Immune checkpoint blockade in hematological malignancies: current state and future potential

Malignant cells are known to evade immune surveillance by engaging immune checkpoints which are negative regulators of the immune system. By restoring the T-lymphocyte mediated anti-tumor effect, immune checkpoint inhibitors (ICI) have revolutionized the treatment of solid tumors but have met rather modest success in hematological malignancies. Currently, the only FDA approved indications for ICI therapy are in classic hodgkin lymphoma and primary mediastinal B cell lymphoma. Multiple clinical trials have assessed ICI therapy alone and in combination with standard of care treatments in other lymphomas, plasma cell neoplasms and myeloid neoplasms but were noted to have limited efficacy. These trials mostly focused on PD-1/PDL-1 and CTLA-4 inhibitors. Recently, there has been an effort to target other T-lymphocyte checkpoints like LAG-3, TIM-3, TIGIT along with improving strategies of PD-1/PDL-1 and CTLA-4 inhibition. Drugs targeting the macrophage checkpoint, CD47, are also being tested. Long term safety and efficacy data from these ongoing studies are eagerly awaited. In this comprehensive review, we discuss the mechanism of immune checkpoint inhibitors, the key takeaways from the reported results of completed and ongoing studies of these therapies in the context of hematological malignancies.

Evaluation of different pharmacokinetically guided IV busulfan exposure ranges on adult patient outcomes after hematopoietic stem cell transplantation

Conditioning intensity contributes significantly to outcomes in allogeneic hematopoietic stem cell transplantation (allo-HSCT). We evaluated two myeloablative conditioning dosing ranges of intravenous (IV) busulfan (Bu) in combination with fludarabine in 70 patients. In 2015, our practice changed to target busulfan area under the curve (AUC) of ≥ 19.7 mg*h/L. We assessed responses in patients receiving busulfan AUCs of < 19.7 mg*h/L (Low-Bu) and ≥ 19.7 mg*h/L (High-Bu). At 18-month median follow-up, no differences in overall survival (OS) and relapse-free survival (RFS) were found between Low-Bu and High-Bu groups (p = 0.35 and p = 0.29, respectively). Relapses occurred in 25.7% of patients. No differences in median time to relapse were noted. Minimal residual disease (MRD)-positive patients had a shorter median OS and RFS than MRD-negative patients. No differences were found in OS and RFS between Low-Bu and High-Bu groups in MRD-positive patients (p = 0.86 and p = 0.83, respectively), or MRD-negative patients (p = 0.56 and p = 0.38, respectively). Non-relapsed mortality (NRM) at 100 days was 3.4% vs. 4.1% in the Low-Bu vs. High-Bu groups. There were no significant differences in the incidence of acute-graft-versus-host disease (aGVHD) (71.4% vs. 63.4%) or chronic GVHD (cGVHD) (48.3% vs. 43.9%) between the groups. The cumulative incidence of grades III-IV aGVHD was 24.1% in Low-Bu group and 22.4% in High-Bu group. In conclusion, targeting a busulfan AUC of > 19.7 mg*h/L with fludarabine does not appear to add an advantage in OS and RFS.

Cryopreserved versus fresh peripheral blood allogeneic stem cell transplantation outcomes in patients receiving post-transplant cyclophosphamide for graft-versus-host prophylaxis during the COVID-19 pandemic: a single center experience

BACKGROUND/OBJECTIVE

Cryopreservation of grafts is not common practice in allogeneic hematopoietic stem cell transplant (HSCT) recipients. However, our center had to use cryopreserved cells for allogeneic HSCT during the COVID-19 pandemic to avoid delays in transplantation due to uncertainty regarding patient and donor exposures.

STUDY DESIGN

We retrospectively evaluated post-transplant engraftment and survival outcomes of adult patients who received cryopreserved versus fresh allografts during the COVID-19 pandemic.

RESULTS

Fifty-five patients with hematologic malignancies received either cryopreserved (n = 34) or fresh (n = 21) allogeneic HSCT using peripheral blood stem cells between January 2020 and December 2020. At a median follow-up time of 15 months, cryopreserved allograft recipients had significantly lower overall survival (OS) (p = 0.02). They also experienced significantly delayed neutrophil (p = 0.01) and platelet engraftments (p < 0.0001), as well as higher red blood cell transfusion-dependence after day + 60 (67.6% vs. 28.6%; p = 0.01). Significantly more cryopreserved allograft recipients received donor lymphocyte infusion than fresh allograft recipients (35.3% vs. 4.8%, p = 0.01). Neither relapse-free survival nor non-relapse mortality differed significantly between the two groups.

