Rapid hematopoietic engraftment following fractionated TBI conditioning and transplantation with CD34(+) enriched hematopoietic progenitor cells from partially mismatched related donors

Heterogeneous Clearance of Antithymocyte Globulin after CD34+-Selected Allogeneic Hematopoietic Progenitor Cell Transplantation

Antithymocyte globulins (ATG) are purified, concentrated preparations of polyclonal immunoglobulin G from hyperimmune serum of horses or rabbits immunized with human thymus lymphocytes. Both the horse and the rabbit products induce immunosuppression as a result of lymphocyte depletion and immune modulation. The exact mechanism of action is unknown but may include T-cell clearance from the circulation and modulation of T-cell activation, homing, and cytotoxic activities. Both horse and rabbit ATG include multiple antibodies against T-cell surface antigens and have been used extensively in allogeneic hematopoietic progenitor cell transplantation (HPCT) for the treatment and prevention of graft-versus-host disease or graft rejection. To quantify the active ATG after HPCT, we developed a flow-based assay to measure residual ATG capable of binding to lymphocytes. In contrast to prior assays that measure total rabbit or horse immunoglobulin, this assay quantitates only the antibody capable of binding to lymphocytes, which presumably reflects the functionally active fraction of the xenoantiserum. Thirty patients with hematologic malignancies underwent T cell-depleted HPCT and had ATG levels assayed during the peritransplantation period. The time required for ATG levels to decay to background was quite variable (mean, 46 days; range, 14-91 days), although most patients demonstrated a rapid early clearance followed by a slower decline. The actual mean half-life was 6.8 days (range, 2.4-14.0 days). The persistence of ATG for months after administration has significant implications for the pace of immune reconstitution after transplantation and is a potentially confounding variable in any study that involves early administration of donor lymphocyte infusions or other cellular transfer. These findings indicate that ATG levels should be explicitly measured in studies that involve early donor lymphocyte administration so that proper conclusions regarding dose, safety, and efficacy can be reached.

Canadian multicenter pilot trial of haploidentical donor transplantation

BACKGROUND

Canadian multicenter pilot study of haploidentical donor.

AIMS

To assess (1) ability to collect suitable graft (CD34+ > or = 5 x 10(6)/kg and CD3 < 1 x 10(5)/kg recipient body weight), (2) toxicity, (3) survival to day +100. ELIGIBILITY: All hematological malignancies and ages; accrual to end after 20 transplants of patients with AML in remission and age less than 55 years.

METHODS

Preparation: Modified Perugia regimen, chemotherapy alone; melphalan 140 mg/m2 day -9, thiotepa 10 mg/kg day -7, fludarabine 40 mg/m2 days -7 to -3, and ATG (Thymoglobulin, Sangstat) days -6 to -2 (total 10.5 mg/kg). Infection prophylaxis: Ganciclovir (GC) 5 mg/kg days 5-20 then x5/week until day +100 then x3/week until 210 (subjects 1-3), foscarnet (FC) 90 mg/kg days 4-21 then short course pre-emptive GC or FC (subjects 4-11); fluconazole; cotrimoxazole. Donors: G-CSF 16 microg/kg daily x5 until second pheresis day. T-cell depletion: CliniMACS (MiltenyiBiotec).

RESULTS

Eleven patients with AML have been transplanted from four centers, eight female, three male, median age 34 (range 19-60). Disease status, first CR 1/11, second CR 4/11, third CR1/11, relapse 5/11. Graft CD34+ > or = 5 x 10(6)/kg was achieved in all cases, median 13.72 x 10(6)/kg (Q1, Q3: 8.26, 17.72; min 5.59, max 22.22), and CD3+ was < 1 x 10(5)/kg in all cases, median of 0.49 x 10(4)/kg (Q1, Q3: 0.30, 2.20; min 0.22, max 4.10). Ten of the 11 patients have died, median survival 103.5 days (Q1, Q3: 61.0, 151.0; min 0, max 290.0). Survival to day +100 6/11 (55%). Four patients died of leukemic relapse, six of infection. Of six patients dying of infection, CMV was a definite cause in four. Of four dying with relapse, CMV was significant in one. Engraftment was assessed in 10 patients who survived >0 days. Granulocyte engraftment (> 0.5 x 10(9)/l) was achieved in all patients, median 11.5 days (Q1, Q3: 10, 17; min 8, max 70). Platelet engraftment (> 20 x 10(9)/l) was achieved in 8 of 10 patients, median 15 days (Q1, Q3: 9, 16; min 9, max 97). The two platelet non-engrafters died on days +45 and +61. Toxicity was low, with one toxic death (day 0), and the Bearman organ toxicity gradings were < or = grade 2 in all other patients. There were no instances of graft-vs.-host disease or graft rejection.

CONCLUSIONS

The problems of graft-vs.-host disease and graft rejection have been removed as barriers to haploidentical transplantation but the slow immune reconstitution limits its general application. Late referrals contribute to a high relapse rate and have delayed an optimal evaluation of the procedure.

