Engineering of a recombinant trivalent single-chain variable fragment antibody directed against rabies virus glycoprotein G with improved neutralizing potency

Human and equine rabies immunoglobulins are currently available for passive immunization against rabies. However, these are hampered by the limited supply and some drawbacks. Advances in antibody engineering have led to overcome issues of clinical applications and to improve the protective efficacy. In the present study, we report the generation of a trivalent single-chain Fv (scFv50AD1-Fd), that recognizes the rabies virus glycoprotein, genetically fused to the trimerization domain of the bacteriophage T4 fibritin, termed ‘foldon’ (Fd). scFv50AD1-Fd was expressed as soluble recombinant protein in bacterial periplasmic space and purified through affinity chromatography. The molecular integrity and stability were analyzed by polyacrylamide gradient-gel electrophoresis, size-exclusion chromatography and incubation in human sera. The antigen-binding properties of the trimeric scFv were analyzed by direct and competitive-ELISA. Its apparent affinity constant was estimated at 1.4 ± 0.25 × 10⁹ M⁻¹ and was 75-fold higher than its monovalent scFv (1.9 ± 0.68 × 10⁷ M⁻¹). The scFv50AD1-Fd neutralized rabies virus in a standard in vitro and in vivo neutralization assay. We showed a high neutralization activity up to 75-fold compared with monovalent format and the WHO standard serum. The gain in avidity resulting from multivalency along with an improved biological activity makes the trivalent scFv50AD1-Fd construct an important reagent for rabies protection. The antibody engineering approach presented here may serve as a strategy for designing a new generation of anti-rabies for passive immunotherapy.     

A pilot study of nimotuzumab plus single agent chemotherapy as second- or third-line treatment or more in patients with recurrent,persistent or metastatic cervical cancer

Nimotuzumab is a humanized IgG1 monoclonal antibody against the EGFR extracellular domain that has been evaluated in solid tumors as a single agent or in combination with chemotherapy and radiation. Cervical cancer patients who are refractory or progressive to first-line chemotherapy have a dismal prognosis, and no second- or third-line chemotherapy is considered standard. This pilot trial aimed to evaluate the efficacy and safety of nimotuzumab in 17 patients with pre-treated advanced refractory or progressive cervical cancer. Nimotuzumab was administered weekly at 200 mg/m² as single agent for 4 weeks (induction phase), then concurrent with 6 21-day cycles of gemcitabine (800 mg/m²) or cisplatin (50 mg/m²) for 18 weeks (concurrent phase) and then once every 2 weeks (maintenance phase). Nimotuzumab could be continued beyond disease progression. Seventeen patients were accrued and evaluated for safety and efficacy. The median number of nimotuzumab applications was 20 (5–96). The median number of chemotherapy cycles administered was 6 (1-6). No toxicity occurred during induction and maintenance phases (single agent nimotuzumab). In the concurrent phase, grade 3 toxicity events observed were leucopenia, anemia and diarrhea in 11.7%, 5.8% and 11.7% respectively. No complete or partial responses were observed. The stable disease (SD) rate was 35%. The median PFS and OS rates were163 days (95% CI, 104 to 222), and 299 days (95% IC, 177 to 421) respectively. Nimotuzumab is well tolerated and may have a role in the treatment of advanced cervical cancer.     

Heterogeneity in the Antibody Response to Foot‐and‐Mouth Disease Primo‐vaccinated Calves

Foot‐and‐mouth disease (FMD) vaccines are routinely used as effective control tools in large regions worldwide and to limit outbreaks during epidemics. Vaccine‐induced protection in cattle has been largely correlated with the FMD virus (FMDV)‐specific antibodies. Genetic control of cattle immune adaptive responses has been demonstrated only for peptide antigens derived from FMDV structural proteins. Here, we quantify the heterogeneity in the antibody response of cattle primo‐vaccinated against FMD and study its association with the genetic background in Holstein and Jersey sires. A total of 377 FMDV‐seronegative calves (122 and 255 calves from 16 and 15 Holstein and Jersey sires, respectively) were included in the study. Samples were taken the day prior to primo‐vaccination and 45 days post‐vaccination (dpv). Animals received commercial tetravalent FMD single emulsion oil vaccines formulated with inactivated FMDV. Total FMDV‐specific antibody responses were studied against three viral strains included in the vaccine, and antibody titres were determined by liquid‐phase blocking ELISA. Three linear hierarchical mixed regression models, one for each strain, were formulated to assess the heterogeneity in the immune responses to vaccination. The dependent variables were the antibody titres induced against each FMDV strain at 45 dpv, whereas sire's ‘breed’ was included as a fixed effect, ‘sire’ was included as a random effect, and ‘farm’ was considered as a hierarchical factor to account for lack of independence of within herd measurements. A significant association was found between anti‐FMDV antibody responses and sire's breed, with lower immune responses found in the Jersey sires’ offspring compared with those from Holstein sires. No significant intrabreed variation was detected. In addition, farm management practices were similar in this study, and results of the serological assays were shown to be repeatable. It therefore seems plausible that differences in the immune response may be expected in the event of a mass vaccination campaigns.     

