Long-term follow-up of persisting mixed chimerism after partially T cell-depleted allogeneic stem cell transplantation

Using red cell phenotyping (RCP) and/or cytogenetics (CYT) we identified 19 patients with persisting mixed chimerism (MC) among 231 patients transplanted with partially T cell-depleted stem cell grafts from HLA-identical siblings. Persisting MC is defined as MC for more than 2 years in patients without any evidence of relapse. Median leukemia-free survival in these patients was 150 (range, 50-218) months. Diagnoses were ALL (n= 10); AML (n = 2); CML (n = 2); NHL (n = 2); MDS (n= 1); MM (n = 1) and SAA (n = 1). Purpose of this study was the long-term follow-up of MC and definition of patterns of chimerism in the various subsets of PBMCs and granulocytes. Using a PCR-STR technique CD3(+)/CD4(+) (T4 lymphocytes), CD3(+)/CD8(+) (T8 lymphocytes), CD45(+)/CD19(+) (B lymphocytes), CD45(+)/CD14(+) (monocytes), CD45(+)/CD15(+) (granulocytes) and CD3(-)/CD56(+) (NK-cells) were analyzed. The majority of patients with persisting MC were conditioned with a less intensive conditioning regimen and had little GVHD. Sequential monitoring of the chimerism resulted in a group of patients (n = 7) with very slow transient mixed chimerism that resulted in complete DC after median 7 years. Another nine patients had a relatively high percentage of persisting autologous cells for a median of 12 years and in three patients we observed a stable low percentage of autologous cells. Only two out of 19 patients (AML-CR1, CML-CP1) relapsed during follow-up. Both patients had a relatively high percentage of autologous cells. Chimerism in granulocytes and PBMC subsets was analyzed at a median of 8 years after SCT in nine patients. In five patients mixed chimerism simultaneously detected by RCP and CYT was associated with MC in all subsets. Within each individual patient the percentages of donor and recipient cells were very different between the different subsets. Two CML-CP1 patients were mixed chimera in only two subsets and in one patient these subsets represented pending relapse. In another two patients mixed chimerism with a very low number of autologous red cells was not found in the PBMCs because of the different sensitivity level of the RCP and the PCR-STR technique. We conclude that in patients with persisting mixed chimerism after partially T cell-depleted SCT a remarkable number of patients had lymphoid malignancies, the majority of the patients were conditioned with less intensive conditioning regimens and the mixed chimerism was not correlated with relapse. Chimerism in granulocytes and PBMC subsets did show great intra-individual differences in the subsets and these data correlated well with RCP and CYT data with the exception of the NK cells.

The type of factor VIII deficient plasma used influences the performance of the Nijmegen modification of the Bethesda assay for factor VIII inhibitors

We have investigated the influence of the type of factor VIII deficient plasma used on the assay results of the Nijmegen modification of the Bethesda method for factor VIII inhibitors. Immuno depleted factor VIII deficient plasmas, lacking besides factor VIII also von Willebrand factor, gave decreased inhibitor titres compared to assay results with factor VIII deficient plasmas containing von Willebrand factor suggesting the need of the latter in the test system for the stability of factor VIII:C. Moreover the performance of the assay with immuno depleted plasma was contaminated in a certain type of this plasma by the presence of a factor VIII:C inhibitor. Chemically depleted factor VIII deficient plasma appeared to give falsely elevated titres when used in combination with other types of deficient plasmas as substrate plasma in the factor VIII:C assay due to the presence of activated factor Va in the preparation. Suggestions are described with respect to the observed limitations in order to obtain reliable results.

Consensus strategy to quantitate malignant cells in myeloma patients is validated in a multicenter study. Belgium-Dutch Hematology-Oncology Group

Recently the Belgium-Dutch Hematology-Oncology group initiated a multicenter study to evaluate whether myeloma patients treated with intensive chemotherapy benefit from additional peripheral stem cell transplantation. To determine treatment response accurately, we decided to quantitate malignant cells. To test a consensus quantitation strategy, 5 centers independently determined the immunoglobulin heavy chain sequences of patient tumor cells and developed allele-specific oligonucleotides (ASO) and ASO-polymerase chain reaction (PCR). We compared the reproducibility of real-time quantitation with quantitation using limiting dilutions. We distributed DNA samples with a 4-log range of tumor cell concentrations and found average quantitation values deviating 74% and 42% from the input values with real-time PCR (1 center) and limiting dilutions (4 centers), respectively. Within single centers we found an average variation coefficient of 0.74, with limiting dilutions not significantly different from the average 0.82 center-to-center variation coefficient. Within a single center, real-time quantitation proved more reproducible (average variation coefficient, 0.36). Quantification was confirmed in 3 patients during treatment in the protocol. This report shows that real-time PCR or limiting dilution assays can be used for quantitation in a single multicenter trial. We present a consensus strategy that allows an accurate comparison of quantitation data generated in independent centers.

