Single-cell Atlas of Penile Cancer Reveals TP53 Mutations as a Driver of an Aggressive Phenotype, Irrespective of Human Papillomavirus Status, and Provides Clues for Treatment Personalization

BACKGROUND AND OBJECTIVE

TP53 loss-of-function (TP53LOF) mutations might be a driver of poor prognosis and chemoresistance in both human papillomavirus (HPV)-independent (HPV-) and HPV-associated (HPV+) penile squamous cell carcinoma (PSCC). Here, we aim to describe transcriptomic differences in the PSCC microenvironment stratified by TP53LOF and HPV status.

METHODS

We used single-cell RNA sequencing (scRNA-seq) and T-cell receptor sequencing to obtain a comprehensive atlas of the cellular architecture of PSCC. TP53LOF and HPV status were determined by targeted next-generation sequencing and sequencing HPV-DNA reads. Six HPV+ TP53 wild type (WT), six HPV- TP53WT, and four TP53LOF PSCC samples and six controls were included. Immunohistochemistry and hematoxylin-eosin confirmed the morphological context of the observed signatures. Prognostic differences between patient groups were validated in 541 PSCC patients using Kaplan-Meier survival estimates.

KEY FINDINGS AND LIMITATIONS

Patients with aberrant p53 staining fare much worse than patients with either HPV- or HPV+ tumors and WT p53 expression. Using scRNA-seq, we revealed 65 cell subtypes within 83 682 cells. TP53LOF tumors exhibit a partial epithelial-to-mesenchymal transition, immune-excluded, angiogenic, and morphologically invasive environment, underlying their aggressive phenotype. HPV- TP53WT tumors show stemness and immune exhaustion. HPV+ TP53WT tumors mirror normal epithelial maturation with upregulation of antibody-drug-conjugate targets and activation of innate immunity. Inherent to the scRNA-seq analysis, low sample size is a limitation and validation of signatures in large PSCC cohorts is needed.

CONCLUSIONS AND CLINICAL IMPLICATIONS

This first scRNA-seq atlas offers unprecedented in-depth insights into PSCC biology underlying prognostic differences based on TP53 and HPV status. Our findings provide clues for testing novel biomarker-driven therapies in PSCC.

PATIENT SUMMARY

Here, we analyzed tissues of penile cancer at the level of individual cells, which helps us understand why patients who harbor a deactivating mutation in the TP53 gene do much worse than patients lacking such a mutation. Such an analysis may help us tailor future therapies based on TP53 gene mutations and human papillomavirus status of these tumors.

Respiratory complex I regulates dendritic cell maturation in explant model of human tumor immune microenvironment

BACKGROUND

Combining cytotoxic chemotherapy or novel anticancer drugs with T-cell modulators holds great promise in treating advanced cancers. However, the response varies depending on the tumor immune microenvironment (TIME). Therefore, there is a clear need for pharmacologically tractable models of the TIME to dissect its influence on mono- and combination treatment response at the individual level.

METHODS

Here we establish a patient-derived explant culture (PDEC) model of breast cancer, which retains the immune contexture of the primary tumor, recapitulating cytokine profiles and CD8+T cell cytotoxic activity.

RESULTS

We explored the immunomodulatory action of a synthetic lethal BCL2 inhibitor venetoclax+metformin drug combination ex vivo, discovering metformin cannot overcome the lymphocyte-depleting action of venetoclax. Instead, metformin promotes dendritic cell maturation through inhibition of mitochondrial complex I, increasing their capacity to co-stimulate CD4+T cells and thus facilitating antitumor immunity.

CONCLUSIONS

Our results establish PDECs as a feasible model to identify immunomodulatory functions of anticancer drugs in the context of patient-specific TIME.

CD4+ T cell activation distinguishes response to anti-PD-L1+anti-CTLA4 therapy from anti-PD-L1 monotherapy

Cancer patients often receive a combination of antibodies targeting programmed death-ligand 1 (PD-L1) and cytotoxic T lymphocyte antigen-4 (CTLA4). We conducted a window-of-opportunity study in head and neck squamous cell carcinoma (HNSCC) to examine the contribution of anti-CTLA4 to anti-PD-L1 therapy. Single-cell profiling of on- versus pre-treatment biopsies identified T cell expansion as an early response marker. In tumors, anti-PD-L1 triggered the expansion of mostly CD8+ T cells, whereas combination therapy expanded both CD4+ and CD8+ T cells. Such CD4+ T cells exhibited an activated T helper 1 (Th1) phenotype. CD4+ and CD8+ T cells co-localized with and were surrounded by dendritic cells expressing T cell homing factors or antibody-producing plasma cells. T cell receptor tracing suggests that anti-CTLA4, but not anti-PD-L1, triggers the trafficking of CD4+ naive/central-memory T cells from tumor-draining lymph nodes (tdLNs), via blood, to the tumor wherein T cells acquire a Th1 phenotype. Thus, CD4+ T cell activation and recruitment from tdLNs are hallmarks of early response to anti-PD-L1 plus anti-CTLA4 in HNSCC.

