Are half HLA (Human Leukocyte Antigen) matched parental donors the main source of donors for allogeneic hematopoietic stem cell transplant in children with refractory leukemia in Hong Kong?

Half HLA-Matched Parental Donors in Allogeneic HSCT for Children with Refractory Leukemia in Hong Kong

The statement that half HLA-matched parental donors are the main source of donors for allogeneic hematopoietic stem cell transplantation in children with refractory leukemia in Hong Kong is likely false based on current evidence, as HLA-matched sibling donors remain the first choice globally, including in China and Hong Kong.

Donor Hierarchy in Allogeneic HSCT

According to current guidelines and evidence, the preferred donor hierarchy for allogeneic HSCT is:

1. HLA-matched sibling donor (MSD) - This remains the gold standard and first choice globally 1
2. Matched unrelated donor (MUD) - When MSD is unavailable 1
3. Haploidentical donor (HID) - Usually a parent or sibling who matches half the HLA markers 1
4. Umbilical cord blood (UCB) - Particularly for pediatric patients 1

The Chinese Society of Hematology explicitly states: "HLA-matched sibling donors are the first choice as allo-HSCT donors" 1. While haploidentical donors (including parents) are important alternatives when matched siblings are unavailable, they are not described as the primary source in Hong Kong specifically.

Evidence Regarding Hong Kong's Practice

The limited Hong Kong-specific evidence available suggests:

• Hong Kong has a Bone Marrow Donor Registry with approximately 100,000 donors, providing a 45% probability of finding an 8/8 HLA match and 65% probability of finding a 7/8 match 2
• This indicates an established unrelated donor program in Hong Kong, contradicting the notion that half-matched parental donors would be the main source

Role of Haploidentical Donors in Pediatric Leukemia

Haploidentical donors (including parents) do play an important role in allogeneic HSCT, particularly when matched donors are unavailable:

• Haploidentical donors are readily available for most patients (parents, siblings) 1
• Recent advances in haploidentical transplantation techniques have improved outcomes 3
• For certain high-risk patients, haploidentical donors may even be preferred due to stronger graft-versus-leukemia effects 1

However, challenges remain with haploidentical transplantation:

• Higher risk of graft-versus-host disease (GVHD) without T-cell depletion 1
• Higher non-relapse mortality compared to matched sibling donors 4
• Increased risk of infections post-transplant 4

Specific Considerations for Children with Refractory Leukemia

For children with refractory leukemia specifically:

• Allogeneic HSCT remains a curative option 5
• Studies of haploidentical HSCT in children are largely limited to T-cell depleted grafts with less encouraging results in advanced leukemia 5
• Recent innovations like αβ T-cell and B-cell depletion have shown promising results in pediatric haploidentical transplants, with outcomes comparable to matched sibling donors 3

Conclusion

While haploidentical parental donors are an important alternative donor source for children with refractory leukemia who lack matched donors, the available evidence does not support the claim that they are the main source of donors for allogeneic HSCT in Hong Kong. HLA-matched sibling donors remain the preferred first choice globally, including in China and Hong Kong, with unrelated donors, haploidentical donors, and cord blood as alternative sources when matched siblings are unavailable.