**8. Results**

14 Immunodeficiency

grade II GVHD. Prospective studies are needed comparing treosulfan/ fludarabine with busulphan and fludarabine,[41-43] where early reports also indicate reduced transplantrelated toxicities and excellent survival. Long-term follow-up is needed to see if this "modified intensity" regimen results in less long-term toxicity and, in particular, infertility, as the gonadal toxicity of busulphan is already well documented[44]. Radioimmunotherapy, in which targeted irradiation of the bone marrow is achieved by using radiolabeled monoclonal antibodies, may be used as a potent myeloablative agent with low intrinsic organ toxicity. Schulz et al. recently reported on the use of radioimmunotherapy with 90Yanti-CD66 for conditioning in 30 pediatric patients undergoing HSCT, including 16 with non-malignant disorders with high co-morbidities. Patients received radioimmunotherapy with fludarabine or melphalan alone or in combination, usually with ATG; one patient was given radioimmunotherapy alone. A highly favorable ratio of marrow dose to other organ dose was demonstrated, and stable engraftment was achieved with complete donor chimerism in 13 out of 16 (81%) patients. One patient with Griscelli syndrome and who had secondary graft failure after the first HLA haploidentical transplantation achieved stable

Antibodies to eliminate host stem cells prior to transplantation could mean that toxic conditioning regimens would not be needed. Administration of ACK2 and an antibody that blocks c-Kit function led to transient removal of >98% of endogenous HSCs in immunedeficient mice[46]. Subsequent transplantation with donor HSCs led to chimerism levels up to 90% compared to only 3% in those without this preconditioning. The pharmacological agent AMD3100, which is a CXCR4 inhibitor, has been shown to induce egress of HSCs out of the marrow and improve levels of donor HSC engraftment relative to untreated recipients[47]. Plerixafor, a CXCR4 inhibitor, may also be a more effective mobilizer of stem cells for donors of PBSCs than granulocyte colony stimulating factor (G-CSF), allowing larger doses of stem cells to be administered, which may lead to more rapid engraftment.

In 1981 the introduction of T lymphocyte depletion to remove of alloreactive lymphocytes from the bone marrow source enabled transplantation across HLA barriers. This meant that patients without an HLA-identical donor could receive T lymphocyte depleted marrow

Profound T-cell depletion is a fundamental prerequisite for haploidentical donor transplantation to avoid severe GVHD and B cell depletion lessens the risk of Epstein Barr Virus (EBV)-related lymphoproliferative disease. Various methods have been used to remove viable T lymphocytes from the graft, including E-rosette lectin depletion and in vitro anti CD52 (CAMPATH-1M anti-lymphocyte antibody which is no longer available). Since the late 1990s European centers performing T lymphocyte–depleted HSCT for patients with PID have used CD34+ stem cell selection rather than T-lymphocyte depletion. The most commonly used method, the Miltenyi Clini-MACS system, uses an organic iron bead attached to an anti-CD34 antibody to isolate purified CD34+ HSCs from the other cells by

complete donor chimerism with radioimmunotherapy alone[45].

**7. Methods of T cell depletion** 

from an HLA-haploidentical parent.

#### **8.1. Severe combined immunodeficiency**

A successful HSCT procedure in patients with primary immunodeficiency should result in a cure of the underlying defect with normal immuno-reconstitution leading to normal immune function and a normal life. The likelihood of a successful outcome depends on the underlying diagnosis, degree of HLA matching from the donor, and pre existing end organ damage. Overall the outcome for patients with SCID is better than that for patients with other PID and has improved over time[8]. The likelihood of cure following HSCT is up to 90% in those SCID patients with a genoidentical donor. Even for those with no HLA identical donor, survival following a T cell depleted haploidentical transplant is approaching 60%. Whilst infusion of the stem cell product without the use of chemotherapy eliminates the potentially fatal effects of conditioning including infection from aplasia and increased risk of pneumonitis and mucositis, the quality of engraftment is compromised. Thus for patients with common gamma chain or JAK3 SCID thymopoiesis may be achieved as T cell precursors engraft in the thymus[50], but B cell engraftment is unlikely and patients will remain on lifelong immunoglobulin replacement as recipient B cells are unable to produce IgM through the IL 21 mediated signalling path and do not undergo immunoglobulin class switching.[51] Patients thus remain at risk of bronchiectasis in the

long term. However, for patients with VDJ recombination defects leading to T- B-NK+ SCID, stem cell infusion will lead to no B cell engraftment and only peripheral T cell engraftment with poor T cell numbers, no thymopoiesis and risk of immunosenescence in the medium term.[52]. So, although conditioning may increase the short term risks, immune function is better in the long term following chemotherapy. Full donor chimerism is not necessary as stable mixed donor chimerism may give adequate immune reconstitution. Best results are achieved in patients diagnosed early with no infection and no end organ damage. Newborn transplantation gives the best results of all[5, 53, 54], giving weight to the argument for newborn screening by detection of T cell receptor excision circles (TRECS) on the neonatal blood spot (Guthrie) card and thus detection of SCID before presentation with a SCID defining illness such as pneumocystis pneumonitis (Table 2).

