The depletion of T cells from haematopoietic stem cell transplants.

OBJECTIVE: In our laboratory, we have developed an immunorosette technique for the depletion of T cells from bone marrow transplants. Tetrameric complexes of monoclonal antibodies are able to form very stable immunorosettes, which are efficiently depleted with the aid of a blood cell separator. Major improvements over the original sheep red blood cell depletion are the use of human (patient or donor derived) erythrocytes instead of sheep-derived cells, and the possibility of using a closed system for separation in a cell separator. In contrast to bone marrow, mobilized haematopoietic stem cell transplants obtained after leucocytapheresis contain higher numbers of T cells. Therefore, a different approach is necessary. METHOD: We have used two CD34 selection systems (Isolex 300SA and the Clinimacs) to perform T-cell depletions from peripheral blood stem cell (PBSC) transplants. RESULTS: Immunorosette T-cell depletion, with CD2/CD3 tetrameric complexes, of bone marrow transplants resulted in a mean 2.5 log depletion of T cells with a yield of 50% of the CD34+ cell population. Stem cell selection of PBSC transplants using one of the CD34 selection procedures resulted in a 4.5 log depiction of T cells for both systems, but with different results for the recovery of CD34+ cells. An increased yield of CD34+ cells was obtained with the Clinimacs procedure (57.9+/-9.0%) in comparison to the Isolex procedure (40.1+/-12.5%). CONCLUSION: Our own immunorosette depletion technique and the two tested CD34 selection methods for stem cell transplants both resulted in a very efficient T-cell depletion with the recovery of 40-60% of the CD34 haematopoietic stem cells present in the transplant.

Multidrug-resistant acute leukemia cells are responsive to prolonged exposure of daunorubicin: implications for liposome-encapsulated daunorubicin.

We examined the cytotoxic effects of free daunorubicin (DNR) and liposome-encapsulated DNR on multidrug-resistant (MDR1) leukemia cells of patients with acute leukemias who had failed primary induction treatment that included DNR. This was analyzed ex-vivo with DNR concentrations and exposure times that normally can be achieved in-vivo for both drugs with induction treatment. The leukemic blasts of patients both with drug-resistant AML and drug-resistant ALL were, ex-vivo, very sensitive to DNR concentrations and exposure times that can be achieved in-vivo by liposome-encapsulated DNR. However, under identical conditions, free DNR and liposome-encapsulated DNR had a similar cytotoxic profile, arguing against a unique mechanism of cytotoxicity by the liposomal constructure. These data suggest that liposome-encapsulated DNR may be preferable to free DNR for the treatment of acute leukemias.

Ether lipids are effective cytotoxic drugs against multidrug-resistant acute leukemia cells and can act by the induction of apoptosis.

We studied the cytotoxic effects of two ether lipids, a relatively new class of anticancer drugs, on multidrug-resistant (MDR1) leukemia cells of patients with acute leukemias who had failed induction treatment. The cytotoxicity of ether lipids was determined by the elimination of clonogenic leukemia cells from leukemic cultures or, in case of failure to generate leukemic cultures, by the inhibition of 3[H]thymidine incorporation in leukemic blasts. At dose levels of 50 microg/ml, a plasma level that can be achieved after oral intake, the MDR1-positive blasts were killed, both of patients with drug-resistant acute myeloid leukemia (AML) and of patients with drug-resistant acute lymphoblastic leukemia (ALL). The leukemic blasts were killed by the induction of apoptosis. These data suggest that ether lipids may be effective antileukemic drugs and that their cytotoxic function is not affected by MDR1.

Complete donor T cell chimerism is accomplished in patients transplanted with bone marrow grafts containing a fixed low number of T cells.

T cell depletion of the bone marrow graft, the most effective method to prevent severe graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT), has resulted in approximately three times more relapses of the disease post-transplant than after non-T cell-depleted BMT. It has been hypothesized that this is caused by the development of mixed T cell chimerism, often observed after T cell depleted BMT, whereas non-T cell-depleted BMT generally results in complete donor T cell chimerism. In order to find an approach of T cell depletion which may avoid the high relapse rate but prevent severe GVHD, we gave marrow recipients a partial T cell-depleted marrow graft containing 1 x 10(5) donor T cells/kg recipient's weight. To investigate whether our approach results in complete donor T cell chimerism, we analyzed post-transplant the origin of purified T cells in 56 patients with hematologic malignancies, including 15 patients at the time they relapsed. The T cells were studied for being of host or donor origin by amplification of four loci of variable number of tandem repeats (VNTR) by PCR. From 6 months post-BMT, all 45 patients who could be analyzed in remission (five had died and six had relapsed within 6 months) had T cells that were exclusively of donor origin. Furthermore, the T cells of 15 patients who had relapsed post-BMT were also exclusively of donor origin. Severe GVHD was never observed. Thus, this approach seems to combine the favorable aspects of both T cell-depleted and non-T cell-depleted BMT.