CONCLUSION

Cryopreservation of allografts in combination with post-transplant cyclophosphamide may negatively affect engraftment and OS outcomes in HSCT recipients.

Outreach: Preliminary safety and efficacy results from a phase 2 study of lisocabtagene maraleucel (liso-cel) in the nonuniversity setting

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Background: Concerns about adverse events (AEs) related to CAR T cell therapy have resulted in administration of this therapy largely in an inpatient setting. OUTREACH (NCT03744676) evaluates safety and efficacy of liso-cel in patients (pts) with R/R large B-cell lymphoma (LBCL) across inpatient and outpatient settings at nonuniversity medical centers (NMCs). Methods: NMCs, including centers naïve to CAR T cell therapy, enrolled adults with R/R LBCL in this open-label, multicenter study. Eligible pts had R/R PET-positive disease after ≥2 lines of prior systemic therapy, ECOG PS ≤1, and adequate organ function. Prior autologous HSCT was allowed. Pts received sequential infusions of equal target doses of CD8+ and CD4+ cells at a total target dose of 100 × 106 CAR+ T cells. Primary endpoint was incidence of grade (G) ≥3 cytokine release syndrome (CRS) graded per 2014 Lee criteria, neurological events (NEs), prolonged cytopenias (Day 29 G ≥3 lab values), and infections. Secondary endpoints were safety and overall response rate (ORR). Outpatient AE monitoring/management was managed by a multidisciplinary CAR T cell therapy team following standard operating procedures (SOPs). Results: At data cutoff, 46 pts (inpatients n = 16, outpatients n = 30) were treated with liso-cel. Inpatients and outpatients had similar demographics and baseline disease characteristics; median age was 63 y (range, 34–83), 63% had diffuse LBCL not otherwise specified, and 91% were refractory to last therapy. Safety data were similar across inpatients and outpatients (Table). Early (study Day ≤4) and overall hospitalization in outpatients was reported in 27% and 63%, respectively; median time to hospitalization was 5 (2–61) days and median length of stay was 6 (1–28) days. For efficacy-evaluable pts (n = 44), ORR was 75% for inpatients and 79% for outpatients; CR rates were 50% and 61%, respectively. Conclusions: Liso-cel was successfully administered to pts with R/R LBCL in the outpatient setting and pts were monitored for CAR T cell therapy–related toxicities by multidisciplinary teams using SOPs. The incidences of severe CRS and NEs and use of tocilizumab and/or corticosteroids were similar in inpatients and outpatients, and consistent with the pivotal study observations (Abramson, The Lancet 2020). Updated data with longer follow-up will be presented. Clinical trial information: NCT03744676. [Table: see text]

Preliminary analysis of a phase 1/2 study of NEXI-001 donor-derived multi-antigen-specific CD8+ T-cells for the treatment of relapsed acute myeloid leukemia (AML) after allogeneic hematopoietic cell transplantation (HCT)

