呼吸道合胞病毒逃逸株对单克隆抗体预防的抵抗

目的探讨体外筛选的呼吸道合胞病毒抗体逃逸株生长特性、F蛋白免疫反应性及在棉鼠体内对抗体免疫预防的抵抗，旨在证实用单克隆抗体免疫预防的负面效应，为今后临床可能出现的抗体逃逸株提供线索。方法呼吸道合胞病毒(RSV)A2株在逐渐升高的Pahvizumab(PZ)浓度环境中连续传代5次并经单噬斑纯化后获得PZ逃逸株MP4。用RT-PCR法扩增A2及MP4全长F基因并自动测序；用微量中和试验鉴定MP4在体外对PZ中和反应的抗性；用Western blot鉴定其F蛋白免疫反应性的变化；最后在棉鼠模型内观察PZ预防A2和MP4感染的效果。结果与A2母株比较，MP4于F基因828位核苷酸发生突变(A→T)，导致272位推导氨基酸由赖氨酸变为甲硫氨酸。MP4在体外及在棉鼠肺内的生长能力无明显改变。MP4F蛋白虽仍可表达于受感染细胞膜上，但不再被PZ识别。动物实验证实，即使大剂量PZ亦不能预防MP4感染。结论体外筛选的PZ逃逸株在棉鼠模型体内对同一抗体的免疫预防具有极强的抗性，类似情况是否会在人体内发生及是否会导致严重后果尚有待进一步研究。     

呼吸道合胞病毒单克隆抗体逃逸株体外适合度变化

目的 Palivizumab(PZ)是针对呼吸道合胞病毒(respiratory syncytial virus,RSV)F蛋白的人源化单克隆抗体(ScAb).本研究观察PZ逃逸株体外适合度变化规律.方法 采用竞争复制法测定两株Pz抵抗株(F212和MP4)的体外适合度.将等量F212和母株A2混合后在HEp-2细胞中连续转代,在不同时间点采用差异噬斑法、核酸序列图谱分析法和限制性片段多态性法分析混合病毒群体中F212和A2的比例.由于MP4在细胞培养和棉鼠肺内复制水平与A2相似,故将A2和MP4按照1:1、10:1、100:1和1000:1的比例混合并在HEp-2细胞中竞争复制,不同时点采用差异噬斑法和核酸序列图谱分析法分析混合病毒群体中MP4和A2比例.结果 等比例混合的F212/A2混合群体在传代至10代时,F212已基本消失,传至35代时仍无F212信号,提示其适合度低于A2.A2/MP4混合病毒群体中,除按1000:1比例预混外,其余所有比例预混的病毒中MP4均成为优势株,因而提示MP4的适合度高于A2.结论 首次发现RSV PZ逃逸株适合度可超过原型株A2,了解适合度增加或降低的机制对减毒活疫苗的研究有理论指导意义.     

呼吸道合胞病毒单克隆抗体逃逸株体内适合度研究

目的 此前研究已在体外筛选获得呼吸道合胞病毒(RSV)Palivizumab(PZ)逃逸株MP4,体外评估发现MP4适合度高于A2母株,本研究在免疫缺陷棉鼠模型中进一步评价MP4体内适合度.方法 采用大剂量环磷酰胺腹腔注射法制备免疫抑制鼠模型,将PZ逃逸株MP4和母株A2等量混合,经鼻腔接种免疫缺陷动物模型,于接种后4天和4周分批处死动物,取动物肺脏组织研磨后采用差异噬斑形成法或核苷酸序列图谱分析法检测混合病毒群体中母株A2和逃逸株MP4的相对含量,以代表MP4相对于A2的适合度.将肺内病毒F基因片段RT-PCR扩增产物克隆并转化大肠杆菌,随机挑取部分菌落再行PCR扩增F基因片段及序列测定,观察F基因第828位碱基并计算A2株和MP4相对含量.结果 差异噬斑法结果显示接种后4天和4周棉鼠肺内病毒混合群体中均以MP4占优,序列图谱分析发现接种后4周8只棉鼠中7只肺内MP4占优.接种后4周克隆的8只棉鼠F基因片段78%(120/154)为MP4基因信号.结论 与体外适合度结果类似,MP4在棉鼠肺内的适合度高于A2母株,提示与MP4基因型相同的逃逸株一旦产生,可能在免疫缺陷个体间传播.     

