Patent ID: 7786047

Claim:
A cDNA library comprising nucleotide sequences coding for a fragment of an immunoglobulin, said immunoglobulin comprising two heavy chain polypeptides containing a variable (V HH ) region and a constant region, said constant region being devoid of a first domain (C H 1), said immunoglobulin being devoid of light chain polypeptides, which fragment forms a determined antigen binding site, wherein said cDNA library is obtained by performing the following steps: (a) treating a sample containing lymphoid cells from a healthy immunized animal selected among Camelids in order to separate the lymphoid cells; (b) separating polyadenylated RNA from other nucleic acids and components of the lymphoid cells; (c) reacting the obtained RNA with a reverse transcriptase in order to obtain cDNA; (d) contacting the cDNA with 5′ primers located in promoter, leader or framework sequences of the V HH sequence of said heavy chain immunoglobulin, and with 3′ primers located in hinge, C H 2, C H 3, 3′ untranslated region or polyA tail sequences; (e) amplifying the DNA; (f) cloning the amplified DNA in a vector; and (g) recovering the obtained clones, wherein said clones encode polypeptides having a preselected specificity for the antigen used for immunization.