Red blood cell phenotyping is a sensitive technique for monitoring chronic myeloid leukaemia patients after T-cell-depleted bone marrow transplantation and after donor leucocyte infusion

Fifteen consecutive patients with Philadelphia chromosome (Ph)-positive chronic myeloid leukaemia (CML) who relapsed from T-cell-depleted bone marrow transplantation (BMT) were successfully treated with donor leucocyte infusions (DLIs). Chimaerism was analysed using red blood cell phenotyping (RCP), and the results were compared with cytogenetic analysis and outcome of qualitative and quantitative polymerase chain reaction (PCR) for breakpoint molecules. In all patients, an increase in autologous erythrocytes and/or a decrease in donor red cells indicated relapse. Donor erythrocytes started to increase from 4 to 20 (median 12) weeks after DLI. At 6 and 12 months after DLI, complete donor chimaerism was found in 11 and 15 patients, respectively, and all patients were in cytogenic remission. A high percentage of autologous red cells at the time of DLI predicted pancytopenia. During relapse and after DLI, the percentage of autologous red cells was strongly correlated with the reappearance and disappearance of Ph-positive metaphases (r = 0.90; P < 0.001 and r = 0.96; P < 0.001 respectively). The same was true for the correlation between the percentage of autologous red cells and positivity/negativity in PCR for Bcr-Abl breakpoint molecules (r = 0.94; P < 0.001). A normalized Bcr-Abl dose of greater than 10-3 in real-time quantitative PCR correlated well with relapse and the presence of autologous red blood cells (r = 0.77; P < 0.001). We conclude that RCP is a sensitive, easy to perform and fast technique for the prediction of pending relapse after BMT for CML. RCP also predicts the response to DLI and the occurrence of bone marrow aplasia after DLI.

Variability of polymerase chain reaction detection of the bcl-2-IgH translocation in an international multicentre study

BACKGROUND

The capacity of the polymerase chain reaction (PCR) to detect very low numbers of cells bearing a t(14;18) translocation has led to its application in assessment of the results of treatment for follicular lymphoma, and suggestions that therapy might be guided by molecular studies. To test the reliability of PCR a collaborative study was undertaken to compare results from different laboratories in Europe and North America.

METHODS

Twenty laboratories with records of publication in molecular diagnostics were sent blood from normal donors with varying numbers of t(14;18)-bearing cells added from a cell line with a translocation in the major breakpoint region (MBR) of the bcl-2 gene. Samples contained 1000, 100, 10, 1 or 0 cells per ml of whole blood and were sent blinded in duplicate. PCR methodology varied widely, with the total number of amplification cycles between 30 and 70, and 13 different primers used for the MBR region. Twelve laboratories used nested PCR and eight single round amplification.

RESULTS

The sensitivity of nested and single round PCR was similar at 100 cells/ml but below this the nested method proved significantly more sensitive. The false positive rate was 28%, with 11 samples from 9 laboratories reported as positive when no t(14;18) cells were added. PCR product size and sequence analysis showed that false positives were due to contamination from cell-line DNA rather than background translocations in the donors. There was no significant difference in false positive rates between nested and single round techniques.

CONCLUSION

The polymerase chain reaction to detect bcl-2-IgH rearrangements is presently carried out with widely disparate results. Further effort is required to bring forward a standard PCR protocol which can be re-tested in different laboratories to improve accuracy and reproducibility. The application of quantitative techniques such as real-time PCR may resolve many of the problems presently encountered.