PD-1- CD45RA+ effector-memory CD8 T cells and CXCL10+ macrophages are associated with response to atezolizumab plus bevacizumab in advanced hepatocellular carcinoma

The combination of atezolizumab plus bevacizumab (atezo/bev) has dramatically changed the treatment landscape of advanced HCC (aHCC), achieving durable responses in some patients. Using single-cell transcriptomics, we characterize the intra-tumoural and peripheral immune context of patients with aHCC treated with atezo/bev. Tumours from patients with durable responses are enriched for PDL1+ CXCL10+ macrophages and, based on cell-cell interaction analysis, express high levels of CXCL9/10/11 and are predicted to attract peripheral CXCR3+ CD8+ effector-memory T cells (CD8 TEM) into the tumour. Based on T cell receptor sharing and pseudotime trajectory analysis, we propose that CD8 TEM preferentially differentiate into clonally-expanded PD1- CD45RA+ effector-memory CD8+ T cells (CD8 TEMRA) with pronounced cytotoxicity. In contrast, in non-responders, CD8 TEM remain frozen in their effector-memory state. Finally, in responders, CD8 TEMRA display a high degree of T cell receptor sharing with blood, consistent with their patrolling activity. These findings may help understand the possible mechanisms underlying response to atezo/bev in aHCC.

Abstract 4122: TIL-containing patient-derived explant cultures reveal role of metformin on antigen presenting cell activation

Globally, breast cancer is among the most diagnosed cancer types for women. Current and upcoming breast cancer therapies are being investigated in combination with compounds that stimulate an immune response, but whether the therapeutic agents themselves have unexpected immunomodulatory effects is often overlooked. Here, we have developed a method to grow 3D cultures of intact fragments of patient-derived tissue (Patient-Derived Explant Cultures; PDECs) to assess the preclinical potential of studying human tumor cells and immune cells simultaneously ex vivo

Single cell sequencing, flow cytometry, gene expression profiling and cytokine profiling data show that the tumor immunocontexture is conserved in PDECs and that these resident immune cells respond to distinct immune stimulus

We performed gene expression profiling, flow cytometry, and cytokine profiling of drug-treated human explants and found that metformin has antitumor potential through the activation of antigen presenting cells. We further validated in vitro that metformin-mediated APC activation is largely through mitochondrial respiration inhibition irrespective of the presence of tumor cells. Our PDEC platform highlights the preclinical potential of ex vivo explants by simultaneously offering information of tumor and immune cell toxicity and mechanism.

Citation Format: Rita J. Turpin, Ruixian Liu, Pauliina Munne, Aino Peura, Jenna Rannikko, Gino Philips, Natasha Salmelin, Elina Hurskainen, Ilida Suleymanova, Minna Mutka, Tuomo Meretoja, Johanna Mattson, Satu Mustjoki, Päivi Saavalainen, Diether Lambrechts, Jeroen Pouwels, Maija Hollmén, Juha Klefström. TIL-containing patient-derived explant cultures reveal role of metformin on antigen presenting cell activation. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4122.

Abstract PO002: Pretreatment immune cell composition and checkpoint ligand expression define the response to immunotherapy in advanced HCC: a study using single-cell sequencing

