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NK CELL CYTOTOXICITY CROSSMATCH: CORRELATION WITH ENGAGEMENT OF INHIBITORY KIR BY HLA.
Mei Han MD 1, Margarita Fallena MD , Yuhong Guo PhD , Yizhou Zou MD and Peter Stastny MD . 1 Internal Medicine, Univ of TX Southwestern Medical Center, Dallas, TX .
It has been postulated that NK cells play a role in reducing disease recurrence through a graft-versus-leukemia effect and in reducing graft-versus-host disease by elimination of dendritic cells. We have previously described a functional NK cell crossmatch measuring cytotoxicity against ConA blasts to correlate with genetics and expression of inhibitory KIR/HLA ligands. In the present report the results of NK cytotoxicity assays between 20 pairs of normal subjects were analyzed by normalizing effector-wise using the target cell line K562, which is devoid of HLA class I and therefore does not engage inhibitory KIR. A correction factor based on the mean killing of K562 by 20 effector cells was generated. Interestingly, the normalized values had a mean cytotoxicity similar to the uncorrected data, but within each group having the same number of KIR/HLA matches the scatter was markedly reduced. Thus standard deviations obtained for each group were reduced when the data was normalized: 1 KIR/HLA match from S.D.=21 to =13, 2 KIR/HLA from S.D.=6 to =4 and 3 KIR/HLA from S.D.=2 to =1. In addition we examined the effect of expression of inhibitory KIR on the effector population of NK cells, by flow cytometry. In the normalized data, when 50% or more of the NK cells could be inhibited, cytotoxicity was lower (8%) than when 25% or less of the NK cells expressed KIR with matched HLA (49%). These differences were statistically highly significant (p<0.0001). In conclusion, responder-wise normalization using a standard target cell (K562) allowed a more accurate evaluation of NK cell cytotoxicity showing clear correlation between cytotoxicity results and genetic KIR/HLA matching and KIR expression on the effector cells.