Exploratory pharmacodynamics and efficacy of PF-06817024 in a Phase 1 study of patients with chronic rhinosinusitis and atopic dermatitis.

PF-06817024 is a humanized antibody against interleukin-33 that has the potential to inhibit type 2 inflammation. An exploratory analysis of the pharmacodynamics and clinical effects of single and repeat doses of PF-06817024 was assessed in patients with chronic rhinosinusitis with nasal polyps (CRSwNP) and patients with moderate-to-severe atopic dermatitis (AD), respectively, as part of a Phase 1, first-in-human study. Rhinosinusitis symptoms were improved, and nasal polyps were decreased in size following treatment with PF-06817024 in patients with CRSwNP. In patients with AD, PF-06817024, in aggregate, reduced disease severity and improved symptoms, as demonstrated by greater percentage decrease from baseline in Eczema Area and Severity Index (EASI) scores and reduced pruritus numerical rating scores, compared with placebo. The efficacy in AD appeared to be bimodal with a sub-group of participants exhibiting high levels of improvement (EASI75 and EASI90) for a sustained period of time after dosing. In patients with CRSwNP, a consistent trend of decrease in eosinophil levels was observed in the PF-06817024 group, compared with placebo. Further research would be needed to confirm the clinical benefit and safety of PF-06817024 as a treatment for allergic diseases. Trial registration ClinicalTrials.gov, NCT02743871. Registered 15 April 2016, https://clinicaltrials.gov/study/NCT02743871?term=NCT02743871&rank=1 .

A Phase 1, randomized, double-blind, placebo-controlled, single- and multiple-dose escalation study to evaluate the safety and pharmacokinetics/pharmacodynamics of PF-06835375, a C-X-C chemokine receptor type 5 directed antibody, in patients with systemic lupus erythematosus or rheumatoid arthritis.

BACKGROUND: The objective of this study was to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of PF­06835375, a potent selective afucosyl immunoglobulin G1 antibody targeting C-X-C chemokine receptor type 5 (CXCR5) that potentially depletes B cells, follicular T helper (Tfh) cells, and circulating Tfh-like (cTfh) cells, in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). METHODS: This first-in-human, multicenter, double-blind, sponsor-open, placebo-controlled Phase 1 study recruited patients aged 18-70 years with SLE or RA. In Part A, patients received single doses of intravenous PF-06835375 (dose range: 0.03-6 mg) or placebo in six sequential single ascending dose (SAD) cohorts. In Part B, patients received repeat doses of subcutaneous PF-06835375 (dose range: 0.3-10 mg) or placebo on Days 1 and 29 in five multiple ascending dose (MAD) cohorts. Tetanus/Diphtheria (Td) and Meningococcal B (MenB/Trumenba™) vaccines were administered at Day 4 (Td and MenB) and Week 8 (MenB only) to assess PF-06835375 functional effects. Endpoints included treatment-emergent adverse events (TEAEs), pharmacokinetic parameters, pharmacodynamic effects on B and cTfh cells, and biomarker counts, vaccine response, and exploratory differential gene expression analysis. Safety, pharmacokinetic, and pharmacodynamic endpoints are summarized descriptively. The change from baseline of B and Tfh cell-specific genes over time was calculated using a prespecified mixed-effects model, with a false discovery rate < 0.05 considered statistically significant. RESULTS: In total, 73 patients were treated (SAD cohorts: SLE, n = 17; RA, n = 14; MAD cohorts: SLE, n = 22; RA, n = 20). Mean age was 53.3 years. Sixty-two (84.9%) patients experienced TEAEs (placebo n = 17; PF-06835375 n = 45); most were mild or moderate. Three (9.7%) patients experienced serious adverse events. Mean t1/2 ranged from 3.4-121.4 h (SAD cohorts) and 162.0-234.0 h (MAD cohorts, Day 29). B and cTfh cell counts generally showed dose-dependent reductions across cohorts (range of mean maximum depletion: 67.3-99.3%/62.4-98.7% [SAD] and 91.1-99.6%/89.5-98.1% [MAD], respectively). B cell-related genes and pathways were significantly downregulated in patients treated with PF-06835375. CONCLUSIONS: These data support further development of PF-06835375 to assess the clinical potential for B and Tfh cell depletion as a treatment for autoimmune diseases. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03334851.

Master protocols and other innovative trial designs in inflammation and immunology to expedite clinical drug development.