Stem Cell Transplantation for Primary Immunodeficiency 17

For those patients presenting late with infection, graft manipulation such as new methods of T cell depletion and add back of virus specific cytotoxic T cells has enabled more rapid immunoreconstitution and viral clearance[55]. For those patients requiring additional support through the transplant period, improvement in paediatric intensive care, close liaison between BMT and PICU teams, and earlier interventions are leading to improved outcomes of patients receiving HSCT but needing to go to PICU. Survival rates are now approaching up to 60%, better survival for those who receive only invasive ventilation and

The results of transplant for other primary immunodeficiencies are historically not so good as those for patients with SCID but are improving over time[8]. This is likely due to a number of factors. Foremost is the adoption of stem cell transplant as a recognised therapy for the underlying condition. As transplant becomes an accepted treatment for a specific condition, patients with end organ disease undergo transplant, and some do not survive. Secondly, patients will need to undergo conditioning chemotherapy in order to prevent rejection of the graft and achieve donor chimerism and are therefore subject to the toxicities associated with conditioning. Thirdly, is the question of the optimum time to perform transplantation. Severe combined immunodeficiencies are usually fatal within the first 18 months of life, patients with other primary immunodeficiencies live longer and can survive into adulthood, albeit with a deteriorating quality of life as they accumulate end organ damage secondary to infection and inflammatory complications of the underlying disease. Registry data has provided good quality information about long term prognosis for some of these disorders, even when appropriate antimicrobial prophylaxis is available, enabling parents, patients and physicians to make informed choices about timing of transplantation[6, 11, 57]. Most non-SCID PIDs are life limiting in the medium to long term, rather than fatal in the first few months of life. As with SCID, results of transplant are better if patients are transplanted whilst younger, without end organ damage. For those with XLP, survival from transplant is significantly better for patients who do not experience haemophagocytic lymphohistiocytosis[58]. In a similar fashion, for patients with chronic granulomatous disease, outcome is better in those that have not had significant fungal infection or inflammatory sequalae[24]. Thus transplantation at an early age before onset of complications gives the best chance of survival and cure but some families may prefer not to put a healthy child through transplant, rather monitoring them closely for significant deterioration and transplant at the first sign of trouble. It is advisable that searches for an appropriate donor are made soon after diagnosis so that transplantation can proceed

The amount of chimerism required to achieve cure depends on the underlying disease. Patients with CD40 ligand require only good T cell donor chimerism which will enable immunoglobulin class switching, whereas Wiskott Aldrich Syndrome patients with incomplete donor chimerism are much more likely to develop auto immune complications[20]. The cell lineage in which donor chimerism is required may not be

worse survival for those with multi organ failure[56].

quickly once the decision to transplant has been made.

**8.2. Other primary immunodeficiencies** 


**Table 2.** Disease defining illness in Primary Immunodeficiency

For those patients presenting late with infection, graft manipulation such as new methods of T cell depletion and add back of virus specific cytotoxic T cells has enabled more rapid immunoreconstitution and viral clearance[55]. For those patients requiring additional support through the transplant period, improvement in paediatric intensive care, close liaison between BMT and PICU teams, and earlier interventions are leading to improved outcomes of patients receiving HSCT but needing to go to PICU. Survival rates are now approaching up to 60%, better survival for those who receive only invasive ventilation and worse survival for those with multi organ failure[56].

#### **8.2. Other primary immunodeficiencies**

16 Immunodeficiency

long term. However, for patients with VDJ recombination defects leading to T- B-NK+ SCID, stem cell infusion will lead to no B cell engraftment and only peripheral T cell engraftment with poor T cell numbers, no thymopoiesis and risk of immunosenescence in the medium term.[52]. So, although conditioning may increase the short term risks, immune function is better in the long term following chemotherapy. Full donor chimerism is not necessary as stable mixed donor chimerism may give adequate immune reconstitution. Best results are achieved in patients diagnosed early with no infection and no end organ damage. Newborn transplantation gives the best results of all[5, 53, 54], giving weight to the argument for newborn screening by detection of T cell receptor excision circles (TRECS) on the neonatal blood spot (Guthrie) card and thus detection of SCID before presentation with a SCID

defining illness such as pneumocystis pneumonitis (Table 2).

