Quantification of Ηbβ^S+ RBCs in SCD recipients of IUHCT with or without a nonmyeloablative postnatal “booster” transplant. RBCs from naïve SCD mice, chimeric SCD mice following IUHCT, chimeric SCD mice that underwent a postnatal “booster” transplant following conditioning with 138 cGy TBI, and naïve SJL/J mice were stained with a FITC conjugated anti-human Ηbβ^S antibody. Representative immunofluorescence images demonstrate no staining of RBCs from SJL/J mice, whereas all RBCs from naïve SCD mice demonstrate positive staining. (A) Chimeric SCD mice following IUHCT alone or IUHCT + postnatal “booster” transplant demonstrated progressively less Ηbβ^S antibody staining, respectively. (B) The degree of anti-Hbβ^S antibody staining in chimeric SCD mice inversely correlated with the percentage of donor Hb noted on HPLC analysis.