Volume 6 (2023) Issue 2 No.2 Pages 42-48
Effective control of the graft-versus-host disease (GVHD) and immune reconstitution are crucial in improving the outcome of allogeneic hematopoietic stem cell transplantation (HSCT) as well as the quality of life of the transplant survivors. Recent basic and clinical studies have deepened our understanding of the mechanisms of the immunological sequelae of HSCT, GVHD, and compromised immune systems. Based on the findings, various novel approaches have also been developed and tested clinically. However, further studies are necessary to develop therapeutic strategies with significant clinical benefits.
Graft-versus-host disease (GVHD) is a major devastating complication of allogeneic hematopoietic stem cell transplantation (HSCT). Acute GVHD develops early after HSCT, typically within 100 d post-transplantation. Chronic GVHD is also a major cause of late non-relapse mortality (NRM) after HSCT and significantly impairs the quality of life of the transplant survivors1. Acute GVHD is an alloreactive T cell-mediated systemic inflammatory disorder, typically involving the skin, gut, and liver2. Chronic GVHD is a more complex wasting syndrome involving various immune effector mechanisms and clinical manifestations1,3. However, effective prevention and treatment of acute GVHD remain challenging.
Allogeneic HSCT is associated with severe immune compromise, with defects in both innate and adaptive immunity. In particular, T-cell recapitulation takes a long time after HSCT. GVHD targets the immune system, and its prophylaxis and treatment with immunosuppressants prevents immune reconstitution (IR). Therefore, a better understanding of transplant immunology is required to develop effective strategies to prevent GVHD and facilitate IR.
Novel Insights into the Biology and Treatment of Acute GVHD
Acute GVHD is a major barrier to successful allogeneic HSCT; it is a leading cause of morbidity and NRM after HSCT. Unfortunately, current therapies for GVHD lack precision and rely on the induction of global immunosuppression, which increases the rates of NRM secondary to infection and the risk of post-transplant relapse. Furthermore, the prevalence of treatment resistance in patients with GVHD and GVHD progression due to severe immune deficiency suggest the importance of mechanisms other than those involved in the alloimmune response in influencing GVHD severity. Morbidity and mortality associated with GVHD are mainly driven by gastrointestinal tract injuries. Therefore, immunosuppression alone may be insufficient to control GVHD after HSCT.
Studies on GVHD pathophysiology have primarily focused on the induction phase of GVHD, particularly the mechanisms of donor T-cell activation by professional and non-professional antigen-presenting cells. However, several recent studies on the mechanisms of target tissue injury have revealed tissue stem cells as targets of GVHD, leading to impaired tissue homeostasis and regeneration. Hence, GVHD is recognized as a disorder of tissue regeneration and repair4. Recent insights into intestinal homeostasis after HSCT have greatly reconciled our understanding of GVHD pathophysiology and helped reshape contemporary GVHD prophylaxis and treatment strategies. Gut GVHD is a major cause of GVHD-associated mortality. Emerging data indicate that intestinal stem cells (ISCs) and their niche Paneth cells are targeted in acute GVHD, leading to the dysregulation of intestinal homeostasis and microbiota5–7. The microbiota and their metabolites shape the immune system and maintain intestinal homeostasis; therefore, intestinal dysbiosis may alter the host susceptibility to GVHD. In the skin, Lgr5+ hair follicle stem cells (HFSCs) exhibit a multipotent capacity to regenerate the epidermis. HFSCs are targeted in GVHD, which impairs the healing process8. These novel findings reconcile GVHD as a disorder of tissue regeneration and repair4. Therefore, protection of tissue stem cells and target tissue cell components may be a novel approach to prevent GVHD and associated infections. R-Spondin is one of the three essential factors involved in the generation of organoids from a single Lgr5+ ISC. R-Spondin is produced by intestinal lymphatic endothelial cells (LECs); the number of LECs is markedly reduced in GVHD, which impairs the production of R-Spondin9, suggesting that the administration of R-Spondin can potentially improve the transplant outcomes. Brief administration of R-Spondin has been reported to protect ISCs and ameliorate systemic GVHD in murine models5,10. Similarly, interleukin (IL)-22 has been reported to protect ISCs and ameliorate systemic GVHD6,11, and various clinical trials on IL-22 are ongoing. Epidermal growth factor (EGF) restores epithelial and mucosal integrity after intestinal injury and EGF plasma levels are low in patients with acute GVHD12. EGF is an inexpensive commercially available drug (urinary-derived human chorionic gonadotropin) that has shown promising results in clinical trials of patients with steroid-refractory acute GVHD13. Glucagon-like peptide 2 (GLP-2) is produced by intestinal L-cells and stimulates intestinal growth and function. Colon biopsies of patients with acute GVHD revealed a low number of L cells as a risk factor for steroid-refractory GVHD13. Administration of the GLP-2 analog, teduglutide, has been reported to protect ISCs and ameliorate GVHD in mice14.
