Gain-of-function mutations in CARD11 promote enhanced aggregation and idiosyncratic signalosome assembly

•Gain-of-function CARD11 variants form shell-like structures (mCADS) in lymphocytes.•mCADS constitutively signal via sustained MALT1 and phospho-IKK association.•Wild type CARD11 cannot form these structures upon antigen receptor stimulation.•mCADS require BCL10 and MAGUK domain interactions for assembly.•Endogenous mCADS are detectable in DLBCL harboring similar CARD11 GOF mutations.