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Background: Allogeneic HCT is a potentially curative therapy for many patients with AML that relies on a graft-versus-leukemia (GvL) effect. Patients who relapse after allogeneic HCT have a poor prognosis and few treatment options. Donor lymphocyte infusion (DLI) can achieve a GvL effect in some patients, however, efficacy is frequently associated with the development graft-versus-host disease (GVHD). There is a substantial need for treatment approaches that enhance the benefit of GVL while decoupling toxicities associated with GVHD. Methods: We report ongoing results from a first-in-human study (NCT04284228) of a non-genetically engineered, donor-derived adoptive cellular therapy product, NEXI-001, which contains multiple populations of CD8+ T cells that recognize different HLA 02.01-restricted peptides from the WT1, PRAME, and Cyclin A1 antigens. NEXI-001 contains T cell memory subtypes that combine anti-tumor potency with long-term persistence. Results: At the time of this analysis, 7 patients with relapsed AML after allogeneic HCT were enrolled. Five Patients were treated with single infusions of NEXI-001 at three different dose levels: 50, 100 and 200 million. Currently, the median follow-up is 5 months. Significantly, GVHD, cytokine release syndrome, neurotoxicity, or NEXI-001-related adverse events were not observed. NEXI-001 treatment resulted in reductions in red blood cell and platelet transfusions and increased donor chimerism. Decreases in myeloblasts in bone marrow and peripheral blood and reduction in the size of an extramedullary myeloid sarcoma were suggestive of an anti-leukemia effect (Table). Correlative studies indicate that NEXI-001 CD8+ cells undergo a rapid proliferation after infusion and are also associated with a robust hostlymphocyte recovery that occurs as quickly Day 3 after infusion. NEXI-001 infused CD8+T cells are detectable by multimer staining in peripheral blood of patients and proliferate over time. TCR sequencing analyses determined that infused NEXI-001 cells contain T cell clones that were undetectable in the peripheral blood of patients at baseline but were detected in blood and bone marrow and persist over time. Conclusions: NEXI-001 has the potential to enhance GvL effect without the associated toxicities of GVHD, cytokine release syndrome, and neurotoxicity. Due to these encouraging results, the trial will proceed with an evaluation of repeated NEXI-001 dosing Clinical trial information: NCT04284228. [Table: see text]

Comparison of Myeloablative versus Reduced-Intensity Conditioning Regimens in Allogeneic Stem Cell Transplantation Recipients with Acute Myelogenous Leukemia with Measurable Residual Disease-Negative Disease at the Time of Transplantation: A Retrospective Cohort Study

The ideal conditioning intensity in allogeneic hematopoietic stem cell transplantation (HSCT) is evolving. Previous prospective studies comparing myeloablative conditioning (MAC) versus reduced-intensity conditioning (RIC) regimens in adults with acute myelogenous leukemia (AML) have shown mixed results. In many of these studies, patients were not stratified based on measurable residual disease (MRD). We evaluated the effect of conditioning intensity on the outcomes of AML patients in complete remission (CR) with flow cytometry evidence of MRD negativity. A total of 135 patients age 20 to 75 years with AML in CR1 or CR2 and flow cytometry evidence of MRD negativity who underwent allogeneic HSCT at our center between 2011 and 2019 were evaluated. We compared overall survival (OS), relapse-free survival (RFS), nonrelapse mortality (NRM), relapse, and acute and chronic graft-versus-host disease (GVHD) in recipients of MAC (n = 89) and RIC (n = 46). Although the patients receiving RIC were older (62 versus 51 years; P < .0001), there were no statistically significant differences between the groups in terms of Eastern Cooperative Oncology Group and European Leukemia Network risk criteria and disease status (CR1 or CR2) at the time of transplantation. At a median follow-up of 24.6 months, no statistically significant differences in OS (hazard ratio [HR], 0.78; 95% confidence interval [CI] 0.42 to 1.42, P = .411) or RFS (HR, 1.004; 95% CI, 0.48 to 2.09, P = .99) were identified. The cumulative incidence of NRM (HR, 0.595; 95% CI, 0.24 to 1.48; P = .2644) and relapse (HR, 1.007; 95% CI, 0.45 to 2.23; P = .9872) was not different between the 2 groups. Grade II-IV and grade III-IV acute GVHD were more frequent in the MAC group (39.3% verses 19.9% [P = .018] and 19.3% versus 2.3% [P < .001], respectively), as was moderate/severe chronic GVHD (23.6% versus 15.8%; P = .038). Our data indicate that conditioning intensity did not appear to affect OS, RFS, NRM, and relapse risk in patients with MRD-negative AML as measured by flow cytometry. RIC resulted in less severe acute and chronic GVHD.

Targeting the Complement Alternative Pathway Permits Graft Versus Leukemia Activity while Preventing Graft Versus Host Disease

PURPOSE

Application of allogeneic hematopoietic cell transplantation (allo-HCT) for patients with hematologic disorders is limited by the development of GVHD. Separation of GVHD and graft-versus-leukemia (GVL) remains a great challenge in the field. We investigated the contribution of individual pathways involved in the complement cascade in GVH and GVL responses to identify specific targets by which to separate these two processes.