Intestinal secretory, Paneth, and goblet cells protect the host from pathogens. Paneth cells in the small intestine secrete antimicrobial peptides that regulate the intestinal ecology. Paneth cell injury in GVHD decreases antimicrobial peptide production, leading to intestinal dysbiosis7,15. Goblet cell injury in GVHD reduces the inner mucus layer, which contains the host defense molecules such as Lypd8, to protect the epithelium from bacterial invasion and facilitate bacterial translocation16. Administration of carbapenems after HSCT facilitates the growth of mucus-degrading Bacteroides and aggravates GVHD17. Thus, both GVHD and carbapenems disturb intestinal homeostasis and exaggerate the vicious cycle of GVHD and infection. IL-25 induces goblet cell hyperplasia. Administration of IL-25 has been reported to protect the goblet cells, prevent infections, and ameliorate GVHD in mice16. Low numbers of Paneth cells in upper gastrointestinal biopsy and goblet cells in colon biopsy are associated with clinical GVHD severity and a high incidence of NRM16,18. Microbial diversity is reduced with Enterococcus dominance in stool samples of patients with GVHD after allo-stem cell transplantation, which is associated with high GVHD-related mortality and low survival rate19,20.
High dose and long duration of systemic corticosteroid treatment for both acute and chronic GVHD are associated with poor transplant outcomes due to increased risks of infection and leukemia relapse21. Recent studies have uncovered previously unrecognized adverse effects of corticosteroids, and long-term corticosteroid treatment has been reported to damage skin stem cells8. Interestingly, the use of carbapenem facilitates the growth of Bacteroides, which degrades mucus in the colon and aggravates GVHD. Therefore, antibiotics disrupt the repair of GVHD-mediated tissue injury.
In summary, GVHD impairs tissue regeneration by inducing ISC injury. Tissue injury caused by a pretransplant conditioning regimen makes tissues more vulnerable to GVHD by impairing various tissue intrinsic properties, such as repair, homeostasis, and microbial ecology22. Hence, strategies to increase the tissue recovery capacity in response to immune insults can facilitate effective tissue repair and restoration of tissue homeostasis. Deeper understanding of GVHD biology can further aid in the development of novel treatment strategies with significant clinical benefits.
Novel Insights into the Biology and Treatment of Chronic GVHD
Allogeneic HSCT is a curative treatment for otherwise incurable hematologic diseases, including malignancies and bone marrow failure syndromes. With improvements in immunosuppressive therapy and supportive care, only a few patients develop acute GVHD, as more patients survive beyond the first year of transplantation. However, chronic GVHD, resulting in clinical manifestations resembling those of autoimmune diseases, remains a major complication after allogeneic HSCT that can cause morbidity and NRM in long-term survivors after HSCT. Similar to autoimmune diseases, both T and B cell responses appear to play important roles in the pathogenesis of chronic GVHD, suggesting a general loss of immune tolerance in affected patients. Recent studies have elucidated T-cell- and B-cell-based pathogenesis of chronic GVHD and proposed a mutual relationship between the two23.
