In sequential PET studies, we observed increased uptake of [11C]PK11195 in one allograft (animal No. 10) at 3 months (Figures 3A and 3B). We could not detect any apparent uptake in the other animals or at any other time points (Figure S2). Intriguingly, the serum level of IFN-γ temporarily increased at 2 months after the transplant in three animals (Figure 3C). An immunofluorescence study conducted at 3.5–4 months showed that MHC-II+ cells were more frequently found in allografts than in autografts, especially in the monkey with increased uptake of [11C]PK11195 (Figure 3D, No. 10). The MHC-II staining never overlapped with that of GFP of the donor cells (Figure 3F), whereas it generally overlapped with that of IBA1 (Figure 3G), indicating that MHC-II was expressed by host-derived microglia. Consistently, the number and density of IBA1+ cells were higher in allografts than in autografts (Figures 3E, 3H, and S4C). An increase in the expression of MHC might trigger the recruitment of circulating immune cells, including T cells. An immunofluorescence study revealed that more CD45+ cells (a marker for pan-leukocytes) accumulated in allografts compared with autografts (Figures 3I and 3J). Most of the CD45+ cells were CD3+ T cells, and 60% of them were CD8+ killer T cells (Figures 3K and 3L). These findings suggest that an acquired immune response was elicited only in the allografts in the primate brain.
allograft
one
observed
3 months
months
serum level of IFN-γ temporarily increased
2 months
months
animals
three
immunofluorescence study conducted
3.5–4 months
months
CD45+ cells
CD8+ killer T cells
60%
%