EXPERIMENTAL DESIGN

We used multiple preclinical murine and human-to-mouse xenograft models involving allo-HCT recipients lacking components of the alternative pathway (AP) or classical pathway (CP)/lectin pathway (LP) to dissect the role of each individual pathway in GVHD pathogenesis and the GVL effect. For translational purposes, we used the AP-specific complement inhibitor, CR2-fH, which localizes in injured target organs to allow specific blockade of complement activation at sites of inflammation.

RESULTS

Complement deposition was evident in intestines of mice and patients with GVHD. In a preclinical setting, ablation of the AP, but not the CP/LP, significantly improved GVHD outcomes. Complement activation through the AP in host hematopoietic cells, and specifically dendritic cells (DC), was required for GVHD progression. AP deficiency in recipients decreased donor T-cell migration and Th1/Th2 differentiation, while increasing the generation of regulatory T cells. This was because of decreased activation and stimulatory activity of recipient DCs in GVHD target organs. Treatment with CR2-fH effectively prevented GVHD while preserving GVL activity.

CONCLUSIONS

This study highlights the AP as a new therapeutic target to prevent GVHD and tumor relapse after allo-HCT. Targeting the AP by CR2-fH represents a promising therapeutic approach for GVHD treatment.

Antigen-specific T cell Redirectors: a nanoparticle based approach for redirecting T cells

Redirection of T cells to target and destroy tumors has become an important clinical tool and major area of research in tumor immunology. Here we present a novel, nanoparticle-based approach to selectively bind antigen-specific cytotoxic T cells (CTL) and redirect them to kill tumors, termed ATR (Antigen-specific T cell Redirectors). ATR were generated by decorating nanoparticles with both an antigen-specific T cell binding moiety, either peptide loaded MHC-Ig dimer or clonotypic anti-TCR antibody, and a model tumor cell binding moiety, anti-CD19 antibody to engage CD19+ tumor cells. ATR stably bind tumor cells and CTL in a dose dependent fashion and stimulate antigen-specific conjugate formation between those cells. ATR induced redirected lysis of tumor cells in vitro, as demonstrated by 51Cr-release killing. In vivo ATR administration led to reduced tumor growth in a SCID/beige human lymphoma treatment model. In summary, ATR represent a novel, nanoparticle based approach for redirecting antigen-specific CTL to kill tumors.

Enrichment and Expansion with Nanoscale Artificial Antigen Presenting Cells for Adoptive Immunotherapy

Adoptive immunotherapy (AIT) can mediate durable regression of cancer, but widespread adoption of AIT is limited by the cost and complexity of generating tumor-specific T cells. Here we develop an Enrichment + Expansion strategy using paramagnetic, nanoscale artificial antigen presenting cells (aAPC) to rapidly expand tumor-specific T cells from rare naïve precursors and predicted neo-epitope responses. Nano-aAPC are capable of enriching rare tumor-specific T cells in a magnetic column and subsequently activating them to induce proliferation. Enrichment + Expansion resulted in greater than 1000-fold expansion of both mouse and human tumor-specific T cells in 1 week, with nano-aAPC based enrichment conferring a proliferation advantage during both in vitro culture and after adoptive transfer in vivo. Robust T cell responses were seen not only for shared tumor antigens, but also for computationally predicted neo-epitopes. Streamlining the rapid generation of large numbers of tumor-specific T cells in a cost-effective fashion through Enrichment + Expansion can be a powerful tool for immunotherapy.

Complement: an overview for the clinician

The complement system is an essential component of the immune system. It is a highly integrative system and has a number of functions, including host defense, removal of injured cells and debris, modulation of metabolic and regenerative processes, and regulation of adaptive immunity. Complement is activated via different pathways and it is regulated tightly by several mechanisms to prevent host injury. Imbalance between complement activation and regulation can manifest in disease and injury to self. This article provides an outline of complement activation pathways, regulatory mechanisms, and normal physiologic functions of the system.

CD47 Enhances In Vivo Functionality of Artificial Antigen-Presenting Cells

PURPOSE

Artificial antigen-presenting cells, aAPC, have successfully been used to stimulate antigen-specific T-cell responses in vitro as well as in vivo. Although aAPC compare favorably with autologous dendritic cells in vitro, their effect in vivo might be diminished through rapid clearance by macrophages. Therefore, to prevent uptake and minimize clearance of aAPC by macrophages, thereby increasing in vivo functionality, we investigated the efficiency of "don't eat me" three-signal aAPC compared with classical two-signal aAPC.

