Silicon micromachining to tissue engineer branched vascular channels for liver fabrication

To date, many approaches to engineering new tissue have emerged and they have all relied on vascularization from the host to provide permanent engraftment and mass transfer of oxygen and nutrients. Although this approach has been useful in many tissues, it has not been as successful in thick, complex tissues, particularly those comprising the large vital organs such as the liver, kidney, and heart. In this study, we report preliminary results using micromachining technologies on silicon and Pyrex surfaces to generate complete vascular systems that may be integrated with engineered tissue before implantation. Using standard photolithography techniques, trench patterns reminiscent of branched architecture of vascular and capillary networks were etched onto silicon and Pyrex surfaces to serve as templates. Hepatocytes and endothelial cells were cultured and subsequently lifted as single-cell monolayers from these two-dimensional molds. Both cell types were viable and proliferative on these surfaces. In addition, hepatocytes maintained albumin production. The lifted monolayers were then folded into compact three-dimensional tissues. Thus, with the use microfabrication technology in tissue engineering, it now seems feasible to consider lifting endothelial cells as branched vascular networks from two-dimensional templates that may ultimately be combined with layers of parenchymal tissue, such as hepatocytes, to form three-dimensional conformations of living vascularized tissue for implantation.

Factors associated with breast implant rupture: pilot of a retrospective analysis

This pilot study's goal was to test the feasibility of a data collection form which will be used in a scale-up study analyzing multiple surgeons' records. The goal of this expanded study will be to develop identifying factors for women who are at greater risk for having ruptured implants and, if necessary, target them for screening, surveillance, or intervention. In the pilot study, we compared factors associated with implant rupture in women with and without rupture. Similar studies have considered one or a few factors at a time and, generally, have given little attention to implant generation. We developed a data collection form after reviewing records of three surgeons. A total of 92 records was collected and analyzed. An important feature in the pilot was to compare the results of patients whose implants the surgeons had both implanted and explanted (n = 34) with those of patients whose implants the surgeons had only explanted (n = 55) (unknown = 3). This comparison could show if including all explantation patients in a surgeon's practice would bias the sample; however, based on this pilot data, concerns regarding this type of bias seem to be minimal. Similar amounts of data (e.g., implant information, history of capsular contracture, etc.) were collectable on patients whose surgeons both implanted and explanted them (87%) and who had different surgeons for implantation and explantation (84%). Though the data from this limited sample cannot offer firm conclusions on rupture associations, a few factors stood out: size of implants (38. 3% of ruptured versus 15.9% of intact implants were 100-200 cm3), history of mammography (46.8% of ruptured versus 24.4% of intact had mammograms, which is likely due to older women with older implants having more mammograms), and history of closed capsulotomy (85.1% of ruptured versus 68.9% of intact). Interestingly, additional procedures performed on the breast (e.g., scar revision, wound repair, etc.) did not affect rupture: both the ruptured and the intact groups had an average of 1.7 procedures performed. The data collection form tested very well in this pilot study. Also, including all patients in the study sample, instead of excluding those who received their implants elsewhere, did not change the results. Though there are not enough data to draw any firm conclusions regarding rupture factors, the collection instrument was rigorously tested and should perform well in an expanded study.

A review of the literature on the etiology of capsular contracture and a pilot study to determine the outcome of capsular contracture interventions

