Impact of methionine oxidation in human IgG1 Fc on serum half-life of monoclonal antibodies

IgG monoclonal antibodies (mAbs) consist of two Fab fragments and one Fc fragment. The Fab fragments contain the variable regions and are responsible for drug specificity (via antigen binding); the Fc fragment contains constant regions and is responsible for effector functions (via interactions with Fcγ receptors) and extended serum half-life (via interaction with the neonatal Fc receptor, FcRn). There are two conserved methionine (Met) residues located in the FcRn binding site of the Fc fragment. It has been shown previously that oxidation of these two Met residues decreases the binding affinity to FcRn. We have further evaluated the impact of Met oxidation on serum half-lives of two humanized IgG1 mAbs in transgenic mice with human FcRn. Variable oxidation levels were obtained by several procedures: exposure to an oxidizing agent, accumulation during extended refrigerated storage, or chromatographic separation. Our results show that Met oxidation can result in a significant reduction of the serum circulation half-life and the magnitude of the change correlates well with the extent of Met oxidation and changes in FcRn binding affinities. The relatively low levels of Met oxidation accumulated during 3 years of refrigerated storage had minimal impact on FcRn binding and no detectable impact on the serum half-life.     

Canonical features of human antibodies recognizing the influenza hemagglutinin trimer interface

Broadly reactive antibodies targeting the influenza A virus hemagglutinin (HA) head domain are thought to be rare and to require extensive somatic mutations or unusual structural features to achieve breadth against divergent HA subtypes. Here we describe common genetic and structural features of protective human antibodies from several individuals recognizing the trimer interface (TI) of the influenza A HA head, a recently identified site of vulnerability. We examined the sequence of TI-reactive antibodies, determined crystal structures for TI antibody–antigen complexes, and analyzed the contact residues of the antibodies on HA to discover common genetic and structural features of TI antibodies. Our data reveal that many TI antibodies are encoded by a light chain variable gene segment incorporating a shared somatic mutation. In addition, these antibodies have a shared acidic residue in the heavy chain despite originating from diverse heavy chain variable gene segments. These studies show that the TI region of influenza A HA is a major antigenic site with conserved structural features that are recognized by a common human B cell public clonotype. The canonical nature of this antibody–antigen interaction suggests that the TI epitope might serve as an important target for structure-based vaccine design.     

Cross-linked versus conventional polyethylene for total hip replacement: a meta-analysis of randomised controlled trials

We conducted a systematic review and meta-analysis of randomised controlled trials comparing cross-linked with conventional polyethylene liners for total hip replacement in order to determine whether these liners reduce rates of wear, radiological evidence of osteolysis and the need for revision. The MEDLINE, EMBASE and COCHRANE databases were searched from their inception to May 2010 for all trials involving the use of cross-linked polyethylene in total hip replacement. Eligibility for inclusion in the review included the random allocation of treatments, the use of cross-linked and conventional polyethylene, and radiological wear as an outcome measure. The pooled mean differences were calculated for bedding-in, linear wear rate, three-dimensional linear wear rate, volumetric wear rate and total linear wear. Pooled risk ratios were calculated for radiological osteolysis and revision hip replacement. A search of the literature identified 194 potential studies, of which 12 met the inclusion criteria. All reported a significant reduction in radiological wear for cross-linked polyethylene. The pooled mean differences for linear rate of wear, three-dimensional linear rate of wear, volumetric wear rate and total linear wear were all significantly reduced for cross-linked polyethylene. The risk ratio for radiological osteolysis was 0.40 (95% confidence interval 0.27 to 0.58; I(2) = 0%), favouring cross-linked polyethylene. The follow-up was not long enough to show a difference in the need for revision surgery.     

The results of two-stage revision TKA using Ceftazidime–Vancomycin-impregnated cement articulating spacers in Tsukayama Type II periprosthetic joint infections

Purpose

This study examined the success and factors associated with failure, of using cement spacers impregnated with high-dose Ceftazidime and Vancomycin when performing two-stage revision for infected total knee arthroplasty (TKA).

