Variability of the alloreactive T-cell response to human leukemic blasts

Area of Science:

• Immunology
• Hematology
• Transplantation Science

Background:

• The graft-versus-leukemia (GVL) effect, mediated by immune responses, is critical for preventing leukemia relapse post-allogeneic bone marrow transplantation (BMT).
• Understanding the interaction between donor lymphocytes and leukemia cells is essential for optimizing GVL responses.

Purpose of the Study:

• To investigate the in vitro graft-versus-leukemia (GVL) effect by evaluating normal donor lymphocyte responses against allogeneic leukemia cells.
• To determine the frequency of cytotoxic T-lymphocyte precursors (pre-CTL) and the role of HLA-DR expression in leukemia recognition.

Main Methods:

• Utilized a limiting dilution technique to quantify pre-CTL frequencies against allogeneic leukemic blasts.
• Employed mixed lymphocyte tumor cell culture (MLTC) to analyze the impact of leukemic HLA-DR expression on T-cell responses.
• Assessed lymphocyte proliferation and inhibited responses using anti-MHC class II monoclonal antibodies.

Main Results:

• Demonstrated significant variability in CTL precursor frequencies among normal donors, dependent on specific leukemia populations.
• Observed extremely low pre-CTL frequencies when using HLA-DR negative leukemias.
• Confirmed a strong correlation (r = 0.953, p < 0.0001) between lymphocyte proliferation and the percentage of HLA-DR expressing leukemic cells.

Conclusions:

• Leukemic cells exhibit highly variable allostimulatory capacities, primarily dictated by their HLA-DR expression.
• HLA-DR expression is central to allo-recognition and the generation of anti-leukemia immune responses.
• Clinical protocols involving T-cell infusions for DR-negative leukemias may not elicit a significant anti-tumor effect.