Allogeneic IUHCTx leads to maturation of host and donor-derived APCs. BALB/c fetuses were transplanted with B6 fetal liver hematopoietic cells and analyzed at 1 and 5 weeks after transplantation. (A) Detection of donor cell cells among host cells in peripheral blood after first gating on CD45⁺ leukocytes. Chimerism was calculated as donor-derived (H-2K^b) CD45⁺ cells/total CD45⁺ cells. (B) Gating strategy to detect host and donor-derived APCs. cDCs (CD11c^HiB220^Low), pDCs (CD11c^dimB220^Hi), and B cells (CD11c⁻B220^Hi) were identified within the H-2K^d (host) or H-2K^b (donor) populations. (C) Comparison of splenic cDCs and circulating leukocyte chimerism (Lk) at 1 and 5 weeks. cDC chimerism was calculated by dividing the number of donor-derived cDCs by the total cDCs in the spleen of engrafted mice. (D) Relative MFI of class II, B7-1, B7-2, and CD40 on host- and donor-derived APCs in spleens of naive and chimeric animals was calculated relative to a baseline population (CD11c⁻B220⁻) to account for experimental variability. Uninjected, n = 9; chimera, n = 7. P values: *<.05, **<.01, ***<.001, ****<.0001 by Student t test.