Haploidentical Bone Marrow Transplantation (Haplo-BMT) is a type of allogeneic bone marrow transplant where the donor is a partial genetic match (haploidentical) to the recipient. This means the donor shares only half of the recipient’s human leukocyte antigens (HLAs). Parents, children, or siblings often serve as haploidentical donors because family members are more likely to be partial matches.

Why Use Haploidentical Transplants?

1. Donor Availability: Finding a fully matched donor (10/10 HLA match) can be challenging, especially for patients from diverse ethnic backgrounds. A haploidentical donor is more readily available within a family.
2. Rapid Access to Transplantation: Reduces delays caused by searching for a matched unrelated donor.
3. Advances in Immunosuppression: Modern approaches allow the successful use of haploidentical transplants while minimizing complications like graft-versus-host disease (GVHD).

Who Can Be a Haploidentical Donor?

• A donor who shares at least 50% of the HLA genes with the recipient.
• Typical haploidentical donors include:
  • Parents (biological mother or father).
  • Children of the recipient.
  • Siblings who are a partial match (not fully HLA-identical).

Procedure Overview

1. Donor Selection:
   • A donor is identified based on HLA compatibility, overall health, and absence of contraindications like infectious diseases.
2. Conditioning Therapy:
   • The recipient undergoes chemotherapy and/or radiation to:
     • Destroy diseased bone marrow.
     • Suppress the immune system to reduce the risk of graft rejection.
3. Graft Infusion:
   • Donor stem cells are collected through:
     • Bone marrow harvest.
     • Peripheral blood stem cell collection (apheresis).
   • The collected stem cells are infused into the recipient’s bloodstream.
4. Post-Transplant Management:
   • Immunosuppressive drugs are administered to prevent graft rejection and GVHD.
   • Recovery is monitored for blood cell counts, infection, and signs of engraftment (new blood cell production).

Advancements in Haplo-BMT

1. Post-Transplant Cyclophosphamide (PTCy):
   • A breakthrough approach in haplo-BMT, where high doses of cyclophosphamide are given shortly after the transplant to:
     • Eliminate alloreactive T cells that cause GVHD.
     • Preserve the graft-versus-tumor effect (where donor immune cells attack remaining cancer cells).
2. Reduced-Intensity Conditioning (RIC):
   • Makes transplantation feasible for older or frail patients by using less toxic chemotherapy regimens.
3. Improved GVHD Management:
   • Advanced immunosuppressive protocols and supportive care reduce the severity and incidence of GVHD.

Benefits of Haploidentical Transplants

1. Increased Donor Availability:
   • Almost every patient has at least one potential haploidentical donor within their family.
2. Shorter Waiting Times:
   • Eliminates the time-consuming process of finding a fully matched unrelated donor.
3. Comparable Outcomes:
   • Modern techniques have improved survival and disease-free outcomes, making them comparable to fully matched transplants.

Risks and Challenges

1. Graft-Versus-Host Disease (GVHD):
   • Despite advances, GVHD remains a significant risk.
2. Graft Failure:
   • There’s a possibility the donor cells fail to engraft and establish new blood cell production.
3. Infections:
   • Due to immunosuppression, recipients are at high risk of infections, especially in the early recovery phase.
4. Relapse:
   • The disease being treated may return.

Indications for Haploidentical Transplant

• Hematologic Cancers:
  • Leukemia (acute myeloid leukemia, acute lymphoblastic leukemia).
  • Lymphoma.
• Non-Malignant Disorders:
  • Severe aplastic anemia.
  • Sickle cell disease and thalassemia.
  • Congenital immunodeficiencies.

Outcomes

With advancements in post-transplant care and immunosuppressive strategies, haploidentical transplants now offer:

• Engraftment Success Rates: Comparable to fully matched unrelated donor transplants.
• Survival Rates: Improved in recent years due to reduced risks of GVHD and better supportive care.
• Broader Access to Treatment: Expands transplant options for patients who lack fully matched donors.

If you’d like further details on the procedure, success rates, or any specific aspect of haploidentical transplantation, feel free to ask!