FIGURE G-2 Cumulative proportion alive (engrafted) (TNC/kg = 2.5 − 5.0 × 10⁷).

dose increases, the HLA effects diminish. The residual differences are largely due to the significantly reduced engraftment rates for 4/6 and 5/6 HLA matches relative to that for a perfect 6/6 HLA match. These results suggest that units with lower cell dose can be given to recipients with a perfect match, whereas the highest cell doses should be given to recipients with 4/6 or 5/6 HLA matches, assuming that two potential recipients are in competition for the same unit. Table G-4 presents a breakdown of cell dose by HLA matches. Table G-4 reveals that 20 percent of all transplants were conducted with low cell doses in patients with 4/6 and 5/6 HLA matches. This amounts to 154 patients for whom the survival rate could have been doubled by use of a medium cell dose, or almost tripled by use of a high cell dose. In addition, 7 percent of all transplants were done using medium or high cell doses in perfectly matched (6/6) patient-donor pairs. These larger cell doses could have potentially been used to increase survival for 4/6 or 5/6 mismatched patients, without compromise to the 6/6 patient had a similar unit with smaller cell dose been available. These two results indicate that over 25 percent of the actual transplants were inefficiently allocated, leading to either unnecessarily poor survival or the use of an unnecessarily high cell dose for a patient-donor pair with a 6/6 HLA match. Both cell dose and HLA match should be considered in the final allocation system.