The objective of this proposal is to develop a Natural Killer (NK) cell-based immunotherapy for the treatment of high risk MDS. NK cells possess germline encoded receptors that help dictate how NK cells react to target cells. These receptors allow NK cells to decide which cells to kill or not, with the addition of powerful signaling from chimeric antigen receptors (CARs), NK cells can still decide which cells to target. Thus, my overarching hypothesis is that NK cells will be optimally suited to eradicate MDS cells and preserve healthy cells. This hypothesis will be evaluated in two interrelated research aims. Aim 1 explores the novel orientation and organization of monomeric CAR NK cells with synapse augmentation, Aim 2 is focused on defining a donor selection algorithm for CAR NK cell products. I will pivot from the standard dimeric CAR designs that lead to dysregulated signaling and cellular dysfunction to an optimized monomeric design that has a stable off state reducing aberrant signaling. Further, donor variability is a critical factor when determining optimal cell source for cell therapies and, to date, the clinical selection parameters for NK cells, I believe, hobbles their full potential. I will utilize in silico protein modeling with functional testing to define a new selection method for donor cell sources. At the conclusion of the EYIA award I will have delineated novel modification of CAR designs and a universal donor bank selection algorithm for CAR NK cells.