423: In Vitro Characterisation of Endogenous Adult Cardiac Progenitors and Their Flux after Ischaemic Injury

graft function following heart transplantation. Methods and Materials: NK cells were characterised via flow cytometric immunophenotyping (using anti-CD3, anti-CD16, antiCD56, anti-CD161) in peripheral blood (n 80). Corresponding paraffin embedded endomyocardial tissue from 39 patients (20 grade 3a, 19 grade 0) was stained for NK cells via CD16 and morphological assessment. Results: Using Spearman’s Rank Co-Efficient, peripheral blood NK cells were depleted in patients with acute rejection compared to stable patients (p 0.021, co-ef 0.499). Furthermore, there was significantly more CD16 NK cells in heart biopsy tissue of patients with acute rejection compared to stable patients (grade 3a vs grade 0, p 0.001, co-ef 0.756). Conclusions: We report the depletion of peripheral blood NK cells, and an increase in intragraft NK cells in patients with acute rejection. This novel data suggests that NK cells migrate from the peripheral circulation to the graft during acute rejection, and adds further weight to the theory that NK cells play a key role in immune mediated acute rejection following heart transplantation, and warrant further attention.