Genome-wide mapping with biallelic markers in Arabidopsis thaliana.

Single-nucleotide polymorphisms, as well as small insertions and deletions (here referred to collectively as simple nucleotide polymorphisms, or SNPs), comprise the largest set of sequence variants in most organisms. Positional cloning based on SNPs may accelerate the identification of human disease traits and a range of biologically informative mutations. The recent application of high-density oligonucleotide arrays to allele identification has made it feasible to genotype thousands of biallelic SNPs in a single experiment. It has yet to be established, however, whether SNP detection using oligonucleotide arrays can be used to accelerate the mapping of traits in diploid genomes. The cruciferous weed Arabidopsis thaliana is an attractive model system for the construction and use of biallelic SNP maps. Although important biological processes ranging from fertilization and cell fate determination to disease resistance have been modelled in A. thaliana, identifying mutations in this organism has been impeded by the lack of a high-density genetic map consisting of easily genotyped DNA markers. We report here the construction of a biallelic genetic map in A. thaliana with a resolution of 3.5 cM and its use in mapping Eds16, a gene involved in the defence response to the fungal pathogen Erysiphe orontii. Mapping of this trait involved the high-throughput generation of meiotic maps of F2 individuals using high-density oligonucleotide probe array-based genotyping. We developed a software package called InterMap and used it to automatically delimit Eds16 to a 7-cM interval on chromosome 1. These results are the first demonstration of biallelic mapping in diploid genomes and establish means for generalizing SNP-based maps to virtually any genetic organism.

Extensive polymorphisms observed in HIV-1 clade B protease gene using high-density oligonucleotide arrays.

Naturally occurring mutations in HIV-1-infected patients have important implications for therapy and the outcome of clinical studies. However, little is known about the prevalence of mutations that confer resistance to HIV-1 protease inhibitors in isolates derived from patients naive for such inhibitors. In the first clinical application of high-density oligonucleotide array sequencing, the sequences of 167 viral isolates from 102 patients have been determined. The DNA sequence of USA HIV-1 clade B proteases was found to be extremely variable and 47.5% of the 99 amino acid positions varied. This level of amino acid diversity is greater than that previously known for all worldwide HIV-1 clades combined (40%). Many of the amino acid changes that are known to contribute to drug resistance occurred as natural polymorphisms in isolates from patients who had never received protease inhibitors.

Accessing genetic information with high-density DNA arrays.

Rapid access to genetic information is central to the revolution taking place in molecular genetics. The simultaneous analysis of the entire human mitochondrial genome is described here. DNA arrays containing up to 135,000 probes complementary to the 16.6-kilobase human mitochondrial genome were generated by light-directed chemical synthesis. A two-color labeling scheme was developed that allows simultaneous comparison of a polymorphic target to a reference DNA or RNA. Complete hybridization patterns were revealed in a matter of minutes. Sequence polymorphisms were detected with single-base resolution and unprecedented efficiency. The methods described are generic and can be used to address a variety of questions in molecular genetics including gene expression, genetic linkage, and genetic variability.

Large-scale identification, mapping, and genotyping of single-nucleotide polymorphisms in the human genome.

Single-nucleotide polymorphisms (SNPs) are the most frequent type of variation in the human genome, and they provide powerful tools for a variety of medical genetic studies. In a large-scale survey for SNPs, 2.3 megabases of human genomic DNA was examined by a combination of gel-based sequencing and high-density variation-detection DNA chips. A total of 3241 candidate SNPs were identified. A genetic map was constructed showing the location of 2227 of these SNPs. Prototype genotyping chips were developed that allow simultaneous genotyping of 500 SNPs. The results provide a characterization of human diversity at the nucleotide level and demonstrate the feasibility of large-scale identification of human SNPs.

Multiplex sequencing by hybridization.

One of the limitations of classical sequencing by hybridization (SBH) is the inefficient use of probes in the "all k-mers" array. This limitation occurs due to the relatively short length (roughly the square root of C) of target that may be reconstructed by an array with C probes. We propose a new strategy, multiplex sequencing by hybridization, that greatly increases the efficiency of target reconstruction. In the typical multiplex SBH method, many different target sequences are simultaneously reconstructed (as compared to a single sequence in classic SBH). This is accomplished by pooling the target sequences and performing several hybridization experiments. This procedure makes more efficient use of probes so that the combined length of sequence reconstructed per DNA array increases significantly as compared to classical SBH.

Successful treatment of heart transplant rejection with photopheresis.

