A method comprising the following substeps: recovering two or more genes, or gene products, or cDNAs, encoding for an immunoreceptor having two or more subunits, which two or more genes, or gene products, are comprised in a given source cell, which method comprises the following steps: a) encapsulation of source cells together with an mRNA capturing moiety in microreactors, in such way that each microreactor comprises one source cell and wherein the mRNA capturing moiety is a bead or particle b) lysis of the cells in the microreactors, release of the cellular mRNA in the lumen of the microreactors, and subsequent attachment thereof to the mRNA capturing moiety c) lysing, or disrupting, the microreactors and reverse transcription of the mRNA attached to the mRNA capturing moieties in solution to obtain the corresponding cDNA gene products d) creating a construct that encompasses the two or more gene products encoding for the subunits of the immunoreceptor, wherein the creation of a construct that encompasses the two or more gene products encoding for the subunits of the immunoreceptor is accomplished by amplifying the cDNA by overlap extension PCR inside microreactors, wherein each microreactor contains a single mRNA capturing moiety resulting from step c), and e) cloning of the PCR product into a plasmid vector to obtain a bi- or multicistronic expression construct; f) thus creating a plasmid library which contains the cDNA encoding for the immunoreceptors of a given source cell population, and creating a library of expressor cells, in which library each cell is capable of expressing two or more genes, or gene products, encoding for the subunits of the recovered immunoreceptor, which library creation comprises the following steps: g) transfecting expressor cells with one bi- or multicistronic expression construct, and h) encapsulating expressor cells into microreactors with one expressor cell per microreactor, and i) culturing the encapsulated cells under conditions which allow protein expression and/or proliferation of the cells. a) encapsulation of source cells together with an mRNA capturing moiety in microreactors, in such way that each microreactor comprises one source cell and wherein the mRNA capturing moiety is a bead or particle b) lysis of the cells in the microreactors, release of the cellular mRNA in the lumen of the microreactors, and subsequent attachment thereof to the mRNA capturing moiety c) lysing, or disrupting, the microreactors and reverse transcription of the mRNA attached to the mRNA capturing moieties in solution to obtain the corresponding cDNA gene products d) creating a construct that encompasses the two or more gene products encoding for the subunits of the immunoreceptor, wherein the creation of a construct that encompasses the two or more gene products encoding for the subunits of the immunoreceptor is accomplished by amplifying the cDNA by overlap extension PCR inside microreactors, wherein each microreactor contains a single mRNA capturing moiety resulting from step c), and e) cloning of the PCR product into a plasmid vector to obtain a bi- or multicistronic expression construct; f) thus creating a plasmid library which contains the cDNA encoding for the immunoreceptors of a given source cell population, and creating a library of expressor cells, in which library each cell is capable of expressing two or more genes, or gene products, encoding for the subunits of the recovered immunoreceptor, which library creation comprises the following steps: g) transfecting expressor cells with one bi- or multicistronic expression construct, and h) encapsulating expressor cells into microreactors with one expressor cell per microreactor, and i) culturing the encapsulated cells under conditions which allow protein expression and/or proliferation of the cells.