EXPERIMENTAL DESIGN

To generate "don't eat me" aAPC, CD47 was additionally immobilized onto classical aAPC (aAPC(CD47+)). aAPC and aAPC(CD47+) were analyzed in in vitro human primary T-cell and macrophage cocultures. In vivo efficiency was compared in a NOD/SCID T-cell proliferation and a B16-SIY melanoma model.

RESULTS

This study demonstrates that aAPC(CD47+) in coculture with human macrophages show a CD47 concentration-dependent inhibition of phagocytosis, whereas their ability to generate and expand antigen-specific T cells was not affected. Furthermore, aAPC(CD47+)-generated T cells displayed equivalent killing abilities and polyfunctionality when compared with aAPC-generated T cells. In addition, in vivo studies demonstrated an enhanced stimulatory capacity and tumor inhibition of aAPC(CD47+) over normal aAPC in conjunction with diverging biodistribution in different organs.

CONCLUSIONS

Our data for the first time show that aAPC functionalized with CD47 maintain their stimulatory capacity in vitro and demonstrate enhanced in vivo efficiency. Thus, these next-generation aAPC(CD47+) have a unique potential to enhance the application of the aAPC technology for future immunotherapy approaches.

Adoptive T cell immunotherapy for cancer

Harnessing the immune system to recognize and destroy tumor cells has been the central goal of anti-cancer immunotherapy. In recent years, there has been an increased interest in optimizing this technology in order to make it a clinically feasible treatment. One of the main treatment modalities within cancer immunotherapy has been adoptive T cell therapy (ACT). Using this approach, tumor-specific cytotoxic T cells are infused into cancer patients with the goal of recognizing, targeting, and destroying tumor cells. In the current review, we revisit some of the major successes of ACT, the major hurdles that have been overcome to optimize ACT, the remaining challenges, and future approaches to make ACT widely available.

Paroxysmal nocturnal hemoglobinuria and the age of therapeutic complement inhibition

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease of hematopoietic stem cells due to a mutation in the PIG-A gene leading to a deficiency of GPI-anchored proteins. Lack of two specific GPI-anchored proteins, CD55 and CD59, leads to uncontrolled complement activation that result in both intravascular and extravascular hemolysis. Free hemoglobin leads to nitric oxide depletion that mediates the pathophysiology of some of the common clinical signs of PNH. Clinical symptoms of PNH include evidence of hemolytic anemia, bone marrow failure, smooth muscle dystonias and thromboses. Treatment options for patients with PNH include bone marrow transplantation, a therapy associated with high morbidity and mortality, or treatment with the complement inhibitor eculizumab. Eculizumab is a first-in-class anti-complement drug that in PNH has been shown to block complement-mediated hemolysis, reduce transfusion dependency, reduce thromboembolic complications and improve the quality of life (QoL) of patients.

Excision of esophageal duplication cysts with robotic-assisted thoracoscopic surgery

This report expands the literature showing that robotic-assisted removal of mediastinal masses or cysts can be a safe and effective technique in the management of intrathoracic disease.

Esophageal duplication cysts are infrequent anomalies of the gastrointestinal tract that are predominantly found in children. The conventional surgical approach for removal of these cysts is an open surgery one with a posterolateral thoracotomy incision. However, more recently, these cysts have been excised via video-assisted thoracoscopic surgery (VATS). In this article, we present 2 pediatric patients treated with successful excision of an esophageal duplication cyst via robotic-assisted thoracoscopic surgery (RATS) using the da Vinci surgical system. With robotic technology, precise dissection and complete resection of the thoracic mass was achieved without violating the esophageal mucosa. There were no complications, and the patients did not require placement of a postoperative chest tube. Pathological examination of the mass was consistent with an esophageal (foregut) duplication cyst in both cases.

