Ramı́rez-Alvarado, Marina

Abstract Background: Immunoglobulin light chain (AL) amyloidosis is a fatal complication of B-cell clonal proliferation. Currently, the best biomarker for treatment monitoring is serum free light chain (FLC) assay. Despite its higher sensitivity, it cannot distinguish clonality thus ultralow levels of monoclonal gammopathy can be missed. Urinary exosomes (UExs) are the smallest members of the extracellular vesicle family that are excreted in the urine. They exhibit different characteristics in patients with AL amyloidosis vs multiple myeloma. This study was undertaken to determine if urinary exosomes have different characteristics in patients AL amyloidosis who progress despite being in complete response (CR) vs those who have a renal response. Methods: UEx were extracted from 4 patients at different stages of AL (Table 1). Immunoglobin light chains (LC) were identified in the UEx using western blotting. Intact immunoglobulin light chains were identified in plasma, UEx, and kidney biopsy amyloid deposits using mass spectrometry (MS). cDNAs from bone marrow plasma cells (BMPC) collected at the time of diagnosis from patient 4 were sequened. Results: Oligomeric LC (250 kd) were identified in the UEx of patient 1 (newly diagnosed, Fig 1a) and 4 (renal progression in CR, Fig 1d) but only monomeric LC (25 kd) were detected in patient 2 (Fig 1b) and 3 (CR and renal response, Fig 1c). MS of the UEx and plasma of patient 4 detected 2 monoclonal λ LC. The mass of one of the LC was consistent with a lambda 6a LC which is also the most common cDNA (IGLV-6-57) found in the BMPC. Amino acid sequences derived from the tryptic digestion of the amyloid deposits matched the predicted sequence of the cDNA. The calculated weight of the peptide produced by the cDNA (23,304 Da ) was within margin of error of the mass of the lambda 6a LC (23,306 Da). The mass of the second LC (23,092 Da) was consistent with a λ4/λ5 LCs. A search of the amino acid and cDNA sequences failed to identify any similarity. The density ratio of the oligomeric LC to monomeric LC in the UEx was 0.47 which was similar to the intensity ratio by MS of the lambda 6a LC (23,306 Da) to the 23,092 Da LC in the blood (0.43). Discussion: Urinary EXs identified oligomeric LC in a patient with progressive renal disease despite achieving a CR. The mass one of the λ LC matched the predicted peptide product of the cDNA obtained from BMPC. The amino acid sequence predicted by the cDNA matched the trypsin digested sequences from the amyloid deposits. This strongly suggests the oligomeric LC represents the amyloidogenic λ6a LC detected in the blood which was being produced by the BMPC clone which is being deposited as amyloid in the kidney. The origin of the second λ LC is unknown but is likely a new monoclonal gammopathy of undetermined significance that developed after the initial bone marrow biopsy. The blood and urine samples were obtained 3 years after the BMPC. The development of a new monoclonal gammopathy in patients with plasma cell dyscrasia is not uncommon. Unfortunately, bone marrow biopsy collected at the time of the urine and blood sample had insufficient number of plasma cells (CR) for analysis. Conclusion: UEx can identify amyloidogenic LC even when current standard methods could not. The persistent presence of the amyloidogenic LC helps explain why patients can progress despite being in CR. The presence of a second λ LC which was not part of the amyloid deposit also has clinical implication. It may explain why some patients do well despite having a persistent monoclonal protein. If these results are confirmed, UEx may have a powerful role in the determination of organ and hematologic response in patients with AL amyloidosis. Disclosures Dispenzieri: Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; Alnylam: Research Funding; GSK: Membership on an entity's Board of Directors or advisory committees; pfizer: Research Funding; Jannsen: Research Funding; Celgene: Research Funding.