Master protocol designs, such as umbrella and basket studies, allow multiple compounds or multiple target populations to be evaluated simultaneously within a single protocol, and have been widely adopted in oncology clinical trials. These novel designs can also be applied in other therapeutic areas, where they could have several benefits over conducting traditional randomized controlled trials. Here, we detail Pfizer's recent implementations of master protocol designs in inflammation and immunology clinical studies, focusing on the opportunities for cost and resource savings and how these designs can expedite the time required to bring new treatments to patients in need.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of PF-06817024 in Healthy Participants, Participants with Chronic Rhinosinusitis with Nasal Polyps, and Participants with Atopic Dermatitis: A Phase 1, Randomized, Double-Blind, Placebo-Controlled Study.

PF-06817024 is a high affinity, humanized antibody that binds interleukin-33, a proinflammatory type 2 cytokine, and thereby has the potential to inhibit downstream type 2 inflammation. This Phase 1, randomized, placebo-controlled study was conducted in 3 parts to evaluate the safety, tolerability, pharmacokinetics (PK), immunogenicity, and pharmacodynamics of escalating single and limited repeat PF-06817024 doses in healthy participants (Part 1), a single dose of PF-06817024 in participants with chronic rhinosinusitis with nasal polyps (Part 2), and repeat doses of PF-06817024 in participants with moderate to severe atopic dermatitis (atoptic dermatitis; Part 3). PF-06817024 was generally well tolerated in all participant populations. Most participants experienced a treatment-emergent adverse event (healthy participants, 78.4% and 100%; participants with chronic rhinosinusitis with nasal polyps, 90.9% and 88.9%; and participants with atoptic dermatitis, 60.0% and 62.5% in the PF-06817024 and placebo groups, respectively). No substantial deviations from dose proportionality were observed for single intravenous doses of 10-1000 mg, indicating linear PK in healthy participants. Mean terminal half-life ranged from 83 to 94 days after single intravenous administration in healthy participants and was similar to that observed after administration in the studied patient populations. Incidences of antidrug antibodies in the studied populations were 10.8%, 9.1%, and 5.0% for healthy participants, participants with chronic rhinosinusitis with nasal polyps, and participants with atoptic dermatitis, respectively. In addition, dose-dependent increases were observed in total serum interleukin-33 levels of treated participants, indicating target engagement. Overall, the PK and safety profile of PF-06817024 supports further investigation of the drug as a potential treatment for allergic diseases.

Efficacy and Safety of the TYK2/JAK1 Inhibitor Brepocitinib for Active Psoriatic Arthritis: A Phase IIb Randomized Controlled Trial.

OBJECTIVE: Brepocitinib is a TYK2/JAK1 inhibitor in development for the treatment of several immunologic diseases. The efficacy and safety of oral brepocitinib were assessed in participants with moderately-to-severely active psoriatic arthritis (PsA) for up to 52 weeks. METHODS: In this placebo-controlled, dose-ranging, phase IIb study, participants were randomized to receive 10 mg, 30 mg, or 60 mg of brepocitinib once daily or placebo, advancing to 30 mg or 60 mg of brepocitinib once daily at week 16. The primary endpoint was the response rate according to the American College of Rheumatology criteria for 20% improvement (ACR20) in disease activity at week 16. Secondary endpoints included response rates according to the ACR50/ACR70 response criteria, 75% and 90% improvement in the Psoriasis Area and Severity Index (PASI75/PASI90) score, and minimal disease activity (MDA) at weeks 16 and 52. Adverse events were monitored throughout the study. RESULTS: Overall, 218 participants were randomized and treated. At week 16, the brepocitinib 30 mg and 60 mg once daily groups had significantly greater ACR20 response rates (66.7% [P = 0.0197] and 74.6% [P = 0.0006], respectively), versus the placebo group (43.3%), and significantly higher ACR50/ACR70, PASI75/PASI90, and MDA response rates. Response rates were maintained or improved through week 52. Adverse events were mostly mild/moderate; serious adverse events (15) in 12 participants (5.5%) included infections in 6 participants (2.8%) in the brepocitinib 30 mg and 60 mg once daily groups. No major adverse cardiovascular events or deaths occurred. CONCLUSION: Treatment with brepocitinib at dosages of 30 mg and 60 mg once daily was superior to placebo at reducing signs and symptoms of PsA. Brepocitinib was generally well tolerated throughout the 52-week study, with a safety profile consistent with those found in other brepocitinib clinical trials.

