HLA-Identical Sibling Donor Bone Marrow Transplantation for Individuals With Severe Sickle Cell Disease Using a Reduced Intensity Conditioning Regimen
HLA-Identical Sibling Donor Bone Marrow Transplantation for Individuals With Severe Sickle Cell Disease Using a Reduced Intensity Conditioning Regimen
Sickle cell disease (SCD) is the most common inherited blood disorder in Saudi Arabia . Its
 clinical severity is widely heterogeneous among patients who share the same genetic mutation
 . Severe frequent pain crisis, recurrent acute chest syndrome and stroke are features of
 severe SCD. Hydroxyurea is an effective treatment of SCD as it ameliorates the severity and
 frequency of pain crisis and acute chest syndrome and decreases mortality, however, it is
 less effective in the prevention and treatment of stroke and other end organ dysfunctions .
 The only readily available cure of SCD is by hematopoietic stem cell transplantation (HSCT) .
 Most children with SCD who are treated by HSCT receive myeloablative conditioning with
 excellent results. The application of reduced intensity (RIC) and non-myeloablative (NMA)
 conditioning regimens are reserved for patients older than 16 years of age because of the
 increased risks of morbidity and mortality after HSCT6. However, infertility and gonadal
 failure after myeloablative conditioning are important barriers to the willingness of
 patients and their families to undergo HSCT . The development of an effective RIC HSCT in SCD
 that might spare the fertility of SCD patients would have obvious merit.

 With the ultimate goal of expanding this curative therapy to SCD patients, we propose to
 investigate HSCT with a RIC conditioning regimen. We will carry out a pilot study of HSCT
 from HLA matched sibling donors using thymoglobulin/fludarabine/melphalan conditioning and
 sirolimus and mycophenolate mofetil (MMF) as GVHD prophylaxis in SCD patients with severe
 complications such as stroke and other severe complications. We hypothesize that HSCT from
 HLA matched sibling using thymoglobulin/fludarabine/melphalan conditioning in SCD will
 maintain a level of stable donor chimerism that is sufficient to cure SCD with minimal
 toxicity.
Busulfan-based myeloablative allogeneic HSCT from an HLA-matched related donor in children is
 associated with high cure rate ranging from 80-90% in different trials, reviewed in 6.
 Lessons learned from these trials include; rabbit ATG significantly contributes to a lower
 graft rejection rate, the presence of stable mixed chimerism is sufficient to cure SCD, and
 the risk of neurological toxicities was minimized by maintaining platelet count greater than
 50,000/uL and hemoglobin level between 9-11g/dL, adding phenytoin prophylaxis, and preventing
 hypertension and hypomagnesemia . We will not present results of these trials here, as the
 focus of this proposal is to investigate the use of NMA/RIC HSCT in SCD.

 2.1 RIC/NMA HSCT in SCD:

 1. Van Besien et al 8 reported transplant results in two adults with SCD who underwent
 allogeneic transplantation from an HLA-identical sibling donor after conditioning with
 fludarabine/melphalan and ATG. One patient was a 40-year-old female who had significant
 end-organ dysfunction related to SCD (renal failure treated by dialysis, pulmonary
 diffusion capacity was reduced by 25% and ischemic stroke) and was heavily transfused
 prior to transplant. She also had RBC alloantibodies and was receiving hydroxyurea and
 erythropoietin. She was conditioned with ATG 30 mg/kg for 4 consecutive days (day -5 to
 day -2), fludarabine 30 mg/m2 i.v. for 4 consecutive days (day -5 to day -2) and
 melphalan 140 mg/m2 i.v. on day -1. The patient had hemodialysis performed on day -5,
 day -3 and day -1 after chemotherapy was administered. On day 0, the patient received an
 infusion of cryopreserved G-CSF-mobilized peripheral blood stem cells (PBSC). GVHD
 prophylaxis consisted of daily tacrolimus and mini methotrexate regimen (5 mg/m2 given
 on days 1, 3 and 6). There was successful neutrophil and platelet engraftment and 100%
 stable chimerism. She developed interstitial pneumonia, possibly secondary to GVHD, 140
 days after transplantation and progressed to respiratory failure leading to her death on
 day 355. The second patient was a 56 year old with SC disease who was heavily
 pretransfused and had multiple SCD complications. She received the same conditioning,
 GVHD prophylaxis, and PBSC source as the first patient. She had 100% donor chimerism but
 died on day 142 secondary to TTP and severe gut GVHD with CNS infection.

 2. Iannone et al 9 described 6 pediatric patients with SCD who underwent bone marrow
 transplant from their HLA matched siblings after conditioning with fludarabine
 50mg/m2/day for 3-5 days and 200 cGy TBI in addition to horse ATG in one patient. GVHD
 prophylaxis included MMF and tacrolimus or cyclosporine with various taper schedules.
 There was minimal toxicity, however, all patients developed graft rejection upon taper
 of immunosuppressive medications.

 3. Horan et al 10 described three SCD patients who were heavily transfused prior to
 transplant and underwent HLA matched sibling transplant after conditioning with
 fludarabine 25mg/m2 on 5 consecutive days before transplantation (days -6 to -2), rabbit
 ATG (Thymoglobulin) on 4 consecutive days before transplantation (days -6 to -2) with
 age adjusted dose, and single dose TBI 200 cGy. GVHD prophylaxis included MMF in the
 first three months and CSA for at least six months. All had graft rejection except one
 when the immunosuppression was tapered. There was no GVHD.