CD4+CD25+Foxp3+ regulatory T cells (Tregs) are known to play a crucial role in maintaining immune tolerance after allogeneic HSCT. We previously demonstrated that altered Treg homeostasis under prolonged lymphopenia after HSCT leads to increased susceptibility to apoptosis in this subset, which results in a relative deficiency of Tregs based on the prolonged imbalance of Treg homeostasis that is associated with a high incidence of extensive chronic GVHD24. To preserve Treg homeostasis, we conducted a clinical trial using low-dose IL-2. IL-2 therapy resulted in the selective increase and decrease in the levels of phosphorylated signal transducer and activator of transcription 5 (STAT5) in Tregs and conventional T cells, respectively, which induced several changes in Treg homeostasis, including increased cell proliferation, thymic export, and resistance to apoptosis. With the restoration of Treg homeostasis after IL-2 therapy, the clinical symptoms of chronic GVHD were reportedly improved in approximately 60% of all patients25,26. These results clearly indicate that alteration in Treg homeostasis is a major pathogenic process in chronic GVHD that can potentially be used as a therapeutic target.
Recent studies have shown that altered B cell homeostasis plays an important role in the pathogenesis of chronic GVHD. Delayed reconstitution of naïve B-cell subsets, including IL-10-producing regulatory B cells, and the compensatory increase in soluble B-cell-activating factor promote the responsiveness of B cells to antigens and increase the survival of activated B cells27. Clinical studies have shown that pathological B-cell depletion by rituximab can suppress the incidence and severity of chronic GVHD28. Murine studies have shown that excessive differentiation of naïve B cells into germinal center B cells results in the deposition of IgG alloantibodies, leading to tissue damage in chronic GVHD target organs29. Based on these findings, inhibitors of Bruton's and spleen tyrosine kinases, which signal downstream of the B-cell receptor, have been developed as treatments for steroid-resistant chronic GVHD29,30.
In addition to the individual mechanisms of T- and B-cells, their interrelationships are also important. In particular, altered T-B interactions in lymph nodes have been shown to be an important aspect of the pathogenesis of chronic GVHD. Studies have demonstrated a significant decrease in T-follicular helper (Tfh) cells, which support B cell activation in lymph nodes, in peripheral blood and increase in the plasma concentration of C-X-C motif chemokine ligand 13, a ligand of C-X-C motif chemokine receptor 5, in patients with active chronic GVHD, suggesting that the migration of Tfh cells from peripheral blood to lymph nodes is an important process in chronic GVHD. Tregs and T-follicular regulatory cells regulate the interaction between B and Tfh cells at the germinal center31,32.
Above-mentioned studies have mainly investigated samples from patients with chronic GVHD after HLA-matched transplantation. However, IR and chronic GVHD after HLA-mismatched transplantation have not yet been properly studied. Clinical studies have suggested that PTCy-based HLA-haploidentical transplantation (PTCY-haplo) and umbilical cord blood transplantation (CBT) are associated with a low incidence of chronic GVHD33,34. Recently, we examined early IR, especially early B-cell lymphogenesis and differentiation, in three different types of alternative donor transplants, including PTCy-haplo, CBT, and T-cell-replete haploidentical peripheral blood with low-dose anti-thymocyte globulin (ATG-haplo), in comparison with HLA-matched peripheral blood transplants35. Our data demonstrated that early IR was very different among different transplant types. Notably, B cell reconstitution within eight weeks post-transplantation was substantially affected by the donor source and presence of acute GVHD. Impaired early recovery of the naïve B cell pool is associated with future development of chronic GVHD. PTCy-haplo restored favorable B-cell homeostasis, leading to the enhanced emergence of naive fractions from the bone marrow and suppression of excessive early activation in peripheral lymph nodes. These findings indicate that abnormal B-cell lymphopoiesis in the very early post-transplant period is a major trigger for the basal pathogenesis of chronic GVHD, and PTCy-haplo is a promising strategy to prevent initial abnormalities and establish long-term immune tolerance in patients with GVHD.
Detailed mechanisms by which PTCy-haplo can restore B-cell lymphogenesis remain unclear but may involve the immune environment early after transplantation. In general, PTCy-haplo may enable an immunologically calm environment by efficiently depleting allo-aggressive effector T cells and sparing Tregs. This may be much less immunogenic than ATG-haplo, in which a haploidentical T-cell replete graft is infused with only low-dose ATG. Our results showing the negative impact of acute GVHD on B-cell lymphogenesis also suggest that aggressive inflammation should be controlled sufficiently to avoid initial B-cell abnormalities. Further studies on animal models will provide insights on the etiology of abnormal B-cell homeostasis and aid in the development of therapeutic and prophylactic approaches for chronic GVHD.
