# Mechanisms of a Novel Combined Immunodeficiency Caused by a Homozygous Mutation in COPG1

> **NIH NIH R01** · BOSTON CHILDREN'S HOSPITAL · 2021 · $442,500

## Abstract

We identified a biallelic K652E mutation in the γ1-COP subunit of the heptameric coat protein I (COPI)
complex in 5 Omani siblings, suffering from recurrent pulmonary infections with encapsulated bacteria, CMV
and EBV viremia. The four older siblings presented with severe CD4+ T cell lymphopenia and increased T cell
apoptosis; the youngest had normal T cell numbers shortly after birth, but developed CMV viremia and CD4+ T
cell lymphopenia at 6 mo.
 Coat proteins deform membranes to generate transport vesicles. They also bind to cargo proteins to
properly sort them into these vesicles, and ensure their transport to specific intracellular compartments. In the
early secretory system, the COPII complex transports cargo from the endoplasmic reticulum (ER) to the Golgi,
while the COPI complex transports select cargo in the other direction, from the Golgi to the ER, and
additionally mediates CDC42-dependent transport through the Golgi. Specific sequences on cargo proteins
recognized by COPI include the di-lysine and the di-arginine motifs. Coat proteins can also bind indirectly to
COPI through transmembrane proteins that act as cargo receptors. These include the KDEL receptor
(KDELR), which links COPI (residing on the cytosolic side of Golgi membrane) to soluble proteins within the
Golgi (lumenal side) that have a KDEL sequence. KDEL proteins are abundant ER proteins involved in protein
folding (chaperones). A fraction of KDEL proteins leak from the ER, and are retrieved from the Golgi to the ER
through the KDELR and COPI. Defect in this retrieval leads to the loss of ER chaperones, which has been
found to induce ER stress.
 Preliminary data show that fibroblasts from patients, and mice homozygous for the K652E γ1-COP
mutation, express the mutant protein, but demonstrate defective COPI-mediated trafficking, and that the
mutation disrupts the binding of the mutant COPI complex to KDELR. Mutant mice have severe
hypogammaglobulinemia and poor antibody responses. Their B cells had increased ER stress and impaired
immunoglobulin (Ig) secretion that was rescued by the ER stress inhibitor TUDCA. T cells from the mutant
were normal in numbers, but had increased ER stress, and displayed increased apoptosis and diminished IL-4
production following sustained activation in vitro.
 We propose to test the hypothesis that the γ1-COP mutation disrupts COPI-mediated trafficking
causing increased ER stress that impairs B and T cell function, increases susceptibility to bacterial
and viral infection, and results in CD4+ T cell lymphopenia secondary to persistent viral infection.
 The studies proposed will elucidate the mechanisms by which a novel monogenic defect that impairs
COPI-mediated trafficking leads to CID with CD4+ T cell lymphopenia, and will test pre-clinically the therapeutic
efficacy of ER stress relieving drugs in this disease.

## Key facts

- **NIH application ID:** 10265627
- **Project number:** 3R01AI139633-04S1
- **Recipient organization:** BOSTON CHILDREN'S HOSPITAL
- **Principal Investigator:** RAIF SALIM GEHA
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $442,500
- **Award type:** 3
- **Project period:** 2020-08-10 → 2023-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10265627

## Citation

> US National Institutes of Health, RePORTER application 10265627, Mechanisms of a Novel Combined Immunodeficiency Caused by a Homozygous Mutation in COPG1 (3R01AI139633-04S1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10265627. Licensed CC0.

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