Early attempts at haploidentical transplants - where the donor's and recipient's tissue types are not a perfect match - frequently ended in death, mainly because of graft versus host disease (GVHD) and graft rejection in transplantation.
In GVHD, the white blood cells in the donor's stem cells attack the recipient's tissue. In graft rejection, transplanted stem cells are destroyed by the donor's body.
However, doctors now have knowledge about the specific cells that cause GVHD which have made half-matched transplants a reality.
Said Dr Rajat Bhattacharyya, a consultant at KK Women's and Children's Hospital's department of paediatric sub-specialities: "With this knowledge, you can actually select and take out these cells."
The process of removing the problematic cells using a machine takes just one day, and once the remaining cells are transplanted, it takes around 10 to 14 days for them to grow and start producing new cells in the patient's body.
Dr Frances Yeap, associate consultant at the National University Hospital's division of paediatric haematology and oncology, said another method is to administer chemotherapy drugs to patients to significantly reduce their T-cells - the immune cells which cause GVHD.
This was started by doctors in Johns Hopkins in the US and is very popular around the world, especially in countries where they do not have the set-up and facilities to do cell manipulation, she added.