Molecularly specific detection of bacterial lipoteichoic acid for diagnosis of prosthetic joint infection of the bone

Abstract

Discriminating sterile inflammation from infection, especially in cases of aseptic loosening versus an actual prosthetic joint infection, is challenging and has significant treatment implications. Our goal was to evaluate a novel human monoclonal antibody (mAb) probe directed against the Gram-positive bacterial surface molecule lipoteichoic acid (LTA). Specificity and affinity were assessed in vitro. We then radiolabeled the anti-LTA mAb and evaluated its effectiveness as a diagnostic imaging tool for detecting infection via immunoPET imaging in an in vivo mouse model of prosthetic joint infection (PJI). In vitro and ex vivo binding of the anti-LTA mAb to pathogenic bacteria was measured with Octet, ELISA, and flow cytometry. The in vivo PJI mouse model was assessed using traditional imaging modalities, including positron emission tomography (PET) with [18F]FDG and [18F]NaF as well as X-ray computed tomography (CT), before being evaluated with the zirconium-89-labeled antibody specific for LTA ([89Zr]SAC55). The anti-LTA mAb exhibited specific binding in vitro to LTA-expressing bacteria. Results from imaging showed that our model could reliably simulate infection at the surgical site by bioluminescent imaging, conventional PET tracer imaging, and bone morphological changes by CT. One day following injection of both the radiolabeled anti-LTA and isotype control antibodies, the anti-LTA antibody demonstrated significantly greater (P < 0.05) uptake at S. aureus-infected prosthesis sites over either the same antibody at sterile prosthesis sites or of control non-specific antibody at infected prosthesis sites. Taken together, the radiolabeled anti-LTA mAb, [89Zr]SAC55, may serve as a valuable diagnostic molecular imaging probe to help distinguish between sterile inflammation and infection in the setting of PJI. Future studies are needed to determine whether these findings will translate to human PJI.

An update on radiotracer development for molecular imaging of bacterial infections

“…As a result, significant abscess-to-muscle ratios were only obtained 3 days post-injection. A mAb (1D9) directed against staphylococcal antigen A, Yersina adhesion A, or the Gram-positive bacterial surface molecule lipoteichoic acid was recently radiolabelled with either 64 Cu or 89 Zr (t 1/2 = 12.7 h and 78.4 h respectively) and evaluated using PET imaging in mice [23,24,26]. 1D9 mAbs clearly Table 1 Infection types, common causative bacterial pathogens (https ://www.uptod ate.com) and clinically approved radiotracer a These tracers are mainly applied in western hospitals as nearly two-thirds of the world's population does not have adequate access to radiological services [130] Infection targeted S. aureus at 3 days post-injection of the tracer with abscess-to-background ratios that were 2-3 times higher than in controls and comparable with ratios obtained with [ 18 F]-FDG ( Fig.…”

Current Clinical Methods for Detection of Peri-Prosthetic Joint Infection

“…With regard to MSIS minor criteria, current research demonstrates both promising and disappointing results. Methods using the detection of biomarkers indicative of an inflammatory response to an infection can be inconclusive at differentiating PJI from aseptic loosening [18,19]. Such biomarkers, measured in the serum and synovial fluid, include CRP detection, leukocyte counts and differential, and measurement of interleukin (IL)-6 levels.…”

“…Monoclonal mouse antibodies are also used to visualize bacteria, because radio-labeled mouse antibody targets lipoteichoic acid (LTA) in gram-positive cell walls [18]. On imaging the infected mice, a weak positive correlation between the bioluminescent signal and standardized uptake values was seen with an R value of 0.767 (R 2 = 0.588), indicating specificity of the radio-labeled antibody, but little direct association between the probes [18]. These bacterial biomarkers give a true determination of the bacterial presence in a surgical site, unlike inflammatory and coagulation markers that detect the presence of a response.…”

Review of nuclear medicine methods applied in diabetology

“…MAb 1D9 clearly targeted S. aureus on the 3 rd day after the radiotracer injection, the ratio of abscess to background was 2-3 times higher than in control groups and comparable to the results obtained from the 18 F-FDG-PET study. MAb 1D9 also showed nonspecific uptake in E. coli infections and lipopolysaccharide--induced sterile inflammations, attributed to the binding of MAb to Fc receptors present in the membrane of the cell-infiltrating macrophages [36][37][38].…”