Screening Chest CT Prior to Allogenic Hematopoietic Stem Cell Transplantation.

Pulmonary complications constitute a major cause of morbidity and mortality in the post-allogenic hematopoietic stem cell transplantation (alloHSCT) period. Although chest X-ray (CXR) is customarily used for screening, we have used chest computed tomography (CT) scans. To characterize the prevalence of abnormalities and explore their impact on alloHSCT eligibility and outcomes post-transplantation, we conducted a retrospective analysis using real-world data collected at our center for adult patients who were evaluated for alloHSCT between January 2013 and December 2020 and identified 511 eligible patients. The most common primary disease was acute myeloid leukemia, in 49% of patients, followed by myelodysplastic syndrome (23%), lymphoma (11%), and acute lymphocytic leukemia (10%). Abnormal screening chest CT results were found in 199 patients (39%). The most frequent detected abnormality was pulmonary nodule, in 78 patients (35%), followed by consolidation in 42 (19%), ground-glass opacification in 33 (15%), bronchitis and bronchiolitis in 25 (11%), pleural effusions in 14 (6%), and new primary cancer in 7 (2%). CXR detected abnormalities in only approximately one-half of the patients (48%) with an abnormal chest CT scan. Among the 199 patients with an abnormal chest CT scan, 98 (49%) underwent further assessment and/or intervention before transplantation. The most common workup was pulmonary consultation in 32%, followed by infectious diseases consultation in 24%. Lung biopsy was obtained in 20%, and antimicrobial therapy was initiated after confirming an infection diagnosis in 20%. Patients with an abnormal chest CT scan demonstrated worse overall survival (P = .032), nonrelapse mortality (P = .015), and pulmonary-related mortality (P < .001) compared to those with a normal chest CT scan. Our study suggests that pretransplantation screening chest CT is beneficial in uncovering invasive infections and underlying malignancies and allows for appropriate interventions before alloHSCT to prevent potentially serious post-transplantation complications without causing a delay in alloHSCT. Nevertheless, abnormal CT findings prior to transplantation may be associated with overall worse prognosis.

Predictors of Covid-19 Vaccination Response After In-Vivo T-Cell-Depleted Stem Cell Transplantation.

Covid-19 vaccination is recommended in allogeneic transplant recipients, but many questions remain regarding its efficacy. Here we studied serologic responses in 145 patients who had undergone allogeneic transplantation using in vivo T-cell depletion. Median age was 57 (range 21-79) at transplantation and 61 (range 24-80) at vaccination. Sixty-nine percent were Caucasian. One third each received transplants from HLA-identical related (MRD), adult unrelated (MUD), or haploidentical-cord blood donors. Graft-versus-host disease (GVHD) prophylaxis involved in-vivo T-cell depletion using alemtuzumab for MRD or MUD transplants and anti-thymocyte globulin for haplo-cord transplants. Patients were vaccinated between January 2021 and January 2022, an average of 31 months (range 3-111 months) after transplantation. Sixty-one percent received the BNT162b2 (bioNtech/Pfizer) vaccine, 34% received mRNA-1273 (Moderna), and 5% received JNJ-78436735 (Johnson & Johnson). After the initial vaccinations (2 doses for BNT162b2 and mRNA-1273, 1 dose for JNJ-7843673), 124 of the 145 (85%) patients had a detectable SARS-CoV-2 spike protein (S) antibody, and 21 (15%) did not respond. Ninety-nine (68%) had high-level responses (≥100 binding antibody units [BAU]/mL)m and 25 (17%) had a low-level response (<100 BAU/mL). In multivariable analysis, lymphocyte count less than 1 × 109/ mL, having chronic GVHD, and being vaccinated in the first year after transplantation emerged as independent predictors for poor response. Neither donor source nor prior exposure to rituximab was predictive of antibody response. SARS-CoV-2 vaccination induced generally high response rates in recipients of allogeneic transplants including recipients of umbilical cord blood transplants and after in-vivo T cell depletion. Responses are less robust in those vaccinated in the first year after transplantation, those with low lymphocyte counts, and those with chronic GVHD.

