**2. Cure of thalassemia by hematopoietic stem cell transplantation**

Thalassemia is a disorder characterized by the formation of abnormal hemoglobin and unequal globin chain synthesis. It is one of the most prevalent genetic disorders in the world. There are a global estimate of 270 million carriers of hemoglobin disorders, 80 million of them carrying β-thalassemia. β-Thalassemia is common in the Southern Asia and Southeast Asian regions (1–40%), especially China and India, Middle East (3%), Mediterranean (1–3%), and in malarial tropical regions due to the selective heterozygote advantage against malaria, thus increasing the frequency of β-thalassemia [11]. Current medical therapy consists of lifelong blood transfusions to maintain hemoglobin levels between 9 and 10 g/dL to suppress the ineffective anemia-causing erythropoiesis. Complications with hemosiderosis or iron overload as a result of frequent transfusions have been curbed with the addition of iron chelation therapy, which has doubled life expectancy [11]. Initial iron chelators were administered as a continuous subcutaneous infusion for 8–12 h daily; however, limitations such as inconvenience, side effects, prohibitive cost, pain and associated reduced compliance of parenteral administration led to the development of oral iron chelators, which have been demonstrated to be safer and easier to be compliant, though still associated with certain side effects. Despite increasing life expectancy and improving quality of life for children with thalassemia, transfusion and chelation therapies have major pitfalls, stopping short of becoming a cure for thalassemia. Endemic areas where thalassemia is most prevalent struggle with the cost of iron chelation and the risks of hyper-transfusion causing blood-transmitted infections such as hepatitis B and C. Developed countries often encounter patient compliance issues, as effective daily chelation administration is often unpleasant and inconvenient. Even with modern transfusion and chelation therapy, only 68% of patients with β-thalassemia are alive at the age of 35 [12]. Although there are considerable advancements in transfusion and iron chelation, HSCT represents the only curative therapy for patients with β-thalassemia currently.

In 1982, the first successful marrow transplantation for thalassemia was performed on a child by Donnall Thomas and his colleagues [13]. Subsequently, the first of several series of transplants for thalassemia was reported by Lucarelli et al. [14–16]. Today, thousands of patients with thalassemia have been treated using HLA-identical sibling donor bone marrow transplantation (BMT). After decades of optimization by the Italian groups [14–16], over 1000 patients with thalassemia and sickle cell disease have been cured, mostly using HLA-identical sibling donor BM. For low-risk Pesaro class 1 or 2 patients, related BMT could achieve outstanding overall survival of 87–95% and thalassemia-free survival of 64–90%, depending on the disease severity [11]. Even with class 3 (with extensive liver damage from iron overload) patients, with certain new preparatory regimens, patients younger than 17 years can achieve survival rates of 93% with only 8% autologous recovery rate [17].

Unfortunately, <30% of adults have HLA-matched siblings, especially in China, where the onechild policy has hindered widespread use of related donor transplantation. Matched unrelated adult donors also remain unavailable for most thalassemia patients, despite proving to be acceptable alternatives for patients with thalassemia who lack a compatible family donor [18]. The lack of available matched unrelated adult donors is often due to the limited size or lack of bone marrow registries for the endemic regions. Despite there being 14 million potential unrelated adult donors registered in various international registries worldwide, current inventories of HLA-matched donors are especially limited for patients of Asian descent, a region where thalassemia is most prevalent, as the majority of the world's adult donor registries are from Caucasian background. With the expansion of donor registries by tens of millions in regions that are prevalent for thalassemia, the scarcity of donors may be alleviated; however, the endeavor of building BM registries of tens of millions donors is quite cost prohibitive, especially given that most of the countries in the endemic regions are developing economies.

Cord blood offers an alternative for the source of hematopoietic stem cells and is a faster and more economical way to increase the supply of donor stem cells. In fact, unrelated donor CBT may offer the best alternative to adult donor HSCT due to a more lenient requirement for HLA matching, allowing patients to find suitable donors from banks that are several orders of magnitude smaller than BM registries. The relaxed HLA matching requirement is a result of less severe GvHD after CBT compared to adult donor HSCT, which resulted in improved quality of life for patients due to the decreased requirement of GvHD prophylaxis. As such, related and unrelated CB may alleviate shortage of matched unrelated donors, since less stringent HLA matching is acceptable. Moreover, due to the lower severity and incidence of GvHD after CBT compared to BMT [19–22], CBT may be preferable to BMT for thalassemia and other nonmalignant diseases, as the decreased GvHD incidence and severity greatly improve quality of life for transplant patients. For thalassemia and other transplant patients with nonmalignant diseases, GvHD offers no advantage of relapse reduction as in the setting as for malignant diseases.

led to the development of oral iron chelators, which have been demonstrated to be safer and easier to be compliant, though still associated with certain side effects. Despite increasing life expectancy and improving quality of life for children with thalassemia, transfusion and chelation therapies have major pitfalls, stopping short of becoming a cure for thalassemia. Endemic areas where thalassemia is most prevalent struggle with the cost of iron chelation and the risks of hyper-transfusion causing blood-transmitted infections such as hepatitis B and C. Developed countries often encounter patient compliance issues, as effective daily chelation administration is often unpleasant and inconvenient. Even with modern transfusion and chelation therapy, only 68% of patients with β-thalassemia are alive at the age of 35 [12]. Although there are considerable advancements in transfusion and iron chelation, HSCT

