BackgroundIn preliminary findings from the recurrent or metastatic cervical cancer cohort of CheckMate 358, nivolumab showed durable anti-tumour responses, and the combination of nivolumab plus ipilimumab showed promising clinical activity. Here, we report long-term outcomes from this cohort.MethodsCheckMate 358 was a phase 1–2, open-label, multicohort trial. The metastatic cervical cancer cohort enrolled patients from 30 hospitals and cancer centres across ten countries. Female patients aged 18 years or older with a histologically confirmed diagnosis of squamous cell carcinoma of the cervix with recurrent or metastatic disease, an Eastern Cooperative Oncology Group performance status of 0 or 1, and up to two previous systemic therapies were enrolled into the nivolumab 240 mg every 2 weeks group, the randomised groups (nivolumab 3 mg/kg every 2 weeks plus ipilimumab 1 mg/kg every 6 weeks [NIVO3 plus IPI1] or nivolumab 1 mg/kg every 3 weeks plus ipilimumab 3 mg/kg every 3 weeks for four cycles then nivolumab 240 mg every 2 weeks [NIVO1 plus IPI3]), or the NIVO1 plus IPI3 expansion group. All doses were given intravenously. Patients were randomly assigned (1:1) to NIVO3 plus IPI1 or NIVO1 plus IPI3 via an interactive voice response system. Treatment continued until disease progression, unacceptable toxicity, or consent withdrawal, or for up to 24 months. The primary endpoint was investigator-assessed objective response rate. Anti-tumour activity and safety were analysed in all treated patients. This study is registered with ClinicalTrials.gov (NCT02488759) and is now completed.FindingsBetween October, 2015, and March, 2020, 193 patients were recruited in the recurrent or metastatic cervical cancer cohort of CheckMate 358, of whom 176 were treated. 19 patients received nivolumab monotherapy, 45 received NIVO3 plus IPI1, and 112 received NIVO1 plus IPI3 (45 in the randomised group and 67 in the expansion group). Median follow-up times were 19·9 months (IQR 8·2–44·8) with nivolumab, 12·6 months (7·8–37·1) with NIVO3 plus IPI1, and 16·7 months (7·2–27·5) with pooled NIVO1 plus IPI3. Objective response rates were 26% (95% CI 9–51; five of 19 patients) with nivolumab, 31% (18–47; 14 of 45 patients) with NIVO3 plus IPI1, 40% (26–56; 18 of 45 patients) with randomised NIVO1 plus IPI3, and 38% (29–48; 43 of 112 patients) with pooled NIVO1 plus IPI3. The most common grade 3–4 treatment-related adverse events were diarrhoea, hepatic cytolysis, hyponatraemia, pneumonitis, and syncope (one [5%] patient each; nivolumab group), diarrhoea, increased gamma-glutamyl transferase, increased lipase, and vomiting (two [4%] patients each; NIVO3 plus IPI1 group), and increased lipase (nine [8%] patients) and anaemia (seven [6%] patients; pooled NIVO1 plus IPI3 group). Serious treatment-related adverse events were reported in three (16%) patients in the nivolumab group, 12 (27%) patients in the NIVO3 plus IPI1 group, and 47 (42%) patients in the pooled NIVO1 plus IPI3 group. There was one treatment-related death due to immune-mediated colitis in the NIVO1 plus IPI3 group.InterpretationNivolumab monotherapy and nivolumab plus ipilimumab combination therapy showed promise in the CheckMate 358 study as potential treatment options for recurrent or metastatic cervical cancer. Future randomised controlled trials of nivolumab plus ipilimumab or other dual immunotherapy regimens are warranted to confirm treatment benefit in this patient population.FundingBristol Myers Squibb and Ono Pharmaceutical.

PURPOSE Nivolumab plus relatlimab and nivolumab plus ipilimumab have been approved for advanced melanoma on the basis of the phase II/III RELATIVITY-047 and phase III CheckMate 067 trials, respectively. As no head-to-head trial comparing these regimens exists, an indirect treatment comparison was conducted using patient-level data from each trial. METHODS Inverse probability of treatment weighting (IPTW) adjusted for baseline characteristic differences. Minimum follow-ups (RELATIVITY-047, 33 months; CheckMate 067, 36 months) were selected to best align assessments. Outcomes included progression-free survival (PFS), confirmed objective response rate (cORR), and melanoma-specific survival (MSS) per investigator; overall survival (OS); and treatment-related adverse events (TRAEs). A Cox regression model compared PFS, OS, and MSS. A logistic regression model compared cORRs. Subgroup analyses were exploratory. RESULTS After IPTW, key baseline characteristics were balanced for nivolumab plus relatlimab (n = 339) and nivolumab plus ipilimumab (n = 297). Nivolumab plus relatlimab demonstrated similar PFS (hazard ratio [HR], 1.08 [95% CI, 0.88 to 1.33]), cORR (odds ratio, 0.91 [95% CI, 0.73 to 1.14]), OS (HR, 0.94 [95% CI, 0.75 to 1.19]), and MSS (HR, 0.86 [95% CI, 0.67 to 1.12]) to nivolumab plus ipilimumab. Subgroup comparisons showed larger numerical differences favoring nivolumab plus ipilimumab with acral melanoma, BRAF -mutant melanoma, and lactate dehydrogenase >2 × upper limit of normal, but were limited by small samples. Nivolumab plus relatlimab was associated with fewer grade 3-4 TRAEs (23% v 61%) and any-grade TRAEs leading to discontinuation (17% v 41%). CONCLUSION Nivolumab plus relatlimab demonstrated similar efficacy to nivolumab plus ipilimumab in the overall population, including most—but not all—subgroups, and improved safety in patients with untreated advanced melanoma. Results should be interpreted with caution.

The pathobiology of rheumatoid inflammatory diseases, including rheumatoid arthritis (RA) and psoriatic arthritis, involves the interplay between innate and adaptive immune components and resident synoviocytes. Single-cell analyses of patient samples and relevant mouse models have characterized many cellular subsets in RA. However, the impact of interactions between cell types is not fully understood. In this study, we temporally profiled murine arthritic synovial isolates at the single-cell level to identify perturbations similar to those found in human RA. Notably, murine macrophage subtypes like those found in RA patients were expanded in arthritis and linked to promoting the function of Th17 cells in the joint. In vitro experiments identified a capacity for murine macrophages to maintain the functionality and expansion of Th17 cells. Reciprocally, murine Th17 cell-derived TNF-α induced CD38+ macrophages that enhanced Th17 functionality. Murine synovial CD38+ macrophages were expanded during arthritis, and their depletion or blockade via TNF-α neutralization alleviated disease while reducing IL-17A-producing cells. These findings identify a cellular feedback loop that promotes Th17 cell pathogenicity through TNF-α to drive inflammatory arthritis.

Background: There is no standardized treatment for metastatic uveal melanoma (MUM) but immune checkpoint inhibitors (ICI) are increasingly used. While ICI has transformed the survival of metastatic cutaneous melanoma, MUM patients do not equally benefit. Factors known to affect ICI response include the hematologic markers, lactate dehydrogenase (LDH) and neutrophil:lymphocyte ratio (NLR). We evaluated the prognostic value of LDH and NLR at the start of ICI and on treatment in MUM. Methods: MUM patients were treated between August 2006 and May 2022 with combination ipilimumab/nivolumab or ipilimumab/nivolumab/pembrolizumab single-agent therapy. Univariable (UVA) and multivariable (MVA) analyses were used to assess the prognostic value of predefined baseline factors on progression-free (PFS) and overall survival (OS). Results: In forty-six patients with MUM treated with ICI, elevated baseline and on-treatment LDH was prognostic for OS (start of ICI, HR (95% CI): 3.6 (1.9–7.0), p < 0.01; on-treatment, HR (95% CI): 3.7 (1.6–8.8), p < 0.01) and PFS (start of ICI, (HR (95% CI): 2.8 (1.5–5.4), p < 0.0001); on-treatment LDH (HR (95% CI): 2.2 (1.1–4.3), p < 0.01). On-treatment NLR was prognostic for PFS (HR (95% CI): 1.9 (1.0–3.9), p < 0.01). On-treatment LDH remained an important contributor to survival on MVA (OS: HR (95% CI): 1.001 (1.00–1.002), p < 0.05); PFS: HR (95% CI): 1.001 (1.00–1.002), p < 0.01). Conclusions: This study demonstrates that LDH and NLR could be useful in the prognostication of MUM patients treated with ICI. Additional studies are needed to confirm the importance of these and other prognostic biomarkers.

Introduction: Hematopoietic stem cell transplantation (HSCT) is associated with various cardiovascular (CV) complications. Due to the lack of recent large cohort studies, the incidence and clinical determinants of acute HSCT-related CV events are ill-defined. Methods: We conducted a multi-center observational study (University of Michigan and Rush University) of adult (≥18 years) patients who underwent autologous or allogeneic HSCT for malignant or non-malignant bone marrow disorders from 2005-2021. Data on demographics, pre-HSCT clinical characteristics, imaging, laboratory findings, and acute (<100 days post-HSCT) CV outcomes were collected through manual chart review. The primary outcome was defined as a composite of death from CV cause, non-fatal myocardial infarction, need for revascularization, new-onset heart failure (HF), new diagnosis of atrial fibrillation/flutter, or sustained ventricular tachycardia. Results: Of 4,262 included patients (mean age at HSCT 56±14 years; 59% male; 82% White), 161 (3.8%) patients experienced an acute CV event (153 events/1,000 person-years). Compared to patients without a CV event, those who developed a CV event were older, had greater burden of CV comorbidities including HF, more likely to be on antihypertensives, statins, and aspirin, and had higher B-type natriuretic peptide and lower high-density lipoprotein pre-HSCT (Table). Pre-HSCT ejection fraction and prior anthracycline exposure were not associated with acute CV events. Conclusions: In the largest cotemporary cohort of adult HSCT patients to date, acute CV events occurred in <5% of patients. Events were more common in older patients with CV comorbidities. highlighting the potential need for improving the pre-HSCT CV risk stratification. The major limitation of this study is the retrospective nature and accompanying selection bias. Future prospective studies should assess evidence-based strategies for risk-stratifying HSCT patients.

Although combination BRAF and MEK inhibitors are highly effective for the 40-50% of cutaneous metastatic melanomas harboring BRAF(V600) mutations, targeted agents have been ineffective for BRAF(V600)wild-type (wt) metastatic melanomas. The SU2C Genomics-Enabled Medicine for Melanoma Trial utilized a Simon two-stage optimal design to assess whether comprehensive genomic profiling improves selection of molecular-based therapies for BRAF(V600)wt metastatic melanoma patients who had progressed on standard-of-care therapy, which may include immunotherapy. Of the response-evaluable patients, binimetinib was selected for 20 patients randomized to the genomics-enabled arm, and nine were treated on the alternate treatment arm. Response rates for 27 patients treated with targeted recommendations included one (4%) partial response, 18 (67%) with stable disease, and eight (30%) with progressive disease. Post-trial genomic and protein pathway activation mapping identified additional drug classes that may be considered for future studies. Our results highlight the complexity and heterogeneity of metastatic melanomas, as well as how the lack of response in this trial may be associated with limitations including monotherapy drug selection and the dearth of available single and combination molecularly-driven therapies to treat BRAF(V600)wt metastatic melanomas.

Key Points Question Is the American Joint Committee on Cancer (AJCC) eighth edition staging of metastatic cutaneous melanoma prognostic in the era of immune checkpoint inhibition? Findings In this cohort study of 357 patients with metastatic cutaneous melanoma treated with immune checkpoint inhibitors, the AJCC eighth edition M staging showed limited prognostic stratification; however, the overall survival rates among patients with liver metastases and those with elevated serum lactate dehydrogenase (LDH) levels were much worse than among patients with metastatic involvement of other organs and those with serum LDH levels in the reference range. The importance of these factors was confirmed in a multi-institutional external validation cohort. Meaning These findings suggest that other biomarkers that are associated with overall survival, such as liver metastases and LDH level, should be considered for emphasis in future staging systems.

Background: BRAF and MEK inhibitors yield objective responses in the majority of BRAFV600E/K mutant melanoma patients, but acquired resistance limits response durations. Preclinical data suggests that intermittent dosing of these agents may delay acquired resistance by deselecting tumor cells that grow optimally in the presence of these agents. S1320 is a randomized phase 2 clinical trial designed to determine whether intermittent versus continuous dosing of dabrafenib and trametinib improves progression-free survival (PFS) in patients with advanced BRAFV600E/K melanoma. Methods: All patients received continuous dabrafenib and trametinib for 8-weeks after which non-progressing patients were randomized to receive either continuous treatment or intermittent dosing of both drugs on a 3-week-off, 5-week-on schedule. Unscheduled treatment interruptions of both drugs for > 14 days were not permitted. Responses were assessed using RECIST v1.1 at 8-week intervals scheduled to coincide with on-treatment periods for patients on the intermittent dosing arm. Adverse events were assessed using CTCAE v4 monthly. The design assumed exponential PFS with a median of 9.4 months using continuous dosing, 206 eligible patients and 156 PFS events. It had 90% power with a two-sided α = 0.2 to detect a change to a median with an a priori hypothesis that intermittent dosing would improve the median PFS to 14.1 months using a Cox model stratified by the randomization stratification factors. Results: 242 patients were treated and 206 patients without disease progression after 8 weeks were randomized, 105 to continuous and 101 to intermittent treatment. 70% of patients had not previously received immune checkpoint inhibitors. There were no significant differences between groups in terms of baseline patient characteristics. The median PFS was statistically significantly longer, 9.0 months from randomization, with continuous dosing vs. 5.5 months from randomization with intermittent dosing (p = 0.064). There was no difference in overall survival between groups (median OS = 29.2 months in both arms p = 0.93) at a median follow up of 2 years. 77% of patient treated continuously discontinued treatment due to disease progression vs. 84% treated intermittently (p = 0.34). Conclusions: Continuous dosing with the BRAF and MEK inhibitors dabrafenib and trametinib yields superior PFS compared with intermittent dosing. Support: NIH/NCI grants CA180888, CA180819, CA180820 Citation Format: Alain Algazi, Megan Othus, Adil Daud, Roger Lo, Janice Mehnert, Thach-Giao Truong, Robert Conry, Kari Kendra, Gary Doolittle, Joseph I. Clark, Michael Messino, Dennis F. Moore, Christopher Lao, Bryan A. Faller, Rangaswamy Govindarajan, Amy Harker-Murray, Luke Dreisbach, James Moon, Kenneth Grossman, Antoni Ribas. SWOG S1320: Improved progression-free survival with continuous compared to intermittent dosing with dabrafenib and trametinib in patients with BRAF mutated melanoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT013.

The randomized phase 2 trial S1320 comparing different dosing schedules of BRAF/MEK inhibitor combination inBRAF-mutated advanced melanoma shows intermittent therapy does not result in superior progression-free survival in patients. Preclinical modeling suggests that intermittent BRAF inhibitor therapy may delay acquired resistance when blocking oncogenicBRAF(V600)in melanoma(1,2). We conducted S1320, a randomized, open-label, phase 2 clinical trial (NCT02196181) evaluating whether intermittent dosing of the BRAF inhibitor dabrafenib and the MEK inhibitor trametinib improves progression-free survival in patients with metastatic and unresectableBRAF(V600)melanoma. Patients were enrolled at 68 academic and community sites nationally. All patients received continuous dabrafenib and trametinib during an 8-week lead-in period, after which patients with non-progressing tumors were randomized to either continuous or intermittent dosing of both drugs on a 3-week-off, 5-week-on schedule. The trial has completed accrual and 206 patients with similar baseline characteristics were randomized 1:1 to the two study arms (105 to continuous dosing, 101 to intermittent dosing). Continuous dosing yielded a statistically significant improvement in post-randomization progression-free survival compared with intermittent dosing (median 9.0 months versus 5.5 months,P = 0.064, pre-specified two-sided alpha = 0.2). Therefore, contrary to the initial hypothesis, intermittent dosing did not improve progression-free survival in patients. There were no differences in the secondary outcomes, including overall survival and the overall incidence of treatment-associated toxicity, between the two groups.

Abstract INTRODUCTION: To determine the recommended Phase II dose of RRx-001, a radiosensitizer with vascular normalizing properties, when used with whole-brain radiation therapy (WBRT) for brain metastases, and to assess whether quantitative changes in perfusion MRI after RRx-001 correlate with response. METHODS AND MATERIALS: Five centers participated in this phase I/II trial of RRx-001 given once pre-WBRT then twice weekly during WBRT (30 Gy/10 fractions). Four dose levels were planned (5 mg/m2, 8.4 mg/m2, 16.5 mg/m2, 27.5 mg/m2). Dose-escalation was managed by the Time-to-Event Continual Reassessment Model (TITE-CRM). Correlative DCE-MRI was performed in a subset of patients and linear mixed models used to correlate change in 24-hour T1, Ktrans (capillary permeability) and Vp (plasma volume) with change in tumor volume. RESULTS: Between 2015–2017, 31 patients were enrolled. Two patients dropped out prior to any therapy and 7 were treated with concurrent temozolomide following a study amendment. Median age was 60 years (range, 30–76) and 17 were male. The most common tumor types were melanoma (58%) and non-small cell lung cancer (20%). No dose-limiting toxicities were observed. The most common severe adverse event was grade 3 asthenia in 6.9% (2/29). The median intracranial response rate was 46% (95%CI 24–68) and median overall survival was 5.2 months (95%CI 4.5–9.4). No neurologic deaths occurred. Among 10 evaluable patients undergoing DCE-MRI, a reduction in Vp 24 hours after RRx-001 was associated with reduced tumor volume at 1 month and 4 months (p≤0.01). CONCLUSION: The addition of RRx-001 to WBRT is safe and well-tolerated with favorable intracranial response rates. Because activity was observed across all dose levels, and in the absence of a dose response, the recommended Phase 2 dose is 10 mg administered twice weekly. A reduction in Vp by DCE-MRI 24 hours after RRx-001 suggests anti-angiogenic activity that is associated with longer-term tumor response.

RRx-001, a novel redox modulator was evaluated as a potential radiosensitizer with WBRT in a multicenter phase I trial for adults with brain metastases. The primary endpoint was to determine MTD. Secondary endpoints included intracranial response rate (IRR), survival and correlation of DCE-MRI parameters with outcome. Dose-escalation was managed by a TITE-CRM design to establish MTD at a 20% estimated DLT rate with four planned dose levels (5, 8.4, 16.5, 27.5 mg/m2). RRx-001 was given pre-WBRT (30 Gy/10 fractions) then twice weekly during WBRT. Target accrual was 30 patients. Correlative DCE-MRI was performed in a subset of patients at baseline, 24 hours post-RRx pre-WBRT, 1 and 4 months. Linear mixed models were used to correlate baseline and change in 24-hour Vp (plasma volume) with change in tumor volume. Between 2/2015-2/2017, 31 patients were enrolled across 5 centers. Two patients dropped out at baseline, and seven were treated with RRx/concurrent temozolomide to be reported separately, for a total of 22 evaluable patients. Median age was 60 years (range 35–85), 13 were male, 55% had melanoma and 23% had NSCLC. No DLTs were observed within 28 days of treatment and 5 patients were treated at the highest dose level. IRR was 50%, five patients survived > 12 months, 3 were alive at last follow-up. Among 10 evaluable patients undergoing DCE-MRI with 64 total lesions at baseline, lower baseline Vp (p=0.002) and reduction in Vp at 24 hours (p=0.001) were associated with reduced tumor volume at 1 and 4 months. RRx-001+WBRT appears well-tolerated in adults with brain metastases, with several long-term survivors and IRR of 50%. Following a single dose of RRx, a reduction in Vp is associated with tumor response at 1 and 4 months, suggesting activity within tumor vasculature and utility as a biomarker of longer-term response.

Background: Nivolumab, a monoclonal antibody of immune checkpoint programmed death 1 on T cells (PD-1), combined with ipilimumab, an immune checkpoint cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) inhibitor, as combination therapy on the one hand and nivolumab as monotherapy on the other, have both demonstrated improved efficacy compared with ipilimumab alone in the CheckMate 067 study. However, the combination resulted in a higher frequency of grade 3/4 adverse events (AEs), which could result in diminished health-related quality of life (HRQoL). Here we report analyses of HRQoL for patients with advanced melanoma in clinical trial CheckMate 067.Patients and methods: HRQoL was assessed at weeks 1 and 5 per 6-week cycle for the first 6 months, once every 6 weeks thereafter, and at two follow-up visits using the European Organization for Research and Treatment of Care Core Quality of Life Questionnaire and the EuroQoL Five Dimensions Questionnaire. In addition to the randomised population, patient subgroups, including BRAF mutation status, partial or complete response, treatment-related AEs of grade 3/4, and those who discontinued due to any reason and due to an AE, were investigated.Results: Nivolumab and ipilimumab combination and nivolumab alone both maintained HRQoL, and no clinically meaningful deterioration was observed over time compared with ipilimumab. In addition, similar results were observed across patient subgroups, and no clinically meaningful changes in HRQoL were observed during follow-up visits for patients who discontinued due to any cause.Conclusion: These results further support the clinical benefit of nivolumab monotherapy and nivolumab and ipilimumab combination therapy in patients with advanced melanoma. The finding that the difference in grade 3/4 AEs between the arms did not translate into clinically meaningful differences in the reported HRQoL may be relevant in the clinical setting. (C) 2017 The Authors. Published by Elsevier Ltd.

9505 Background: In CheckMate 067, NIVO (anti-PD-1) plus IPI (anti-CTLA-4) significantly improved progression-free survival (PFS) and objective response rate (ORR) vs IPI alone in pts with MEL (N Engl J Med 2015;373:23). We report updated efficacy and safety results from this study. Methods: Treatment-naïve pts (N=945) were randomized 1:1:1 to NIVO 1 mg/kg Q3W + IPI 3 mg/kg Q3W for 4 doses (followed by NIVO 3 mg/kg Q2W), NIVO 3 mg/kg Q2W + placebo, or IPI 3 mg/kg Q3W for 4 doses + placebo, until progression or unacceptable toxicity. Pts were stratified by PD-L1 status, BRAFmutation status, and M-stage. Co-primary endpoints were PFS and overall survival (data remain immature). Secondary endpoints included efficacy by PD-L1 status and safety. Results: At ≥18 months of follow-up, median PFS continued to be significantly longer for NIVO+IPI and NIVO vs IPI (P<0.001), and was numerically longer for NIVO+IPI vs NIVO alone (Table). Median duration of response in 181/314 (57.6%) NIVO+IPI responders has not been reached, and was 22.3 and 14.4 months in 138/316 (43.7%) NIVO and 60/315 (19.0%) IPI responders, respectively. Median PFS was also numerically longer with NIVO+IPI vs NIVO or IPI regardless of PD-L1 tumor expression (Table). For NIVO+IPI, NIVO, and IPI groups, median PFS was 15.5, 5.6, and 4.0 months in pts with a BRAF mutation and was 11.3, 7.1, and 2.8 months in pts with wild-type BRAF, respectively. The frequency and types of drug-related grade 3/4 AEs were consistent with earlier reports (NIVO+IPI, 56.5%; NIVO, 19.8%; IPI, 27.0%). Conclusions: NIVO+IPI and NIVO alone continue to demonstrate superior clinical activity vs IPI monotherapy. NIVO+IPI appears to have greater efficacy than either agent alone, regardless of PD-L1 expression or BRAF mutation status. Clinical trial information: NCT01844505.Median PFS (95% CI) NIVO+IPI NIVO IPI ITT population 11.5 (8.9–16.7) 6.9 (4.3–9.5) 2.9 (2.8–3.4) HR (95% CI) vs NIVO 0.76 (0.60–0.92)a — — PD-L1 expression ≥5% NR (9.7–NR) 22.0 (8.9–NR) 3.9 (2.8–4.2) HR (95% CI) vs NIVO 0.87 (0.54–1.41)a — — <5% 11.1 (8.0–22.2) 5.3 (2.8–7.1) 2.8 (2.8–3.1) HR (95% CI) vs NIVO 0.74 (0.58–0.96)a — — HR, hazard ratio; NR, not reached. aExploratory endpoint.

