Generation of transgene-free hematopoietic stem cells from human induced pluripotent stem cells.

Hematopoietic stem cells (HSCs) are the rare cells responsible for the lifelong curative effects of hematopoietic cell (HC) transplantation. The demand for clinical-grade HSCs has increased significantly in recent decades, leading to major difficulties in treating patients. A promising but not yet achieved goal is the generation of HSCs from pluripotent stem cells. Here, we have obtained vector- and stroma-free transplantable HSCs by differentiating human induced pluripotent stem cells (hiPSCs) using an original one-step culture system. After injection into immunocompromised mice, cells derived from hiPSCs settle in the bone marrow and form a robust multilineage hematopoietic population that can be serially transplanted. Single-cell RNA sequencing shows that this repopulating activity is due to a hematopoietic population that is transcriptionally similar to human embryonic aorta-derived HSCs. Overall, our results demonstrate the generation of HSCs from hiPSCs and will help identify key regulators of HSC production during human ontogeny.

Design and Validation of an Automated Process for the Expansion of Peripheral Blood-Derived CD34+ Cells for Clinical Use After Myocardial Infarction.

We previously demonstrated that intracardiac delivery of autologous peripheral blood-derived CD34+ stem cells (SCs), mobilized by granulocyte-colony stimulating factor (G-CSF) and collected by leukapheresis after myocardial infarction, structurally and functionally repaired the damaged myocardial area. When used for cardiac indication, CD34+ cells are now considered as Advanced Therapy Medicinal Products (ATMPs). We have industrialized their production by developing an automated device for ex vivo CD34+ -SC expansion, starting from a whole blood (WB) sample. Blood samples were collected from healthy donors after G-CSF mobilization. Manufacturing procedures included: (a) isolation of total nuclear cells, (b) CD34+ immunoselection, (c) expansion and cell culture recovery in the device, and (d) expanded CD34+ cell immunoselection and formulation. The assessment of CD34+ cell counts, viability, and immunophenotype and sterility tests were performed as quality tests. We established graft acceptance criteria and performed validation processes in three cell therapy centers. 59.4 × 106 ± 36.8 × 106 viable CD34+ cells were reproducibly generated as the final product from 220 ml WB containing 17.1 × 106 ± 8.1 × 106 viable CD34+ cells. CD34+ identity, genetic stability, and telomere length were consistent with those of basal CD34+ cells. Gram staining and mycoplasma and endotoxin analyses were negative in all cases. We confirmed the therapeutic efficacy of both CD34+ -cell categories in experimental acute myocardial infarct (AMI) in immunodeficient rats during preclinical studies. This reproducible, automated, and standardized expansion process produces high numbers of CD34+ cells corresponding to the approved ATMP and paves the way for a phase I/IIb study in AMI, which is currently recruiting patients. Stem Cells Translational Medicine 2019;8:822&832.

Human Apoptotic Cells, Generated by Extracorporeal Photopheresis, Modulate Allogeneic Immune Response.

The induction of specific and sustainable tolerance is a challenging issue in organ transplantation. The discovery of the immunosuppressive properties of apoptotic cells in animal models has paved the way for their use in human transplantation. In this work, we aimed to define a stable, reproducible, and clinically compatible production procedure of human apoptotic cells (Apo-cells). Using a clinically approved extracorporeal photopheresis technique, we have produced and characterized phenotypically and functionally human apoptotic cells. These Apo-cells have immunosuppressive properties proved in vitro and in vivo in NOD/SCID/γC mice by their capacity to modulate an allogeneic response following both a direct and an indirect antigen presentation. These results brought the rationale for the use of Apo-cells in tolerance induction protocol for organ transplantation.

Intracavernous Injections of Bone Marrow Mononucleated Cells for Postradical Prostatectomy Erectile Dysfunction: Final Results of the INSTIN Clinical Trial.