Methods

A retrospective analysis was performed using a prospectively collected database of 82 patients (median age 68 years, range 39–87) with a confirmed deep TKA infection treated with a two-stage revision. All cement spacers were impregnated with high-dose Ceftazidime and Vancomycin. The rate of success was recorded—an association between failure of treatment, and patient factors, previous surgical treatment, and microbial characteristics was sought.

Results

The mean time to infection from index arthroplasty was 45 months (range 3–240). The initial two-stage revision was successful in 70/82 patients (85.4 %), who remained free of infection at average follow-up of 36.2 months (range 24–85). A second two-stage revision for infection was required in 12/82 patients (14.6 %), which was successful in 4/12 (33 %). A third two-stage revision was performed in three patients, all of whom had a polymicrobial infection of which only one patient had successful eradication of infection. Recurrent infection was correlated with irrigation and debridement with implant retention prior to initial two-stage revision (p < 0.01), polymicrobial infections (p = 0.035), and infections presenting <6 months after index surgery (p = 0.031). No correlation was seen with age, BMI, type of organism, diabetes mellitus, or Charlson Comorbidity Index.

Conclusion

The findings of this study suggest that the combination of Ceftazidime and Vancomycin in cement spacers is as efficacious as other published single or combined antibiotic mixtures, which is clinically relevant to clinicians treating this difficult problem in the setting of patients with compromised renal function.

     

The benefit of revision knee arthroplasty for component malrotation after primary total knee replacement

Purpose

Revision surgery for component malrotation in the painful TKA is a relatively novel indication. The purpose of this study was to assess the benefit of revision TKA for component malrotation with regard to the clinical and functional outcomes.

Methods

Our retrospective case–control study included 51 patients who underwent revision surgery for malrotation with mean follow up of 42 months. They were equally matched to patients who had surgery for aseptic loosening.

Results

Knee society scores improved from 44/49 to 75/60 (p < 0.001) for the study group and 44/47 to 76/57 (p < 0.001) for the control group. There was no statistical difference between the groups, including for VAS scores, narcotic reduction or patient satisfaction. Our study showed that revision surgery for malrotation is as beneficial as surgery for aseptic loosening with regard to clinical and functional outcome.

Conclusions

We recommend CT in painful TKA to assess component malrotation for which revision TKA is beneficial.     

Theory, Measurement and Hard Times: Some Issues for HIV/AIDS Research

Economic and political instability and related “big events” are widespread throughout the globe. Although they sometimes lead to epidemic HIV outbreaks, sometimes they do not—and we do not understand why. Current behavioural theories do not adequately address these processes, and thus cannot provide optimal guidance for effective intervention. Based in part on a critique of our prior “pathways” model of big events, we suggest that cultural–historical activity theory (CHAT) may provide a useful framework for HIV research in this area. Using CHAT concepts, we also suggest a number of areas in which new measures should be developed to make such research possible.     

Surgical management of healed slipped capital femoral epiphysis

Slipped capital femoral epiphysis (SCFE) results in posterior and inferior displacement of the epiphysis on the femoral neck. In most centers, the recommended initial management of stable SCFE is in situ pinning. Minimal reduction with in situ pinning is recommended for unstable SCFE. This approach does not restore the normal anatomy of the hip joint, and the resulting proximal femoral deformity may cause femoroacetabular impingement. Patients with femoroacetabular impingement experience reduced hip range of motion as well as hip pain, and they are at risk of early-onset hip osteoarthritis. Techniques for managing this deformity include arthroscopic femoral neck osteochondroplasty, a limited anterior hip approach or surgical hip dislocation, and flexion intertrochanteric osteotomy. These surgical techniques should be considered for patients with healed SCFE deformity who present with hip pain at an early age.