B-cell lymphocytosis and reprogramming due to biallelic CARD11 mutations

Area of Science:

• Immunology
• Genetics
• Molecular Biology

Background:

• CARD11 protein regulates T and B cell receptor signaling, crucial for adaptive immunity.
• Germline CARD11 mutations cause severe inborn errors of immunity (IEI) in children.
• Somatic CARD11 mutations are linked to B cell malignancies.

Purpose of the Study:

• Identify the genetic cause of BENTA disease in a patient with a history of early childhood death.
• Characterize immune cell phenotypes and functions in the affected patient.
• Elucidate the molecular mechanisms underlying CARD11-driven B cell proliferation.

Main Methods:

• Whole exome sequencing to identify genetic variants.
• Flow and mass cytometry for immune cell phenotyping.
• Single cell RNA sequencing and in vitro assays to determine molecular mechanisms.
• Ectopic expression of wild-type and mutant CARD11 to assess functional impacts.

Main Results:

• A novel homozygous CARD11 mutation, R331P, was identified as the genetic basis of BENTA disease.
• The mutation causes massive expansion of naive B cells with an aberrant transcriptional program.
• Autosomal recessive BENTA exhibits exaggerated B cell lymphocytosis compared to mono-allelic forms.
• Ectopic CARD11 R331P expression induces constitutive NF-κB activity in T and B cells, indicating a gain-of-function.

Conclusions:

• Defined a novel autosomal recessive form of BENTA disease.
• The CARD11 R331P mutation is a gain-of-function variant causing BENTA in homozygosity.
• Further research into mutation-driven B cell dysfunction may illuminate B lymphomagenesis mechanisms.