Cytotoxic CD4 T cells in the mucosa and in cancer.

CD4 T cells were initially described as helper cells that promote either the cellular immune response (Th1 cells) or the humoral immune response (Th2 cells). Since then, a plethora of functionally distinct helper and regulatory CD4 T cell subsets have been described. CD4 T cells with cytotoxic function were first described in the setting of viral infections and autoimmunity, and more recently in cancer and gut dysbiosis. Regulatory CD4 T cell subsets such as Tregs and T-regulatory type 1 (Tr1) cells have also been shown to have cytotoxic potential. Indeed, Tr1 cells have been shown to be important for maintenance of stem cell niches in the bone marrow and the gut. This review will provide an overview of cytotoxic CD4 T cell development, and discuss the role of inflammatory and Tr1-like cytotoxic CD4 T cells in maintenance of intestinal stem cells and in anti-cancer immune responses.

Combining nilotinib and PD-L1 blockade reverses CD4+ T-cell dysfunction and prevents relapse in acute B-cell leukemia.

Patients with acute lymphoblastic leukemia have experienced significantly improved outcomes due to the advent of chimeric antigen receptor (CAR) T cells and bispecific T-cell engagers, although a proportion of patients still relapse despite these advances. T-cell exhaustion has been recently suggested to be an important driver of relapse in these patients. Indeed, phenotypic exhaustion of CD4+ T cells is predictive of relapse and poor overall survival in B-cell acute lymphoblastic leukemia (B-ALL). Thus, therapies that counter T-cell exhaustion, such as immune checkpoint blockade, may improve leukemia immunosurveillance and prevent relapse. Here, we used a murine model of Ph+ B-ALL as well as human bone marrow biopsy samples to assess the fundamental nature of CD4+ T-cell exhaustion and the preclinical therapeutic potential for combining anti-PD-L1 based checkpoint blockade with tyrosine kinase inhibitors targeting the BCR-ABL oncoprotein. Single-cell RNA-sequence analysis revealed that B-ALL induces a unique subset of CD4+ T cells with both cytotoxic and helper functions. Combination treatment with the tyrosine kinase inhibitor nilotinib and anti-PD-L1 dramatically improves long-term survival of leukemic mice. Depletion of CD4+ T cells prior to therapy completely abrogates the survival benefit, implicating CD4+ T cells as key drivers of the protective anti-leukemia immune response. Indeed, treatment with anti-PD-L1 leads to clonal expansion of leukemia-specific CD4+ T cells with the aforementioned helper/cytotoxic phenotype as well as reduced expression of exhaustion markers. These findings support efforts to use PD1/PD-L1 checkpoint blockade in clinical trials and highlight the importance of CD4+ T-cell dysfunction in limiting the endogenous anti-leukemia response.

Phenotypic and Functional Diversity in Regulatory T Cells.

The concept that a subset of T cells exists that specifically suppresses immune responses was originally proposed over 50 years ago. It then took the next 30 years to solidify the concept of regulatory T cells (Tregs) into the paradigm we understand today - namely a subset of CD4+ FOXP3+ T-cells that are critical for controlling immune responses to self and commensal or environmental antigens that also play key roles in promoting tissue homeostasis and repair. Expression of the transcription factor FOXP3 is a defining feature of Tregs, while the cytokine IL2 is necessary for robust Treg development and function. While our initial conception of Tregs was as a monomorphic lineage required to suppress all types of immune responses, recent work has demonstrated extensive phenotypic and functional diversity within the Treg population. In this review we address the ontogeny, phenotype, and function of the large number of distinct effector Treg subsets that have been defined over the last 15 years.

The utility of prognostic indices, early events, and histological subtypes on predicting outcomes in non-follicular indolent B-cell lymphomas.

Indolent B-cell lymphomas other than follicular lymphoma account for up to 10% of all B-cell neoplasms. While they typically follow a slowly progressive course, some patients experience rapid progression and early mortality. Prognostic scoring systems have not been adopted, hindering the ability of clinicians or researchers to predict outcomes, or risk-stratify patients during clinical trials. To address this, we evaluated the utility of existing prognostic indices and novel, early disease-related outcomes, to predict subsequent long term survival. Baseline characteristics and outcomes data were generated from a longitudinal cohort study that prospectively enrolled 632 patients newly diagnosed with marginal zone lymphoma, lymphoplasmacytic lymphomas, or B-cell lymphomas not otherwise specified, beginning in 2002. The International Prognostic Index (IPI), Follicular Lymphoma International Prognostic Index (FLIPI), and MALT International prognostic index (MALT-IPI) demonstrated c-statistics that ranged from 0.593-0.612 for event-free survival (EFS), and 0.683-0.714 for overall survival (OS). Patients who attained event-free survival at 12 months (EFS12) experienced similar mortality to the US general population (standardized mortality ratio [SMR] 1.19; 95% CI 0.95-1.46). Patients who did not attain EFS12 had subsequent worse morality (SMR 3.14 (95% CI 2.05-4.59). The MALT-IPI demonstrated utility in predicting subsequent long-term outcomes among patients with non-follicular indolent B-cell lymphomas. This index should be used by clinicians giving guidance to patients at the time of initial diagnosis, and risk stratification during clinical studies. The divergent long-term outcomes experienced by patients who do or do not attain EFS12 suggest there exists a subset of patients who harbor high-risk disease. Future research efforts should focus on methods to identify these patients at the time of diagnosis, in order to enable risk-tailored therapy.

