Treg-protected donor lymphocyte infusions: a new tool to address the graft-versus-leukemia effect in the absence of graft-versus-host disease in patients relapsed after HSCT

Mauro Di Ianni, Paola Olioso, Raffaella Giancola, Stella Santarone, Annalisa Natale, Gabriele Papalinetti, Ida Villanova, Stefano Baldoni, Ambra Di Tommaso, Tiziana Bonfini, Patrizia Accorsi, Paolo Di Bartolomeo

In high-risk acute leukemia patients undergoing haploidentical hematopoietic stem cell transplantation (HSCT), adoptive immunotherapy with T regulatory cells (Tregs) and T conventional cells (Tcons) prevented acute and chronic graft-versus-host disease (GvHD), favored post-transplant immunological reconstitution and was associated with a powerful graft-versus-leukemia (GvL) effect. With a particularly innovative approach, we developed a treatment with a Treg-protected donor lymphocyte infusion (DLI) for patients with early relapse after HSCT and we report here the results obtained in the first patient with APL (M3v) relapsed after a second matched allogeneic HSCT (15% blasts and 75% of donor cells in bone marrow). The patient received a first infusion of 2.5 × 10(6)/kg Tregs derived from matched donor followed 7 days later by 5 × 10(6)/kg Tcons. GvL effect was strongly evident as the percentage of leukemic cells decreased to 5%. A second infusion of Tregs (2.5 × 10(6)/kg) and Tcons (2 × 10(6)/kg) was performed. No GvHD was observed. Disease evaluation showed the absence of blastic cells at flow-cytometry, a normal caryotype and full donor chimerism. We also observed NOTCH1 down-regulation in peripheral blood. This new immunotherapy approach showed that Treg-protected DLI is effective in preventing GvHD and is associated with a strong GvL effect.