Relevance and potential of natural killer cells in stem cell transplantation

NK cell-based immunotherapies against tumors

Natural killer (NK) cells provide the first line of defence against pathogens and tumors. Their activation status is regulated by pro-inflammatory cytokines and by ligands that either target inhibitory or activating cell surface receptors belonging to the immunoglobulin-like, C-type lectin or natural cytotoxicity receptor families. Apart from non-classical HLA-E, membrane-bound heat shock protein 70 (Hsp70) has been identified as a tumor-specific recognition structure for NK cells expressing high amounts of the C-type lectin receptor CD94, acting as one component of an activating heterodimeric receptor complex. Full-length Hsp70 protein (Hsp70) or the 14-mer Hsp70 peptide T-K-D-N-N-L-L-G-R-F-E-L-S-G (TKD) in combination with pro-inflammatory cytokines enhances the cytolytic activity of NK cells towards Hsp70 membrane-positive tumors. Based on these findings cytokine/TKD-activated NK cells were adoptively transferred in tumor patients. These findings were compared to results of clinical trials using cytokine-activated NK cells.

In vitro effects of vitamin C and selenium on NK activity of patients with beta-thalassemia major

In this study, the in vitro effects of vitamin C and selenium on natural killer (NK) cell activity of ss-thalassemia major patients was investigated. At first, significant decreased NK activity was found at E:T ratios of 1:1, 5:1, and 10:1 in whole thalassemia patients. Low-dose selenium treatment enhanced NK activity in patients but there was no change in the control group. High-dose selenium decreased NK activity significantly in splenectomized patients. Different doses vitamin C enhanced NK activity significantly in both splenectomized and unsplenectomized patients. According to these results, selenium dosage should be arranged carefully in thalassemia patients, whereas vitamin C can be used confidently.

The Pathophysiology of Acute Graft-Versus-Host Disease

Despite improvements in allogeneic stem cell transplantation, acute graft-versus-host disease (GVHD) remains a significant problem after transplantation, and it is still a major cause of post-transplant mortality. Disease progression is characterized by the differentiation of alloreactive T cells to effector cells leading to tissue damage, recruitment of additional inflammatory cell populations and further cytokine dysregulation. To make the complex process of acute GVHD more explicit, the pathophysiology of acute GVHD is often divided into three different phases. This review summarizes the mechanisms involved in the three phases of acute GVHD.

Ex vivo expansion of natural killer cells for clinical applications

BACKGROUND

Immunotherapy with NK cells has been limited by the inability to obtain sufficient numbers of pure NK cells suitable for manipulation and expansion. The goal of this study was to isolate CD56(+) cells (CD3(-)/CD56(+), CD3(+)/CD56(+)) and expand them under culture conditions compliant with current good manufacturing practices.

METHODS

Magnetic cell-selection technology, using paramagnetic CD56 microbeads and cell selection columns, was used to isolate a CD56(+) population containing both CD3(-)/56(+) NK (60.6+/-10.8%) and CD3(+)/56(+) NK T cells (30.4+/-8.6%) to initiate the expansion studies. The isolated CD56(+) cells were cultured in X-Vivo10 serum-free media supplemented with 10% human AB serum and 500 U/mL recombinant human IL-2 or 500 U/mL IL-2 plus 10 ng/mL recombinant human IL-15 for 14 days. Cultures were fed fresh media and cytokines every 3-4 days, and were evaluated for cell expansion, phenotype, and cytotoxicity at the end of the culture period.

RESULTS

Significant expansion of CD56 cells occurred only during the second week of culture. Although an average of two log expansions was observed, there was substantial cell-expansion variability, depending on the donor, and even when the same donor was tested on different occasions. The cytotoxicity of selected and expanded CD56(+) cells at a low E:T ratio was significantly higher than the starting population, but was comparable to non-separated PBMC expanded for 2 weeks under the same conditions. IL-15 (in combination with IL-2) induced higher killing at the 1:1 E:T ratio than IL-2 alone. Since CD3 cells were not depleted upfront, the expansion of CD3(+)CD56(+) cells was 2-3 times that of CD3(-)CD56(+) cells. NK cells that express the FcgammaRIII (CD16) can mediate Ab-dependent cellular cytotoxicity, and can contribute to enhanced efficacy of MAb treatment. Under the given culture conditions, only moderate expansion of CD56(+)/CD3(-)/CD16(+) cells occurred, with the majority of cells being CD56(+)/CD3(+)/CD16(+) cells.

DISCUSSION

Our studies suggest that the positive magnetic cell-separation method provides a good basis for obtaining enriched CD56(+) cells but expansion conditions need to be optimized.