**Table 2.** Disease defining illness in Primary Immunodeficiency

The results of transplant for other primary immunodeficiencies are historically not so good as those for patients with SCID but are improving over time[8]. This is likely due to a number of factors. Foremost is the adoption of stem cell transplant as a recognised therapy for the underlying condition. As transplant becomes an accepted treatment for a specific condition, patients with end organ disease undergo transplant, and some do not survive. Secondly, patients will need to undergo conditioning chemotherapy in order to prevent rejection of the graft and achieve donor chimerism and are therefore subject to the toxicities associated with conditioning. Thirdly, is the question of the optimum time to perform transplantation. Severe combined immunodeficiencies are usually fatal within the first 18 months of life, patients with other primary immunodeficiencies live longer and can survive into adulthood, albeit with a deteriorating quality of life as they accumulate end organ damage secondary to infection and inflammatory complications of the underlying disease. Registry data has provided good quality information about long term prognosis for some of these disorders, even when appropriate antimicrobial prophylaxis is available, enabling parents, patients and physicians to make informed choices about timing of transplantation[6, 11, 57]. Most non-SCID PIDs are life limiting in the medium to long term, rather than fatal in the first few months of life. As with SCID, results of transplant are better if patients are transplanted whilst younger, without end organ damage. For those with XLP, survival from transplant is significantly better for patients who do not experience haemophagocytic lymphohistiocytosis[58]. In a similar fashion, for patients with chronic granulomatous disease, outcome is better in those that have not had significant fungal infection or inflammatory sequalae[24]. Thus transplantation at an early age before onset of complications gives the best chance of survival and cure but some families may prefer not to put a healthy child through transplant, rather monitoring them closely for significant deterioration and transplant at the first sign of trouble. It is advisable that searches for an appropriate donor are made soon after diagnosis so that transplantation can proceed quickly once the decision to transplant has been made.

The amount of chimerism required to achieve cure depends on the underlying disease. Patients with CD40 ligand require only good T cell donor chimerism which will enable immunoglobulin class switching, whereas Wiskott Aldrich Syndrome patients with incomplete donor chimerism are much more likely to develop auto immune complications[20]. The cell lineage in which donor chimerism is required may not be obvious. A patient with IPEX syndrome was cured although T cells appeared to be recipient, because on detailed study, the only donor cells were found to be the FOXP3+ cells[59], required to cure the condition. On the other hand, donor B cells are required in CgC or JAK-3 deficient SCID to achieve independence from immunoglobulin substitution[51, 60], but recipient B cells are functional in SCID due to defects in IL7Ra.

Stem Cell Transplantation for Primary Immunodeficiency 19

(2mg/kg) is standard first line treatment. If the patient fails to respond to this, then a variety of other agents may be tried including monoclonal antibodies such as infliximab, alemtuzimab, antithymocyteglobulin, mesenchymal stem cells and extra corporeal phototherapy but none have yet proven to be consistently effective. Veno occlusive disease is a risk factor particularly in those with osteopetrosis, with pre-existing liver disease or under going conditioning with busulphan or cyclophosphamide. Prophylaxis with defibrotide is effective at preventing veno-occlusive disease and treating if necessary[62]. Haemorrhagic cystitis is a rare complication following HSCT, associated with adenovirus or BK virus infection, associated with T cell depletion or prolonged immunosuppression.

Treatment is as for patients undergoing HSCT for other indications[63].

**Liver**

2 25-50% 51-100 20-30

3 Generalised erythema 101-255 >30

**Bilirubin μmol/l** 

1 Maculopapular <25% 34-50 10-19.9 (or 500-1000ml/day)

4 Exfoliation/vesicles >256 Severe abdo pain +/- ileus

I 1-2 0 0 normal II 1-3 1 1 mild decrease III 2-3 2-3 2-3 marked decrease IV 2-4 2-4 2-4 incapacitated

**10. Post transplantation immuno-reconstitution** 

disease may impair or abrogate this process[65].

**Grade Skin stage Liver stage Gut stage Clinical performance** 

Full immunoreconstitution can take up to 2 years post transplant. Most patients remain on immunoglobulin replacement for around 6 months post transplant or until evidence of immunoglobulin production (gauged by measuring IgM production). Ongoing immunosuppression or graft versus host disease will delay assessment of antibody production. Thymopoiesis can be measured by documenting an increase in recent thymic emigrants measured by TRECS or surrogate markers such as CD27 or CD31 on T cells. Thymopoiesis normally occurs around 120 days post transplant[64]. Graft versus host

Once immunoglobulin production is established, immunoglobulin replacement should be discontinued. After a wash out period of 3 months, primary vaccinations with non-live antigens can begin, having assessed base line specific antibody levels. The response to

**Gut**

**Diarrhoea vol. ml/kg/day**  (or if >50kg body weight)

(or 1000-1500ml/day)

(or>1500ml/day)

**Stage Skin** 

Adapted from Jacobsohn DA[69] **Table 3.** Staging of acute GVHD

**% body surface area** 
