Introduction: Immune checkpoint inhibitors (ICI) are increasingly being used to treat numerous cancer types. Together with improved recognition of toxicities, this has led to more frequent identification of rare immune-related adverse events (irAE), for which specific treatment strategies are needed. Neutropenia is a rare hematological irAE that has a potential for a high mortality rate because of its associated risk of sepsis. Prompt recognition and timely treatment of this life-threatening irAE are therefore critical to the outcome of patients with immune-related neutropenia.Methods: This multicenter international retrospective study was conducted at 17 melanoma centers to evaluate the clinical characteristics, diagnostics, treatment, and outcomes of melanoma patients with grade 4 neutropenia (<500 neutrophils/µl blood) treated with ICI between 2014 and 2020. Some of these patients received metamizole in addition to ICI (ICI+/met+). Bone marrow biopsies (BMB) of these patients were compared to BMB from non-ICI treated patients with metamizole-induced grade 4 neutropenia (ICI-/met+).Results: In total, 10 patients (median age at neutropenia onset: 66 years; seven men) with neutropenia were identified, equating to an incidence of 0.14%. Median onset of neutropenia was 6.4 weeks after starting ICI (range 1.4–49.1 weeks). Six patients showed inflammatory symptoms, including fever (n=3), erysipelas (n=1), pharyngeal abscess (n=1), and mucositis (n=1). Neutropenia was diagnosed in all patients by a differential blood count and additionally performed procedures including BMB (n=5). Nine of 10 patients received granulocyte colony-stimulating factors (G-CSF) to treat their grade 4 neutropenia. Four patients received systemic steroids (including two in combination with G-CSF, and one in combination with G-CSF and additional ciclosporin A). Four patients were treated with one or more antibiotic treatment lines, two with antimycotic treatment, and one with additional antiviral therapy. Five patients received metamizole concomitantly with ICI. One fatal outcome was reported. BMB indicated a numerically lower CD4+ to CD8+ T cells ratio in patients with irNeutropenia than in those with metamizole-induced neutropenia.Conclusion: Grade 4 neutropenia is a rare but potentially life-threatening side effect of ICI treatment. Most cases were sufficiently managed using G-CSF; however, adequate empiric antibiotic, antiviral, and antimycotic treatments should be administered if neutropenic infections are suspected. Immunosuppression using corticosteroids may be considered after other causes of neutropenia have been excluded.

Purpose: Recent studies have demonstrated HLA class II (HLA-II)–dependent killing of melanoma cells by cytotoxic CD4 T cells. We investigated evolution of HLA-II–loss tumors that escape cytotoxic CD4 T-cell activity and contribute to immunotherapy resistance. Experimental Design: Melanoma cells from longitudinal metastases were studied for constitutive and IFN-inducible HLA-II expression, sensitivity towards autologous CD4 T cells, and immune evasion by HLA-II loss. Clinical significance of HLA-II–low tumors was determined by analysis of transcriptomic data sets from patients with immune checkpoint blockade (ICB). Results: Analysis of longitudinal samples revealed strong intermetastatic heterogeneity in melanoma cell–intrinsic HLA-II expression and subclonal HLA-II loss. Tumor cells from early lesions either constitutively expressed HLA-II, sensitizing to cytotoxic CD4 T cells, or induced HLA-II and gained CD4 T-cell sensitivity in the presence of IFNγ. In contrast, late outgrowing subclones displayed a stable CD4 T-cell–resistant HLA-II–loss phenotype. These cells lacked not only constitutive but also IFNγ-inducible HLA-II due to JAK1/2-STAT1 pathway inactivation. Coevolution of JAK1/2 deficiency and HLA-II loss established melanoma cross-resistance to IFNγ and CD4 T cells, as detected in distinct stage IV metastases. In line with their immune-evasive phenotype, HLA-II–low melanomas showed reduced CD4 T-cell infiltrates and correlated with disease progression under ICB. Conclusions: Our study links melanoma resistance to CD4 T cells, IFNγ, and ICB at the level of HLA-II, highlighting the significance of tumor cell–intrinsic HLA-II antigen presentation in disease control and calling for strategies to overcome its downregulation for improvement of patient outcome.

Zusammenfassung: Obwohl das kutane Melanom nur etwa 4 % aller Hautkrebsarten (einschließlich des nichtmelanozytären Hautkrebses) ausmacht, ist es für 80 % aller durch Hautkrebs verursachten Todesfälle verantwortlich. Die Einführung von Immuncheckpointinhibitoren führte zu einer erheblichen Verbesserung des Langzeitüberlebens von Patienten im fortgeschrittenen Stadium unabhängig vom BRAF-Mutations-Status. Neben der zielgerichteten Therapie für Patienten mit BRAF-mutiertem Melanom sind Immuntherapien die Behandlungsoptionen der Wahl im fortgeschrittenen Stadium und seit 2018 auch in der adjuvanten Therapie. Aktuell wird in Studien die Wirksamkeit von Therapiekombinationen sowie Sequenztherapien mit zielgerichteten und Immuntherapien geprüft.