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Immune checkpoint inhibitors (ICI), which target immune regulatory pathways to unleash antitumor responses, have revolutionized cancer immunotherapy. Despite the remarkable success of ICI immunotherapy, a significant proportion of patients whose tumors respond to these treatments develop immune-related adverse events (irAE) resembling autoimmune diseases. Although the clinical spectrum of irAEs is well characterized, their successful management remains empiric. This is in part because the pathogenic mechanisms involved in the breakdown of peripheral tolerance and induction of irAEs remain elusive. Herein, we focused on regulatory T cells (Treg) in individuals with irAEs because these cells are vital for maintenance of peripheral tolerance, appear expanded in the peripheral blood of individuals with cancer, and abundantly express checkpoint molecules, hence representing direct targets of ICI immunotherapy. Our data demonstrate an intense transcriptomic reprogramming of CD4+CD25+CD127− Tregs in the blood of individuals with advanced metastatic melanoma who develop irAEs following ICI immunotherapy, with a characteristic inflammatory, apoptotic, and metabolic signature. This inflammatory signature was shared by Tregs from individuals with different types of cancer developing irAEs and individuals with autoimmune diseases. Our findings suggest that inflammatory Treg reprogramming is a feature of immunotherapy-induced irAEs, and this may facilitate translational approaches aiming to induce robust antitumor immunity without disturbing peripheral tolerance.

Cytomegalovirus (CMV) infection/disease has been repeatedly reported in patients treated with immune-checkpoint inhibitors (ICIs) and most commonly involves patients with relapsed/refractory (R/R) immune-related adverse events (irAEs). In the current study, we present a patient with melanoma who developed CMV gastritis during treatment with pembrolizumab in the absence of irAEs and without previous or current immunosuppression. Moreover, we review the literature regarding CMV infection/disease in patients treated with ICIs for solid malignancies. We present the currently available data on the pathogenesis, clinical characteristics, endoscopic findings, and histologic features and highlight the potential differences among cases complicating R/R irAEs versus those occurring in patients who are immunosuppression naive. Finally, we discuss the currently available data regarding potential useful diagnostic tools as well as the management of these patients.

Introduction. The BNT162b2 vaccine against SARS-CoV-2 has a proven efficacy and a favorable safety profile. In cancer patients under immunotherapy in the form of immune checkpoint inhibitors (ICIs), the efficacy of the vaccine has not been thoroughly studied, while a theoretical concern about the triggering of immune related adverse events (irAEs) by the vaccine has also been raised. Patients and methods. We conducted a prospective, non-interventional study on the immunogenicity and safety of the BNT162b2 vaccine in patients with advanced or metastatic melanoma treated with ICIs. Blood samples were obtained 0-4 days before the first and 12-21 days after the second dose of the vaccine for the quantification of the SARS-CoV-2 anti-spike antibody with an ELISA and immunophenotyping of the T and myeloid cell subpopulations. Active recording of the AEs for a two-month period was conducted. Results. Forty patients were included in the study. All but one (97.3%) achieved seroconversion after two doses of the vaccine and no correlations of the antibody titers with any of the studied parameters (age, gender, stage and duration of the disease, type of ICI, previous treatment, etc.) were found. Moreover, no differences in the subpopulations of the T cells (including the T-regulatory cells) or the myeloid cells were found pre- and post-vaccination. All AEs were low-grade, while one case or arthritis exacerbation was noted.Discussion. The seroconversion rate in the studied population was high, comparable to that of healthy subjects, while no major safety issues were raised during the safety follow-up. Finally, no derangements in the subpopulations of T cells or myeloid cells were noted. This is the first study focusing on the immunogenicity, safety, and effect on the blood cell immunophenotype status of anti-SARS-Cov-2 vaccines in patients with melanoma treated with ICIs.

Immune checkpoint inhibitors (ICI), which target immune regulatory pathways to unleash antitumor responses, have revolutionized cancer immunotherapy. Despite the remarkable success of ICI immunotherapy, a significant proportion of patients whose tumors respond to these treatments develop immune-related adverse events (irAE) resembling autoimmune diseases. Although the clinical spectrum of irAEs is well characterized, their successful management remains empiric. This is in part because the pathogenic mechanisms involved in the breakdown of peripheral tolerance and induction of irAEs remain elusive. Herein, we focused on regulatory T cells (Treg) in individuals with irAEs because these cells are vital for maintenance of peripheral tolerance, appear expanded in the peripheral blood of individuals with cancer, and abundantly express checkpoint molecules, hence representing direct targets of ICI immunotherapy. Our data demonstrate an intense transcriptomic reprogramming of CD4+CD25+CD127− Tregs in the blood of individuals with advanced metastatic melanoma who develop irAEs following ICI immunotherapy, with a characteristic inflammatory, apoptotic, and metabolic signature. This inflammatory signature was shared by Tregs from individuals with different types of cancer developing irAEs and individuals with autoimmune diseases. Our findings suggest that inflammatory Treg reprogramming is a feature of immunotherapy-induced irAEs, and this may facilitate translational approaches aiming to induce robust antitumor immunity without disturbing peripheral tolerance.