The etiology of capsular contracture is unclear and probably multifactorial. This review covers the literature on several proposed contracture factors, including filler material, implant placement, surface texture, and bacterial infection. The pilot study's goal was to test the feasibility of a data collection form, which could be used in a scaled-up study analyzing multiple surgeon's records. The goal of the expanded version of this study will be to determine the efficacy of available interventions for capsular contracture, including surveillance. The Breast Implant Public Health Project, LLC (BIPHP), piloted a retrospective review of outcomes in women who had interventions to relieve capsular contracture or had chosen a wait-and-watch approach. An evaluation of the efficacy of various treatments can help women decide if they want to pursue treatment at all and, if so, which treatment might offer them the best solution. BIPHP researchers (E.E.A., M.E.) developed a data collection form after reviewing records of three surgeons (B.C., W.P., V.L.Y.). During the data collection using the same records, we tested a randomization process to identify women with capsular contracture who underwent various interventions, including a wait-and-watch strategy, and those who had no mention of any intervention or waiting approach. Data were gathered on a total of 90 breasts with capsular contracture (scored Baker I-IV or qualitatively), of which 45 underwent a total of 102 interventions for capsular contracture. Interventions were classified as "closed capsulotomy," "surgical," or "watchful waiting." Closed capsulotomy was performed most often (47%), followed by surgery (29%) and watchful waiting (21%). Presurgical Baker scores averaged higher in breasts that underwent surgery (3.1) than for watchful waiting (2.5) or closed capsulotomy (2.3). Though closed capsulotomies had 100% of outcomes scoring "improved" or "same," 58% of the breasts underwent the procedure more than once, suggesting that the favorable outcome was short-lived. The wait-and-watch approach resulted in scores of either "same" or "worse"; surgery (open capsulotomy, repositioning, or capsulectomy) resulted in 79% improved, 16% same, and 5% worse outcomes in breasts with outcomes listed. In all intervention procedure categories, outcomes were frequently unavailable; they were noted only 60% of the time (52/87). The missing 40% may have resulted from the doctor's failure to note it in the chart, satisfied patients not returning for additional treatment, or dissatisfied patients seeking treatment elsewhere. Generally, the data collection forms and procedures were workable; however, we uncovered issues to address in the scale-up of this pilot study: (1) the outcome report rate was 60%; (2) though Baker scores are commonly used to evaluate the degree of capsular contracture, it seems that grade I may have different meanings for different surgeons, which would need to be clarified; (3) participating surgeons will need to divulge standard-of-care items that they may not have included in medical records, but routinely performed (e.g., patient massage, use of prophylactic antibiotics); and (4) records were initially separated by "implant," then researchers realized that a more useful collection would be by "breast." The latter approach captures the history of the breast in one record, which may be more important to contracture than the differences in implants. With the modifications discussed, the study can be scaled up to encompass as many records as necessary to achieve robust statistical power. These data will add to the existing literature regarding factors associated with capsular contracture and identify factors that affect the successful outcome of capsular contracture interventions.

8-methyl-pyridoxatin: A novel N-hydroxy pyridone from fungus OS-F61800 that induces erythropoietin in human cells

In the course of screening for small-molecule modulators of erythropoietin gene expression, a novel N-hydroxy pyridone was isolated from a culture of OS-F61800. Its structure was elucidated by extensive 1H and 13C NMR spectroscopic and chemical studies. This compound induced erythropoietin gene expression fivefold at a concentration of 0.3 microM, which is about threefold greater potency than our previously identified erythropoietin inducers.

Lack of long-term effects of in utero exposure to zidovudine among uninfected children born to HIV-infected women. Pediatric AIDS Clinical Trials Group Protocol 219/076 Teams

CONTEXT

With the success of zidovudine chemoprophylaxis for prevention of perinatal transmission of the human immunodeficiency virus (HIV), an increasing number of HIV-exposed but uninfected children will have in utero exposure to zidovudine and other antiretroviral drugs.

OBJECTIVE

To evaluate the long-term effects of in utero exposure to zidovudine vs placebo among a randomized cohort of uninfected children.

DESIGN

Prospective cohort study based on data collected during Pediatric AIDS Clinical Trials Group Protocol 076, a perinatal zidovudine HIV prevention trial, and Protocol 219, a long-term observational protocol.

SETTING

Pediatric research clinics in the United States.

PATIENTS

Two hundred thirty-four uninfected children born to 230 HIV-infected women enrolled in Protocol 076 and followed up through February 28, 1997, in Protocol 219 (122 in the zidovudine group and 112 in the placebo group).