Efficacy and safety of oral ritlecitinib for the treatment of active nonsegmental vitiligo: A randomized phase 2b clinical trial.

BACKGROUND: Vitiligo is a chronic autoimmune disorder characterized by depigmented patches of the skin. OBJECTIVE: To evaluate the efficacy and safety of ritlecitinib, an oral JAK3 (Janus kinase)/TEC (tyrosine kinase expressed in hepatocelluar carcinoma) inhibitor, in patients with active nonsegmental vitiligo in a phase 2b trial (NCT03715829). METHODS: Patients were randomized to once-daily oral ritlecitinib ± 4-week loading dose (200/50 mg, 100/50 mg, 30 mg, or 10 mg) or placebo for 24 weeks (dose-ranging period). Patients subsequently received ritlecitinib 200/50 mg daily in a 24-week extension period. The primary efficacy endpoint was percent change from baseline in Facial-Vitiligo Area Scoring Index at week 24. RESULTS: A total of 364 patients were treated in the dose-ranging period. Significant differences from placebo in percent change from baseline in Facial-Vitiligo Area Scoring Index were observed for the ritlecitinib 50 mg groups with (-21.2 vs 2.1; P < .001) or without (-18.5 vs 2.1; P < .001) a loading dose and ritlecitinib 30 mg group (-14.6 vs 2.1; P = .01). Accelerated improvement was observed after treatment with ritlecitinib 200/50 mg in the extension period (n = 187). No dose-dependent trends in treatment-emergent or serious adverse events were observed across the 48-week treatment. LIMITATIONS: Patients with stable vitiligo only were excluded. CONCLUSIONS: Oral ritlecitinib was effective and well tolerated over 48 weeks in patients with active nonsegmental vitiligo.

Safety and Efficacy of Ritlecitinib and Brepocitinib in Alopecia Areata: Results from the Crossover Open-Label Extension of the ALLEGRO Phase 2a Trial.

The 24-week, double-blind period of the ALLEGRO phase 2a trial (NCT02974868) evaluated the safety and efficacy of ritlecitinib (Jak3/tyrosine kinase expressed in the hepatocellular carcinoma inhibitor) and brepocitinib (tyrosine kinase 2/Jak1 inhibitor) in patients with alopecia areata; patients could subsequently continue treatment in a 24-week single-blind extension, followed by a crossover open-label extension, described in this article. Patients who did not achieve ≥30% improvement from baseline in Severity of Alopecia Tool score at the end of the single-blind extension entered a 24-week crossover open-label extension: the ritlecitinib group switched to brepocitinib, and the brepocitinib group switched to ritlecitinib. Eighteen patients switched to brepocitinib, and five switched to ritlecitinib. Six treatment-emergent adverse events were reported by five patients; no new safety risks were observed after crossover. An exploratory efficacy evaluation showed that none of the five patients receiving ritlecitinib in the crossover open-label extension achieved ≥30% improvement from baseline in Severity of Alopecia Tool score or improvement in eyebrow/eyelash assessments. Four of 16 patients receiving brepocitinib achieved ≥30% improvement from baseline in Severity of Alopecia Tool score or better; 4 of 15 and 5 of 12 showed improvement in eyebrow and eyelash assessments, respectively. Although the small number of patients precludes firm conclusions regarding efficacy, the data suggest that some patients with alopecia areata and inadequate response to ritlecitinib after ≥24 weeks show benefit after switching to brepocitinib.

Ritlecitinib and brepocitinib demonstrate significant improvement in scalp alopecia areata biomarkers.

BACKGROUND: Janus kinase (JAK) inhibitors have shown encouraging results in the treatment of alopecia areata (AA), an autoimmune form of hair loss, in small, uncontrolled studies and case reports. OBJECTIVE: We conducted a biopsy substudy during the randomized, double-blind, placebo-controlled first 24 weeks of a phase 2a clinical trial that evaluated the efficacy and safety of ritlecitinib, an inhibitor of JAK3 and the tyrosine kinase expressed in hepatocellular carcinoma (TEC) kinase family, and brepocitinib, an inhibitor of tyrosine kinase 2 (TYK2)/JAK1 in the treatment of AA. METHODS: Change in biomarkers in lesional scalp biopsy samples between baseline and weeks 12 and 24 was an exploratory end point, and 46 patients participated from the ritlecitinib (n = 18), brepocitinib (n = 16), and placebo (n = 12) groups. Correlations of biomarkers with hair regrowth, measured using the Severity of Alopecia Tool (SALT) score, were also evaluated. CLINICAL TRIAL REGISTRATION: NCT02974868. RESULTS: At week 24, both ritlecitinib and brepocitinib demonstrated improvement exceeding 100% in the lesional scalp transcriptome toward a nonlesional profile. At week 12, the improvements in scalp tissue were greater with brepocitinib than ritlecitinib; however, at week 24, the improvements were greater with ritlecitinib. CONCLUSIONS: For both ritlecitinib and brepocitinib, improvement in the SALT scores was positively associated with expression of TH1 markers and negatively associated with expression of hair keratins. Larger, long-term clinical trials are warranted.

