Ex vivo assessment of anti-host and anti–third-party alloreactivity. MLR cultures were established using splenocytes obtained from nonmanipulated B6 controls (A) or 4- to 6-month-old BALB/c-SCID recipients receiving B6 NTCD via IUT (B) or TBI-conditioned BALB/c recipients of B6 TCD BM (C). Day-4 peak MLR responses to B6 (donor strain), BALB/c (host strain), or B10.BR (third-party strain) alloantigen-bearing stimulator cells were quantified. Mean values are shown. In all instances, one standard deviation of the mean was less than 84 cpm. Similar findings were observed on days 3 and 5 (not shown). The individual recipient animal number is presented as indicated on the x-axis. On the y-axis are the cpm obtained in the absence of scintillant amplification.