Application of a polymorphic Y microsatellite to the detection of post bone marrow transplantation chimaerism

In Vivo Persistence of Donor Cells following Adoptive Transfer of Allogeneic Dendritic Cells in HIV-Infected Patients

Peripheral blood samples from HIV-seropositive individuals enrolled in a pilot clinical trial investigating the use of allogeneic dendritic cell therapy were evaluated for mixed chimerism. In this study, dendritic cells from HLA-identical, HIV-seronegative siblings were used. Patients received an infusion of dendritic cells pulsed with HIV MN gp160 protein or with peptides from HLA-A2 restricted epitopes of env, gag, and pol proteins every month for 6–9 months. Of the five allogeneic dendritic cell recipients, two showed increases in HIV antigen-specific immune responses. Allele-specific polymorphisms were identified in three sib-pairs that allowed infused donor cells to be detected using sensitive PCR-based molecular methods. Analysis of blood samples from patients showed similar patterns of donor cell persistence after the first infusion, in that cells were detectable for at least 1 week. Also, differences were observed in the kinetics of cell survival between the first and subsequent infusion cycles in all three patients. This suggests variation in HIV-specific immune responses detected among these three patients was not due to differences in persistence of infused donor cells.

Significance of chimerism in hematopoietic stem cell transplantation: new variations on an old theme

The main goal of post-transplantation monitoring in hematopoietic stem cell transplantation (HSCT) is to predict negative events, such as disease relapse, graft rejection and graft-versus-host disease, in order to intervene with appropriate therapy. In this context, chimerism analysis is an important method in monitoring post HSCT outcome. Mixed chimerism (MC) is mainly evaluated to define engraftment and relapse. Detection of MC is a prerequisite in both myeloablative and nonmyeloablative HSCT, in order to assess the graft status and decide later therapeutic strategies such as donor lymphocyte infusion. In this review, we discuss various techniques including erythrocyte phenotyping, cytogenetic analysis, fluorescent in situ hybridization, restriction fragment length polymorphism, STR/VNTR analysis and real-time quantitative PCR, along with the various methods used to detect minimal residual disease (MRD) in different diseases such as chronic myeloid leukemia, acute myelomonocytic leukemia or acute lymphoblastic leukemia. The review mainly highlights the optimal methodological approach, which needs to be informative, sensitive and quantitatively accurate for MC detection. Future of post HSCT graft monitoring lies in the selection of the most accurate and sensitive technique to determine both MC and MRD. Such an approach would be helpful in not only determining relapse or rejection, but also in ascertaining various responses to different treatment modalities.

Predominant hematopoietic origin of cell-free DNA in plasma and serum after sex-mismatched bone marrow transplantation

BACKGROUND

Despite current interest in the biology and diagnostic applications of cell-free DNA in plasma and serum, the cellular origin of this DNA is poorly understood. We used a sex-mismatched bone marrow transplantation model to study the relative contribution of hematopoietic and nonhematopoietic cells to circulating DNA.

METHODS

We studied 22 sex-mismatched bone marrow transplantation patients. Paired buffy coat and plasma samples were obtained from all 22 patients. Matching serum samples were also obtained from seven of them. Plasma DNA, serum DNA, and buffy coat were quantified by real-time PCR of the SRY and beta-globin gene DNA. To investigate the effects of blood drawing and other preanalytical variables on plasma DNA concentrations, blood samples were also collected from 14 individuals who had not received transplants. The effects of blood sampling by syringe and needle, centrifugation, and time delay in blood processing were studied.

RESULTS

The median percentage of Y-chromosome DNA in the plasma in female patients receiving bone marrow from male donors (59.5%) differed significantly (P <0.001) from that in the male patients receiving bone marrow from female donors (6.9%). This indicated that plasma DNA in the bone marrow transplantation recipients was predominantly of donor origin. Compared with paired plasma samples, serum samples had a median 14-fold higher DNA concentration, with the additional DNA being of donor origin. Control experiments indicated that none of the three tested preanalytical variables contributed to a significant change in cell-free DNA concentration.

CONCLUSIONS

After bone marrow transplantation, the DNA in plasma and serum is predominantly hematopoietic in origin. Apart from the biological implications of this observation, this finding suggests that plasma and serum can be used as alternative materials for the study of postbone marrow transplantation chimerism.

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.

