
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Molecular Oncology, Markers, Clinical Correlates |
Departments of Experimental Oncology [C. B., E. M., L. P., R. B., C. G-P.] and Immunohematology [F. R., C. L.], Istituto Nazionale Tumori, 20133 Milan, Italy, and Section of Hematology, University of Milan, S. Gerardo Hospital, Monza 20052, Italy [G. M. C., P. P., E. P., C. G-P.]
| ABSTRACT |
|---|
|
|
|---|
A total of 56 CML patients in chronic phase were studied. Twenty-two patients were studied at diagnosis without any treatment (group I). Fourteen patients were receiving IFN (group II), 14 patients were being treated with hydroxyurea (group III), and 6 patients were on different regimens (group IV). Patients were initially assessed for general immunological competence using both in vivo and in vitro assays. Patients were also selected for the expression of HLA-DR0401, the HLA specificity known to present peptide B/A1 to CD4 lymphocytes.
With the exception of the six patients in group IV, the results of all these assays (in vitro phytohemagglutinin/tetanus toxoid responses, in vivo skin reaction to ubiquitous antigens) in CML patients did not significantly differ from those obtained in normal donors, thus excluding the presence of generalized immunosuppression. Eight patients with HLA-DR0401 and a b3/a2 type of fusion were identified and further studied. In these eight patients dendritic cells were obtained from adherent peripheral blood mononuclear cells and used to stimulate CD4 lymphocytes. No patient developed a specific response to the bcr/abl peptide, although patients lymphocytes proliferated in response to a promiscuous tetanus toxoid peptide in all but one case. In contrast, response to the bcr/abl peptide was observed in seven of eight HLA-DR0401 healthy donors tested. These data suggest that immunocompetent, HLA-DR0401+ CML patients are unable to respond to peptide B/A1, at difference from healthy donors. The implication of these results for the immunotherapy of CML is discussed.
| INTRODUCTION |
|---|
|
|
|---|
An important preliminary information is represented by the knowledge of what HLA-binding motifs are present inside the BCR/ABL fusions. Our group mapped the class I HLA-binding motifs for 44 OFPs (6) . Common motifs are present in all CML subtypes, with p190 and the b3/a2 form of p210 being the two types with the most frequent binding motifs. In addition, several groups reported that peptides encompassing the Bcr/abl fusion region and presenting HLA-binding motifs can, indeed, bind HLA molecules and can be recognized by both CD8 and CD4 lymphocytes (7, 8, 9, 10, 11) . These peptide-specific lymphocytes have been shown in some, but not all, instances to cross-react with CML cells expressing the relevant HLA specificity and the appropriate bcr/abl fusion type.
With a single exception (10) , all these data have been obtained using healthy donor lymphocytes, and almost no information is available on the ability of effectors obtained from CML patients to recognize bcr/abl-derived peptides. The difficulty in obtaining patient data in this particular disease stems, in part, from the usual low percentage of lymphocytes in the mononuclear fractions isolated from the peripheral blood, due to the massive presence of leukemic cells, in part, from the assumption that lymphocytes of CML patients could be generally suppressed by the disease and/or the chemotherapy the patients receive.
In fact, in different types of leukemia, highly abnormal immune status was shown, even years after treatment discontinuation (12) .
In this study, 56 CML patients in chronic phase were studied, with respect to their overall immune status and regarding the ability to recognize a bcr/abl peptide, which was previously shown to be immunogenic in normal donors.
| MATERIALS AND METHODS |
|---|
|
|
|---|
80% of CD4.
HLA Typing.
Class II (DR and DQ loci) typing was obtained
through genomic PCR with biotinilated primers, using the single
specific primers hybridization assay (Inno-LiPA DRB assay; Innogenetics
NV, Ghent, Belgium).
Determination of the BCR/ABL Fusion Type.
A reverse transcription-PCR technique was used, as described previously
(13)
. A single set of primers directed against the b2 exon
of BCR and the a2 exon of ABL was used. The b3/a2 product generates a
417-bp band, the b2/a2 translocation produced a 342-bp band.
PHA and TT Assay.