Facilitating T-cell immune reconstitution after haploidentical transplantation in adults

Delayed reconstitution of cellular immunity following T-cell-depleted, CD34-enriched, allogeneic hematopoietic progenitor cell transplantation (HPCT) is the major cause of morbidity and mortality following haploidentical transplantation in adults. This is illustrated in our recent study of 28 high-risk adult patients (median age 31) who were treated with conditioning regimens containing antithymocyte globulin (ATG) before T-cell-depleted, CD34-enriched allogeneic HPCT. Overall mortality was 93% (26/28 patients) with a median survival of 4 months posttransplant. Poor cellular immune reconstitution contributed to death of 21/28 patients, with eight deaths due to opportunistic infections and seven deaths due to relapse. While recovery of normal numbers of circulating NK cells and B-cells occurred within the first 1-2 months posttransplant, recovery of normal numbers of blood T-cells was suppressed for more than 1 year. The mean half-life of active ATG levels in serum was 6 days; rapid clearance suggested that residual ATG did not contribute to the delay of posttransplant T-cell reconstitution. Rapid T-cell reconstitution was seen only in younger patients, indicating that poor thymic function and the absence of T-cells in the graft are the major causes of delayed recovery of cellular immunity. Improved cellular immunity after T-cell-depleted haploidentical HPCT will thus require novel strategies to adoptively transfer antigen specific donor T-cells without inducing lethal graft-versus-host disease (GvHD). This problem has been addressed in a preclinical murine model of MHC-mismatched bone marrow transplantation. Donor T-cells treated ex vivo with fludarabine or a UVA light-activated psoralen compound (amotosalen) have a markedly reduced ability to induce GvHD, yet the treated T-cells confer protection against murine cytomegalovirus and an infused leukemic cell line. Polyclonal donor T-cells reconstituted the blood and lymphoid compartments posttransplant and expanded in vivo. Derivatives of ex-vivo-treated donor T-cells retained the ability to produce cytokines and proliferate in response to antigen challenge. The mechanism of reduced GvHD potential of ex-vivo-treated T-cells appears to be selection of a subset of memory donor T-cells that do not initially home to secondary lymphoid organs and have reduced capacity for producing inflammation in the immediate posttransplant period. Direct selection of the memory subset by high-speed FACS confirmed the improved therapeutic index in the murine model system. Preclinical data indicate the feasibility of treating human T-cells with fludarabine, psoralen, or direct selection based upon the memory phenotype to efficiently produce a population of polyclonal donor T-cells with reduced GvHD activity. A planned clinical phase 1 trial of adoptive therapy utilizing ex vivo psoralen-treated donor T-cells in recipients of T-cell-depleted haploidentical HPCT is presented.

Haploidentical transplantation for acute lymphoblastic leukemia in childhood

Haploidentical transplantation in childhood acute lymphoblastic leukemia (ALL) is a promising option for children lacking a suitable donor. We have updated our series of patients with ALL and report the results. Additionally, we reviewed the literature and try to embed our own experiences in the published results. We performed HLA-mismatched stem cell transplantations with megadoses of purified positively selected mobilized peripheral blood CD34+ progenitor cells (PBPC) from adult donors in 27 children with acute lymphoblastic leukemia (ALL) in first (CR1 n = 7), second (CR2 n = 10), or third (CR3 n = 4) complete remission, and in refractory state (NR n = 6). The patients received a mean number of 19.1+/-11.3 x 10(6)/kg purified CD34+ and a mean number of 15.5+/-24.2 x 10(3)/kg CD3+ T-cells. No additional graft-versus-host disease (GVHD) prophylaxis was used, except as short-term CSA in the first 3 patients. The myeloablative treatment was based on busulfan in 12 and on TBI in 14 patients. One patient was grafted with a non-myeloablative approach. Engraftment was rapid in 26 patients, with two patients suffering from a rejection. These two and one patient with initial non-engraftment had been successfully regrafted. The probability of survival of the total group is 0.34+/-0.09; the 12 patients transplanted in remission showed a probability of survival of 0.44+/-0.11. None of the patients transplanted in non-remission survived. There was no statistical difference in survival for patients with a 1, 2 or 3 antigen mismatched donor (out of 6 HLA antigens) or for patients in 1st, 2nd or 3rd remission. Causes of death were relapses in 10 patients, veno-occlusive disease (VOD) in 1, multi-organ failure (MOF) in 2 and infections in 4 patients. 3/24 evaluable patients without any additional GVHD-prophylaxis developed grade 1 or 2 GVHD. Ten patients were treated with additional donor lymphocyte infusion (DLI), from which 4 developed a maximum grade 3 GVHD. We conclude that the HLA barrier can be overcome by transplantation of megadoses of highly purified CD34+ PBPC and GVHD can effectively be prevented. This approach offers a promising treatment option for patients with acute lymphoblastic leukemia needing urgently transplantation but lacking a suitable donor.