Influence of extracorporeal photopheresis on clinical and laboratory parameters in chronic graft-versus-host disease and analysis of predictors of response

We report 28 patients with advanced chronic graft-versus-host disease (cGVHD) treated with extracorporeal photopheresis (ECP). All had failed conventional immunosuppressive therapy. Of the patients, 27 had extensive cGVHD and 20 had more than 50% cutaneous surface area involvement. ECP was initiated approximately 2 years after onset of cGVHD and 3 years following allogeneic stem cell transplantation and administered fortnightly for 4 months and then monthly. Response was assessed using quantifiable disease measures, including skin score, liver function tests (LFTs), blood counts, and lung function tests. Regression analysis allowed assessment of any pretreatment clinical or laboratory parameters that predicted response. There were 25 patients who completed 3 months and 21 who completed 6 months of treatment. Systemic immunosuppression was stable or reduced in 86% of patients. There were 3 patients who died from cGVHD. After 6 months, median skin scores were 53% lower (P =.003) in sclerodermoid and lichenoid disease. Of 6 patients with mucosal ulceration, 3 improved. A nonsignificant improvement of LFTs occurred. We infer that ECP is effective even in patients with extensive cutaneous cGVHD of 2 years duration that is resistant to conventional therapy. Furthermore, both sclerodermoid and lichenoid subtypes responded. However, no baseline parameters predicted a favorable response to ECP, so patient selection must continue to be made on clinical grounds.

Role of immunotherapy in stem cell transplantation

Relapse of the underlying malignancy continues to be a major problem after both autologous and allogeneic stem cell transplantation. Over the years, it has been recognized that immune-mediated graft-versus-tumor effects are crucially involved in eliminating minimal disease and controlling its recurrence after stem cell transplantation. This recognition has led to a number of studies that have attempted to stimulate a cellular immune response in the recipient, especially after allogeneic transplantation. Immunotherapy after autologous transplantation has to take into consideration the fact that patients' immune cells frequently are compromised and tolerance to the host tumor may have developed. Hence, trials involving the administration of cytokines (such as with interleukin and interferon) have shown limited benefits. This situation is different for allogeneic transplantation for which the infusion of donor lymphocytes has shown disease regression, especially in patients with chronic leukemias. However, such treatment is effective only if the patient has limited disease, and severe graft-versus-host disease frequently has to be accepted as a complication. This fact has led investigators to pursue the generation of specific lymphocytes that can recognize tumor antigens but not necessarily induce graft-versus-host disease. Such studies are in the early stages, and although some promising results have been observed, it is unclear at this point if the antitumor effect can be separated sufficiently from the graft-versus-host disease mediated by allogeneic lymphocytes. More recently, it has been shown that natural killer (NK) cells can have an antitumor effect in myeloid malignancies, particularly if the cells are allogeneic and do not recognize self-HLA antigens. At this point, it appears that engineered T-lymphocytes and allogeneic NK cells may be useful in preventing or treating relapse after allogeneic transplantation. It remains to be seen if such novel cellular therapies can also be implemented after autologous transplantation via the use of engineered allogeneic immune cells.

Immunomodulatory effects of extracorporeal photochemotherapy in patients with extensive chronic graft-versus-host disease

Extracorporeal photochemotherapy (ECP) has been associated with clinical improvement in several patients with acute and chronic graft-versus-host disease (cGVHD) after allogeneic bone marrow transplantation, but the mechanism of action is unknown. This study tested the hypothesis that in patients with cGVHD, ECP modulates alloreactivity by affecting activated lymphocyte populations or by altering the interaction between effector lymphocytes and antigen-presenting cells (APCs). Ten patients who had refractory cGVHD were treated with ECP, and the clinical response to and immunologic effects of this therapy were assessed. Seven patients had a response and 3 had no change in clinical manifestations of cGVHD. One patient died from catheter-related sepsis. Immunologic effects observed after ECP included normalization of inverted ratios of CD4 to CD8 cells, an increase in the number of CD3-CD56+ natural killer (NK) cells, and a decrease in CD80+ and CD123+ circulating dendritic cells. The results suggest that ECP modulates both NK cells and APC populations in patients with cGVHD.