MAIN OUTCOME MEASURES

Physical growth measurements, immunologic parameters, cognitive/developmental function, occurrence of neoplasms, and mortality data assessed every 6 months for children younger than 24 months and yearly thereafter or as clinically indicated. Baseline echocardiogram and funduscopic evaluations were collected before 36 months of age.

RESULTS

Median age of children at time of last follow-up visit was 4.2 years (range, 3.2-5.6 years). There were no significant differences between children exposed to zidovudine and those who received placebo in terms of sequential data on lymphocyte subsets; weight, height, and head circumference z scores; and cognitive/developmental function. No deaths or malignancies occurred. Two children (both exposed to zidovudine) are being followed up for abnormal, unexplained ophthalmic findings. One child exposed to zidovudine had a mild cardiomyopathy on echocardiogram at the age of 48 months; the child is clinically asymptomatic.

CONCLUSIONS

No adverse effects were observed in HIV-uninfected children with in utero and neonatal exposure to zidovudine followed up for as long as 5.6 years. Continued prospective evaluations of children born to HIV-infected women who are exposed to antiretroviral or immunotherapeutic agents are critical to assess the long-term safety of interventions that prevent perinatal HIV transmission.

The concentrations of clinafloxacin in alveolar macrophages, epithelial lining fluid, bronchial mucosa and serum after administration of single 200 mg oral doses to patients undergoing fibre-optic bronchoscopy

The concentrations of clinafloxacin were measured in serum, bronchial mucosa, alveolar macrophages and epithelial lining fluid after single 200 mg oral doses of clinafloxacin had been administered to 15 subjects who were undergoing bronchoscopy. Concentrations were measured using a microbiological assay method. Mean concentrations in serum, bronchial mucosa, alveolar macrophages and epithelial lining fluid at a mean of 1.27 h post-dose were 1.54, 2.65, 15.60 and 2.71 mg/L respectively. These site concentrations exceeded the MIC90 for common respiratory pathogens and indicate that clinafloxacin is likely to be effective in the treatment of a wide range of respiratory tract infections.

Epolones: novel sesquiterpene-tropolones from fungus OS-F69284 that induce erythropoietin in human cells

In the course of our screening for small molecule modulators of erythropoietin gene expression, two novel sesquiterpene tropolones and pycnidone were isolated from a culture of OS-F69284 (ATCC 74390). Their structures were elucidated by extensive 1H and 13C NMR spectroscopic studies and chemical reactions. These compounds induced erythropoietin gene expression 5-fold at a concentration of 1-1.6 microM.

Requirements for binding and signaling of the kinase domain receptor for vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is a dimeric hormone that controls much of vascular development through binding and activation of its kinase domain receptor (KDR). We produced analogs of VEGF that show it has two receptor-binding sites which are located near the poles of the dimer and straddle the interface between subunits. Deletion experiments in KDR indicate that of the seven IgG-like domains in the extracellular domain, only domains 2-3 are needed for tight binding of VEGF. Monomeric forms of the extracellular domain of KDR bind approximately 100 times weaker than dimeric forms showing a strong avidity component for binding of VEGF to predimerized forms of the receptor. Based upon these structure-function studies and a mechanism in which receptor dimerization is critical for signaling, we constructed a receptor antagonist in the form of a heterodimer of VEGF that contained one functional and one non-functional site. These studies establish a functional foundation for the design of VEGF analogs, mimics, and antagonists.

Concentrations of levofloxacin (HR 355) in the respiratory tract following a single oral dose in patients undergoing fibre-optic bronchoscopy