A human minor histocompatibility antigen specific for B cell acute lymphoblastic leukemia

Human minor histocompatibility antigens (mHags) play an important role in the induction of cytotoxic T lymphocyte (CTL) reactivity against leukemia after human histocompatibility leukocyte antigen (HLA)-identical allogeneic bone marrow transplantation (BMT). As most mHags are not leukemia specific but are also expressed by normal tissues, antileukemia reactivity is often associated with life-threatening graft-versus-host disease (GVHD). Here, we describe a novel mHag, HB-1, that elicits donor-derived CTL reactivity in a B cell acute lymphoblastic leukemia (B-ALL) patient treated by HLA-matched BMT. We identified the gene encoding the antigenic peptide recognized by HB-1-specific CTLs. Interestingly, expression of the HB-1 gene was only observed in B-ALL cells and Epstein-Barr virus-transformed B cells. The HB-1 gene-encoded peptide EEKRGSLHVW is recognized by the CTL in association with HLA-B44. Further analysis reveals that a polymorphism in the HB-1 gene generates a single amino acid exchange from His to Tyr at position 8 within this peptide. This amino acid substitution is critical for recognition by HB-1-specific CTLs. The restricted expression of the polymorphic HB-1 Ag by B-ALL cells and the ability to generate HB-1-specific CTLs in vitro using peptide-loaded dendritic cells offer novel opportunities to specifically target the immune system against B-ALL without the risk of evoking GVHD.

In AML t(8;21) colony growth of both leukemic and residual normal progenitors is restricted to the CD34+, lineage-negative fraction

In an earlier study we observed residual normal colonies in the CD34+, lineage-negative fraction in AML with a differentiated phenotype. The phenotype of both normal and leukemic progenitors in AML M2, t(8;21) was the subject of this study. The specific translocation enabled discrimination of normal and leukemic cells. Bone marrow samples from eight patients were evaluated for CD34 and the differentiation markers CD33, CD19 and CD56. Growth in all phenotypic fractions was measured in a single cell assay, which enabled quantification of plating efficiency, colony size and determination of progenitor cell origin. No growth was observed in the CD34-negative fraction. In the CD34+, lineage-positive fraction only clusters up to 20 cells were found in 6/8 samples. In 7/8 samples highly proliferative myeloid, erythroid and mixed colonies were cloned from the CD34+/CD56-CD19-CD33- fraction with a frequency between 1 and 12%. Such large colonies grew at a lower frequency (1-6%) from the CD34+/CD56 fraction (4/8 samples), the CD34+/CD56-CD19- fraction (5/8 samples) and from the CD34+/CD19- fraction (1/8 samples), respectively. Among the colonies consisting of more than 150 cells, only 3/45 evaluated were positive for the AML1/ETO fusion transcript. On the other hand, 8/19 colonies with less than 150 cells were AML1/ETO positive. This study shows that like normal progenitors leukemic progenitors are also present exclusively in the lineage-negative fraction in AML M2 t(8;21). A similar hierarchy of proliferation and differentiation was found for these leukemic progenitors, the smaller colony size fitting with their limited proliferation capacity. The frequency of leukemic progenitors was in the same range as their normal counterparts and detectable only after enrichment for the CD34+, lineage-negative population.

Quantitation of minimal residual disease in Philadelphia chromosome positive chronic myeloid leukaemia patients using real-time quantitative RT-PCR

We used a recently developed system for real-time quantitative polymerase chain reaction (PCR) to determine residual disease in patients with chronic myeloid leukaemia. The expression of the Bcr-Abl hybrid oncogene was determined and normalized by using the PBGD housekeeping gene product as endogenous reference. The sensitivity and reproducibility of the assay was tested on cell line K562. A dilution of Bcr-Abl-positive cell line K562 remained positive at up to 250 fg of RNA. 10 copies of Bcr-Abl DNA in water could still be detected. The dynamic range of the method spanned six orders of magnitude. Analysis of 10 identical assays on K562 RNA resulted in a variation of 15%. To test the feasibility of normalization of Bcr-Abl dosage by the PBGD product, we compared the efficiencies of the RT-PCRs in 150 patient analyses. We concluded that PBGD was a suitable and stringent quality control standard. Three patients who were treated with donor leucocyte infusions for chronic myeloid leukaemia who had relapsed after bone marrow transplantation were followed over time. The normalized Bcr-Abl dosage was compared to the results of cytogenetics. Cytogenetic analysis was negative below a normalized Bcr-Abl dose of about 3 x 10(-2). This semi-automated method is fast, sensitive and accurate and enables a high throughput of samples.