Photopheresis is a potential therapy for rejection in which reinfusion of mononuclear cells exposed to ultraviolet-A light ex vivo, after treatment with 8-methoxypsoralen in vivo, initiates host immune responses that specifically inhibit the cytotoxicity of the photomodulated mononuclear cells. Between May 1990 and January 1991, 7 heart transplant (HT) patients (age 42.2 +/- 16.7 [mean +/- SD] years) on triple immunosuppression (cyclosporine, corticosteroids, and azathioprine) had 9 episodes of non-hemodynamically compromising moderate rejection that were treated with photopheresis. These episodes of rejection occurred at an average of 114.4 +/- 180.5 (range 8-575) days after HT. After oral administration the mean serum level of 8-methoxypsoralen achieved was 129.0 +/- 72.4 ng/ml. An average of 10.4 +/- 9.6 x 10(9) mononuclear cells were treated with each photopheresis procedure. Photopheresis was performed twice when less than 5 x 10(9) mononuclear cells had been treated with the first procedure. Of 9 rejection episodes treated with photopheresis, 5 required 1 procedure and 4 required 2 procedures. Photopheresis was used to treat a single episode of rejection in 5 pts. and 2 separate rejection episodes in 2 additional pts. Eight of 9 episodes of rejection were successfully reversed by photopheresis as assessed by endomyocardial biopsy (EMB) performed 7 days after treatment. Immunohistochemical analysis of EMB samples revealed that postphotopheresis cell counts for T cells, B cells, and macrophages were reduced compared to pretreatment values and correlated with the histopathologic resolution of rejection. Hemodynamics were normal prephotopheresis and remained unchanged at the time when the postphotopheresis EMB showed no evidence rejection No adverse effects have been observed with photopheresis. Over a follow-up period of 5.3 +/- 4.0 months, rejection and infection rates/pt./follow-up months were 0.3 +/- 0.4 and 0.04 +/- 0.07, respectively. The preliminary, short term results of this pilot study indicate that photopheresis may be efficacious in the treatment of moderate rejection in hemodynamically stable HT patients and thus may be an alternative to corticosteroid pulses.

Using oligonucleotide probe arrays to access genetic diversity.

As the Human Genome Project and related efforts identify and determine the DNA sequences of human genes, it is important that highly reliable and efficient mechanisms are found to access individual genetic variation. It is only through a greater understanding of genetic diversity that the true benefit of the Human Genome Project will be realized. One approach, hybridization to high-density arrays of oligonucleotides, is a fast and effective means of accessing this genetic variation. Light-directed chemical synthesis has been used to generate miniaturized, high-density arrays of oligonucleotide probes. Application-specific oligonucleotide probe array designs have been developed for the rapid screening of characterized genes. Dedicated instrumentation and software have been developed for array hybridization, fluorescence detection and data acquisition and analysis. In a specific and challenging application, oligonucleotide probe arrays have been used to screen the reverse transcriptase and protease genes of the highly polymorphic HIV-1 genome to explore genetic diversity and detect mutations conferring resistance to antiviral drugs. Results from this application strongly suggest that oligonucleotide probe arrays will be a powerful tool for rapid investigations in sequence checking, pathogen detection, expression monitoring and DNA molecular recognition.

Endomyocardial biopsy findings after photopheresis treatment of cardiac transplant rejection.

Photopheresis is a potential therapy for allograft rejection in which reinfusion of mononuclear cells exposed to ultraviolet-A irradiation after pretreatment with 8-methoxypsoralen may initiate immunosuppressive responses. Endomyocardial biopsies (EMBs) of cardiac transplant recipients with moderate acute rejection (IHSLT grades 2 and 3) treated with photopheresis (7 patients/9 treatments) and followed for six months or more were evaluated and compared with biopsies of patients treated with corticosteroids (7 patients/8 treatments) and followed for a similar time period. The first posttreatment EMB showed improvement in 100% of corticosteroid-treated patients, compared with 56% of photopheresis-treated patients (p < 0.005). Interstitial infiltrates of >90% T-lymphocytes were present in a greater percentage of photopheresis-treated patients than in corticosteroid-treated patients on the first five posttreatment EMBs (p < 0.005) as follows: EMB 1, 90% vs. 25%; EMB 2, 90% vs. 25%; EMB 3, 78% vs. 0%; EMB 4, 56% vs. 0%, EMB 5, 56% vs. 0%. Postphotopheresis EMBs also showed giant cell reaction in 1 patient and extensive band-like infiltrates in 3 patients. Our results suggest that interstitial T-cell infiltrates are more prevalent and persist longer after photopheresis than after corticosteroid treatment of heart allograft rejection. Whether these T-lymphocytes are alloreactive or mediate immunosuppressive signals is unknown. The use of new immunosuppressive therapies may modify endomyocardial biopsy findings, requiring adjustment of the diagnostic criteria for assessing and grading allograft rejection.

Fidelity probes for DNA arrays.

One current approach to quality control in DNA array manufacturing is to synthesize a small set of test probes that detect variation in the manufacturing process. These fidelity probes consist of identical copies of the same probe, but they are deliberately manufactured using different steps of the manufacturing process. A known target is hybridized to these probes, and those hybridization results are indicative of the quality of the manufacturing process. It is not only desirable to detect variations, but also to analyze the variations that occur, indicating in what process step the manufacture changed. We describe a combinatorial approach which constructs a small set of fidelity probes that not only detect variations, but also point out the manufacturing step in which a variation has occurred. This algorithm is currently being used in mass-production of DNA arrays at Affyetrix.