We recently reported stage I of a phase 1/2 clinical trial of cell therapy to treat postradical prostatectomy erectile dysfunction (INSTIN, INtra-cavernous STem-cell INjection clinical trial, NCT01089387). In this first stage, four doses of intracavernous autologous bone marrow mononuclear cells (BM-MNCs) were tested in 12 patients. Here, we report the results of stage II, in which six additional patients received the optimal dose identified in stage I (109 BM-MNCs), and the long-term results in the 12 patients included in stage I. The objectives were to assess the safety and efficacy of this new treatment. In stage II, no patients had side effects, and the erectile function improvements were similar to those seen in stage I: after 6 months, significant improvements versus baseline were noted in International Index of Erectile Function-15 intercourse satisfaction (7.8±3.1 vs 2.2±3.4, p=0.033) and erectile function (18±8.3 vs 3.7±4.1, p=0.035) domains. In stage I patients, after a mean follow-up of 62.1±11.7 mo, there were no prostate cancer recurrences, and erectile function scores were somewhat lower compared with the 1-yr time point. These findings suggest that intracavernous BM-MNC injections are safe and improve erectile function. The decline in erectile function over time suggests a need for assessing repeated injections. PATIENT SUMMARY: We report a phase 1/2 pilot clinical trial of cell therapy consisting in intracavernous injection of bone marrow mononuclear cells to treat postradical prostatectomy erectile dysfunction. Erectile function was improved after 6 mo in the patients given 1×109 cells. No serious side effects (life threatening or requiring hospitalisation) occurred after a mean follow-up of 62.1 mo in the first 12 patients.

Safety of Intracavernous Bone Marrow-Mononuclear Cells for Postradical Prostatectomy Erectile Dysfunction: An Open Dose-Escalation Pilot Study.

UNLABELLED: Evidence from animal models replicating postradical prostatectomy erectile dysfunction (pRP-ED) suggests intracavernous injection of bone marrow-mononuclear cells (BM-MNCs) as a promising treatment approach for pRP-ED. We conducted a phase 1/2 pilot clinical trial of intracavernous autologous BM-MNC injection to treat pRP-ED (NCT01089387). Twelve patients with localized prostate cancer and vasculogenic pRP-ED refractory to maximal medical treatment were divided into four equal groups treated with escalating BM-MNC doses (2×10(7), 2×10(8), 1×10(9), 2×10(9)). Tolerance was the primary endpoint. Secondary endpoints were the effects on erectile function and penile vascularization at 6 mo, as assessed using the International Index of Erectile Function-15 and Erection Hardness Scale questionnaires, and color duplex Doppler ultrasound. We measured the peak systolic velocity in cavernous arteries and assessed endothelial function using the penile nitric oxide release test. No serious side effects occurred. At 6 mo versus baseline, significant improvements of intercourse satisfaction (6.8±3.6, 3.9±2.5, p=0.044) and erectile function (17.4±8.9, 7.3±4.5, p=0.006) domains of the International Index of Erectile Function-15 and Erection Hardness Scale (2.6±1.1, 1.3±0.8, p=0.008) were observed in the total population. Spontaneous erections showed significantly greater improvement with the higher doses. Clinical benefits were associated with improvement of peak systolic velocity and of % penile nitric oxide release test and sustained after 1 yr. Our results need to be confirmed by phase 2 clinical trials. PATIENT SUMMARY: We report a phase 1/2 pilot clinical trial investigating cell therapy with injection of bone marrow mononucleated cells to treat postradical prostatectomy erectile dysfunction. No serious side effects occurred. Improvements of erectile function and penile vascularization were noted. Further studies are required to confirm these preliminary results.

Quality control of extracorporeal photochemotherapy: Proliferation assay using CFSE validated according to ISO 15189:2007 standards.

BACKGROUND: For the last 40 years, the technique of extracorporeal photopheresis (ECP) has constantly developed. Among irradiation systems, those called "off-line" allow the validation of the quality of the cell therapy product. The inhibition of the proliferation of lymphocytes after ultraviolet irradiation (UVA) is usually verified by the tritiated thymidine assay as in vitro proliferation assay. The document presented here describes the results obtained while performing the setting up of an alternative proliferation assay using flow cytometry according to ISO 15189:2007 Standard. METHODS: Cells samples taken before and after UVA irradiation were labeled with CarboxyFluorescein Succinimidyl Ester (CFSE) and then cultured with phytohemagglutinin-A (PHA). After 3 days, an analysis of the CFSE staining was realized by flow cytometry. In order to validate the shift in the method used according to Standard, the following tests were performed: 1) comparison with the reference method, 2) robustness test, 3) reagents stability. RESULTS: Comparison method demonstrated that the sensitivity of the CFSE test is 100%, the specificity is 89%, and the concordance is almost complete. The CFSE test is robust regarding parameters like cell concentration or PHA concentration. PHA and CFSE are stable for 6 months and one year, respectively. CONCLUSION: Validation of this alternative test, according to the ISO 15189:2007 Standard, has demonstrated good concordance with reference method. The results of the robustness and stability of reagents are appropriate for its routine use. Thus, the benefits of alternative technique make it a wise choice for the quality control of ECP in a cell therapy laboratory.

