Lisa Cook

Differences in the Phenotype, Cytokine Gene Expression Profiles, and In Vivo Alloreactivity of T Cells Mobilized with Plerixafor Compared with G-CSF

Plerixafor (Mozobil) is a CXCR4 antagonist that rapidly mobilizes CD34+ cells into circulation. Recently, plerixafor has been used as a single agent to mobilize peripheral blood stem cells for allogeneic hematopoietic cell transplantation. Although G-CSF mobilization is known to alter the phenotype and cytokine polarization of transplanted T cells, the effects of plerixafor mobilization on T cells have not been well characterized. In this study, we show that alterations in the T cell phenotype and cytokine gene expression profiles characteristic of G-CSF mobilization do not occur after mobilization with plerixafor. Compared with nonmobilized T cells, plerixafor-mobilized T cells had similar phenotype, mixed lymphocyte reactivity, and Foxp3 gene expression levels in CD4+ T cells, and did not undergo a change in expression levels of 84 genes associated with Th1/Th2/Th3 pathways. In contrast with plerixafor, G-CSF mobilization decreased CD62L expression on both CD4 and CD8+ T cells and altered expression levels of 16 cytokine-associated genes in CD3+ T cells. To assess the clinical relevance of these findings, we explored a murine model of graft-versus-host disease in which transplant recipients received plerixafor or G-CSF mobilized allograft from MHC-matched, minor histocompatibility–mismatched donors; recipients of plerixafor mobilized peripheral blood stem cells had a significantly higher incidence of skin graft-versus-host disease compared with mice receiving G-CSF mobilized transplants (100 versus 50%, respectively, p = 0.02). These preclinical data show plerixafor, in contrast with G-CSF, does not alter the phenotype and cytokine polarization of T cells, which raises the possibility that T cell–mediated immune sequelae of allogeneic transplantation in humans may differ when donor allografts are mobilized with plerixafor compared with G-CSF.

A pilot study evaluating the safety and CD34+ cell mobilizing activity of escalating doses of plerixafor in healthy volunteers

This study evaluated the safety and CD34+ cell mobilizing activity of escalating doses of plerixafor in healthy volunteers. Three cohorts of six subjects received two different doses of plerixafor separated by at least 2 weeks to allow for adequate pharmacodynamic wash‐out. The following dosing cohorts were evaluated: 0·24 and 0·32 mg/kg (Cohort 1); 0·32 and 0·40 mg/kg (Cohort 2); and 0·40 and 0·48 mg/kg (Cohort 3). Circulating CD34+ cells were measured 0, 2, 4, 6, 8, 10, 12, 14, 18 and 24 h after each dose. Blood colony‐forming units were measured at baseline and 6 h after each dose. Common adverse events were diarrhoea, injection site erythema, perioral numbness, sinus tachycardia, headache, nausea, abdominal distention and injection site pain. No dose limiting toxicities occurred. When higher doses of plerixafor were administered, there was a trend towards higher peak CD34+ counts and CD34+ area under the curves, although these differences did not achieve statistical significance, perhaps due to intra‐subject variability. Together, these data show that the higher doses of plerixafor evaluated in this study are reasonably safe and suggest that a larger study should be performed to definitively answer whether increased numbers of CD34+ cell are mobilized with higher doses of plerixafor.

Effect of high-dose plerixafor on CD34+ cell mobilization in healthy stem cell donors: results of a randomized crossover trial

Hematopoietic stem cells can be mobilized from healthy donors using single-agent plerixafor without granulocyte colony-stimulating factor and, following allogeneic transplantation, can result in sustained donor-derived hematopoiesis. However, when a single dose of plerixafor is administered at a conventional 240 μg/kg dose, approximately one-third of donors will fail to mobilize the minimally acceptable dose of CD34+ cells needed for allogeneic transplantation. We conducted an open-label, randomized trial to assess the safety and activity of high-dose (480 μg/kg) plerixafor in CD34+ cell mobilization in healthy donors. Subjects were randomly assigned to receive either a high dose or a conventional dose (240 μg/kg) of plerixafor, given as a single subcutaneous injection, in a two-sequence, two-period, crossover design. Each treatment period was separated by a 2-week minimum washout period. The primary endpoint was the peak CD34+ count in the blood, with secondary endpoints of CD34+ cell area under the curve (AUC), CD34+ count at 24 hours, and time to peak CD34+ following the administration of plerixafor. We randomized 23 subjects to the two treatment sequences and 20 subjects received both doses of plerixafor. Peak CD34+ count in the blood was significantly increased (mean 32.2 versus 27.8 cells/μL, P=0.0009) and CD34+ cell AUC over 24 hours was significantly increased (mean 553 versus 446 h cells/μL, P<0.0001) following the administration of the 480 μg/kg dose of plerixafor compared with the 240 μg/kg dose. Remarkably, of seven subjects who mobilized poorly (peak CD34+ ≤20 cells/μL) after the 240 μg/kg dose of plerixafor, six achieved higher peak CD34+ cell numbers and all achieved higher CD34+ AUC over 24 hours after the 480 μg/kg dose. No grade 3 or worse drug-related adverse events were observed. This study establishes that high-dose plerixafor can be safely administered in healthy donors and mobilizes greater numbers of CD34+ cells than conventional-dose plerixafor, which may improve CD34+ graft yields and reduce the number of apheresis procedures needed to collect sufficient stem cells for allogeneic transplantation. (ClinicalTrials.gov, identifier: NCT00322127)