The role of latent Epstein-Barr virus (EBV) infection in the pathogenesis of low-grade B cell non-Hodgkin lymphoma (B-NHL) has not been studied. We therefore investigated the incidence of latent EBV infection in a group of patients with leukemic low-grade B-NHL, as well as the incidence of viral latent membrane protein 1 (LMP1) oncoprotein expression in the same patient group. Furthermore, in an attempt to elucidate the role of this viral oncoprotein in non-EBV-related lymphomas, we correlated the expression of LMP1 with the level of oxidative stress, a parameter related to apoptosis. In the present study we detected lower levels of oxidative stress in the sera of LMP1-positive patients. This possibly implies an anti-apoptotic role of this viral oncoprotein in low-grade B cell lymphomas. However, LMP1 expression status did not affect expression of the major anti-apoptotic gene BCL-2.

We report here the interesting case of a 76-year-old man with severe proteinuria who was diagnosed with systemic mastocytosis accompanied by a clonal non-mast-cell lineage haematological disorder (a non-secretory plasma cell dyscrasia). This is a unique report of systemic mastocytosis with a non-secretory plasma cell dyscrasia and nephrotic syndrome. The pathophysiological relevance between these entities along with the probability of occult amyloidosis is discussed.

Abstract 1560 Background Epstein-Barr virus (EBV) is a ubiquitous pathogen that chronically infects B lymphocytes and is implicated in the pathogenesis of lymphoproliferative diseases. Latent membrane protein 1 (LMP1), the major oncoprotein of the virus, has been shown to inhibit apoptosis and trigger survivin expression in malignant cell lines. Although EBV has not been implicated in the pathogenesis of low grade B-cell lymphomas, LMP1-mRNA has been detected in a significant proportion of patients with chronic lymphocytic leukemia (CLL). LMP1 is known for its antiapoptotic properties, but recent data show that LMP1 can simultaneously induce and inhibit apoptosis in B-cells. These opposite functions of LMP1 have not been studied in patients with low grade B-cell lymphomas. Objectives Our objectives were to detect LMP1-mRNA in patients with leukemic low grade B-cell lymphomas ant to investigate the postulated apoptotic properties of the protein, by correlating its expression to survivin levels. Patients and Methods Peripheral whole blood from 64 patients with leukemic low grade B-cell lymphomas was tested by qRT-PCR for the presence of BXLF-1 gene of EBV. The patients' characteristics are shown in table 1 . All positive samples were tested by conventional PCR for LMP1-mRNA. Subsequently, survivin m-RNA levels were measured by qRT-PCR in all samples and compared between LMP1 positive and negative patients (Mann-Whitney U Test). Results The BXLF-1 gene was detected in 27/64 (42.1%) patients. LMP1-mRNA was detected in 23/64 (35.9%) patients and in 23/27 (85.2%) EBV-positive patients. Among CLL patients, LMP1-mRNA was detected in 19/44 (43.2%). Finally, surviving-mRNA levels were found to be 8.37 times higher in EBV-negative vs EBV-positive patients, (p=0.002) and 7.19 times higher in LMP1-negative vs LMP1-positive patients (p=0.009). The results are reported in detail in Table 1 . Discussion Data from this year's studies suggest that LMP1 may exert both antiapoptotic and apoptotic functions. While the carboxy-terminal domain of LMP1 drives the proliferation and survival of EBV-infected B cells in vitro and in vivo, LMP1 may activate, through its amino-terminal six-transmembrane domains (6TM), the transmembrane receptor proteins PERK, ATF6 and IRE-1, leading to unfolded protein response (UPR) induction. UPR is a cellular stress response that promotes apoptosis. In different environments, LMP1 signaling may show differences regarding its apoptotic effects on B lymphocytes. In our study, we detected LMP1-mRNA in 43.2% of CLL patients, a proportion significantly higher than previously reported (14%). Moreover, for the first time, LMP1-mRNA was detected in patients with other than CLL low grade B-cell lymphomas ( Table 1 ). In patients with leukemic low grade B-cell lymphomas, in the pathogenesis of which EBV is not causally implicated, LMP1 may have apoptotic instead of anti-apoptotic properties, as evidenced by the lower survivin m-RNA levels in LMP1-positive patients. This finding deserves further investigation, in order to reveal the clinical significance of the different functions of LMP1 in non-EBV related lymphomas. Table 1 . Patients' characteristics and results Characteristic All patients EBV(+) 1 EBV(−) 1 P * No of Subjects, N (%) 64 (100%) 27 (42.2) 37 (57.8) Age, Mean (range) 68.2 (44–82) 67.9 (44–82) 69.2 (56–79) 0.701 Male to female ratio 1.13 1.44 0.95 0.442 Lymphoproliferative disease 0.164 Chronic lymphocytic leukemia, N (%) 44 (68.8) 20 (74.1) 24 (64.9) Splenic marginal zone lymphoma, N (%) 11 (17,2) 2 (7.4) 9 (24.3) Mantle cell lymphoma, N (%) 5 (7,8) 3 (11.1) 2 (5.4) Hairy cell leukemia, N (%) 2 (3.1) 1 (3.7) 1 (2.7) Follicular lymphoma, N (%) 2 (3,1) 1 (3.7) 1 (2.7) Previous treatment, N (%) 15 (23.4) 6 (22.2) 9 (24.3) 0.847 Viral load, copies/ml (range) NA 2164.2 (79–15600) NA NA Measurable LMP1-mRNA, N (%) 23 (35.9) 23 (85.2) 0 (0) NA Survivin levels 2 11.17 1.33 0.001 * p for group differences. 1 EBV(+), EBV(−) are used to indicate positivity for the BXLF-1 gene of EBV by PCR. 2 Relative gene expression between positive and negative blood samples was calculated by using the 2-delta-CT method. Disclosures: No relevant conflicts of interest to declare.