Successful immunization following cord blood transplantation in a child with Diamond-Blackfan anemia

Cord blood in regenerative medicine: do we need immune suppression?

Cord blood is currently used as an alternative to bone marrow as a source of stem cells for hematopoietic reconstitution after ablation. It is also under intense preclinical investigation for a variety of indications ranging from stroke, to limb ischemia, to myocardial regeneration. A major drawback in the current use of cord blood is that substantial morbidity and mortality are associated with pre-transplant ablation of the recipient hematopoietic system. Here we raise the possibility that due to unique immunological properties of both the stem cell and non-stem cell components of cord blood, it may be possible to utilize allogeneic cells for regenerative applications without needing to fully compromise the recipient immune system. Issues raised will include: graft versus host potential, the immunogenicity of the cord blood graft, and the parallels between cord blood transplantation and fetal to maternal trafficking. The previous use of unmatched cord blood in absence of any immune ablation, as well as potential steps for widespread clinical implementation of allogeneic cord blood grafts will also be discussed.

Recommendations for immunizations in stem cell transplantation

Investigations over the past decade have documented that there is a decline in immunity to vaccine preventable diseases in many SCT recipients. The majority of immunization studies conducted in SCT recipients to date support the use of multi-dose regimens for most protein and polysaccharide-conjugate vaccine antigens. The consensus immunization schedule recommended by ACIP/IDSA/ASBMT provides guidance for centers to utilize available vaccines in their SCT populations. With the exception of pneumococcal disease, a schedule beginning at 12 months after SCT is reasonable given the low incidence of disease in HSCT recipients for most of the recommended vaccines and improved immune reconstitution in most recipients by one year post transplant. SCT recipients respond poorly to unconjugated pneumococcal polysaccharide vaccine and the development of polysaccharide-protein conjugate vaccines against S. pneumoniae holds promise to impact potentially on clinical disease in this population. In addition, the strategy of donor immunization may also be effective in eliciting early protective immune responses to vaccine antigens. Future challenges will be the development of safe and effective vaccines against the viral pathogens responsible for considerable morbidity and mortality after SCT.

The role of donor age in naive T-cell recovery following allogeneic hematopoietic stem cell transplantation: the younger the better

The high incidence of opportunistic infections after unrelated bone marrow transplantation has been reported. Delayed lymphocyte recovery may be associated with opportunistic infections. Immune reconstitution is influenced by recipient age and graft-vs-host disease. However, the role of donor age is largely unknown. When the effect of donor age on lymphocyte reconstitution post-transplant was examined in the murine allogeneic hematopoietic stem cell transplantation, the recovery of CD4+ naive T-cells in early post-transplant period was correlated inversely with donor age. Clinically, recipient mice transplanted from younger donors showed significantly higher survival rate and mitogenic responses than adult donors. Since CD4+ naive T-cells are mainly involved in primary immune responses to newly encountered antigens and play an important role in host defense, faster recovery of CD4+ naive T-cells in younger donors may contribute to the reduced mortality in early post-transplant period. Therefore, it is better to choose a younger donor if sufficient cell dose is available. In this review, age-related changes in hematopoiesis and lymphopoiesis as well as thymus-dependent and thymus-independent pathways following allogeneic hematopoietic stem cell transplantation are discussed.