We initiated a clinical trial of nonmyeloablative haploidentical stem-cell transplantation (SCT) using MEDI-507, an immunoglobulin-G1 monoclonal anti-CD2 antibody. The trial was based on a preclinical major histocompatibility complex-mismatched bone marrow transplant model in which graft-versus-host disease (GVHD) was prevented and mixed chimerism as a platform for adoptive cellular immunotherapy was reliably induced. Twelve patients (three cohorts of four patients each) received cyclophosphamide, MEDI-507, and haploidentical unmanipulated bone marrow (n=8) or ex vivo T-cell-depleted peripheral blood stem cells (n=4) for chemorefractory hematologic malignancy. A two-dose regimen and schedule modifications of MEDI-507 were undertaken because of graft loss in the first cohort of four patients and GVHD in the second cohort. With ex vivo T-cell-depleted peripheral blood SCT, mixed chimerism occurred in all four patients without GVHD. Two patients, however, subsequently lost their grafts. Nonmyeloablative preparative therapy with MEDI-507 and haploidentical SCT have led to the reliable induction of at least transient mixed chimerism as a potential platform for adoptive cellular immunotherapy.
The major barriers to successful haploidentical hematopoietic stem-cell transplantation (SCT) are graft-versus-host disease (GVHD) and related complications (1). A substantial preclinical experience has shown that sustained donor chimerism is achievable after nonmyeloablative conditioning and major histocompatibility complex (MHC)-mismatched SCT (2-4). In a murine model, mixed lymphohematopoietic chimerism is reliably achieved after a preparative regimen consisting of cyclophosphamide, vigorous in vivo T-cell depletion using monoclonal anti-CD4 and anti-CD8 antibodies, thymic irradiation, and MHC-mismatched SCT (3). These mixed chimeric mice are resistant to the induction of GVHD after delayed donor lymphocyte infusions (DLIs), despite a potent lymphohematopoietic graft-versus-host reaction that converts their mixed chimerism to full donor hematopoiesis and mediates potent graft-versus-leukemia effects (3,5).
By the use of this murine model, we demonstrated for the first time that sustained mixed (or full) donor hematopoiesis is achievable after a cyclophosphamide and antithymocyte globulin-based nonmyeloablative regimen and human leukocyte antigen-mismatched donor transplantation (6). All of the recipients who were evaluated developed acute GVHD or graft loss, however, indicating an insufficient in vivo depletion of donor or host T cells. Consequently, the regimen was modified to include MEDI-507, an immunoglobulin-G1 anti-CD2 humanized monoclonal antibody derived from a rodent parent antibody (BTI-322) (BioTransplant, Inc., Charlestown, MA) (7,8), to effect a greater and more sustained depletion of T cells.
Twelve patients with chemorefractory hematologic malignancies received MEDI-507 as a component of their nonmyeloablative preparative regimen for haploidentical SCT. According to the Food and Drug Administration guidelines and the Dana Farber Partners Cancer Care Institutional Review Board, cohorts of four patients were evaluated before proceeding with additional enrollment. Stopping rules (requiring revision of the protocol) consisted of more than one instance of graft failure or grade III and IV GVHD or transplant-related mortality in each group of four patients. Details regarding the conditioning regimen used in this study have been published (9). Peripheral blood chimerism was measured weekly by either flow cytometry or analyses of microsatellite variable numbers of tandem repeats. On the basis of pharmacokinetic data, the first four patients received a MEDI-507 test dose of 0.1 mg/kg on day -2 followed by therapeutic doses of 0.6 mg/kg on days -1, 0, and +1. Cyclophosphamide was administered at a dose of 50 mg/kg on days -5, -4, and -3. Thymic irradiation (700 cGy) was delivered on day -1 to patients (n=10) who had not received previous mediastinal radiation therapy. Cyclosporine was begun on day -1, and then in the absence of GVHD, it was tapered and discontinued by approximately day +35 posttransplant. Patients with mixed chimerism and no evidence of GVHD were eligible to receive a prophylactic DLI, intended to convert their mixed chimerism to full donor hematopoiesis, or a therapeutic DLI could be given for disease recurrence or progression.
Characteristics of the first cohort of four patients and their outcomes are shown in Table 1. The experience in the first four patients was remarkable for the lack of acute toxicity from MEDI-507. A profound in vivo T-cell depletion occurred, lasting more than 2 months in all patients (Table 1). No patient developed acute GVHD. Two patients, however, developed a prominent engraftment syndrome with pulmonary edema, and one patient developed diffuse alveolar hemorrhage (10). Therapy with high-dose corticosteroids followed by taper and discontinuation over 3 to 7 weeks resulted in the resolution of the pulmonary manifestations of engraftment syndrome in both cases. Because both patients subsequently lost their grafts, these early pulmonary complications may have resulted from an interaction between donor and host T cells (as a result of a host-versus-graft alloresponse). Early multilineage mixed-lymphohematopoietic chimerism was observed in all four patients. However, this was followed by complete loss of donor hematopoiesis in all patients between days +14 and +75 posttransplant, despite DLIs given to two patients for conversion of chimerism and to two patients for disease progression (Table 1).
