Deconstructing the peptide-MHC specificity of T cell recognition.

In order to survey a universe of major histocompatibility complex (MHC)-presented peptide antigens whose numbers greatly exceed the diversity of the T cell repertoire, T cell receptors (TCRs) are thought to be cross-reactive. However, the nature and extent of TCR cross-reactivity has not been conclusively measured experimentally. We developed a system to identify MHC-presented peptide ligands by combining TCR selection of highly diverse yeast-displayed peptide-MHC libraries with deep sequencing. Although we identified hundreds of peptides reactive with each of five different mouse and human TCRs, the selected peptides possessed TCR recognition motifs that bore a close resemblance to their known antigens. This structural conservation of the TCR interaction surface allowed us to exploit deep-sequencing information to computationally identify activating microbial and self-ligands for human autoimmune TCRs. The mechanistic basis of TCR cross-reactivity described here enables effective surveillance of diverse self and foreign antigens without necessitating degenerate recognition of nonhomologous peptides.

Racial and ethnic differences in predictors of participation in an intergenerational social connectedness intervention for older adults.

BACKGROUND: Social connectedness is a key determinant of health and interventions have been developed to prevent social isolation in older adults. However, these interventions have historically had a low participation rate amongst minority populations. Given the sustained isolation caused by the COVID-19 pandemic, it is even more important to understand what factors are associated with an individual's decision to participate in a social intervention. To achieve this, we used machine learning techniques to model the racial and ethnic differences in participation in social connectedness interventions. METHODS: Data were obtained from a social connectedness intervention that paired college students with Houston-area community-dwelling older adults (> 65 yo) enrolled in Medicare Advantage plans. Eligible participants were contacted telephonically and asked to complete the 3-item UCLA Loneliness Scale. We used the following machine-learning methods to identify significant predictors of participation in the program: k-nearest neighbors, logistic regression, decision tree, gradient-boosted decision tree, and random forest. RESULTS: The gradient-boosted decision tree models yielded the best parameters for all race/ethnicity groups (96.1% test accuracy, 0.739 AUROC). Among non-Hispanic White older adults, key features of the predictive model included Functional Comorbidity Index (FCI) score, Medicare prescription risk score, Medicare risk score, and depression and anxiety indicators within the FCI. Among non-Hispanic Black older adults, key features included disability, Medicare prescription risk score, FCI and Medicare risk scores. Among Hispanic older adults, key features included depression, FCI and Medicare risk scores. CONCLUSIONS: These findings offer a substantial opportunity for the design of interventions that maximize engagement among minority groups at greater risk for adverse health outcomes.

Peptidic degron in EID1 is recognized by an SCF E3 ligase complex containing the orphan F-box protein FBXO21.

EP300-interacting inhibitor of differentiation 1 (EID1) belongs to a protein family implicated in the control of transcription, differentiation, DNA repair, and chromosomal maintenance. EID1 has a very short half-life, especially in G0 cells. We discovered that EID1 contains a peptidic, modular degron that is necessary and sufficient for its polyubiquitylation and proteasomal degradation. We found that this degron is recognized by an Skp1, Cullin, and F-box (SCF)-containing ubiquitin ligase complex that uses the F-box Only Protein 21 (FBXO21) as its substrate recognition subunit. SCF(FBXO21) polyubiquitylates EID1 both in vitro and in vivo and is required for the efficient degradation of EID1 in both cycling and quiescent cells. The EID1 degron partially overlaps with its retinoblastoma tumor suppressor protein-binding domain and is congruent with a previously defined melanoma-associated antigen-binding motif shared by EID family members, suggesting that binding to retinoblastoma tumor suppressor and melanoma-associated antigen family proteins could affect the polyubiquitylation and turnover of EID family members in cells.

Membrane association of the CD3ε signaling domain is required for optimal T cell development and function.

The TCR:CD3 complex transduces signals that are critical for optimal T cell development and adaptive immunity. In resting T cells, the CD3ε cytoplasmic tail associates with the plasma membrane via a proximal basic-rich stretch (BRS). In this study, we show that mice lacking a functional CD3ε-BRS exhibited substantial reductions in thymic cellularity and limited CD4- CD8- double-negative (DN) 3 to DN4 thymocyte transition, because of enhanced DN4 TCR signaling resulting in increased cell death and TCR downregulation in all subsequent populations. Furthermore, positive, but not negative, T cell selection was affected in mice lacking a functional CD3ε-BRS, which led to limited peripheral T cell function and substantially reduced responsiveness to influenza infection. Collectively, these results indicate that membrane association of the CD3ε signaling domain is required for optimal thymocyte development and peripheral T cell function.

