The TCR is composed of two of 4 possible subunits, alpha, beta, gamma and delta. Most adult T-cells are made of alpha-beta subunits, gamma-delta T-cells are found primarily in the GI tract of adults. Despite being less commonly used as components of an active TCR, gamma and delta TCR subunit genes rearrange earlier in the development than the alpha or beta subunit genes. Thus many gamma gene rearrangements are not “productive” of active T-cells, and these rearrangements do not always have to be “in-frame” (see figure below).
TCR-gamma IgH, “in-frame”
The TCR-gamma gene is less complex than the beta subunit gene and is far easier to evaluate by PCR. Some lymphomas can be difficult to diagnose by standard methodologies and TCR-gamma subunit gene monoclonality can be used as a marker to identify clonal lymphoid populations and aid in the overall diagnosis of a lymphoid neoplasm.
A classic example of the utility of clonality assessment in diagnosis is the cutaneous T-cell lymphoma, mycosis fungoides, which is difficult to diagnose by histologic or clinical grounds.
