Sequencing the peripheral blood B and T cell repertoire - Quantifying robustness and limitations.

The adaptive immune response generates a large repertoire of T cells with T-cell receptors (TCR and TCR) and B cells with immunoglobulins (Ig). The repertoire changes in response to antigen stimulation both through amplification of specific cells (clonal expansion) as well as somatic hypermutation of immunoglobulins. Alterations of the immune repertoire have been observed in response to acute disease, such as external pathogens, or chronic diseases, such as autoimmunity and cancer. Here we establish experimental and analytical protocols for quantifying the peripheral blood of healthy human individuals by profiling the immune repertoire for the Complementarity determining region 3 (CDR3) of the variable regions of TCR (CDRβ3) and the IgG heavy chain (CDRH1, CDRH2, CDRH3). The results demonstrate that 40 ml of blood are sufficient to reliably capture the 10,000 most common TCR and 1000 most common IgG and determine their relative frequency in the circulation. We conclude that by using an accessible sample size of human PBMC one is able to robustly monitor alterations in the immune repertoire.