The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-LCK interactions.

CD4+ T cell activation is driven by five-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3γε, CD3δε, and CD3ζζ) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3ζ, ZAP70, and PLCγ1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.

Pharmacokinetics, Safety, and Tolerability of a Single 5-Day Treatment of Tirbanibulin Ointment 1% in 100 cm2 : A Phase 1 Maximal-Use Trial in Patients with Actinic Keratosis.

Tirbanibulin ointment 1% is approved in the United States and Europe for the treatment of actinic keratosis with demonstrated efficacy, safety, and tolerability when applied over a field up to 25 cm2 . This Phase 1 maximal-use trial determines the plasma pharmacokinetics, safety, and tolerability of tirbanibulin ointment 1% applied to 100 cm2 of the face or balding scalp in adults with actinic keratosis. Twenty-eight patients self-applied tirbanibulin once daily for a single 5-day treatment course. On Day 5, the mean maximum plasma concentration was 1.06 ng/mL and area under the plasma concentration-time curve during a dosing interval was 16.2 ng â€¢ h/mL. Systemic exposure was approximately 4-fold higher than in a previous pharmacokinetic study with a 25 cm2 field, consistent with the increase in the treated area. Tirbanibulin applied to a 100-cm2 treatment field showed favorable safety and tolerability. The most common treatment-emergent adverse events were application site reactions (in 35.7% of patients). All treatment-emergent adverse events and most of the tolerability signs were mild/moderate and resolved or returned to baseline by Day 29. In summary, under maximal-use conditions, tirbanibulin ointment 1% was safe and well tolerated supporting its potential use over a field up to 100 cm2 .

The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-LCK interactions.

CD4+ T cell activation is driven by 5-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3γε, CD3δε, and CD3ζζ) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee, et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3ζ, ZAP70, and PLCγ1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.

Safety, pharmacokinetics, and efficacy of ruxolitinib cream in children and adolescents with atopic dermatitis.

BACKGROUND: Therapies for children with atopic dermatitis (AD) have safety and tolerability concerns that may limit long-term use. Ruxolitinib cream, a Janus kinase (JAK) inhibitor, is effective and well tolerated in adolescents and adults with AD. OBJECTIVE: To analyze the safety and tolerability of ruxolitinib cream in pediatric patients. Pharmacokinetics and efficacy were also evaluated in this phase 1 study (NCT03257644). METHODS: Patients aged 2 to 17 years with AD (affected body surface area 8%-20%; Investigator's Global Assessment score ≥2) were enrolled stepwise in 6 age-descending, strength-increasing cohorts to apply 0.5%, 0.75%, or 1.5% ruxolitinib cream twice daily for 28 days. Safety, pharmacokinetics, and efficacy were analyzed at baseline, week 2 (day 10), and week 4 (day 29). RESULTS: Among 71 patients, 44 (62.0%) had a baseline Investigator's Global Assessment score of 3; median (range) body surface area affected at baseline was 12.2% (1.7%-20.4%). Ruxolitinib cream was well tolerated, with 4 patients (5.6%) experiencing treatment-related adverse events (all grades 1/2). No clinically meaningful changes in mean chemistry or hematology values were observed, and no consistent pattern of change in bone biomarkers was detected. Mean plasma ruxolitinib levels within each cohort (range, 23.1-97.9 nM) were well below the half-maximal inhibitory concentration for thrombopoietin phosphorylation of STAT3 (281 nM). All cohorts experienced improvements in exploratory efficacy end points. CONCLUSION: Ruxolitinib cream was well tolerated in pediatric patients with AD, with no effect on blood counts or bone biomarkers. Mean plasma concentration was low. Efficacy was consistent with data from previous studies in adolescents and adults. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03257644.

Enhancing and inhibitory motifs regulate CD4 activity.

CD4+ T cells use T cell receptor (TCR)-CD3 complexes, and CD4, to respond to peptide antigens within MHCII molecules (pMHCII). We report here that, through ~435 million years of evolution in jawed vertebrates, purifying selection has shaped motifs in the extracellular, transmembrane, and intracellular domains of eutherian CD4 that enhance pMHCII responses, and covary with residues in an intracellular motif that inhibits responses. Importantly, while CD4 interactions with the Src kinase, Lck, are viewed as key to pMHCII responses, our data indicate that CD4-Lck interactions derive their importance from the counterbalancing activity of the inhibitory motif, as well as motifs that direct CD4-Lck pairs to specific membrane compartments. These results have implications for the evolution and function of complex transmembrane receptors and for biomimetic engineering.

Tapinarof Cream 1% for Extensive Plaque Psoriasis: A Maximal Use Trial on Safety, Tolerability, and Pharmacokinetics.