In 1982, the first successful marrow transplantation for thalassemia was performed on a child by Donnall Thomas and his colleagues [13]. Subsequently, the first of several series of transplants for thalassemia was reported by Lucarelli et al. [14–16]. Today, thousands of patients with thalassemia have been treated using HLA-identical sibling donor bone marrow transplantation (BMT). After decades of optimization by the Italian groups [14–16], over 1000 patients with thalassemia and sickle cell disease have been cured, mostly using HLA-identical sibling donor BM. For low-risk Pesaro class 1 or 2 patients, related BMT could achieve outstanding overall survival of 87–95% and thalassemia-free survival of 64–90%, depending on the disease severity [11]. Even with class 3 (with extensive liver damage from iron overload) patients, with certain new preparatory regimens, patients younger than 17 years can achieve

Unfortunately, <30% of adults have HLA-matched siblings, especially in China, where the onechild policy has hindered widespread use of related donor transplantation. Matched unrelated adult donors also remain unavailable for most thalassemia patients, despite proving to be acceptable alternatives for patients with thalassemia who lack a compatible family donor [18]. The lack of available matched unrelated adult donors is often due to the limited size or lack of bone marrow registries for the endemic regions. Despite there being 14 million potential unrelated adult donors registered in various international registries worldwide, current inventories of HLA-matched donors are especially limited for patients of Asian descent, a region where thalassemia is most prevalent, as the majority of the world's adult donor registries are from Caucasian background. With the expansion of donor registries by tens of millions in regions that are prevalent for thalassemia, the scarcity of donors may be alleviated; however, the endeavor of building BM registries of tens of millions donors is quite cost prohibitive, especially given that most of the countries in the endemic regions are developing economies.

Cord blood offers an alternative for the source of hematopoietic stem cells and is a faster and more economical way to increase the supply of donor stem cells. In fact, unrelated donor CBT may offer the best alternative to adult donor HSCT due to a more lenient requirement for HLA matching, allowing patients to find suitable donors from banks that are several orders of magnitude smaller than BM registries. The relaxed HLA matching requirement is a result of less severe GvHD after CBT compared to adult donor HSCT, which resulted in improved quality of life for patients due to the decreased requirement of GvHD prophylaxis. As such,

represents the only curative therapy for patients with β-thalassemia currently.

184 Umbilical Cord Blood Banking for Clinical Application and Regenerative Medicine

survival rates of 93% with only 8% autologous recovery rate [17].

Unrelated CBT for treatment of thalassemia has improved significantly with judicious CB graft selection and consideration of a number of factors, including transplant age, Pesaro class, CB processing, cell dose and post-thaw processing. Working exclusively with CB produced by Chow's proprietary MaxCell technologies, Jaing et al. achieved thalassemia-free survival close to that of related CB transplantations [5, 6]; however, other studies using traditional red cell reduced (RCR) CB (referred to as 1st Gen CB processing elsewhere in this book) produced poor results and the authors advocated cautious use of CB only in clinical trials [3]. Transplant center experience is an important factor in increasing CBT for thalassemia. Although unrelated CBT has the potential for curing thalassemia, thereby drastically improving the quality of life for the patient, it is still not considered optimal even with the industry's best practice due to CB donor scarcity in thalassemia endemic areas, especially for MaxCell CB products, and lack of optimal results for RCR CB. Even so, as blood transfusion and iron chelation therapies are prohibitively expensive and not widely accessible in thalassemia endemic regions, unrelated CBT becomes a viable alternative that is less costly in the long run. In addition, it should be noted that unrelated CBT offers patients significant potential benefits—quality of life and increased life expectancy—thus increasing the need for the optimization of CBT to better treat patients.

Recently, a number of studies have shown significant success using related and unrelated donor CBT. As expected, cell dose is the most critical factor for CBT success, as revealed by almost every major study to date [19–22]. Theoretically cell dose may be less of a problem for thalassemia since CBT is usually performed at an early age when patients have smaller body mass and require less cell dose; however, due to the difficulties of eradicating the endogenous erythron, cell dose has been found to be just as critical for both related and unrelated CBT for thalassemia [6, 7, 23–26]. For unrelated CBT for thalassemia, Jaing *et al*. [6] established institutional guidelines of 2.5 × 107 /kg for single unit CBT and >3.7 × 107 /kg combined nucleated cell dose for double CBT, with at least one unit exceeding 2 × 107 /kg. Moreover, at Chang Gung, following the Minnesota recommendations of CD34+ cell dose of 1.7 × 105 /kg minimum for single unit CBT [27], with the combined CD34+ cell dose exceeding 3.0 × 105 /kg for double CBT.

Due to the proven central importance of cell dose in CBT, different groups have employed various strategies to optimize nucleated and CD34+ cell doses, such as the supplementation of BM stem cells from the same donor to the CB graft [28–30], the use of double CBT when single CB units do not have sufficient cell doses [5, 6, 26, 31–35], the avoidance of post-thaw wash (when indicated), which invariably results in loss of cells [5, 6, 26, 32–50], and usage of MaxCell CB as red cell reduction results in decreased cell recovery [4–7, 26, 31–55].

Various other approaches have been tried to improve the outcome of CBT for thalassemia, ranging from preference for superior HLA matches [4, 6, 26, 31, 34, 37, 51–53], usage of related HLA-identical donors [23–25], directed sibling cord blood bank efforts [30, 56], consideration of non-inherited maternal antigen (NIMA) matches [57], preference for IV busulfan over oral formulations [6, 58], the addition of thiotepa to the conditioning regimen [24, 25], reduced intensity conditioning regimens [3, 59, 60], the avoidance of methotrexate in the prophylaxis regimen [23–25], third-party MSC co-infusion [59], and intrabone direct injection of cord blood products [61, 62].