Axicabtagene Ciloleucel in Patients Ineligible for ZUMA-1 Because of CNS Involvement and/or HIV: A Multicenter Experience.

Secondary central nervous system lymphoma (SCNSL) is associated with poor prognosis and new therapeutic approaches are needed. The pivotal trial that led to US Food and Drug Administration (FDA) approval of axicabtagene ciloleucel excluded patients with SCNSL and human immunodeficiency virus. In this multi-institutional retrospective study, 14 SCNSL patients treated with axicabtagene ciloleucel, 3 of whom had human immunodeficiency virus, experienced rates of severe neurotoxicity and complete response of 32% and 58%, respectively. This is similar to rates observed in the pivotal ZUMA-1 trial that led to the approval of axi-cel at median follow-up of 5.9 months. Chimeric antigen receptor T-cell therapy is potentially a life-saving therapy for SCNSL patients and should not be withheld.

Long-term clinical outcomes of tisagenlecleucel in patients with relapsed or refractory aggressive B-cell lymphomas (JULIET): a multicentre, open-label, single-arm, phase 2 study.

BACKGROUND: In the primary analysis of the pivotal JULIET trial of tisagenlecleucel, an autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, the best overall response rate was 52% and the complete response rate was 40% in 93 evaluable adult patients with relapsed or refractory aggressive B-cell lymphomas. We aimed to do a long-term follow-up analysis of the clinical outcomes and correlative analyses of activity and safety in the full adult cohort. METHODS: In this multicentre, open-label, single-arm, phase 2 trial (JULIET) done at 27 treatment sites in ten countries (Australia, Austria, Canada, France, Germany, Italy, Japan, the Netherlands, Norway, and the USA), adult patients (≥18 years) with histologically confirmed relapsed or refractory large B-cell lymphomas who were ineligible for, did not consent to, or had disease progression after autologous haematopoietic stem-cell transplantation, with an Eastern Cooperative Oncology Group performance status of 0-1 at screening, were enrolled. Patients received a single intravenous infusion of tisagenlecleucel (target dose 5 × 108 viable transduced CAR T cells). The primary endpoint was overall response rate (ie, the proportion of patients with a best overall disease response of a complete response or partial response using the Lugano classification, as assessed by an independent review committee) at any time post-infusion and was analysed in all patients who received tisagenlecleucel (the full analysis set). Safety was analysed in all patients who received tisagenlecleucel. JULIET is registered with ClinialTrials.gov, NCT02445248, and is ongoing. FINDINGS: Between July 29, 2015, and Nov 2, 2017, 167 patients were enrolled. As of Feb 20, 2020, 115 patients had received tisagenlecleucel infusion and were included in the full analysis set. At a median follow-up of 40·3 months (IQR 37·8-43·8), the overall response rate was 53·0% (95% CI 43·5-62·4; 61 of 115 patients), with 45 (39%) patients having a complete response as their best overall response. The most common grade 3-4 adverse events were anaemia (45 [39%]), decreased neutrophil count (39 [34%]), decreased white blood cell count (37 [32%]), decreased platelet count (32 [28%]), cytokine release syndrome (26 [23%]), neutropenia (23 [20%]), febrile neutropenia (19 [17%]), hypophosphataemia (15 [13%]), and thrombocytopenia (14 [12%]). The most common treatment-related serious adverse events were cytokine release syndrome (31 [27%]), febrile neutropenia (seven [6%]), pyrexia (six [5%]), pancytopenia (three [3%]), and pneumonia (three [3%]). No treatment-related deaths were reported. INTERPRETATION: Tisagenlecleucel shows durable activity and manageable safety profiles in adult patients with relapsed or refractory aggressive B-cell lymphomas. For patients with large B-cell lymphomas that are refractory to chemoimmunotherapy or relapsing after second-line therapies, tisagenlecleucel compares favourably with respect to risk-benefit relative to conventional therapeutic approaches (eg, salvage chemotherapy). FUNDING: Novartis Pharmaceuticals.

Colonization With Fluoroquinolone-Resistant Enterobacterales Decreases the Effectiveness of Fluoroquinolone Prophylaxis in Hematopoietic Cell Transplant Recipients.