Based on our understanding of its pathogenesis, various novel therapies are being developed to treat chronic GVHD. Although there is an increase in the treatment options for chronic GVHD, there are no available biomarkers to support the treatment choices. Therefore, future studies should focus on the identification of clinically relevant biomarkers for GVHD. With the continuous development of treatment strategies for chronic GVHD in both basic and clinical research, the quality of life of long-term survivors after allo-HSCT is expected to improve.
Towards Predictable IR after Transplantation
Severe immune compromise with defects in both innate and adaptive immunity is observed after allogeneic HSCT. While restoration of innate immunity typically occurs in the first month after transplantation, defects in adaptive immunity persist for a long period36–40. These defects arise from the need to eradicate the recipient immune response to prevent the rejection of non-self HSCs and suppress the donor immune system to prevent overwhelming hyperacute GVHD. Successful HSCT involves the re-establishment of T cell immunity, especially CD4+ T cell immunity, in the post-transplant period. Reconstitution of T cell immunity occurs by both homeostatic expansion of infused populations at the time of transplant (early IR) and de novo thymic-dependent T cell production over a long period (months to years). Research over the last two decades has revealed that the pace of this process is affected by the recipient age, donor/host human leukocyte antigen (HLA) disparity, intensity of the conditioning regimen, method of GVHD prophylaxis, incidence of GVHD, and graft composition41. IR generally takes up to 1-2 years, but a significant number of patients require an even longer recovery period36–40.
Some of the factors controlling IR, such as the recipient age, are non-modifiable. Approaches to minimize the incidence of GVHD have profound effects on the pace of post-transplant IR. Standard approaches for the prevention of GVHD include serotherapy (rabbit-ATG and alemtuzumab) to eliminate T cells via antibody-dependent cellular cytotoxicity, use of calcineurin inhibitors to limit T-cell activation, and use of methotrexate and mycophenolate mofetil to limit the proliferation of T cells. These approaches are effective in limiting the incidence of GVHD in HLA-matched HSCT and CBT patients; however, they are insufficient to control GVHD in HLA-mismatched transplant patients. In addition to serotherapy, approaches to limit the incidence of GVHD by eliminating donor T cells either before or after infusion include in vivo and ex vivo depletion of T cells. Currently, three methods are available for T cell depletion: positive selection of
We previously found that early CD4+ T-cell reconstitution can predict the survival of patients after HSCT47. We found that a threshold of CD4+ IR, 50 CD4+ T-cells/μL, within 100 d post-transplantation is associated with decreased NRM and improved event-free and overall survival. A retrospective analysis of a large cohort of adult and pediatric recipients of CD34+ HSCT also reported similar findings43. Moroever, this measure of early CD4+ T-cell reconstitution can overcome the risk associated with GVHD and virus reactivation42,46,47. A prospective individualized ATG dosing trial showed that the IR of CD4+ T cells is better predicted by individualizing the ATG dose, as it decreases NRM and improves the overall survival40. Variable exposure to other agents, such as fludarabine, has also been reported to influence the transplant outcomes, such as overall survival48. Developing a simple and easily replicable milestone that is informative regardless of the recipient age, indication for transplant, and transplant platform will help in optimizing the design of new predictable transplant platforms that can be feasibly used in small centers as well as those with limited resources49.
In the future, strategies should be developed to effectively predict IR (CD4+ IR), reduce toxicity (virus reactivation) and NRM (after transplantation), and achieve better disease control in GVHD49. Pharmacokinetics and dynamics are important in achieving this goal.
TT wrote the abstract and introduction as well as the section on
This study was supported by Japan Society for the Promotion of Science KAKENHI (25293217 and
Conflicts of Interest
KM declare no conflict of interest. Disclosure forms provided by the authors are available on the website.
1.Jagasia MH, Greinix HT, Arora M, Williams KM, Wolff D, Cowen EW, et al. National institutes of health consensus development project on criteria for clinical trials in chronic graft-versus-host disease: I. The 2014 Diagnosis and Staging Working Group report. Biol Blood Marrow Transplant. 2015; 21: 389-401 e1.
2.Zeiser R, Blazar BR. Acute graft-versus-host disease – biologic process, prevention, and therapy. N Engl J Med. 2017; 377: 2167-79.