Concentrations of levofloxacin were measured in bronchial biopsies, alveolar macrophages (AM), epithelial lining fluid (ELF) and serum following a single oral dose. Concentrations were measured by a microbiological assay method. A total of 35 patients undergoing fibre-optic bronchoscopy were studied. Mean serum, AM, ELF and biopsy concentrations were as follows. 0.5 h: 4.73 mg/L, 19.1 mg/L, 4.74 mg/L and 4.3 mg/kg; 1 h: 6.6 mg/L, 32.5 mg/L, 10.8 mg/L and 8.3 mg/kg; 2 h: 4.9 mg/L, 41.9 mg/L, 9.0 mg/L and 6.5 mg/kg; 4 h: 4.1 mg/L, 27.7 mg/L, 10.9 mg/L and 6.0 mg/kg; and 6-8 h: 4.0 mg/L, 38.4 mg/L, 9.6 mg/L and 4.0 mg/kg respectively. Mean serum and AM concentrations at 12-24 h were 1.2 and 13.9 mg/L respectively (concentrations in biopsy and ELF were only measurable in three of the six patients). These concentrations exceed the MIC90s of the common respiratory pathogens, Haemophilus influenzae (0.015 mg/L), Moraxella catarrhalis (0.06 mg/L) and Streptococcus pneumoniae (1 mg/L) and suggest that levofloxacin should be efficacious in the treatment of community- and hospital-acquired respiratory infection.

Ruptured or intact: what can linear echoes within silicone breast implants tell us?

OBJECTIVE

During sonographic evaluation of silicone breast implants for possible rupture, we have frequently encountered several patterns of linear echoes within the implants. To our knowledge, the significance of this finding has not been established in the literature. The purpose of this study was to determine whether internal echoes are significant in predicting implant rupture.

SUBJECTS AND METHODS

Thirty-three patients with 64 silicone implants were prospectively entered into a study that included gray-scale sonography of the implants and subsequent surgical removal. Echo patterns within the implants were retrospectively evaluated on hard-copy films and compared with the integrity of the implant at surgery.

RESULTS

Three categories of internal echo patterns were identified: "thick linear echoes." "thin linear echoes," and "commas." One or more of these echo patterns were seen in 57 (89%) of the 64 implants. Thick linear echoes were seen in 23 (36%) of the 64 implants, thin linear echoes were seen in 33 (52%) of the 64 implants, and commas were seen in 47 (73%) of the 64 implants. All echo patterns were seen in intact and ruptured implants with nearly equal frequency. We found no statistical significance for any echo pattern in predicting whether an implant was ruptured or intact. Of the 64 implants, four were entirely free of internal echoes. All four implants were intact.

CONCLUSION

A variety of linear echoes can be seen in most silicone breast implants on gray-scale sonography. The presence or absence of linear echoes is not useful in predicting implant rupture. Complete absence of internal echoes, while highly predictive of an intact implant, is infrequently seen.

Concentrations of trovafloxacin in bronchial mucosa, epithelial lining fluid, alveolar macrophages and serum after administration of single or multiple oral doses to patients undergoing fibre-optic bronchoscopy

Concentrations of trovafloxacin were measured in serum, alveolar macrophages, epithelial lining fluid and bronchial mucosa following single and multiple oral doses. Concentrations were determined using a microbiological assay method. There were 18 subjects in the single dose and nine subjects in the multiple dose groups. After single dosing, mean concentrations in serum, alveolar macrophages, epithelial lining fluid and bronchial mucosa at 6, 12 and 24 h were as follows: 6 h, 1.41 mg/L, 19.06 mg/L, 3.01 mg/L and 1.52 mg/kg; 12 h, 0.85 mg/L, 16.22 mg/L, 4.8 mg/L and 1.01 mg/kg; 24 h, 0.37 mg/L, 10.23 mg/L, 0.93 mg/L, and no measurable concentration, respectively. After multiple dosing (approximately 6 h post-dose) the corresponding concentrations were 1.47 mg/L, 34.3 mg/L, 10.21 mg/L and 1.67 mg/kg, respectively. These concentrations exceed the MIC90s for the common respiratory pathogens, Haemophilus influenzae 0.06 mg/L, Moraxella catarrhalis 0.008 mg/L and Streptococcus pneumoniae 0.12 mg/L and suggest that trovafloxacin should be efficacious in the treatment of community- and hospital-acquired respiratory infections.