The novel combination of atezolizumab/bevacizumab has demonstrated unprecedented response rates in a subgroup of advanced hepatocellular carcinoma (aHCC) patients. In order to understand why only a subset of aHCC patients respond to immunotherapy targeting the PD-1/PD-L1 axis, we subjected pre-treatment tissue biopsies from 31 aHCC patients, with mainly non-viral etiologies, to simultaneous single-cell transcriptome (scRNAseq) and T-cell receptor (scTCRseq) sequencing, providing an integrative view of the tumor-microenvironment of aHCC (n=91 169 cells). The therapeutic targets, PD-1 and PD-L1 are expressed in tumor-infiltrating T-cells versus myeloid cells and tumor cells, respectively. Myeloid cells in tumors responding to immunotherapy (according to mRECIST) express significantly higher levels of PD-L1 (p=0.014) compared to non-responders and this is driven by pro-inflammatory PD-L1 expressing CXCL10+ macrophages, involved in T-cell recruitment. In contrast, non-responding tumors are infiltrated by immature CX3CR1+ macrophages and CCR2+ ‘monocyte-like’ macrophages (p=0.009 and p=0.01, respectively). Interestingly, the composition of tumor-infiltrating T-cells did not differ significantly between patient groups. However, responding tumors were characterized by a more clonal baseline T-cell receptor repertoire (p=0.007). Single-cell T-cell receptor sequencing revealed that this clonality was present in activated, effector T-cells, while non-responders had a higher proportion of non-clonal T-cells (p=0.01) concentrated within naïve and memory-like T-cell phenotypes. In conclusion, this is the first and largest aHCC cohort to correlate single-cell sequencing data with clinical outcomes. Prior to treatment, differences in abundancy and ligand expression in small clusters of immune cells as well as difference in baseline T-cell clonality drive response to checkpoint inhibition in aHCC.

Citation Format: Sarah Cappuyns, Gino Philips, Vincent Vandecaveye, Chris Verslype, Eric Van Cutsem, Diether Lambrechts, Jeroen Derkervel. Pretreatment immune cell composition and checkpoint ligand expression define the response to immunotherapy in advanced HCC: a study using single-cell sequencing [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PO002.

Abstract PR03: Pretreatment immune cell composition and checkpoint ligand expression define the response to immunotherapy in advanced HCC: a study using single-cell sequencing

The novel combination of atezolizumab/bevacizumab has demonstrated unprecedented response rates in a subgroup of advanced hepatocellular carcinoma (aHCC) patients. In order to understand why only a subset of aHCC patients respond to immunotherapy targeting the PD-1/PD-L1 axis, we subjected pre-treatment tissue biopsies from 31 aHCC patients, with mainly non-viral etiologies, to simultaneous single-cell transcriptome (scRNAseq) and T-cell receptor (scTCRseq) sequencing, providing an integrative view of the tumor-microenvironment of aHCC (n=91 169 cells). The therapeutic targets, PD-1 and PD-L1 are expressed in tumor-infiltrating T- cells versus myeloid cells and tumor cells, respectively. Myeloid cells in tumors responding to immunotherapy (according to mRECIST) express significantly higher levels of PD-L1 (p=0.014) compared to non-responders and this is driven by pro-inflammatory PD-L1 expressing CXCL10+ macrophages, involved in T-cell recruitment. In contrast, non-responding tumors are infiltrated by immature CX3CR1+ macrophages and CCR2+ ‘monocyte-like’ macrophages (p=0.009 and p=0.01, respectively). Interestingly, the composition of tumor-infiltrating T-cells did not differ significantly between patient groups. However, responding tumors were characterized by a more clonal baseline T-cell receptor repertoire (p=0.007). Single-cell T-cell receptor sequencing revealed that this clonality was present in activated, effector T-cells, while non-responders had a higher proportion of non-clonal T-cells (p=0.01) concentrated within naïve and memory-like T-cell phenotypes. In conclusion, this is the first and largest aHCC cohort to correlate single-cell sequencing data with clinical outcomes. Prior to treatment, differences in abundancy and ligand expression in small clusters of immune cells as well as difference in baseline T-cell clonality drive response to checkpoint inhibition in aHCC.

Citation Format: Sarah Cappuyns, Gino Philips, Vincent Vandecaveye, Chris Verslype, Eric Van Cutsem, Diether Lambrechts, Jeroen Derkervel. Pretreatment immune cell composition and checkpoint ligand expression define the response to immunotherapy in advanced HCC: a study using single-cell sequencing [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PR03.

The pulmonary vasculature in lethal COVID-19 and idiopathic pulmonary fibrosis at single cell resolution

Aims

SARS-CoV-2 infection causes COVID-19, which in severe cases evokes life-threatening acute respiratory distress syndrome (ARDS). Transcriptome signatures and the functional relevance of non-vascular cell types (e.g. immune and epithelial cells) in COVID-19 are becoming increasingly evident. However, despite its known contribution to vascular inflammation, recruitment/invasion of immune cells, vascular leakage and perturbed hemostasis in the lungs of severe COVID-19 patients, an in-depth interrogation of the endothelial cell (EC) compartment in lethal COVID-19 is lacking. Moreover, progressive fibrotic lung disease represents one of the complications of COVID-19 pneumonia and ARDS. Analogous features between idiopathic pulmonary fibrosis (IPF) and COVID-19 suggest partial similarities in their pathophysiology, yet, a head-to-head comparison of pulmonary cell transcriptomes between both conditions has not been implemented to date.

