Assessment of the effector function of CMV-specific CTLs isolated using MHC-multimers from granulocyte-colony stimulating factor mobilized peripheral blood

Preservation of Antigen-Specific Functions of αβ T Cells and B Cells Removed from Hematopoietic Stem Cell Transplants Suggests Their Use As an Alternative Cell Source for Advanced Manipulation and Adoptive Immunotherapy

Hematopoietic stem cell transplantation is standard therapy for numerous hematological diseases. The use of haploidentical donors, sharing half of the HLA alleles with the recipient, has facilitated the use of this procedure as patients can rely on availability of a haploidentical donor within their family. Since HLA disparity increases the risk of graft-versus-host disease, T-cell depletion has been used to remove alloreactive lymphocytes from the graft. Selective removal of αβ T cells, which encompass the alloreactive repertoire, combined with removal of B cells to prevent EBV-related lymphoproliferative disease, proved safe and effective in clinical studies. Depleted αβ T cells and B cells are generally discarded as by-products. Considering the possible use of donor T cells for donor lymphocyte infusions or for generation of pathogen-specific T cells as mediators of graft-versus-infection effect, we tested whether cells in the discarded fractions were functionally intact. Response to alloantigens and to viral antigens comparable to that of unmanipulated cells indicated a functional integrity of αβ T cells, in spite of the manipulation used for their depletion. Furthermore, B cells proved to be efficient antigen-presenting cells, indicating that antigen uptake, processing, and presentation were fully preserved. Therefore, we propose that separated αβ T lymphocytes could be employed for obtaining pathogen-specific T cells, applying available methods for positive selection, which eventually leads to indirect allodepletion. In addition, these functional T cells could undergo additional manipulation, such as direct allodepletion or genetic modification.

Streptamer technology allows accurate and specific detection of CMV-specific HLA-A*02 CD8+ T cells by flow cytometry

BACKGROUND

Multimer technology is widely used to screen antigen-specific immune recovery after allogeneic hematopoietic stem cell transplantation (allo-HSCT) as it enables identification, enumeration, phenotypic characterization and isolation of virus-specific T-cells. Novel approaches of multimerization might improve on classical tetramer staining; however, their use as standard monitoring technique to quantify antigen-specific cells has not been validated yet. We have compared two of these available multimeric complexes: pentamer and streptamer to select the best strategy for the incorporation into clinical monitoring practice.

METHODS

CMVpp65^495-503 -specific HLA-A*02:01 CD8⁺ T lymphocytes (CTL^A *^02:01 -CMVpp65^495-503 ) were examined with pentamer and streptamer in peripheral blood cells of 77 healthy volunteers. Quantitative and qualitative analyses were performed to compare the precision and repeatability, sensitivity and accuracy and specificity of both technologies by flow cytometry.

RESULTS

Standard deviation for both techniques was less than 0.05 showing that they are repetitive and precise. Both techniques significantly correlated at high frequencies (r_Spearman  = 0.9422; P < 0.0001) but it was lost at lower levels (<1%) of CTL^A *^02:01 -CMVpp65^495-503 (r_Spearman  = 0.3351; P = 0.1376). Streptamer is more accurate for the detection of CTL^A *^02:01 -CMVpp65^495-503 providing significantly closer values to the theoretical ones (P < 0.0001) as pentamer binds unspecifically to a notable proportion of non-CMV-specific CD8⁺ T-cells.

CONCLUSION

Our results suggest that streptamer multimer provides precise, accurate and specific results to detect CTL^A *^02:01 -CMVpp65^495-503 by flow cytometry. Streptamer multimer can be used not only for the monitoring of early CTL^A *^02:01 -CMVpp65^495-503 reconstitution in immunosuppressed patients following allo-HSCT but also, in conjunction with its reversibility role, for the isolation of CTL^A *^02:01 -CMVpp65^495-503 for its future use in adoptive immunotherapy. © 2016 International Clinical Cytometry Society.