Donor-specific anti-HLA antibodies after bone-graft transplantation. Impact on a subsequent renal transplantation: a case report

Comparison between placental and skeletal muscle ECM: in vivo implantation

PURPOSE OF THE STUDY

Several tissues have been decellularized and their extracellular matrices used as allogeneic or xenogeneic scaffolds, either in orthotopic or heterotopic implantations, for tissue engineering purposes. Placentas have abundant matrix, extensive microvascular structure, immunomodulatory properties, growth factors and are discarded after birth, representing an interesting source of extracellular matrix. This study aimed at comparing decellularized canine placentas and murine skeletal muscles to regenerate skeletal muscles in a rat model.

MATERIALS AND METHODS

Muscle pockets were created at the posterior limbs of male Wistar rats, where the muscle- and placenta-derived extracellular matrices were implanted. Macroscopic, histological, and immunohistochemical analyses were performed after 3, 15, and 45 days of surgeries.

RESULTS

On the third day, intense inflammatory reaction, with macrophages (CD163⁺) and proliferative cells (PCNA⁺) being observed in control group and adjacent to the decellularized matrices. The percentage of proliferative cells was higher in placenta than in muscle matrices. Macrophages CD163^{+ high} were higher in muscles than in placentas, whereas CD163^{+ low} were higher in placentas than in muscle ECM, at days 3 and 15. Placental matrices were not completely degraded at day 15, as opposed to the muscular ones. After 45 days, both matrices were resorbed and morphologically normal myofibers, with reduction of cell infiltration, were observed.

CONCLUSIONS

These results demonstrated that xenogeneic placental ECM, implanted heterotopically (representing a biologically critical and challenging microenvironment), induced local inflammatory reactions similar to the allogeneic muscle ECM, implanted orthotopically. Thus, placenta-derived extracellular matrix must be further explored in regenerative medicine.

Donor-Specific Human Leukocyte Antigen Antibody Formation After Allograft Glenoid Reconstruction Occurs But Does Not Impact Clinicoradiographic Outcomes

BACKGROUND

Recurrent shoulder instability is a prevalent condition, with glenoid bone loss as a common cause. Arthroscopic repair using distal tibial allografts provides long-lasting treatment by restoring glenoid surface area and presumably avoids risks of sensitization against donor human leukocyte antigen (HLA). Two case studies have challenged this assumption, suggesting that small bone allografts are able to induce host adaptive immune responses to donor HLA. The incidence of small bone allograft HLA sensitization and its effects on resorption and patient outcomes are unclear.

PURPOSE/HYPOTHESIS

The purpose was to assess the rate of sensitization against donor HLA after distal tibial allograft procedures for shoulder instability due to glenoid bone loss and to find whether HLA sensitization negatively affects patient-reported and radiographic outcomes. We hypothesized that sensitized patients would have worse radiographic and self-reported outcomes compared with nonsensitized patients.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A total of 71 patients with a mean age of 28.85 years (range, 13.58-61.31 years) were enrolled, with 58 patients submitting sufficient pre- and postoperative blood samples for HLA antibody testing. In patients who developed HLA antibodies postoperatively, donor HLA typing was used to confirm donor-specific sensitization. Pre- and postoperative computerized tomography scans (0.9 ± 0.8 years follow-up) were used to grade resorption based on the modified Zhu resorption grade classification (ie, grade 0 = no resorption; grade 1 = less than 25% resorption; grade 2 = between 25% and 50% resorption; and grade 3 = larger than 50% resorption). The Western Ontario Shoulder Instability Index outcome scores were obtained preoperatively and at regular postoperative appointments. Resorption and outcome data were compared between sensitized and nonsensitized patients using the Fisher exact test, independent 2-tailed Student t tests, and the Wilcoxon rank-sum test to determine the effect of HLA sensitization on radiographic and patient-reported outcomes.

RESULTS

A total of 7 (12.1%) patients with sufficient HLA samples were sensitized against donor HLA postoperatively. Sensitized patients did not have significantly higher rates of resorption (21.9% vs 14.3%, 21.9% vs 28.6%, 43.8% vs 28.6%, and 12.5% vs 28.6% for respective resorption grades 0-3; P = .67; α = .05). Self-reported outcomes were not statistically significant between sensitized and nonsensitized patients (24.9 ± 27.61 vs 40.16 ± 18.99; P = .37; α = .05) and did not differ significantly based on resorption grade (47.4 ± 0.0 vs 55.2 ± 18.8, 30.4 ± 15.8 vs 39.9 ± 20.9, 41.2 ± 0.0 vs 39.1 ± 13.1, and -24.9 ± 0 vs 24.4 ± 19.6 for resorption grades 0-3; P > .05; α = .05).

CONCLUSION

Sensitization against donor HLA after small bone graft allografting was not previously considered but has been brought to light as a possibility. Aside from potential complications for future organ transplants, HLA sensitization does not introduce a risk for adverse outcomes or higher grades of resorption compared with nonsensitized patients after small bone allografting for shoulder instability.

