A novel stem cell transplantation method incorporating memory T cells is enabling clinicians at KK Women’s and Children’s Hospital (KKH) to improve treatment for children with severe and high-risk haematological and genetic conditions.

KKH is among the first academic medical centres in the world to utilise two unique iterations of TCR alpha beta and CD45RA depletion for haploidentical stem cell transplantation in children. The first approach performs only one stem cell collection from the donor, and then the cells are divided in defined portions for TCR alpha beta or CD45RA depletion, with the final product infused on the same day. The second approach infuses CD45RA depleted memory T cells several weeks before the stem cell transplantation, allowing control of active infections and some recovery of the immune system and organ function for a safer transplant thereafter.

Haploidentical stem cell transplantation is carried out using haematopoietic stem cells from donors who are haploidentical (‘haplo’ referring to half tissue matched) family members, such as a parent or sibling. This form of stem cell transplantation is associated with a high risk of graft versus host disease (GVHD), a condition where the donor transplant’s immune cells attack the recipient’s tissues.

“As medical science has advanced, the discovery of selective T cell depletion using CD45RA depletion now allows clinicians to target and deplete naïve T cells (CD45RA positive cells) that cause GVHD, while selecting and preserving memory T cells (CD45RO cells) which are responsible for providing immunity against viral infections and cancer cells, and have little risk of GVHD,” shares Dr Rajat Bhattacharyya, Senior Consultant, Haematology/Oncology Service, KKH.

“This is an improvement over earlier selection processes by being more selective in cell depletion.”

Better treatment outcomes with lowered risk of infections and relapse

The novel combination of TCR alpha beta and CD45RA depletion for a stem cell transplant exploits the immune system to the patient’s advantage, with the key factor being the addition of measured amounts of CD45RA depleted memory T cells to augment the immune system, while the TCR alpha beta depleted component provides other beneficial cells such as natural killer (NK) cells, gamma delta T cells, and dendritic cells in addition to blood stem cells.

With previously known methods, such as CD34 enrichment or TCR alpha beta and CD19 depletion, some patients with severe and high-risk conditions, such as acute leukaemia and haemoglobinopathy, could experience relatively high rates of graft rejection, fatal infection and disease recurrence.

At KKH, the combined TCR alpha beta and CD45RA depleted stem cell transplant method has successfully been used to manage children with very high-risk leukaemia, including those who have relapsed after a conventional stem cell transplant.

Novel use of TCR alpha beta and CD45RA depleted stem cell transplant for children with transfusion-dependent thalassemia

The KKH team has expanded the use of CD45RA depleted selective T cell depletion to enhance the management of transfusion-dependent thalassaemia in children, enabling them to become independent of life-long blood transfusions.

The most severe type of thalassaemia, a haematological condition in which the patient produces defective red cells which break down easily, thalassaemia major is characterised by severe anaemia and a lifelong dependence on red blood cell transfusions. About five per cent of the population in Singapore are thalassaemia carriers.

Under a new protocol introduced at KKH in August 2018, all paediatric patients with transfusion-dependent thalassaemia but without a matched donor are offered a T-cell depleted haploidentical stem cell transplant, being one of the few centres in the world to successfully enable children with transfusion-dependent thalassaemia to avoid the need for lifelong blood transfusion even without a good match.

Dr Rajat Bhattacharyya (left) with Prof Leung Wing Hang (right) in discussion.

This treatment enables the donor cells to engraft in the bone marrow, changing the entire blood production mechanism to produce healthier red and white blood cells and platelets. With a successful stem cell transplant, the child’s haemoglobin becomes similar to that of the healthy donor, and the child will no longer require blood transfusions.

To date, three paediatric patients with transfusion-dependent thalassaemia have undergone a haploidentical stem cell transplant at KKH, with two successfully remaining blood transfusion-independent. The third patient is currently undergoing treatment towards transfusion independence.

In situations where there is no tissue-matched unaffected sibling or a tissue-matched unrelated donor available, haploidentical stem cell transplantation using TCR alpha beta and CD45RA depletion is increasingly becoming an alternative treatment for transfusion-dependent thalassaemia across the globe, as it eliminates the barrier of requiring a full tissue-matched donor for a stem cell transplantation.

“This treatment method can enable parents of children with thalassaemia to successfully become stem cell donors,” Dr Bhattacharyya shares.

Case study: Child with severe immunodeficiency survives with mother's transplanted stem cells

A child with severe combined immunodeficiency (SCID) presented at KKH with multiple serious infections a few months after birth, and required prolonged ventilation support. An extremely rare genetic condition, SCID can present early in life with serious infections that can be potentially fatal. The condition has an estimated frequency of one in 50,000 live births globally.

To help the child develop a new immune system, the KKH care team planned to perform a stem cell transplant using the TCR alpha beta and CD45RA depletion method.

“Typically, memory T cells are given to patients with infections after stem cell transplantation. However, in this instance, as the child was very sick, it was not safe to perform a stem cell transplant right away,” shares Prof Leung Wing Hang, Senior Consultant, Haematology/Oncology Service, KKH, who was a key adviser in the planning of the child’s treatment and management.

“To stabilise the child, we first supplied a small amount of memory T cells from the mother – which served as immediate immune active cells to control the infections, and allowed time for some recovery of the child's organ function and immune system,” says Prof Leung, who is also Chair, SingHealth Duke-NUS Tan Cheng Lim – CCF Professorship in Paediatric Oncology.

For the extraction of memory T cells, a unit of blood was collected from the mother and manipulated by CD45RA depletion to create aliquots of memory T cells. One portion was freshly infused into the child, and other portions were frozen and infused at intervals to gradually optimise the immune function of the child.

This novel approach of leading with memory T cell transfusion enabled the child to become eligible for stem cell transplant thereafter. Once the child’s condition stabilised, the care team proceeded to perform a haploidentical stem cell transplantation for the child using TCR alpha beta depletion, with the mother as the haploidentical stem cell donor.

The transplant was completed successfully with minimal toxicity while the child was provided ventilation and intensive care support. Currently 20 months’ post-transplant, the child is well at home with minimal need for medications and no major morbidity.

Raising the bar of cancer and cell therapy in Singapore

The KKH team is continuing to explore innovative approaches to haploidentical stem cell transplantation, with the guidance of Prof Leung Wing Hang, Senior Consultant, Haematology/Oncology Service, KKH, who helms the hospital’s Paediatric Cellular and Immunotherapy Programme.

Conferred the SingHealth Duke-NUS Tan Cheng Lim – CCF Professorship in Paediatric Oncology in April 2018, Prof Leung is focusing on establishing a Chimeric Antigen Receptor T Cell (CAR-T) and NK cell programme for Singapore, in collaboration with the Health Sciences Authority, to build a state-of-the-art transplant and cell therapy programme to provide excellent transplant care, and to conduct leading-edge research while nurturing a new generation of physician-scientists.