Summary. In this report, we describe two patients with idiopathic hypereosinophilic syndrome (HES) who received a non-myeloablative allogeneic transplantation following a reduced-intensity preparative regimen of melphalan and fludarabine. In both cases, complete donor chimaerism and remission were achieved, and have lasted for more than 10 months. This report provides proof of principle for the feasibility of non-myeloablative transplantation for patients with idiopathic HES, who can show co-morbidity due to eosinophilic infiltration of their organs.

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Background.Most patients with primary CNS lymphoma (PCNSL), an aggressive extranodal lymphoma confined to the CNS, have a poor prognosis in spite of development of chemotherapy regimens. First-line treatment consists of high-dose methotrexate-based (HD-MTX) regimen followed by consolidation with autologous stem cell transplantation or whole brain radiotherapy. Given that this tumor manifests predominantly in older patients with median age of 65 years, many patients are unable to tolerate intensive chemotherapy. Moreover, most patients eventually present with relapsed or refractory (r/r) disease. Relapse or refractory (r/r) PCNSL has a poor prognosis with median overall survival not exceeding 3.5 months (Langner-Lemercier et al, 2016) and these patients should be offered a clinical trial whenever possible. These groups are in need of safe, tolerable and effective therapeutic approaches. Primary testicular lymphoma (PTL) shares biological and clinical similarities with PCNSL and often present with CNS involvement. Such patients are also in need of new approaches, especially if they are refractory or not suitable to HD-MTX. Given high PD-1/PD-L1 expression in tumor microenvironment (Berghoff, 2014), immune checkpoint inhibitors were successfully tested in r/r PCNSL and PTL setting. However, data are still scarce and limited to case series (Nayak et al., 2017; Graber et al. 2020). Here we present Pavlov University experience of the treatment of PCNSL and PTL with CNS involvement with PD-1 inhibitor nivolumab. Methods.Eight patients, 2 men and 6 women, with PCNSL and one patient with PTL with CNS involvement treated at the Pavlov University between 2017 and 2020 were included into analysis. Median age at a diagnosis was 62 (28-66) years. Two patients (22%) had ECOG score 3-4 and therefore could not be considered for intensive MTX containing frontline treatment. In all of the cases the tumor histological type was diffuse large B-cell lymphoma. All patients had parenchymal involvement: 7 patients had multifocal disease; deep structures were involved in 2 patients. One patient had leptomeningeal involvement. Nivolumab was used in a first-line setting in 2 patients (22%). In 7 (78%) patients with relapsed/refractory disease, the median number of treatment lines prior to nivolumab was 1 (1-7). Nivolumab was given every 2 weeks in the 100 mg dose. Adverse events were defined according to NCI CTC-AE 5.0. Results.At the time of analysis, the median follow-up was 18 (3-44) months. Median number of nivolumab cycles was 10 (2-23). Seven (78%) patients had an objective response: complete response in 3 patients (33.3%) and partial response in 4 patients (44.4%). Two patients (22.2%) were refractory to treatment. Two-year overall survival (OS) was 44% with median OS of 12 months. Two-year progression-free survival (PFS) was 26% with median of PFS 12 months. Оne responder had a moderate increase of tumor volume on MRI after two months of therapy followed by complete disappearance of brain lesions on sequential imaging at 4 months after treatment initiation. Nivolumab therapy appeared safe with only one patient (11%) having severe adverse event, namely grade 3 alanine aminotransferase and aspartate aminotransferase increase. Conclusion.Nivolumab appears to be safe and effective therapy in PCNSL and PTL with CNS involvement both in first-line and r/r setting. However, in our cohort majority of patients relapsed that suggest that consolidation therapy after remission induction with nivolumab may be crucial for long-term remissions. We also demonstrate that pseudoprogression might be also observed in PCNSL during immunotherapy. Large-scale trials are needed to generate strong evidence for the use of PD-1 inhibitors in PCNSL. Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: Nivolumab is an anti-PD-1 inhibitor approved for classical Hodgkin lymphoma. There is early clinical data suggesting the efficiency of nivolumab in PCNS lymphoma (Nayak, 2017)