Background Antithymocyte globulin (ATG) has been increasingly used to prevent graft-vs-host disease (GVHD), however, its impact on immune reconstitution is relatively unknown. Here we studied (1) immune reconstitution after ATG-conditioned hematopoietic cell transplantation (HCT), (2) determined factors influencing the reconstitution, and (3) compared it to non-ATG-conditioned HCT. Methods Immune cell subset counts were determined at 1–24 months posttransplant in 125 HCT recipients who received ATG during conditioning. The subset counts were also determined in 46 non-ATG-conditioned patients (similarly treated). Results (1) Reconstitution after ATG-conditioned HCT was fast for innate immune cells, intermediate for B cells and CD8 T cells, and very slow for CD4 T cells and invariant NKT (iNKT) cells. (2) Faster reconstitution after ATG-conditioned HCT was associated with higher number of cells of the same subset transferred with the graft in case of memory B cells, naïve CD4 T cells, naïve CD8 T cells, iNKT cells and myeloid dendritic cells; lower recipient age in case of naïve CD4 T cells and naïve CD8 T cells; cytomegalovirus recipient seropositivity in case of memory/effector T cells; absence of GVHD in case of naïve B cells; lower ATG serum levels in case of most T cell subsets including iNKT cells, and higher ATG levels in case of NK cells and B cells. (3) Compared to non-ATG-conditioned HCT, reconstitution after ATG-conditioned HCT was slower for CD4 T cells, and faster for NK cells and B cells. Conclusions ATG worsens reconstitution of CD4 T cells but improves reconstitution of NK and B cells.

Uncontrolled studies have suggested that bone marrow-derived mesenchymal stem cells (MSCs) may be effective against acute graft-versus-host disease (aGVHD). We conducted a multicenter, randomized study to assess the efficacy of using ex vivo cultured adult human MSC (remestemcel-L) in addition to second-line therapy to treat steroid-refractory aGVHD (NCT00366145). In total, 260 patients, 6 months to 70 years of age, were enrolled from August 2006 to May 2009 and were randomized 2:1 to receive 8 intravenous infusions of remestemcel-L or placebo, given over 4 weeks, in addition to second-line therapy according to institutional standards. Four additional infusions over 4 weeks were indicated for patients with incomplete response at day 28. Randomization was stratified by aGVHD grade. Efficacy and safety were assessed through 180 days of follow-up, with the primary endpoint being durable complete response (DCR), defined as complete resolution of aGVHD symptoms for any period of at least 28 days after beginning treatment. Remestemcel-L did not meet the primary endpoint of greater DCR in the intent-to-treat population (35% versus 30%; P = 0.42). In post hoc analyses, patients with liver involvement who received at least 1 infusion of remestemcel-L had a higher DCR, and higher overall complete or partial response rate (OR) than those who received placebo (29% versus 5%; P = .047). Among high-risk patients (aGVHD grades C and D), remestemcel-L demonstrated significantly higher OR at day 28 than placebo (58% versus 37%; P = 0.03). Furthermore, pediatric patients had a higher OR with MSCs compared with placebo (64% versus 23%; P = .05). Similar rates of adverse events were observed between treatment groups. Remestemcel-L was safe and well tolerated. Results of this study did not demonstrate superior DCR compared with placebo when added to standard of care. The favorable clinical responses seen in some patient subsets may warrant further investigation.

CD127 expression on CD8 + T cells, consistent with their rapid clonal expansion and differentiation. Multiplexed Luminex cytokine analysis demonstrated high-level secretion of IL-18 and IL-1RA, with no increased secretion of TNF, IL-1b or IL-17 despite severe GvHD.The four treated recipients demonstrated rapid donor engraftment, but, unlike the controls, they were significantly protected against clinical and immunologic GvHD: They displayed neither the skin rash nor the profuse diarrhea noted in the control animals, and flow cytometric analysis demonstrated control of T cell proliferation, maintenance of CD127 expression levels, and inhibition of IL-18 and IL-1RA cytokine secretion. Conclusions: We have established a robust model of MHC haploidentical HSCT and GvHD using an MHC-defined Rhesus macaque colony. We find that unprotected primate GvHD is characterized by rapid T cell proliferation, with concomitant loss of expression of CD127 on CD8 + T cells. In addition, it is associated with high level secretion of IL-18 and IL-1RA. Finally, we find that CD28/CD40-directed costimulation blockade in combination with sirolimus can effectively inhibit the clinical, cellular and serum hallmarks of GvHD during primate haploidentical BMT. This approach thus may deserve close scrutiny as a possible clinical strategy for GvHD prevention. . Dose-level-C accrual is ongoing. Concurrent immunosuppression was allowed.11 patients accrued; 7 and 4 at dose-levels-A and -B. Median age was 44 years (30-57). Median time from HSCT and cGVHD was 1021 (420-4714) and 784 (117-2233) days. cGVHD sites were skin (11 pts), mouth (6 pts), eyes (4 pts), liver (3 pts), lung (2 pts), esophagus (1 pt). Patients had a median of 3 (range, 1-3) concurrent immunosuppressives: steroids (11 pts), sirolimus (5 pts), MMF (5 pts), tacrolimus (4 pts). Discontinued prior therapies were rituximab (6 pts), ECP (4 pts), MMF (2 pts), sirolimus (2 pts), cyclosporine (1 pt), thalidomide (1 pt), denileukin-diftitox (1 pt), alemtuzumab (1 pt).No dose-limiting toxicity (DLT) GVHD flare occurred. One patient (lvl-A) had CTC grade-4 hemolytic-uremic-syndrome after Hemophilus-B bacteremia at 5 weeks of IL-2 (and prednisone, tacrolimus, sirolimus), reported as a DLT. No other DLT occurred. Another patient (lvl-A) had CTC grade-4 MRSA pneumonia at 8 weeks, unrelated to IL-2 (on prednisone, sirolimus, MMF; also had MRSA pneumonia pre-IL-2). No other significant infection was documented. One patient (lvl-B) discontinued IL-2 at 4 days for CTC grade-1 fatigue.Of 9 evaluable patients, 5 had a partial response, 1 had a mixed response, and 3 had stable disease. Responses were scored in skin and liver (mouth, eye received topical therapy). 4 of 5 responders chose extended IL-2 (range, 1.5-15 months) given clinical benefit. The 5 th , with resolving liver cGVHD, had IL-2 withheld for MRSA pneumonia. He died of progressive liver cGVHD off IL-2.IL-2 induced a 3-5-fold increase in CD4 + CD25 + CD127-Tregs (Table). At 1, 2, 4, 6 and 8 weeks, IL-2 increased Treg significantly over ba...

Summary:A syndrome of microangiopathic hemolytic anemia, renal dysfunction and neurological abnormalities was first noted in bone marrow transplant recipients 22 years ago. Now known as transplantation-associated thrombotic microangiopathy (TA-TMA) to distinguish it from other thrombotic microangiopathies, this disorder responds poorly to conventional treatments for thrombotic thrombocytopenic purpura. In this review, we discuss the incidence and risk factors for TA-TMA and describe a pathophysiologic model of the disorder based on results obtained from laboratory models of the thrombotic microangiopathies. We conclude by suggesting possible approaches to the early diagnosis and treatment of TA-TMA based on this model that may warrant testing in future clinical trials.