Methods and Results

We performed single nucleus RNA-seq (snRNA-seq) on frozen lungs from 7 deceased COVID-19 patients, 6 IPF explant lungs and 12 controls. The vascular fraction, comprising 38,794 nuclei, could be subclustered into 14 distinct EC subtypes. Non-vascular cell types, comprising 137,746 nuclei, were subclustered and used for EC-interactome analyses. Pulmonary ECs of deceased COVID-19 patients showed an enrichment of genes involved in cellular stress, as well as signatures suggestive of dampened immunomodulation and impaired vessel wall integrity. In addition, increased abundance of a population of systemic capillary and venous ECs was identified in COVID-19 and IPF. COVID-19 systemic ECs closely resembled their IPF counterparts, and a set of 30 genes was found congruently enriched in systemic ECs across studies. Receptor-ligand interaction analysis of ECs with non-vascular cell types in the pulmonary micro-environment revealed numerous previously unknown interactions specifically enriched/depleted in COVID-19 and/or IPF.

Conclusions

This study uncovered novel insights into the abundance, expression patterns and interactomes of EC subtypes in COVID-19 and IPF, relevant for future investigations into the progression and treatment of both lethal conditions.

Translational perspective

While assessing clinical and molecular characteristics of severe and lethal COVID-19 cases, the vasculature’s undeniable role in disease progression has been widely acknowledged. COVID-19 lung pathology moreover shares certain clinical features with late-stage IPF – yet an in-depth interrogation and direct comparison of the endothelium at single-cell level in both conditions is still lacking. By comparing the transcriptomes of ECs from lungs of deceased COVID-19 patients to those from IPF explant and control lungs, we gathered key insights the heterogeneous composition and potential roles of ECs in both lethal diseases, which may serve as a foundation for development of novel therapeutics.

Phase II study of cisplatin (C), gemcitabine (G) and gefitinib for advanced urothelial carcinoma (UC): Analysis of the second cohort of CALGB 90102

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Background: The epidermal growth factor receptor (EGFR) is frequently expressed in UC and carries a poor prognosis. C has preclinical synergy with gefitinib and GC plus gefitinib was safe in lung cancer patients (pts). In a UC trial of GC using fixed dose rate infusion of G plus gefitinib, Gr 4 and 5 toxicities led to premature closure of the study after 27 patients. Because toxicity was felt to be related to the fixed dose rate infusion of G, accrual was resumed with a standard G dosing schedule in a second cohort. Methods: Eligible pts had measurable N2, N3 or M1 disease; PS of 0–2; CrCl of > 50 ml/min; adequate organ function; no prior systemic combination chemotherapy. Treatment consisted of C 70 mg/m2 D1, G 1000 mg/m2 D1+8 given over 30 min every 3 weeks concurrent with gefitinib 500 mg/day PO for a maximum of 6 cycles. Responders received maintenance gefitinib 500 mg/day until progression. Results: In 55 eligible pts with a median age of 64 years, 67% (of 49) had visceral metastases and 91% had PS of 0–1. Objective response (CR+PR) was observed in 51% (95% CI = 37–65). With a median follow up of 13.2 mo, the median time to progression was 8 mo (95% CI = 6.8–9.2) on the basis of 45 events, and the median overall survival was 14.4 mo (95% CI = 10.7–20.9) on the basis of 26 deaths. No lethal toxicity was seen. Gr 4 toxicities included Gr 4 neutropenia (20%) and Gr 4 metabolic/electrolyte disorders in 13%. Gr 3 and 4 diarrhea was observed in 25% and 2 % of pts respectively and Gr 3 skin rash in 16% of pts. Conclusions: The combination of GC and gefitinib has acceptable toxicity in advanced UC. However, the relative contribution of gefitinib to the efficacy of this regimen remains uncertain. These preliminary results do not suggest a substantial improvement upon historical results with GC alone in advanced UC.

No significant financial relationships to disclose.