Effects of mixed chimerism and immune modulation on GVHD, disease recurrence and survival after HLA-identical marrow transplantation for hematologic malignancies

BACKGROUND

The success of allogeneic bone marrow transplantation(allo-BMT) is affected by underlying disease relapse. Although mixed chimerism(MC) is not necessarily a poor prognostic factor, several groups have suggested that MC is associated with an increased risk of disease relapse. There is evidence that patients with MC benefit from additional immunotherapy if the treatment is started in minimal residual disease status(mixed chimerism status), not in frank hematological relapse. The purposes of this study are to evaluate 1) the risk for relapse or graft rejection in correlation to persistent MC status after allo-BMT, and 2) the possibility of preventing relapse by immune modulation treatments (withdrawal or rapid taper-off of post-transplant immuno-suppression, additional interferon treatment, or the administration of donor lymphocytes) in hematologic malignancies.

PATIENTS AND METHODS

Of 337 allogeneic donor-recipient pairs between March 1996 and August 1998, 12 patients who showed persistent or progressive MC and who received immune modulation treatments were evaluated. Twelve patients, median age 31 years(range 9 to 39 years), received an allo-BMT for: acute myelogenous leukemia(AML, n = 5), chronic myelogenous leukemia(CML, n = 4), acute lymphocytic leukemia(ALL, n = 3). Serial polymerase chain reaction(PCR) analysis of YNZ 22-, 33.6-minisatellites or Y chromosome-specific PCR analysis at short term intervals(pre- and post-transplant 1, 3, 6, 9, ... months) was performed. Once MC was detected, immune modulation treatments on the basis of increasing MC in an early phase of recurrence of underlying disease were started.

RESULTS

Nine of 12 patients converted to complete chimerism(CC) (AML 5/5, CML 3/4, ALL 1/3). Four of 9 CC patients developed graft-versus-host disease(GVHD) grade < or = 2 during immune modulation. All were treated successfully with steroids. Three patients who were not converted to CC showed relapse of underlying diseases or graft failure.

CONCLUSION

The results demonstrate that, in patients with hematologic malignancies after allo-BMT, persistent MC is associated with relapse of underlying diseases or graft failure. Furthermore, when patients receive early immune modulation treatment, MC can be changed to complete donor pattern chimerism and ultimately prevent relapse.

Comparative serial quantitative measurements of chimaerism following unmanipulated allogeneic transplantation of peripheral blood stem cells and bone marrow

Serial samples were collected from 38 patients following allogeneic transplantation using either unmanipulated peripheral blood stem cells (PBSC) (n = 18) or bone marrow (BM) (n = 20) to assess the incidence of mixed chimaerism using PCR amplification of five VNTR regions. After amplification, products were analysed using the Applied Biosystems ABI PRISM 377 Automated DNA Sequencer and GeneScan software GenoTyper program to determine a quantitative measure of chimaerism. The sensitivity of detection using this method was 0.1%. In the immediate post-transplant period (up to day 30) a significantly lower incidence of mixed chimaerism (MC) occurred in recipients of PBSC compared to BM (P < 0.0005). Between 1 and 6 months there was a significantly lower incidence of low-level MC in patients receiving PBSCT compared to BMT (4/14 v 8/11 respectively, P = 0.04) in patients who had not rejected their grafts or relapsed. Similarly, beyond 6 months 0/9 PBSCT patients compared to 4/9 BMT patients showed MC (P = 0.02). Beyond day 30 13/33 (39%) patients showed intermittent low-level MC, but this was not predictive for subsequent relapse. A rapidly increasing proportion of recipient haemopoiesis was predictive of graft rejection or relapse. Stable continuous MC without relapse was seen in one patient transplanted with PBSC for severe aplastic anaemia. These results suggest that the incidence of intermittent low-level MC is relatively high in the first 6 months following unmanipulated haemopoietic stem cell transplantation but reduces with time and is significantly lower in recipients of PBSC.

Prospective study of microchimerism in transplant recipients

BACKGROUND

We evaluated peripheral blood microchimerism in 48 consecutive organ transplant recipients (35 kidneys, ten livers, one kidney-liver, one kidney-pancreatic islet, one kidney pancreas) up to 12 months post-transplantation. Patients were categorized according to the presence or absence of rejection episodes, and the patterns of microchimerism in the two groups were then compared.

METHODS

DNA was extracted from donor, pre-transplant, and post-transplant peripheral blood samples. Several polymerase chain reaction (PCR)-based assays were developed for the detection of microchimerism. Assay sensitivities ranged from 0.0001 to 3%.