Assessing Antibody Strength: Comparison of MFI,C1q,and Titer Information

The presence of donor‐specific HLA antibodies before or after transplantation may have different implications based on the antibody strength. Yet, current approaches do not provide information regarding the true antibody strength as defined by antigen–antibody dissociation rate. To assess currently available methods, we compared between neat mean fluorescence intensity (MFI) values, C1q MFI values, ethylenediaminetetraacetic acid (EDTA)‐treated samples, as well as titration studies and peak MFI values of over 7000 Luminex‐based single‐antigen HLA antibody data points. Our results indicate that neat MFI values do not always accurately depict antibody strength. We further showed that EDTA treatment (6%) does not always remove all inhibitory factors compared with C1q or titration studies. In this study of patients presenting with multiple antibody specificities, a prozone effect was observed in 71% of the cohort (usually not affecting all antibody specificities within a single serum sample, though). Similar to titration studies, the C1q assay was able to address the issue of potential inhibition; however, its limitation is its low sensitivity and inability to detect the presence of weak antibodies. Titration studies are the only method among the approaches used in this study to provide information suggesting antigen–antibody dissociation rates and are, therefore, likely to provide better indication of true antibody strength.     

HLA‐G*01:04∼UTR3 Recipient Correlates With Lower Survival and Higher Frequency of Chronic Rejection After Lung Transplantation

Lung transplantation (LTx) is a valid therapeutic option for selected patients with end‐stage lung disease. Soluble HLA‐G (sHLA‐G) has been associated with increased graft survival and decreased rejection episodes in solid organ transplantation. HLA‐G haplotypes named UTRs, defined by SNPs from both the 5′URR and 3′UTR, have been reported to reliably predict sHLA‐G level. The aim of this retrospective study was to determine the impact of HLA‐G alleles and UTR polymorphism from LTx recipients on anti‐HLA allo‐immunization risk, overall survival and chronic rejection (CLAD). HLA‐G SNPs were genotyped in 124 recipients who underwent LTx from 1996 to 2010 in Marseille, 123 healthy individuals and 26 cystic fibrosis patients not requiring LTx. sHLA‐G levels were measured for 38 LTx patients at D0, M3 and M12 and for 123 healthy donors. HLA‐G*01:06～UTR2 was associated with a worse evolution of cystic fibrosis (p = 0.005) but not of long‐term survival post‐LTx. HLA‐G*01:04～UTR3 haplotype was associated with lower levels of sHLA‐G at D0 and M3 (p = 0.03), impaired long‐term survival (p = 0.001), increased CLAD occurrence (p = 0.03) and the production of de novo donor‐specific antibodies (DSA) at M3 (p = 0.01). This study is the first to show the deleterious association of different HLA‐G alleles and UTRs in LTx.     

Development and Impact of De Novo Anti‐HLA Antibodies in Pediatric Heart Transplant Recipients

There is increasing evidence that de novo anti‐HLA antibodies, more specifically de novo donor‐specific antibodies (DSA) following solid organ transplantation may be associated with negative outcomes including rejection in the first year and graft loss. Limited data are available in pediatric heart transplant recipients. We sought to prospectively determine the incidence, class and early impact of de novo anti‐HLA antibodies in a cohort of pediatric heart transplant recipients. Serial panel reactive antibody testing posttransplant was performed in 25 patients (14 males) transplanted between January 2008 and June 2010. Five patients were sensitized pretransplant; all patients had negative direct crossmatch. Seventy‐two percent developed de novo anti‐HLA antibodies at a median of 2.6 weeks (IQR 1.2 weeks to 6.2 months) posttransplant; 67% of these were DSA. The majority of recipients in our cohort developed de novo anti‐HLA antibodies within the first year posttransplant, with two‐thirds being donor‐specific. Acute cellular rejection, though frequent, was not different in patients with antibody development regardless of class or specificity, and there was no antibody‐mediated rejection, graft loss or early cardiac allograft vasculopathy.     

cPRA Increases With DQA,DPA, and DPB Unacceptable Antigens in the Canadian cPRA Calculator

A calculated panel reactive antibody (cPRA) estimates the percentage of donors with unacceptable antigens (UA) for a recipient. cPRA may be underestimated in transplant candidates with UA to DQA, DPA, and DPB if these are not included in the calculation program. To serve the National Canadian Transplant Programs, a cPRA calculator was developed with complete molecular typing for all donors at HLA‐A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPA1, and DPB1, all resolved to serologic equivalents. The prevalence of UA at DQA, DPA and DPB was evaluated in a sensitized regional population. The impact of adding these additional UA to cPRA was calculated alone and in combination, and compared to the baseline cPRA for UA at A, B, C, DR, DR51/52/53, and DQ. Of 740 sensitized transplant candidates, 18% of total and 32% with cPRA≥95% had DQA UA. Twenty‐seven percent of total and 54% with cPRA≥95% had DPB UA. Of 280/740 subjects with these UA, 36/280 (13%) had cPRA increase of >20% when they were included, 7% increased cPRA to ≥80% and 6% to ≥95%. Inclusion of DQA, DPA, and DPB UA in Canadian cPRA calculations improves the accuracy of cPRA where these are relevant in allocation.     

Potential deleterious role of anti‐Neu5Gc antibodies in xenotransplantation

Human beings do not synthesize the glycolyl form of the sialic acid (Neu5Gc) and only express the acetylated form of the sugar, whereas a diet‐based intake of Neu5Gc provokes a natural immunization and production of anti‐Neu5Gc antibodies in human serum. However, Neu5Gc is expressed on mammal glycoproteins and glycolipids in most organs and cells. We review here the relevance of Neu5Gc and anti‐Neu5Gc antibodies in the context of xenotransplantation and the use of animal‐derived molecules and products, as well as the possible consequences of a long‐term exposure to anti‐Neu5Gc antibodies in recipients of xenografts. In addition, the importance of an accurate estimation of the anti‐Neu5Gc response following xenotransplantation and the future contribution of knockout animals mimicking the human situation are also assessed.