Long term efficacy of peripheral androgen blockade on prostate cancer: CALGB 9782

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Background: The treatment of patients with a rising PSA after definitive local therapy is controversial. Patients are reluctant to undergo androgen suppression due to side effects and interest focuses on the timing and intensity of additional therapy. The use of peripheral androgen blockade in this setting is appealing. Methods: Patients with a rising PSA after definitive local therapy were enrolled in a multi-institutional trial. Accrual of 101 patients lasted from Sept 30, 1998 to July 16, 2001. All patients had undergone previous definitive local therapy at least 1 year, and no more than 10 years prior to enrollment. All patients had a repeated rising PSA, above 1 ng/ml, with no detectable evidence of recurrent disease. CT and bone scans were negative. Patients received a combination of oral therapy consisting of Finasteride, at a dose of 5 mg/day, and Flutamide, at a dose of 250 mg TID. Results: The median age was 71, with a median baseline testosterone level of 322 ng/dl. A >80% PSA decline was seen in 91/94, (97%) of the patients. Three other patients had PSA declines of 77%, 73% and 38%, all of which were maintained for at least 28 days. The median time to PSA nadir was 3.2 months. The current median follow-up is 59 months. To date, only 22 patients have progressed, with 47 patients still on peripheral androgen blockade. Eight patients have died without progression, and 22 patients went off therapy for other reasons not related to progression. Also noted were patients showing PSA responses to Flutamide withdrawal, and per protocol remaining on Finasteride. Toxicity to date remains very mild. Conclusions: Peripheral androgen blockade showed excellent activity produced durable PSA responses in this select group of patients. While the clinical significance of a decline in PSA alone is not fully understood_the durability of these PSA responses is encouraging. The median duration of progression free survival and overall survival has not been reached, and is likely to be longer than five years. Quality of life data is undergoing further analysis. This report supports further study of less aggressive treatments for patients who have only a rising PSA after definitive local therapy.

No significant financial relationships to disclose.

DNA replication regulation protein Mcm7 as a marker of proliferation in prostate cancer

BACKGROUND

Recent studies have shown that minichromosome maintenance (MCM) proteins (Mcm2-7) may be useful proliferation markers in dysplasia and cancer in various tissues.

AIMS

To investigate the use of Mcm7 as a proliferation marker in 79 lymph node negative prostate cancers and compare it with Ki-67, a commonly used cell proliferation marker.

METHODS

The percentage of proliferating cells (proliferation index; PI) was calculated for basal and luminal epithelial cells in benign prostate tissue, prostatic intraepithelial neoplasia (PIN), and epithelial cells in adenocarcinoma. The PI for each biomarker was correlated with the preoperative prostate specific antigen concentration, the Gleason score, surgical resection margin status, and the AJCC pT stage for each patient.

RESULTS

The mean PIs for Ki-67 and Mcm7 were: benign luminal epithelium 0.7 and 1.2 and benign basal epithelium 0.8 and 8.2; PIN non-basal epithelium 4.9 and 10.6 and PIN basal epithelium 0.7 and 3.1; adenocarcinoma 9.8 and 22.7, respectively. Mcm7 had a significantly higher mean PI (p<0.0001) than Ki-67 for all cell categories except benign luminal epithelial cells. Mcm7 was a better discriminatory marker of proliferation between benign epithelium, PIN, and invasive adenocarcinoma (p<0.0001) than Ki-67. The drop in Mcm7 mean basal cell PI from benign epithelium to PIN epithelium was significantly larger than for Ki-67 (p<0.0001). Mcm7 had a significantly higher PI than Ki-67 at each risk level.

CONCLUSION

Mcm7 may be a useful proliferation marker in prostatic neoplasia and warrants further evaluation as a complementary tool in the diagnosis of PIN and prostate carcinoma.

A comparison of the lactate Pro, Accusport, Analox GM7 and Kodak Ektachem lactate analysers in normal, hot and humid conditions