Purified CD4/CD8 cells, obtained from patients or donors, were seeded
at 105 cells/well. PHA (Murex, Temple Hile,
England) was added at 1 µg/ml, and proliferation was assessed as
[3H]TdR uptake (6-h incubation) after 72 h
of culture. For proliferation to TT (Connaugh Laboratory, Toronto,
Canada; 10 µg/ml), 2 x 105
cells/well were cultured for 6 days and labeled with
[3H]TdR for the last 18 h of culture, as
described (12)
. Stimulation index was calculated as the
ration between mean cpm of stimulated lymphocytes and
unstimulated ones.
Delayed Type Skin Reaction to Ubiquitous Antigens.
The Multitest assay (Institut Merieux, Lyon, France) was used. The skin
was prepared with ethyl ether; the eight-prong comb containing seven
different antigens (tetanus and diphteria toxoids, mumps, candida,
tricophyton, tubercolin, and streptococcus) and a negative control was
then applied to the skin. Each individual skin area was allowed to
absorb the overlying antigen for 2 min, and then separately wiped. The
reaction was read after 48 h, as mean diameter of induration,
using the ball-point technique (14)
.
Peptides.
The following peptides were used: B/A1, a 17-mer Bcr/abl peptide
(ATGFKQSSKALQRPVAS), was produced under Good Medical Practice
conditions by Bachem AG (Bubendorf, Switzerland) and kindly supplied by
Dr. O. Leeksma (Leiden University Medical Center, Leiden, the
Netherlands). Peptide 12 (NSVDDALINSTKIYSYFPSVI; produced by Medprobe,
Oslo, Norway) is a TT-derived peptide thaw that was shown to be
presented by multiple HLA DR molecules, including DR4
(15)
.
Preparation of APCs.
DCs were used as APCs. Autologous DCs were obtained from adherent PBMCs
after 814 days of culture in RPMI 10% HS supplemented with
granulocyte macrophage colony-stimulating factor (Sandoz, 200 units/ml)
and interleukin-4 (kindly provided by Schering-Plough; 200 units/ml),
washed, pulsed with the appropriate peptide at 50 µM at
37°C (in the presence of 2.5 µg/ml ß2-m) for 4 h in
serum-free RPMI (SF-RPMI), and irradiated at 4000 cGy.
In Vitro Lymphocyte Stimulation.
Purified CD4 cells (108) were stimulated with
irradiated peptide-pulsed DCs (107) in SF-RPMI.
Cells were seeded in 24-well plates; after 4 h, HS (10%) was
added. On day 10, and weekly thereafter, the cells were restimulated
with equal numbers of autologous irradiated (4000 cGy) peptide-pulsed
PBMCs. One day after each stimulation, interleukin-2 (10 units/ml) was
added. The proliferative activity was assessed after the third
stimulation and then weekly, 2 days after each stimulation.
Proliferative Assay.
Cells (5 x 104) were cultured for 48 h
with irradiated (4000 cGy) autologous PBMCs in absence or presence of
peptide. After an additional 18 h, cells were harvested and
transferred to a filter (spot-on filtermat; Pharmacia,
Buckinghmanshire, United Kingdom). [3H]TdR
uptake was determined by a 1205 betaplate liquid scintillation counter
(Wallac, Turku, Finland). Six replicates were performed for each
experimental point. Values are expressed as mean cpm; bars
represent SE and are displayed only when they exceed 5% of the
respective mean.
Statistical Analysis.
Students t test and Fishers exact test were performed.
Ps <0.05 were considered significant.
| RESULTS |
|---|
|
|
|---|
or with hydroxyurea. All
patients had an Eastern Cooperative Oncology Group performance status
of 0-1.
|
|
|
| DISCUSSION |
|---|
|
|
|---|
In our study, the generation of lymphocytes specific for a bcr/abl peptide in CML patients was investigated. An important preliminary information was represented by the assessment of the immunological competence of these patients. In fact, several reports indicated the presence of generalized immunosuppression in several types of cancers (12 , 17) . Our results indicate that, with the exception of few patients receiving more intensive chemotherapy, the CML patients in chronic phase analyzed in our study were immunologically competent. Although IFN-receiving patients (group II) produced in some cases higher responses than patients in groups I or III, no group substantially differed from the normal donor group (V).
