Does the emergence and persistence of donor-derived leukaemia-reactive cytotoxic T lymphocytes protect patients given an allogeneic BMT from recurrence? Results of a preliminary study

In vitro evaluation of graft-versus-graft alloreactivity as a tool to identify the predominant cord blood unit before double cord blood transplantation

The transplantation of two cord blood (CB) units obtained from unrelated donors (double CBT) is an effective strategy for adult patients with hematologic malignancies. Sustained hematopoiesis after double CBT is usually derived from a single donor, and only a few transplantation recipients displaying a stable mixed donor-donor chimerism have been reported. We investigated the mechanisms underlying single-donor predominance in double CBT by studying in vitro the role of the graft-versus-graft cell-mediated immune effect in two-way mixed-lymphocyte culture, along with the contribution of differential hematopoietic progenitor (HP) potency in HP mixed cultures. Results for the two-way mixed-lymphocyte culture showed that despite the weak and variable alloantigen-specific cytotoxic potential displayed by CB mononuclear cells, an immune-mediated dominance for one of the two CB units was detected in the majority of experiments. Alloantigen-induced cytotoxic activity was directed toward both CB-HP and phytohemagglutinin (PHA)-activated T lymphoblastoid cells. The CB unit with the higher fold expansion of CD34(+) cells in single-expansion culture was prevalent in the HP mixed-expansion culture, as shown by DNA chimerism evaluation. Based on these data, we hypothesize that the dominant CB unit is able to develop prevalent cytotoxic activity toward activated lymphocytes of the other CB unit, thereby preventing them from exerting alloantigen-specific cytotoxic potential against both activated lymphocytes and HPs of the dominant unit. In accordance with this hypothesis, we propose the evaluation of alloantigen-induced cytotoxic activity generated in two-way mixed-lymphocyte culture and directed toward PHA-activated T lymphoblastoid cells as a tool to identify the potentially predominant CB unit before double CBT.

Expansion of antileukaemia CTL lines and clones for adoptive cell therapy in paediatric patients given allogeneic haematopoietic stem cell transplantation

Recurrence of the original disease remains the main cause of treatment failure in patients given allogeneic haematopoietic stem cell transplantation for either acute or chronic leukaemia. Infusion of donor lymphocytes (DLI) is useful for rescuing patients with chronic myeloid leukaemia, while this option is of limited value in patients with acute leukaemia. Moreover, DLI may cause fatal graft-versus-host disease (GvHD) or prolonged myelosuppression. A more sophisticated approach is that of generating and expanding ex vivo T-cell lines or clones able to selectively or preferentially lyse leukaemia blasts, while sparing non neoplastic targets. In this review, we will summarize the results we have obtained in vitro utilizing an approach based on the generation of leukaemia reactive cytotoxic T-lymphocytes through the use of apoptotic leukaemia cells as source of tumor antigens. Our approach proved to be feasible and effective in the experimental model for different types of leukaemia, even when the donor was HLA-disparate with the recipient. This strategy has to be tested in the clinical setting for proving its efficacy in preventing/treating leukaemia recurrence.

Single-cell cloning of human, donor-derived antileukemia T-cell lines for in vitro separation of graft-versus-leukemia effect from graft-versus-host reaction

In previous studies, we showed the possibility of expanding in vitro polyclonal CTL lines directed against patient leukemia cells using effector cells derived from both HLA-matched and HLA-mismatched hematopoietic stem cell donors. Some CTL lines, especially those derived from an HLA-disparate donor, displayed residual alloreactivity against patient nonmalignant cells. In this study, we evaluated the possibility of separating in vitro CTLs with selective graft-versus-leukemia (GVL) activity from those potentially involved in the development of graft-versus-host disease (GVHD) through single T-cell cloning of antileukemia polyclonal CTL lines. We showed that CTLs that were expanded from a single T-cell clone (TCC), able to selectively kill leukemia blasts and devoid of alloreactivity towards nonmalignant cells, can be obtained from antileukemia alloreactive polyclonal CTL lines. TCCs expressed a wide repertoire of different T-cell receptor (TCR)-Vbeta families, mainly produced IFNgamma and interleukin 2, irrespective of CD8 or CD4 phenotype, and could be extensively expanded in vitro without losing their peculiar functional features. The feasibility of our approach for in vitro separation of GVL from GVH reaction opens perspectives for using TCCs, which are selectively reactive towards leukemia blasts, for antileukemia adoptive immune therapy approaches after hematopoietic stem cell transplantation, in particular from HLA-mismatched donors.