Cellular immunotherapy of malignancies using the clonal natural killer cell line NK-92

For years activated natural killer (A-NK) cells have been explored with respect to their efficacy in anticancer therapy, but, except for some anectdotal reports, no clear clinical benefit has been shown. However, as the understanding about the interactions of NK cells and tumor cells advances, the use of A-NK cells might be revisited with more sophisticated approaches that pay tribute to mechanisms which allow tumor cells to escape immune surveillance. Here the highly cytotoxic NK cell line NK-92 seems to be an attractive alternative for use in adoptive immunotherapy, because it was shown to exhibit substantial antitumor activity against a wide range of malignancies in vitro as well as in xenografted SCID mice. NK-92 cells are characterized by an almost complete lack of killer cell immunglobulin-like receptors (KIRs) yet conserved ability to perforin and granzyme B-mediated cytolytic activity, which make them unique among the few established NK and T cell-like cell lines. NK-92 is the only natural killer cell line that has entered clinical trials. Here we discuss the current status of development of this cell line for adoptive immunotherapy (AIT) of malignancies and review our first clinical experience in patients with advanced cancer who have received repeated transfusions of irradiated NK-92 in a phase I/II trial. Also we discuss issues that address safety aspects of immunotherapy with clonal cell lines and describe further manipulations, which hold the potential of significantly improving the clinical outcome of AIT with NK-92.

The CD3- 16+ 56+ NK cell count independently predicts autologous blood stem cell mobilization

Better predictive factors for autologous blood stem cell mobilization (BSCM) are needed. The purpose of this study was to determine if an independent association exists between lymphocyte or NK cell counts and BSCM. Data were analyzed on 141 consecutive patients aged 19-69 years (median 45) who received combined chemotherapy plus G-CSF for BSCM, and who had measurements of immune cells prior to BSCM. Of the 141 patients, 41% had breast cancer, 14% Hodgkin's disease, 34% non-Hodgkin's lymphoma, and 11% other diagnoses. BSCM involved dose-intensive cyclophosphamide, etoposide, cisplatin (DICEP) plus G-CSF 300 microg (<70 kg) or 480 microg (>70 kg) for 45% of patients, while the remaining 55% received other chemotherapy plus similar doses of G-CSF. Only a single apheresis was performed for 94% of patients. The following factors were analyzed for predictors of BSCM: age, gender, prior chemotherapy, prior radiotherapy, diagnosis, disease status, marrow involvement, mobilization regimen, Hb, WBC, platelet count, B cell, T cell, and NK cell counts. The peripheral blood CD34+ counts on the first day of apheresis (PBCD34) were 6-1783 x 10(6)/l (median 150). The PBCD34 count correlated strongly with the number of CD34+ cells collected/l blood apheresed and with the number of CD34+ cells collected/kg. By multivariate analysis using continuous variables, relapsed status (P = 0.0003), not using DICEP mobilization (P = 0.0001), female gender (P = 0.0057), low platelet count (P = 0.051), and low CD3- 16+ 56+ count (P = 0.0158) were associated with low PBCD34 counts. Using categorical variables, the only factors that independently predicted a PBCD34 count <150 x 10(6)/l were: >1 prior chemotherapy regimen (odds ratio = 5.12, P = 0.0003), not using DICEP mobilization (odds ratio = 4.94, P = 0.0001), and CD3- 16+ 56+ count <125 x 10(6)/l (odds ratio= 2.58, P = 0.0157). In conclusion, the CD3- 16+ 56+ count may be a useful additional predictor of BSCM and warrants further study.

Acute graft-vs-host disease: pathobiology and management

Acute graft-vs-host disease (GVHD) is a major obstacle to safe allogeneic hematopoietic stem cell transplantation (HSCT), leading to a significant morbidity and mortality. GVHD occurs when transplanted donor T lymphocytes react to foreign host cells. It causes a wide variety of host tissue injuries. This review focuses on the pathobiological basis, clinical aspects, and current management strategies of acute GVHD. Afferent phase of acute GVHD starts with myeloablative conditioning, i.e., before the infusion of the graft. Total-body irradiation (TBI) or high-dose chemotherapy regimens cause extensive damage and activation in host tissues, which release inflammatory cytokines and enhance recipient major histocompatibility complex (MHC) antigens. Recognition of the foreign host antigens by donor T cells and activation, stimulation, and proliferation of T cells is crucial in the afferent phase. Effector phase of acute GVHD results in direct and indirect damage to host cells. The skin, gastrointestinal tract, and liver are major target organs of acute GVHD. Combination drug prophylaxis in GVHD is essential in all patients undergoing allogeneic HSCT. Steroids have remained the standard for the treatment of acute GVHD. Several clinical trials have evaluated monoclonal antibodies or receptor antagonist therapy for steroid-resistant acute GVHD, with different successes in a variety of settings. There are some newer promising agents like mycophenolate mofetil, glutamic acid-lysine-alanine-tyrosine (GLAT), rapamycin, and trimetrexate currently entering in the clinical studies, and other agents are in development. Future experimental and clinical studies on GVHD will shed further light on the better understanding of the disease pathobiology and generate the tools to treat malignant disorders with allogeneic HSCT with specific graft-vs-tumor effects devoid of GVHD.