This study aimed to compare the performance of a new portable lactate analyser against other standard laboratory methods in three conditions, normal (20 +/- 1.3 degrees C; 40 +/- 5 % RH), hot (40 +/- 2.5 degrees C; 40 +/- 5 % RH), and humid (20 +/- 1.1 degrees C; 82 +/- 6 % RH) conditions. Seven healthy males, ([Mean +/- SE]: age, 26.3 +/- 1.3 yr; height, 177.7 +/- 1.6 cm; weight, 77.4 +/- 0.9 kg, .VO(2)max, 56.1 +/- 1.9 ml x kg x min(-1)) undertook a maximal cycle ergometry test to exhaustion in the three conditions. Blood was taken every 3 min at the end of each stage and was analysed using the Lactate Pro LT-1710, the Accusport, the Analox GM7 and the Kodak Ektachem systems. The MANOVA (Analyser Type x Condition x Workload) indicated no interaction effect (F(42,660), = 0.45, p > 0.99, Power = 0.53). The data across all workloads indicated that the machines measured significantly differently to each other (F(4,743) = 14.652, p < 0.0001, Power = 1.00). The data were moderately to highly correlated. We conclude that the Lactate Pro is a simple and effective measurement device for taking blood lactate in a field or laboratory setting. However, we would caution against using this machine to compare data from other machines.

Erythrocyte glutathione deficiency in symptom-free HIV infection is associated with decreased synthesis rate

Although several studies have documented intra- and extracellular glutathione (GSH) deficiency in asymptomatic human immunodeficiency virus (HIV) infection, the mechanisms responsible for the altered GSH homeostasis remain unknown. To determine whether decreased synthesis contributes to this alteration of GSH homeostasis, a primed-constant infusion of [2H2]glycine was used to measure the fractional and absolute rates of synthesis of GSH in five healthy and five symptom-free HIV-infected subjects before and after supplementation for 1 wk with N-acetylcysteine. The erythrocyte GSH concentration of the HIV-infected group was lower (P < 0.01) than that of the control group (1.4 +/- 0.16 vs. 2.4 +/- 0.08 mmol/l). The smaller erythrocyte GSH pool of the HIV-infected group was associated with a significantly slower (P < 0.01) absolute synthesis rate of GSH (1.15 +/- 0.14 vs. 1.71 +/- 0.15 mmol. l-1. day-1) compared with controls. Cysteine supplementation elicited significant increases in both the absolute rate of synthesis and the concentration of erythrocyte GSH. These results suggest that the GSH deficiency of HIV infection is due in part to a reduced synthesis rate secondary to a shortage in cysteine availability.

Pre-clinical evaluation of probes to detect t(8;21) AML minimal residual disease by fluorescence in situ hybridization

The 8;21 translocation in acute myeloid leukemia (AML) results in a consistent fusion transcript, AML1/ETO. Long-term clinical remission occurs in some patients despite incomplete eradication of AML1/ETO as demonstrated by RT-PCR, thus limiting the usefulness of this assay. An important future goal will be to determine if there is a level of minimal residual disease (MRD) in patients below which relapse is unlikely. For the detection of MRD, we have developed reagents for fluorescence in situ hybridization (FISH) that identify both derivative 8 and 21 chromosomes with a high analytical sensitivity. In t(8;21) AML cells, two fused signals were detected in addition to the normal 8 and 21 alleles. The sensitivity and specificity of this probe mixture were analyzed in cell lines and patient bone marrows. One and two randomly juxtaposed signals were observed in 2.4 and 0.04% of normal cells, respectively. However, these were easily differentiated from t(8;21) cells by the absence of signals from the normal alleles. Using as criteria the presence of two fused signals plus the normal alleles, we observed no false positives among 5,000 normal cells. The probe correctly identified 20/20 patients with t(8;21) AML and 10/10 non-t(8;21) patients. In cell dilution experiments, the analytical sensitivity of this reagent was equal to that of the X chromosome and Y chromosome alpha-satellite probes. These optimized probes should facilitate the quantitative assessment and study of MRD in t(8;21) AML.

ETO and AML1 phosphoproteins are expressed in CD34+ hematopoietic progenitors: implications for t(8;21) leukemogenesis and monitoring residual disease

To study acute myelogenous leukemia 1 (AML1) transcription factor, ETO protein, and t(8;21) AML chimeric AML1/ ETO protein in normal hematopoiesis and in leukemia, we raised rabbit antisera to a bacterially expressed polypeptide containing amino acid residues 1 to 220 of ETO and to synthetic peptides extending from residues 528 to 548 of ETO and 32 to 50 of AML1. The latter was selected to have little chance of cross-reactivity with other members of the PEBP2 alpha family. With affinity-purified reagents, we observed immunofluorescent staining for both AML1 and ETO in the nucleus of HEL, K562, and Kasumi-1 leukemic cell lines, the last from a t(8;21) AML. Biochemical analysis confirmed specificity of the antibodies and the nuclear localization of the antigens, the latter being exclusive for AML1 and primary for ETO. Immunoprecipitations of metabolically labeled 32P-proteins from Kasumi-1 cells show that AML1 and ETO are phosphorylated on serine and threonine. Investigations with normal bone marrow reveal AML1 and ETO are coexpressed in megakaryocytes and that each is expressed in a portion of the approximately 10-microns-diameter cells residing there. Using a CD34+ enriched population mobilized to peripheral blood, we found AML1 and, unexpectedly, ETO present in these cells. Because of this, we conclude that the expression of ETO in hematopoietic cells is not by itself leukemogenic. Also, because ETO would not be exclusively expressed as part of chimeric AML1/ETO in leukemic patients, its presence cannot be used to monitor t(8;21) AML residual disease.

