setting of acute GvHD (aGvHD). MDSC transferred to lethally irradiated recipients of allogeneic donor hematopoietic grafts are exposed to an intense inflammatory environment associated with aGvHD, which we now show directly undermines their suppressive capacity. Under conditioning regimen and GvHD inflammatory settings, MDSC rapidly lose suppressor function and their potential to inhibit GvHD lethality, which is associated with their induced conversion towards a mature inflammasome-activated state. We find even brief in vitro exposure to inflammasome-activating mediators negates the suppressive potential of cultured murine and human-derived MDSCs. Consistent with a role for the inflammasome, donor MDSC deficient in the adaptor ASC (Apoptosis-associated speck-like protein containing a CARD), that assembles inflammasome complexes, conferred improved survival of mice developing GvHD compared to wild-type donor MDSC. These data suggest the use of MDSC as a therapeutic approach for preventing GvHD and other systemic inflammatory conditions will be more effective when combined with approaches limiting in vivo MDSC inflammasome activation empowering MDSCs to maintain their suppressive potential

Activation of p53 in Immature Myeloid Precursor Cells Controls Differentiation into Ly6c+CD103+Monocytic Antigen-Presenting Cells in Tumors

CD103(+) dendritic cells are critical for cross-presentation of tumor antigens. Here we have shown that during immunotherapy, large numbers of cells expressing CD103 arose inmurine tumors via direct differentiation of Ly6c(+) monocytic precursors. These Ly6c(+)CD103(+) cells could derive from bone-marrow monocytic progenitors (cMoPs) or from peripheral cells present within the myeloid-derived suppressor cell (MDSC) population. Differentiation was controlled by inflammation-induced activation of the transcription factor p53, which drove upregulation of Batf3 and acquisition of the Ly6c(+)CD103(+) phenotype. Mice with a targeted deletion of p53 in myeloid cells selectively lost the Ly6c(+)CD103(+) population and became unable to respond to multiple forms of immunotherapy and immunogenic chemotherapy. Conversely, increasing p53 expression using a p53-agonist drug caused a sustained increase in Ly6c(+)CD103(+) cells in tumors during immunotherapy, which markedly enhanced the efficacy and duration of response. Thus, p53-driven differentiation of Ly6c(+)CD103(+) monocytic cells represents a potent and previously unrecognized target for immunotherapy

Bystander Activation and Anti-Tumor Effects of CD8+ T Cells Following Interleukin-2 Based Immunotherapy Is Independent of CD4+ T Cell Help

<div><p>We have previously demonstrated that immunotherapy combining agonistic anti-CD40 and IL-2 (IT) results in synergistic anti-tumor effects. IT induces expansion of highly cytolytic, antigen-independent “bystander-activated” (CD8⁺CD44^high) T cells displaying a CD25⁻NKG2D⁺ phenotype in a cytokine dependent manner, which were responsible for the anti-tumor effects. While much attention has focused on CD4+ T cell help for antigen-specific CD8+ T cell expansion, little is known regarding the role of CD4+ T cells in antigen-nonspecific bystander-memory CD8+ T cell expansion. Utilizing CD4 deficient mouse models, we observed a significant expansion of bystander-memory T cells following IT which was similar to the non-CD4 depleted mice. Expanded bystander-memory CD8+ T cells upregulated PD-1 in the absence of CD4+ T cells which has been published as a hallmark of exhaustion and dysfunction in helpless CD8+ T cells. Interestingly, compared to CD8+ T cells from CD4 replete hosts, these bystander expanded cells displayed comparable (or enhanced) cytokine production, lytic ability, and in vivo anti-tumor effects suggesting no functional impairment or exhaustion and were enriched in an effector phenotype. There was no acceleration of the post-IT contraction phase of the bystander memory CD8+ response in CD4-depleted mice. The response was independent of IL-21 signaling. These results suggest that, in contrast to antigen-specific CD8+ T cell expansion, CD4+ T cell help is not necessary for expansion and activation of antigen-nonspecific bystander-memory CD8+ T cells following IT, but may play a role in regulating conversion of these cells from a central memory to effector phenotype. Additionally, the expression of PD-1 in this model appears to be a marker of effector function and not exhaustion.</p></div