The development and / or course of chronic lymphocytic leukemia (CLL) may be driven by the recognition of antigens through the B cell receptor (BCR). While it has been recognized that the diversity of epitope recognition may be astonishingly confined in CLL, knowledge on antigens recognized by CLL BCRs is still limited. Here, we identified and characterized an epitope recognized by a defined CLL BCR which may broaden our view on potential mechanisms of antigenic drive in CLL.
The B- cell receptor of a random CLL-patient was cloned and expressed as Fab fragment in E.coli. Random phage display reptile litanies we skeletal on the immobilized Fab and landed peptides were tested for specific binding. Specific clones we sequenced and sequences were analyzed for homology to known proteins. Recognition of candidate proteins was verified in brooding assays or recombinant proteins.
Screening random phage display peptide libraries, we identified a CLL BCR epitope mimic that displayed a high degree of homology to a conserved peptide string in the variable region of immunoglobulin heavy and light chains. CLL BCR binding to this epitope as well as binding to full length heavy and light immunoglobulin chains was verified by binding assays and a protein array screening. Interestingly, the CLL BCR also interacted with itself, as the identified epitope was also present in its own primary amino acid sequence.
These findings suggest the possibility of self-recognition of BCRs within the CLL cell membrane or BCR interactions between neighboring CLL cells. This may potentially result in autostimulation of the leukemic cell independent of “exogenous” antigens and may account for self-sufficient signaling of some CLL-BCRs in driving disease progression. As the peptide mimicking this immunoglobulin epitope is known to be recognized by BCRs of other CLL cases in addition to the index case investigated here, such autostimulatory mechanisms may be relevant to a large number of CLL patients.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.