抗SARS冠状病毒中和活性单克隆抗体的筛选及其结合位点分析

目的 建立能分泌具有中和活性的抗SARS-CoV单克隆抗体（McAb）细胞株，制备有中和活性的抗SARS-CoV MeAb，用于SARS-CoV感染的早期特异诊断和进行SARS-CoV结构蛋白的功能研究。方法 用灭活纯化sARS-c0V（BJ01株）免疫BALB／c小鼠，通过细胞融合技术，建立能稳定分泌SAILS病毒MeAb的杂交瘤细胞系，然后用中和试验进一步筛选分泌具有中和活性的抗SARS-CoV MeAb细胞株。利用SARS-CoV的S和N蛋白的不同长度肽段通过EusA鉴定McAb的特异结合区域，分析S和N蛋白不同区域诱导产生抗体的能力和特性。结果 建立了12株能稳定分泌抗SARS-CoV McAb的杂交瘤细胞株，间接免疫荧光法检测抗体效价在1：320～1：20 480之间，其中6株具有较好的中和SARS-CoV的能力。具有中和活性的McAb中，3株是针对S蛋白的，2株是针对N蛋白的。其中抗S蛋白的中和抗体活性比抗N蛋白的中和抗体活性高，另外1株可能是针对SARS-CoV的其他结构蛋白的。进一步对6株抗S蛋白的McAb的特异抗原结合表位分析，发现其中3株结合位点在S蛋白第12～311氨基酸之间，2株在第310～535氨基酸之间，后者中和效价高于前者，另1株是针对S2蛋白的，SARS病毒的受体结合区正位于第310～535氨基酸这一区段。具有中和活性的McAb通过间接免疫荧光、ELISA、酶标免疫组化法和胶体金方法对SARS病毒进行检测，都显示出高度的特异性和良好亲和力。结论 成功制备了具中和活性的抗SARS-CoV单克隆抗体，并分别测定了McAb对S蛋白和N蛋白的特异抗原结合活性，初步确定了S蛋白的中和表位。为今后SARS病毒的特异诊断、结构蛋白的功能分析和重组疫苗的研制奠定了较好的基础。     

从噬菌体库中筛选抗SARS病毒S蛋白的Fab中和活性抗体研究

目的 从SARS病毒噬菌体抗体库中筛选出具有中和活性的抗S蛋白Fab片段抗体。方法ELISA方法对抗体库进行富集筛选及人源抗体克隆结合活性的测定，竞争ELISA初步筛选有中和活性的抗体，中和试验进一步确定中和活性，进而对其序列进行测定和分析。结果特异性富集了抗S蛋白噬菌体抗体，竞争ELISA筛选出两株抗体可部分阻断中和抗体2C5与S蛋白的结合，中和试验确定其具有一定巾和活性，编号为M1A和P8A，测序结果表明它们为两株不同的抗体克隆。结论筛选获得了两株抗体可部分中和SARS病毒活性，它们的获得为探索SARS病毒感染的被动免疫治疗打下了一定基础。     

马传染性贫血病毒囊膜蛋白GP90的表达及其免疫效果研究

目的：探索马传染性贫血病毒（EIAV）野毒株（强毒，LN）和疫苗毒株（弱毒，DLV）的囊膜蛋白GP90作为鉴别诊断试剂的效果及基因工程疫苗的可能性。方法：将中国EIAV疫苗株（DLV）及其亲本毒株辽毒株（LN）接种于驴外周血白细胞培养物，提取前病毒DNA，并以其为模板，经聚合酶链法（PCR）扩增出LN和DLV的GP90片段，在Bac-to-Bac杆状病毒表达系统表达。表达的GP90蛋白经金属离子亲和层析（IMAC）纯化后免疫小鼠，ELISA法检测抗EIAV抗体，中和试验检测中和抗体活性。同时对DLV和LN GP90的核苷酸与氨基酸进行比较。结果：DLV和LN GP90核苷酸序列的同源性为95．3％，氨基酸序列的同源性为87.7％。未加佐剂组抗体滴度为800，佐剂组抗体滴度达1600;不加佐剂组的中和抗体滴度在40－80之间，加佐剂组中和抗体滴度在80－160之间。结论：成功构建了分别表达EIAV野毒株LN和疫苗毒株DLV囊膜蛋白GP90的重组杆状病毒，大量表达的蛋白纯化后纯度较好，该纯化产物在小鼠体内可激发良好的体液免疫应答。     