3.Zeiser R, Blazar BR. Pathophysiology of chronic graft-versus-host disease and therapeutic targets. N Engl J Med. 2017; 377: 2565-79.
4.Chakraverty R, Teshima T. Graft-versus-host disease: a disorder of tissue regeneration and repair. Blood. 2021; 138: 1657-65.
5.Takashima S, Kadowaki M, Aoyama K, Koyama M, Oshima T, Tomizuka K, et al. The Wnt agonist R-Spondin1 regulates systemic graft-versus-host disease by protecting intestinal stem cells. J Exp Med. 2011; 208: 285-94.
6.Hanash AM, Dudakov JA, Hua G, O'Connor MH, Young LF, Singer NV, et al. Interleukin-22 protects intestinal stem cells from immune-mediated tissue damage and regulates sensitivity to graft versus host disease. Immunity. 2012; 37: 339-50.
7.Eriguchi Y, Takashima S, Oka H, Shimoji S, Nakamura K, Uryu H, et al. Graft-versus-host disease disrupts intestinal microbial ecology by inhibiting Paneth cell production of alpha-defensins. Blood. 2012; 120: 223-31.
8.Takahashi S, Hashimoto D, Hayase E, Ogasawara R, Ohigashi H, Ara T, et al. Ruxolitinib protects skin stem cells and maintains skin homeostasis in murine graft-versus-host disease. Blood. 2018; 131: 2074-85.
9.Ogasawara R, Hashimoto D, Kimura S, Hayase E, Ara T, Takahashi S, et al. Intestinal lymphatic endothelial cells produce R-Spondin3. Sci Rep. 2018; 8: 10719.
10.Hayase E, Hashimoto D, Nakamura K, Noizat C, Ogasawara R, Takahashi S, et al. R-Spondin1 expands Paneth cells and prevents dysbiosis induced by graft-versus-host disease. J Exp Med. 2017; 214: 3507-18.
11.Lindemans CA, Calafiore M, Mertelsmann AM, O'Connor MH, Dudakov JA, Jenq RR, et al. Interleukin-22 promotes intestinal-stem-cell-mediated epithelial regeneration. Nature. 2015; 528: 560-4.
12.Holtan SG, Newell LF, Cutler C, Verneris MR, DeFor TE, Wu J, et al. Low EGF in myeloablative allotransplantation: association with severe acute GvHD in BMT CTN 0402. Bone Marrow Transplant. 2017; 52: 1300-3.
13.Holtan SG, Hoeschen AL, Cao Q, Arora M, Bachanova V, Brunstein CG, et al. Facilitating resolution of life-threatening acute GVHD with human chorionic gonadotropin and epidermal growth factor. Blood Adv. 2020; 4: 1284-95.
14.Norona J, Apostolova P, Schmidt D, Ihlemann R, Reischmann N, Taylor G, et al. Glucagon-like peptide 2 for intestinal stem cell and Paneth cell repair during graft-versus-host disease in mice and humans. Blood. 2020; 136: 1442-55.
15.Jenq RR, Ubeda C, Taur Y, Menezes CC, Khanin R, Dudakov JA, et al. Regulation of intestinal inflammation by microbiota following allogeneic bone marrow transplantation. J Exp Med. 2012; 209: 903-11.
16.Ara T, Hashimoto D, Hayase E, Noizat C, Kikuchi R, Hasegawa Y, et al. Intestinal goblet cells protect against GVHD after allogeneic stem cell transplantation via Lypd8. Sci Transl Med. 2020; 12: eaaw0720.
17.Hayase E, Hayase T, Jamal MA, Miyama T, Chang CC, Ortega MR, et al. Mucus-degrading Bacteroides link carbapenems to aggravated graft-versus-host disease. Cell. 2022; 185: 3705-19 e14.
18.Levine JE, Huber E, Hammer ST, Harris AC, Greenson JK, Braun TM, et al. Low Paneth cell numbers at onset of gastrointestinal graft-versus-host disease identify patients at high risk for nonrelapse mortality. Blood. 2013; 122: 1505-9.
19.Peled JU, Gomes ALC, Devlin SM, Littmann ER, Taur Y, Sung AD, et al. Microbiota as predictor of mortality in allogeneic hematopoietic-cell transplantation. N Engl J Med. 2020; 382: 822-34.