The Bentham Unit: a pilot remand and assessment service for male mentally disordered remand prisoners. II: Report of an independent evaluation

BACKGROUND

Findings are presented from an evaluation of a pilot remand and assessment service--the Bentham Unit. The aims of the Bentham Unit are to provide rapid assessment, identify mentally disordered remand prisoners, and speed their transfer from prison to NHS care, where a need is indicated.

METHOD

The number, rate and speed of referral, assessment and transfer to NHS care of offenders remanded to Wormwood Scrubs prison during periods before and after the Bentham Unit opened were compared.

RESULTS

The service attracted a large volume of referrals. Between the two periods, significant increases in the numbers of referrals and hospital disposals, and major reductions in the interval between reception on remand into the prison, NHS assessment and transfer to NHS care, were observed.

CONCLUSIONS

The aims of the unit were met. Implications for service configurations are discussed.

Oxygen protocols for the prevention of hypoxemia. A review for case managers

Case managers are challenged by the need to ensure quality care for patients in the face of increasing demands on the health care system to provide more economic care. These economic pressures often cause hospitalized patients to be transferred from critical care areas earlier than in years past. As a result, hypoxemia-inadequate oxygenation of the blood-is emerging as a serious patient safety problem in noncritical care areas of the hospital. The medical literature recently has begun to document hypoxemia in some patient groups on the general care floor, where continuous monitoring of patients' respiratory status usually is no longer employed. The serious health consequences of hypoxemia, the fact that it can affect nearly any hospitalized patient, and the potentially high cost of treating hypoxemia-related morbidity are drawing the attention of the medical community. Case managers are in a position to address this emerging problem by working with hospitals and health care institutions to identify at-risk patients and develop strategies to improve both clinical and financial outcomes. Patient care protocols are one effective strategy to standardize monitoring of patients deemed to be at risk. Early detection and treatment of hypoxemia have the potential to improve patient care while significantly reducing medical costs.

A biomechanical study of the flexor digitorum superficialis: effects of digital pulley excision and loss of the flexor digitorum profundus

Many reports have been devoted to characterizing the significance of the pulleys for the flexor digitorum profundus (FDP). However, no comparable work has been published on the flexor digitorum superficialis (FDS). This study characterized the FDS in a human cadaver model. Eleven fresh-frozen cadaver hands were used. By using a tensiometer, data were gathered for tendon excursion, tendon load, and work of flexion. Changes in efficiency were caused by excision of annular pulleys A1, A2, A3, and the palmar aponeurotic pulley. We also measured the effect of FDP excision on FDS efficiency. Sectioning of the A2 and A3 pulleys together caused statistically significant losses of efficiency in all three parameters (work, load, and excursion). When the FDP was removed from a finger with an intact pulley system, losses in both work and excursion efficiencies were significant. Removing the FDP while cutting different pulleys caused significant decrease in FDS excursion efficiency. We conclude that A2 and A3 are the most important pulleys for maintaining normal FDS function, and that the presence of the FDP in the digital sheath is essential for optimal FDS excursion efficiency.

Novel analog of atrial natriuretic peptide selective for receptor-A produces increased diuresis and natriuresis in rats

Atrial natriuretic peptide (ANP) binds to natriuretic peptide receptor-A (NPR-A), a membrane guanylyl cyclase, and to natriuretic peptide receptor-C (NPR-C), which plays a role in peptide clearance. Rat ANP (rANP) mutants that bind rat NPR-A selectively over rat NPR-C were isolated from randomized libraries of rANP-display phage by differential panning. One variant was identified with reduced NPR-C binding; rANP (G16R, A17E, Q18A) [rANP(REA18)]. Synthetic rANP(REA18) was equipotent with rANP in stimulating cGMP production from cloned rat NPR-A (ED50 = 1.8 nM) and was reduced in NPR-C binding by approximately 200-fold. When infused into conscious rats at 0.325 microg/min for 30 min rANP elicited an identical decrease in blood pressure compared with 0.25 microg/min of rANP(REA18), however the natriuretic (P < 0.05) and diuretic (P = 0.07) responses to rANP(REA18) were greater. These data are consistent with a role for NPR-C as a local decoy receptor attenuating NPR-A effects in the kidney, where these receptors are coexpressed. Improved NPR-A specificity could provide more effective natriuretic peptides for treatment of acute renal failure or heart failure.