Upregulated expression of complement inhibitory proteins on bladder cancer cells and anti-MUC1 antibody immune selection

Membrane complement inhibitors (CD46, CD55 and CD59) are upregulated in some human cancers indicating that they play a role in immune evasion. We investigated complement inhibitor expression in bladder cancer and examined the hypothesis that selective pressure of an antibody response (anti-MUC1) results in the upregulated expression of complement inhibitors on tumor cells. Paired samples of tumor and normal tissue from 22 bladder cancer patients were analyzed for expression of MUC1, CD46, CD55 and CD59, and matched serum samples analyzed for anti-MUC1 IgM and IgG levels. Relationships between anti-MUC1 antibody levels and complement inhibitor expression were investigated. MUC1 mRNA was upregulated in 86% of tumor samples. CD46 was upregulated in 77%, CD55 in 55% and CD59 in 59% of tumors. Low titer anti-MUC1 IgM was detected in normal human sera, but was elevated in 41% of the bladder cancer patients. Anti-MUC1 IgG was virtually absent from normal sera, but present in 32% of the cancer patients. There was a direct relationship between anti-MUC1 antibody titer and expression level of complement inhibitors. Analysis of the correlation of each antibody with the expression of each complement inhibitor by Spearman's rank test revealed a strong correlation between both anti-MUC1 IgM and IgG levels and increased expression of CD46 and CD55, and combined anti-MUC1 IgM/IgG levels correlated with increased expression of all 3 complement inhibitors. In conclusion, the data demonstrate upregulated complement inhibitor expression and the presence of an anti-MUC1 antibody response in bladder cancer patients and support the hypothesis of antibody-mediated immune selection.

Complement-Dependent P-Selectin Expression and Injury following Ischemic Stroke

The mechanisms that contribute to inflammatory damage following ischemic stroke are poorly characterized, but studies indicate a role for both complement and P-selectin. In this study, we show that compared with wild-type mice, C3-deficient mice showed significant improvement in survival, neurological deficit, and infarct size at 24 h after middle cerebral artery occlusion and reperfusion. Furthermore, P-selectin protein expression was undetectable in the cerebral microvasculature of C3-deficient mice following reperfusion, and there was reduced neutrophil influx, reduced microthrombus formation, and increased blood flow postreperfusion in C3-deficient mice. We further investigated the use of a novel complement inhibitory protein in a therapeutic paradigm. Complement receptor 2 (CR2)-Crry inhibits complement activation at the C3 stage and targets to sites of complement activation. Treatment of normal mice with CR2-Crry at 30 min postreperfusion resulted in a similar level of protection to that seen in C3-deficient mice in all of the above-measured parameters. The data demonstrate an important role for complement in cerebrovascular thrombosis, inflammation, and injury following ischemic stroke. P-selectin expression in the cerebrovasculature, which is also implicated in cerebral ischemia and reperfusion injury, was shown to be distal to and dependent on complement activation. Data also show that a CR2-targeted approach of complement inhibition provides appropriate bioavailability in cerebral injury to enable complement inhibition at a dose that does not significantly affect systemic levels of serum complement activity, a potential benefit for stroke patients where immunosuppression would be undesirable due to significantly increased susceptibility to lung infection.

Microarray analysis of A549 cells infected with rabbitpox virus (RPV): a comparison of wild-type RPV and RPV deleted for the host range gene, SPI-1

A documented consequence of poxvirus infections is global inhibition of host protein synthesis and reduction in mRNA levels. We examined this mRNA decrease by infecting A549 cells, derived from a human lung carcinoma, with rabbitpox virus (RPV), or RPV deleted for the serine protease inhibitor SPI-1 (RPVDeltaSPI-1), which exhibits a growth defect on A549 cells. At various times postinfection, mRNA profiles were analyzed using Affymetrix U95AV2 microarrays. There was a decline in overall cellular mRNA levels beginning at 2.5 hpi, and by 5 hpi, mRNA levels were drastically reduced for the majority of genes. However, several mRNAs increased, including those of heat-shock genes. Finally, a comparison of host mRNA profiles of RPV- to RPVDeltaSPI-1-infected cells revealed subtle differences in mRNA levels at 5 and 12 hpi. In summary, while there was a global decrease of host mRNA levels, the induction of selected mRNAs may be required for a successful poxvirus infection.