Myofibril size variation along the length of extraocular muscle in rabbit and rat. I: orbital layer

It is generally assumed that a muscle fiber is structurally uniform along its length. That assumption is not consistent with the observed variation of myofibrillar profile size along the length of both singly innervated fibers (SIFs) and multiply innervated fibers (MIFs) in the orbital (outer) layer of extraocular muscle (EOM). Muscle fibers were reconstructed in serial sections along the orbital layer of rabbit and rat EOM. For both the SIFs and MIFs, myofibril profile size was smallest (narrowest) near the endplate. In the SIFs of rat, for example, the myofibril profiles were 28% wider at a distance of 1.5 mm from the endplate than at the endplate itself. Measures of profile size included the mean intercept length and the mean shortest path from test points within the profile to the profile boundary. The possible effect of sarcomere length variation was controlled by normalizing the myofibrillar profile size data to a constant spacing of the myosin filament lattice. This morphometric approach was also used to quantify the further increase of profile size that occurs in the end portions of the orbital MIFs where the myobrillar organization is typically ill-defined.

Intermitochondrial junctions in the extraocular muscle of the rat

Intermitochondrial junctions with a spacing of 17-21 nm were observed in the superior rectus muscle of a rat. Periodic rounded densities are aligned midway between the apposed outer mitochondrial membranes at some of these junctions. Such densities have a diameter of about 8-10 nm and a center-to-center spacing of about 26-30 nm. These junctions occur in cases where one mitochondrial profile is enclosed within another or where two profiles are interlocked so that their combined overall form has a smoothly contoured profile. Intermitochondrial junctions seem not to have been previously described in muscle, but have been reported in other kinds of tissues. In agreement with those previous reports, the presently observed intermitochondrial junctions usually involve mitochondria that display atypical features indicative of tissue abnormality or stress. Such junctions were never observed in normal extraocular muscle.

Distribution of mitochondrial and lipidic alterations in abnormal extraocular muscle of rat

An abnormal superior rectus muscle of rat displayed marked differences in the respective distributions of mitochondrial alterations and excessive lipid accumulations, both of which are thought to be indicators of faulty oxidative metabolism. The mitochondrial alterations were widespread, extending over 46% of muscle length. In contrast, the excess lipids extended over but 11% of the muscle length and were virtually confined to the end-plate region. The end plates themselves were essentially normal. These data raise the possibility that the end-plate region may exhibit a locally greater deficit of oxidative metabolism, due to a possibly higher metabolic requirement needed to support the localized end-plate potential activity.

Latter reorganization of membrane-glycogen complexes in rabbit extraocular muscle

Characteristic modes of secondary reorganization were observed in membrane-glycogen complexes of rabbit extraocular muscle. These included (a) an irregular widening or narrowing of the intracisternal space, (b) a loss of the typical intracisternal flocculent densities, and (c) the acquisition of intercisternal flocculent densities. In irregularly widened cisternae, the membranes tended to remain closely adjacent to the intervening glycogen layer, thereby forming triads composed of a glycogen layer enclosed within the apposing membranes of adjacent cisternae. In the absence of glycogen particles from contiguous portions of several lamellae, the membranes became compacted to form myeloidlike figures. Degenerating complexes sometimes displayed distention of intercisternal spaces and layers of atypically small particles. The above modifications of membrane-glycogen complexes would be compatible with the notion that these structures are involved in the process of glycogen metabolism, as opposed to the previously suggested notion that these structures are transient vehicles for the accumulation of glycogen masses.