BACKGROUND: Levofloxacin prophylaxis is recommended to prevent gram-negative bloodstream infections (BSIs) in patients with prolonged chemotherapy-induced neutropenia. However, increasing fluoroquinolone resistance may decrease the effectiveness of this approach. METHODS: We assessed the prevalence of colonization with fluoroquinolone-resistant Enterobacterales (FQRE) among patients admitted for hematopoietic cell transplantation (HCT) from November 2016 to August 2019 and compared the risk of gram-negative BSI between FQRE-colonized and noncolonized patients. All patients received levofloxacin prophylaxis during neutropenia. Stool samples were collected upon admission for HCT and weekly thereafter until recovery from neutropenia, and underwent selective culture for FQRE. All isolates were identified and underwent antimicrobial susceptibility testing by broth microdilution. FQRE isolates also underwent whole-genome sequencing. RESULTS: Fifty-four of 234 (23%) patients were colonized with FQRE prior to HCT, including 30 of 119 (25%) allogeneic and 24 of 115 (21%) autologous HCT recipients. Recent antibacterial use was associated with FQRE colonization (P = .048). Ninety-one percent of colonizing FQRE isolates were Escherichia coli and 29% produced extended-spectrum ß-lactamases. Seventeen (31%) FQRE-colonized patients developed gram-negative BSI despite levofloxacin prophylaxis, compared to only 2 of 180 (1.1%) patients who were not colonized with FQRE on admission (P < .001). Of the 17 gram-negative BSIs in FQRE-colonized patients, 15 (88%) were caused by FQRE isolates that were genetically identical to the colonizing strain. CONCLUSIONS: Nearly one-third of HCT recipients with pretransplant FQRE colonization developed gram-negative BSI while receiving levofloxacin prophylaxis, and infections were typically caused by their colonizing strains. In contrast, levofloxacin prophylaxis was highly effective in patients not initially colonized with FQRE.

Sequential intensive chemotherapy followed by autologous or allogeneic transplantation for refractory lymphoma.

We evaluate the safety of bendamustine as a bridge to stem cell transplantation (SCT) in patients with relapsed/refractory lymphoma and residual disease after salvage therapy. Thirty-four subjects without complete responses (CR) received bendamustine 200 mg/m2/day for 2 days followed 14 days later by SCT. Sixteen subjects in partial remission (PR) with maximal FDG-PET SUVs ≤8 prior to bendamustine received autologous SCT, while 13 with suboptimal responses were allografted. Five subjects did not proceed to transplant. No bendamustine toxicities precluded transplantation and no detrimental effect on engraftment or early treatment-related mortality (TRM) was attributable to bendamustine. At 1 year, 75% of auto-recipients and 31% of allo-recipients were alive with CR. Two subjects in the autologous arm developed therapy-related myeloid neoplasia (t-MN). In conclusion, a bendamustine bridge to SCT can be administered without early toxicity to patients with suboptimal responses to salvage chemotherapy. However this approach may increase the risk of t-MN. (NCT02059239).Supplemental data for this article is available online at here.

Specific Class I HLA Supertypes but Not HLA Zygosity or Expression Are Associated with Outcomes following HLA-Matched Allogeneic Hematopoietic Cell Transplant: HLA Supertypes Impact Allogeneic HCT Outcomes.

Maximizing the probability of antigen presentation to T cells through diversity in HLAs can enhance immune responsiveness and translate into improved clinical outcomes, as evidenced by the association of heterozygosity and supertypes at HLA class I loci with improved survival in patients with advanced solid tumors treated with immune checkpoint inhibitors. We investigated the impact of HLA heterozygosity, supertypes, and surface expression on outcomes in adult and pediatric patients with acute myeloid leukemia (AML), myelodysplastic syndrome, acute lymphoblastic leukemia, and non-Hodgkin lymphoma who underwent 8/8 HLA-matched, T cell replete, unrelated, allogeneic hematopoietic cell transplant (HCT) from 2000 to 2015 using patient data reported to the Center for International Blood and Marrow Transplant Research. HLA class I heterozygosity and HLA expression were not associated with overall survival, relapse, transplant-related mortality (TRM), disease-free survival (DFS), and acute graft-versus-host disease following HCT. The HLA-B62 supertype was associated with decreased TRM in the entire patient cohort (hazard ratio [HR], 0.79; 95% CI, 0.69 to 0.90; P = .00053). The HLA-B27 supertype was associated with worse DFS in patients with AML (HR = 1.21; 95% CI, 1.10 to 1.32; P = .00005). These findings suggest that the survival benefit of HLA heterozygosity seen in solid tumor patients receiving immune checkpoint inhibitors does not extend to patients undergoing allogeneic HCT. Certain HLA supertypes, however, are associated with TRM and DFS, suggesting that similarities in peptide presentation between supertype members play a role in these outcomes. Beyond implications for prognosis following HCT, these findings support the further investigation of these HLA supertypes and the specific immune peptides important for transplant outcomes.