人类免疫缺陷病毒感染细胞毒性T细胞逃逸突变的研究进展

人类免疫缺陷病毒（HIV）-1感染者体内活化的细胞毒性T细胞（CTL）反应不足以清除病毒，这是由于HIV。1在HLA限制的CTL压力下经常发生逃逸突变。但是，部分CTL逃逸突变会造成HIV病毒适应性的下降。近年来，人们对HIV-1感染中CTL逃逸突变的特征以及不同位点的逃逸突变在疾病进程中的作用进行了比较深入的研究，因而探讨CTL压力下HIV逃逸突变的规律有助于了解HIV-1自然感染中的免疫保护机制，并为开发有效的HIV疫苗提供依据。     

军团菌逃逸巨噬细胞杀伤效应的分子机制研究

目的：通过体外构建军团菌感染的细胞模型，探索caspase 3激活与军团菌逃逸巨噬细胞杀伤作用的相互关系。 方法： 军团菌感染巨噬细胞后，用激光共聚焦显微镜和荧光阅读机测定胞内caspase 3的活性。并在caspase 3抑制剂应用前后对军团菌在发生凋亡的巨噬细胞内的生长复制状况进行检测。 结果： 激光共聚焦显微术以及caspase 3荧光底物的分析结果显示，嗜肺性军团菌毒力株感染巨噬细胞后能够大幅度激活caspase 3，而去除毒力的突变菌株不具备这种能力。军团菌在感染巨噬细胞后不同的时间内，军团菌在胞内不断地复制繁殖，而毒力去除的突变株却没有复制能力。当胞内caspase 3的活性被抑制后，军团菌毒力株的复制繁殖能力也有了显著性的抑制。 结论： 军团菌感染巨噬细胞后能够在极短的时间内激活 caspase 3,并通过诱导巨噬细胞的凋亡来逃逸巨噬细胞的杀菌作用和发挥致病效应。     

抗人巨细胞病毒中和性人源基因工程抗体的研究

目的 研究抗人巨细胞病毒(HCMV)人源基因工程抗体。方法 采用噬菌体表面展示技术。首先从HCMV感染者外周血中分离淋巴细胞，提取RNA，逆转录后用特异性引物扩增轻、重链基因。然后插入噬菌体载体pComb3，构建噬菌体抗体库。使用纯化的HCMV病毒裂解物对噬菌体抗体库进行4轮富集，然后通过ELISA筛选阳性克隆，并对获得的克隆进行功能鉴定。结果 克隆和表达了3株抗HCMV人源Fab抗体，经ELISA证明均具有抗原结合活性，间接免疫荧光试验证明具有较高的特异性，最后通过病毒中和试验证明其中2株具有中和活性。结论 获得2株抗HCMV人源Fab抗体，具有一定的中和活性，为下一步研究抗HCMV人源全抗体奠定了基础。     

5株呼吸道合胞病毒地方株F蛋白基因序列分析

目的呼吸道合胞病毒（ＲＳＶ）Ｆ蛋白是ＲＳＶ感染免疫中最重要的病毒蛋白，为了解我国ＲＳＶ地方株Ｆ蛋白的基因状况和变异特征，随机选取北京、广州、长春和河北四个地区具有不同流行特征的ＲＳＶ地方株（Ａ亚型）５株，进行ＲＳＶＦ蛋白全基因的核苷酸序列分析。方法以提取的病毒ｍＲＮＡ为模板进行ＲＴ－ＰＣＲ扩增、目的基因的克隆及序列测定，对地方株及原型株的序列进行比较分析。结果地方株Ｆ蛋白基因与原型株Ａ２株有很高的同源性，核苷酸全序列的同源性为９５．１％～９６．１％，氨基酸同源性为９６．７％～９７．４％。核苷酸有义突变率为２２．６％～２５．９％。３非编码区的核苷酸序列比蛋白编码区变异显著。河北地方株（Ｅ７３株）在３非编码区有６个核苷酸的插入。Ｆ２亚单位的氨基酸变异高于Ｆ１亚单位。在北京地方株（ＺＨＳ１３株）Ｆ１亚单位内，由具有中和能力单克隆抗体所识别的抗原表位区中存在一个氨基酸的变异。结论我国ＲＳＶ地方株与原型株之间的Ｆ蛋白基因尽管存在一定的变异，但仍有很高的同源性。地方株间Ｆ蛋白的核苷酸、氨基酸变异的位置及形式很相似，提示我国ＲＳＶ的不同流行特征可能并非由于Ｆ蛋白的基因变异所致。     

Respiratory syncytial virus escape mutant derived in vitro resists palivizumab prophylaxis in cotton rats