Regulatory CD4+CD25hi T cells conserve their function and phenotype after granulocyte colony-stimulating factor treatment in human hematopoietic stem cell transplantation.

Acute graft-versus-host disease (aGVHD), mediated by CD4(+) and CD8(+) effector T cells, is a life-threatening complication in hematopoietic stem cell transplantation. CD4(+)CD25(hi) regulatory T cells (T(reg)) have been shown to modulate tolerance to aGVHD in murine models. Based on these observations, we examined their role in the prevention of aGVHD in patients who underwent transplantation with peripheral blood-mobilized hematopoietic stem cells after administration of granulocyte colony-stimulating factor. The effects of the G-CSF on the phenotype, frequency, and function of CD4(+)CD25(hi) T cells were analyzed in grafts and after transplantation to determine whether these cells were regulatory T cells. CD4(+)CD25(hi) T cells could be detected at the same frequency before and after granulocyte colony-stimulating factor administration in the donors' peripheral blood. The isolation of these cells from the grafts or from the recipients' peripheral blood after transplantation revealed that they were suppressive to the same extent as T(reg) isolated from healthy volunteers. Their number and frequency were estimated in the grafts and the results indicated that protection against aGVHD was not dependent on the T(reg) amount transferred to the recipients. Similarly there was no correlation between the number of circulating CD4(+)CD25(hi) T cells in the recipients' peripheral blood during the early period after transplantation and the outcome of aGVHD.

Immunologic and clinical effects of injecting mature peptide-loaded dendritic cells by intralymphatic and intranodal routes in metastatic melanoma patients.

PURPOSE: A phase I/II trial was conducted to evaluate clinical and immunologic responses after intralymphatic and intranodal injections of mature dendritic cells. EXPERIMENTAL DESIGN: Fourteen patients with a metastatic melanoma received matured dendritic cells, loaded with Melan-A/MART-1 and/or NA17-A peptides and keyhole limpet hemocyanin. The cells were matured overnight with Ribomunyl, a toll-like receptor ligand, and IFN-gamma, which ensured the production of high levels of interleukin-12p70. Dendritic cells were injected at monthly intervals, first into an afferent lymphatic and then twice intranodally. Immunologic responses were monitored by tetramer staining of circulating CD8(+) lymphocytes and delayed-type hypersensitivity tests. RESULTS: Dendritic cell vaccination induced delayed-type hypersensitivity reactivity toward NA17-A-pulsed, keyhole limpet hemocyanin-pulsed, and Melan-A-pulsed dendritic cells in 6 of 10, 4 of 11, and 3 of 9 patients, respectively. Four of the 12 patients analyzed by tetramer staining showed a significantly increased frequency of Melan-A-specific T cells, including one patient vaccinated only with NA17-A-pulsed dendritic cells. Furthermore, 2 of the 12 analyzed patients had a significant increase of NA17-A-specific T cells, including one immunized after an optional additional treatment course. No objective clinical response was observed. Two patients were stabilized at 4 and 10 months and three patients are still alive at 30, 39, and 48 months. CONCLUSIONS: Injections into the lymphatic system of mature peptide-loaded dendritic cells with potential TH1 polarization capacities did not result in marked clinical results, despite immunologic responses in some patients. This highlights the need to improve our understanding of dendritic cell physiology.

Immune responses of breast cancer patients to mutated epidermal growth factor receptor (EGF-RvIII, Delta EGF-R, and de2-7 EGF-R).

Mutated epidermal growth factor receptor (EGF-RvIII, DeltaEGF-R, and de2-7 EGF-R) is the result of an 801-bp deletion within the extracellular domain of wild-type EGF-R and is expressed by breast carcinomas, but not by normal breast tissues. EGF-RvIII is expressed both on the surface and in the cytoplasm of tumor cells. Thus, EGF-RvIII is a potential tumor-specific target for both Abs and T cells. However, it is not known whether breast cancer patients can raise immune responses to EGF-RvIII expressed by their tumors. The demonstration of EGF-RvIII-specific immune responses in patients would suggest that immunization of patients with EGF-RvIII vaccines is feasible, because these vaccines may boost a pre-existing immune response. We have evaluated humoral and cellular immune responses to EGF-RvIII in 16 breast cancer patients and three healthy donors. Seven of 16 patients developed EGF-RvIII-specific Abs that bound to isolated EGF-RvIII protein or the protein expressed by EGF-RvIII-transfected mouse fibroblasts. The Abs that bound to EGF-RvIII did not bind to wild-type EGF-R, and anti-EGF-RvIII Abs were not found in the sera of healthy donors. Three patients had EGF-RvIII peptide-specific lymphoproliferative responses, and two of these patients also had humoral immune responses. Humoral and cellular immune responses correlated with EGF-RvIII expression by patients' tumors in most cases. These studies demonstrate that breast cancer patients specifically recognize EGF-RvIII with an overall immune response rate of 50%, suggesting that patients may benefit from vaccination against EGF-RvIII, boosting pre-existing immune responses.

