IL-6 controls leukemic multipotent progenitor cell fate and contributes to chronic myelogenous leukemia development

Clinical and histopathologic review of Schnitzler syndrome: the Mayo Clinic experience (1972-2011)

BACKGROUND

Schnitzler syndrome is a rare multisystem disorder, defined by urticaria and monoclonal gammopathy, that is associated with malignancy. Considered a neutrophilic urticarial dermatosis, previous reports have included patients with leukocytoclastic vasculitis.

OBJECTIVE

We sought to better define the clinical features, histopathology, and outcomes of Schnitzler syndrome.

METHODS

We retrospectively reviewed clinical records and cutaneous histopathology of all patients with Schnitzler syndrome seen at our institution from January 1, 1972, through July 31, 2011.

RESULTS

Of the 20 patients identified, 80% had IgM κ monoclonal gammopathy; others had IgG λ (10%), IgG κ (5%), or IgM κ+λ (5%). Patients had fevers (85%), arthralgias (70%), leukocytosis (70%), increased erythrocyte sedimentation rate (70%), bone pain (50%), lymphadenopathy (40%), and organomegaly (5%); 45% developed a hematologic malignancy. Histopathologic examination (n = 14) showed predominantly neutrophilic perivascular and interstitial inflammation (57%) or predominantly mononuclear cell perivascular inflammation (29%), with eosinophils in 50% of cases. None showed leukocytoclastic vasculitis.

LIMITATIONS

Our study was limited by its retrospective design.

CONCLUSION

We added 20 patients to approximately 100 reported cases of Schnitzler syndrome. Neutrophilic urticarial dermatosis was the most common histopathologic pattern, but mononuclear cells were predominant in many cases and the infiltrates often contained eosinophils. A high index of suspicion and careful clinicopathologic correlation are needed to avoid diagnostic delays in this syndrome associated with hematologic malignancy.

Altered microenvironmental regulation of leukemic and normal stem cells in chronic myelogenous leukemia

We characterized leukemia stem cells (LSC) in chronic phase chronic myelogenous leukemia (CML) using a transgenic mouse model. LSC were restricted to cells with long-term hematopoietic stem cell (LTHSC) phenotype. CML LTHSC demonstrated reduced homing and retention in the bone marrow (BM), related to decreased CXCL12 expression in CML BM, resulting from increased G-CSF production by leukemia cells. Altered cytokine expression in CML BM was associated with selective impairment of normal LTHSC growth and a growth advantage to CML LTHSC. Imatinib (IM) treatment partially corrected abnormalities in cytokine levels and LTHSC growth. These results were validated using human CML samples and provide improved understanding of microenvironmental regulation of normal and leukemic LTHSC and their response to IM in CML.

Role of STAT3 in Transformation and Drug Resistance in CML

Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identification of bcr-abl led to the discovery and rapid translation into the clinic of bcr-abl kinase inhibitors. Although, bcr-abl inhibitors are efficacious, experimental evidence indicates that targeting bcr-abl is not sufficient for elimination of minimal residual disease found within the bone marrow (BM). Experimental evidence indicates that the failure to eliminate the leukemic stem cell contributes to persistent minimal residual disease. Thus curative strategies will likely need to focus on strategies where bcr-abl inhibitors are given in combination with agents that specifically target the leukemic stem cell or the leukemic stem cell niche. One potential target to be exploited is the Janus kinase (JAK)/signal transducers and activators of transcription 3 (STAT3) pathway. Recently using STAT3 conditional knock-out mice it was shown that STAT3 is critical for initiating the disease. Interestingly, in the absence of treatment, STAT3 was not shown to be required for maintenance of the disease, suggesting that STAT3 is required only in the tumor initiating stem cell population (Hoelbl et al., 2010). In the context of the BM microenvironment, STAT3 is activated in a bcr-abl independent manner by the cytokine milieu. Activation of JAK/STAT3 was shown to contribute to cell survival even in the event of complete inhibition of bcr-abl activity within the BM compartment. Taken together, these studies suggest that JAK/STAT3 is an attractive therapeutic target for developing strategies for targeting the JAK-STAT3 pathway in combination with bcr-abl kinase inhibitors and may represent a viable strategy for eliminating or reducing minimal residual disease located in the BM in CML.