Persistent expansions of CD4+ CD8+ peripheral blood T cells

Area of Science:

• Immunology
• Cell Biology
• Hematology

Background:

• CD4+ CD8+ T cells are typically rare in peripheral blood, comprising less than 2% of normal T cells.
• These cells are primarily involved in T cell differentiation within the thymus.

Purpose of the Study:

• To investigate persistent expansions of circulating CD4+ CD8+ T cells in nine individuals.
• To characterize the immunophenotype and T-cell receptor (TCR) gene rearrangements of these expanded CD4+ CD8+ T cells.
• To explore the potential implications of these findings in the context of immune system disorders.

Main Methods:

• Flow cytometry for immunophenotypic analysis of CD4+ CD8+ T cells, including expression of activation and memory/naive markers.
• Southern blot hybridization using TCR beta and TCR gamma probes to assess clonality.
• Morphological assessment for large granular lymphocyte (LGL) features.

Main Results:

• Nine individuals showed persistent expansions of circulating CD4+ CD8+ T cells (11% to 43%).
• Three cases exhibited LGL morphology without overt lymphoproliferative disorders.
• TCR gene analysis suggested monoclonal, oligoclonal, or polyclonal expansions.
• Immunophenotyping revealed CD8 dim expression in most cases, lack of activation antigens, and high expression of CD2, CD29, CD56, and CD57.
• Coexpression of CD45RA and CD45RO in some cases indicated an intermediate T cell state.

Conclusions:

• The observed CD4+ CD8+ T cell expansions represent a spectrum of conditions, from normal to reactive or proliferative.
• These cases can present with LGL morphology or LGL-associated antigens, with or without lymphocytosis.
• Careful follow-up investigations are warranted for individuals with these expanded CD4+ CD8+ T cell populations.