An inadequate supply of amino acids leads to accumulation of uncharged tRNAs, which can bind and activate GCN2 kinase to reduce translation. Here, we show that glutamine-specific tRNAs selectively ...become uncharged when extracellular amino acid availability is compromised. In contrast, all other tRNAs retain charging of their cognate amino acids in a manner that is dependent upon intact lysosomal function. In addition to GCN2 activation and reduced total translation, the reduced charging of tRNA
Gln
in amino-acid-deprived cells also leads to specific depletion of proteins containing polyglutamine tracts including core-binding factor α1, mediator subunit 12, transcriptional coactivator CBP and TATA-box binding protein. Treating amino-acid-deprived cells with exogenous glutamine or glutaminase inhibitors restores tRNA
Gln
charging and the levels of polyglutamine-containing proteins. Together, these results demonstrate that the activation of GCN2 and the translation of polyglutamine-encoding transcripts serve as key sensors of glutamine availability in mammalian cells.
A robust network of transcription factors and an open chromatin landscape are hallmarks of the naive pluripotent state. Recently, the acetyllysine reader Brd4 has been implicated in stem cell ...maintenance, but the relative contribution of Brd4 to pluripotency remains unclear. Here, we show that Brd4 is dispensable for self-renewal and pluripotency of embryonic stem cells (ESCs). When maintained in their ground state, ESCs retain transcription factor binding and chromatin accessibility independent of Brd4 function or expression. In metastable ESCs, Brd4 independence can be achieved by increased expression of pluripotency transcription factors, including STAT3, Nanog or Klf4, so long as the DNA methylcytosine oxidases Tet1 and Tet2 are present. These data reveal that Brd4 is not essential for ESC self-renewal. Rather, the levels of pluripotency transcription factor abundance and Tet1/2 function determine the extent to which bromodomain recognition of protein acetylation contributes to the maintenance of gene expression and cell identity.
How immune dysregulation affects recovery from COVID-19 infection in patients with cancer remains unclear. We analyzed cellular and humoral immune responses in 103 patients with prior COVID-19 ...infection, more than 20% of whom had delayed viral clearance. Delayed clearance was associated with loss of antibodies to nucleocapsid and spike proteins with a compensatory increase in functional T cell responses. High-dimensional analysis of peripheral blood samples demonstrated increased CD8+ effector T cell differentiation and a broad but poorly converged COVID-specific T cell receptor (TCR) repertoire in patients with prolonged disease. Conversely, patients with a CD4+ dominant immunophenotype had a lower incidence of prolonged disease and exhibited a deep and highly select COVID-associated TCR repertoire, consistent with effective viral clearance and development of T cell memory. These results highlight the importance of B cells and CD4+ T cells in promoting durable SARS-CoV-2 clearance and the significance of coordinated cellular and humoral immunity for long-term disease control.
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•Cancer patients with persistent COVID-19 infection have low humoral immune responses•Robust CD8+ T cell responses are unable to clear virus in B cell-depleted patients•Potent CD4+ T cell responses are in B cell-depleted patients with viral clearance
Lyudovyk et al. analyze immunological factors required for SARS-CoV-2 clearance in patients with cancer. They observe delayed viral clearance in patients with impaired humoral immunity despite broad and functional antiviral CD8+ T cell responses. However, B cell-deficient patients with robust CD4+ T cell responses were frequently able to achieve efficient viral clearance.
Fahrner and colleagues investigated the immune response of patients with cancer and cancer-free individuals to SARS-CoV-2 and found that a propensity toward an IL5-predominant Th2/Tc2 response was ...predictive of susceptibility to infection. The results of this study also suggest that a cellular response against the Spike 1 protein receptor binding domain (S1-RBD) region of the SARS-CoV-2 proteome contributes to protection and that mutations in this region may drive viral evolution and immune escape. See related article by Fahrner et al., p. 958 (8).
