Transcobalamin receptor antibodies in autoimmune vitamin B12 central deficiency

Vitamin B12 is critical for hematopoiesis and myelination. Deficiency can cause neurologic deficits including loss of coordination and cognitive decline. However, diagnosis relies on vitamin B12 measurement in the blood which may not accurately reflect levels in the brain. Using programmable phage display, we identified an autoantibody targeting the transcobalamin receptor (CD320) in a patient with progressive tremor, ataxia, and scanning speech. Anti-CD320 impaired cellular uptake of cobalamin (B12) in vitro. Despite normal serum levels, B12 was nearly undetectable in her cerebrospinal fluid (CSF). Immunosuppressive treatment and high-dose systemic B12 supplementation were associated with increased CSF B12 levels and clinical improvement. Optofluidic screening enabled rapid isolation of a patient-derived monoclonal antibody that impaired B12 transport across an in vitro model of the blood-brain barrier. Autoantibodies targeting the same epitope of CD320 were identified in 7 other patie..., Programmable Phage Display
We adapted a previously published protocol for phage immunoprecipitation sequencing (PhIP-seq). A library containing 731,724 49-amino acid peptides with 25-amino acid overlaps was cloned into T7 bacteriophage. Patient CSF was incubated with 1010 plaque forming units of the phage library, antibodies were enriched with protein A/G magnetic beads, and antibody-bound phage was amplified in E. coli before a second round of immunoprecipitation. Enriched phage lysates were adaptor ligated and barcoded prior to pair-end sequencing on an Illumina Novaseq to a depth of 2 million reads per sample. Reads were trimmed, aligned at the amino-acid level using RAPSearch, and normalized to sequencing depth to generate reads per 100,000 bases (RPK) for each sample. Enriched peptides were identified by calculating the fold-change of normalized counts between samples immunoprecipitated with CSF or magnetic beads only. The Benjamini-Hochberg method was used to correct for multiplic..., , # Transcobalamin Receptor Antibodies in Autoimmune Vitamin B12 Central Deficiency

[https://doi.org/10.5061/dryad.6djh9w18j](https://doi.org/10.5061/dryad.6djh9w18j)

## Description of the data and file structure

NID0063_peptide.csv -> normalized RPK file of peptide enrichments for mock IP (BEAD), GFAP commercial Ab IP, and Case 1 CSF IP (NID0063)

NID0063_gene.csv -> normalized RPK file of gene-level enrichments for mock IP (BEAD), GFAP commercial Ab IP, and Case 1 CSF IP (NID0063)

B12_K562_combo.csv -> CRISPRi screen hit list; negative effect size indicates that the knockdown impaired holotranscobalamin uptake; positive effect size indicates that the knockdown promoted uptake; confidence score and FDR calculated using caSTLE (Morgens et al, 2016).

REP1_NEG_S15_L003_R1_001.fastq.gz -> fastq file of replicate 1 of CRISPRi screen, bottom 5% B12 uptake

REP1_POS_S16_L003_R1_001.fastq.gz -> fastq file of replicate 1 of CRISPRi screen, top 5% B12 uptake

REP2_NEG_S17_L003_...