Adoptive immunotherapy with CB following chemotherapy for patients with refractory myeloid malignancy: chimerism and response.

We conducted a prospective evaluation of cord blood (CB)-derived adoptive cell therapy, after salvage chemotherapy, for patients with advanced myeloid malignancies and poor prognosis. Previously, we reported safety, feasibility, and preliminary efficacy of this approach. We present updated results in 31 patients who received intensive chemotherapy followed by CB infusion and identify predictors of response. To enhance the antileukemic effect, we selected CB units (CBU) with shared inherited paternal antigens and/or noninherited maternal antigens with the recipients. Twenty-eight patients with acute myeloid leukemia (AML), 2 with myelodysplastic syndrome, and 1 in chronic myeloid leukemia myeloid blast crisis were enrolled; 9 had relapsed after allogeneic transplant. Response was defined as <5% blasts in hypocellular bone marrow at 2 weeks after treatment. Thirteen patients (42%) responded; a rate higher than historical data with chemotherapy only. Twelve had CBU-derived chimerism detected; chimerism was a powerful predictor of response (P < .001). CBU lymphocyte content and a prior transplant were associated with chimerism (P < .01). Safety was acceptable: 3 patients developed mild cytokine release syndrome, 2 had grade 1 and 2 had grade 4 graft-versus-host disease. Seven responders and 6 nonresponders (after additional therapy) received subsequent transplant; 5 are alive (follow-up, 5-47 months). The most common cause of death for nonresponders was disease progression, whereas for responders it was infection. CB-derived adoptive cell therapy is feasible and efficacious for refractory AML. Banked CBU are readily available for treatment. Response depends on chimerism, highlighting the graft-versus-leukemia effect of CB cell therapy. This trial was registered at www.clinicaltrials.gov as #NCT02508324.

Publisher Correction: Manufacturing and preclinical validation of CAR T cells targeting ICAM-1 for advanced thyroid cancer therapy.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Manufacturing and preclinical validation of CAR T cells targeting ICAM-1 for advanced thyroid cancer therapy.

While the majority of thyroid cancer patients are easily treatable, those with anaplastic or poorly differentiated recurrent thyroid carcinomas have a very poor prognosis with a median survival of less than a year. Previously, we have shown a significant correlation between ICAM-1 overexpression and malignancy in thyroid cancer, and have pioneered the use of ICAM-1 targeted CAR T cells as a novel treatment modality. For clinical translation of this novel modality, we designed CAR T cells possessing micromolar rather than nanomolar affinity to ICAM-1 to avoid cytotoxicity in normal cells with basal levels of ICAM-1 expression. Herein, we report the automated process of CAR T cell manufacturing with CliniMACS Prodigy (Miltenyi Biotec) using cryopreserved peripheral blood leukocytes from apheresis collections. Using Prodigy, thawed leukopak cells were enriched for CD4+ and CD8+ T cells, subjected to double transduction using lentiviral vector, and expanded in culture for a total of 10 days with a final yield of 2-4 × 109 cells. The resulting CAR T cells were formulated for cryopreservation to be used directly for infusion into patients after thawing with no further processing. We examined cross-reactivity of CAR T cells toward both human and murine ICAM-1 and ICAM-1 expression in human and mouse tissues to demonstrate that both efficacy and on-target, off-tumor toxicity can be studied in our preclinical model. Selective anti-tumor activity in the absence of toxicity provides proof-of-concept that micromolar affinity tuned CAR T cells can be used to target tumors expressing high levels of antigen while avoiding normal tissues expressing basal levels of the same antigen. These studies support the initiation of a phase I study to evaluate the safety and potential efficacy of micromolar affinity tuned CAR T cells against newly diagnosed anaplastic and refractory or recurrent thyroid cancers.

