Allogeneic stem cell transplantation (allo-SCT) is a potent treatment, and sometimes the only curative treatment for aggressive hematological malignancies. The therapeutic efficacy is attributed to the graft-versus-tumor (GVT) response, during which donor-derived CD8+ T cells become activated by recipient minor histocompatibility antigens (MiHA) presented on dendritic cells (DC). Consequently, these alloreactive donor T cells clonally expand, acquire effector functions and kill MiHA-positive malignant cells. However, in a substantial number of patients persistence and recurrence of malignant disease is observed, indicating that insufficient GVT immunity is induced. This is reflected by our observation that not all patients develop a productive CD8+ T cell response towards MiHA mismatched between the recipient and donor. We found that the PD-1/PD-L1 co-inhibitory pathway is involved in dampening MiHA-specific CD8+ T cell expansion and function post-transplantation. Therefore, a promising strategy to induce or boost GVT immune responses is pre-emptive or therapeutic vaccination with ex vivo-generated donor DCs loaded with MiHA that are exclusively expressed by recipient hematopoietic cells and their malignant counterparts. In contrast to pre-emptive donor lymphocyte infusion (DLI) with polyclonal donor T cells, this MiHA-DC vaccination approach has less risk of inducing graft-versus-host disease (GVHD) and the potency to induce more efficient GVT-associated T cell immunity. In addition, the potency of this DC vaccine will be further enhanced by interference with the PD-1/PD-L1 co-inhibitory pathway, using siRNA mediated PD-L1/PD-L2 silencing.

Inclusion Criteria:

• Patients with AML, myelodysplasia (MDS), ALL, CML (accelerated or blast phase), CLL, MM, malignant NHL or HL, who underwent HLA-matched allo-SCT
• Patients positive for HLA-A2 and/or HLA-B7
• Patients positive for HA-1, LRH-1 and/or ARHGDIB transplanted with corresponding MiHA-negative donor
• Patients ≥18 years of age
• WHO performance 0-2
• Witnessed written informed consent

Exclusion Criteria:

• Life expectancy < 3 months
• Severe neurological or psychiatric disease
• Progressive disease needing cytoreductive therapy
• HIV positivity
• Patients with acute GVHD grade 3 or 4
• Patients with severe chronic GVHD
• Patients with active infections (viral, bacterial or fungal) that require specific therapy. Acute anti-infectious therapy must have been completed within 14 days prior to study treatment
• Severe cardiovascular disease (arrhythmias requiring chronic treatment, congestive heart failure or symptomatic ischemic heart disease)
• Severe pulmonary dysfunction
• Severe renal dysfunction (serum creatinine > 3 times normal level)
• Severe hepatic dysfunction (serum bilirubin or transaminases > 3 times normal level)
• Patients with known allergy to shell fish