Antitumor Necrosis Factor-like Ligand 1A Therapy Targets Tissue Inflammation and Fibrosis Pathways and Reduces Gut Pathobionts in Ulcerative Colitis.

BACKGROUND: The first-in-class treatment PF-06480605 targets the tumor necrosis factor-like ligand 1A (TL1A) molecule in humans. Results from the phase 2a TUSCANY trial highlighted the safety and efficacy of PF-06480605 in ulcerative colitis. Preclinical and in vitro models have identified a role for TL1A in both innate and adaptive immune responses, but the mechanisms underlying the efficacy of anti-TL1A treatment in inflammatory bowel disease (IBD) are not known. METHODS: Here, we provide analysis of tissue transcriptomic, peripheral blood proteomic, and fecal metagenomic data from the recently completed phase 2a TUSCANY trial and demonstrate endoscopic improvement post-treatment with PF-06480605 in participants with ulcerative colitis. RESULTS: Our results revealed robust TL1A target engagement in colonic tissue and a distinct colonic transcriptional response reflecting a reduction in inflammatory T helper 17 cell, macrophage, and fibrosis pathways in patients with endoscopic improvement. Proteomic analysis of peripheral blood revealed a corresponding decrease in inflammatory T-cell cytokines. Finally, microbiome analysis showed significant changes in IBD-associated pathobionts, Streptococcus salivarius, S. parasanguinis, and Haemophilus parainfluenzae post-therapy. CONCLUSIONS: The ability of PF-06480605 to engage and inhibit colonic TL1A, targeting inflammatory T cell and fibrosis pathways, provides the first-in-human mechanistic data to guide anti-TL1A therapy for the treatment of IBD.

Anti-TL1A Antibody PF-06480605 Safety and Efficacy for Ulcerative Colitis: A Phase 2a Single-Arm Study.

BACKGROUND & AIMS: An immune component of inflammatory bowel disease is up-regulated tumor necrosis factor-like ligand 1A (TL1A). Anti-TL1A antibodies such as PF-06480605, a fully human immunoglobulin G1 monoclonal antibody, may have therapeutic potential. METHODS: This Phase 2a, multicenter, single-arm, open-label study (TUSCANY) evaluated safety, tolerability, efficacy, pharmacokinetics, and immunogenicity in PF-06480605-treated participants with moderate to severe ulcerative colitis (UC). Participants received 500 mg intravenous PF-06480605 every 2 weeks, 7 doses total, with a 3-month follow-up period. Primary safety and efficacy endpoints were the incidence of adverse events (AEs) and week 14 endoscopic improvement (EI) (Mayo endoscopic subscore = 0 or 1), respectively. Secondary endpoints included total soluble TL1A (free/drug-bound) (sTL1A), incidence of anti-drug and neutralizing antibodies, PF-06480605 concentrations, and changes in fecal calprotectin and high-sensitivity C-reactive protein. Histology was assessed at week 14. RESULTS: The study enrolled 50 participants; 42 completed. Of 109 treatment-emergent AEs, 18 were treatment-related. The most common AEs were UC disease exacerbation and arthralgia (6 participants each). Four serious AEs, no deaths, and no malignancies were reported. Week 14 EI was observed in a statistically significant proportion of participants (38.2% [uniformly minimum-variance unbiased estimator, per protocol population]). Minimal histologic disease was observed after treatment (Robarts Histopathology Index ≤5: 33.3%; Geboes Index ≤3.2: 47.6%). sTL1A increase over time from baseline indicated sustained target engagement. Forty-one participants (82%) tested positive for anti-drug antibodies and 5 (10%) for neutralizing antibodies. CONCLUSIONS: PF-06480605 demonstrated an acceptable safety profile and statistically significant EI in participants with moderate to severe UC, warranting further study in a larger participant cohort. Tissue histopathology analyses support this conclusion. TRIAL REGISTRATION NUMBER: https://clinicaltrials.gov/NCT02840721.

