pComb3H, a derivative of pComb3 optimized for expression of human fragments, is a phagemid

Phagemid

A phagemid or phasmid is a type of cloning vector developed as a hybrid of the filamentous phage M13 and plasmids to produce a vector that can grow as a plasmid, and also be packaged as single stranded DNA in viral particles...

 used to express proteins such as zinc finger proteins and antibody fragments on phage pili for the purpose of phage display

Phage display

Phage display is a method for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages to connect proteins with the genetic information that encodes them. Phage Display was originally invented by George P...

selection.

For the purpose of phage production, it contains the bacterial ampicillin resistance gene (for B-lactamase), allowing the growth of only transformed bacteria.