Haploidentical hematopoietic stem cell transplant (haplo HSCT) is a type of allogeneic transplantation where the donor is a first-degree relative—such as a parent, sibling, or child—who matches at exactly half (50%) of the recipient’s human leukocyte antigen (HLA) markers.
Key characteristics and clinical considerations for haploidentical HSCT include:
Role and Indications
- Alternative Donor Source: It is considered a primary alternative when a preferred 10/10 matched related donor (MRD) or matched unrelated donor (MUD) is unavailable.
- Broad Availability: Because it only requires a half-match, most patients have a willing donor readily available within their immediate family.
The Standard of Care: Post-Transplant Cyclophosphamide (PTCy)
A defining feature of modern haploidentical HSCT is the use of post-transplant cyclophosphamide for graft-versus-host disease (GVHD) prophylaxis.
- Purpose: PTCy is required to suppress the donor’s T-lymphocytes, which otherwise would recognize the recipient’s “foreign” antigens and cause severe injury to host organs.
- Regimen: The standard prophylaxis often includes tacrolimus, mycophenolate, and PTCy (typically 50 mg/kg IV on days +3 and +4).
Advantages
- Donor Access: Rapid acquisition time compared to searching donor registries.
- Cost and Outcomes: Lower acquisition costs than umbilical cord blood (UCB) and lower non-relapse mortality (NRM) compared to MUD, mismatched unrelated donors (MMUD), or UCB.
- Survival: Recent randomized trials have demonstrated improved overall survival with haploidentical transplant compared to UCB transplant.
Disadvantages and Risks
- Infection Risk: There is a high risk of infection, particularly viral, during the post-transplant period.
- Engraftment: Engraftment may be delayed when using post-transplant cyclophosphamide.
- GVHD Severity: Without appropriate T-cell depletion or PTCy, GVHD can be severe due to the significant HLA mismatch.
Synonyms
Haploidentical HSCT, haplo HSCT