Suppressive properties of human CD4+CD25+ regulatory T cells are dependent on CTLA-4 expression.

It has been demonstrated that T cells with regulatory properties are present within the peripheral blood CD4(+)CD25(+) T cell compartment. Here, we describe an original method to purify human CD4(+)CD25(+)CD152(+) T lymphocytes as living cells by forcing the exportation of CTLA-4 molecules stored in intracellular vesicules at the cell surface. By doing so, we demonstrate that CD4(+)CD25(+) T cells contain a smaller and more homogeneous population enriched in cells with in vitro regulatory activity. Moreover, we show that this enrichment in regulatory T cells is associated with an increased expression of Foxp3 and that CD4(+)CD25(+)CD152(+) T lymphocytes display a much stronger suppressive activity in controlling in vitro proliferation of alloantigen-specific T cells than CD4(+)CD25(+)CD152(-) T lymphocytes purified in parallel. Lastly, by purifying such cells expressing CTLA-4, we demonstrate that indeed CTLA-4 is involved in CD4(+)CD25(+)CD152(+) T cell regulatory activity, while suppressive cytokines are not.

Loss of heterozygosity, a frequent but a non-exclusive mechanism responsible for HLA dysregulation in non-Hodgkin's lymphomas.

The frequent alteration of human leucocyte antigen (HLA) class I molecule expression observed in non-Hodgkin's lymphomas (NHL), similarly to solid tumours, has been reported to favour tumoral escape from the immune system. In order to identify the underlying mechanisms, we analysed 15 HLA defective NHL including partial (n = 10) and total class I (n = 5) loss, as well as HLA class II defects (n = 5). The HLA defect concerned HLA-A and -B antigens in 14 of 15 cases. In the cases with partial defect, the use of specific allelic monoclonal antibodies detected a defect of both alleles of A or B loci in six of seven tested cases. Allelic reverse transcription polymerase chain reaction (RT-PCR) demonstrated defects in six of nine cases, including four alterations of both A and B mRNA alleles. Real-time quantitative RT-PCR (RQ-PCR) did not detect the HLA-DR transcript in the two negative HLA-DR lymphomas, contrasting with the presence of CMH II transactivator (CIITA) transcript. Loss of heterozygosity (LOH) was detected in nine of 14 cases through variable pattern of nine microsatellites markers of the HLA locus. Taken together, these findings demonstrate the complexity and the variability of the mechanisms underlying HLA protein deficiencies with a high frequency of LOH. The diversity of these mechanisms indicates the importance of positive selection of HLA altered clones in the development of these NHL cases.

NOD2/CARD15 gene polymorphisms in Crohn's disease: a genotype- phenotype analysis.

OBJECTIVES: Three recently identified NOD2/CARD15 mutations have been described associated with an increased susceptibility Crohn's disease (CD). Our aim was to examine the potential association of these NOD2 mutations with CD and different subsets of CD phenotypes in our population. METHODS: Two hundred and five well-defined CD patients from north-western France and 95 ethnically matched healthy controls were genotyped for mutations R702W, G908R and Leu1007insC by DNA sequencing. Allele and genotype frequencies of NOD2 variants were examined in the whole series of CD and in different subgroups of CD phenotypes defined by the clinical characteristics of the Vienna classification (age at diagnosis, location and behaviour) or by histological features (granuloma). RESULTS: Carriers of at least one NOD2/CARD15 variant were significantly more frequent in CD than in controls (38.0% versus 20.0%, P < 0.002), and the R702W allele was the most significant contributor to this NOD2 association with CD. Homozygotes and compound heterozygotes combined had a higher risk of CD (odds ratio = 12.0, P < 0.0026) than simple heterozygotes for any variant (odds ratio = 2.2, P < 0.013) compared with subjects with no variant. Univariate analysis revealed that carriage of at least one NOD2 mutation was significantly associated with ileal involvement (P < 0.03), and stricturing evolution (P < 0.0015). Granuloma was associated with an excess of the R702W allele (16.1% versus 8.0%, Pc < 0.035), and was correlated with a young age at diagnosis, whatever the NOD2/CARD15 genotype. Multivariate analysis demonstrated that carriage of NOD2/CARD15 mutants, especially R702W, was primarily and independently associated both with stricturing evolution of CD and the presence of granuloma. CONCLUSIONS: In our population, all NOD2/CARD15 mutant genotypes, especially compound heterozygosity, were found to increase the risk of CD, but R702W was the sole allele showing a significant association with CD. In addition, we confirm the positive and independent association of the R702W mutation with stricturing behaviour and describe a second one with the presence of granuloma.

