Functional and selective targeting of adenovirus to high-affinity fc gammareceptor I-positive cells by using a bispecific hybrid adapter

Adenovirus (Ad) efficiently delivers its DNA genome into a variety of cells and tissues, provided that these cells express appropriate receptors, incl uding the coxsackie-adenovirus receptor (CAR), which binds to the terminal knob domain of the viral capsid protein fiber. To render CAR-negative cells susceptible to Ad infection, we have produced a bispecific hybrid adapter protein consisting of the amino-terminal extracellular domain of the human CAR protein (CARex) and the Fc region of the human immunoglobulin G1 protei n, comprising the hinge and the CH2 and CH3 regions. CARex-Fc was purified from COS7 cell supernatants and mixed with Ad particles, thus blocking Ad i nfection of CAR-positive but Fc receptor-negative cells. The functionality of the CARex domain was further confirmed by successful immunization of mic e,vith CARex-Fc followed by selection of a monoclonal anti-human CAR antibo dy (El-l), which blocked Ad infection of CAR-positive cells. When mixed wit h Ad expressing eGFP, CARex-Fc mediated an up to 250-fold increase of trans gene expression in CAR-negative human monocytic cell lines expressing the h igh-affinity Fc gamma receptor I (CD64) but not in cells expressing the low -affinity Fc gamma receptor II (CD32) or III (CD16), These results open new perspectives for Ad-mediated cancer cell vaccination, including the treatm ent of acute myeloid leukemia.