The Novel Use of Hyperbaric Oxygen Therapy to Improve Umbilical Cord Blood Stem Cell Engraftment in Irradiated NOD/SCID Mice: What Did We Learn?

UCB is also an attractive stem cell source for transplantation because of the ease of procurement, the absence of donor risks, and reduced risk of transmissible infections. Unfortunately, outcomes of UCB stem cell transplantation are less than optimal because of low cell dose in umbilical cord blood units and defects in homing to bone marrow, which result in both delayed engraftment and delayed immune recovery, both of which increase the mortality rate in UCB transplants. In these experiments, we investigated the use of hyperbaric oxygen therapy (HBO) to improve cord blood stem cell homing and engraftment post irradiation.

Six to eight week old NOD/ SCID mice were sublethally irradiated 24 hours prior to cord blood stem cell infusion. The irradiated mice were then divided into two groups (10 mice each). One group of mice served as the control group were mice remained under normoxic conditions. The second group of animals, the HBO group, six hours prior to cord blood stem cell infusion, were exposed to two hours of hyperbaric conditions in a hyperbaric chamber, with 100% oxygen for 2 hours at 2.5 atmospheres absolute (ATA). Erythropoietin (epo) level was checked by ELISA, at time of cord blood stem cell infusion, and was used as a surrogate marker for effective HBO therapy. Prior to CD34+ cord blood stem cell injection, cryopreserved cord blood units obtained from St. Louis Cord Blood Bank were processed for CD34+ selection followed by their transduction with a luciferase lentivirus so that they can be serially imaged, using Xenogen-IVIS imaging system, for engraftment into the bone marrow. Subsequently, cord blood stem cells (7 × 10⁴ / 100 uL) in sterile PBS were administered by tail vein injection. The mice were weighed every other day and were sacrificed at 9–10 weeks post cord blood stem cell infusion. Peripheral blood and spleen tissue were obtained to determine donor engraftment by flow cytometry. Bone tissue was harvested for immunohistochemistry staining for human CD45.

Mean epo level in the HBO group was significantly lower than the mean epo level in the control group (226.7 ± 18.02 versus 294.4 ± 14.35 pg/ml (P=.0148)), consistent with effective HBO therapy. The average photon emission, or radiance, measured using the average of ventral and dorsal photon emission values per group, starting week 5, peaked at 7 weeks in the control mice, while peaked at 5 weeks in the HBO group. Since only ventral photon emission values were available during the first 4 weeks, an earlier peak in HBO group could not be excluded. One mouse in each group died, which was thought to be secondary to excessive bleeding related to mandible bleeding. No significant differences in median percentage peripheral blood or spleen engraftment were detected between the two groups. Interestingly, the HBO mice demonstrated a higher mean body weight started day 36 post cord blood stem cell infusion and continued until the end of study. Conclusions: HBO treatment did not result in detectable differences in terms of mean percentage peripheral blood or spleen engraftment at the end of study. However, HBO treated mice, compared to controls, showed an earlier photon emission peak values followed by lower photon emission values overtime. This earlier peak might have corresponded to the significant increase in weight noticed in the HBO mice starting week 5 post cord blood stem cell infusion.

*We acknowledge the help we received from St. Louis Cord Blood Bank who provided the cryopreserved cord blood units for this research.

No relevant conflicts of interest to declare.