Palivizumab (PZ) is the only monoclonal antibody in human use against an infectious disease. PZ is a humanized monoclonal antibody that recognizes the fusion protein of respiratory syncytial virus (RSV). PZ prophylaxis reduces the likelihood of hospitalization for young children at risk for severe RSV infections. The quasispecies nature of RNA viruses allows rapid emergence of viruses with a selective advantage. A PZ resistant virus was selected by passage of RSV in the presence of PZ in cell culture. The cell culture-derived virus was completely resistant to PZ prophylaxis in cotton rats. The increasing use of PZ, and in particular, the use of PZ in immunosuppressed patients, provide opportunities for resistant viruses to emerge. Whether such viruses will appear and be of clinical significance for humans is unknown. Preclinical studies in cotton rats predicted the efficacy of PZ in humans; these results suggest that if PZ resistant viruses arise in humans, PZ prophylaxis may be ineffective.     

Selection and characterization of human respiratory syncytial virus escape mutants resistant to a polyclonal antiserum raised against the F protein

A human respiratory syncytial virus (HRSV) neutralization escape mutant was obtained after 56 serial passages in the presence of a polyclonal antiserum raised against the F protein. Nucleotide sequence analysis of this escape mutant virus revealed two amino acid substitutions: Asn268Ile and Val533Met. When this virus was allowed to grow in the absence of the anti-F polyclonal serum, only the mutation Asn268Ile was stably maintained. Both the double and single escape mutant viruses lost reactivity with mAbs belonging to antigenic site II of the fusion protein of RSV. Mutation Asn268Ile has already been reported in RS viruses that are resistant to mAbs 47F and 11 and palivizumab (PZ). We have thus identified a novel mutation (Val533Met) in the transmembrane domain of the F protein that was selected under immune pressure.     

Molecular characterization of respiratory syncytial viruses infecting children reported to have received palivizumab immunoprophylaxis

BackgroundRespiratory syncytial virus (RSV) is a major cause of respiratory infections in children. Palivizumab (PZ) is the only RSV-specific immunoprophylaxis approved by the U.S. Food and Drug Administration. Mutations leading to amino acid substitutions in the PZ binding site of the RSV F protein have been associated with breakthrough RSV infections in patients receiving PZ.ObjectiveTo detect PZ resistance conferring mutations in RSV strains from children who received PZ.Study designChildren aged ≤24 months on October 31 who were hospitalized or had outpatient visits for respiratory illness and/or fever during October–May 2001–2008 in 3 US counties were included. PZ receipt was obtained from parent interviews and medical records among children subsequently infected with RSV. Archived nasal/throat swab specimens were tested for RSV by real-time RT-PCR. The coding region of the PZ binding site of the RSV F protein was sequenced using both Sanger and pyrosequencing methods.ResultsOf 8762 enrolled children, 375 (4.3%) were tested for RSV and had a history of PZ receipt, of which 56 (14.9%) were RSV-positive and 45 of these had available archived specimens. Molecular typing identified 42 partial F gene sequences in specimens from 39 children: 19 single RSV subgroup A, 17 subgroup B and 3 mixed infections. Nucleotide substitutions were identified in 12/42 (28.6%) RSV strains. PZ resistance mutations were identified in 4 (10.2%) of the 39 children, of which one had documented PZ receipt.ConclusionsAlthough RSV PZ resistance mutations were infrequent, most RSV-associated illnesses in children with a history of PZ receipt were not due to strain resistance.     

A single amino acid change within antigenic domain II of the spike protein of bovine coronavirus confers resistance to virus neutralization

The spike glycoprotein is a major neutralizing antigen of bovine coronavirus (BCV). Conformational neutralizing epitopes of group A and group B monoclonal antibodies (MAbs) have previously been mapped to two domains at amino acids 351 to 403 (domain I) and amino acids 517 to 621 (domain II). To further map antigenic sites, neutralization escape mutants of BCV were selected with a group A MAb which has both in vitro and in vivo virus-neutralizing ability. The escape mutants were demonstrated to be neutralization resistant to the selecting group A MAb and remained sensitive to neutralization by a group B MAb. In radioimmunoprecipitation assays, the spike proteins of neutralization escape mutants were shown to have lost their reactivities with the selecting group A MAb. Sequence analysis of the spike protein genes of the escape mutants identified a single nucleotide substitution of C to T at position 1583, resulting in the change of alanine to valine at amino acid position 528 (A528V). The mutation occurs in domain II and in a location which corresponds to the hypervariable region of the spike protein of the coronavirus mouse hepatitis virus. Experimental introduction of the A528V mutation into the wild-type spike protein resulted in the loss of MAb binding of the mutant protein, confirming that the single point mutation was responsible for the escape of BCV from immunological selective pressure.     