Influence of serum levels on leukemic cell destruction by the ether lipid ET-18-OCH3.

The effect of serum on the antineoplastic action of the alkyl-lysophospholipid 1-octadecyl-2-O-methyl-sn-glycerol-3-phosphocholine (ET-18-OCH3) was studied in two human leukemia cell lines, HL60 and K562, and in leukemic cells of patients. Decreasing amounts of serum in the culture medium enhanced the cytotoxic action of ET-18-OCH3 dramatically in both cell lines and in the leukemic cells, as measured by cell survival and proliferation. Uptake of ET-18-OCH3 was likewise increased at reduced serum levels. Similar effects were obtained when fetal calf serum (FCS) in the culture medium was substituted by bovine serum albumin (BSA, fatty acid free). Selectivity of the alkyl-lysophospholipid at reduced serum or BSA level was demonstrated by clonogenic assays of normal marrow progenitor cells. Our study provides an optimalization of the purging conditions in autologous bone marrow transplantation, by using a low concentration of BSA during ET-18-OCH3 treatment (20 micrograms/ml for 4 h) in serum-free culture medium.

Adsorption and uptake of the alkyllysophospholipid ET-18-OCH3 by HL-60 cells during induction of differentiation by dimethylsulfoxide.

The human leukemic cell line HL-60 is highly sensitive to the antineoplastic agent alkyllysophospholipid, 1-octadecyl-2-methyl-sn-glycerol-3-phosphocholine (ET-18-OCH3). We investigated the adsorption and uptake of radiolabeled ET-18-OCH3 in undifferentiated HL-60 cells and during differentiation to granulocytes induced by dimethylsulfoxide. HL-60 cells become less sensitive to the cytotoxic action of ET-18-OCH3 during differentiation. The decrease in sensitivity is correlated with a decrease in both adsorption and uptake of [3H]ET-18-OCH3 during differentiation. Binding studies revealed that the binding of ET-18-OCH3 to both undifferentiated and differentiated HL-60 cells is non-saturable which renders the existence of a specific binding place highly unlikely.

The cytotoxicity of alkyl-lysophospholipid on clonogenic leukemia cells and on normal bone marrow progenitor cells is highly, but differentially, increased by cryopreservation.

We studied the cytotoxic effect of alkyl-lysophospholipid (ALP) in combination with cryopreservation on human clonogenic leukemia cells from 10 patients with acute leukemia and on normal bone marrow progenitors (committed stem cells) from 10 donors, in order to assess the applicability of ALP as a purging agent in autologous bone marrow transplantation (ABMT). The tumoricidal effect of ALP was greatly increased by the cryopreservation procedure, both on leukemic progenitors and to a lesser extent on normal bone marrow progenitors. The cytotoxic effects of ALP and of cryopreservation were synergistic. As a consequence, the ALP dose for ex vivo purging has to be adjusted. Furthermore, the cryopreservation procedure itself is more cytotoxic for leukemic progenitors than for normal marrow progenitors, indicating that cryopreservation has a purging effect in AMBT.

Alkyllysophospholipid ET-18-OCH3 acts as an activator of protein kinase C in HL-60 cells.

HL-60 cells are very sensitive to the cytotoxic action of ether lipids. Several hypotheses have been proposed to explain this cytotoxicity. We investigated the influence of the alkylphospholipid ET-18-OCH3 on the activity of protein kinase C. HL-60 cells were incubated with ET-18-OCH3 at a concentration of 20 micrograms/ml for 4 h. After the incubation the membrane fraction of the HL-60 cells was isolated and the activity of protein kinase C was determined while it was still associated with the membrane, using the synthetic peptide substrate [Ser25]-protein kinase C (19-31) as a protein kinase C specific substrate. The activity of the membrane-bound protein kinase C was increased in HL-60 cells treated with ET-18-OCH3 compared to untreated HL-60 cells. The increase in protein kinase C activity was not a consequence of translocation and appeared to be additive to the effect of the phorbol ester 12-myristate 13-acetate. In contrast, solubilized protein kinase C from HL-60 cells could be inhibited or stimulated in vitro by ET-18-OCH3, dependent on the mode of addition of ET-18-OCH3 and phospholipids.