Outcomes among North American patients with diffuse large B-cell lymphoma are independent of tumor Epstein-Barr virus positivity or immunosuppression.

The prevalence, presenting clinical and pathological characteristics, and outcomes for patients with diffuse large B-cell lymphoma that is Epstein-Barr virus positive remain uncertain as does the impact of congenital or iatrogenic immunosuppression. Patients with newly diagnosed diffuse large B-cell lymphoma with available tissue arrays were identified from the University of Iowa/Mayo Clinic Molecular Epidemiology Resource. Patients infected with human immunodeficiency virus or who had undergone a prior organ transplant were excluded. Epstein-Barr virus-associated ribonucleic acid testing was performed on all tissue arrays. A history of significant congenital or iatrogenic immunosuppression was determined for all patients. At enrollment, 16 of the 362 (4.4%) biopsies were positive for Epstein-Barr virus. Thirty-nine (10.8%) patients had a significant history of immunosuppression. Patients with Epstein-Barr-positive diffuse large B-cell lymphoma had no unique clinical characteristics but on pathology exhibited a higher frequency of CD30 positivity (25.0% versus 8.1%, respectively; P<0.01), and non-germinal-center subtype (62.5% versus 34.1%, respectively; P<0.01). No baseline clinical characteristics were associated with a history of immunosuppression. With a median follow up of 59 months, and after adjustment for International Prognostic Index, there was no association of Epstein-Barr virus positivity or immunosuppression with event-free survival at 24 months (odds ratio=0.49; 95% confidence interval: 0.13-1.84 and odds ratio=0.81; 95% confidence interval: 0.37-1.77) or overall survival (hazard ratio=0.86; 95% confidence interval: 0.38-1.97 and hazard ratio=1.00; 95% confidence interval: 0.57-1.74). In contrast to non-Western populations, our North American population had a low prevalence of Epstein-Barr virus-positive diffuse large B-cell lymphoma that did not convey an adverse prognosis. A history of immunosuppression, while known to be a risk factor for the development of diffuse large B-cell lymphoma, did not affect subsequent prognosis.

Rare case of simultaneous enterococcal endocarditis and prosthetic joint infection.

A 59-year-old man was admitted with a 3-month history of daily fevers as well as bilateral knee pain and swelling. Medical history was significant for bilateral knee arthroplasties 4 years prior to admission. Two sets of peripheral blood cultures as well as bilateral knee synovial fluid grew Enterococcus faecalis within 10 hours. Transoesophageal echocardiography revealed aortic and mitral valve vegetations suggestive of infectious endocarditis, with severe regurgitation secondary to large size. The patient's hospitalisation was complicated by acute heart failure, necessitating emergent mitral valve repair and aortic valve replacement, followed shortly thereafter by bilateral total knee arthroplasty resection with placement of antibiotic spacers. He was treated with intravenous penicillin and gentamicin for 4 months and recovered fully. He underwent repeat bilateral knee arthroplasties and was placed on amoxicillin for 6 months postoperatively, with no further evidence of infection.

The pathogenesis of Epstein-Barr virus persistent infection.

Epstein-Barr virus (EBV) maintains a lifelong infection. According to the germinal center model (GCM), latently infected B cells transit the germinal center (GC) to become resting memory cells. Here, the virus resides quiescently, occasionally reactivating to infect new B cells, completing the cycle of infection. The GCM remains the only model that explains EBV biology and the pathogenesis of lymphoma. Recent work suggests modifications to the model notably that the virus contributes only modestly to the GC process and predictions from mathematical models that quiescence within memory B cells shapes the overall structure of viral infection but is not essential for persistence. Rather, it is the cycle of infection which allows viral persistence at the very low levels observed.

Persistence of Epstein-Barr virus in self-reactive memory B cells.

Epstein-Barr virus infection has been epidemiologically associated with the development of multiple autoimmune diseases, particularly systemic lupus erythematosus and multiple sclerosis. Currently, there is no known mechanism that can account for these associations. The germinal-center (GC) model of EBV infection and persistence proposes that EBV gains access to the memory B cell compartment via GC reactions by driving infected cells to differentiate using the virus-encoded LMP1 and LMP2a proteins, which act as functional homologues of CD40 and the B cell receptor, respectively. The ability of LMP2a, when expressed in mice, to allow escape of autoreactive B cells suggests that it could perform a similar role in infected GC B cells, permitting the survival of potentially pathogenic autoreactive B cells. To test this hypothesis, we cloned and expressed antibodies from EBV(+) and EBV(-) memory B cells present during acute infection and profiled their self- and polyreactivity. We find that EBV does persist within self- and polyreactive B cells but find no evidence that it favors the survival of pathogenic autoreactive B cells. On the contrary, EBV(+) memory B cells express lower levels of self-reactive and especially polyreactive antibodies than their uninfected counterparts do. Our work suggests that EBV has only a modest effect on the GC process, which allows it to access and persist within a subtly unique niche of the memory compartment characterized by relatively low levels of self- and polyreactivity. We suggest that this might reflect an active process where EBV and its human host have coevolved so as to minimize the virus's potential to contribute to autoimmune disease.