Depletion of cytotoxic (CD8+) T cells impairs implant fixation in rat cancellous bone

As cytotoxic (CD8 + ) T cells seem to impair shaft fracture healing, we hypothesized that depletion of CD8 + cells would instead improve healing of cancellous bone. Additionally, we also tested if CD8‐depletion would influence the healing of ruptured Achilles tendons. Rats received a single injection of either anti‐CD8 antibodies or saline and put through surgery 24 h later. Three different surgical interventions were performed as follows: (1) a drill hole in the proximal tibia with microCT (BV/TV) to assess bone formation; (2) a screw in the proximal tibia with mechanical evaluation (pull‐out force) to assess fracture healing; (3) Achilles tendon transection with mechanical evaluation (force‐at‐failure) to assess tendon healing. Furthermore, CD8‐depletion was confirmed with flow cytometry on peripheral blood. Flow cytometric analysis confirmed depletion of CD8 + cells ( p  < 0.001). Contrary to our hypothesis, depletion of CD8 + cells reduced the implant pull‐out force by 19% ( p  < 0.05) and stiffness by 34% ( p  < 0.01), although the bone formation in the drill holes was the same as in the controls. Tendon healing was unaffected by CD8‐depletion. Our results suggest that CD8 + cells have an important part in cancellous bone healing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res