Do mesenchymal stromal cells abrogate the immune response in massive cortical allograft recipients?

Abstract

OBJECTIVE: To evaluate the humoral and cellular immune response against bone associated antigens when delivered in a vaccine, and to evaluate the immunomodulation on the aforementioned immune response with the addition of adipose-derived mesenchymal stromal cells (AD-MSCs). ANIMALS: 68 C57BL/6 mice PROCEDURES: Femur fragments harvested from Balb/C or C57BL/6 mice were resuspended in PBS and cationic liposomal DNA complexes (CLDC) to create an allograft or autograft vaccine, respectively. A positive control vaccine was created utilizing bovine alkaline phosphatase (ALP) resuspended in PBS and CLDC. Twenty C57BL/6 mice were divided into four treatment groups: non-vaccinated (n=5), ALP vaccine recipients (n=5), allograft bone vaccine recipients (n=5), or autograft bone vaccine recipients (n=5). Forty-eight C57BL/6 mice were divided into the same 4 vaccine treatment groups (n=16), and received either intravenous AD-MSCs (n=8) or a subcutaneous injection of AD-MSCs (n=8). All mice received an initial vaccine on Day 1 and a booster vaccine on Day 7, followed by euthanasia on Day 21. Blood was collected on Day 1 and Day 7 just prior to vaccination, and on Day 21 just prior to euthanasia. Serum was subjected to an antibody detection ELISA to evaluate the humoral response. Spleens were collected and flow cytometry was used to evaluate T cell proliferation as an indicator of the cellular immune response. RESULTS: The bone vaccines did no elicit a detectable humoral immune response to the total bone antigen vaccine used in this model. The addition of AD-MSCs had no effect on the lack of a detectable humoral immune response. The T cell response towards a bone antigen was dampened in mice previously vaccinated with a bone vaccine. This effect was most pronounced when looking at the T cell response towards an allograft bone antigen in mice previously vaccinated with an allograft bone vaccine, particularly with the addition of AD-MSCs. CONCLUSIONS AND CLINICAL RELEVANCE: The bone vaccine model used in this study allowed evaluation of the humoral and cellular immune response towards bone associated antigens. The model suggests that recipients of an allograft bone vaccine will dampen the T cell proliferation seen upon second exposure to the bone antigens. This model could be used in future vaccine studies looking at the effect of vaccinating mice with a bone vaccine prior to undergoing a limb-salvage procedure. If efficacious, the bone vaccine model may provide a new treatment option for decreasing the risk of transplant rejection following massive limb reconstruction.