Analysis of Gene Expression Patterns in Human Postburn Hypertrophic Scars

Hypertrophic scars cause cosmetic disfigurement and limited mobility in burn patients. To better understand the molecular pathophysiology of hypertrophic scar formation, microarray analyses were performed on normal skin and hypertrophic scars from four burn patients. Microarray analyses were determined in an effort to identify genes whose expression discriminated between normal skin and mature, hypertrophic scars. Surgical biopsies were obtained from two pediatric and two adult patients 6 to 15 months after burn injury. Total RNA was isolated from the samples and subjected to microarray analysis using the Affymetrix U95Av2 GeneChip. Results from this analysis revealed 31 probe sets representing genes that were consistently up-regulated at least two-fold in hypertrophic scar specimens from all four patients and four probe sets that were down-regulated. The significance analysis of microarrays algorithm also identified 35 probe sets whose increased expression resulted in the hierarchal clustering of the hypertrophic scar and normal tissue, seven of which were identical to the six genes identified by paired analyses. These six genes all displayed elevated levels of expression in the scar tissue. Proteins encoded by the genes identified included germline oligometric matrix protein, matrix metalloproteinase-16, collagen type 1alpha, pleiotrophin, and thrombospondin-4. Although the results presented here suggest that there may be unique patterns of gene expression in hypertrophic scars that may be important in the evaluation and treatment of hypertrophic scarring, the results must be confirmed with larger datasets.

The Saccharomyces cerevisiae HSP12 gene is activated by the high-osmolarity glycerol pathway and negatively regulated by protein kinase A

The HSP12 gene encodes one of the two major small heat shock proteins of Saccharomyces cerevisiae. Hsp12 accumulates massively in yeast cells exposed to heat shock, osmostress, oxidative stress, and high concentrations of alcohol as well as in early-stationary-phase cells. We have cloned an extended 5'-flanking region of the HSP12 gene in order to identify cis-acting elements involved in regulation of this highly expressed stress gene. A detailed analysis of the HSP12 promoter region revealed that five repeats of the stress-responsive CCCCT motif (stress-responsive element [STRE]) are essential to confer wild-type induced levels on a reporter gene upon osmostress, heat shock, and entry into stationary phase. Disruption of the HOG1 and PBS2 genes leads to a dramatic decrease of the HSP12 inducibility in osmostressed cells, whereas overproduction of Hog1 produces a fivefold increase in wild-type induced levels upon a shift to a high salt concentration. On the other hand, mutations resulting in high protein kinase A (PKA) activity reduce or abolish the accumulation of the HSP12 mRNA in stressed cells. Conversely, mutants containing defective PKA catalytic subunits exhibit high basal levels of HSP12 mRNA. Taken together, these results suggest that HSP12 is a target of the high-osmolarity glycerol (HOG) response pathway under negative control of the Ras-PKA pathway. Furthermore, they confirm earlier observations that STRE-like sequences are responsive to a broad range of stresses and that the HOG and Ras-PKA pathways have antagonistic effects upon CCCCT-driven transcription.

Osmostress response of the yeast Saccharomyces

Exposure of yeast cells to high osmolarities leads to dehydration, collapse of ion gradients over the plasma membrane and decrease in cell viability. The response of yeast cells to high external osmolarities is designated osmostress response. It is likely that both osmoregulatory and general stress reactions are involved in this so far poorly understood process. Part of the response aims at raising the internal osmotic potential, i.e. the production of osmolytes such as glycerol, and exclusion of toxic solutes. In addition, heat-shock proteins and trehalose are synthesized, probably to protect cellular components and to facilitate repair and recovery. Recent analyses of osmosensitive yeast mutants strongly suggest the involvement of protein kinase-mediated signal-transduction pathways in the maintenance of the osmotic integrity of the cell. This has stimulated interesting hypotheses as to the actual osmosensing mechanism.

Osmostress-induced changes in yeast gene expression

When Saccharomyces cerevisiae cells are exposed to high concentration of NaCl, they show reduced viability, methionine uptake and protein biosynthesis. Cells can acquire tolerance against a severe salt shock (up to 1.4 M NaCl) by a previous treatment with 0.7 M NaCl, but not by a previous heat shock. Two-dimensional analysis of [3H]-leucine-labelled proteins from salt-shocked cells (0.7 M NaCl) revealed the elevated rate of synthesis of nine proteins, among which were the heat-shock proteins hsp12 and hsp26. Northern analysis using gene-specific probes confirmed the identity of the latter proteins and, in addition, demonstrated the induction of glycerol-3-phosphate dehydrogenase gene expression. The synthesis of the same set of proteins is induced or enhanced upon exposure of cells to 0.8 M sucrose, although not as dramatically as in an iso-osmolar NaCl concentration (0.7 M).