3D-Printed Polymeric Biomaterials for Health Applications.

3D printing, also known as additive manufacturing, holds immense potential for rapid prototyping and customized production of functional health-related devices. With advancements in polymer chemistry and biomedical engineering, polymeric biomaterials have become integral to 3D-printed biomedical applications. However, there still exists a bottleneck in the compatibility of polymeric biomaterials with different 3D printing methods, as well as intrinsic challenges such as limited printing resolution and rates.

The aged microenvironment impairs BCL6 and CD40L induction in CD4 T follicular helper cell differentiation.

Weakened germinal center responses by the aged immune system result in diminished immunity against pathogens and reduced efficacy of vaccines. Prolonged contacts between activated B cells and CD4 T cells are crucial to germinal center formation and T follicular helper cell (Tfh) differentiation, but it is unclear how aging impacts the quality of this interaction. Peptide immunization confirmed that aged mice have decreased expansion of antigen-specific germinal center B cells and reduced antibody titers.

Aging of lymphoid stromal architecture impacts immune responses.

The secondary lymphoid organs (SLOs) undergo structural changes with age, which correlates with diminishing immune responses against infectious disease. A growing body of research suggests that the aged tissue microenvironment can contribute to decreased immune function, independent of intrinsic changes to hematopoietic cells with age. Stromal cells impart structural integrity, facilitate fluid transport, and provide chemokine and cytokine signals that are essential for immune homeostasis.

Age-Associated Changes to Lymph Node Fibroblastic Reticular Cells.

The decreased proportion of antigen-inexperienced, naïve T cells is a hallmark of aging in both humans and mice, and contributes to reduced immune responses, particularly against novel and re-emerging pathogens. Naïve T cells depend on survival signals received during their circulation among the lymph nodes by direct contacts with stroma, in particular fibroblastic reticular cells. Macroscopic changes to the architecture of the lymph nodes have been described, but it is unclear how lymph node stroma are altered with age, and whether these changes contribute to reduced naïve T cell maintenance.

Central tolerance is impaired in the middle-aged thymic environment.

One of the earliest hallmarks of immune aging is thymus involution, which not only reduces the number of newly generated and exported T cells, but also alters the composition and organization of the thymus microenvironment. Thymic T-cell export continues into adulthood, yet the impact of thymus involution on the quality of newly generated T-cell clones is not well established. Notably, the number and proportion of medullary thymic epithelial cells (mTECs) and expression of tissue-restricted antigens (TRAs) decline with age, suggesting the involuting thymus may not promote efficient central tolerance.

Age-Related Changes in Thymic Central Tolerance.

Thymic epithelial cells (TECs) and hematopoietic antigen presenting cells (HAPCs) in the thymus microenvironment provide essential signals to self-reactive thymocytes that induce either negative selection or generation of regulatory T cells (Treg), both of which are required to establish and maintain central tolerance throughout life. HAPCs and TECs are comprised of multiple subsets that play distinct and overlapping roles in central tolerance. Changes that occur in the composition and function of TEC and HAPC subsets across the lifespan have potential consequences for central tolerance.

Polycomb Repressive Complex 2 is essential for development and maintenance of a functional TEC compartment.

Thymic epithelial cells (TEC) are essential for thymocyte differentiation and repertoire selection. Despite their indispensable role in generating functional T cells, the molecular mechanisms that orchestrate TEC development from endodermal progenitors in the third pharyngeal pouch (3 PP) are not fully understood. We recently reported that the T-box transcription factor TBX1 negatively regulates TEC development.

CCR8 is expressed by post-positive selection CD4-lineage thymocytes but is dispensable for central tolerance induction.

Following positive selection, thymocytes migrate into the medulla where they encounter diverse self-antigens that induce central tolerance. Thymocytes expressing T cell receptors (TCRs) with high affinity for self-antigens displayed by medullary antigen presenting cells (APCs) undergo either negative selection or diversion to the regulatory T cell (Treg) lineage, thus ensuring maturation of non-autoreactive T cells. Because many self-antigens are expressed by only a small percentage of medullary thymic epithelial cells, thymocytes must enter the medulla and efficiently scan APCs therein to encounter the full array of self-antigens that induce central tolerance.

Detecting T Cell Activation Using a Varying Dimension Bayesian Model.

The detection of T cell activation is critical in many immunological assays. However, detecting T cell activation in live tissues remains a challenge due to highly noisy data. We developed a Bayesian probabilistic model to identify T cell activation based on calcium flux, a dramatic increase in intracellular calcium concentration that occurs during T cell activation.

Chemokine-Mediated Choreography of Thymocyte Development and Selection.

As they differentiate, thymocytes encounter spatially restricted cues critical for differentiation and selection of a functional, self-tolerant T cell repertoire. Sequential migration of developing T cells through distinct thymic microenvironments is enforced by the ordered expression of chemokine receptors. Herein, we provide an updated perspective on T cell differentiation through the lens of recent advances that illuminate the dynamics of chemokine-driven thymocyte migration, localization, and interactions with stromal cells.

EBI2 contributes to the induction of thymic central tolerance in mice by promoting rapid motility of medullary thymocytes.

Maturing thymocytes enter the thymic medulla, where they encounter numerous self-antigens presented by antigen presenting cells (APCs). Those thymocytes that are strongly self-reactive undergo either negative selection or diversion into the regulatory T-cell lineage. Although the majority of the proteome is expressed in the medulla, many self-antigens are expressed by only a minor fraction of medullary APCs; thus, thymocytes must efficiently enter the medulla and scan APCs to ensure central tolerance.

Analysis of Thymocyte Migration, Cellular Interactions, and Activation by Multiphoton Fluorescence Microscopy of Live Thymic Slices.

Thymocytes migrate through discrete compartments within the thymus, engaging in cellular interactions essential for their differentiation into functional and self-tolerant T cells. Thus, understanding the temporal and spatial behavior of thymocytes within an intact thymic microenvironment is critical for elucidating processes governing T cell development. Towards this end, we describe methods for preparing thymic explant slices, in which the migration of thymocytes through three-dimensional space can be probed using time-lapse, multiphoton fluorescence microscopy.

Endogenous dendritic cells from the tumor microenvironment support T-ALL growth via IGF1R activation.

Primary T-cell acute lymphoblastic leukemia (T-ALL) cells require stromal-derived signals to survive. Although many studies have identified cell-intrinsic alterations in signaling pathways that promote T-ALL growth, the identity of endogenous stromal cells and their associated signals in the tumor microenvironment that support T-ALL remains unknown. By examining the thymic tumor microenvironments in multiple murine T-ALL models and primary patient samples, we discovered the emergence of prominent epithelial-free regions, enriched for proliferating tumor cells and dendritic cells (DCs).

CCR4 promotes medullary entry and thymocyte-dendritic cell interactions required for central tolerance.

Autoimmunity results from a breakdown in central or peripheral tolerance. To establish central tolerance, developing T cells must enter the thymic medulla, where they scan antigen-presenting cells (APCs) displaying a diverse array of autoantigens. If a thymocyte is activated by a self-antigen, the cell undergoes either deletion or diversion into the regulatory T cell (T reg) lineage, thus maintaining self-tolerance.

The Contribution of Chemokines and Migration to the Induction of Central Tolerance in the Thymus.

As T cells develop, they migrate throughout the thymus where they undergo essential bi-directional signaling with stromal cells in distinct thymic microenvironments. Immature thymocyte progenitors are located in the thymic cortex. Following T cell receptor expression and positive selection, thymocytes undergo a dramatic transition: they become rapidly motile and relocate to the thymic medulla.