Extrathymic development and function of human T-lymphocytes from bone marrow cells in vitro

Area of Science:

• Immunology
• Cell Biology
• Hematology

Background:

• T-lymphocyte development typically occurs in the thymus.
• Bone marrow (BM) contains progenitor cells that can differentiate into various immune cells.
• Understanding extrathymic T-cell development is crucial for regenerative medicine.

Purpose of the Study:

• To investigate the potential of human bone marrow (BM) CD7+ CD3- cells to develop into functional T-lymphocytes outside the thymus.
• To characterize the phenotype, proliferation, cytokine response, and cytotoxic activity of these extrathymically derived T-cell clones.
• To assess the autoreactivity of these T-cell clones.

Main Methods:

• Sorting of human BM CD7+ CD3- cells.
• Culture under limiting dilution with allogeneic stimulator cells, interleukin (IL) 2, and phytohemagglutinin (PHA).
• Analysis of T-cell receptor (TCR) expression, CD4/CD8 surface markers, proliferation, cytokine mRNA accumulation, and cytotoxic activity against various targets.

Main Results:

• All cultured BM-derived clones expressed CD3 and alpha/beta T-cell receptor (TCR2), with a balanced CD4+ and CD8+ subset distribution.
• Clones exhibited autocrine proliferation and responded to IL-2, IL-4, and IL-7, accumulating various cytokine mRNAs.
• A significant proportion of clones displayed lectin-dependent and natural killer (NK)-target cell lysis, but limited lysis of lymphokine-activated killer (LAK)-susceptible targets and no lysis of autologous targets.

Conclusions:

• Human BM CD7+ CD3- cells can differentiate into functional T-lymphocytes extrathymically in vitro.
• These extrathymically derived T-cells acquire cytotoxic and proliferative capabilities.
• The lack of autoreactivity suggests a potential for safe therapeutic applications.