Recurrent mutations in the spliceosome are observed in several human cancers, but their functional and therapeutic significance remains elusive. SF3B1, the most frequently mutated component of the spliceosome in cancer, is involved in the recognition of the branch point sequence (BPS) during selection of the 3' splice site (ss) in RNA splicing. Here, we report that common and tumor-specific splicing aberrations are induced by SF3B1 mutations and establish aberrant 3' ss selection as the most frequent splicing defect. Strikingly, mutant SF3B1 utilizes a BPS that differs from that used by wild-type SF3B1 and requires the canonical 3' ss to enable aberrant splicing during the second step. Approximately 50% of the aberrantly spliced mRNAs are subjected to nonsense-mediated decay resulting in downregulation of gene and protein expression. These findings ascribe functional significance to the consequences of SF3B1 mutations in cancer.

Given advanced age, comorbidities, and immune dysfunction, CLL patients may be at particularly high risk of infection and poor outcomes related to coronavirus disease-19 (COVID-19). Robust analysis of outcomes for CLL patients, particularly examining effects of baseline characteristics and CLL-directed therapy, is critical to optimally manage CLL patients through this evolving pandemic. CLL patients diagnosed with symptomatic COVID-19 across 43 international centers (n=198) were included. Hospital admission occurred in 90%. Median age at COVID-19 diagnosis was 70.5 years. Median CIRS score was 8 (range 4-32). Thirty-nine percent were treatment-naïve ("watch and wait") while 61% had received ≥1 CLL-directed therapy (median 2, range 1-8). Ninety patients (45%) were receiving active CLL therapy at COVID-19 diagnosis, most commonly BTK inhibitors (BTKi; n=68/90, 76%). At a median follow-up of 16 days, the overall case fatality rate (CFR) was 33%, though 25% remain admitted. "Watch and wait" and treated cohorts had similar rates of admission (89% vs. 90%), ICU admission (35% vs. 36%), intubation (33% vs. 25%), and mortality (37% vs. 32%). CLL-directed treatment with BTKi at COVID-19 diagnosis did not impact survival (CFR 34% vs. 35%), though BTKi was held during COVID-19 course for most patients. These data suggest that the subgroup of CLL patients admitted with COVID-19, regardless of disease phase or treatment status, are at high risk of death. Future epidemiologic studies are needed to assess SARS-CoV-2 infection risk, these data should be validated independently, and randomized studies of BTKi in COVID-19 are needed to provide definitive evidence of benefit.