Stimulation of peripheral blood and intestinal mucosa cells by synthetic CpG oligodeoxynucleotides.

The breakdown of tolerance to autologous bacterial flora has been implicated as a major factor contributing to the initiation and perpetuation of chronic inflammation in inflammatory bowel diseases (IBD). To test whether bacterial DNA is at the origin of inflammation in IBD, we have examined the response of lamina propria (LPMC) or peripheral mononuclear cells (PBMC) and purified T cells from IBD patients and control patients to stimulations with a set of oligodeoxynucleotides (ODNs) characterized by the presence or absence of cytosine-guanosine dinucleotides (CpG) and/or 3' poly-guanosine (poly-G) extension. Furthermore we have evaluated the costimulatory activities of these ODNs on T cells activated via CD2 or CD3 pathway. We demonstrated that CpG ODNs induce higher proliferation of LPMC from inflammatory intestinal mucosa compared to healthy mucosa. We confirmed that CpG ODNs do not directly costimulate peripheral blood T cells activated by CD3 pathway. Finally, we revealed that CpG or non-CpG ODNs with 3' poly-G extension inhibit completely CD2 activation of purified PB or LP T-cells whereas only CpG ODNs without poly-G extension enhance proliferation and IFN-gamma production of PB T cells stimulated by CD2 pathway only in presence of NK and NK T cells. Our data suggest that NK T cells may be the primary target of ODNs and play a crucial role in indirect T-cell activation by ODN.

Genetic analysis of multiple sclerosis in Europeans: French data.

We report the results of a genome-wide screen for linkage disequilibrium (LD) in multiple sclerosis (MS) performed on 200 cases, 200 controls and 200 case-parent trios from France employing pooled DNA methodology. A total of 3510 microsatellite markers supplied through the GAMES collaborative were analysed and ranked according to their evidence for association. The most promising 117 markers were then followed up in a two-step validation process. In the first step, additional PCR of the DNA pools was performed in order to refine the ranking order. In the second step, markers were genotyped in individual cases and parents from the trio families. Seven markers showing nominally significant allele frequency differences between affected and unaffected emerged-D6S265, D12S1064, TNFa, D7S1824, D14S1426, D14S605 and D21S2051. These potential associations will require confirmation in further studies.

Genetic interaction of CTLA-4 with HLA-DR15 in multiple sclerosis patients.

Multiple sclerosis is a chronic inflammatory disease of the central nervous system with a genetic component. Until now, the more consistent association with the disease is found with the major histocompatibility complex, especially HLA-DRB1*1501-DQB1*0602 haplotype. In this report, we demonstrate the interaction of Cytotoxic T Lymphocyte-associated antigen 4 (CTLA-4 [CD152]) gene with DRB1*15 haplotype in multiple sclerosis genetic susceptibility. Our data were obtained from two European independent family-based studies including 610 multiple sclerosis family trios. Ann Neurol 2003;54:119-122

Induction of cellular immunity by anti-idiotypic antibodies mimicking GD2 ganglioside.

Gangliosides are potentially useful targets for tumor destruction by antibodies. However, the role of gangliosides in T cell-mediated immunity to tumors is unclear. We produced three murine monoclonal anti-idiotypic antibodies (Ab2) against a monoclonal antibody (Ab1) that binds strongly to melanoma-associated GD2 ganglioside and weakly to GD3 ganglioside. All three Ab2 induced anti-anti-idiotypic antibodies (Ab3) with Ab1-like binding specificity to tumor cells and antigen in rabbits. The Ab3 specifically bound to GD2(+) tumor cells and isolated GD2, and shared idiotopes with the Ab1. Two of the three Ab2 induced GD2-specific delayed-type hypersensitivity responses in BALB/c and C57BL/6 mice, but not in C57BL/6/CD4(-/-) mice. Peripheral blood mononuclear cells (PBMC) from a melanoma patient proliferated specifically in response to in vitro stimulation with Ab2. Proliferation was accompanied by Th1-type cytokine production. Our studies demonstrate the induction of ganglioside-specific T cell-dependent immunity by Ab2 in mice. These T cells showed specific reactivity to ganglioside expressed by tumor cells.