Adoptive Immunotherapy with Cord Blood for the Treatment of Refractory Acute Myelogenous Leukemia: Feasibility, Safety, and Preliminary Outcomes.

Adoptive immunotherapy has shown efficacy in patients with relapsed/refractory acute myelogenous leukemia (AML). We conducted a prospective evaluation of cord blood (CB)-based adoptive cell therapy following salvage chemotherapy in patients with AML or myelodysplastic syndrome (MDS) and describe the safety and early outcomes of this approach. To enhance the antileukemic effect, we selected CB units (CBUs) with a shared inherited paternal antigen (IPA) and/or noninherited maternal antigen (NIMA) match with the recipients. Furthermore, the CBUs had total nucleated cell (TNC) dose <2.5 × 107/kg and were at least 4/6 HLA-matched with the patients; a higher allele-level match was preferred. Heavily pretreated adult patients with AML/MDS were enrolled. CBU searches were performed for 50 patients. CBUs with shared IPA targets were identified for all, and CBUs with NIMA matches were found for 80%. Twenty-one patients underwent treatment (AML, primary induction failure, n = 8; refractory relapse, n = 10, including 7 recipients of previous allogeneic HSCT; blast crisis chronic myelogenous leukemia, n = 1; MDS, n = 2). Most received combination chemotherapy; those not fit for intensive treatment received a hypomethylating agent. Response was defined as <10% residual blasts in hypocellular bone marrow at approximately 2 weeks after treatment. Ten of the 19 evaluable patients responded, including 5 of the 7 recipients of previous transplant. Response was seen in 4 of 4 patients with full CBU-derived chimerism, 2 of 2 of those with partial, low-level chimerism and 4 of 12 of the recipients with no detectable CBU chimerism. The most common adverse events were infections (bacterial, n = 5; viral, n = 2; fungal, n = 5). Grade IV acute graft-versus-host disease (GVHD) developed in 2 patients with full CBU chimerism; 2 other patients had grade 1 skin GVHD. A total of 11 patients died, 7 from disease recurrence and 4 from infections (1 early death; the other 3 in remission at the time of death). Overall, 12 patients proceeded to allogeneic HSCT; of those, 7 had responded to treatment, 3 had not (and had received additional therapy), and 2 had persistent minimal residual disease. In conclusion, the use of CB as adoptive immunotherapy in combination with salvage chemotherapy for patients with refractory AML/MDS is feasible, can induce disease control, can serve as a bridge to allogeneic HSCT, and has an acceptable incidence of adverse events. Alloreactivity was enhanced through the selection of CBUs targeting a shared IPA and/or NIMA match with the patients. CBUs with lower cell doses, already available in the CB bank and unlikely to be adequate grafts for adult transplants, can be used for cell therapy within a short time frame.

Granulocyte Colony-Stimulating Factor Use after Autologous Peripheral Blood Stem Cell Transplantation: Comparison of Two Practices.