20.Stein-Thoeringer CK, Nichols KB, Lazrak A, Docampo MD, Slingerland AE, Slingerland JB, et al. Lactose drives Enterococcus expansion to promote graft-versus-host disease. Science. 2019; 366: 1143-9.
21.Martin PJ. How I treat steroid-refractory acute graft-versus-host disease. Blood. 2020; 135: 1630-8.
22.Wu SR, Reddy P. Tissue tolerance: a distinct concept to control acute GVHD severity. Blood. 2017; 129: 1747-52.
23.MacDonald KP, Hill GR, Blazar BR. Chronic graft-versus-host disease: biological insights from preclinical and clinical studies. Blood. 2017; 129: 13-21.
24.Matsuoka K, Kim HT, McDonough S, Bascug G, Warshauer B, Koreth J, et al. Altered regulatory T cell homeostasis in patients with CD4+ lymphopenia following allogeneic hematopoietic stem cell transplantation. J Clin Invest. 2010; 120: 1479-93.
25.Koreth J, Matsuoka K, Kim HT, McDonough SM, Bindra B, Alyea EP, 3rd, et al. Interleukin-2 and regulatory T cells in graft-versus-host disease. N Engl J Med. 2011; 365: 2055-66.
26.Matsuoka K, Koreth J, Kim HT, Bascug G, McDonough S, Kawano Y, et al. Low-dose interleukin-2 therapy restores regulatory T cell homeostasis in patients with chronic graft-versus-host disease. Sci Transl Med. 2013; 5: 179ra43.
27.Sarantopoulos S, Stevenson KE, Kim HT, Cutler CS, Bhuiya NS, Schowalter M, et al. Altered B-cell homeostasis and excess BAFF in human chronic graft-versus-host disease. Blood. 2009; 113: 3865-74.
28.Cutler C, Kim HT, Bindra B, Sarantopoulos S, Ho VT, Chen YB, et al. Rituximab prophylaxis prevents corticosteroid-requiring chronic GVHD after allogeneic peripheral blood stem cell transplantation: results of a phase 2 trial. Blood. 2013; 122: 1510-7.
29.Srinivasan M, Flynn R, Price A, Ranger A, Browning JL, Taylor PA, et al. Donor B-cell alloantibody deposition and germinal center formation are required for the development of murine chronic GVHD and bronchiolitis obliterans. Blood. 2012; 119: 1570-80.
30.Dubovsky JA, Flynn R, Du J, Harrington BK, Zhong Y, Kaffenberger B, et al. Ibrutinib treatment ameliorates murine chronic graft-versus-host disease. J Clin Invest. 2014; 124: 4867-76.
31.Forcade E, Kim HT, Cutler C, Wang K, Alho AC, Nikiforow S, et al. Circulating T follicular helper cells with increased function during chronic graft-versus-host disease. Blood. 2016; 127: 2489-97.
32.Khoder A, Sarvaria A, Alsuliman A, Chew C, Sekine T, Cooper N, et al. Regulatory B cells are enriched within the IgM memory and transitional subsets in healthy donors but are deficient in chronic GVHD. Blood. 2014; 124: 2034-45.
33.Mehta RS, Holtan SG, Wang T, Hemmer MT, Spellman SR, Arora M, et al. Composite GRFS and CRFS outcomes after adult alternative donor HCT. J Clin Oncol. 2020; 38: 2062-76.
34.Sugita J, Atsuta Y, Nakamae H, Maruyama Y, Ishiyama K, Shiratori S, et al. Comparable survival outcomes with haploidentical stem cell transplantation and cord blood transplantation. Bone Marrow Transplant. 2022; 57: 1681-8.
35.Iwamoto M, Ikegawa S, Kondo T, Meguri Y, Nakamura M, Sando Y, et al. Post-transplantation cyclophosphamide restores early B-cell lymphogenesis that suppresses subsequent chronic graft-versus-host disease. Bone Marrow Transplant. 2021; 56: 956-9.
36.Hakim FT, Memon SA, Cepeda R, Jones EC, Chow CK, Kasten-Sportes C, et al. Age-dependent incidence, time course, and consequences of thymic renewal in adults. J Clin Invest. 2005; 115: 930-9.