Histological and immunohistochemical comparison of two different allogeneic bone grafting materials for alveolar ridge reconstruction: A prospective randomized trial in humans

Background

Preclinical studies have hypothesized a possible immunological reponse to allogeneic materials due to detection of remnants of potential immunogenic molecules. However, their impact on integration, bone remodeling and immunological reaction after the augmentation procedure is largely unknown and a direct correlation of analytical data and evaluation of human biopsies is missing.

Purpose

The present study aimed to compare two commercially available allogeneic materials regarding their content of cellular remnants as well as the bone remodeling, and integration and potential immunologic reactions on a histological and immunohistochemical level, integrating also in vitro analytical evaluation of the specific batches that were used clinically.

Materials and Methods

Twenty patients were randomly assigned to treatment with Maxgraft or Puros for lateral ridge augmentation in a two‐stage surgery. After a mean healing period of 5 months, implants were placed and biopsies were taken for histological, immunhistochemical, and histomorphometrical evaluation regarding bone remodeling and inflammation, protein concentrations in vitro and the presence of MHC molecules of the same batches used clinically.

Results

No differences in clinical outcome, histological, immunohistochemical, and in vitro protein analysis between the two bone grafting materials were observed. Active bone remodeling, amount of newly formed bone, and residual grafting material was independent of the materials used, but varied between subjects. MHC1 residues were not detected in any sample.

Conclusions

Within the limitations of this study, both tested materials yielded equivalent results in terms of clinical outcome, new bone formation, and lack of immunological potential on a histological and immunohistochemical level.

Detection of major histocompatibility complex molecules in processed allogeneic bone blocks for use in alveolar ridge reconstruction

OBJECTIVES

Because processed allogenic bone blocks contain remnants of cells and other organic material, the present study examined the putative presence of major histocompatibility complex (MHC) molecules in protein extracts derived from processed allogeneic bone blocks.

STUDY DESIGN

Protein content and the immunogenic potential of 3 different processed allografts (Osteograft, DIZG, Berlin, Germany; Caput femoris, DIZG, Berlin, Germany; Human Spongiosa, Charité Tissue Bank, Berlin, Germany) were assessed by protein extraction and analysis of the presence of MHC class 1 and 2 molecules prior to grafting. MHC concentration was measured by using enzyme-linked immunosorbent assay.

RESULTS

Protein content in the allograft materials varied between 0.87 and 1.61 µg protein/mg. In the allograft Human Spongiosa, no MHC was detected, whereas in the allogeneic bone blocks Osteograft and Caput femoris MHC 1 (0.04-0.037 ng/mg graft material) and in Osteograft MHC class 2 molecules were detectable.

CONCLUSIONS

The results of the present study suggest that despite thorough processing, a potential antigenicity of allografts is not eliminated. MHC molecules in allografts may sensitize the immune system.

Custom-milled individual allogeneic bone grafts for alveolar cleft osteoplasty-A technical note

INTRODUCTION

Bone grafts from the iliac crest are most commonly used for osteoplasties of the cleft alveolus. To preclude undue donoresite morbidity custom-milled allogeneic bone grafts might be an appropriate choice.

MATERIAL AND METHODS

This technical note showcases the repair of an alveolar cleft using an individualized allogeneic bone graft in a 36-year old female patient. She was asking for an alternative to the iliac crest bone grafting. Her alveolus was successfully build up by a custom-milled cancellous bone block allograft (maxgraft^® 80 bonebuilder).

RESULTS

Custom-milled cancellous bone block allografts can greatly facilitate alveolar cleft repair and may present an effective treatment option under the premise that resorption resistance corresponds to autografts.

CONCLUSION

Further clinical studies are needed to explore the potential of bone block allografts for alveolar cleft osteoplasty.

Allosensitization Following Bone Graft

It is recognized that patients may become sensitized to donor-specific HLA antigens as a result of previous antigenic exposures, classically through previous transplantation, pregnancy, or blood transfusion. We present an unusual case of a patient who unexpectedly developed a range of anti-HLA antibodies following orthopedic surgery where a bone graft was deployed intraoperatively. We describe the case of a 52-year-old man awaiting a renal transplantation, undergoing elective orthopedic surgery requiring a small-volume bone graft. His postoperative antibody profile was found to be substantially changed compared to his previous negative samples, with the presence of HLA-DR, DQ, and DP specificities, at levels that would be likely to give a positive flow cytometry crossmatch and therefore according to local procedures required listing as unacceptable antigens for organ allocation. We perform a literature review of all previous cases of allosensitization following bone graft. This case is the first to demonstrate allosensitization following minor surgery with ;low-volume bone graft. Previous evidence is very limited and pertains only to massive osteochondral surgery for trauma or malignancy, and is confounded by potential concomitant blood transfusion. Clinicians should be aware of the risk of allosensitization where bone grafts are used.