 4. Horwitz et al 11 reported the outcome in two adult SCD patients who underwent HLA
 matched sibling transplant and PBSC was the source of graft in both cases. Conditioning
 was TBI 200 cGy followed by fludrabine 24-30 mg/m2 for 4 days and cyclophosphamide 500
 mg/m2 for four days and alemtuzumab 100mg for five days. MMF was given in the first 100
 days post transplant. Both engrafted successfully with no GVHD and a follow up of 20
 months.

 5. Krishnamurti et al described the use of RIC in seven SCD patients, age range 6-16 years.
 The conditioning was busulfan 3.2 mg/kg on day -8 and -7, fludarabine 35mg/m2 on days -6
 to -2, equine ATG 30mg/kg on days -5 to -1, and total lymphoid irradiation. GVHD
 prophylaxis was CSA and MMF. CSA was tapered starting day +180 and MMF taper varied from
 +45 to +220 day. Six patients had stable mixed chimerism after stopping CSA and MMF. One
 patient had late graft failure. There was a low rate of GVHD.

 6. Hsieh et al reported the use of non-myeloablative conditioning in SCD patients older
 than 16 years of age. Graft source was GCSF mobilized PBSC from HLA matched siblings
 with at least 10 X106 CD34/kg of recipient weight. Conditioning was alemtuzumab (total
 1mg/kg divided on days -7 to -3) and single dose TBI 300 cGy on day -2. Presence of
 major ABO incompatibility was one of the exclusion criteria for this study. Sirolimus
 was used as GVHD prophylaxis and to prevent graft rejection. Nine of 10 patients
 engrafted successfully and had stable chimerism, however, all patients continue to be on
 sirolimus. None of patients had GVHD. They recently updated these promising results in a
 total of 30 patients and were able to taper off sirolimus in 15 patients.

 2.2 Rationale for using thymoglobulin/fludarabine/melphalan conditioning RIC is a feasible
 option for patients with SCD and can successfully cure the disease. A pre-transplant backbone
 regimen consisting of Alemtuzumab or ATG, fludarabine, and melphalan has been applied
 successfully in SCD patients as described above. We anticipate that the toxicity risk is
 lower than the full myeloablative conditioning using busulfan and cyclophosphamide (BU/CY).
 Melphalan was reported to cause infertility, mostly when we used with other chemotherapy
 agents. The use of melphalan alone in the conditioning regimen was reported before to
 potentially preserve fertility in women. So our regimen could potentially preserve fertility
 at higher rate compared to BU/CY.

 2.3 Rationale for pre-transplant immunosuppression therapy with hydroxyurea Individuals with
 hemoglobinopathies have in general adequate T cell function and active bone marrow that can
 lead to higher risk of graft rejection especially among patients who are heavily transfused.
 Experience with class 3 thalassemia patients showed that pretreatment with hydroxyurea,
 azathioprine, and fludarabine decreased the risk of graft rejection and allowed the use of
 lower dose cyclophosphamide . So we will use hydroxyurea prior to transplant to minimize the
 risk of graft rejection associated with RIC in sickle cell anemia.

 2.4 Rationale for using sirolimus and MMF as GVHD prophylaxis: Post-grafting
 immunosuppression appears crucial to ensuring stable engraftment; an early taper appears to
 contribute to late graft rejection in several of the series. Sirolimus is an inhibitor of the
 mammalian target of rapamycin (mTOR) and it induces immune tolerance and was used
 successfully as GVHD prophylaxis in adult SCA patients who underwent RIC/ NMA. Sirolimus in
 combination with calcineurin inhibitors or MMF was utilized effectively in pediatric patients
 19-21. However, studies showed increased risk of veno-occlusive disease with the combination
 of sirolimus and MMF and increased risk of transplant-associated thrombotic microangiopathy
 when combined with tacrolimus especially among patients who received busulfan-based
 conditioning 22-24. We will be using a RIC regimen so we do not anticipate that the
 combination of sirolimus and MMF will cause excess toxicity.
Inclusion Criteria:

 -  1. SCD patients who are 3-18 years old. 2. SCD (HbSS, HbSβ° thalassemia or any
 genotype) with at least one of the following conditions:

 1. Clinically significant neurologic event (stroke) or any neurologic defect lasting
 > 24 hours and accompanied by an infarct on cerebral magnetic resonance imaging
 (MRI)

 2. Minimum of two episodes of acute chest syndrome within the preceding 2-year
 period defined as new pulmonary alveolar consolidation involving at least one
 complete lung segment (associated with acute symptoms including fever, chest
 pain, tachypnea, wheezing, rales or cough that is not attributed to asthma or
 bronchiolitis) despite adequate supportive care measures

 3. History of 3 or more severe pain events per year in the 2 years prior to
 enrollment.

 3. Availability of 10/10 genotypically HLA identical related donor 4. In patients
 who have been treated by regular RBC transfusions >12 months, with a liver biopsy
 that shows no evidence of cirrhosis or active hepatitis 5. Patients must have a
 Karnofsky score ≥ 50 or WHO/ECOG ≥ 2 for patients age ≥ 16, Lansky score ≥ 50 for
 patients age < 16.

 6. Adequate cardiac function: shortening fraction of > 25% or ejection fraction
 of > 55% by echocardiogram 7. Adequate renal function: serum creatinine within
 normal limits or creatinine clearance >70 ml/min/1.73 m2 8. Adequate liver
 function: Total bilirubin within normal limits and AST/ALT <2.5x upper limit of
 normal

 Exclusion Criteria:

 -  1. Patients with symptomatic cardiac insufficiency or arrhythmia. 2. Patients with
 cirrhosis on liver biopsy. 3. Hepatitis B, hepatitis C, or HIV seropositive patients.
 4. Patients with other disease that would increase toxicity of transplant.