A method of preparing an antibody therapeutic is provided comprising: (a) providing a dissociated cell sample from at least one solid tumor sample obtained from a patient; (b) loading the dissociated cell sample into a microfluidic device having a flow region and at least one isolation region fluidically connected to the flow region; (c) moving at least one B cell from the dissociated cell sample into at least one isolation region in the microfluidic device, thereby obtaining at least one isolated B cell; and (d) using the microfluidic device to identify at least one B cell that produces antibodies capable of binding to cancer cells. The cancer cells can be the patient's own cancer cells. Also provided are methods of treating patients, methods of labeling or detecting cancer, engineered T or NK cells comprising antibodies or fragments thereof, and engineered antibody constructs.