Survival in first or second remission after lymphocyte-depleted transplantation for Philadelphia chromosome-positive CML in first chronic phase

We studied the outcome of BMT in 38 consecutive CML patients in CP1 who received transplants depleted of lymphocytes using counterflow centrifugation. In all patients the conditioning regimen was intensified by the addition of anthracyclines. Donors were HLA, MLC-identical siblings. Six patients (16%) died within 6 months. All 37 patients with a follow-up of more than 0.5 months engrafted and only one (3%) suffered from acute GVHD > or = grade 3. Chronic GVHD was evaluable in 33 patients and was extensive in six (18%). The projected 5-year probabilities of hematologic, cytogenetic and molecular relapse were 30% (95% confidence interval (CI), 10-49%), 35% (95% CI, 14-56%), and 34% (95% CI, 13-55%), respectively. The projected 5-year probability of survival was 68% (95% CI, 50-86%). Projected at 5 years, probabilities of leukemia-free survival (LFS) in hematologic, cytogenetic and molecular remission were 55% (95% CI, 37-73%), 51% (95% CI, 32-69%), and 51% (95% CI, 32-70%), respectively. All patients with relapse but one who relapsed in blastic phase were treated with retransplantation (n = 1) or with the infusion of lymphocytes (n = 6). Six patients regained second hematologic remission and five entered second cytogenetic and molecular remission. Including these patients, the probability of survival in first or second hematologic remission at the end of follow-up was 68% (95% CI, 50-86%). The probabilities of survival in first or second cytogenetic and molecular remission at the end of follow-up were both 61% (95% CI, 42-80%). We advocate revaluation of T cell depletion of donor marrow for patients with CML-CP1, especially for those at high risk of developing GVHD.

CD34 selections from myeloma peripheral blood cell autografts contain residual tumour cells due to impurity, not to CD34+ myeloma cells

Malignant cells in haemopoietic autografts can contribute to post-transplant relapse. Engraftment of myeloma patients with CD34+ peripheral blood progenitors selected from total autografts reduces the number of tumour cells infused by 2.7-4.5 logs. Residual tumour cells detected in CD34+ selected cells may be due to selection impurity or the existence of malignant CD34+ progenitors. In three patients we evaluated the CD34 purity and tumour load of total autografts, CD34+ progenitors selected with immunomagnetic beads and highly purified CD34+ progenitors obtained in two rounds of selection (combining magnetic with flow cytometry activated cell sorting) to determine the cause of residual tumour cells in CD34 selections. Using allele-specific oligonucleotides (ASO) complementary to the unique Ig heavy chain sequence (CDRIII region) of the malignant clone, semi-quantitative ASO-PCR was capable of detecting one malignant cell in 10(4)-10(5) normal white blood cells. Selection of CD34+ cells from bone marrow (BM) with approximately 20% malignant plasma cells resulted in a 1.4 log reduction of tumour burden. Using two-colour flow-cytometry we observed CD34-, BB4+ malignant plasma cells contaminating this CD34 selection. Prior to sorting, peripheral blood cell autografts (PBCA) contained approximately 0.1% malignant cells. Selection of > 99% pure CD34+ cells using immunomagnetic beads (Dynal) resulted in an approximate 2 log reduction of malignant cells, but residual tumour cells were still detectable. ASO-PCR detected no malignant cells in > 99.9% pure CD34+ peripheral blood progenitors obtained with two rounds of selection (combining magnetic with flow cytometry activated cell sorting). We conclude that CD34+ malignant cells are not detectable in myeloma PBCA and that residual tumour cells in CD34 selections are due to contaminating CD34-negative cells.

Intensification of the conditioning regimen by the addition of anthracyclines results in a higher incidence of sustained molecular remissions after allogeneic bone marrow transplantation for chronic myeloid leukaemia with marrow depleted of lymphocytes by counterflow centrifugation

BACKGROUND

Relapse remains a significant problem in patients after bone marrow transplantation. The aim of the study was an effort to decrease the incidence of relapses in patients transplanted for chronic myeloid leukaemia (CML) by different conditioning regimens.

METHODS AND RESULTS

28 patients with CML who underwent allogeneic bone marrow transplantation with grafts depleted of 98% of lymphocytes were divided into two groups according to the conditioning regimen used. Patients in group 1 were conditioned without anthracyclines, and patients in group 2 were conditioned with the addition of anthracyclines. Bone marrow samples taken 6 and 12 months after BMT, and annually thereafter, were analyzed by polymerase chain reaction (PCR) for residual disease. Median time of bone marrow sampling and medium number of samples analyzed did not differ significantly between two groups of patients. In group 1, consisting of 11 patients, 40% of samples were negative, and in group 2 with 17 patients, PCR was negative in 79% of samples. It is evident that the addition of anthracyclines favourably influences posttransplantation development.

CONCLUSIONS

The addition of anthracyclines to the conditioning regimen in recipients of grafts depleted of 98% of lymphocytes, significantly decreases the incidence of relapses even 4 years after BMT.