Abstract Introduction: AL amyloidosis is a very heterogeneous disease. Prognosis is a function of organ tropism, extent of organ damage, and ability of tissues to heal, the last of which relates both to hematologic response and intrinsic toxicity of the light chain. Using mass spectroscopy (MS) technology, we are able to distinguish immunoglobulin light chain variable gene family (IGVL) usage on clinical samples. The goal of this study was to evaluate if IGVL usage impacts patient outcomes in patients with light chain amyloidosis (AL). Methods: IGVL usage was determined by mass spectroscopy (MS) of amyloid in clinical tissue specimens of Mayo Clinic patients. Specimens were from fat pad (n=257), bone marrow (n=172), myocardium (n=113), gastrointestinal (n=58), kidney (n=20), lung (n=15), and nerve (n=5). For those cases for which the IGVL could not be identified--not otherwise specified (NOS)—but constant region could be identified as lambda or kappa, we assume that the amyloid consisted primarily of immunoglobulin light chain gene constant regions or variable genes with somatic mutations making them uninterpretable to our matching algorithms. The medical records from these 700 patients were abstracted for relevant clinical and laboratory data. Results: The baseline characteristics of patients are shown in table 1. Three hundred and thirty-two patients have died with a median follow-up of surviving patients of 38 months. The estimated median survival for the entire population is 59 months. Out of 700 patients, 214 (31%) achieved a CR or a VGPR, 432 (62%) were not evaluable (NE) for hematologic or organ response, and 54 (8%) achieved a PR or did not respond (NR). The distribution of IGVL cases is shown in table 2. Overall survival (OS) for the whole group was not different across different IGVLs on univariate analysis, but when corrected for hematologic response, outcomes differed significantly based on IGVL. Patients could be further assembled into two groups, based on risk for death on univariate analyses: an IGVL high risk, which included KV1, LV1, LV2, LV3, and LV6; and low risk, which included all other cases (Figure). In a multivariate model that included level of hematologic response (CR/VGPR versus PR/NR/NE) and IGVL, IGVL family was independently associated with overall survival (RR=1.5 (95% CI 1.2-1.9, p=0.008). The risk ratio for CR/VGPR was 0.28 (95% CI 0.20-0.38, p<0.0001). This effect persisted when either the Mayo 2006 or the 2012 staging system was included in the multivariate. Conclusion: IGVL usage appears to have prognostic significance in patients who have not achieved VGPR or better to initial chemotherapy. Table 1. Baseline characteristics of patients N= 700 Age 63 (32-94) Male, (%) 447 (64%) Biopsy site Solid organ/Soft tissue 271 (39%) Fat pad 257 (37%) Bone Marrow 172 (25%) Organ involvement Cardiac 432 (62%) Renal 346 (49%) Gastrointestinal 168 (24%) Liver 56 (8%) Nerve 107 (15%) Lung 42 (6%) Soft Tissue 92 (13%) Organs involved 1 321 (46%) 2 228 (33%) ≥3 151 (22%) Laboratory characteristics NTBNP, pg/ml 2547 (11.3-70000) Troponin, ng/ml 0.03 (0.001-0.84) dFLC, mg/dl 26 (0.04-2330) Cardiac Stage 1 59 (18%) 2 125 (38%) 3 144 (44%) Table 2. Variable region family distribution. Light Chain N=700 N (%) KV1 107 (15%) KV2 3 (0.4%) KV3 17 (2%) KV4 25 (4%) KV6 1 (0.1%) LV1 85 (12%) LV2 64 (9%) LV3 118 (17%) LV4 3 (0.4%) LV6 97 (14%) LV8 1 (0.1%) LV9 1 (0.1%) Kappa NOS1 34 (4%) Lambda NOS1 140 (19%) Heavy chain amyloidosis 4 (0.6%) 1 No IGVL family could be identified Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 747 Background: Light chain amyloidosis is a monoclonal plasma cell proliferative disorder characterized by multiorgan deposition of monoclonal light chain derived amyloid fibrils. The diffuse organ infiltration by the amyloid fibrils leads to various AL related clinical features. Therapy of AL has been primarily aimed at elimination or control of the monoclonal plasma cells, thus decreasing the light chain available for amyloid formation. Assessment of response to therapy has been grouped into hematological response demonstrating elimination or reduction of the monoclonal population and organ response demonstrating actual improvement in its structure or function. Given the potentially long delay in observing organ improvement, hematological response has been the surrogate short term marker for long term outcome given the relatively rapid decline seen in the monoclonal protein with effective therapy, as well as studies showing improved long term outcome with a hematological response, especially complete response. However, conventional hematological response criteria give priority to the intact monoclonal protein rather than the light chain, which is the amyloidogenic protein. We hypothesized that a light chain response will correlate better with outcome than changes in the intact monoclonal protein levels. Methods: We identified 348 patients who had undergone stem cell transplant (SCT) for AL from among a large group of patients undergoing different treatments for AL, and in whom serial tests results were available. We identified the lowest value attained following SCT for various hematological response parameters (intact serum M-protein [MP], the difference between involved and uninvolved serum free light chain [FLC-diff], and urine M-protein [UP]) before an alternate therapy was instituted. We first estimated the best cutoff for the degree of change in each parameter that predicted 5-year survival from SCT. Cox proportional hazards model was used for multivariable analysis of factors influencing overall survival (OS). Results: We first examined the relative contribution of the MP and the FLC-diff on the overall survival following transplant. The best cutoff for reduction in FLC-diff to predict OS at 5 years from SCT was 88% if all patients were considered and 90% if only those with a baseline FLC diff > 7.5 mg/dL were considered. The best cutoff for MP reduction was 40% for 5 year survival for all patients and 67% for those with a baseline MP > 1.0 gm/dL. We then looked at the impact of FLC reduction and MP reduction in a multivariable analysis using OS as endpoint. For all patients, FLC reduction, but not MP reduction significantly impacted outcome, and results were similar when considering patients with MP>1.0 gm/dl and FLC-diff > 7.5 mg/dl at baseline. Among those with a baseline FLC-diff >7.5 mg/dL (n=125), the overall survival was 35 mos from SCT for those with less than 90% decrease in FLC-diff (45 pts) compared to not reached for those with at least 90% decrease (80 pts); P < 0.001 (Figure). Conclusions: The current study supports the notion that reductions in the free light chain parameters represent a more useful measure of hematological response that translates into better overall survival and possible better chance at organ improvement. A reduction in the FLC difference of 90% appears to correlate best with prolonged survival. Disclosures: Kumar: CELGENE: Research Funding; MILLENNIUM: Research Funding; BAYER: Research Funding; GENZYME: Research Funding; NOVARTIS: Research Funding. Gertz:celgene: Honoraria; millenium: Honoraria, Membership on an entity's Board of Directors or advisory committees. Lacy:celgene: Research Funding.