Cellular immunotherapy and cancer

Recent data indicate that cellular immune responses can produce an anticancer effect. Two types of cellular immune responses appear to be clinically relevant: antigen specific immunity mediated by T cells that recognize tumor-associated peptide antigen expressed on surface HLA class I or class II molecules, and antigen nonspecific immune responses mediated by natural killer (NK) cells that are activated by the failure to recognize cognate "self" HLA class I molecules. The graft-versus-tumor effect of allogeneic transplants using HLA-matched donors is mediated by antigen-specific T cells, while allogeneic transplantation using HLA mismatched donors can also lead to donor NK cells with potent antitumor activity. HLA mismatched haplo-identical transplants can exert a powerful antileukemia effect based on expansion of antigen nonspecific donor NK cells, but slow recovery of donor T cells is associated with a profound immune deficiency and increased opportunistic infections that limit the overall clinical success of this type of transplant maneuver. The focus for most immunologic maneuvers designed to enhance the graft-versus-tumor effect has been on strategies to expand or enhance the activity of antigen-specific donor T cells that recognize host tumor cells. In the case of hematologic malignancies, the activity of donor T cells against tumor cells is regulated by dendritic cells, which can augment or inhibit cellular immune responses. Future successes in enhancing the patients' own cellular immune responses to cancer will likely be based on activation of T cells by the appropriate dendritic cell subset and, in the case of tumors that have down-regulated HLA class I expression, by activated NK cells.

Allogeneic peripheral blood stem cell transplantation from two- or three-loci-mismatched related donors in adult Japanese patients with high-risk hematologic malignancies

With the increasing frequency of haploidentical transplantation, it is becoming more important to establish the degree of HLA mismatch that can be accepted. We retrospectively analyzed clinical data of 50 adult Japanese patients with high-risk hematologic malignancies who underwent allogeneic peripheral blood stem cell transplantation (PBSCT) from two- or three-loci-mismatched related donors with HLA class I and II gene disparities in the graft-versus-host direction. They were treated at 20 transplant centers between 1996 and 2002. In all, 18 patients received unmanipulated PBSC, while 32 received purified CD34+ blood cells. Conventional (n=31) or reduced-intensity (n=19) conditioning regimens were used. Of the 39 patients (78%) who survived for > or =28 days after transplant, 37 (95%) achieved neutrophil engraftment, while graft failure and rejection occurred in two of 39 (5%) and three of 37 (8%) patients, respectively. Stepwise Cox regression analysis revealed a significantly lower incidence of grades II-IV acute GVHD in patients receiving purified CD34+ cells (hazard ratio 0.32; 95% CI 0.12-0.84; P=0.022). By 1 year post transplant, 28 patients (56%) had died of transplant-related problems, including infectious complications (30%). Although the number of patients is small, our data suggest that transplant-related problems, particularly infectious complications, are major obstacles to the success of this therapy.

Pharmacokinetics and pharmacodynamics of anti-thymocyte globulin in recipients of partially HLA-matched blood hematopoietic progenitor cell transplantation

Polyclonal anti-thymocyte globulin (ATG) administered before allogeneic blood hematopoietic progenitor cell transplantation reduces the risks of graft rejection and graft-versus-host disease, but may delay posttransplant immune reconstitution caused by delayed clearance of ATG from the blood. We studied graft-versus-host disease, infections, and the kinetics of immune reconstitution in 28 patients with very poor-risk hematologic malignancies who received lymphocyte-depleted, CD34(+) cell-enriched hematopoietic progenitor cell grafts from partially HLA-matched related donors (PMRD). The incidence of these clinical events was correlated with blood ATG levels in 19 transplant recipients who received rabbit ATG (r-ATG, thymoglobulin) during conditioning. Total r-ATG and the fraction of ATG antibodies that bind human cells (active ATG) were measured for up to 45 days posttransplantation using enzyme-linked immunosorbent assay and flow cytometry assays. Three patients received equine ATG (e-ATG; total dose of 60 mg/kg/day), 3 patients received 10 mg/kg r-ATG, and 22 patients received 6 mg/kg r-ATG during conditioning. All evaluable patients engrafted. Median numbers of blood CD4(+) and CD8(+) T cells at 100 days posttransplantation were 15 and 8 cells/microL, respectively. Acute graft-versus-host disease developed in 3 of 3 recipients of e-ATG and 1 of 25 recipients of r-ATG. Rapid T-cell reconstitution was seen only in younger patients. Overall mortality was 93% (26/28 patients) with poor immune reconstitution contributing to death in 21 of 28 patients. Recipients of 6 mg/kg r-ATG had peak levels of total and active r-ATG of 64+/-20 microg/mL and 9.2+/-5.8 microg/mL, respectively, with clearance of active r-ATG (t(1/2)6 days) to sub-therapeutic levels (<1 microg/mL) by a median of 15 days posttransplantation (range, 8-38 days). Delayed immune reconstitution is likely a consequence of ex vivo and in vivo purging of donor T cells in the graft coupled with inadequate thymic function rather than persistence of active r-ATG in the blood for months posttransplantation.