ZAP70 in B-CLL cells related to the expression in NK cells is a surrogate marker for mutational status.

The strongest prognostic factor in chronic B-cell lymphocytic leukemia (CLL) is the mutational status of the immunoglobulin heavy chain variable region (IGHV) genes. Determination of this mutational status is laborious and therefore not applied in routine diagnostics. A search for "surrogate markers" has been conducted over the past few years. One of the most promising surrogate markers is ZAP70, but standardization of the measurement of ZAP70 has proven to be difficult. Conventionally, ZAP70 expression in CLL cells is related to ZAP70 expression in T cells. We propose a new method in which ZAP70 expression in NK cells is used as reference (new NK-MFI method). We have measured ZAP70 expression in samples of 45 previously untreated CLL patients. ZAP70 in CLL cells related to ZAP70 in NK cells correlated better to cytogenetic risk profile and mutational status than the conventional methods. Negativity of both ZAP70 (new NK-MFI method) and CD38 resulted in a probability of 90% for mutated IGHV genes. In conclusion, ZAP70 expression in CLL cells related to ZAP70 expression in NK cells is a better surrogate marker for mutational status than the conventional T cell related methods.