Hematopoietic stem cell transplant (HCT) is responsible for impressive cure rates of chemotherapy refractory leukemia and other malignancies. However, life-threatening opportunistic infections including cytomegalovirus (CMV) diminish full curative potential of HCT by raising morbidity and mortality throughout post-HCT recovery. Antiviral drugs which limit CMV viremia exact a cost of morbidity including renal dysfunction, neutropenia and immune suppression. Substituting toxic antivirals with a vaccine that stimulates multiple immune mechanisms may improve HCT outcomes. The vaccine is composed of an HLA promiscuous tetanus T-helper epitope covalently attached to an HLA-A2-restricted CTL epitope from CMV that stimulated a strong immune response in healthy adults and HCT recipients (HCT-R) when combined with a single stranded oligodeoxyonucleo-tide adjuvant and TLR9 agonist, PF03512676 (Pfizer). Subsequent to the completed Phase 1b trial in healthy adults, we initiated a randomized 2-arm pilot Phase 1b trial (Pilot) in both matched related (MRD) and unrelated (URD) donor HCT-R. Interim analysis of the Pilot in HCT-R supports the vaccine concept because preliminary data shows greater CMV-specific immunity, lower rates of CMV reactivation and chronic GVHD in the vaccine versus observational arm. In this application, we will advance this vaccine concept (CMVPepVax) by conducting 2 randomized, blinded and placebo-controlled Phase 2 trials to prevent CMV reactivation in HCT-R jointly with the University of Minnesota.
In Specific Aim (SA) 1, we will conduct Trial 1 that is powered to test the primary endpoint of reduced CMV reactivation and disease in MRD-HCT. CMV-positive HCT-R will be randomized into a vaccine (VA) and a placebo (PA) arm, and given 2 injections spaced 4 weeks apart, while donors will be simultaneously and conjointly randomized to receive a single vaccination 2-5 weeks prior to stem cell collection. The effect of donor vaccination on improving HCT-R outcomes will be a secondary endpoint, thereby allowing up to 67% of donors to decline, yet still have power for effect on HCT-R outcomes. Immunologic 20 endpoints will be quantified by frequency measurements of CMV-specific T cells using HLA multimers and functional studies with T-box transcription factors, T-bet and Eomes. Importantly, this study will test our novel observations that NK cells respond to CMV reactivation after HCT by activating a specific NKG2C+ long-lasting (memory) response that can be mimicked using CMVPepVax, which would have significant general impact on the field. In SA2, Trial 2 will test protective function of CMVPepVax in higher risk URD and umbilical cord blood (UCB) recipients. This trial will employ the same format as Trial 1 except no donor involvement to address a broad range of URD settings, or lesser matched UCB grafts, all resulting in a higher risk of CMV reactivation and disease compared to MRD. The goal is to capitalize on our Phase 1 success with CMVPepVax by conducting Phase 2 studies that will not only establish the therapeutic benefit for HCT-R at risk for complications of CMV infection, but as well define the immunologic basis for this protection.
Hematopoietic stem cell transplantation (HCT) is one of the most successful cancer therapeutic approaches, yet side effects that include infectious complications limit its effectiveness. Among the infectious complications that are most severe are herpes virus infections including cytomegalovirus (CMV). Building upon our successful safety trial in healthy volunteers of the CMV peptide therapeutic called CMVPepVax, we will expand the investigation by conducting 2 consecutive randomized, placebo-controlled Phase 2 trials whose outcome will be a definitive answer whether our approach is effective in at-risk patients and spares them toxicity of anti- viral chemotherapy.