Emergence of antitumor cytolytic T cells is associated with maintenance of hematologic remission in children with acute myeloid leukemia

Although the graft-versus-leukemia effect of allogeneic bone marrow transplantation (BMT) is of paramount importance in the maintenance of disease remission, the role played by the autologous T-cell response in antitumor immune surveillance is less defined. We evaluated the emergence of antileukemia cytotoxic T-lymphocyte precursors (CTLp's) and the correlation of this phenomenon with maintenance of hematologic remission in 16 children with acute myeloid leukemia (AML), treated with either chemotherapy alone (5 patients) or with autologous BMT (A-BMT, 11 patients). Antileukemia CTLp's were detectable in 8 patients in remission after induction chemotherapy; none of them subsequently had a relapse. Of the 8 patients who did not show detectable CTLp frequency while in remission after induction chemotherapy, 7 subsequently experienced leukemia relapse. In patients undergoing A-BMT, molecular fingerprinting of the TCR-Vbeta repertoire, performed on antileukemia lines, demonstrated that selected antileukemia T-cell clonotypes, detectable in bone marrow before transplantation, survived ex vivo pharmacologic purging and were found in the recipient after A-BMT. These data provide evidence for an active role of autologous T cells in the maintenance of hematologic remission and also suggest that quantification of antileukemia CTLp frequency may be a useful tool to identify patients at high risk for relapse, thus potentially benefiting from an allogeneic antitumor effect.

Targeted immunotherapy in acute myeloblastic leukemia: from animals to humans

Immunity against acute myeloid leukemia (AML) is demonstrated in humans by the graft-versus-leukemia effect in allogeneic hematopoietic stem cell transplantation. Specific leukemic antigens have progressively been discovered and circulating specific T lymphocytes against Wilms tumor antigen, proteinase peptide or fusion-proteins produced from aberrant oncogenic chromosomal translocations have been detected in leukemic patients. However, due to the fact that leukemic blasts develop various escape mechanisms, antileukemic specific immunity is not able to control leukemic cell proliferation. The aim of immunotherapy is to overcome tolerance and boost immunity to elicit an efficient immune response against leukemia. We review different immunotherapy strategies tested in preclinical animal models of AML and the human trials that spurred from encouraging results obtained in animal models, demonstrate the feasibility of immunotherapy in AML patients.

Generation and ex vivo expansion of cytotoxic T lymphocytes directed toward different types of leukemia or myelodysplastic cells using both HLA-matched and partially matched donors

OBJECTIVE

Successful priming and in vitro expansion of anti-leukemia cytotoxic T lymphocytes (CTL) are preliminary conditions for designing approaches of adoptive immunotherapy in patients with hematological malignancies undergoing allogeneic hematopoietic stem cell transplantation (HSCT). In this study, we evaluated the possibility of generating and expanding in vitro CTL directed toward different types of either leukemia or myelodysplastic cells, using both HLA-matched and partially matched donors.

PATIENTS AND METHODS

Eleven donor/recipient pairs were enrolled; donor-derived dendritic cells, pulsed with patient blast cells, were used to generate CTL.

RESULTS

Anti-leukemia CTL lines were successfully obtained from 10 of 11 donors. After repeated rounds of stimulation, CTL lines showed, along with an increase in cytotoxic activity, a variable but continuous expansion of cultured cells. In order to increase the magnitude of CTL expansion, two anti-leukemia CTL lines were further stimulated using allogeneic feeder cells, anti-CD3, and low doses of interleukin-2 (IL-2). This stimulation gave rise to 150-fold to 270-fold expansion of the absolute number of cultured cells. Most cultures showed either absent or low reactivity of anti-leukemia CTL against patient non-leukemia cells. Three anti-leukemia CTL lines displayed a more pronounced cytotoxicity against nonmalignant recipient cells, which was always lower than that observed against leukemia blasts (LB). Spectratyping analysis of the TCR-Vbeta subfamilies revealed a preferential expansion of oligoclonal populations that persisted in CTL lines following repeated rounds of stimulation.

CONCLUSIONS

Results provide the biological background for designing protocols of adoptive immunotherapy for the control of minimal residual disease in patients with hematological malignancies given HSCT.