Conditioning with rabbit versus horse ATG dramatically alters clinical outcomes in identical twins with severe aplastic anemia transplanted with the same allogeneic donor

Severe aplastic anemia (SAA) is a rare disorder leading to bone marrow failure, which if left untreated, is invariably fatal. Conventional therapies with immunosuppressive therapy or allogeneic hematopoietic stem cell transplantation (HSCT) are highly effective. HSCT can offer a greater outcome in younger patients who have an available HLA match-related donor. Recent studies showing the addition of antithymocyte globulin (ATG) to the conditioning regimen improves engraftment and reduces the risk of graft-versus-host disease (GVHD).There are currently two ATG preparations in the USA, equine (or horse) and rabbit ATG. These agents are pharmacologically distinct, having significant differences in their pharmacokinetics and in vivo immunosuppressive effects [N Engl J Med 365(5):430–438, 2011]. Here, we report a case of two monozygotic twins with constitutional SAA that evolved to myelodysplastic syndrome (MDS) who both underwent allogeneic peripheral blood stem cell transplantation (PBSC) from the same single HLA antigen mismatched sibling donor with the only difference in the transplant regimen being the type of ATG used in the preparative regimen; one twin received horse ATG and the other received rabbit ATG during conditioning. This report emphasizes that dramatic differences in donor T cell chimerism and clinical outcomes including GVHD can occur as a consequence of the type of ATG that is utilized in the transplant conditioning regimen. These differences highlight that these agents should not be considered interchangeable drugs when used in this setting.

Rapid donor T-cell engraftment increases the risk of chronic graft-versus-host disease following salvage allogeneic peripheral blood hematopoietic cell transplantation for bone marrow failure syndromes

The risk of graft‐rejection after allogeneic hematopoietic cell transplantation using conventional cyclophosphamide‐based conditioning is increased in patients with bone marrow failure syndromes (BMFS) who are heavily transfused and often HLA‐alloimmunized. Fifty‐six patients with BMFS underwent fludarabine‐based reduced‐intensity conditioning and allogeneic peripheral blood progenitor cell (PBPC) transplantation at a single institution. The conditioning regimen consisted of intravenous cyclophosphamide, fludarabine, and equine antithymocyte globulin. Graft‐versus‐host disease (GVHD) prophylaxis included cyclosporine A alone or in combination with either mycophenolate mofetil or methotrexate. To reduce the risk of graft‐rejection/failure, unmanipulated G‐CSF mobilized PBPCs obtained from an HLA‐identical or single HLA‐antigen mismatched relative were transplanted rather than donor bone marrow. Despite a high prevalence of pretransplant HLA‐alloimmunization (41%) and a heavy prior transfusion burden, graft‐failure did not occur with all patients having sustained donor lympho‐hematopoietic engraftment. The cumulative incidence of grade II–IV acute‐GVHD and chronic‐GVHD was 51.8% and 72%, respectively; with 87.1% surviving at a median follow‐up of 4.5 years. A multivariate analysis showed pretransplant alloimmunization and rapid donor T‐cell engraftment (≥95% donor by day 30) were both significantly (P < 0.05) associated with the development of chronic‐GVHD (adjusted HR 2.13 and 2.99, respectively). These data show fludarabine‐based PBPC transplantation overcomes the risk of graft‐failure in patients with BMFS, although rapid donor T‐cell engraftment associated with this approach appears to increase the risk of chronic‐GVHD. (Clinicaltrials.gov identifier: NCT00003838). Am. J. Hematol. 88:874–882, 2013.

Durable remission of mantle cell lymphoma relapsing a third time after allogeneic hematopoietic stem cell transplantation treated with rituximab, bortezomib, donor lymphocytes, and pegylated interferon.

Although there has been noteworthy progress in the treatment of mantle cell lymphoma (MCL) over the past decade,1 disease relapse after dose-intensive chemotherapy or autologous stem cell transplantation remains problematic.2-4 Allogeneic hematopoietic stem cell transplantation (allo-HCT) is capable of curing patients with relapsed MCL, including those with disease progression after autologous stem cell transplantation.3 Disease remission after allo-HCT is attributable to the cytoreductive effects of dose-intensive conditioning and to donor T-cellemediated graft-versus-tumor effects.3-8 Even when patients relapse after an allo-HCT, donor lymphocyte infusions (DLIs) leading to graft-versus-MCL effects can still induce long-term disease remission in a subset of patients. However, for patients relapsing after DLI, long-term disease control is rare because tumors frequently develop mechanisms to evade donor immunity. We report a patient with MCL with multiple relapses after reduced-intensity conditioning (RIC) allo-HCT and DLIs who achieved a fourth disease remission that is ongoing more than 3 years after the last relapse after treatment with a combination of rituximab/bortezomib, pegylated interferon (PEG-IFN), and a ninth DLI. This case suggests that graft-versus-tumor (GVT) effects can still be bolstered years after an allogeneic transplant, even in patients who have relapsed multiple times, by DLIs whose efficacy may be enhanced by combination with interferon (IFN)-based cytokine treatment.