Agonist MHC-peptide complexes in the immunological synapse (IS) signal through T cell receptor (TCR) microclusters (MCs) that converge into a central supramolecular activation cluster (cSMAC). The ...determinants and function of the cSMAC remain unknown. We demonstrate an essential role for ubiquitin (Ub) and TSG101, but less so for HRS, in signal processing events at the cSMAC. Using siRNA in primary T cells, we show that Ub recognition by TSG101 is required for cSMAC formation, TCR MC signal termination, TCR downregulation, and segregation of TCR-MHC-peptide from PKC-θ-enriched signaling complexes. Weak agonist MHC-peptide induced CD80-dependent TCR MCs that dissociated in the center of the IS without recruiting TSG101. These results support TSG101-dependent recognition of CD80-independent TCR MCs as a molecular checkpoint for TCR downregulation.
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► TSG101 is recruited to the immunological synapse by strong TCR ligation ► TSG101 is required for cSMAC formation in response to strong TCR ligands ► TSG101 sorts strong ligand-engaged TCR from CD28 and into LBPA-rich structures ► Weak TCR ligation does not recruit TSG101 or induce cSMAC formation
Summary
Rituximab‐containing salvage chemotherapy followed by high‐dose therapy and autologous stem cell transplant (ASCT) in chemosensitive patients remains the standard of care for patients with ...relapsed and refractory diffuse large B‐cell lymphoma (DLBCL). However, its role in those patients achieving less than a complete response to first‐line therapy (primary refractory disease) in the rituximab era is not well defined. We reviewed the outcomes of 82 transplant‐eligible patients with primary refractory DLBCL who underwent salvage therapy with the intent of administering high‐dose therapy and ASCT to patients achieving chemosensitive remission. The estimated 3‐year overall and progression‐free survival for all patients was 38% and 29%, respectively, and 65% and 60% respectively for patients proceeding to stem cell transplant. Long‐term remission was achieved in 45% of patients achieving a partial response (PR) to initial induction therapy and <20% of patients with stable or progression of disease following initial therapy. These results suggest that salvage chemotherapy with the intent of subsequent high‐dose therapy and ASCT remains a feasible strategy in certain patients with primary refractory DLBCL, particularly for those achieving a PR to frontline therapy. The primary barrier to curative therapy in patients with primary refractory disease is resistance to salvage therapy, and future studies should be aimed towards increasing the response rate in this population.
Corticosteroids, anti-CD20 agents, immunotherapies, and cytotoxic chemotherapy are commonly used in the treatment of patients with cancer. It is unclear how these agents affect patients with cancer ...who are infected with SARS-CoV-2. We retrospectively investigated associations between SARS-CoV-2-associated respiratory failure or death with receipt of the aforementioned medications and with pre-COVID-19 neutropenia. The study included all cancer patients diagnosed with SARS-CoV-2 at Memorial Sloan Kettering Cancer Center until June 2, 2020 (N = 820). We controlled for cancer-related characteristics known to predispose to worse COVID-19 as well as level of respiratory support during corticosteroid administration. Corticosteroid administration was associated with worse outcomes prior to use of supplemental oxygen; no statistically significant difference was observed in sicker cohorts. In patients with metastatic thoracic cancer, 9 of 25 (36%) and 10 of 31 (32%) had respiratory failure or death among those who did and did not receive immunotherapy, respectively. Seven of 23 (30%) and 52 of 187 (28%) patients with hematologic cancer had respiratory failure or death among those who did and did not receive anti-CD20 therapy, respectively. Chemotherapy itself was not associated with worse outcomes, but pre-COVID-19 neutropenia was associated with worse COVID-19 course. Relative prevalence of chemotherapy-associated neutropenia in previous studies may account for different conclusions regarding the risks of chemotherapy in patients with COVID-19. In the absence of prospective studies and evidence-based guidelines, our data may aid providers looking to assess the risks and benefits of these agents in caring for cancer patients in the COVID-19 era.
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