Abstract Urinary extracellular vesicles (uEVs) have been used as a biomarker tool for detection of low abundance immunoglobulin-based targets in uEVs with heterogeneous high protein mixtures. This protocol outlines a pre-incubation method to minimize non-specific secondary antibody binding. Additionally, we include our approach for standardization of uEV amounts used for sample comparison. We propose that these and knowledge of the detection limit for target proteins are strategies applicable to other laboratories working with complex heterogeneous samples.

SummaryThis study evaluated the differences in clinical features of 1077 newly diagnosed AL amyloidosis patients with renal involvement (n = 229, 21%), both cardiac and renal involvement (n = 443, 41%) and cardiac involvement (n = 405, 38%). Significant differences in dFLC (difference in involved and uninvolved light chains) were noted (renal, both, cardiac median: 83, 234 and 349 mg/l, P < 0.001). The proportion of patients with ≥ 10% bone marrow plasma cells (BMPCs) was lowest in renal only patients: 44%, 57%, 64%, respectively, P < 0.001. In a multivariate linear regression model incorporating organ involvement type and BMPCs ≥10%, organ involvement was a significant predictor of dFLC (P < 0.001). Median overall survival (OS) across the three groups was 83 vs. 19 vs. 16 months (P < 0.001) in patients not undergoing transplant and 5‐year OS in patients undergoing transplant was 90% vs. 75% vs. 64% (P = 0.007), respectively. In conclusion, renal involvement alone or renal + cardiac involvement in AL amyloidosis is associated with lower circulating light chain burden, which cannot be fully explained by BMPC burden alone. Increased sensitivity of the kidney to light chains, given significant interactions with the renal tubular system and secretion of modified light chain products may play a role in pathogenesis of renal AL amyloidosis and warrants further investigation.

Light chain (AL) amyloidosis is a devastating, complex, and incurable protein misfolding disease.