Cytomegalovirus infection causes delayed platelet recovery after bone marrow transplantation.

The pathogenic effect of cytomegalovirus (CMV) infection on the hematopoietic recovery after bone marrow transplantation (BMT) was retrospectively studied in 87 recipients of (nonpurged) autologous BMT and in 56 recipients of allogeneic BMT from HLA-identical siblings. Indications for autologous BMT were lymphomas or acute leukemias and for allogeneic BMT various malignancies or aplastic anemia. Patients were divided for the study in two groups, CMV-positive and CMV-negative on the basis of the CMV status pretransplant, and CMV-negative patients were kept CMV-negative by the local transfusion policy. In allogeneic BMT recipients, platelet recovery was significantly slower in CMV-positive patients than in CMV-negative patients (platelets greater than 50,000 cells/microL after 41 days v 27 days, P = .007). This difference held true when patients with acute graft-versus-host disease above grade I were excluded (platelets greater than 50,000 cells/microL after 42 days v 24 days, P = .01). In autologous BMT, the negative effect on platelet recovery was present in patients with lymphomas, but absent in patients with acute leukemias. Patients with acute leukemias had a very delayed recovery of platelets and granulocytes after autologous BMT, irrespective of the CMV status, probably due to the original stem cell disorder. Platelet recovery was significantly slower in CMV-positive autologous BMT recipients with lymphomas than in those not infected (platelets greater than 50,000 cells/microL after 36 days v 24 days, P = .0002). The presence of CMV infection had no effect on the recovery of granulocytes in autologous or allogeneic BMT. These data show that CMV infection causes delayed platelet recovery after BMT; however, in autologous BMT, the underlying disease (ie, acute leukemia) is more determinant for hematopoiesis after BMT.

Selective killing of malignant cells from leukemic patients by alkyl-lysophospholipid.

We studied the effects of the alkyl-lysophospholipid, 1-octadecyl-2-methyl-sn-glycerol-3-phosphocholine (ALP), on human leukemia cells from 56 patients with various leukemias and on normal bone marrow progenitors in order to assess the application of ALP as an in vitro marrow-purging agent. The tumoricidal activity was analyzed by the elimination of clonogenic leukemia cells (leukemic colony-forming cells), by the inhibition of the proliferative capacity [( 3H]thymidine incorporation) of leukemia cells, and by the elimination of viable leukemia cells measured with flow cytometry. The tumoricidal activity of ALP was dose and incubation time related, as, although to a lesser extent, held true for normal marrow progenitors. For some leukemias the ALP dose necessary for the elimination of 100% of the leukemic colony-forming cells is probably too toxic for normal marrow cells. The results of this study strongly support the possibility that ALP is a promising purging agent in the majority of patients with leukemias.

A fixed low number of T cells in HLA-identical allogeneic bone marrow transplantation.

Allogeneic bone marrow transplantation (BMT) in humans is hampered mainly by graft-versus-host disease (GVHD). Ex vivo T-cell depletion of the marrow graft has decreased the incidence and severity of GVHD, but has resulted in a higher incidence of graft failure and of relapse of the disease. In order to find an optimal T-cell number that avoids the extreme risks on both sides, we performed BMTs with a fixed low number of T cells. Thirty-one patients received marrow grafts, containing 1 x 10(5) T cells per kilogram body weight, from their HLA-identical sibs. All patients, except one, received cyclosporin A. Engraftment of donor marrow cells occurred in all patients and (late) graft rejections are not observed to date. Eighteen of 30 (60%) evaluable patients had acute GVHD, grade I (10 patients) or grade II (8 patients), limited to the skin in all patients. Chronic GVHD, also limited to the skin, was found in 9 of 27 (33%) evaluable patients. Incidence but not severity of GVHD in our study seems similar to that observed in non-T-cell depleted marrow grafting. Relapse was observed in 1 of 13 leukemic patients transplanted in first (or second) remission or first chronic phase with a follow-up of at least 6 months. These results suggest that with a fixed low number of T cells severe GVHD and failure to engraft can be avoided. More patients and longer follow-up are necessary for conclusions regarding relapse rate and late graft failure.