Identification and analysis of alloreactive T lymphocytes from peripheral blood mononuclear cells.

Alloreactive T-cell responses against mismatched MHC or minor histocompatibility antigens may result in deleterious graft-versus-host disease (GVHD) and increased morbidity and mortality in allogeneic hematopoietic stem cell transplantation (allo-HSCT). Nevertheless, these T-cell responses may be directed against residual tumor cells (the graft-versus-tumor effect, GVT), thus preventing relapse of the disease. Recent findings have shown that CD45RA⁺ naïve T cells, but not CD45RA^- memory T cells are the major contributors to GVHD, thus leading to clinical trials where CD45RA⁺-depleted, memory-enriched T-cell products are adoptively transferred following allo-HSCT to prevent GVHD and enhance immune reconstitution. However, residual alloreactivity may still be present in the memory T-cell compartment, thus contributing to prevent disease relapse by GVT. Here, we describe a simple cell-based protocol to identify alloreactive naïve and memory T cells by co-culturing T-cell subsets and third-party antigen-presenting cells. The responding cells are identified following dilution of carboxyfluorescein succinimidyl ester (CFSE) and upregulation of the activation marker CD25. These CFSE-diluting cells can be further phenotyped by high-dimensional flow cytometry, or purified with a cell sorter for downstream genomic and functional assays.