Sickle Cell Disease in an Older Adult Population: A Retrospective Review of Health Care Resource Utilization.

Sickle cell disease (SCD) has a history of health inequity, as patients with SCD are primarily Black and often marginalized from the health care system. Although recent health care and treatment advancements have prolonged life expectancy, it may be insufficient to support the complex needs of the growing population of older adults with SCD. This retrospective study used a cohort (N = 812) of Medicare Advantage beneficiaries 45 years and older (ages: 45-54, 55-64, 65-74, 75-89) with SCD to identify associations of SCD-related complications and comorbidities with emergency department (ED) visits, potentially avoidable ED visits, all-cause hospitalization, and potentially avoidable hospitalizations, 2018-2020. The 75-89 age group had lower odds of an ED visit (OR 0.56; 95% CI 0.32-1.00), 65-74 age group had lower odds of an ED visit (OR 0.49; 95% CI 0.31-0.78) and hospitalization (OR 0.50; 95% CI 0.31-0.79), compared with the 45-54 age group. Acute chest syndrome was associated with increased odds of an ED visit (OR 2.02; 95% CI 1.10-3.71), avoidable ED visit (OR 1.87; 95% CI 1.14-3.06), and hospitalization (OR 3.61; 95% CI 2.06-6.31). Pain was associated with increased odds of an ED visit (OR 2.64; 95% CI 1.85-3.76), an avoidable ED visit (OR 3.08; 95% CI 1.90-4.98), hospitalization (OR 1.51; 95% CI 1.02-2.24), and avoidable hospitalization (OR 6.42; 95% CI 1.74-23.74). Older adults with SCD have been living with SCD for decades, often while managing pain crises and complications associated increased incidence of an ED visit and hospitalization. The characteristics and needs of this population must continue to be examined to increase preventative care and reduce costly emergent health care resource utilization.

Leveraging Public-Private Partnerships During COVID-19: Providing Virtual Field Opportunities for Student Learners and Addressing Social Isolation in Older Adults.

While preventive and management measures are important to mitigate the spread of COVID-19, strategies like social distancing can have devastating effects on older adults who are already at risk for social isolation and loneliness. In response, two Colleges of Health Professions (Social Work and Nursing) at a large public University leveraged a partnership with a national health and wellbeing company to address social isolation and loneliness in Houston area older adults during the COVID-19 pandemic. This intergenerational linkage initiative involved 707 older adults and 177 graduate social work and nursing students. This study describes the process of developing a virtual educational opportunity for students while also meeting the needs of vulnerable older adults in Houston, the third largest, and one of the most diverse cities in the U.S. Findings include student/learner outcomes, as well as self-reported improvements in loneliness scores, and unhealthy physical and mental health days among enrolled older adults.

Correlates of Social Isolation Among Community-Dwelling Older Adults During the COVID-19 Pandemic.

Background: The past year has severely curtailed social interactions among older adults given their high rates of COVID-19 morbidity and mortality. This study examined social, behavioral, and medical correlates of social isolation among community-dwelling older adults during the COVID-19 pandemic and stratified findings to explore unique differences in two typically neglected populations, African American and Hispanic older adults. Methods: Working with community-based organizations and senior living centers, the research team administered a survey to older adults 55 years of age and older (n = 575). The survey assessed COVID-19 prevention behaviors, medical conditions, and lived experiences, including feelings of social isolation, in the target population. Responses to a previously validated social isolation question informed a dichotomous social isolation dependent variable. Multivariable logistic regression was used to adjust for sociodemographic characteristics, medical conditions, unmet caregiving needs, and COVID-19 prevention behaviors. Results from the regression model were stratified by race/ethnicity to examine correlates of social isolation in African American and Hispanic older adults, separately. Results: Overall, female sex and a higher level of education were also positively associated with social isolation (OR = 2.46, p = 0.04; OR = 5.49, p = 0.02) while having insurance exhibited an inverse relationship (OR = 0.25, p = 0.03). Unmet caregiving needs were strongly associated with social isolation (OR = 6.41, p < 0.001) as was having any chronic conditions (OR = 2.99, p = 0.02). Diabetes was the single strongest chronic condition predictor of social isolation. Among minority older adults, a different pattern emerged. For Hispanic older adults, language, unmet caregiving needs, and social distancing were strongly associated with social isolation; while unmet caregiving needs, having 1+ chronic conditions and adhering to social distancing guidelines were significant predictors in African American older adults. Conclusion: These findings suggest that social isolation affects older adults in a myriad of ways and support the need for culturally sensitive initiatives to mitigate the effect of social isolation in these vulnerable populations.

