Abstract
Stem cell therapies have a great potential for the treatment of diseases. However, overcoming the host immune response to allogeneic stem cell grafts without the need of a strong immunosuppression remains an elusive goal. The current method for tolerance of grafts involves the use of systemic immunosuppression for the remaining life of the patient. This method can potentially make the patient more vulnerable to opportunistic infections and/or cancer. The removal of the immunosuppression has been shown to place the transplanted graft at risk. Therefore, it is essential for the recipient’s immune system to be insensitive to the donor’s Major Histocompatibility Complex (MHC). The immune system, specifically T cells play a major role in the rejection of the donor stem cells. MHC class I are also the antigens that cause rejection of allogeneic stem cells by host T cells. Previous studies have shown that activated NK cells could be useful in donor-specific tolerance, such as that using donor bone marrow. Different NK subsets could be used as clinical tools and may offer additional advantages when used as potential veto cells when compared to whole NK cell populations. We have applied this method in examining the tolerance of mouse embryonic stem cells (mESCs). It is seen that ES cells at different stages have different levels of MHC. ES cells seem to be naturally immunosuppressive, giving it an added advantage. Since ES cells have such great potential, it is important to understand its immunogenicity before it can be applied as treatments. In this study we hypothesized that the activated donor NK cells will act as “veto” cells by suppressing or deleting the host NK cells and Cytotoxic T Lymphocytes (CTLs) to prevent reactivity against the mESCs. This can potentially provide a strong immunosuppression post-transplant that is not limiting as the current method of systemic immunosuppression. B6 ALAKs were sorted for the separation of the NK subsets. Their functions were examined using a chromium release assay. An inhibition assay showed non-inhibitory Ly49 C/I+ subset function as more effective BALB/c suppressors compared to the Ly49 G2/A+ and whole ALAK populations. The long term killing assay showed at 72 hours, both NK and CD4+ T cells were susceptible to allogeneic killing by activated NK cells. Imaging allowed for visual detection of the mESC in vivo. The teratoma prevention further showed differential growth patterns between the subsets and between the administration routes of NK cells.