Hemophilia A (HA) is a hemorrhagic disorder caused by a decrease/absence of coagulation Factor VIII (FVIII) in circulation. Management involves administration of FVIII to prevent bleeding episodes. The most serious complication of this replacement therapy is the development of inhibitory anti-FVIII antibodies which neutralize the infused FVIII. Low zone tolerance (LZT) is a state in which the immune system is unresponsive to an antigen induced by repeated prior exposure to low doses of said antigen. Previous animal studies exploring LZT demonstrated successful T-cell tolerance induction by this mechanism. This study investigated whether the administration of low-dose FVIII could induce immune tolerance to FVIII in a HA mouse model.
HA mice received intravenous FVIII at doses ranging from 0.01 IU/kg - 5 IU/kg to determine the most promising doses (0.25 IU/kg, 2.5 IU/Kg) to further investigate. Naïve mice were treated with 0.25 IU/kg or 2.5 IU/kg weekly for 6 weeks, then immunized with 25 IU/kg FVIII weekly for 4 weeks. Following a two-week rest period (week 12), all mice received a 25 IU/Kg booster shot. Blood was collected on weeks 7, 11 and 13 and anti-FVIII antibody concentrations were measured by ELISA. Control mice received phosphate buffered saline (PBS) during weeks 1-6 of the experiment, followed by identical immunizations as stated above.
Within the 2.5 IU/Kg FVIII treatment group, 11% of the mice developed tolerance to the treatment, indicated by undetectable anti-FVIII IgG titer by ELISA. The remaining 89% of these mice developed high titer antibodies, therefore they were not tolerized to FVIII. In the PBS treatment group, 62% of the mice developed high anti-FVIII antibodies. Conversely, 50% of the mice treated with 0.25 IU/kg were tolerized to FVIII and the remaining mice had significantly reduced antibody titers when compared to the controls. Moreover, upon booster dose injection, 100% of 0.25 IU/kg and 2.5 IU/Kg treated mice that were previously tolerized retained tolerance, suggesting that tolerance through low-dose injections is maintained upon FVIII re-exposure.
The LZT experiment conducted here shines light on a new approach to preventing FVIII inhibitors. This study suggests that frequently administering low doses of FVIII effectively induces tolerance to FVIII in HA mice. Moreover, treatment through LZT induction may confer long lasting protection against inhibitor development as indicated by the retention of tolerance in mice subjected to a rest period and post-treatment booster shot. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/28849 |
| Date | 11 1900 |
| Creators | Zaheer, Wajeeha |
| Contributors | Chan, Anthony, Medical Sciences (Thrombosis & Haemostasis & Atherosclerosis) |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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