BACKGROUND: Tapinarof is a novel topical therapeutic aryl hydrocarbon receptor modulating agent in development for the treatment of psoriasis and atopic dermatitis. OBJECTIVE: This multicenter, open-label trial assessed the safety, tolerability, pharmacokinetics (PK), and efficacy of tapinarof cream 1% once daily (QD) under maximal use conditions in extensive plaque psoriasis. METHODS: Adults with a baseline Physician Global Assessment (PGA) score of ≥ 3 and body surface area (BSA) involvement ≥ 20% received tapinarof cream 1% QD for 29 days. Safety and tolerability assessments included adverse events (AEs) and local tolerability scales. PK parameters were calculated using non-compartmental analysis. Efficacy assessments included change in PGA, Psoriasis Area and Severity Index score, and %BSA affected. RESULTS: Twenty-one patients were enrolled. Common AEs were folliculitis, headache, back pain, and pruritus (none led to discontinuation). Tapinarof plasma exposure was low, with the majority of concentrations being below detectable limits. At day 29, 14 patients (73.7%) had a ≥ 1-grade improvement in PGA score and six patients (31.6%) had a ≥ 2-grade improvement; four patients (21.1%) achieved treatment success (PGA 0 or 1 and ≥ 2-grade improvement). CONCLUSION: Tapinarof cream 1% QD was well tolerated, with limited systemic exposure and significant efficacy at 4 weeks in patients with extensive plaque psoriasis. ClinicalTrials.gov Identifier NCT04042103.

A biomimetic five-module chimeric antigen receptor (5MCAR) designed to target and eliminate antigen-specific T cells.

T cells express clonotypic T cell receptors (TCRs) that recognize peptide antigens in the context of class I or II MHC molecules (pMHCI/II). These receptor modules associate with three signaling modules (CD3γε, δε, and ζζ) and work in concert with a coreceptor module (either CD8 or CD4) to drive T cell activation in response to pMHCI/II. Here, we describe a first-generation biomimetic five-module chimeric antigen receptor (5MCAR). We show that 1) chimeric receptor modules built with the ectodomains of pMHCII assemble with CD3 signaling modules into complexes that redirect cytotoxic T lymphocyte (CTL) specificity and function in response to the clonotypic TCRs of pMHCII-specific CD4+ T cells, and 2) surrogate coreceptor modules enhance the function of these complexes. Furthermore, we demonstrate that adoptively transferred 5MCAR-CTLs can mitigate type I diabetes by targeting autoimmune CD4+ T cells in NOD mice. This work provides a framework for the construction of biomimetic 5MCARs that can be used as tools to study the impact of particular antigen-specific T cells in immune responses, and may hold potential for ameliorating diseases mediated by pathogenic T cells.

Bonds Voyage! A Dissociative Model of TCR-CD3 Triggering Is Proposed.

How the T cell receptor (TCR)-CD3 complex activates T cells is debated. In this issue of Immunity, Brazin et al. (2018) propose that TCR engagement under force releases the CD3 signaling modules to disperse and adopt signaling active states.

Reciprocal TCR-CD3 and CD4 Engagement of a Nucleating pMHCII Stabilizes a Functional Receptor Macrocomplex.

CD4+ T cells convert the time that T cell receptors (TCRs) interact with peptides embedded within class II major histocompatibility complex molecules (pMHCII) into signals that direct cell-fate decisions. In principle, TCRs relay information to intracellular signaling motifs of the associated CD3 subunits, while CD4 recruits the kinase Lck to those motifs upon coincident detection of pMHCII. But the mechanics by which this occurs remain enigmatic. In one model, the TCR and CD4 bind pMHCII independently, while in another, CD4 interacts with a composite surface formed by the TCR-CD3 complex bound to pMHCII. Here, we report that the duration of TCR-pMHCII interactions impact CD4 binding to MHCII. In turn, CD4 increases TCR confinement to pMHCII via reciprocal interactions involving membrane distal and proximal CD4 ectodomains. The data suggest that a precisely assembled macrocomplex functions to reliably convert TCR-pMHCII confinement into reproducible signals that orchestrate adaptive immunity.

Domain-swapped T cell receptors improve the safety of TCR gene therapy.

T cells engineered to express a tumor-specific αß T cell receptor (TCR) mediate anti-tumor immunity. However, mispairing of the therapeutic αß chains with endogenous αß chains reduces therapeutic TCR surface expression and generates self-reactive TCRs. We report a general strategy to prevent TCR mispairing: swapping constant domains between the α and ß chains of a therapeutic TCR. When paired, domain-swapped (ds)TCRs assemble with CD3, express on the cell surface, and mediate antigen-specific T cell responses. By contrast, dsTCR chains mispaired with endogenous chains cannot properly assemble with CD3 or signal, preventing autoimmunity. We validate this approach in cell-based assays and in a mouse model of TCR gene transfer-induced graft-versus-host disease. We also validate a related approach whereby replacement of αß TCR domains with corresponding γδ TCR domains yields a functional TCR that does not mispair. This work enables the design of safer TCR gene therapies for cancer immunotherapy.

A Mechanical Switch Couples T Cell Receptor Triggering to the Cytoplasmic Juxtamembrane Regions of CD3ζζ.

The eight-subunit T cell receptor (TCR)-CD3 complex is the primary determinant for T cell fate decisions. Yet how it relays ligand-specific information across the cell membrane for conversion to chemical signals remains unresolved. We hypothesized that TCR engagement triggers a change in the spatial relationship between the associated CD3ζζ subunits at the junction where they emerge from the membrane into the cytoplasm. Using three in situ proximity assays based on ID-PRIME, FRET, and EPOR activity, we determined that the cytosolic juxtamembrane regions of the CD3ζζ subunits are spread apart upon assembly into the TCR-CD3 complex. TCR engagement then triggered their apposition. This mechanical switch resides upstream of the CD3ζζ intracellular motifs that initiate chemical signaling, as well as the polybasic stretches that regulate signal potentiation. These findings provide a framework from which to examine triggering events for activating immune receptors and other complex molecular machines.