T cell dynamics in chronic lymphocytic leukemia under different treatment modalities.

BACKGROUND Using next-generation sequencing (NGS), we recently documented T cell oligoclonality in treatment-naive chronic lymphocytic leukemia (CLL), with evidence indicating T cell selection by restricted antigens. EXPERIMENTAL DESIGN Here, we sought to comprehensively assess T cell repertoire changes during treatment in relation to: (i) treatment type [fludarabine-cyclophosphamide-rituximab (FCR) versus ibrutinib (IB) versus rituximab-idelalisib (R-ID)], and (ii) clinical response, by combining NGS immunoprofiling, flow cytometry and functional bioassays. RESULTS T cell clonality significantly increased at: (i) 3 months in the FCR and R-ID treatment groups, and (ii) over deepening clinical response in the R-ID group, with a similar trend detected in the IB group. Notably, in constrast to FCR that induced T cell repertoire reconstitution, B cell receptor signaling inhibitors (BcRi) preserved pre-treatment clones. Extensive comparisons both within CLL as well as against T cell receptor sequence databases showed little similarity with other entities, but instead revealed major clonotypes shared exclusively by CLL patients, alluding to selection by conserved CLL-associated antigens. We then evaluated the functional effect of treatments on T cells and found that: (i) R-ID upregulated the expression of activation markers in effector memory T cells, and (ii) both BcRi improved anti-tumor T cell immune synapse formation, in marked contrast to FCR. CONCLUSIONS Taken together, our NGS immunoprofiling data suggest that BcRi retain T cell clones that may have developed against CLL-associated antigens. Phenotypic and immune synapse bioassays support a concurrent restoration of functionality, mostly evident for R-ID, arguably contributing to clinical response.