Induction of T lymphocytes specific to human gastric cancer using HLA-A matched allogeneic gastric tumor cells

Tumor-specific cytotoxic T lymphocytes (CTLs) from patients with early-stage tumors are usually more efficient at attacking tumor cells than CTLs from the progressing tumor stages. The authors investigated the antitumor activity of CTLs from gastric cancer patents and healthy donors. In this study, peripheral blood lymphocytes (PBLs) from gastric cancer patients and healthy donors were stimulated with HLA-A matched allogeneic gastric cancer cells such as KATO-3, MKN45, and SGC7901. Three different populations of lymphocyte, p5-CTL-KATO, h4-CTL-MKN45, and h4-CTL-KATO, were induced and expanded. Flow cytometry analyses showed that 85.2% to 97.8% of these cells were CD3-positive and 45.5% to 51.2% were CD8-positive. The induced CTLs efficiently kill HLA-A2 or HLA-A24 gastric cancer cells through CTL-mediated cytotoxicity. However, no effects were observed for other cancer cells or HLA-A2 negative gastric cancer cells. The specific cytotoxicity of the induced CTLs was further confirmed by cold-target inhibition and monoclonal antibody blockage. These results suggest that CTL-mediated cytotoxicity specific for tumor cells can be produced by stimulating PBLs from healthy donors using HLA-A matched tumor cells, which will lead to the development of new immunotherapeutic strategies to kill cancer cells.

The clinical implications of mixed lymphocyte reaction with leukemic cells

To evaluate the clinical implications of a mixed lymphocyte reaction between leukemic cells and lymphocytes from HLA-matched sibling donors, we attempted to generate donor-derived, graft-versus-leukemia-effective cells and to define their characteristics. We studied 8 patients with chronic myelogenous leukemia (CML), including 5 patients in the chronic phase (CP), 3 patients in the accelerated phase (AP), and 2 patients with acute myelogenous leukemia (AML) in their first complete remission. Cells from these patients were used as stimulators in a mixed lymphocyte reaction.The effects of natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs) were separated by observing tests for cytotoxicity to target cells, including K562 cells, the patient's leukemic cells, and phytohemagglutinin (PHA) blasts. Donor-derived antileukemic CTLs againstthe patient's own leukemic cells are productive in vitro. The efficacy of generating CTLs against leukemic target cells was (in decreasing order) AML, CML-CP, and CML-AP. Cytotoxic activity against leukemic targets was prominent in 4 cases--2 CML-CP and the 2 AML cases. On the contrary, the 3 cases of CML-AP showed low CTL activity. In cases showing 1 positive result among 3 targets (K562 cells, the patient's leukemic cells, and PHA blasts), the relapse rate was significantly lower (P = .022) on follow-up (median, 33 months; 7-40 months) after hematopoietic stem cell transplantation. By a combined analysis of the cytotoxicity effects for all 3 target cells, we were able to demonstrate a correlation between leukemic relapse and the variable degree of the cytotoxicity test results. Although the total sample numbers for this study were low, we speculate that these results may come from differences in the individual characteristics of the leukemic cells that are in line with their clinical disease status.

Allogeneic MHC class I ligands and their role in positive and negative regulation of human cytotoxic effector cells

The allogeneic mixed lymphocyte culture (MLC) has served as an important experimental system for elucidating the cellular and molecular basis of human lymphocyte responses. Complex mixtures of lymphocytes are stimulated by disparate alloantigens, inducing cellular activation and generating a cytokine milieu that is an excellent breeding ground for the proliferation and differentiation of many distinct lymphocyte subsets. Cloning of individual lymphocytes following alloactivation has allowed various cytotoxic lymphocytes to be isolated and characterized with respect to phenotype and specificity. These analyses have revealed that all types of cytotoxic effector cells are regulated by interactions with MHC-peptide ligands, however, the consequences of these interactions can result in opposite functional outcomes. In this review we summarize how allogeneic MHC class I-peptide ligands positively or negatively regulate the activities of four distinct groups of cytotoxic lymphocytes and how this information might be transferred into clinical use.

