To Dose or Not to Dose: Are IL-10 and IL-6 Accurate Biomarkers to Detect Leptomeningeal Involvement in Small B-Cell Lymphoproliferation?

Identifying the etiology of neurological symptoms in hematological malignancies is still a challenging issue. Lymphomatous meningitis (LM) is mainly described in aggressive systemic B-cell lymphomas (diffuse large B-cell (DLBCL) and Burkitt lymphomas), and is associated with poor prognosis. Leptomeningeal involvement in small B-cell lymphoproliferation is a rare, poorly described condition, mentioned only in case reports. The diagnosis relies on the combination of non-specific central nervous system (CNS) symptoms (headaches, paraplegia, etc.) or psychiatric symptoms, and the cytological detection of tumor cells in the cerebrospinal fluid (CSF). However, cell analysis has a low sensitivity here due to the small drawn volumes of CSF samples, their poor cellularity and cell viability. Soluble biomarkers can be measured by multiplex techniques on small sample volumes, hence can overcome cytological limitations and seem fairly interesting for further investigations.

The aim of the present study was to evaluate the diagnostic value of interleukin (IL)-10 and IL-6 quantification combined with the IL-10:IL-6 ratio in CSF of patients suffering from LM secondary to systemic small B-cell lymphoproliferations.

Seventeen patients suffering from LM were included in the study: 4 with chronic lymphocytic leukemia (CLL), 2 with mantle-cell lymphoma (MCL) and 11 with Waldenström's macroglobulinemia (WM). All patients presented CNS symptoms associated with documented LM (revealed either by conventional cytology and/or flow cytometry) at the diagnostic stage and before intrathecal chemotherapy. IL-10 and IL-6 quantifications were performed in CSF using the quantitative Cytometric Bead Array^® technique (human IL-10 CBA kit and human IL-6 CBA kit; BD Biosciences^TM) on a FACSCanto II flow cytometer (BD Biosciences^TM) following the manufacturer's recommendations, with a limit of detection of 2.5 pg/ml.

All CLL and MCL patients displayed an undetectable level of IL-10 (<2.5 pg/ml) along with undetectable (<2.5 pg/ml) or low level of IL-6 (n=6; range <2.5-14 pg/ml) in the CSF. These results suggest that IL-10 and IL-6 are not increased in secondary LM in these two malignancies. WM patients had a more heterogeneous distribution and are divided into 2 groups: undetectable IL-10 (n=4) or positive IL-10 (n=7; range 4-39 pg/ml with a median value of 18 pg/ml). We therefore calculated the IL-10:IL-6 ratio in this group, setting the threshold at 1 as firstly described in primary vitroretinal lymphomas and more recently in primary central nervous system lymphoma (PCNSL). Two patients displayed a ratio >1; one had WM transformed into DLBCL in CNS (IL-10= 21pg/ml; IL-6= 7pg/ml; IL-10:IL-6= 3), and the other had a PCNSL simultaneously diagnosed in CSF (IL-10= 18pg/ml; IL-6= 4pg/ml; IL-10:IL-6= 4.5). Other patients with a ratio <1 have a documented Bing Neel syndrome (BNS) and an absence of any other aggressive B-cell lymphoma. Furthermore, IL-6 levels were higher in CSF of BNS patients (n=9; range 4-540 pg/ml with a median value of 32 pg/ml) than in CLL and MCL patients. Our findings demonstrate the need of IL-10 and IL-6 quantification with the use of IL-10:IL-6 ratio at diagnosis of LM in small B-cell lymphoproliferations to exclude any other aggressive B-cell malignancy. Further investigation of IL-6 concentration may be useful in BNS diagnosis regardless of the ratio because some data demonstrate a central role of IL-6 in WM pathophysiology. Besides, it has already been reported that CCL5 production by tumor microenvironment in WM leads to IL-6 and IgM secretion through the JAK/STAT signaling pathway.

In conclusion, we describe for the first time that IL-10 concentration in the CSF is not increased in small B-cell lymphoproliferations with LM. However, we report its usefulness in revealing more aggressive lymphomas in the context of either a transformation or when associated with another "hidden" lymphoma such as PCNSL. Supplementary data will be prospectively collected to confirm our preliminary results. On one hand, it seems important to study CLL cases with or without Richter syndrome, and on the other hand to further explore the role of IL-6 in BNS.