Central tolerance mechanisms in B-cell malignancies

ABSTRACT Humans produce each day ~100 million autoreactive B-cells that express potentially harmful autoantibodies. This burden of autoreactive B-cells requires a powerful purging mechanism, termed central tolerance, to prevent autoimmune disease. During the previous period of this R01, we discovered that central tolerance mechanisms not only remove newly formed autoreactive B-cells but also eliminate B-cell tumors that originate from early stages of B-cell development, namely B-cell acute lymphoblastic leukemia (ALL), mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). Hence, central tolerance could represent a previously unrecognized vulnerability in B-cell tumors that is orthogonal to conventional mechanisms of drug-resistance. B-ALL represents the most frequent type of cancer in children. MCL and CLL are common in adults and remain incurable diseases. Small molecule inhibitors of kinases downstream of the B-cell receptor (BCR) have substantially extended survival, although treatment with kinase-inhibitors alone invariably selects for drug- resistance and relapse. Approximately 1.4 million people in the US are currently living with or recovering from B- cell malignancies (SEER), highlighting the importance of efforts to reduce toxicity and minimize late effects. Central tolerance mechanisms sense and eliminate transformed B-cells based on pathological signaling: Normal antigen encounter results in a short transient pulse of PI3K-activation, slow Ca2+-oscillations, tonic NF-B activation and positive selection. We discovered two distinctive features of pathological signaling that initiate central tolerance mechanisms:  Persistent PI3K-signaling (Aim 1) forces aberrant increases of cell size, causing ATP-depletion (AMPK- phosphorylation) and energy crisis.  High-frequency Ca2+-oscillations (Aim 2) in pathological B-cells are decoded by NFAT instead of NF- B, induce NFAT-dependent anergy and cell death. Here we test the overarching hypothesis that central tolerance mechanisms represent a novel class of therapeutic targets in B-cell tumors that arise from early B-cell development (B-ALL, CLL and MCL). Given their B-cell intrinsic activity, targeting of central tolerance mechanisms is expected to have minimal side- effects.