37.Mackall CL, Fleisher TA, Brown MR, Andrich MP, Chen CC, Feuerstein IM, et al. Age, thymopoiesis, and CD4+ T-lymphocyte regeneration after intensive chemotherapy. N Engl J Med. 1995; 332: 143-9.
38.Ishaqi MK, Afzal S, Dupuis A, Doyle J, Gassas A. Early lymphocyte recovery post-allogeneic hematopoietic stem cell transplantation is associated with significant graft-versus-leukemia effect without increase in graft-versus-host disease in pediatric acute lymphoblastic leukemia. Bone Marrow Transplant. 2008; 41: 245-52.
39.Le Blanc K, Barrett AJ, Schaffer M, Hagglund H, Ljungman P, Ringden O, et al. Lymphocyte recovery is a major determinant of outcome after matched unrelated myeloablative transplantation for myelogenous malignancies. Biol Blood Marrow Transplant. 2009; 15: 1108-15.
40.Savani BN, Mielke S, Rezvani K, Montero A, Yong AS, Wish L, et al. Absolute lymphocyte count on day 30 is a surrogate for robust hematopoietic recovery and strongly predicts outcome after T cell-depleted allogeneic stem cell transplantation. Biol Blood Marrow Transplant. 2007; 13: 1216-23.
41.Toubert A, Glauzy S, Douay C, Clave E. Thymus and immune reconstitution after allogeneic hematopoietic stem cell transplantation in humans: never say never again. Tissue antigens. 2012; 79: 83-9.
42.Scordo M, Bhatt V, Hilden P, Smith M, Thoren K, Cho C, et al. Standard antithymocyte globulin dosing results in poorer outcomes in overexposed patients after ex vivo CD34(+) selected allogeneic hematopoietic cell transplantation. Biol Blood Marrow Transplant. 2019; 25: 1526-35.
43.Soiffer RJ, Kim HT, McGuirk J, Horwitz ME, Johnston L, Patnaik MM, et al. Prospective, Randomized, Double-Blind, Phase III Clinical Trial of anti-t-lymphocyte globulin to assess impact on chronic graft-versus-host disease-free survival in patients undergoing HLA-matched unrelated myeloablative hematopoietic cell transplantation. J Clin Oncol. 2017; 35: 4003-11.
44.Admiraal R, Nierkens S, Bierings MB, Bredius RGM, van Vliet I, Jiang Y, et al. Individualised dosing of anti-thymocyte globulin in paediatric unrelated allogeneic haematopoietic stem-cell transplantation (PARACHUTE): a single-arm, phase 2 clinical trial. Lancet Haematol. 2022; 9: e111-20.
45.Admiraal R, Nierkens S, de Witte MA, Petersen EJ, Fleurke GJ, Verrest L, et al. Association between anti-thymocyte globulin exposure and survival outcomes in adult unrelated haemopoietic cell transplantation: a multicentre, retrospective, pharmacodynamic cohort analysis. Lancet Haematol. 2017; 4: e183-91.
46.Admiraal R, van Kesteren C, Jol-van der Zijde CM, Lankester AC, Bierings MB, Egberts TC, et al. Association between anti-thymocyte globulin exposure and CD4+ immune reconstitution in paediatric haemopoietic cell transplantation: a multicentre, retrospective pharmacodynamic cohort analysis. Lancet Haematol. 2015; 2: e194-203.
47.Lakkaraja M, Scordo M, Mauguen A, Cho C, Devlin S, Ruiz JD, et al. Antithymocyte globulin exposure in CD34+ T-cell-depleted allogeneic hematopoietic cell transplantation. Blood Adv. 2022; 6: 1054-63.
48.Langenhorst JB, van Kesteren C, van Maarseveen EM, Dorlo TPC, Nierkens S, Lindemans CA, et al. Fludarabine exposure in the conditioning prior to allogeneic hematopoietic cell transplantation predicts outcomes. Blood Adv. 2019; 3: 2179-87.
49.Bertaina A, Abraham A, Bonfim C, Cohen S, Purtill D, Ruggeri A, et al. An ISCT Stem Cell Engineering Committee Position Statement on Immune Reconstitution: the importance of predictable and modifiable milestones of immune reconstitution to transplant outcomes. Cytotherapy. 2022; 24: 385-92.