Hetrick, MeLea

Objective Despite the reported clinical significance of anti-C1q immunoglobulin G autoantibodies (anti-C1q) for SLE and the development of anti-C1q commercial kits, their performance characteristics in routine patient evaluation remain poorly defined. Methods In this cross-sectional study, an unselected cohort of 107 patients with suspicion of a systemic autoimmune disease and 102 controls were included and evaluated for anti-C1q autoantibodies with three kits (Bühlmann, Orgentec and Werfen). Patients in the unselected cohort were classified as having SLE or a mimicker condition. Disease activity was assessed using Systemic Lupus Erythematosus Disease Activity Index (SLEDAI)-2K and SLE patients were subclassified based on the presence of lupus nephritis (LN) (history/active). Each kit was assessed for diagnostic performance. The degree of association between anti-C1q and SLEDAI/complement levels was assessed using the Spearman correlation coefficient (rho). Between-kit agreement was evaluated using Fleiss Ƙ. Results Werfen had the best performance in discriminating patients with SLE from non-SLE (area under the curve (AUC)=0.76), whereas for the SLE versus mimicker comparison Bühlmann (AUC=0.71) and Werfen (AUC=0.71) exhibited adequate discrimination. Among patients with SLE, all kits exhibited poor discrimination of patients with history of LN versus non-renal SLE, but Orgentec displayed good discrimination for patients with active LN from non-active LN (AUC=0.74). A positive correlation was observed between anti-C1q and SLEDAI scores, whereas a negative correlation was found between anti-C1q and complement C3 and C4 across all kits. Agreement for SLE between the three kits was moderate (Ƙ=0.42). Conclusion Anti-C1q can identify patients with SLE and correlate with global and renal disease activity, highlighting their potential to function as follow-up markers in SLE. Agreement with commercial anti-C1q kits is variable. Further studies are required to harmonise anti-C1q kits for optimal routine patient evaluation.

Abstract Objectives A matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) method (Mass-Fix) as a replacement for gel-based immunofixation (IFE) has been recently described. To utilize Mass-Fix clinically, a validated automated method was required. Our aim was to automate the pre-analytical processing, improve positive specimen identification and ergonomics, reduce paper data storage and increase resource utilization without increasing turnaround time. Methods Serum samples were batched and loaded onto a liquid handler along with reagents and a barcoded sample plate. The pre-analytical steps included: (1) Plating immunopurification beads. (2) Adding 10 μl of serum. (3) Bead washing. (4) Eluting the immunoglobulins (Igs), and reducing to separate the heavy and light Ig chains. The resulting plate was transferred to a second low-volume liquid handler for MALDI plate spotting. MALDI-TOF mass spectra were collected. Integrated in-house developed software was utilized for sample tracking, driving data acquisition, data analysis, history tracking, and result reporting. A total of 1,029 residual serum samples were run using the automated system and results were compared to prior electrophoretic results. Results The automated Mass-Fix method was capable of meeting the validation requirements of concordance with IFE, limit of detection (LOD), sample stability and reproducibility with a low repeat rate. Automation and integrated software allowed a single user to process 320 samples in an 8 h shift. Software display facilitated identification of monoclonal proteins. Additionally, the process maintains positive specimen identification, reduces manual pipetting, allows for paper free tracking, and does not significantly impact turnaround time (TAT). Conclusions Mass-Fix is ready for implementation in a high-throughput clinical laboratory.

Abstract AL is a rare plasma cell disorder, resulting from clonal bone marrow plasma cells secreting immunoglobulin light chains (LC), which aggregate abnormally into fibrils, and leads to amyloid deposits in different organs. Previous studies using LC immunopurification and MALDI-TOF/MS (MASS-FIX) on patients with known plasma cell disorders (PCDs), demonstrated that monoclonal LC from AL patients display unusually complex mass to charge spectra (m/z) for their LCs at much higher frequencies than other PCDs such as multiple myeloma. We hypothesized that these were post-translational modification, presumably glycoforms. Here, we report investigations into LC glycosylation using MASS- FIX. Serum from 212 lambda and 72 kappa AL patients were collected following Mayo Clinic IRB guidelines. LC was purified from serum using nanobody enrichment method, followed by MASS-FIX. The LCs spectra acquired on MASS-FIX were visually analyzed and were classified into different patterns. The kappa and lambda LC mass distributions with abnormal complex patterns were interrogated for the presence of glycosylation by exposure to the LC to a deglycoslylating enzyme (PNGase F) and analysis of LC mass distribution using MASS-FIX and by LC-ESI-Orbitrap. Monoclonal LCs demonstrating significantly mass shifted peak outside the normal kappa and lambda mass distribution were observed in 31% of kappa and 6% of lambda patients with AL. In order to determine if this characteristic mass shift was due to glycosylation, 16 kappa and 6 lambda LCs were treated with a PNGase F and LC spectrum were re-examined by MASS-FIX and LC-ESI-Orbitrap. The monoclonal LCs whose masses were significantly shifted beyond normal kappa and lambda mass distributions were found to shift to lower molecular weight after PNGase F treatment, confirming the presence of N-glycosylation. Moreover, an additional 5 kappa and 23 lambda samples had other complex patterns, typically with multiple additional peaks at increments of 162 Da. These samples did not shift with PNGase F suggesting either glycation or O-glycosylation. This work is significant as it confirms that N-glycosylated LCs are over represented in patients with AL in comparison to other PCDs. In patients with AL, the frequency of N-glycosylation of kappa LC clones was 5 times higher than that of lambda LC clones. More work is needed to explore the mechanism for this finding, the role of glycosylation in fibril formation, and the other complex patterns observed. In addition, MASS-FIX method used in this work is currently being validated in the clinical lab such that rapid detection of N-glycosylation in patients with monoclonal gammopathies will be possible routinely, potentially leading to earlier clinical suspicion for AL among patients with monoclonal gammopathies and hence to earlier detection of AL. Citation Format: Sanjay Kumar, Angela Dispenzieri, Surendra Dasari, Paolo Milani, Giampaolo Merlini, MeLea Hetrick, David Barnidge, Benjamin Madden, David Murray. Mass spectrometric approach to identify N-glycosylation of light chain in patients with immunoglobulin light chain amyloidosis (AL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2693.