Gene Expression Sets and Renal Profiling from the Rain (Renal AL Amyloid Involvement and NEOD00) Trial

INTRODUCTION: Despite the high prevalence of kidney involvement in patients with light chain (AL) amyloidosis, a significant knowledge gap exists in understanding how immunoglobulin light chains drive kidney injury. The chief reason is the lack of molecular data from high-quality kidney tissue samples from this patient population. The RAIN trial (NCT03168906) was a phase 2B randomized placebo-controlled, open-label clinical trial that evaluated the efficacy of NEOD001, a monoclonal antibody targeting amyloid fibrils, versus placebo in patients with AL nephropathy. OBJECTIVES: Identifying amyloid-specific molecular signatures in kidney biopsy tissue obtained from AL patients with nephropathy.MATERIALS& METHODS: Renal biopsies were collected on all RAIN participants before randomization to NEOD001 or placebo. Trial clinical data was incorporated to link tissue, molecular, and kidney function data. The histologic assessment included a composite scarring injury score (CSIC) as determined by the degree of glomerular and tubulointerstitial scarring, and a novel amyloid score (AS), as quantified by the extent and distribution of amyloid deposition. Glomerular (G) and tubulointerstitial compartments were micro-dissected and sequenced separately. To identify enriched pathways in AL nephropathy, the expression data was compared to the glomerular and tubular expression profiles of healthy living donor (LD) from the Nephrotic Syndrome Study Network (NEPTUNE) study. Differentially expressed genes (DEGs) were determined with the R limma package based on the voom transformed log2 count data with an FDR of <=0.05. The AL and NEPTUNE datasets were merged and batch-corrected using ComBat. RESULTS: Ten patients were enrolled and randomized in the RAIN trial (5 NEOD001 and five placeboes) before trial closure in April 2018. Kidney tissue was available in nine of the ten patients. Cluster analysis revealed two distinct patient clusters (G1 and G2) within the glomerular and tubulointerstitial compartments. Key data of kidney function and biopsy morphology by compartment and cluster type are shown in Table 1. Despite similar eGFR, there was a higher AS and a non-significant increase in 24-hour urine protein in the glomeruli of individuals in the G2 patient cluster. Subcomponent analysis of AS revealed that the increase in amyloid score in G2 was driven almost entirely by an increase in mesangial and capillary wall amyloid deposition. Pathway enrichment in Amyloid kidney disease versus LD: IPA analysis identified unique activation signatures in the glomeruli and tubules. In the glomeruli of biopsies from the G2 cluster, there was evidence of increased TNF, IFNG, IL33 and VEGFA cytokine activity and a predicted increase in canonical PI3K/Akt signaling and innate immune responses. Tubules showed increased activation of transcriptional regulators TP53, TP73, increased cytokine signaling of IFNG, TGFb1 and VEGF. There was also a predicted activation of major canonical pathways including B cell receptor signaling, PI3K/AKT and Ephrin receptor signaling (Fig 1). Pathway Enrichment in G2 versus G1: Glomeruli showed activation of fibrotic pathways accompanied by a reduction in metabolic processes including gluconeogenesis, lipid transport and xenobiotics. There was an increase in canonical signaling of LPS/IL-1 mediated inhibition of RXR function that drives increased IL1 and TNF release from macrophages. Transcriptomic evidence of TNF activation was also noted in the TI. CONCLUSIONS: The RAIN trial closed prematurely, and thus no conclusions can be reached about the efficacy of NEOD001 in patients with AL nephropathy. However, these limited data revealed the presence of two distinct molecular subtypes of AL nephropathy. Whether these distinct molecular subtypes reflect different stages of the disease along a continuous spectrum or are of unique prognostic entities in themselves remains unclear. Detailed studies, of a larger cohort of patients including investigating diseased tissue at a single cell resolution can help identify the response of individual kidney cell types. Understanding the cellular responses of key cell types to injury from amyloid deposits could provide novel therapeutic targets to mitigate renal injury and improve patient outcomes.

No relevant conflicts of interest to declare.