High frequency variation in mammary tumor virus expression in cell culture.

Clonal derivatives of C3HMT murine mammary cell lines in culture demonstrate conversion of mammary tumor virus (MMTV) expression at a rate of appriximately 6 per 100 clones. This alteration is largely unidirectional from a relatively high level (MMTV(H)) to a 10 fold lower level (MMTV(L)). This high rate of MMTV(L) variant conversion is in apparent contrast to the presumably mutational rate (approximately 3 per million cells) that governs development of resistance to 6-thioguanine (TG) in the same mammary cells. In somatic cell hybrids between different MMTV TGr clones and mouse or hamster TK- cells, expression of constitutive levels of MMTV and responsiveness to dexamethasone induction is dominant. Thus MMTV expression is regulated by at least two levels of positive control, constitutive expression and glucocorticoid stimulation, but the former is subject to a high rate of variant formation.

Long-term follow-up of heart transplant recipients treated with murine antihuman mature T cell monoclonal antibody (OKT3): the Loyola experience.

We describe the long-term follow-up of 25 patients treated with murine antihuman mature T cell (OKT3) monoclonal antibody at Loyola University Medical Center. After OKT3 rescue therapy, 12 patients were monitored for 16.5 +/- 6.5 months. Twenty-two moderate and three severe rejection episodes occurred 11 to 469 days (166.8 +/- 126.0) after OKT3 therapy in nine of 12 patients. During the follow-up period three patients died, and one required retransplantation because of recurrent rejection. The coronary arteries of three failed allografts had severe intimal thickening and infiltration with lymphocytes. Thirteen patients received OKT3 for prophylactic immunosuppression, and their course was compared to that of 13 patients who underwent transplantation during the same period but were given prophylactic horse antihuman thymocyte globulins (HATG). There were no differences between the two drugs with respect to long-term incidence and severity of rejection and infection, cardiac allograft function, and survival. Our results indicate that, despite successful reversal with OKT3, heart transplant recipients with refractory rejection remain plagued by recurrent rejection. Cardiac allografts in recipients who die as a result of recurrent rejection show evidence of immune-mediated vasculitis, which results in severe and diffuse coronary luminal narrowing. OKT3 and HATG appear to be equally effective for rejection prophylaxis.

Photopheresis versus corticosteroids in the therapy of heart transplant rejection. Preliminary clinical report.

BACKGROUND: Photopheresis is a technique in which reinfusion of mononuclear cells exposed to UV-A light ex vivo after in vivo treatment with 8-methoxypsoralen initiates host-immunosuppressive responses. METHODS AND RESULTS: To determine if photopheresis safely reverses International Society for Heart and Lung Transplantation (ISHLT) rejection grades 2, 3A, and 3B without hemodynamic compromise, 16 heart transplant patients with ISHLT rejection grades 2, 3A, and 3B were randomized to photopheresis or corticosteroid therapy. The average number of mononuclear cells treated with each photopheresis procedure was 9.8 +/- 9.1 x 10(9) (mean +/- SD). Photopheresis and corticosteroids reversed eight of nine and seven of seven episodes of rejection, respectively. The median time from initiation of treatment to rejection reversal was 25 days (range, 6-67 days) in the photopheresis group and 17 days (range, 8-33 days) in the corticosteroid group. Hemodynamics were normal before either treatment and did not change after reversal of rejection. No adverse reactions occurred with photopheresis, and all patients in either treatment group are alive. CONCLUSIONS: These preliminary, short-term results in prospectively randomized patients indicate that photopheresis may be as effective as corticosteroids for treating ISHLT rejection grades 2, 3A, and 3B. The apparently low toxicity and potential efficacy of photopheresis warrant further analysis of its role in the prevention and treatment of heart transplant rejection.

Analysis of high density expression microarrays with signed-rank call algorithms.

MOTIVATION: We consider the detection of expressed genes and the comparison of them in different experiments with the high-density oligonucleotide microarrays. The results are summarized as the detection calls and comparison calls, and they should be robust against data outliers over a wide target concentration range. It is also helpful to provide parameters that can be adjusted by the user to balance specificity and sensitivity under various experimental conditions. RESULTS: We present rank-based algorithms for making detection and comparison calls on expression microarrays. The detection call algorithm utilizes the discrimination scores. The comparison call algorithm utilizes intensity differences. Both algorithms are based on Wilcoxon's signed-rank test. Several parameters in the algorithms can be adjusted by the user to alter levels of specificity and sensitivity. The algorithms were developed and analyzed using spiked-in genes arrayed in a Latin square format. In the call process, p-values are calculated to give a confidence level for the pertinent hypotheses. For comparison calls made between two arrays, two primary normalization factors are defined. To overcome the difficulty that constant normalization factors do not fit all probe sets, we perturb these primary normalization factors and make increasing or decreasing calls only if all resulting p-values fall within a defined critical region. Our algorithms also automatically handle scanner saturation.