The use of capillary electrophoresis to monitor the stability of a dual-action cephalosporin in solution

Ro 23-9424 is a broad-spectrum antibacterial agent consisting of a cephalosporin and a quinolone moiety which are held together by an ester linkage. This compound has limited solubility in water but is more soluble at alkaline pH. Such high pH values, however, lead to stability problems due to the lability of the ester linkage, and result in the formation of the free quinolone and cephalosporin moieties. The balance between solubility and stability presents a challenge in formulation development for this compound. Thus, it is important to effectively monitor the stability of Ro 23-9424 after it has been reconstituted in different solvent systems. In this manner, a diluent which does not lead to degradation of the drug can be identified. A capillary electrophoresis method was developed and validated to monitor the stability of Ro 23-9424. The method was found to meet acceptable criteria for method precision, system precision, linearity and limits of detection and quantitation. The method was used to monitor the stability and measure the half-life of Ro 23-9424 in water and in an L-arginine-sodium benzoate-saline diluent designed to mimic the drug delivery system. This work shows that capillary electrophoresis can be used to compare the stability of a drug in different solutions as an aid in formulation development.

Stability of reamed and unreamed intramedullary tibial nails: a biomechanical study

We examined the correlation of bone mineral density and bone strength in the cadaver tibia, and looked in vitro at the relative stability of tibial fractures fixed with either reamed or unreamed tibial nails. Bone-mineral density correlated well with bone strength (r = 0.946), but paired tibias did not correlate closely. The unreamed nail-bone construct was less stable than the reamed construct in each pair tested (P < 0.05), and a comparison of all bones showed it to be less stable at all levels of our testing regimen, including failure (P < 0.01). Bending and breakage was seen in four of the smaller unreamed interlocking screws (4 mm).

Diagnosis of breast implant rupture: imaging findings and relative efficacies of imaging techniques

OBJECTIVE

The purpose of this study was to compare the efficacies of mammography, sonography, CT, and MR imaging in the detection of breast implant rupture and to analyze the imaging findings.

SUBJECTS AND METHODS

Thirty-two women with 63 silicone breast implants participated in the study. All but one had signs and symptoms suggestive of rupture, and all had requested that their implants be removed before they were enrolled in this imaging study. All patients had film-screen mammography, sonography, CT, and MR imaging. Twenty-two ruptures were found at surgery; 21 were intracapsular and one was extracapsular. The relative efficacies of the imaging studies were determined, and the imaging findings were compared with the surgical results.

RESULTS

Of the 32 women with 63 implants, mammographic sensitivity for detecting implant rupture was only 23% but the specificity was 98%. Sonography had a higher sensitivity (59%), but its specificity was significantly lower (79%). CT had a sensitivity of 82% and a specificity of 88%. MR was the only imaging technique that consistently provided evidence that enabled the evaluation of intracapsular and extracapsular ruptures. The sensitivity and specificity of MR imaging were 95% and 93%, respectively.

CONCLUSION

Our results show that MR imaging is more sensitive and specific for the detection of breast implant rupture than is mammography, CT, or sonography.

Recognition by HLA-A2-restricted cytotoxic T lymphocytes of endogenously generated and exogenously provided synthetic peptide analogues of the influenza A virus matrix protein