Our study was focused on a peptide derived from the b3/a2 type of bcr/abl protein that was previously shown to be immunogenic for donor lymphocytes expressing the HLA DR0401 molecule and to cross-react with leukemic blasts expressing the HLA DR0401 specificity and the b3/a2 type of BCR/ABL fusion.
To obtain a sufficient number of such patients (b3/a2 and HLA DR-401), a large population had to be screened. Our results indicate that patients lymphocytes, although functionally competent and expressing both the right type of fusion protein and the appropriate restriction element, failed to recognize peptide B/A1.
Because no generalized immunosuppression was found in these patients, tolerance to peptide B/A1 should be present. In addition, because DCs obtained from the patients lymphocytes could effectively present a TT peptide, the observed lack of response to peptide B/A1 seems to be more linked to a T-cell defect than to an APC defect. Our data do not permit to discriminate whether such tolerance was induced by the leukemic cells or whether it preceded the onset of leukemia. It is worth noting that some distinct HLA specificities are associated with a decreased incidence of CML (18) ; therefore, it is possible that some HLA molecules be more (or less) capable to present peptides derived from the bcr/abl protein. However, no such information is available for HLA DR0401.
On the other hand, our data, as well as previously published reports (7) , show that HLA DR0401 can, indeed, present peptide B/A1, either in a synthetic form or derived through the intracellular processing of the Bcr/abl protein in leukemic cells.
Thus, the most likely explanation for our results can reside in the induction of tolerance operated by the leukemic cells in the patients studied and reported here. It is worth mentioning that these patients, although in stable chronic phase, were all PCR positive and harbored a significant tumor load of several billion leukemic cells. It is, therefore, possible that the high number of leukemic cells cause tolerance to the bcr/abl protein by anergizing specific lymphocytes.
These data suggest that strategies aimed at bypassing such tolerance should be the object of future research. In addition, it is possible that different peptides deriving from the junctional region of the Bcr/abl protein could result more immunogenic in CML patients. However, as they presently stand, these results do not support the use of peptide B/A1 in immunotherapeutic approaches to CML. Alternative strategies, either immunological or nonimmunological (19 , 20) , are needed to achieve specific control of CML and of the other neoplasias caused by the bcr/abl OFP.
| FOOTNOTES |
|---|
1 Supported in part by the Italian Association for
Cancer Research (420.198.662), the Italian Research Council, Istituto
Superiore di Sanità (881A/10), BIOMED-2 Grant BMH4-CT96-0848, and
European Union-Tumori Grant BMH4-CT96-5006. ![]()
2 To whom requests for reprints should be
addressed, at Istituto Nazionale Tumori, Oncogenic Fusion Proteins
Unit, Department of Experimental Oncology, Via Venezian 1, 20133 Milan,
Italy. Phone: 39-2-239-0818; Fax: 39-2-239-0764; E-mail: Gambacorti{at}istitutotumori.mi.it ![]()
3 The abbreviations used are: CML, chronic myeloid
leukemia; OFP, oncogenic fusion protein; PBMC, peripheral blood
mononuclear cell; HS, human AB serum; TT, tetanus toxoid; APC,
antigen-presenting cell; PHA, phytohemagglutinin; DC, dendritic cell. ![]()
Received 9/29/99; revised 1/18/00; accepted 1/24/00.
| REFERENCES |
|---|
|
|
|---|
present in acute promyelocytic leukemia cells. Blood, 81: 1369-1375, 1993.
hybrid protein by lymphocytes of acute promyelocytic leukemia patients. Clin. Cancer Res., 2: 593-600, 1996.[Abstract]
This article has been cited by other articles:
![]() |
M. Yasukawa, H. Ohminami, K. Kojima, T. Hato, A. Hasegawa, T. Takahashi, H. Hirai, and S. Fujita HLA class II-restricted antigen presentation of endogenous bcr-abl fusion protein by chronic myelogenous leukemia-derived dendritic cells to CD4+ T lymphocytes Blood, September 1, 2001; 98(5): 1498 - 1505. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |