Search

Diffuse large B-cell lymphoma (DLBCL), the most common B-cell non-Hodgkin lymphoma rarely presents with circulating lymphoma cells (CL) at diagnosis. Previous studies were limited by small sample size precluding robust analysis. Hence, we evaluated the prognostic relevance of CL cells in newly diagnosed DLBCL patients. Based on peripheral blood (PB) immunophenotyping, patients were grouped into CL + and CL−. CL was defined as detectable clonally restricted B-cells that matched the actual or expected B-cell immunophenotype of DLBCL. The primary endpoint was progression-free survival (PFS), and secondary endpoints included overall survival (OS) and diagnosis-to-treatment interval (DTI). Among the 1266 patients with DLBCL, 621 had PB flow at diagnosis, and after excluding patients not meeting eligibility criteria, 588 cases remained. Among these, 85 (15%) were CL + and 503 were CL- (85%). Patients in CL + group were younger (67 vs. 70 years, p = 0.03) with a higher proportion of non-bulky disease (85% vs. 56%, p < 0.0001), normal albumin (79% vs. 54%, p < 0.0001), and MYC/BCL2 and/or BCL6 rearrangements (18% vs. 7%, p = 0.003) compared to the CL − group. Patients with CL at diagnosis had significantly inferior PFS and OS compared with those without CL. After adjusting for factors associated with inferior PFS and OS in univariable analysis, presence of CL remained significantly associated with inferior PFS (HR = 2.04, 95%CI = 1.47–2.84, p < 0.0001) and OS (HR = 1.61, 95%CI = 1.1–2.36, p = 0.01), respectively. There was no significant difference in DTI between the two groups. Given the prognostic relevance associated with presence of CL, clinicians should consider checking PB flow at diagnosis in all newly diagnosed DLBCL patients. [ABSTRACT FROM AUTHOR]

Follicular lymphoma (FL) is the most common indolent B‐cell non‐Hodgkin lymphoma. Circulating lymphoma (CL) cells can be seen at diagnosis in some FL patients, however, previous studies evaluating this have shown mixed results. Therefore, we sought to evaluate the impact of CL at diagnosis on outcomes in patients with newly diagnosed FL using data from a single center. Patients were divided into CL+ and CL− based on immunophenotyping via peripheral blood (PB) flow cytometry. CL was defined as detectable clonally restricted B‐cells that matched the actual or expected B‐cell immunophenotype of FL. The primary endpoint was progression‐free survival (PFS) after first‐line treatment and secondary endpoints included overall response rate (ORR), overall survival (OS), diagnosis to treatment interval (DTI), progression of disease within 2 years of diagnosis (POD24), and cumulative incidence of transformation between the two groups. Among the 541 patients with FL, 204 had PB flow cytometry performed at diagnosis, and after excluding patients not meeting the eligibility criteria, 147 cases remained with 24 (16%) CL+ at diagnosis. Patients in the CL+ group were younger (53 vs. 58 years, p = 0.02), had more extranodal involvement (83% vs. 44%, p < 0.01), follicular lymphoma international prognostic index 3–5 (55% vs. 31%, p = 0.01), and a higher proportion received first‐line immunochemotherapy (75% vs. 43%, p = 0.01) compared to the CL−group. The median PFS was not significantly different between CL+ (6.27 years, 95% CI = 3.61‐NR) and CL− (6.61 years, 95% CI = 5.10–9.82) cohorts regardless of the first‐line treatment or level of absolute PB CL cells. There was no significant difference in ORR, median OS, DTI, POD24, and cumulative incidence of transformation between the two groups. In our study, we found that the presence of CL cells at diagnosis in FL in the contemporary era did not impact outcomes and survival. [ABSTRACT FROM AUTHOR]

Aggressive T-cell lymphomas (TCL) account for 10–15% of non-Hodgkin lymphomas (NHL) with weaker responses and shorter durations to chemotherapy than other types of NHL. Current therapies for patients with relapsed/refractory Cutaneous T-cell lymphoma (CTCL) have limited efficacy, and short durations of response. Gemcitabine and liposomal doxorubicin have shown single-agent activity in TCL and combined have activity in relapsed B-cell lymphomas. We evaluated outcomes of 18 patients with relapsed/refractory aggressive TCL (13 CTCL, 5 PTCL) treated with a gemcitabine plus liposomal doxorubicin (GemDox) combination and evaluated outcomes with a specific focus on CTCL patients. Significant responses were observed in CTCL patients with an overall response rate of over 80%. In all patients, objective responses were seen in eight patients (50%), with six patients (5 CTCL) able to proceed to allogeneic stem cell transplant. Given limited treatment options for r/r CTCL, GemDox should be considered a therapeutic option in relapsed/refractory CTCL. [ABSTRACT FROM AUTHOR]

Mycosis fungoides (MF) and Se'zary syndrome (SS) are forms of cutaneous T cell lymphoma (CTCL) that pose significant challenges in their clinical management, particularly in refractory and advanced-stage disease. With the emergence of novel therapeutic modalities however, there are increasing opportunities to exploit the current understanding of pathophysiologic mechanisms of MF/SS for treatment. This review summarizes recent advances in the treatment of MF/SS, with a focus on monoclonal antibodies, immunotherapies, and Janus kinase (JAK) inhibitors, including ongoing clinical trials. [ABSTRACT FROM AUTHOR]

Given the paucity of data surrounding the prognostic relevance of circulating lymphoma (CL) in Waldenström macroglobulinemia (WM), we sought to evaluate the impact of CL at diagnosis on outcomes in patients with WM. Patients were divided into CL+ and CL-based on the results of flow cytometry. The endpoints included assessing progression-free survival (PFS), overall survival (OS), and diagnosis-to-treatment interval (DTI) between the two groups. Among the 308 patients with WM, 69 met the eligibility criteria with 42 and 27 in CL+ and CLgroups, respectively. The two groups were well balanced in regard to all the baseline characteristics. The ORR was numerically higher in the CL+ group compared to the CL-group (81% versus 61%, respectively), however, the CR +VGPR rates were similar between the two groups. The median PFS was not significantly different between the two groups (6.3 years in the CL- group versus not reached [NR] in the CL+ group) regardless of the first-line therapy. There was no significant difference in median OS between the CL- and CL+ groups (13 years versus NR). Although the median DTI was shorter in the CL+ group compared to CL- group, the significance was lost in the multivariable analysis. In this study (largest-to-date) evaluating the impact of CL on outcomes in patients with newly diagnosed WM, we did not find the prognostic utility of CL in WM. Future studies should explore the correlation of CL with other biological factors that impact the outcomes in WM patients. [ABSTRACT FROM AUTHOR]

Background: Mantle cell lymphoma (MCL) is a rare B-cell non-Hodgkin lymphoma subtype which remains incurable despite multimodal approach including chemoimmunotherapy followed by stem cell transplant, targeted approaches such as the BTK inhibitor ibrutinib, and CD19 chimeric antigen receptor (CAR) T cells. CD74 is a nonpolymorphic type II integral membrane glycoprotein identified as an MHC class II chaperone and a receptor for macrophage migration inhibitory factor. Our group previously reported on CD74's abundant expression in MCL and its ability to increase via pharmacological inhibition of autophagosomal degradation. Milatuzumab, a fully humanized anti-CD74 monoclonal antibody, demonstrated significant activity in preclinical lymphoma models but failed to provide meaningful benefits in clinical trials mainly due to its short half-life. We hypothesized that targeting CD74 using a CAR-T cell would provide potent and durable anti-MCL activity. Methods: We engineered a second generation anti-CD74 CAR with 4-1BB and CD3ζ signaling domains (74bbz). Through in silico and rational mutagenesis on the scFV domain, the 74bbz CAR was functionally optimized for superior antigen binding affinity, proliferative signaling, and cytotoxic activity against MCL cells in vitro and in vivo. Results: Functionally optimized 74bbz CAR-T cells (clone 42105) induced significant killing of MCL cell lines, and primary MCL patient samples including one relapse after commercial CD19 CAR-T cell therapy with direct correlation between antigen density and cytotoxicity. It significantly prolonged the survival of an animal model established in NOD-SCIDγc−/− (NSG) mice engrafted with a human MCL cell line Mino subcutaneously compared to controls. Finally, while CD74 is also expressed on normal immune cell subsets, treatment with 74bbz CAR-T cells resulted in minimal cytotoxicity against these cells both in vitro and in vivo. Conclusions: Targeting CD74 with 74bbz CAR-T cells represents a new cell therapy to provide a potent and durable and anti-MCL activity. [ABSTRACT FROM AUTHOR]

Background: Relapsed or refractory Hodgkin lymphoma (R/R HL) is a challenging disease with limited treatment options beyond brentuximab vedotin and checkpoint inhibitors. Herein we present the time‐trend analysis of R/R HL patients who received allogeneic hematopoietic cell transplantation (allo‐HCT) at our center from 2001–2017. Methods: The patients were divided into two distinct treatment cohorts: era1 (2001–2010), and era2 (2011–2017). The primary endpoint was overall survival (OS). Secondary endpoints included progression‐free survival (PFS), non‐relapse mortality (NRM), and cumulative incidence of acute and chronic graft versus host disease (GVHD). Results: Among the 51 patients included in the study, 29 were in era1, and 22 were in era2. There was decreased use of myeloablative conditioning in era2 (18% vs. 31%) compared to era1 and 95% of patients in era2 previously received brentuximab Vedotin (BV). Haploidentical donors were seen exclusively in era2 (0% vs. 14%) and more patients received alternative donor transplants (7% vs. 32%) in era2. The 4‐year OS (34% vs. 83%, p < 0.001) and 4‐year PFS (28% vs. 62%, p = 0.001) were significantly inferior in era1 compared to era2. The incidence of 1‐year NRM was lower in era2 compared to era1 (5% vs. 34%, p = 0.06). The cumulative incidence of acute GVHD at day 100 was similar in both eras (p = 0.50), but the incidence of chronic GVHD at 1 year was higher in era2 compared to era1 (55% vs. 21%, p = 0.03). Conclusions: Despite the advent of novel therapies, allo‐HCT remains an important therapeutic option for patients with R/R HL. [ABSTRACT FROM AUTHOR]

Simple Summary: Relapsed or refractory classical Hodgkin lymphoma remains a difficult treatment challenge. Despite responses with the checkpoint inhibitors nivolumab and pembrolizumab, patients eventually progress. Combining other treatments with checkpoint inhibitors may provide more frequent and durable responses in this setting. We conducted a phase II study in relapsed or refractory Hodgkin lymphoma combining nivolumab with the Bruton's tyrosine kinase inhibitor ibrutinib. Although we did not find an increase in the response rate of this combination compared to that previously reported, responses tended to be durable even in patients who progressed on nivolumab therapy prior to enrollment. Larger studies combining Bruton's tyrosine kinase inhibitors with checkpoint blockade are warranted, especially in patients who had progressed previously on checkpoint inhibitor therapy. Background: Relapsed or refractory classical Hodgkin lymphoma (cHL) remains a difficult treatment challenge. Although checkpoint inhibitors (CPI) have provided clinical benefit for these patients, responses are generally not durable, and progression eventually occurs. Discovering combination therapies which maximize the immune response of CPI therapy may overcome this limitation. We hypothesized that adding ibrutinib to nivolumab will lead to deeper and more durable responses in cHL by promoting a more favorable immune microenvironment leading to enhanced T-cell-mediated anti-lymphoma responses. Methods: We conducted a single arm, phase II clinical trial testing the efficacy of nivolumab in combination with ibrutinib in patients ≥18 years of age with histologically confirmed cHL who had received at least one prior line of therapy. Prior treatment with CPIs was allowed. Ibrutinib was administered at 560 mg daily until progression in combination with nivolumab 3 mg/kg IV every 3 weeks for up to 16 cycles. The primary objective was complete response rate (CRR) assessed per Lugano criteria. Secondary objectives included overall response rate (ORR), safety, progression free survival (PFS), and duration of response (DoR). Results: A total of 17 patients from two academic centers were enrolled. The median age of all patients was 40 (range 20–84). The median number of prior lines of treatment was five (range 1–8), including 10 patients (58.8%) who had progressed on prior nivolumab therapy. Most treatment related events were mild (

The treatment landscape of classical Hodgkin lymphoma (cHL) has undergone significant changes over the past 20 years. Gradual improvements have been made in the management of cHL patients, particularly in prolonging the survival rate for those in the relapsed setting. Most of these improvements came with the addition of brentuximab vedotin and PD1 blockade (nivolumab and pembrolizumab) into the current cHL treatment algorithms. On the other hand, the treatment approach to cHL has become more complex than ever before, with multiple ways to add and sequence therapies to achieve long-term remission. In this review, we will discuss the most up-to-date evidence on the management of cHL patients with the inclusion of ongoing clinical trials in cHL. We will provide a general overview of the current therapeutic landscape of cHL in light of these most recent data. We conclude with our perspective on how the approach to cHL treatment may evolve in the future. [ABSTRACT FROM AUTHOR]

Background: Mantle cell lymphoma (MCL) is a rare, highly heterogeneous type of B-cell non-Hodgkin's lymphoma. The sumoylation pathway is known to be upregulated in many cancers including lymphoid malignancies. However, little is known about its oncogenic role in MCL. Methods: Levels of sumoylation enzymes and sumoylated proteins were quantified in MCL cell lines and primary MCL patient samples by scRNA sequencing and immunoblotting. The sumoylation enzyme SAE2 was genetically and pharmacologically targeted with shRNA and TAK-981 (subasumstat). The effects of SAE2 inhibition on MCL proliferation and cell cycle were evaluated using confocal microscopy, live-cell microscopy, and flow cytometry. Immunoprecipitation and orbitrap mass spectrometry were used to identify proteins targeted by sumoylation in MCL cells. Results: MCL cells have significant upregulation of the sumoylation pathway at the level of the enzymes SAE1 and SAE2 which correlated with poor prognosis and induction of mitosis associated genes. Selective inhibition of SAE2 with TAK-981 results in significant MCL cell death in vitro and in vivo with mitotic dysregulation being an important mechanism of action. We uncovered a sumoylation program in mitotic MCL cells comprised of multiple pathways which could be directly targeted with TAK-981. Centromeric localization of topoisomerase 2A, a gene highly upregulated in SAE1 and SAE2 overexpressing MCL cells, was lost with TAK-981 treatment likely contributing to the mitotic dysregulation seen in MCL cells. Conclusions: This study not only validates SAE2 as a therapeutic target in MCL but also opens the door to further mechanistic work to uncover how to best use desumoylation therapy to treat MCL and other lymphoid malignancies. [ABSTRACT FROM AUTHOR]

Peripheral T-cell lymphomas (PTCLs) are a group of heterogeneous lymphomas with poor overall prognosis, particularly in the setting of relapsed/refractory PTCL. Given the limited efficacy of current therapies, several different novel therapies encompassing multiple different mechanisms of action have been evaluated for relapsed and refractory PTCLs. In this review, we explore the current standard of care for relapsed/refractory PTCL, and evaluate in depth novel and emerging therapies, their scientific basis, and current trials for relapsed/refractory PTCL. [ABSTRACT FROM AUTHOR]

Extranodal natural killer/T(NK/T)-cell lymphoma (ENKTL) is a rare subtype of non-Hodgkin lymphoma that typically presents with an isolated nasal mass, but a sizeable minority present with advanced stage disease and have a significantly poorer prognosis. Those with limited disease are standardly treated with chemotherapy and radiation while those with advanced stage disease are treated with L-asparaginase containing chemotherapy regimens. The addition of modern radiation therapy techniques and the incorporation of L-asparaginase into chemotherapy regimens have significantly improved outcomes in this disease, but relapses and death from relapsed disease remain frequent. Given the high rate of relapse, several novel therapies have been evaluated for the treatment of this disease. In this review, we explore the current standard of care for ENKTL as well as novel therapies that have been evaluated for its treatment and the biologic understanding behind these therapies. [ABSTRACT FROM AUTHOR]

T-Cell malignancies are a group of heterogeneous disorders composed of primary cutaneous T-cell lymphomas (CTCLs), peripheral T-cell lymphomas (PTCLs), and T-cell leukemias, including T-cell large granular lymphocytic leukemia (T-LGLL). Cases of patients with combined T-cell malignancies and plasma cell dyscrasias (PCD) are reported in the literature, but these are mostly limited to case reports or small case series with <10 patients. Here, we described the clinical course of 26 patients and report baseline characteristics and clinical outcomes including overall survival (OS), progression-free survival (PFS), and objective response rates (ORRs) in this unique population. There was no survival difference in patients with CTCL or T-LGLL and concomitant PCD when treated with standard therapy directed at the T-cell malignancy when compared to historical controls. However, patients with PTCL and concomitant PCD had significantly inferior outcomes with rapid progression and worse OS and PFS at 1.7 years (p=0.006) and 4.8 months (p=0.08), respectively, when compared to historical controls for patients with PTCL, although the limited number of patients included in this analysis precludes drawing definitive conclusions. Treatment directed at the T-cell malignancy resulted in the eradication of the PCD clone in multiple patients (15.4%) including one with multiple myeloma (MM) who experienced a complete response after starting therapy directed at the T-cell malignancy. For patients with T-cell malignancies and concomitant PCD, treatment with standard T-cell-directed therapies is recommended based on this analysis with continued follow-up and monitoring of the concomitant PCD. Further studies are needed to definitively elucidate the increased risk of relapse in patients with PTCL and concomitant PCD, and larger, multi-center cohorts are needed to validate these findings across T-cell malignancies and PCDs. [ABSTRACT FROM AUTHOR]

Waldenström macroglobulinemia (WM) is a rare B‐cell lymphoproliferative malignancy. Autologous hematopoietic cell transplantation (auto‐HCT) is considered in a subset of WM patients with relapsed disease. While registry data has shown a benefit for auto‐HCT in relapsed WM, there is a paucity of data on outcomes of patients relapsing after auto‐HCT. Eligibility criteria included adult patients with relapsed/refractory WM who underwent auto‐HCT between 2007 and 2017. The primary endpoint was post‐relapse overall survival (PR‐OS). Secondary endpoints were to identify factors prognostic of PR‐OS. Of the 48 patients with WM who underwent auto‐HCT, 22 (46%) experienced relapse following auto‐HCT. Median PR‐OS of relapsed WM patients after auto‐HCT (n = 22) was not reached (NR) (95% confidence interval [CI]: 17.5 months‐NR). Among patients who relapsed <1 year versus ≥1 year from auto‐HCT, the median PR‐OS was 18.4 months (95%CI: 0.8‐NR) months and NR (95%CI: 17.5‐NR), respectively (p = 0.06). Of note, disease status at the time of transplant, CR/VGPR versus partial remission did not appear to impact PR‐OS. The median PR‐OS was significantly longer in patients who received ibrutinib in the post‐transplant setting compared to those who did not (NR vs. 18.4 months, 95%CI: 9.1‐NR, p = 0.02). On univariable analysis, the presence of complex karyotype (RR = 4.87, 95% CI = 1.22–19.53) and a higher number of prior lines of therapy (RR = 1.81, 95% CI = 1.23–2.67) were associated with a significantly higher risk of relapse. This is the only study to date that evaluated outcomes of WM patients who relapsed following auto‐HCT and provides a benchmark for future trials evaluating survival following auto‐HCT relapse. [ABSTRACT FROM AUTHOR]

Diffuse large B‐cell lymphoma featuring overexpression of MYC and B‐Cell Lymphoma 2 (double expressor lymphoma, DEL) is associated with poor outcomes. Existing evidence suggesting improved outcomes for DEL with the use of more intensive regimens than R‐CHOP is restricted to younger patients and based on limited evidence from low patient numbers. We retrospectively evaluated the impact of intensive frontline regimens versus R‐CHOP in a multicenter analysis across 7 academic medical centers in the United States. We collected 90 cases of DEL, 46 out of 90 patients (51%) received R‐CHOP and 44/90 (49%) received an intensive regimen, which was predominantly DA‐EPOCH‐R. Treatment cohorts were evenly balanced for demographics and disease characteristics, though the intensive group had a higher lactate dehydrogenase (LDH, 326 vs. 230 U/L p = 0.06) and presence of B‐symptoms (50% vs. 22%, p = 0.01) compared to the R‐CHOP cohort. There was no difference in PFS (median 53 vs. 38 months, p = 0.49) or overall survival (67 vs. not reached months, p = 0.14) between the R‐CHOP and intensive therapy cohorts, respectively. On multivariate analysis, intensive therapy was associated with a hazard ratio of 2.35 (95% CI 0.74–7.41), though this was not statistically significant. Additionally, a subgroup analysis of intermediate high‐risk lymphoma defined by IPI ≥3 did not identify a difference in survival outcomes between regimens. We conclude that in our multi‐center cohort there is no evidence supporting the use of intensive regimens over R‐CHOP, suggesting that R‐CHOP remains the standard of care for treating DEL. [ABSTRACT FROM AUTHOR]

Follicular Lymphoma (FL) is the most common subtype of indolent B cell non-Hodgkin lymphoma. The clinical course can be very heterogeneous with some patients being safely observed over many years without ever requiring treatment to other patients having more rapidly progressive disease requiring multiple lines of treatment for disease control. Front-line treatment of advanced FL has historically consisted of chemoimmunotherapy but has extended to immunomodulatory agents such as lenalidomide. In the relapsed setting, several exciting therapies that target the underlying biology and immune microenvironment have emerged, most notable among them include targeted therapies such as phosphoinositide-3 kinase and Enhancer of Zeste 2 Polycomb Repressive Complex 2 inhibitors and cellular therapies including chimeric antigen receptor T cells and bispecific T cell engagers. There are several combination therapies currently in clinical trials that appear promising. These therapies will likely reshape the treatment approach for patients with relapsed and refractory FL in the coming years. In this article, we provide a comprehensive review of the emerging and investigational therapies in FL and discuss how these agents will impact the therapeutic landscape in FL. [ABSTRACT FROM AUTHOR]

Mantle cell lymphoma (MCL) is a rare, B cell non-Hodgkin's lymphoma with highly heterogeneous clinical presentation and aggressiveness. First-line treatment consists of intensive chemotherapy with autologous stem cell transplant for the fit, transplant eligible patients, or less intensive chemotherapy for the less fit (and transplant-ineligible) patients. Patients eventually relapse with a progressive clinical course. Numerous therapeutic approaches have emerged over the last few years which have significantly changed the treatment landscape of MCL. These therapies consist of targeted approaches such as BTK and BCL2 inhibitors that provide durable therapeutic responses. However, the optimum combination and sequencing of these therapies is unclear and is currently investigated in several ongoing studies. Furthermore, cellular therapies such as chimeric antigen receptor (CAR) T cells and bispecific T cell engager (BiTe) antibodies have shown impressive results and will likely shape treatment approaches in relapsed MCL, especially after failure with BTK inhibitors. Herein, we provide a comprehensive review of past and ongoing studies that will likely significantly impact our approach to MCL treatment in both the frontline (for transplant eligible and ineligible patients) as well as in the relapsed setting. We present the most up to date results from these studies as well as perspectives on future studies in MCL. [ABSTRACT FROM AUTHOR]

Cancer therapies trigger diverse cellular responses, ranging from apoptotic death to acquisition of persistent therapy-refractory states such as senescence. Tipping the balance toward apoptosis could improve treatment outcomes regardless of therapeutic agent or malignancy. We find that inhibition of the mitochondrial protein BCL-xL increases the propensity of cancer cells to die after treatment with a broad array of oncology drugs, including mitotic inhibitors and chemotherapy. Functional precision oncology and omics analyses suggest that BCL-xL inhibition redirects the outcome of p53 transcriptional response from senescence to apoptosis, which likely occurs via caspase-dependent down-modulation of p21 and downstream cytostatic proteins. Consequently, addition of a BCL-2/xL inhibitor strongly improves melanoma response to the senescence-inducing drug targeting mitotic kinase Aurora kinase A (AURKA) in mice and patient-derived organoids. This study shows a crosstalk between the mitochondrial apoptotic pathway and cell cycle regulation that can be targeted to augment therapeutic efficacy in cancers with wild-type p53. [Display omitted] • BCL-2/xL inhibition redirects therapeutic response from senescence to apoptosis • BCL-2/xL inhibition results in degradation of p21 which, in turn, prevents senescence • Loss of p21 enables p53-mediated apoptosis after treatment with anti-mitotic drugs • Combining BCL2/xL inhibitors with anti-mitotic drugs is effective against melanoma Bharti et al. develop an actionable strategy to improve the efficacy of cancer therapies. They show that adding an agent that targets mitochondrial proteins can increase the likelihood of cancer cells dying during treatment with some of the traditional chemotherapies and emerging drugs. This strategy is effective in melanoma models. [ABSTRACT FROM AUTHOR]

IL-17 is the founding member of a novel family of proinflammatory cytokines that defines a new class of CD4+ effector T cells, termed ‘Th17.’ Mounting evidence suggests that IL-17 and Th17 cells cause pathology in autoimmunity, but little is known about mechanisms of IL-17RA signaling. IL-17 through its receptor (11.-17RA) activates genes typical of innate immune cytokines, such as TNFα and IL-1β, despite minimal sequence similarity in their respective receptors. A previous bioinformatics study predicted a subdomain in IL-17-family receptors with homology to a Toll/IL-1R (TIR) domain, termed the ‘SEFIR domain.’ However, the SEFIR domain lacks motifs critical for bona fide TIR domains, and its functionality was never verified. Here, we used a reconstitution system in IL-17RA-null fibroblasts to map functional domains within IL-17RA. We demonstrate that the SEFIR domain mediates IL-17RA signaling independently of classic TIR adaptors, such as MyD88 and TRIF. Moreover, we identified a previously undescribed ‘TIR-like loop’ (TILL) required for activation of NF-κB, MAPK, and up-regulation of C/EBPβ and C/EBPδ. Mutagenesis of the TILL domain revealed a site analogous to the LPSd mutation in TLR4, which renders mice insensitive to LPS. However, a putative salt bridge typically found in TIR domains appears to be dispensable. We further identified a C-terminal domain required for activation of C/EBPβ and induction of a subset IL-17 target genes. This structure-function analysis of a IL-17 superfamily receptor reveals important differences in IL-17RA compared with IL-1/rLR receptors. [ABSTRACT FROM AUTHOR]