Status of Cytomegalovirus Prevention and Treatment in 2000

Cytomegalovirus (CMV) infection continues to be a problem in selected populations following hematopoietic stem cell transplantation (SCT). Although there have been no new antiviral agents for management of this infection in recent years, the methods for using the existing agents have improved with newer assays for detection of virus. In addition, our understanding of immunity to CMV has undergone considerable expansion. This paper will address these new aspects relating to CMV infection in the setting of SCT.

In Section I Dr. Zaia reviews the pathogenesis of CMV and the current epidemiology of CMV disease following marrow or blood allo-SCT with emphasis on late-onset disease. The current lab tests available for preemptive management are summarized including the role for conventional shell vial cultures, and a comparison of the CMV antigenemia assay with the new nucleic acid-based assays, including the hybrid capture assay, the NASBA assay, and “real-time” PCR assays. Use of antiviral agents with these tests in the preemptive management of CMV infection is discussed.

Ultimately, what is necessary is restoration of adequate CMV immunity, and that requires understanding the basics of the CMV-specific immune response. In Section II, Dr. Sissons traces the evolution of the CTL response from primary infection into memory and reviews recent advances in the understanding of cytotoxic T cell based immunity to CMV, based on the use of T cell clonotypic analysis and markers of T cell memory and activation, with conventional CTL functional assays.

In Section III Dr. Riddell presents approaches to correction of the problem of CMV pathogenesis, namely direct restoration of the CMV-specific cellular immune deficiency. Attempts at passive therapies will be reviewed with the focus on current problems and approaches to these problems.

In Section IV, Dr. Diamond presents work on the identification of multiple HLA-allele specific cytotoxic T cell epitopes specific for CMV-pp65 and - pp150. Specific epitopes are recognized by CMV-seropositive individuals including healthy donors, SCT recipients, and AIDS patients, indicating their potential usefulness as vaccines. One of these epitopes is recognized by most individuals who express the HLA A*0201 Class I allele. Pre-clinical evaluation in HLA2.1 transgenic mice of vaccine structures utilizing this epitope, and alternative delivery systems are described. Possible methods for vaccination of donor and/or recipient of a SCT as well as their limitations, utilizing synthetic or viral vaccines, are discusseed.

Status of Cytomegalovirus Prevention and Treatment in 2000

Cytomegalovirus (CMV) infection continues to be a problem in selected populations following hematopoietic stem cell transplantation (SCT). Although there have been no new antiviral agents for management of this infection in recent years, the methods for using the existing agents have improved with newer assays for detection of virus. In addition, our understanding of immunity to CMV has undergone considerable expansion. This paper will address these new aspects relating to CMV infection in the setting of SCT.

In Section I Dr. Zaia reviews the pathogenesis of CMV and the current epidemiology of CMV disease following marrow or blood allo-SCT with emphasis on late-onset disease. The current lab tests available for preemptive management are summarized including the role for conventional shell vial cultures, and a comparison of the CMV antigenemia assay with the new nucleic acid-based assays, including the hybrid capture assay, the NASBA assay, and “real-time” PCR assays. Use of antiviral agents with these tests in the preemptive management of CMV infection is discussed.

Ultimately, what is necessary is restoration of adequate CMV immunity, and that requires understanding the basics of the CMV-specific immune response. In Section II, Dr. Sissons traces the evolution of the CTL response from primary infection into memory and reviews recent advances in the understanding of cytotoxic T cell based immunity to CMV, based on the use of T cell clonotypic analysis and markers of T cell memory and activation, with conventional CTL functional assays.

In Section III Dr. Riddell presents approaches to correction of the problem of CMV pathogenesis, namely direct restoration of the CMV-specific cellular immune deficiency. Attempts at passive therapies will be reviewed with the focus on current problems and approaches to these problems.

In Section IV, Dr. Diamond presents work on the identification of multiple HLA-allele specific cytotoxic T cell epitopes specific for CMV-pp65 and - pp150. Specific epitopes are recognized by CMV-seropositive individuals including healthy donors, SCT recipients, and AIDS patients, indicating their potential usefulness as vaccines. One of these epitopes is recognized by most individuals who express the HLA A*0201 Class I allele. Pre-clinical evaluation in HLA2.1 transgenic mice of vaccine structures utilizing this epitope, and alternative delivery systems are described. Possible methods for vaccination of donor and/or recipient of a SCT as well as their limitations, utilizing synthetic or viral vaccines, are discusseed.