Experiments were carried out to determine whether complexes between MHC class I molecules and synthetic peptides are representative of those formed under more physiologically relevant conditions, with peptides derived intracellularly from processed antigens. Lysis of cells sensitized with exogenously provided and endogenously generated peptide analogues of the optimal nonameric peptide 58-66 (GILGFVFTL; derived from the influenza virus matrix protein) was compared. Endogenous loading was accomplished by expressing minigene DNA coding for alanine-substituted analogues of peptide 58-66 in HLA-A2-positive cells. Susceptibility to lysis by HLA-A2-restricted, peptide-specific cytotoxic lymphocytes was compared with lysis of cells sensitized with the same synthetic peptides. Although results were quite comparable, differences were observed. The endogenously presented analogues 58-66L60A, G61A, T65A, and L66A were recognized more efficiently than the corresponding exogenously presented analogues. This difference in recognition was most striking for peptide 58-66G61A. These results indicate the need for caution in using synthetic peptides in defining peptide binding motifs. Additional experiments with endogenously expressed analogues of 58-66 with substitutions other than alanine were carried out to define the interaction between this peptide and HLA-A2. Results are compatible with the interpretation that residues 58, 59, and 60 interact with pockets A, B, and D, respectively, in the HLA-A2 binding groove and that these interactions contribute to peptide binding.

Sequence motifs important for peptide binding to the human MHC class I molecule, HLA-A2

Previous studies have indicated that most HLA-A2-binding peptides are 9 amino acid (aa) residues long, with a Leu at position 2 (P2), and a Val or Leu at P9. We compared the binding properties of different peptides by measuring the rate of dissociation of beta 2-microglobulin from peptide-specific HLA-A2 complexes. The simplest peptide that we identified that could form HLA-A2 complexes had the sequence (in single letter aa code) GLFGGGGGV, indicating that three nonglycine aa are sufficient for binding to HLA-A2. To determine whether most nonapeptides that contained Leu at P2 and Val or Leu at P9 could bind to HLA-A2, we tested the binding of nonapeptides selected from published HIV and melanoma protein sequences, and found that six of seven tested formed stable HLA-A2 complexes. We identified an optimal antigenic undecapeptide from the cytomegalovirus gB protein that could form stable HLA-A2 complexes that contained apparent anchor residues at P2 and P11 (sequence FIAGN-SAYEYV), indicating that the spacing between anchor residues can be somewhat variable. Finally, we tested the importance of every aa in the influenza A matrix peptide 58-66 (sequence GILGFVFTL) for binding to HLA-A2, by using Ala-substituted and Lys-substituted peptides. We found that multiple positions were important for stable binding, including P2, P3, P5-P7, and P9. We conclude that the P2 and P9 anchor residues are of prime importance for peptide binding to HLA-A2. However, other peptide side chains (especially at P3) contribute to the stability of the interaction. In certain cases, the optimal length for peptide binding can be longer than 9 residues.

Sequence motifs important for peptide binding to the human MHC class I molecule, HLA-A2

Previous studies have indicated that most HLA-A2-binding peptides are 9 amino acid (aa) residues long, with a Leu at position 2 (P2), and a Val or Leu at P9. We compared the binding properties of different peptides by measuring the rate of dissociation of beta 2-microglobulin from peptide-specific HLA-A2 complexes. The simplest peptide that we identified that could form HLA-A2 complexes had the sequence (in single letter aa code) GLFGGGGGV, indicating that three nonglycine aa are sufficient for binding to HLA-A2. To determine whether most nonapeptides that contained Leu at P2 and Val or Leu at P9 could bind to HLA-A2, we tested the binding of nonapeptides selected from published HIV and melanoma protein sequences, and found that six of seven tested formed stable HLA-A2 complexes. We identified an optimal antigenic undecapeptide from the cytomegalovirus gB protein that could form stable HLA-A2 complexes that contained apparent anchor residues at P2 and P11 (sequence FIAGN-SAYEYV), indicating that the spacing between anchor residues can be somewhat variable. Finally, we tested the importance of every aa in the influenza A matrix peptide 58-66 (sequence GILGFVFTL) for binding to HLA-A2, by using Ala-substituted and Lys-substituted peptides. We found that multiple positions were important for stable binding, including P2, P3, P5-P7, and P9. We conclude that the P2 and P9 anchor residues are of prime importance for peptide binding to HLA-A2. However, other peptide side chains (especially at P3) contribute to the stability of the interaction. In certain cases, the optimal length for peptide binding can be longer than 9 residues.