Administration of granulocyte colony-stimulating factor (G-CSF) after autologous peripheral blood stem cell transplantation (PBSCT) is generally recommended to reduce the duration of severe neutropenia; however, data regarding the optimal timing of G-CSFs post-transplantation are limited and conflicting. This retrospective study was performed at NewYork-Presbyterian/Weill Cornell Medical Center between November 5, 2013, and August 9, 2016, of adult inpatient autologous PBSCT recipients who received G-CSF empirically starting on day +5 (early) versus on those who received G-CSF on day +12 only if absolute neutrophil count (ANC) was <0.5 × 109/L (ANC-driven). G-CSF was dosed at 300 µg in patients weighing <75 kg and 480 µg in those weighing ≥75 kg. One hundred consecutive patients underwent autologous PBSCT using either the early (n = 50) or ANC-driven (n = 50) G-CSF regimen. Patient and transplantation characteristics were comparable in the 2 groups. In the ANC-driven group, 24% (n = 12) received G-CSF on day +12 and 60% (n = 30) started G-CSF earlier due to febrile neutropenia or at the physician's discretion, 6% (n = 3) started after day +12 at the physician's discretion, and 10% (n = 5) did not receive any G-CSF. The median start day of G-CSF therapy was day +10 in the ANC-driven group versus day +5 in the early group (P < .0001). For the primary outcome, the median time to neutrophil engraftment was 12 days (interquartile range [IQR] 11-13 days) in the early group versus 13 days (IQR, 12-14 days) in the ANC-driven group (P = .07). There were no significant between-group differences in time to platelet engraftment, 1-year relapse rate, or 1-year overall survival. The incidence of febrile neutropenia was 74% in the early group versus 90% in the ANC-driven group (P = .04); however, there was no significant between-group difference in the incidence of positive bacterial cultures or transfer to the intensive care unit. The duration of G-CSF administration until neutrophil engraftment was 6 days in the early group versus 3 days in the ANC-driven group (P < .0001). The median duration of post-transplantation hospitalization was 15 days (IQR, 14-19 days) in the early group versus 16 days (IQR, 15-22 days) in the ANC-driven group (P = .28). Our data show that early initiation of G-CSF (on day +5) and ANC-driven initiation of G-CSF following autologous PBSCT were associated with a similar time to neutrophil engraftment, length of stay post-transplantation, and 1-year overall survival.

DNMT3A Mutational Status Affects the Results of Dose-Escalated Induction Therapy in Acute Myelogenous Leukemia.

PURPOSE: DNA methyltransferase 3A (DNMT3A) is one of the commonly mutated genes in acute myelogenous leukemia (AML). Reports on the prognostic significance of DNMT3A mutations have been inconsistent, and most of the data are available only for patients 60 years of age or younger. We hypothesized that this inconsistency is due to an interaction between the dose of anthracycline used in induction therapy and DNMT3A status. We studied whether patients with DNMT3A-mutated AML treated with standard dose anthracyclines had an inferior survival compared with patients with other mutation profiles or those who received high-dose therapy. EXPERIMENTAL DESIGN: A total of 152 patients in this retrospective cohort study (median age, 54 years) with de novo AML underwent induction therapy and next-generation sequencing of 33 commonly mutated genes in hematologic malignancies, including DNMT3A, FLT3-ITD, NPM1, and IDH1/2. Cox regression was used to know whether those with DNMT3A mutations who were treated with standard dose anthracycline had inferior survival. RESULTS: DNMT3A mutations, found in 32% of patients, were not associated with an inferior survival. Dose escalation of anthracycline in the induction regimen was associated with improved survival in those with DNMT3A mutations but not those with wild-type DNMT3A. Patients with DNMT3A mutations who received standard dose induction had shorter survival time than other patient groups (10.1 months vs. 19.8 months, P = 0.0129). This relationship remained significant (HR, 1.90; P = 0.006) controlling for multiple variables. CONCLUSIONS: Patients with DNMT3A-mutated AML have an inferior survival when treated with standard-dose anthracycline induction therapy. This group should be considered for high-dose induction therapy.

Interleukin 6 mediated recruitment of mesenchymal stem cells to the hypoxic tumor milieu.

Mesenchymal stem cells (MSCs) are a heterogeneous population of non-hematopoietic precursor cells predominantly found in the bone marrow. They have been recently reported to home towards the hypoxic tumor microenvironment in vivo. Interleukin-6 is a multifunctional cytokine normally involved in the regulation of the immune and inflammatory response. In addition to its normal function, IL-6 signaling has been implicated in tumorigenesis. Solid tumors develop hypoxia as a result of inadequate O(2) supply. Interestingly, tumor types with increased levels of hypoxia are known to have increased resistance to chemotherapy as well as increased metastatic potential. Here, we present evidence that under hypoxic conditions (1.5% O(2)) breast cancer cells secrete high levels of IL-6, which serve to activate and attract MSCs. We now report that secreted IL-6 acts in a paracrine fashion on MSCs stimulating the activation of both Stat3 and MAPK signaling pathways to enhance migratory potential and cell survival. Inhibition of IL-6 signaling utilizing neutralizing antibodies leads to attenuation of MSC migration. Specifically, increased migration is dependent on IL-6 signaling through the IL-6 receptor. Collectively, our data demonstrate that hypoxic tumor cells specifically recruit MSCs, which through activation of signaling and survival pathways facilitate tumor progression.