Bcl6 is required for CD4 T cell differentiation into T follicular helper cells (Tfh). In this study, we examined the role of IL-6 in early processes of in vivo Tfh differentiation, because the timing and mechanism of action of IL-6 in Tfh differentiation have been controversial in vivo. We found that early Bcl6+CXCR5+ Tfh differentiation was severely impaired in the absence of IL-6; however, STAT3 deficiency failed to recapitulate that defect. IL-6R signaling activates the transcription factor STAT1 specifically in CD4 T cells. Strikingly, we found that STAT1 activity was required for Bcl6 induction and early Tfh differentiation in vivo. IL-6 mediated STAT3 activation is important for downregulation of IL-2Rα to limit Th1 cell differentiation in an acute viral infection. Thus, IL-6 signaling is a major early inducer of the Tfh differentiation program unexpectedly mediated by both STAT3 and STAT1 transcription factors.

Humans and mice deficient in the adaptor protein SAP (Sh2d1a) have a major defect in humoral immunity, resulting from a lack of T cell help for B cells. The role of SAP in this process is incompletely understood. We found that deletion of receptor Ly108 (Slamf6) in CD4(+) T cells reversed the Sh2d1a(-/-) phenotype, eliminating the SAP requirement for germinal centers. This potent negative signaling by Ly108 required immunotyrosine switch motifs (ITSMs) and SHP-1 recruitment, resulting in high amounts of SHP-1 at the T cell:B cell synapse, limiting T cell:B cell adhesion. Ly108-negative signaling was important not only in CD4(+) T cells; we found that NKT cell differentiation was substantially restored in Slamf6(-/-)Sh2d1a(-/-) mice. The ability of SAP to regulate both positive and negative signals in T cells can explain the severity of SAP deficiency and highlights the importance of SAP and SHP-1 competition for Ly108 ITSM binding as a rheostat for the magnitude of T cell help to B cells.

Cytokines are important modulators of lymphocytes, and both interleukin-21 (IL-21) and IL-6 have proposed roles in T follicular helper (Tfh) differentiation, and directly act on B cells. Here we investigated the absence of IL-6 alone, IL-21 alone, or the combined lack of IL-6 and IL-21 on Tfh differentiation and the development of B cell immunity in vivo. C57BL/6 or IL-21(-/-) mice were treated with a neutralizing monoclonal antibody against IL-6 throughout the course of an acute viral infection (lymphocytic choriomeningitis virus, LCMV). The combined absence of IL-6 and IL-21 resulted in reduced Tfh differentiation and reduced Bcl6 protein expression. In addition, we observed that these cytokines had a large impact on antigen-specific B cell responses. IL-6 and IL-21 collaborate in the acute T-dependent antiviral antibody response (90% loss of circulating antiviral IgG in the absence of both cytokines). In contrast, we observed reduced germinal center formation only in the absence of IL-21. Absence of IL-6 had no impact on germinal centers, and combined absence of both IL-21 and IL-6 revealed no synergistic effect on germinal center B cell development. Studying CD4 T cells in vitro, we found that high IL-21 production was not associated with high Bcl6 or CXCR5 expression. TCR stimulation of purified naïve CD4 T cells in the presence of IL-6 also did not result in Tfh differentiation, as determined by Bcl6 or CXCR5 protein expression. Cumulatively, our data indicates that optimal Tfh formation requires IL-21 and IL-6, and that cytokines alone are insufficient to drive Tfh differentiation.