Ex vivo priming for long-term maintenance of antileukemia human cytotoxic T cells suggests a general procedure for adoptive immunotherapy

Adoptive cellular immunotherapy has proven to be a successful approach in preventing and curing cytomegalovirus infection and Epstein-Barr virus-associated lymphomas after bone marrow transplantation. Translation of this approach for preventing leukemia relapse after bone marrow transplantation might require ex vivo priming and long-term maintenance of leukemia blast-specific T cells. To accomplish this goal, procedures were optimized for the in vitro priming of naive CD8 using dendritic cells activated by CD40 ligation, interleukin-12 (IL-12), and IL-7. Using T lymphocytes and dendritic cells obtained from HLA-matched allogeneic bone marrow transplantation donors and leukemia blasts as a source of tumor antigens, anti-acute myeloid leukemia cytotoxic T lymphocytes (CTLs) were induced. In these experiments, it was found that though it is possible to induce CTLs using immature dendritic cells, IL-12, and IL-7, obtaining long-term CTLs requires the presence of CD4 T cells in the priming phase. Using this approach, long-term antileukemia CTL lines could be generated from 4 of 4 bone marrow donors. Because this procedure does not require definition of the target antigen and because it selects responding cells from a virgin T-cell repertoire, its general application is suggested in adoptive immunotherapy and in the definition of tumor rejection antigens.

Human alloantigen-specific anergic cells induced by a combination of CTLA4-Ig and CsA maintain anti-leukemia and anti-viral cytotoxic responses

The success of allogeneic hematopoietic stem cell transplantation from HLA-disparate donors depends on the development of new strategies for graft-versus-host disease prevention able to target specifically donor antihost alloreactivity, while preserving GVL and antiviral immune surveillance. Recent experimental and clinical work has shown the feasibility of an approach based on induction of anergy to host alloantigens through blockade of B7/CD28 costimulatory signal in donor T cells, but data on the impact of this strategy on the recovery of the immune system are still lacking. We devised an ex vivo method for induction of host alloantigen-specific unresponsiveness based on treatment with the B7/CD28 blocking agent CTLA4-Ig associated with CsA. We then proceeded to assess the maintenance of an effective immune response towards viral pathogens and tumor cells after CTLA4-Ig/CsA treatment, by measuring the frequency of CTL precursors directed against CMV- and EBV-infected targets, and against autologous leukemic blasts. We demonstrated that (1) CTLA4-Ig and CsA can act synergistically in inducing a state of unresponsiveness to alloantigens; (2) the number of leukemia-reactive, EBV-specific and CMV-specific CTLp is not impaired by CTLA4-Ig/CsA treatment. Our data provide the first direct in vitro evidence that it is possible to preserve antiviral and antileukemia effector cells after blockade of CD28/B7 interaction during MLR.

Cytotoxic T lymphocyte precursor frequency as a predictor of acute graft-versus-host disease in bone marrow transplantation from HLA-identical siblings

The measurement of precursor frequencies of donor anti-recipient cytotoxic T lymphocytes (CTL-p) has been shown to predict the incidence and the severity of acute graft-versus-host disease (aGVHD) in unrelated donor bone marrow transplantation (BMT). In HLA-identical sibling BMT, where aGVHD is most likely caused by minor histocompatibility antigen mismatches, this assay did not appear to be sensitive enough to provide similar predictive information. In this study, the CTL-p frequencies and the incidence and severity of aGVHD in 51 onco-hematological patients transplanted from HLA-identical siblings were compared. Sibling donors were selected on the basis of HLA identity using serological typing for HLA-A, B, C antigens, whereas HLA-DRB was tested by molecular analysis. Sibling identity was also confirmed by DNA heteroduplex analyses. Fifteen out of 21 (71%) patients with high precursor frequency (>1:100 x 10(3)) and 12 out of 30 (40%) with low precursor frequency (<1:100 x 10(3)) experienced clinically significant (II-IV) aGVHD. A significant correlation (P = 0.04) between CTL-p frequency and severe aGVHD was demonstrated. Moreover there was a positive trend for a high frequency response according to an increasing grade of aGVHD, which was statistically significant (P = 0.04). In our experience the CTL-p assay is a helpful predictive test for aGVHD in HLA-identical sibling BMT, indicating high risk patients possibly requiring additional prophylaxis.