Efficacy and Safety of PF-06651600 (Ritlecitinib), a Novel JAK3/TEC Inhibitor, in Patients With Moderate-to-Severe Rheumatoid Arthritis and an Inadequate Response to Methotrexate.

OBJECTIVE: To evaluate the efficacy and safety of PF-06651600 (ritlecitinib), an irreversible inhibitor of JAK3 and the tyrosine kinase expressed in hepatocellular carcinoma (TEC) kinase family, in comparison with placebo in patients with rheumatoid arthritis (RA). METHODS: An 8-week, phase II, double-blind, parallel-group study was conducted. Seventy patients who were seropositive for anti-citrullinated protein antibodies and/or rheumatoid factor were randomized 3:2 to receive oral PF-06651600 (200 mg once daily) or placebo for 8 weeks. Eligible patients had an inadequate response to methotrexate, and the study design allowed up to 50% of patients to have previously received 1 tumor necrosis factor inhibitor that was inadequately effective and/or not tolerated. The primary end point was change from baseline in the Simplified Disease Activity Index (SDAI) score at week 8, assessed by Bayesian analysis using an informative prior distribution for placebo response. RESULTS: Mean change from baseline in the SDAI score at week 8 was greater in the PF-06651600 group (-26.1 [95% credible interval -29.7, -22.4]) than in the placebo group (-16.8 [95% credible interval -20.9, -12.7]; P < 0.001). Most adverse events (AEs) were mild in severity, and no treatment-related serious AEs, severe AEs, or deaths were reported. The most common classes of AE were infections and infestations as well as skin and subcutaneous tissue disorders; there was 1 mild case of herpes simplex in the PF-06651600 group that was considered to be treatment related, which resolved within 3 days without study treatment discontinuation or antiviral therapy. CONCLUSION: Treatment with the oral JAK3/TEC inhibitor PF-06651600 (200 mg once daily) was associated with significant improvements in RA disease activity and was generally well-tolerated in this small 8-week study.

QuickRNASeq: Guide for Pipeline Implementation and for Interactive Results Visualization.

Sequencing of transcribed RNA molecules (RNA-Seq) has been used wildly for studying cell transcriptomes in bulk or at the single-cell level (Wang et al., Nat Rev Genet, 10:57-63, 2009; Ozsolak and Milos, Nat Rev Genet, 12:87-98, 2011; Sandberg, Nat Methods, 11:22-24, 2014) and is becoming the de facto technology for investigating gene expression level changes in various biological conditions, on the time course, and under drug treatments. Furthermore, RNA-Seq data helped identify fusion genes that are related to certain cancers (Maher et al., Nature, 458:97-101, 2009). Differential gene expression before and after drug treatments provides insights to mechanism of action, pharmacodynamics of the drugs, and safety concerns (Dixit et al., Genomics, 107:178-188, 2016). Because each RNA-Seq run generates tens to hundreds of millions of short reads with size ranging from 50 to 200 bp, a tool that deciphers these short reads to an integrated and digestible analysis report is in high demand. QuickRNASeq (Zhao et al., BMC Genomics, 17:39-53, 2016) is an application for large-scale RNA-Seq data analysis and real-time interactive visualization of complex data sets. This application automates the use of several of the best open-source tools to efficiently generate user friendly, easy to share, and ready to publish report. Figures in this protocol illustrate some of the interactive plots produced by QuickRNASeq. The visualization features of the application have been further improved since its first publication in early 2016. The original QuickRNASeq publication (Zhao et al., BMC Genomics, 17:39-53, 2016) provided details of background, software selection, and implementation. Here, we outline the steps required to implement QuickRNASeq in user's own environment, as well as demonstrate some basic yet powerful utilities of the advanced interactive visualization modules in the report.

Efficacy and safety of an interleukin 6 monoclonal antibody for the treatment of systemic lupus erythematosus: a phase II dose-ranging randomised controlled trial.