The second cohort of four patients (Table 2) received MEDI-507 according to a revised dose and schedule. The test dose of MEDI-507 was administered on day -7, followed by doses of 0.6 mg/kg on each of days -6 and -5. This change in the dose and timing of MEDI-507 administration was intended to provide a more prolonged exposure of host T cells to the antibody, hopefully lessening the problem of graft loss. The earlier time of administration and lower dose of MEDI-507 were also intended to allow for clearance of the antibody (before the intended day of the first DLI). One patient experienced transient chest pain and shortness of breath during the infusion of the test dose on day -7. The following two treatment doses were given without incident. One of the four patients treated with this regimen died on day +14 posttransplant as the result of multiorgan failure and was not evaluated for engraftment or GVHD. One patient developed grade IV GVHD and died on transplant day +110 as the result of posttransplant lymphoproliferative disease. One patient developed grade II acute GVHD and then extensive chronic GVHD, but he maintained an excellent performance status until his sudden death of an unexplained cause on day +456 posttransplant. The third patient evaluated developed transient mixed chimerism followed by graft loss on day +41 posttransplant (despite a prophylactic DLI of 3.0×107 CD3+ T cells given on day +151). Pharmacokinetic and flow cytometric analyses demonstrated that MEDI-507 levels were cleared faster and that T-cell recovery was more rapid (Table 2) in this second cohort compared with the first four recipients of MEDI-507. Two of the three patients evaluated showed levels below 100 ng/mL on day +35, and all patients showed levels below that by day +63 posttransplant.
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On the basis of the sustained engraftment in two of the three patients evaluated in this second cohort of MEDI-507 treatment, albeit with GVHD, the protocol was modified to include ex vivo T-cell depletion of granulocyte colony-stimulating factor mobilized peripheral blood stem cells (PBSC), using an Isolex (Baxter Oncology Deerfield, IL) CD34+ cell-selection device. This was undertaken in an effort to prevent GVHD (by the T-cell depletion of the PBSC product and in vivo donor T-cell depletion with MEDI-507) and to enhance the probability of sustained engraftment (by in vivo host T-cell depletion with MEDI-507 and the infusion of increased numbers of CD34+ progenitor cells with the PBSC product). Four patients with chemorefractory diffuse large B-cell lymphoma were treated with this revised regimen. MEDI-507 dosing was the same as in the second cohort of patients. The median number (range) of infused CD34+ and CD3+ cells was 10.6 (5.0-14.9) × 106/kg and 8.9 (6.7-16.0) × 104/kg, respectively. One patient experienced transient chest pain and shortness of breath with wheezing during infusion of the test dose on day -7. The following two treatment doses were given without complication. The first of four patients developed transient mixed chimerism in the absence of GVHD followed by graft loss on day +77 posttransplant. He has had an ongoing antitumor response despite the lack of detectable donor chimerism after three subsequent prophylactic DLIs and is presently progression-free 1 year posttransplant. The second patient developed split lineage chimerism with a predominance of donor myeloid cells and host T cells. After a DLI of 5×106/kg CD3+ T cells on day +66, her T-cell chimerism converted to full donor chimerism in the absence of GVHD. A third patient developed a pattern of split lineage chimerism similar to that in the second patient. Because of early disease progression, he received a higher dose of DLI (2.5×107/kg CD3+ T cells) on day +51, which resulted in an increase in donor T cells accompanied by skin-limited grade II GVHD, which responded promptly to corticosteroid therapy. The fourth patient also developed predominantly donor myeloid (but host T-cell) chimerism. Serial chimerism studies showed a progressive loss of donor chimerism. After recovery of host hematopoiesis, she experienced progression of her lymphoma. A DLI was given on day +96 posttransplant, but a subsequent chimerism analysis showed no evidence of donor hematopoiesis.
To duplicate the conditions demonstrated in the successful murine model of nonmyeloablative MHC-mismatched SCT in which DLI mediated graft-versus-leukemia without GVHD occurs (5), a GVH-free state of mixed chimerism as an immunologic platform for DLI is believed to be essential. This requires a vigorous depletion of both donor and host T cells until at least the time of DLI administration. In the first two cohorts of MEDI-507-treated patients, graft failure or GVHD was observed in all patients. With vigorous ex vivo T-cell depletion (to deplete donor T cells and prevent GVHD from the SCT) and administration of MEDI-507 in vivo (to deplete host T cells and the remaining T cells that may be infused with the stem-cell product), such a GVH-free state of mixed chimerism is achievable. DLI can be given in this situation with the conversion of T-cell chimerism and manageable (or absent) GVHD. To effect a more durable engraftment, additional strategies are being considered, including the addition of fludarabine to the preparative regimen.
MEDI-507 is a well-tolerated component of a nonmyeloablative preparative regimen for haploidentical SCT. At least transient lymphohematopoietic chimerism has occurred in all patients with this regimen, and GVHD has been prevented in most. Ex vivo T-cell depletion of the stem-cell product may be important in preventing GVHD and creating the mixed chimeric platform necessary for successful adoptive cellular immunotherapy (by DLI). Durable progression-free survival was observed in two patients with chemorefractory hematologic malignancies despite graft loss. Although an antitumor effect of the high-dose cyclophosphamide cannot be discounted, it is highly unlikely that a sustained remission would have resulted from chemotherapy alone, given the chemorefractory nature of the patients' tumors. These observations, therefore, indicate that either a transient graft-versus-malignancy effect occurred with initial chimerism or a host T-cell-mediated antitumor response was induced. The optimal strategy for increasing the possibility of a durable antitumor response remains to be determined.