RESULTS

Microchimerism was detected only in sex-mismatched cases (male donors and female recipients) using nested PCR for a Y-chromosome marker. There were ten such cases (six kidneys, two livers, and two combined organ transplants). In patients without rejection (n = 7), there was a peak of donor-DNA at 1-3 wk post-transplantation followed by a second peak between 3 wk and 4 months. In patients with biopsy-proven rejection (n = 3), the peaks were absent and the levels of microchimerism were extremely low (< 0.001%). Microchimerism levels declined in all 10 patients and were barely detectable 1 yr post-transplantation. Microchimerism was not detected in the remaining 38 patients despite using a battery of sensitive PCR-based assays.

CONCLUSIONS

In our study, microchimerism was detected using the Y-chromosome PCR assay only and the level of donor-DNA in a given patient varied over time. This study highlights the difficulties in establishing a correlation between microchimerism and transplant tolerance.

Evaluation of seven PCR-based assays for the analysis of microchimerism

OBJECTIVE

The presence of small numbers of cells of donor origin in the circulation of recipients of organ transplants (microchimerism) may correlate with immunologic tolerance. As part of our ongoing studies on microchimerism, we evaluated the utility of seven PCR-based assays for the detection of the less abundant DNA in paired mixtures (100 ng total DNA).

DESIGN AND METHODS

DNA samples were screened to identify pairs informative for one or more PCR assays. DNA mixtures from the informative pairs were then analyzed using at least one assay. The assays were based on the X-Y homologous region; a Y chromosome microsatellite locus; three autosomal microsatellite loci; the D1S80 minisatellite locus; and sequence specific oligonucleotide probe (SSOP) analysis of the HLA DRB1 locus.

RESULTS

About 0.1% of male DNA against a background of female DNA was detectable using primers for the X-Y homologous region, but the sensitivity was increased to 0.0001% using nested primers for the Y chromosome microsatellite marker. Analysis of the minor DNA component was difficult with the three autosomal microsatellite assays because of the presence of shadow bands. Similar problems with the D1S80 assay were resolved using more stringent PCR conditions, and the sensitivity was 0.1%. Using the DRB1 locus, we were able to detect 1% DNA in the mixed samples.

CONCLUSIONS

These studies show that: (a) nested PCR for the Y chromosome is the most sensitive assay for the detection of microchimerism; (b) D1S80 is a useful marker for microchimerism; (c) additional optimization of analytical conditions is required if autosomal microsatellite markers and the SSOP assay are to be used for microchimerism analysis.

Microsatellite markers in leukaemia and lymphoma: comments on a timely topic

Microsatellites are unique highly polymorphic and informative genetic markers dispersed in the human genome. Their detection by PCR is rapid and a wide variety of DNA sources including archival material are available for diagnostic purposes. Microsatellite typing of haematological neoplasms may be applied to the search for loss of heterozygosity at loci possibly harbouring tumour suppressor genes, for example in acute lymphoblastic leukaemia. The technique may detect submicroscopical chromosomal deletions which are not visible in the leukaemic karyotype. RER+ tumours exhibiting microsatellite instability appear to be rare among haematological cancers with the possible exception of lymphoid tumours in immunosuppressed patients and lymphomas derived from mucosa-associated lymphoid tissue. An X-chromosomal microsatellite near the human androgen receptor gene (HUMARA) may be used for clonal X-inactivation analysis. Microsatellites therefore represent a collection of powerful genetic markers suitable to tackle questions relevant to basic research and clinical problems in leukaemia and lymphoma.

High-resolution detection of PCR products from a microsatellite marker using a nonradioisotopic technique

We report a safe, rapid, and economical method for polymerase chain reaction (PCR)-based genotype analysis using a microsatellite marker specific for the human chromosome 18 locus, D18S53. This method does not involve radioisotopes and makes use of ethidium bromide fluorescence to detect PCR products. Our method enables direct analysis and easy detection of PCR products on nondenaturing polyacrylamide gels. The genotyping using this method can be scaled up to 100 samples at one time by adding a step of "double loading" of samples in a single sequencing size gel. We could resolve PCR products and DNA fragments, differing in size by only 2 bp, in the range of 150-200 bp by a 7% nondenaturing polyacrylamide gel. This technique can be applied for population-based genomic screening and linkage analysis.