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Phenotypic and functional evaluation of CD3+CD4-CD8- T cells in human CD8 immunodeficiency
Iván Bernardo1, Esther Mancebo, Ignacio Aguiló
1Servicio de Inmunología, Hospital Universitario 12 de Octubre, Avda. de Córdoba s/n, Madrid, Spain.
Insights
In human CD8 immunodeficiency, double negative T cells may be cytotoxic T lymphocytes. CD8 is not essential for cytotoxicity but impacts T cell development and proliferation.
Area of Science:
- Immunology
- Cell Biology
- Human Genetics
Background:
- Human CD8 immunodeficiency presents with absent CD8(+) lymphocytes and a surplus of CD4(-)CD8(-) (double negative) T lymphocytes.
- This study investigates the hypothesis that double negative T cells represent the CD8-expressing cytotoxic T lymphocyte lineage in CD8-deficient individuals.
Observation:
- Peripheral blood mononuclear cells and isolated double negative T lymphocytes from CD8-deficient patients were analyzed for phenotype and function.
- Transfected 293T cells expressing wild-type or mutated CD8α revealed cytoplasmic retention of mutated CD8α protein.
Findings:
- Double negative cells exhibited an effector/effector memory phenotype, with under-representation of naive T cells.
- Low T-cell receptor excision circles and a skewed T-cell receptor-V repertoire suggest suboptimal thymic selection in CD8 absence.
- In vitro, double negative cells displayed mild defects in cytotoxic function and reduced proliferation.
Implications:
- Double negative T cells may function as major histocompatibility complex class-I restricted T cells with cytolytic capabilities.
- The CD8 co-receptor is dispensable for cytotoxic ability but crucial for generating cytotoxic T lymphocyte precursors and mature T cell proliferation in humans.
Background:
Human CD8 immunodeficiency is characterized by undetectable CD8(+) lymphocytes and an increased population of CD4(-)CD8(-) (double negative) T lymphocytes.
Design And Methods:
We hypothesized that the double negative subset corresponds to the cellular population that should express CD8 and is committed to the cytotoxic T lymphocyte lineage. To assess this, we determined the phenotype and function of peripheral blood mononuclear cells and/or magnetically isolated double negative T lymphocytes from two CD8-deficient patients. To analyze the expression and co-localization with different organelles, 293T cells were transfected with plasmids bearing wild-type or mutated CD8α.
Results:
CD8α mutated protein was retained in the cytoplasm of transfected cells. The percentages of double negative cells in patients were lower than the percentages of CD8(+) T cells in healthy controls. Double negative cells mostly had an effector or effector memory phenotype whereas naïve T cells were under-represented. A low concentration of T-cell receptor excision circles together with a skewed T-cell receptor-V repertoire were observed in the double negative population. These data suggest that, in the absence of CD8 co-receptor, the thymic positive selection functions suboptimally and a limited number of mature T-cell clones would emerge from the thymus. In vitro, the double negative cells showed a mild defect in cytotoxic function and decreased proliferative capacity.
Conclusions:
It is possible that the double negative cells are major histocompatibility complex class-I restricted T cells with cytolytic function. These results show for the first time in humans that the presence of the CD8 co-receptor is dispensable for cytotoxic ability, but that it affects the generation of thymic precursors committed to the cytotoxic T lymphocyte lineage and the proliferation of mature cytotoxic T cells.
