Compositions and methods for stimulating natural killer cells

An NK cell expanding composition comprising a membrane-bound inverted Fc domain bound to an external surface of a feeder cell, an engineered PM particle, or an engineered exosome, wherein the inverted Fc domain is part of a fusion protein comprising a transmembrane domain linked to the amino terminus of the inverted Fc domain, wherein the amino terminus of the inverted Fc domain is oriented towards the feeder cell, engineered PM particle, or engineered exosome, and wherein the transmembrane domain comprises a signal anchor sequence selected from the transmembrane domain of neuraminidase, the signal-anchor from parainfluenza virus hemagglutinin-neuraminidase, the signal-anchor from the transferrin receptor, the signal-anchor from the MHC class II invariant chain, the signal-anchor from P glycoprotein, the signal-anchor from asialoglycoprotein receptor, and the signal-anchor from a neutral endopeptidase.