HLA-DPB1 as an Independent Predictor of Non-Relapse Mortality at Identical Match Scores: Evidence for a Primary Unscored Information Channel in Unrelated Donor Selection

Power law analysis of outcome variance within HLA match score groups across N=35,471 transplant pairs. Within-group overdispersion is 6-9x binomial expectation at every match level. At identical 9/10 match scores, PBM immunopeptidome divergence produces a 6.8 percentage point difference in 3-year overall survival. HLA-DPB1 carries HR_NRM = 1.50 and is not in the standard 10/10 cascade. Patient age asymmetry carries HR = 1.78 at identical match scores. Three actionable protocol recommendations: add HLA-DPB1 to the cascade, formalize age asymmetry scoring, adopt immunopeptidome divergence as tiebreaker.