Monoclonal anti-idiotypic antibody mimicking the gastrointestinal carcinoma-associated epitope CO17-1A elicits antigen-specific humoral and cellular immune responses in colorectal cancer patients.

Monoclonal rat anti-idiotypic antibody (Ab2) BR3E4 mimicking the colorectal carcinoma (CRC)-associated epitope CO17-1A induced antigen-specific humoral and cellular immune responses in mice and rabbits. Ab2 BR3E4 was administered in a phase I trial to CRC patients either as intact IgG or as F(ab')(2) coupled to keyhole limpet hemocyanin (KLH). There was a trend for the F(ab')(2)-KLH-immunized patients to show higher immune response rates (18/21 and 5/15 patients with anti-anti-idiotypic antibodies and T cells, respectively) than the IgG-immunized patients (15/23 and 3/15 patients positive). Clinical responses were rare in these patients with liver metastases.

Inhibition of cytolytic T lymphocyte proliferation by autologous CD4+/CD25+ regulatory T cells in a colorectal carcinoma patient is mediated by transforming growth factor-beta.

Cancer patients often develop CTLs that lyse autologous tumor cells in culture. However, tumors can progress in vivo despite the presence of CTLs. Various mechanisms have been reported to down-modulate CTL functions. In this study, the role of CD4+/CD25+ regulatory T cells in CTL induction and proliferation of established CTLs was investigated in a patient with CRC. CD4+ cytotoxic and regulatory T-cell lines were derived from the peripheral blood mononuclear cells of the same patient in mixed-lymphocyte tumor culture. The cytotoxic T-cell line and a clonal derivative specifically lysed the autologous tumor cells but not the B lymphocytes. Only HLA-A1-matched allogeneic CRC cells were lysed by the CTL clone. The clone produced IFN-gamma and TNF-alpha. The regulatory CD4+/CD25+ T-cell line was tumor cell-dependent in its growth but did not lyse autologous tumor cells. This T-cell line suppressed pokeweed mitogen responses of allogeneic lymphocytes, proliferative activity of the established, autologous CTLs, and induction of CTLs in autologous, freshly isolated peripheral blood mononuclear cells. The immunosuppressive effect of the CD4+/CD25+ regulatory T cells was mediated by transforming growth factor-beta and did not require cell-to-cell contact. Thus, although CRC patients can develop specific CTLs against their tumors, the development of regulatory T cells may allow the escape of tumor cells from immune surveillance by the CTLs in vivo.

Quantitative assessment of hematopoietic chimerism after bone marrow transplantation by real-time quantitative polymerase chain reaction.

We have developed a real-time quantitative polymerase chain reaction (PCR) assay using TaqMan technology (Applied Biosystems, Foster City, CA) for monitoring donor cell engraftment in allogenic hematopoietic stem cell transplant recipients. For this purpose, we selected 19 specific sequence polymorphisms belonging to 11 human biallelic loci located on 9 different chromosomes. Using a set of specially designed primers and fluorogenic probes, we evaluated the 19 markers' informativity on a panel of 126 DNA samples from 63 recipient/donor pairs. In more than 90% of these pairs, discrimination between recipient and donor genetic profile was possible. By using serial dilutions of mixed DNAs, we evaluated the linearity and sensitivity of the method. A linear correlation with r higher than 0.98 and a sensitivity of 0.1% proved reproducible. Fluorescent-based PCR of short tandem repeats (STR-PCR) and real-time PCR chimerism assay were compared with a panel of artificial cell mixtures. The main advantage of the real-time PCR method over STR-PCR chimerism assays is the absence of PCR competition and plateau biases, and results evidenced greater sensitivity and linearity with the real-time PCR method. Furthermore, different samples can be tested in the same PCR run with a final result in fewer than 48 hours. Finally, we prospectively analyzed patients who received allografts and present 4 different clinical situations that illustrate the informativity level of our method. In conclusion, this new assay provides an accurate quantitative assessment of mixed chimerism that can be useful in guiding early implementation of additional treatments in hematopoietic stem cell transplantation.