MECHANISTIC IMPACT OF OLIGOMER POISONING BY DOMINANT-NEGATIVE CARD11 VARIANTS

Tight regulation of lymphocytes is critical for sustaining human health and prevention of infectious, neoplastic, and autoimmune diseases. Molecular regulation in lymphocytes occurs at several steps during lymphocyte activation to generate a controlled response that will clear the causal antigen while minimizing harm to the host. CARD11 is an essential, multi-domain cytoplasmic protein that regulates lymphocyte activation, proliferation, and survival by functioning as a scaffold downstream of T and B cell receptor engagement by cognate antigen. CARD11 signals through four defined steps and leads to activation of the NF-κB, JNK, and mTOR pathways to elicit the adaptive immune response. Dysregulated CARD11 signaling, specifically through the inheritance of mutant CARD11 alleles, has been shown to cause primary immunodeficiency diseases in patients. This research aims to contribute fundamental knowledge as to how the inheritance of a single dominant-negative loss-of-function (LOF) CARD11 allele results in defective lymphocyte signaling and activation. We interrogated the steps in the CARD11 signaling cycle to branched pathways in genetically engineered T cells expressing LOF CARD11 variants in both the absence and presence of wild-type CARD11. We identified the mechanistic basis for dominant-negative CARD11 variants and provide insights into how some LOF alleles may cause disease when heterozygous while others cause disease only when homozygous. We discovered that strong dominant-negative CARD11 mutations can affect two known steps in the CARD11 signaling cycle: Step 1, CARD11 Opening and Step 2, Cofactor Association. These key findings open possibilities for the development of targeted therapies aimed to treat and improve outcomes for patients with CARD11-mediated primary immunodeficiency diseases