Membrane-glycogen complexes in rabbit extraocular muscle

Analysis of 432 electron micrographs of membrane-glycogen complexes revealed that: (1) Golgi apparatus is closely associated with 4.2% of the complexes, such associations occurring irrespective of the degree of glycogen loading in the complex. (2) Apparent ribosomes are seen in association with about 30% of the complexes, either attached to membranes or enclosed between cisternae. (3) In longitudinal sections of the muscle fibers, complexes may form columns which extend for as much as 40 microns along the fiber. (4) Various cytoplasmic organelles may become enclosed within a complex. (5) Some cisternae of a complex may assume the form of randomly oriented tubules, in contrast to the typical systematic array of flattened cisternae. (6) Some cisternae of a complex may become distended in a wide and uneven manner, in contrast to the typical narrow and even distension.

Cytoplasmic inclusions in rabbit extraocular muscle

Cytoplasmic inclusion bodies, similar to those previously described in abnormal and normal human extraocular muscle, were observed in the orbital surface layer of the superior rectus muscle in rabbit. These inclusion bodies are composed of a flocculent material of low density studded with granular foci of increased density. In sequential samples of serially reconstructed muscle fibers visualized by electron microscopy, cytoplasmic inclusion bodies were seen in 4.5% of 1187 samples through multiply innervated fibers that vary systematically in diameter along their length; inclusion bodies were also seen in 0.8% of 354 samples through multiple innervated fibers of constant diameter. Cytoplasmic inclusion bodies were not seen in 1838 samples through singly innervated fibers. These data suggest that such inclusion bodies may occur preferentially in multiply innervated fibers. The present findings are not compatible with previous suggestions that such cytoplasmic inclusion bodies may be indicative of a pathologic or aging process. These findings are consistent with previous suggestions that such inclusion bodies are to be considered as normal structures in extraocular muscle.

Variation of mitochondrial volume fraction along multiply innervated fibers in rabbit extraocular muscle

Mitochondrial volume fraction was compared among three regions along the length of six multiply innervated fibers (MIFs) in the orbital surface layer of rabbit superior rectus. These MIFs are of about 5 micrometer diameter toward the middle of their length, and of about 15 micrometer diameter toward their proximal and distal ends. The region of highest volume fraction (26%) was located toward the proximal end of their segment of minimal diameter, in apparent association with endplate-like nerve junctions. The region of lowest volume fraction (8%) was located at their distal segment of maximal diameter. The region toward the distal end of their segment of minimal diameter displayed an intermediate volume fraction (15%). These mitochondrial volume fractions were further analyzed in terms of the relative contributions of the I-band, the A-band, and the subsarcolemmal mitochondrial clusters. Comparable changes in mitochondrial content occur in both the I-band and A-band; in the fibers' distal segment of maximal diameter, however, the mitochondrial volume fraction in the A-band (5%) is lower than in the I-band (11%). These modifications of mitochondrial content along the fibers' length occur irrespective of the contributions of the subsarcolemmal mitochondrial clusters.

The distribution of membrane-glycogen complexes in the orbital surface layer of rabbit superior rectus

The distribution of membrane--glycogen complexes along the length of individual muscle fibers was compared among three fiber populations in the orbital surface layer of rabbit superior rectus. These three populations were (a) 61 singly innervated fibers (SIFs), (b) 10 multiply innervated fibers of relatively constant 10 micrometer diameter (10 micrometer MIFs), and (c) 22 multiply innervated fibers which are of about 5 micrometer diameter toward the middle of their length and of about 15 micrometer diameter toward their proximal and distal segments (5--15 micrometer MIFs). The orbital surface layer was sampled by electron microscopy at 68 sequential locations. Membrane--glycogen complexes were not seen in any of the 1738 samples of the SIFs. In the MIFs, such complexes were observed in 14% of the 1541 samples. However, both the 10 micrometer MIFs and 5--15 micrometer MIFs displayed a preferential concentration of membrane--glycogen complexes toward their distal fiber portions, and such complexes were seen in about 50% of the MIF samples near the beginning of the muscle's distal third. In the distal portion of 5--15 micrometer MIFs, there was a direct relationship between their increasing fiber diameter and their increasing frequency of occurrence of membrane--glycogen complexes.

Structural alterations of the junctional region in extraocular muscle of dystrophic mice. I. Modifications of sole-plate nuclei

Sole-plate nuclei of the C57Bl/6Jdy2j dystrophic mouse showed apparent selective susceptibility to various forms of structural alteration. Pyknosis and chromatin fragmentation were seen in addition to vacuolar and membranous nuclear inclusions. These were often associated with neuromuscular junctions with markedly reduced or virtually absent junctional folding. Membranous proliferations also occurred nearby sole-plate nuclei of such flattened junctions.