Single domain antibodies (sdAbs) are the recombinantly-expressed variable domain from camelid (or shark) heavy chain only antibodies and provide rugged recognition elements. Many sdAbs possess excellent affinity and specificity; most refold and are able to bind antigen after thermal denaturation. The sdAb A3, specific for the toxin Staphylococcal enterotoxin B (SEB), shows both sub-nanomolar affinity for its cognate antigen (0.14 nM) and an unusually high melting point of 85°C. Understanding the source of sdAb A3’s high melting temperature could provide a route for engineering improved melting temperatures into other sdAbs. The goal of this work was to determine how much of sdAb A3’s stability is derived from its complementarity determining regions (CDRs) versus its framework. Towards answering this question we constructed a series of CDR swap mutants in which the CDRs from unrelated sdAbs were integrated into A3’s framework and where A3’s CDRs were integrated into the framework of the other sdAbs. All three CDRs from A3 were moved to the frameworks of sdAb D1 (a ricin binder that melts at 50°C) and the anti-ricin sdAb C8 (melting point of 60°C). Similarly, the CDRs from sdAb D1 and sdAb C8 were moved to the sdAb A3 framework. In addition individual CDRs of sdAb A3 and sdAb D1 were swapped. Melting temperature and binding ability were assessed for each of the CDR-exchange mutants. This work showed that CDR2 plays a critical role in sdAb A3’s binding and stability. Overall, results from the CDR swaps indicate CDR interactions play a major role in the protein stability.

Melorheostosis is a rare sclerosing bone dysplasia that most commonly affects the lower extremity long bones in a sclerotomal distribution. Melorheostosis of the spine is a particularly rare manifestation of this disease. In the appendicular skeleton, melorheostosis has a pathognomonic imaging appearance of flowing hyperostosis resembling melted candle wax flowing down the margins of a candlestick. In the spine, it can have a variety of imaging manifestations from unilateral focal sclerotic lesions resembling enostoses, to more bulky and deformative hyperostosis that span and fuse multiple adjacent spinal segments. This combination of nonaggressive radiologic features makes melorheostosis a particularly important diagnosis for radiologists to understand so that they may spare their patients unnecessary biopsy. Here we present the clinical features and computed tomography findings in a 33-year-old male with spinal melorheostosis involving the first and second cervical vertebrae.

Primary hyperparathyroidism is most commonly caused by adenoma formation in one of the 4 parathyroid glands. The presence of ectopic parathyroid tissue is relatively common and can lead to difficulties in identification and treatment if affected by adenoma. This report describes the case of a 45-year-old female who presented 10 years status post thyroidectomy with symptomatic hyperparathyroidism and found to have ectopic parathyroid adenoma in the anterior mediastinum. Parathyroid scintigraphy with 99m-Technetium sestamibi and computed tomography were used for localization of the adenoma to a 1.9-centimeter para-aortic nodule. Computed tomography-guided transsternal cryoablation was subsequently performed for treatment, with intraoperative evaluation of serum parathyroid and calcium levels for confirmation. This case highlights that a sharp increase in parathyroid hormone immediately after cryoablation is not necessary for successful confirmation of the procedure. It additionally contributes to the growing literature on computed tomography-guided cryoablation as a legitimate alternative to surgery for treatment of ectopic parathyroid adenoma.