Translating in vitro prediction of cytotoxic T cell alloreactivity to hematopoietic stem cell transplantation outcome

•We investigate the clinical relevance of the CTLp assay in HLA mismatched HSCT.•A negative CTLp assay predicts for a low mortality rate after HLA mismatched HSCT.•Previously an AA mismatch score was developed which predicts for a negative CTLp.•The AA mismatch score needs validation to identify permissive HLA mismatches for HSCT.

IntroductionPreviously we developed a weighted amino acid (AA) mismatch score predictive for cytotoxic T cell (CTL) alloreactivity (in vitro CTLp assay) based on the structure of the HLA class I molecule. The aim of this study is to confirm the clinical relevance of the CTLp assay and to validate the AA mismatch score as an alternative and easy to use tool to predict permissible mismatches in hematopoietic stem cell transplantation (HSCT).MethodsWe selected patients transplanted with a 9/10 single HLA class I mismatched graft (n = 171) at three Dutch HSCT centers. A CTLp assay was performed in 73 donor–recipient pairs. As a control we selected 168 10/10 HLA matched pairs that were matched to the 9/10 single HLA class I mismatched pairs for HSCT year, donor type, patient age and diagnosis.ResultsWe observed that pairs with negative a CTLp assay had statistically significant decreased incidence of mortality after HSCT comparable to that of 10/10 HLA matched pairs. However, the weighted AA mismatch score did not significantly predict any HSCT end point of interest.ConclusionFurther investigation is needed to unravel the mechanisms involved in causing the beneficial effect of a negative CTLp assay, before other alternative tools to predict HSCT outcome may be developed.