Immune checkpoint inhibitors and allogeneic hematopoietic stem cell transplantation

Immune checkpoint inhibitors, such as anti-CTLA-4 and anti-PD-1 antibodies, have revolutionized cancer therapy, particularly in the treatment of malignant melanoma and lung cancer. Allogeneic hematopoietic stem cell transplantation (allo-HCT) is another form of immunotherapy and is being widely used to cure high-risk hematological malignancies. However, more than one-third of patients suffer a relapse after allo-HCT and often have a poor prognosis. A phase I/Ib study to assess the safety and efficacy of ipilimumab (anti-CTLA-4 antibody) for the treatment of relapsed hematological malignancies after allo-HCT has shown that induction treatment with ipilimumab led to remissions in some patients, including those with myeloid malignancies, without eliciting severe graft versus host disease (GVHD). The efficacy of treatment with anti-PD-1 antibodies before or after allo-HCT has been reported in some case reports and in one retrospective study, but one case of fatal GVHD caused by anti-PD-1 antibody therapy after allo-HCT raises a concern. Considering that remission status after transplantation is a strong prognostic factor in allo-HCT, immune checkpoint inhibitors might work better during post-remission consolidation than during induction. Further studies on immune checkpoint inhibitors in the treatment of hematological malignancies are warranted.