Combined analysis of T cell receptor γ and immunoglobulin heavy chain gene rearrangements at the single‐cell level in lymphomas with dual genotype

By prospectively studying immunoglobulin heavy chain gene (IgH) and T cell receptor gamma (TCRgamma) gene rearrangements in 398 lymphoma cases, a dual genotype was observed in 13% of B cell and 11% of T cell lymphomas. According to histological subtype, the highest incidence was observed for mantle cell lymphomas (32%) and lymphoplasmacytic lymphoma (21%) among B cell lymphomas, and for angioimmunoblastic lymphoma (AILT) (46%) and Sézary syndrome (SS) (50%) among T cell lymphomas. To determine whether the dual genotype corresponds to the presence of two distinct monoclonal populations or to the presence of both rearrangements within the same lymphoma cells, single-cell microdissection was used after immunohistochemistry and a single-cell combined IgH and TCRgamma gene analysis was designed after a whole-genome amplification step. This protocol was applied to the study of two nodal B cell lymphomas (one diffuse large B cell lymphoma and one mantle cell lymphoma) and two cutaneous T cell lymphomas (one AILT and one SS). Two cases (SS and mantle cell lymphoma) were true bigenotypic lymphomas, as both IgH and TCRgamma monoclonal rearrangements were detected in the same cells. Conversely, in the diffuse large B cell lymphoma and AILT cases, large CD22+ single cells exhibited only the monoclonal IgH rearrangement but not the TCRgamma gene that was detected in CD3+ single cells. Such an approach allows the identification of true bigenotypic lymphoma among dual genotypic lymphoma. Specific genetic alterations may be further amplified from microdissected cryopreserved material, such as the t(11;14) breakpoint detected in bigenotypic B cells of the mantle cell lymphoma case.