Vaccination strategies to improve outcome of hematopoietic stem cell transplant in leukemia patients: early evidence and future prospects

Allogeneic hematopoietic stem cell transplantation (HSCT) has largely improved the prognosis of leukemia patients. However, relapse is still a major concern. One promising option for the prevention of relapse is vaccination therapy. The post allogeneic HSCT period provides a unique platform for vaccination, because tumor burden is minimal, lymphopenic condition allows for rapid expansion of cytotoxic T cells (CTLs), donor-derived CTLs are not exhausted and inflammatory condition is caused by allo reactions. Tumor cells, dendritic cells and peptides have been used as vaccines targeting leukemia-associated antigens or minor histocompatibility antigens. Clinical trials with several types of vaccines for post-HSCT patients showed that the vaccination induced immunological response and might benefit patients with minimal residual disease, while their effect in patients with advanced disease were limited. To enhance the effect, vaccination in combination with other immune-modulatory drugs such as checkpoint antibodies is now being considered.