Allogeneic bone marrow transplantation for juvenile myelomonocytic leukaemia: a single centre experience and review of the literature

Juvenile myelomonocytic leukaemia (JMML) is a rare paediatric disease and allogeneic stem cell transplantation is the only curative approach. The roles of pretransplant treatment, conditioning regimen and graft-versus-host disease (GVHD) are still unclear. Eleven children with JMML underwent allogeneic BMT in our institution. Donors were matched unrelated (n = 6) matched siblings (n = 4) and one mismatch family donor. Transplant-related mortality (TRM) was 36%. Three patients relapsed after transplantation. Two of three patients with relapse are in continuous remission after donor lymphocyte infusion or second BMT, respectively. To evaluate the role of pretransplant treatment, conditioning regimen and GVHD, we have summarised our series with other published single centre reports and give an overview on a total of 65 patients with JMML who underwent allogeneic BMT. No significant correlation between pretransplant treatment, conditioning regimen and TRM could be observed. Overall relapse rate is high (47%). TBI is associated with a significantly higher relapse rate (P = 0.012). Other conditioning modalities, intensive chemotherapy and splenectomy prior to stem cell transplantation do not seem to have a significant impact on relapse rate. Patients with or without GVHD showed no significant difference in relapse rate (58% vs 45%). In the event of relapse after transplantation withdrawal of immunosuppression, donor lymphocyte infusion or second transplant was successful in 6/11 patients. Graft-versus-leukaemia effect seems to play an essential role in bone marrow transplantation for JMML.

Poor outcome in children with refractory/relapsed leukemia undergoing bone marrow transplantation with mismatched family member donors

The utility of bone marrow transplantation for childhood leukemia in patients unable to achieve a remission prior to transplant is controversial. To address this issue, we analyzed a subset of patients with advanced leukemia entered on prospective transplant trials at our hospital. Fifty-eight patients with ALL or AML (age 1-19) were identified. They had failed standard chemotherapy and were in relapse (22 in 1st, 27 in 2nd, three in 3rd, and three in 4th) or had never achieved an initial remission (three) at the time of transplant. Fifty-two patients received marrow from mismatched family members (haplo or DR-identical), while six received marrow from matched siblings. Most patients received myeloablative therapy consisting of total body irradiation, etoposide, cyclophosphamide, and cytosine arabinoside. Marrow from mismatched donors was T cell depleted. Only one of 52 patients transplanted with a mismatched donor survived long-term while three of six patients transplanted in relapse with a fully matched sibling donor are alive 6-10 years post BMT. The major causes of death were infection (39%) and relapse (28%). Acute GVHD grade III-IV was noted in 7% of patients. A comparable group of patients with leukemia transplanted at our center in remission using similarly mismatched family member donors (haplo or DR-identical) had an event-free survival of 28%. In conclusion, our data suggest that BMT utilizing mismatched family member donors is a poor option for patients in relapse at the time of transplant. New treatment strategies need to be developed to effectively manage these patients.

Depletion of Alloreactive T Cells by a Specific Anti–Interleukin-2 Receptor p55 Chain Immunotoxin Does Not Impair In Vitro Antileukemia and Antiviral Activity

The success of bone marrow transplantation (BMT) from HLA-disparate donors depends on the development of new strategies able, on one hand, to efficiently prevent graft-versus-host disease (GVHD) and, on the other hand, to protect leukemic patients from relapse and infections. Using an immunotoxin (IT) directed against the  chain (p55) of the human interleukin-2 receptor (RFT5-SMPT-dgA), we previously showed that it is possible to kill mature T cells activated against a specific HLA complex by a one-way mixed lymphocyte culture (MLC). The present study was performed to investigate whether this protocol of allodepletion affects the capacity of residual T cells to display antileukemia and antiviral activity evaluated by limiting dilution assays (LDA), measuring the frequency of cytotoxic T-lymphocyte precursors (CTLp) directed against autologous leukemic blasts (LB) and cytomegalovirus (CMV)- and Epstein-Barr virus (EBV)-infected target cells. Antileukemia activity was evaluated in peripheral blood mononuclear cells (PBMC) of 3 patients treated for acute myeloid leukemia who had developed a high frequency of LB-reactive CTLp after either autologous or allogeneic BMT. Results demonstrate that (1) depletion with RFT5-SMPT-dgA efficiently inhibited MLC; (2) fresh PBMC of patients yielded a high frequency of LB-reactive CTLp comparable to that of the mock-treated PBMC; and (3) effector cells obtained after allodepletion fully retained the capacity to lyse pretransplant LB. By contrast, the frequency of CTLp directed against patient’s pretransplant BM remission cells was always undetectable. Data obtained in 4 healthy donors showed that specifically allodepleted T cells recognized and killed autologous CMV-infected fibroblasts and autologous EBV–B-lymphoblastoid cell lines. In conclusion, our data indicate that allodepletion using RFT5-SMPT-dgA efficiently removed alloreactive cells, while sparing in vitro antileukemic and antiviral cytotoxic responses.