Examining Changes in Healthy Days After Health Coaching.

PURPOSE: To describe changes in health-related quality of life (HRQOL) related to variation in demographic characteristics, program goals, and program participation, among health coaching program participants. DESIGN: A retrospective observational study of a health coaching program. SETTING AND PARTICIPANTS: A total of 2169 adults enrolled in an individually purchased or employer-sponsored health plan from a large health and well-being company, who participated in a health coaching program between January 2016 and April 2017. INTERVENTION: The health coaching program used evidence-based behavior change strategies to encourage skill development, self-monitoring, and goal setting/achievement. Health coaching program modalities included online and telephonic coaching sessions. MEASURES: Demographic characteristics (gender, age, race, income), goal categories (weight management, fitness, nutrition, stress management, other), program modality (online, telephonic, both), engagement level (low, medium, high), and Healthy Days, a validated HRQOL measure developed by the Centers for Disease Control and Prevention. ANALYSIS: t Tests, mixed analysis of variance (ANOVA). RESULTS: There were significant ( P < .05) reductions in average total unhealthy days (UHDs) across all goal categories. Mixed ANOVAs identified a significant main effect for time, for all demographic characteristics ( P values < .05), and a significant effect for program modality ( P < .0001), time ( P < .0001), and interaction effects, between program modality and time, on average UHD ( P = .01). CONCLUSION: Our findings indicate significant reductions in UHD, following 6 months of health coaching, and support the use of HRQOL measures, which are known to be highly correlated with traditional measures of health, to evaluate health coaching programs.

Primary Care Provider Encounter Cadence and HbA1c Control in Older Patients With Diabetes.

INTRODUCTION: Primary care provider encounters are associated with health and well-being; however, limited evidence guides optimal primary care provider rate of visit, referred to as encounter cadence. This study measures associations between primary care provider encounter cadence and diabetes outcomes among individuals newly diagnosed with type 2 diabetes mellitus. METHODS: In this retrospective cohort study, 7,106 people enrolled in Medicare Advantage and newly diagnosed with type 2 diabetes mellitus between July 1, 2012 and June 30, 2013 were identified and followed for 36 months. Two methods measured primary care provider encounter cadence: total primary care provider encounters (frequency) and quarters with primary care provider encounter (regularity). Logistic regression measured relationships between primary care provider encounter cadence and non-insulin diabetes medication adherence, HbA1c control, emergency department visits, and inpatient admissions. Non-insulin diabetes medication adherence was defined according to the National Committee for Quality Assurance, Healthcare Effectiveness Data and Information Set specifications and measured using healthcare claims data. Post-hoc models examined adherence and diabetes control among those nonadherent (n=5,212) and with noncontrolled HbA1c (n=326) during the encounter/cadence period. Data were extracted and analyzed in 2017. RESULTS: Adjusted models indicated that both frequency (AOR=1.08, 95% CI=1.06, 1.10) and regularity (AOR=1.18, 95% CI=1.13, 1.22) of primary care provider encounters were associated with increased odds of adherence. Post-hoc analyses indicated that more frequent (AOR=1.12, 95% CI=1.10, 1.15) and regular (AOR=1.27, 95% CI=1.22, 1.33) primary care provider encounters were associated significantly with adherence and were associated directionally with HbA1c control. CONCLUSIONS: More frequent and regular primary care provider encounters are associated with an increased likelihood of non-insulin diabetes medication adherence. These findings contribute to data needed to establish evidence-based guidelines for primary care provider encounter cadence for those newly diagnosed with type 2 diabetes mellitus.

Patient-Centered Medical Home Recognition and Diabetes Control Among Health Centers: Exploring the Role of Enabling Services.

The patient-centered medical home (PCMH) model has been considered a promising approach to improve chronic care delivery, particularly among patients with diabetes. There is theoretical support to suggest that certain nonmedical services, such as enabling services (eg, case management, social work, transportation), embedded within PCMH could be contributing to successful model implementation. It remains unclear whether PCMH recognition or enabling services are related to diabetes control. Federally Qualified Health Centers (FQHCs) are an important setting in which to study this relationship given the considerable effort required to implement the PCMH model and the ubiquity of enabling services in these safety net settings. This cross-sectional, population-based study used 2012 data from the Health Resources and Services Administration's Uniform Data System and PCMH Recognition Initiative Dataset to determine whether PCMH recognition status was associated with diabetes control rates among FQHCs, while controlling for covariates including enabling services. The study linear regression model estimated that PCMH recognition was associated with a 1.5% increase in the proportion of patients with controlled diabetes (B = 0.015; 95% CI 0.002, 0.027). Clinic region, patient age, and race/ethnicity groups also were related to diabetes control; however, enabling services were not. These findings suggest there is a positive association between PCMH recognition and diabetes control rates among FQHCs. Future research, using data that accurately reflect the provision and utilization of PCMH primary care functions and related enabling services, is needed to fully understand the relationship between the PCMH model and population health measures such as diabetes control.

Studying Dynamic Plasma Membrane Binding of TCR-CD3 Chains During Immunological Synapse Formation Using Donor-Quenching FRET and FLIM-FRET.

Over the last decade, advancements in the time and space resolution of microscopy technologies have enabled dissection of the molecular events involved in T cell Immunological Synapse (IS) formation. Using a combination of Förster Resonance Energy Transfer (FRET) and Fluorescence Lifetime Imagining Microscopy (FLIM), we have demonstrated dynamic plasma membrane binding by cytoplasmic domains of T cell receptor (TCR)-associated CD3 chains and other T cell transmembrane receptors. We have developed methods for imaging such membrane binding both at steady state and during receptor triggering at the IS. Plasma membrane binding by cytoplasmic domains may represent a novel mechanism for regulating the signaling function of important receptors in the immune system.

Multicomponent Injectable Hydrogels for Antigen-Specific Tolerogenic Immune Modulation.

Biomaterial scaffolds that enrich and modulate immune cells in situ can form the basis for potent immunotherapies to elicit immunity or reëstablish tolerance. Here, the authors explore the potential of an injectable, porous hydrogel to induce a regulatory T cell (Treg) response by delivering a peptide antigen to dendritic cells in a noninflammatory context. Two methods are described for delivering the BDC peptide from pore-forming alginate gels in the nonobese diabetic mouse model of type 1 diabetes: encapsulation in poly(lactide-co-glycolide) (PLG) microparticles, or direct conjugation to the alginate polymer. While particle-based delivery leads to antigen-specific T cells responses in vivo, PLG particles alter the phenotype of the cells infiltrating the gels. Following gel-based peptide delivery, transient expansion of endogenous antigen-specific T cells is observed in the draining lymph nodes. Antigen-specific T cells accumulate in the gels, and, strikingly, ≈60% of the antigen-specific CD4+ T cells in the gels are Tregs. Antigen-specific T cells are also enriched in the pancreatic islets, and administration of peptide-loaded gels does not accelerate diabetes. This work demonstrates that a noninflammatory biomaterial system can generate antigen-specific Tregs in vivo, which may enable the development of new therapies for the treatment of transplant rejection or autoimmune diseases.

Laying the Foundation: Factors Associated With Medical Home Recognition Among Health Centers.

INTRODUCTION: The characteristics associated with medical home recognition among federally qualified health centers were explored. The results will help guide the transformation of health centers and other providers to the medical home model of practice. METHODS: This study included the universe of 1,198 federally qualified health centers in calendar year 2012; the data were collected in 2013 and analyzed in 2014-2015. Using the 2012 Uniform Data System, descriptive statistics were calculated and differences in means of health center characteristics by third-party medical home recognition status were tested. Multivariable logistic regression models examined correlates of recognition. RESULTS: In 2012, 17.3% of health centers had third-party medical home recognition. Health centers in the Northeast had more than three times the odds of being recognized as medical homes, compared with health centers located in the South (OR=3.3, p<0.001). Health centers with medical home recognition were larger and had higher odds of having electronic health records in all sites (OR=3.08, p<0.001). Recognized health centers had a higher percentage of total staffing composed of behavioral health specialists, compared with health centers that had not attained medical home recognition in 2012 (OR=1.06, p<0.001). CONCLUSIONS: These findings highlight the importance of monitoring which types of health centers are falling behind, encouraging the adoption of health information technology, and enabling the recruitment of onsite behavioral health staffing.

Binding of the cytoplasmic domain of CD28 to the plasma membrane inhibits Lck recruitment and signaling.

The T cell costimulatory receptor CD28 is required for the full activation of naïve T cells and for the development and maintenance of Foxp3(+) regulatory T (Treg) cells. We showed that the cytoplasmic domain of CD28 was bound to the plasma membrane in resting cells and that ligand binding to CD28 resulted in its release. Membrane binding by the CD28 cytoplasmic domain required two clusters of basic amino acid residues, which interacted with the negatively charged inner leaflet of the plasma membrane. These same clusters of basic residues also served as interaction sites for Lck, a Src family kinase critical for CD28 function. This signaling complex was further stabilized by the Lck-mediated phosphorylation of CD28 Tyr(207) and the subsequent binding of the Src homology 2 (SH2) domain of Lck to this phosphorylated tyrosine. Mutation of the basic clusters in the CD28 cytoplasmic domain reduced the recruitment to the CD28-Lck complex of protein kinase Cθ (PKCθ), which serves as a key effector kinase in the CD28 signaling pathway. Consequently, mutation of either a basic cluster or Tyr(207) impaired CD28 function in mice as shown by the reduced thymic differentiation of FoxP3(+) Treg cells. On the basis of these results, we propose a previously undescribed model for the initiation of CD28 signaling.

Differential expression of the human CD8beta splice variants and regulation of the M-2 isoform by ubiquitination.

The CD8alphabeta heterodimer functions as a coreceptor with the TCR, influencing the outcome of CD8(+) T cell responses to pathogen-infected and tumor cells. In contrast to the murine CD8B gene, the human gene encodes alternatively spliced variants with different cytoplasmic tails (M-1, M-2, M-3, and M-4). At present, little is known about the expression patterns and functional significance of such variants. We used quantitative RT-PCR to demonstrate differential mRNA expression patterns of these splice variants in thymocytes and in resting, memory, and activated primary human CD8(+) T cells. In total CD8(+) T cells, mRNA levels of the M-1 variant were the most predominant and levels of M-3 were the least detected. The M-4 isoform was predominant in effector memory CD8(+) T cells. Upon stimulation of CD8(+) T cells, the M-2 variant mRNA levels were elevated 10-20-fold relative to resting cells in contrast to the other isoforms. Curiously, the M-2 isoform was not expressed on the cell surface in transfected cell lines. Using fluorescent chimeras of the extracellular domain of mouse CD8beta fused to the cytoplasmic tails of each isoform, the M-2 isoform was localized in a lysosomal compartment regulated by ubiquitination of a lysine residue (K215) in its cytoplasmic tail. In contrast, upon short-term stimulation, the M-2 protein localized to the cell surface with the TCR complex. The relatively recent evolution of CD8B gene splice variants in the chimpanzee/human lineage is most likely important for fine-tuning the CD8(+) T cell responses.

Mapping the binding site on CD8 beta for MHC class I reveals mutants with enhanced binding.

In an effective immune response, CD8+ T cell recognition of virally derived Ag, bound to MHC class I, results in killing of infected cells. The CD8alphabeta heterodimer acts as a coreceptor with the TCR, to enhance sensitivity of the T cells to peptide/MHC class I, and is two orders of magnitude more efficient as a coreceptor than the CD8alphaalpha. To understand the important interaction between CD8alphabeta and MHC class I, we created a panel of CD8beta mutants and identified mutations in the CDR1, CDR2, and CDR3 loops that decreased binding to MHC class I tetramers as well as mutations that enhanced binding. We tested the coreceptor function of a subset of reducing and enhancing mutants using a T cell hybridoma and found similar reducing and enhancing effects. CD8beta-enhancing mutants could be useful for immunotherapy by transduction into T cells to enhance T cell responses against weak Ags such as those expressed by tumors. We also addressed the question of the orientation of CD8alphabeta with MHC class I using CD8alpha mutants expressed as a heterodimer with wild-type CD8alpha or CD8beta. The partial rescuing of binding with wild-type CD8beta compared with wild-type CD8alpha is consistent with models in which either the topology of CD8alphaalpha and CD8alphabeta binding to MHC class I is different or CD8alphabeta is capable of binding in both the T cell membrane proximal and distal positions.