OBJECTIVES: This phase II trial evaluated the efficacy and safety of an interleukin (IL) 6 monoclonal antibody for systemic lupus erythematosus (SLE). METHODS: Patients with active disease were randomised to placebo or PF-04236921 10 mg, 50 mg or 200 mg, subcutaneously, every 8 weeks with stable background therapy. SLE Responder Index (SRI-4; primary end point) and British Isles Lupus Assessment Group-based Composite Lupus Assessment (BICLA) were assessed at week 24. Post hoc analysis identified an enriched population based upon planned univariate analyses. RESULTS: 183 patients received treatment (placebo, n=45; 10 mg, n=45; 50 mg, n=47; 200 mg, n=46). The 200 mg dose was discontinued due to safety findings and not included in the primary efficacy analysis. The SRI-4 response rates were not significant for any dose compared with placebo; however, the BICLA response rate was significant for 10 mg (p=0.026). The incidence of severe flares was significantly reduced with 10 mg (n=0) and 50 mg (n=2) combined versus placebo (n=8; p<0.01). In patients with greater baseline disease activity (enriched population), the SRI-4 (p=0.004) and BICLA (p=0.012) response rates were significantly different with 10 mg versus placebo. Four deaths (200 mg, n=3; 10 mg, n=1) occurred. The most frequently reported adverse events included headache, nausea and diarrhoea. CONCLUSIONS: PF-04236921 was not significantly different from placebo for the primary efficacy end point in patients with SLE. Evidence of an effect with 10 mg was seen in a post hoc analysis. Safety was acceptable for doses up to 50 mg as the 200 mg dose was discontinued due to safety findings. TRIAL REGISTRATION NUMBER: NCT01405196; Pre-results.

Markers of inflammation in alveolar cells exposed to fine particulate matter from prescribed fires and urban air.

OBJECTIVE: To assess the effect of fine particulate matter (PM(2.5)) from different particle sources on tumor necrosis factor- (TNF-) α, we measured TNF production from rat alveolar macrophages (AM) and human dendritic cells (DC) exposed to PM(2.5) from different sources. METHODS: Fire-related PM(2.5) samples, rural ambient, and urban indoor and outdoor samples were collected in the Southeast United States. Tumor necrosis factor release was measured from rat AM and human DC following incubation with PM(2.5). RESULTS: Tumor necrosis factor release in AMs was greatest for fire-related PM(2.5) compared with other samples (TNF: P value = 0.005; mortality: P value = 0.005). Tumor necrosis factor releases from the DCs and AMs exposed to fire-associated PM(2.5) were strongly correlated (r = 0.87, P value < 0.0001). CONCLUSIONS: Particulate matter exposure produces TNF release consistent with pulmonary inflammation in rat AMs and human DCs, with the response in rat AMs differing by particle source.

Understanding the function of CD1-restricted T cells.

CD1 molecules bind foreign lipid antigens as they survey the endosomal compartments of infected antigen-presenting cells. Unlike T cells that recognize CD1-restricted foreign lipids, CD1-restricted T cells that are self-antigen-reactive function as 'auto-effectors' that are rapidly stimulated to carry out helper and effector functions upon interaction with CD1-expressing antigen-presenting cells. The functional distinctions between subsets of CD1-restricted T cells, and the pathways by which these cells both influence the inflammatory and tolerogenic effects of dendritic cells and activate natural killer cells and other lymphocytes, provide insight into how CD1-restricted T cells regulate antimicrobial responses, antitumor immunity and the balance between tolerance and autoimmunity.

CD1-mediated gamma/delta T cell maturation of dendritic cells.

Immature myeloid dendritic cells (DCs) express only low levels of major histocompatibility complex (MHC) class II but express high levels of CD1 a, b, and c antigen-presenting molecules at the cell surface. As Vdelta1+ gamma/delta T cells are the main tissue subset of gamma/delta T cells and they are known to recognize CD1c in the absence of specific foreign antigen recognition, we examined the possible interaction of these T cells with immature DCs. We show that CD1-restricted gamma/delta T cells can mediate the maturation of DCs. DC maturation required cell-cell contact and could be blocked by antibodies against CD1c. The maturation process was partially mediated by tumor necrosis factor alpha. Importantly, immature DCs matured in the presence of lipopolysaccharide and CD1-restricted gamma/delta T cells produced bioactive interleukin-12p70. In addition, these DCs were able to efficiently present peptide antigens to naive CD4+ T cells. CD1-restricted gamma/delta T cell recognition of immature DCs provides the human immune system with the capacity to rapidly generate a pool of mature DCs early during microbial invasion. This may be an important source of critical host signals for T helper type 1 polarization of antigen-specific naive T cells and the subsequent adaptive immune response.