A Single Amino Acid Change within Antigenic Domain II of the Spike Protein of Bovine Coronavirus Confers Resistance to Virus Neutralization

The spike glycoprotein is a major neutralizing antigen of bovine coronavirus (BCV). Conformational neutralizing epitopes of group A and group B monoclonal antibodies (MAbs) have previously been mapped to two domains at amino acids 351 to 403 (domain I) and amino acids 517 to 621 (domain II). To further map antigenic sites, neutralization escape mutants of BCV were selected with a group A MAb which has both in vitro and in vivo virus-neutralizing ability. The escape mutants were demonstrated to be neutralization resistant to the selecting group A MAb and remained sensitive to neutralization by a group B MAb. In radioimmunoprecipitation assays, the spike proteins of neutralization escape mutants were shown to have lost their reactivities with the selecting group A MAb. Sequence analysis of the spike protein genes of the escape mutants identified a single nucleotide substitution of C to T at position 1583, resulting in the change of alanine to valine at amino acid position 528 (A528V). The mutation occurs in domain II and in a location which corresponds to the hypervariable region of the spike protein of the coronavirus mouse hepatitis virus. Experimental introduction of the A528V mutation into the wild-type spike protein resulted in the loss of MAb binding of the mutant protein, confirming that the single point mutation was responsible for the escape of BCV from immunological selective pressure.     

Genetic susceptibility to respiratory syncytial virus infection in inbred mice

Differences in the severity of respiratory syncytial virus (RSV)-induced lower respiratory disease in infants have been attributed to multiple environmental and genetic factors. To identify the genetic factor(s) influencing RSV susceptibility, we examined RSV infection in eight inbred mouse strains. Lung RSV titers differed significantly between mouse strains: the RSV titers were 15-fold higher in AKR/J (permissive) mice compared with C57BL/6J (resistant) mice at 4 days after inoculation. This strain-specific difference in RSV titers suggested that susceptibility to RSV infection was attributable to genetic differences between strains. To examine the mode of inheritance of RSV susceptibility, F1 and backcross (F1 x AKR/J) progeny were infected and RSV titers determined. RSV titers in the F1 progeny were similar to those found in the resistant (C57BL/6J) parent, suggesting resistance was inherited as a dominant trait. The distribution of RSV titers in backcross progeny were discordant with that predicted for a single gene effect, suggesting susceptibility was influenced by more than one gene. These data suggest that RSV susceptibility is a multigenic trait that should be amenable to resolution by genomic analysis.     

Genetic control of resistance of chick embryo cultures to RSV (RAV 50).

The genetic control of resistance of chick embryo cultures to RSV (RAV 50) was studied in crosses between the highly inbred Reaseheath lines, I, C and W and in the test-cross between WC(F1) and RPRL line 7. Embryo cultures resistant to RSV(RAV2) were also resistant to RSV(RAV 50). Genetic analysis of the segregation results of resistance and susceptibility in the F2, back-crosses, and test-cross populations suggests that the tvb genes pleiotropically control the resistance of the embryo cultures to RSV(RAV 50).     

Novel mutations in the respiratory syncytial virus G gene identified in viral isolates from a girl with severe combined immune deficiency treated with intravenous immune globulin.

BACKGROUND: Respiratory syncytial virus (RSV) can cause prolonged infections in individuals with compromised immunity. OBJECTIVES: To investigate whether RSV evolves during prolonged infection in an immunocompromised host. STUDY DESIGN: We sequenced the envalope glycoprotein genes of RSV obtained at three time points during a 59-day period from a 4-year-old female with severe combined immune deficiency (SCID) treated with intravenous immunoglobulin (IVIG). RESULTS: Sporadic silent mutations were found in the SH, G and F genes among three RSV samples collected at days 0, 19 and 59. Premature stop codons at amino acid positions 257 and 278 were present in the RSV G glycoprotein gene sequenced from each time point. None of the 48 RSV G sequences available on GenBank or any of 50 genetically diverse clinical isolates of RSV contained these mutations. These premature stop codon mutations occurred at the same positions of the G glycoprotein gene as those described in in vitro monoclonal-antibody resistant mutants reported elsewhere. CONCLUSION: Our patient was most likely infected with a single RSV strain that did not mutate during the study period. This strain contains unique mutations that may have previously evolved in this individual who had prolonged infection and was treated with monthly IVIG.