The RSC nucleosome-remodeling complex is required for Cohesin's association with chromosome arms.

The fidelity of chromosome segregation requires that the cohesin protein complex bind together newly replicated sister chromatids both at centromeres and at discrete sites along chromosome arms. Segregation of the yeast 2 micro plasmid also requires cohesin, which is recruited to the plasmid partitioning locus. Here we report that the RSC chromatin-remodeling complex regulates the differential association of cohesin with centromeres and chromosome arms. RSC cycles on and off chromosomal arm and plasmid cohesin binding sites in a cell cycle-regulated manner 15 min preceding Mcd1p, the central cohesin subunit. We show that in rsc mutants Mcd1p fails to associate with chromosome arms but still binds to centromeres, and that consequently, the arm regions of mitotic sister chromosomes separate precociously while cohesion at centromeres is unaffected. Our data suggest a role for RSC in facilitating the loading of cohesin specifically onto chromosome arms, thereby ensuring sister chromatid cohesion and proper chromosome segregation.

The yeast RSC chromatin-remodeling complex is required for kinetochore function in chromosome segregation.

The accurate segregation of chromosomes requires the kinetochore, a complex protein machine that assembles onto centromeric DNA to mediate attachment of replicated sister chromatids to the mitotic spindle apparatus. This study reveals an important role for the yeast RSC ATP-dependent chromatin-remodeling complex at the kinetochore in chromosome transmission. Mutations in genes encoding two core subunits of RSC, the ATPase Sth1p and the Snf5p homolog Sfh1p, interact genetically with mutations in genes encoding kinetochore proteins and with a mutation in centromeric DNA. RSC also interacts genetically and physically with the histone and histone variant components of centromeric chromatin. Importantly, RSC is localized to centromeric and centromere-proximal chromosomal regions, and its association with these loci is dependent on Sth1p. Both sth1 and sfh1 mutants exhibit altered centromeric and centromere-proximal chromatin structure and increased missegregation of authentic chromosomes. Finally, RSC is not required for centromeric deposition of the histone H3 variant Cse4p, suggesting that RSC plays a role in reconfiguring centromeric and flanking nucleosomes following Cse4p recruitment for proper chromosome transmission.

Yeast RSC function is required for organization of the cellular cytoskeleton via an alternative PKC1 pathway.

RSC is a 15-protein ATP-dependent chromatin-remodeling complex related to Snf-Swi, the prototypical ATP-dependent nucleosome remodeler in budding yeast. Despite insight into the mechanism by which purified RSC remodels nucleosomes, little is known about the chromosomal targets or cellular pathways in which RSC acts. To better understand the cellular function of RSC, a screen was undertaken for gene dosage suppressors of sth1-3ts, a temperature-sensitive mutation in STH1, which encodes the essential ATPase subunit. Slg1p and Mid2p, two type I transmembrane stress sensors of cell wall integrity that function upstream of protein kinase C (Pkc1p), were identified as multicopy suppressors of sth1-3ts cells. Although the sth1-3ts mutant exhibits defects characteristic of PKC1 pathway mutants (caffeine and staurosporine sensitivities and an osmoremedial phenotype), only upstream components and not downstream effectors of the PKC1-MAP kinase pathway can suppress defects conferred by sth1-3ts, suggesting that RSC functions in an alternative PKC1-dependent pathway. Moreover, sth1-3ts cells display defects in actin cytoskeletal rearrangements and are hypersensitive to the microtubule depolymerizing drug, TBZ; both of these defects can be corrected by the high-copy suppressors. Together, these data reveal an important functional connection between the RSC remodeler and PKC1-dependent signaling in regulating the cellular architecture.